摘要:

The Faraday Society is tzot responsiblc for opiiiiotu cxpvcssed bcfore it by Authors or Speakers. OF F O U N D E D 1903. TO ?ROMY)TE THE STUDY OF ELECTROCHEMISTRY, ELECTROMETALLURQV, CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED 8UBdECT8. ~ ~~ ~ ~~ ~- ~~ ~ VOL. VII. JUNE, 1912. PART 3. THE ‘ ( PARAGON ” ELECTRIC FURNACE AND RECENT DEVELOPMENTS IN METALLURGY. BY JOH. HARDEN. ( A Paper read before tlze Faraday Society on Tuesday, October 3, 1911, Mr. F. W. HARBORD, VICE-PRESIDENT, iiz the Clznir.) Recent developments in the art of steel refining in the electric furnace have called for certain modifications in the design calculated to meet the requirements of the metallurgist. A retrospective view of the electrometallurgy of recent years will make this clear. When the late Dr.Kjellin, whose untimely decease we all had to lament on last New Year’s Eve, designed his induction furnace about 1894-98, his primary object was to create an efficient melting machine for high-class crucible steel, pure and simple, without any consideration of refining pos- sibilities which were deemed unnecessary with the high-class raw material employed in the manufacture of such steel. That this furnace has filled this demand in capacities up to 4 tons and more has in course of time been amply verified, though the progress, the author regrets to state, has been very much retarded in this country, chiefly on account of the power question, as “surplus” power is scarce in most steel plants and is considered more necessary for other purposes, though it has been repeatedly proved that a clear saving of from 61 10s.to Lz per ton of steel, in the melting, can be effected with this furnace. It is well known that very little refining as regards sulphur and phosphorus can be effected in the induction furnace on account of its small slag surface, and the comparatively low temperature of the slag (though degasifying is daily carried out in a large Kjellin furnace by a prominent Continental firm, the Poldihutte A.G. in Bohemia). The reason for this behaviour is quite obvious, but a crude analogy may serve as an illustration, Imagine there are two cups of water on the table, one containing hot and the other cold water, and let us drop a lump of hard crystal sugar into both; as is well known, the sugar will dissolve much more rapidly in the hot water.If some special salt VOL. VII-TQ184 THE “PARAGON” ELECTRIC FURNACE AND is added, it may be found to dissolve quite readily in the hot, but not at all in the cold water. The impurities in the steel may be considered to act precisely in the same way ; they dissolve readily in a superheated slag blanket of a temperature considerably higher than that of the steel, while a slag of the same or lower temperature than the steel may dissolve but little or none of the impurities. As to the gases, another crude analogy may be taken for comparison. Take, for instance, a vessel containing soda-water or any other liquid in which gases are occluded. If the flame of a burner is applied over the surface of the liquid some of the gases may be made to escape somewhat quicker (especially if the liquid is stirred, either by the action of the heat or otherwise), but if the flame is applied from beneath the liquid the degasifying is undoubtedly carried on much more quickly, as at the same time the lower portion of the liquid is rapidly brought to the surface and the gas expanded by the heat.These considerations, among others, brought the author to work out the design known as the ‘( Paragon” furnace, slides of which are to be shown on the screen. In this furnace the bath is heated, as is easily seen (Fig. I), both from the surface of the slag by means of suitably arranged arcs and also at the same time from the sides and beneath the bath, by means of side plates of second-class conductors, similar to those which have been used for some four to five years in the R.ochling-Rodenhauser furnace.In this manner the metallurgist has it in his hands to apply the maximum heat exactly where he wishes to have it, since both circuits are made to be regulated at will. Thus during the desulphurisation and dephosphorisation the slag is heated to a temperature higher than that of the steel, while during the period of degasifying the bulk of the power is conveyed to the bath through the bottom and sides.RECENT DEVELOPMENTS IN METALLURGY 185 This design brings in other important improvements. For example, it Is quite easy to start the furnace from cold by means of the arcs, which obviates the necessity of filling in liquid charge as a means of starting the non-elec- trode furnaces.Furthermore, the electrode question in plain arc furnaces may in many cases become a serious one, as large electrodes for furnaces of greater capacities are exceedingly difficult to obtain, and always very expensive, especially if the losses are to be considered. Owing to the nature of the “ Paragon” furnace, where only a smaller part of the power enters the furnzce through the electrodes, this drawback is con- siderably reduced (Fig 2). If, for instance, the upper limit of a plain arc furnace is, say, 20 tons, on account of the difficulty in obtaining large enough elec- trodes it will be found that this capacity can be doubled with the (( Paragon” type, as only about half of the power is required to pass through the elec.186 THE (( PARAGON ’’ ELECTRIC FURNACE AND trodes.It is true that with some designs of furnaces the electrodes may be coupled in parallel, but this is also possible in the “ Paragon,” and this statement therefore holds good in this case also. The electrodes for a 30-ton three-phase ‘ I Paragon ” furnace (Fig. 3) should have a cross-section of 16 in. x 16 in., or 255 sq. in., and in a 50-ton furnace FIG. 3.-Showing a 30-ton Paragon Furnace. the electrodes should be 24 in. x 24 in., or 576 sq. in., which would still only give a maximum of 24.5 to 26 amps. per sq. in., which, as experience has proved, is well within reasonable limits, both from an electrical and manu- facturing point of view. This would correspond to plain arc furnaces having a capacity of only 12-14 tons and 18-22 tons. In fact, it may safely be said that as far as the electrodes are concerned any capacity possible with the plain arc furnace may be doubled with the “Paragon” design.A further advantage in this design is the greater durability of the roof. It is well known that the roof is the part of an arc furnace which is most186 THE (( PARAGON ’’ ELECTRIC FURNACE AND trodes. It is true that with some designs of furnaces the electrodes may be coupled in parallel, but this is also possible in the “ Paragon,” and this statement therefore holds good in this case also. The electrodes for a 30-ton three-phase ‘ I Paragon ” furnace (Fig. 3) should have a cross-section of 16 in. x 16 in., or 255 sq. in., and in a 50-ton furnace FIG. 3.-Showing a 30-ton Paragon Furnace. the electrodes should be 24 in.x 24 in., or 576 sq. in., which would still only give a maximum of 24.5 to 26 amps. per sq. in., which, as experience has proved, is well within reasonable limits, both from an electrical and manu- facturing point of view. This would correspond to plain arc furnaces having a capacity of only 12-14 tons and 18-22 tons. In fact, it may safely be said that as far as the electrodes are concerned any capacity possible with the plain arc furnace may be doubled with the “Paragon” design. A further advantage in this design is the greater durability of the roof. It is well known that the roof is the part of an arc furnace which is mostRECENT DEVELOPMENTS IN METALLURGY 187 rapidly destroyed by the action of the hot gases. In the (‘ Paragon” furnace the destructive action is minimised, as only a smaller part of the power is acting on the slag.In cases where electrodes are more or less unobtainable the same design may still be used with advantage when gas firing is used as a substitute for the electrodes, while the electric power is applied only through the side plates. One may perhaps remark that in this case the gas firing alone will be sufficient, but it will be seen on closer consideration that the electric heating is still of great advantage if the analogy with the liquid containing occluded gas, which should be driven out, is remembered. Besides, the desulphurisation and deoxidation require a considerable temperature, and in order to obtain this one has to blow in a sufficient quantity of air with the gas, which easily renders the flame slightly oxidising, thus making the deoxidation of the steel difficult.If electric heating is applied as described, the desired temperature can easily be obtained in the right direction by maintaining a reducing atmosphere, and a more thorough refining should be possible without incurring a higher cost. Finally, the melting down of cold material with gas should be more economical in this particular case than with the electric furnace proper, since no very high temperature is required to liquefy low-grade iron ; but it is the subsequent refining, apart from the dephosphorisation, which demands the higher heat energy, and this can be applied in a more efficient way by means of the side plates conducting the electric power to the furnace.These furnaces have been patented by the author and the Grondal Kjellin Co., Ltd. A trial furnace is just being built in Germany, and designed by Mr. Roden- hauser and the Rochlings Iron and Steel Works, where the side plates only are provided for. Experiments have proved that sufficient power can be converted to the bath in this way to give the steel the temperature required. The construction of this furnace has progressed so far that the author hoped to bring some figures of the results obtained before this meeting ; certain delays in the delivery of the electrical parts have, however, frustrated this, but the results are expected to be ready for publication shortly, It is expected that this design will enable the constructors to provide furnaces up to 50 tons capacity.Having now broached the question of very large furnaces, in fact of the largest size possible under present conditions, the author wishes to mention a few words about a new furnace of the smallest size, suitable for laboratory purposes, &c. It is a long-felt want of the steel-maker to be able to carry out trial melts on a small scale, especially for alloys, before making up a proper charge. This is of great importance in the case of such alloy steels in which expensive ferro-alloys are a prominent constituent. The old method of making a trial in a pot in the crucible furnace is both time-robbing and very uncertain. This new furnace should be a real boon to the crucible steel-maker, as it enables him to make melts from a few pounds in weight up to several hundredweights in a most easy and con- trollable way.The furnace is known as the (‘ Helberger ” furnace (see Fig. 4), and the author has acquired the agency for this apparatus in this country. It consists of an electrically heated ordinary plumbago crucible, lined in such a way as not to react upon the charge. Any form of electric current may be used, but alternating current of from 25 to 60 cycles is pre-188 THE “PARAGON” ELECTRIC FURNACE AND ferable, therefore the heavy outlay of a motor generator is in most cases unnecessary. The furnace and the crucible are open at the top, so that the contents can easily be watched and additions made. The temperature is very easily regu- lated by means of a handle ; heats of 3,000~ C. have been obtained in these furnaces, which will even permit the melting of platinum and other very refractory metals. The furnaces are made either to be tilted or else with detachable crucible for direct pouring; they are delivered complete, ready for use, at quite reasonable prices.The melting cost compares very favourably with other methods for small capacities ; a few .figures will show this :- IOO kg. steel require 75 kilowatt hours. IOO kg. copper require 30 kilowatt hours. I kg. platinum requires 10 kilowatt hours. The following temperatures of the crucible were obtained :-- The temperature was still higher after the last reading, but the pyrometer used did not enable any higher readings to be taken. From this it will be seen that any temperature required for trial purposes in steel-making may be easily obtainable, With regard to accessories for steel-making, it may be stated that such ferro-alloys as ferro-tungsten are now being made in the electric furnace on a commercial scale in this country by Electric Furnaces 8z Smelters, Ltd., in their new works at Luton, three furnaces are in use alternatively, and alloys are produced in considerable quantities. Ferro-tungsten as low as 0.25 per cent. in carbon has been made, though 0.5 per cent. is more usual. Alsoferru- tantalum is being made as a speciality, and it is believed that this new alloy will no doubt be of considerable interest to the steel-maker. The power supply is 500 volts direct current, which is being converted into alternating current, 25 cycles, 50 to 90 volts, by means of a motor generator.

ISSN:0014-7672    

DOI:10.1039/TF9120700183

出版商:RSC    

年代:1912

数据来源: RSC

摘要:

188 THE “PARAGON” ELECTRIC FURNACE AND DISCUSSION. Mr. W. Murray Morrison (communicated Ociober 17, 1911) : I regret very much that it will be impossible for me to be present at the adjourned discussion to-day. The Society is to be congratulated on the practical papers contributed by Mr. J. Hard6n and Mr. D. F. Campbell on recent progress in the electro- metallurgy of iron and steel. One would like to have seen some records of the type of furnace de- scribed by Mr. Hardkn, and perhaps he may at some later date be good enough to contribute some further data relative to that to the Society. I presume the top electrodes and those in the furnace linings are in parallel. The theoretical considerations which he puts forward in support of the advantage of the electrodes embedded in the lining appear to be sound atRECENT DEVELOPMENTS IN METALLURGY 189 first sight, but it is to my mind rather doubtful as to whether the practical considerations will not outweigh any advantages which may be secured.The resistance through the lining of the furnace will no doubt be somewhat considerable, and I should expect that the radiation losses would be material. This is more or less evidenced by the fact that the necessity is recognised of cooling the metallic electrodes. Power will be required for this purpose, and I imagine a considerable percentage of energy will be lost through radiation. Further, it would appear as if the life of furnace linings would be more considerable in the case of the Hhroult or similar furnace. In dealing with the capacity of the ‘I Paragon ” furnace as compared with furnaces of other types, Mr.Hard& estimates the capacity of the former at double that of the latter. Assuming his arguments to be correct this can only refer to the size of the top electrodes, for obviously a furnace of double the capacity would be of double the size. I take it, however, Mr. HardCn merely refers to the limiting factor being the size of electrodes, and that on this account the (‘ Paragon” furnace could be built of a larger size for a given superficial area of electrodes. Mr. Colin C. Gow : We all listened to the papers read by Messrs. Hardkn and Kilburn Scott with much interest as bringing to one’s notice furnaces for metallurgical work of a distinctly novel character. There are just one or two points upon which I would ask the gentlemen for enlightenment.Referring to Mr. Hardkn’s paper (p. 184), the following statement appears : ‘‘ Thus during the desulphurisation and dephosphorisation the slag is heated to a temperature higher than that of the steel, while during the period of degasifying the bulk of power is conveyed to the bath through the bottom and sides.” I am not quite aware as to how Mr. Hardkn would define the freedom of a bath of steel from gases, or would determine that condition. However, I will assume that if a bath sample be taken and then poured into a small mould the tendency of the steel to rise will be an indication of the presence of oxides and probably gas to some extent, and vice versa. The condition of the bath as shown by this simple and, so far as I am aware, the only practical test, will no doubt meet the requirements of Mr.Hardkn’s definition of degasification. During my experience with the simplest type of arc furnace I have always found that a bath sample will invariably lie quiet in the mould as soon as the sulphur has been eliminated ; in fact, the desulphurisation by the reducing slag is never complete until the oxides have been removed from the bath, thus enabling calcium carbide to exist in the slag without decomposition. This has been borne out by analyses. In short, the elimination of gas or oxides is in a way a function of the desulphurising conditions. If, however, Mr. Hard& finds it necessary when using his “ Paragon” furnace to degasify (quoting his term) after the removal of sulphur, it would be of interest to know the approximate power consumption and further time required when degasifying I ton of steel together with the additional expenditure entailed thereby.If Mr. Hard& does not accept the simple test mentioned above as a proof of the freedom of a bath of steel from gas, is it possible that he has actually determined analytically the occluded nitrogen and any other gas before and after his process of degasification ? In this case it would be of exceptional interest to know the relative mechanical tests which the steel would give before and after treatment in his furnace. I would like to add that my experience as regards this problem refers to mild steel 0.1 per cent. C. besides medium and high carbon steels.Deoxidation is a term which all steel-makers understand, whereas degasi-190 T H E “PARAGON” ELECTRIC FURNACE AND fication should be spoken of with the utmost reserve until more light has been thrown on a subject which is at present so little understood and open to misinterpretation. Mr. D. F. Campbell : Mr. Hardkn’s paper was specially interesting as it gave his ideas about the results which he hoped to obtain with the type of furnace that marks an important stage in the evolution of furnace design. It is more interesting because it is being built by the firm at Volklingen who have done so niuch to develop the induction principle. The simple Kjellin furnace, with its modifications suggested by Frick, Hiorth, and others, marks one extreme. Mr. Rodenhauser’s improvements enabling slag to be used for refining may be considered another stage in the tendency towards the arc- refining electric furnace, while Mr.Hardkn carries this one stage further. The metallurgy of steel refining may be said to be the metallurgy of slags, and from this point of view we should undoubtedly suppose the simple arc furnace to be the most efficient. In this furnace steel can be made and deoxidised, and there is no doubt that sufficient heat can get to the bottom of the bath of steel, which proves that the necessity of passing the current through the steel as a means of heating is a fallacy. The slag reactions may perhaps be divided into those which are ordinary heat reactions, such as are obtained in a basic open-hearth furnace, and those which are peculiar to the electric furnace, and include those which require the intense temperature of the arc.Mr. Hardkn has realised the importance of this. There is no doubt that electrodes are the cause of expense and trouble in operating an electric furnace, and one of the great advantages that have been put forward for the induction or resistance principle is the absence of these electrodes. Unfortunately Mr. Hardkn’s design does not eliminate this objectionable feature, but also has certain complications in the hearth furnace which would be offensive in my opinion to the practical steel- maker. He argues that “ the reduction in the cross-sectional area of electrodes is an important item, but at least 50 per cent. of the electrode consumption in any furnace is due to disintegration or pointing of the electrodes, which is entirely independent of the amount of current passing through the electrodes, and is just as serious in the case of the smaller carbon as in the larger electrodes required in the simple arc furnace.If Mr. Hiirdh can give us a furnace without electrodes in which efficient slag reactions can be maintained, it would be a great advance, but if he finds it necessary to have the electrodes with all their complicated mechanism, and the only compensation being a slightly reduced cross-sectional area, I do not think that this furnace will prove to be a great advance on present practice. Mr. Hard& speaks of impurities dissolving in a superheated slag blanket, and mentions the importance of having this heated considerably higher than the steel.With this principle I completely agree, but if heating the slag is sufficient there appears to be no necessity to pass current through the steel and the bottom of the furnace which involves serious difficulties. In the Siemens process the heat is entirely applied on the slag surface, the only objection being that in this process, oxygen, which is one of the most serious impurities in steel, must be introduced for the combustion of fuel. The value of electric steel-making depends upon the reducing conditions which can be maintained, and the application of heat on special slags to carry out the refining process without turning further than necessary from standard steel-making practice. Mr. Hardkn mentions the serious nature of roof repairs in arc furnaces, but with a properly designed Hkroult furnace this item does not exceed 2$d.RECENT DEVELOPMENTS IN METALLURGY 191 to 3d.per ton of steel, and a roof recently taken off a furnace working in England had made 86 heats, melting and refining cold scrap. The reference to the small laboratory furnace is interesting, but its limitations are undoubtedly those of the crucible process, and I must take exception to the author’s statement that the old method of making a trial in a pot in the crucible furnace is both time-robbing and very uncertain. While the furnace described may be of great value for laboratory experi- ments and other purposes, I do not think that it will ever compete with the crucible process for making steel under strictly commercial conditions, and as a furnace for making trial melts to work in conjunction with an electric refining furnace it will unfortunately be of no use because it will not be able to get the slag reactions which are the fundamental principle on which depends the economic application of the electric refining furnace for large tonnage.Dr. H. Borns : I am sorry that I was not present at the last meeting, because I should have liked to ask Mr. Hard& a few questions. My point is this. Mr. Hard& practically advocates a combination of arc heating and resistance heating. But some metallurgists, notably W. Conrad, do not believe that the molten iron in the bath can to any profitable degree be further heated by the current from electrodes of the second class. Conrad filled a furnace with molten iron, inserted electrodes, and sent currents through these and the iron.The electrodes were rods of iron, and he really took resistance measurements of the molten iron. Yet those measurements showed that there was, in his case, no possibility of heating the fused iron ; the cooling of the electrodes would have carried away all the heat thus introduced. With electrodes of large area and with induction furnaces the conditions are no doubt more favourable. Mr. Hard& and R6chling- Rodenhauser, who, I belicve, first applied the hearth electrodes of the second class, will have made experiments, Can Mr. Hardin give us particulars? Has he taken temperature measurements? As regards the area of the electrodes, Mr. Hardhi speaks of 24 in. sq.for 50-ton and also for 30-ton furnaces, which, I think, nobody has yet constructed. Could he state the dimensioiis for 5-ton furnaces ? Mr. M. Ruthenburg said he, saw no advantage in the bottom electrode. There had been a great deal of experimental work done in connection with bottom electrodes at Niagara, and they had been abandoned. There was no doubt that water cooling an electrode below a furnace was liable to be very dangerous. On the other hand, there was no danger in water cooling above, as no harm would arise if water came into contact with the slag. Dr. J. A. Harker thought the Society was to be congratulated on having secured three such excellent papers for the evening’s programme. As regarded Mr. Hardbn’s furnace, he would like to ask him what was the conductivity of the side electrodes ? A great deal would depend upon that.Furthermore, what thickness were these, and was it necessary that all the lining of the furnace should be made of such expensive material as, say, magnesite ? He agreed that water-cooling was a source of trouble, and that air-cooling was a great advantage. He was much interested in the Helberger furnace. What was the size of the crucible mentioned on p. 187 ? From the description given of the furnace, it seemed difficult to know what was happening in the crucible, and whether it was full or empty, He would imagine that the conductivity of the crucible and its contents would be of some importance. A great deal of the current would be short-circuited through the contents of the crucible unless it was192 THE “PARAGON” ELECTRIC FURNACE AND made of a material that insulated at high temperatures.In this case, the greatest heat would not be generated where it was wanted. They had made a similar furnace at the National Physical Laboratory, but had only obtained a rather low efficiency in the arrangement, which was an induction furnace in which the usual crucible was replaced by a D-shaped piece, with water- cooled clamps at the ends of the straight limb forming the furnace tube. On the whole, it had not been very successful, as the design was bad from an electrical point of view and the power factor was low. The Chairman said he would like to add a few remarks before calling upon the author to reply to the very interesting discussion which had taken place.Mr. Hard& had referred to a trial furnace being built in Germany where side plates only were provided for. Did his experiments lead him to anticipate that sufficient heat could be obtained in the furnace by resistance alone ? I t was necessary for the steel bath to be sufficiently heated so that the slag action was rapid and effective ; but in the resistance and induction furnaces, so far as his experience went, it had been found impossible to get sufficient heat in the slag to obtain the fluidity necessary for rapid purifica- tion; this might possibly be done in the Gin furnace with its narrow channels, but this furnace was impracticable for other reasons. Mr. J. Hardkn, in reply, said that in answer toDr. Harker the side plates in the “ Paragon” furnace were fairly good conductors, although not, of course, as good as metal.He had been asked whether metal other than steel had been melted, Tests had been made in which 5 kilogrammes of copper had melted utilising 10-15 kilowatts. With regard to the use of the side plates only he had tried this with a small furnace. The experiment was very crude, but he had got good melts, and had proved at least that the charge could be kept liquid by means of side plates alone. In answer to Mr. Morrison the top electrode and the side plate were in parallel in separate circuits. The life of the lining on the side plates was a t least as long as that of the other part of the lining. It was important that the side conductors should be large, a good portion of the bath being covered by them.He would reply that the efficiency of a 10-ton Kochling-Rodenhauser furnace using side plates was Go to a maximum of 72 per cent. In reply to Mr. Campbell, hc said that the induction principle had not been abandoned. The original Kjellin furnace was only invented for melting pure Swedish raw metal. In order to carry out refining side plates were added in this furnace, and the combination was quite satisfactory, the power factor being higher than it would be if side plates alone were used. This led to the conclusion that side plates might be used with advantage in other furnaces than the Rochling-Rodenhauser, and after some trials this was fully verified ; thus the ( ( Paragon ” furiiacc developed out of the Rochling-Rodenhauser furnace, It is quite true that if the electrodes could be done away with altogether, it would be of advantage ; seeing that for certain purposes this is hardly alto- gether possible, it will at least be appreciated that they can be reduced con- siderably in size for a given output of steel, disregarding the cause of the wear and tear.The (( pointing ” of the electrodes need not be very marked, if the snielt is properly conducted ; this indicates that the slag conditions need to be rectified, in which case the electrode will burn eveil. Heating of the slag for the purpose of refining is usually required by the steel-maker. But this does not mean that the whole of the power need to be conveyed to the charge through the slag bath as is the case in the “arc” It was objected that this would cause considerable heat losses.RECENT DEVELOPMENTS IN METALLURGY 193 furnace, and as it is admitted that the electrodes generally are a nuisance, it is desirous to at least reduce their size as far as possible, and it therefore seems to me that the heating from below the bath is quite justified.It is quite significant that Mr. Campbell mentions the refining in the Siemens’ open-hearth furnace. Here the refining is carried out solely from the surface of the bath, and although this process is giving a very fair result, most steel-makers will probably agree that the result could be improved. The objection to using six electrodes instead of three was that it lead to difficulties with the roof. Mr. Harbord had asked whether side plates alone would give sufficient heat in a wide bath, narrow channels being ruled out by the “ pinch effect.” He had made a great many experiments to find out the action of the side plates, and he had found that sufficient heat could be obtained with side plates only.With regard to the suggestion to do away altogether both with side plates and electrodes, it might be of interest to mention that a friend of his had used a crucible with coils and had melted steel therein, merely by means of the eddy current in the solid metal. After the recalescence point was reached, however, the magnetic properties of the steel disappeared, but still he was able actually to pour the metal. Of course, the shape of the coils was of great importance here, and it was necessary to have it as close as possible to the crucible.A distinguished metallur- gist had stated that the presence of carbide was not absolutely necessary, but it was an indication that all the sulphur had been driven out, and the proper temperature maintained. When speaking of degasification he had in mind occulated CO and similar gases ; he had not made determinations of the nitrogen in the steel. With regard to the Helberger furnace, Rodenhauser had recently written a book on electric furnaces in which he had more or less condemned the Hel- berger as a steel-making furnace. This was not fair, as the furnace had proved to be very valuable for making trial steel melts, especially alloy steels. Mr. Campbell stated that the furnace was of 110 use to steel manufacturers. A year ago the chief metallurgist of the United States Steel Corporation wanted a purely melting furnace and asked especially for one of a type like the Helberger, which was at that time in the experimenting stage only.This would prove that the steel-makers actually do require such a furnace. In reply to Dr. Harker’s question about the Helberger furnace, the crucible is open at the top, and access can be obtained to the charge through the upper contact plate, so as to examine the charge, &c. The charge does not conduct the current, as has been verified in many trials. The crucible is lined in such a way as to prevent this. No “pinch effect” is experienced in this furnace. In reply to Dr. Borns, he wished to say that he himself had fused down a charge with electrodes, and, after disconnecting these, superheated the metal with such “side plates” only, on several occasions.Furthermore, he had seen several charges of tons actually melted down from cold metal, the “ side plates ” had been heated previously. This, he thought, would repudiate Mr. Conrad’s statement, which cannot therefore have been based on actual experiments. He fully agreed that the trial carried out by Mr. Conrad would not lead to a success; owing to pending patent applications, their own arrangements could not, however, yet be fully described, but the said fact remained, and he hoped to be able to give full details at a later date. On The power factor was very low. With regard to the question of degasification. Its further formation was superfluous.I94 THE ‘‘ PARAGON ” ELECTRIC FURNACE these occasions a great number of measurements were also taken, bearing out the facts. The carbon dimensions for a 5-ton 3-phase furnace should, for practical reasons, be about 9 in. by 9 in. Referring to Mr. Ruthenburg’s remarks, the fact that he simply states that the “bottom electrodes,” as he calls this arrangement, would show no advantage without giving logical reasons for such statements, shows that he must be unfamiliar with this class of design. In his-Mr. H5rd&n’s--design there is no cooling water below the metal; the steel plates are cooled by enforced air-draught. The experiments at Niagara prove nothing, as long as it cannot be shown that electrodes and other arrangements identical with those in the “ Paragon ” furnace had been tried and failed. It is clear that minor details which cannot be embodied in a paper like the present, play a very important r6le in practice and steady work on a problem which is by no means a physical impossibility is sure to lead to distinct results, and ought not to be treated slightingly at the onset. As to the Chairman’s remarks, he wished to say that trials were being carried out which so far have proved very promising, but it was too early to give any data.

ISSN:0014-7672    

DOI:10.1039/TF9120700188

出版商:RSC    

年代:1912

数据来源: RSC

摘要:

PROGRESS IN THE ELECTROMETALLURGY OF IRON AND STEEL. BY DONALD F. CAMPBELL, B.A., A.R.S.M. ( A Paper read before the Faraday Society, Tuesday, October 3, 1911, Mr. F. W. HARBORD, VICE-PRESIDENT, in the Clzair.) The development of electrometallurgical methods of smelting is prob- ably the most important advance of recent years, both in electrical and metallurgical science. Although the last few years have seen the introduc- tion of few fundamental principles or processes, the all-important evolution from the laboratory to the commercial stage has, in many cases, been accom- plished, more especially in the electrothermic processes to which I would refer, and increase of efficiency and reduced cost of production are the problems receiving most attention at the present time. Generally speaking, power supply is one of the chief factors in this work, but this is the case in a varying degree, and we must consider briefly the influence of the various commercial factors which may produce the maximum profit in any electrometallurgical enterprise, to understand intelligently the distribution of the industry in various parts of the world.The potential wealth of Scandinavia as regards water-power supply and transport facilities is probably unrivalled, and consequently the industries in which power is of prime importance arc highly developed, such as the manufacture of nitrates, cyanamide, carbide of calcium, ferro-silicon, and the smelting of refractory lead-zinc ores and iron ore. The power-cost factor in the manufacture of these products is high, and would be quite prohibitive in any country such as England, where the price of electricity is at least three times that of the usual cost in Scandinavia. The waterfalls and torrents of the Alps in Savoy and Switzerland are another source of cheap power, and consequently the production of ferro- alloys and aluminium is profitably carried on at Neuhausen, L'Argentikre, and elsewhere, the latter industry being especially favoured by the proximity of immense deposits of bauxite, the ore from which all aluminium is obtained, which occur near Marseilles.As types of water-power stations may be mentioned Trollhattan in Sweden, which already has 50,000 h.p. in operation, generated at 10,000 volts and 25 periods by four turbines of 12,500 h.p. capacity each, and four units of similar capacity are nearly completed.This station has been built by the Government for general distribution, and power is supplied at 44s. per horse. power year for electric smelting. The usual power station constructed exclusively for furnace work is, however, of a different nature, and another typical example may be taken from L'Argentikre where 40,000 h.p. is developed by machines of 850 h.p. and 1500 h.p., each generating at the voltage required, and direct connected to the furnace bus-bars without switches, &c., the control being entirely at the water-gate of the turbine. Niagara Falls is I95196 PROGRESS I N THE another important source of power of medium price, and the centre of several industries, notably the manufacture of aluminium, carbide, ferro-alloys, and carborundum.In the case of the electrometallurgy of iron and steel, there are many other important factors in addition to the cost of power.; but the two questions of smelting iron ores to make pig iron or steel direct from ores and the melting and refining of steel possess fundamental differences, and must accordingly be considered separately. The reduction of iron ores has only made headway in Scandinavia and the Pacific Coast of America, and, with the possible exception of Central Canada, these are the only points at which it is likely to find general application for many years. Both these countries are without coking coal, but have large quantities of timber available for charcoal. On the Pacific Coast pig iron is brought thousands of miles by train from the Eastern States or by sea from China, although water-power is plentiful, iron ore of remarkable purity is found, and wood slabs and sawdust, produced as a waste product from the saw-mills, are available for charcoal manufacture. In Sweden large deposits of ore still remain, though the price of charcoal is increasing as the supply decreases, owing to the exhaustion of the forests and the growing demand for wood-pulp.The iron-masters, having foreseen a time when it will be impossible to make pig iron profitably unless some reduction in the; consumption of charcoal per ton of pig iron can be made, devoted about L20,ooo for the erection of works tct evolve some process to overcome this unsatisfactory state of affairs. The electric furnace solves this difficulty, as charcoal is required only as a reducing agent and not as a source of heat, so that the consumption is reduced two-thirds ; in other words, the available charcoal will profitably smelt more than double the quantity of ore by the development of the enormous possibilities of the waterfalls provided the power can be produced at 33s.per horse-power year under the conditions and prices now prevailing for charcoal and pig iron. This development will be closely watched with the greatest interest by political economists, as the balance of power in Europe is influenced by the distribution of the world’s iron and steel trades ; and it is interesting to note that the prestige of nations varies with the importance of this fundamental industry, as is exemplified in the high position of Britain and the growth of the iron and steel trades of Germany in recent years.That this new development will strengthen Sweden, especially in the north, is beyond doubt ; but there is another important development which will undoubtedly restore the balance to a great extent, namely, the electric refining of steel, which can be carried on in any country, irrespective of exceedingly low cost of power. The position of Sweden has been dependent to a great extent on the fact that the pig iron made from local ores and charcoal is of exceptional purity and commands a high price, because it was impossible to refine the steel made from impure materials. The use of the electric steel furnace is removing this preference enjoyed by the Swedish manufacturer owing to the natural resources of his country, and pure steel can now be made by the Germans from the impure ores in Luxemburg, by the French in Lorraine, or the British in Cleveland.The results of smelting operations at Trollhattan in Sweden, at Hkroult in California with 2,000-k.~. furnaces, and at Domnarvet with 3,000-k.w. fur- naces, prove conclusively that this type of furnace can compete profitably with the small Swedish charcoal blast furnaces if power costs less than 33s.ELECTROMETALLURGY OF IRON AND STEEL 197 per kilowatt year at the present state of our practice, and important improvements are to be expected, as was the case with the steel furnace, which is in a more advanced state of development. This figure for the cost of power is quite reasonable, and leaves a margin of profit for the power company where general conditions are favourable.In California the price of power is about 50s. per kilowatt year, but the cost of ore is lower and that of pig iron higher than in Sweden. It is interesting to note that the furnaces developed independently at Hbroult, California, and in Sweden are almost identical in construction, and undoubtedly the greatest credit is due to the careful and persistent work of the engineers in charge of the operations at these three pioneer works, and such men as Noble and Ljungberg, who have had the foresight and courage to supply the necessary capital to develop this process from a theoretical to a commercial and profitable basis. The furnaces are two or three phase, and have three, four, or six electrodes.The troubles at present experienced are the difficulty of maintaining a circulation of gas in the furnace without excessive electrode consumption or other means of forcing the heat up the charge in such a way as to increase the active zone in the furnace-in other words, to avoid an excessive concen- tration of heat near the electrodes, and properly to utilise the rich gas given off from the furnace. Minor improvements of this character are being coiistantly made, and the process generally improved thereby. The refining of steel by electricity is, however, of even greater interest, on account of its high state of development, wide application, and its economic importance in Britain. A few years ago the best steel could only be made from the purest minerals, the domestic supply of which is approaching exhaustion.Now pure steel of excellent quality can be made from inferior ores such as those of Cleveland and Lincolnshire, and the price of power in England is sufficiently low to make this a profitable operation. Statistics show that the rate of growth of electric refining has been more rapid than that of other important processes, and the output of electrically refined steel for five important countries has risen from approximately 30,000 tons in 1908 to izo,ooo tons in 1910, and a further increase will probably be maintained this year. Perhaps this is due to its varied application, as it has been already found profitable for the manufacture of many classes of tool and special steels aiid castings.But the question that is now before progressive steel-makers is of much greater significance. Will the electric furnace, which has already absorbed over 30 per cent. of the high-class steel trade, be applied generally, in conjunction with the basic or acid Bessemer converter, to compete with open-hearth steel in the matter of cost? At present it can only compete with acid open-hearth steel for price, though in quality it is superior to any steel made by these methods, and consequently its general adoption would mean an improvement in quality which is now so necessary to meet the requirements of modern engineering. Many steel-makers think it impossible, but German and American engineers are giving this problem the most serious consideration, and several zo-ton electric furnaces are now being erected with complete confidence to prove the economy of this very application as a duplex process. Owing to the nature of the native ore deposits, Germany IS dependent on the basic Bessemer process for the production of cheap steel.Sixty per cent, of the output is made by this process, but it is now realised that the steel so produced is not sufficiently reliable for modern requirements, and some improvement in quality is essential if this process of Thomas and Gilchrist is to survive, and several plants are now adding electric refining to solve198 PROGRESS IN THE this difficulty, which is so serious to them because 97 per cent. of the steel output is by basic processes, 60 per cent. being Bessemer, and 37 per cent.open-hearth. In America there is no basic Bessemer production, but the basic open-hearth process accounts for 59 per cent. of production. If the electric furnace is generally adopted as an adjunct of the basic Bessemer process, its application to Germany’s output of steel alone would absorb about 250,000 k.w. per annum and mean a wide application of electricity. The generation of power for steel works generally, and electric furnaces in particular, must be briefly discussed. The load factor is high, and the power factor above ’9 in furnace work, so that all machines can operate at high efficiency. In a 100,000-h.p. central station at one of the works of the United States Steel Corporation, where 2,000-k.~. Hkroult furnaces are used, gas engines using blast furnace waste products, supplemented by steam engines, are the prime movers. Similar furnaces are to be used in a most interesting works, which are unique in England, because a large rolling mill, blowing engines, auxiliary motors, electric and open-hearth furnaces will all be driven by gas from the company’s blast furnaces and by-product coke ovens FIG.4. without the burning of any other coal or fuel. Under such conditions the cost of power is under -25d. per kilowatt hour. In the case of steam turbines, which are also used in England for furnace work, the cost is from *4--5d., while corporation supplies are also used at the high figure of -65d. per kilowatt hour. The current used in steel refining may be single-, two- or three-phase and of any commercial periodicity. Furnaces of 2,000-k.~.capacity are working with frequencies from 25 to 60, though modifications of design are necessary for high periodicity if a good power factor is to be main- tained. The variations in load have been stated to be a serious trouble, and when melting scrap on circuits used for lighting purposes this may be the case, though precautions can be taken to overcome this trouble, and with properly designed machinery these shocks can be practically absorbed, and the variations of voltage kept within the necessary limits, even with small central stations.198 PROGRESS IN THE this difficulty, which is so serious to them because 97 per cent. of the steel output is by basic processes, 60 per cent. being Bessemer, and 37 per cent.open-hearth. In America there is no basic Bessemer production, but the basic open-hearth process accounts for 59 per cent. of production. If the electric furnace is generally adopted as an adjunct of the basic Bessemer process, its application to Germany’s output of steel alone would absorb about 250,000 k.w. per annum and mean a wide application of electricity. The generation of power for steel works generally, and electric furnaces in particular, must be briefly discussed. The load factor is high, and the power factor above ’9 in furnace work, so that all machines can operate at high efficiency. In a 100,000-h.p. central station at one of the works of the United States Steel Corporation, where 2,000-k.~. Hkroult furnaces are used, gas engines using blast furnace waste products, supplemented by steam engines, are the prime movers.Similar furnaces are to be used in a most interesting works, which are unique in England, because a large rolling mill, blowing engines, auxiliary motors, electric and open-hearth furnaces will all be driven by gas from the company’s blast furnaces and by-product coke ovens FIG. 4. without the burning of any other coal or fuel. Under such conditions the cost of power is under -25d. per kilowatt hour. In the case of steam turbines, which are also used in England for furnace work, the cost is from *4--5d., while corporation supplies are also used at the high figure of -65d. per kilowatt hour. The current used in steel refining may be single-, two- or three-phase and of any commercial periodicity.Furnaces of 2,000-k.~. capacity are working with frequencies from 25 to 60, though modifications of design are necessary for high periodicity if a good power factor is to be main- tained. The variations in load have been stated to be a serious trouble, and when melting scrap on circuits used for lighting purposes this may be the case, though precautions can be taken to overcome this trouble, and with properly designed machinery these shocks can be practically absorbed, and the variations of voltage kept within the necessary limits, even with small central stations.198 PROGRESS IN THE this difficulty, which is so serious to them because 97 per cent. of the steel output is by basic processes, 60 per cent. being Bessemer, and 37 per cent. open-hearth. In America there is no basic Bessemer production, but the basic open-hearth process accounts for 59 per cent.of production. If the electric furnace is generally adopted as an adjunct of the basic Bessemer process, its application to Germany’s output of steel alone would absorb about 250,000 k.w. per annum and mean a wide application of electricity. The generation of power for steel works generally, and electric furnaces in particular, must be briefly discussed. The load factor is high, and the power factor above ’9 in furnace work, so that all machines can operate at high efficiency. In a 100,000-h.p. central station at one of the works of the United States Steel Corporation, where 2,000-k.~. Hkroult furnaces are used, gas engines using blast furnace waste products, supplemented by steam engines, are the prime movers.Similar furnaces are to be used in a most interesting works, which are unique in England, because a large rolling mill, blowing engines, auxiliary motors, electric and open-hearth furnaces will all be driven by gas from the company’s blast furnaces and by-product coke ovens FIG. 4. without the burning of any other coal or fuel. Under such conditions the cost of power is under -25d. per kilowatt hour. In the case of steam turbines, which are also used in England for furnace work, the cost is from *4--5d., while corporation supplies are also used at the high figure of -65d. per kilowatt hour. The current used in steel refining may be single-, two- or three-phase and of any commercial periodicity. Furnaces of 2,000-k.~.capacity are working with frequencies from 25 to 60, though modifications of design are necessary for high periodicity if a good power factor is to be main- tained. The variations in load have been stated to be a serious trouble, and when melting scrap on circuits used for lighting purposes this may be the case, though precautions can be taken to overcome this trouble, and with properly designed machinery these shocks can be practically absorbed, and the variations of voltage kept within the necessary limits, even with small central stations.ELECTROMETALLURGY OF IRON AND STEEL 199 Progress both in the metallurgical and mechanical details of the steel furnace is continuous. Two years ago the power consumption used for melting and refining cold scrap under best conditions was 750 kilowatt hours per ton, but one furnace in England has required a power consump- tion of only 575 kilowatt hours per ton for the last 527 tons manufactured.The difficulties of making good electrodes have been one of the principal difficulties, but now a material of excellent quality is obtainable from several manufacturers, and the consumption of carbons has undoubtedly been reduced 50 per cent. during the last three years by improvements in manipu- lation and material, and breakdowns are no more frequent with experienced men than in the case of the old-established processes. The operation and design of a steel furnace requires experience if satis- factory results are expected, and difficulties always occur when any new design or problem is being worked out.The usual operation is the removal of sulphur, phosphorus, and oxides from steel which may or may not be previously melted, and the addition of carbon and various alloys. The progress of these reactions is shown diagrammatically in the illustration (p. 198), the first part being carried on with an oxidising slag and the second under reducing conditions. It must be remembered that a large number of engineers of the highest technical training and international experience are constantly engaged in improving furnace design and metallurgical methods on behalf of powerful industrial organisations. Careful and expensive experimental work has been going on for years, and many of the furnaces and processes, which are continually being patented and published, have been tried and abandoned by those controlling large electrochemical works. Improvement must be sought by increasing the general efficiency of the best processes we have at the present time rather than by radical changes in furnace construction. In all questions of design it is essential to bear in mind first and foremost metallurgical requirements, and electrical considerations always must take a secondary place. The neglect of this important principle has caused the failure of the majority of the numerous furnaces which in recent years have been described in technical journals, but abandoned because they are based on incomplete theoretical data with little or no commercial practice, whereas the most successful electric steel furnace of to-day follows as closely as possiblc the best basic open-hearth practice with the simplest possible application of electrical heat energy.

ISSN:0014-7672    

DOI:10.1039/TF9120700195

出版商:RSC    

年代:1912

数据来源: RSC

摘要:

ELECTROMETALLURGY OF IRON AND STEEL 199 DISCUSSION. Mr. W. Murray Morrison (communicated) : The particulars given by Mr. Campbell in liis paper are of great interest, and serve to show to what a very great extent the electrometallurgy of iron and steel has developed within recent years. Great strides have been made in that period, and there is no doubt that the electric furnace for the production of higher qualities of steel has undoubtedly come to stay. I should like to ask Mr. Campbell if he can give some figures showing the best efficiency attained to in more recent average working practice for the electrode consumption. The figures he gives showing the increased efficiency attained to in kilowatt output show a considerable advance, and I should like to ask whether the 575 kilowatt hours per ton to which he refers is a measure of the total energy used for the production of the 527 tons referred to, or whether this is a mean figure.In other words, is the peak load considerably in excess of this figure, in which case a generator of larger size would require to be installed?200 PROGRESS IN THE The curve which Mr. Campbell showed on the screen was most interest- ing. The great variation in the purity of the product both in the case of best quality crucible steel and electric steel is marked, and in neither case does it appear to follow a straight line law. Mr. M. Ruthenburg, referring to Mr. Campbell’s remarks about the action of nickel, chrome, sulphur, and phosphorus of unknown quantity in scrap used in the electric furnace, said the action was purely thermochemical and happened in an open-hearth or any other furnace.The origin of the scrap would tell pretty closely what its sulphur and phosphorus contents were, and if Mr. Campbell had told us how to get the nickel out and leave the chrome, there would be something in it, the facts being that he could not do otherwise than what he did. Mr. E r n e s t P. Hollis said with regard to the power costs quoted by Mr. Campbell, he pointed out that in his experience authors of papers inad- vertently did our country an injustice when they compared costs in this country and abroad. We could generate power from coal in this country at a cost which would compare very favourably with power generated from coal in any part of the world, and also with all but the most easily developed waterfalls.Mr. Campbell’s lowest American costs were 025d. per kelvin, but power had been supplied for electrochemical work in this country at 0.165d. per kelvin for many years now, and probably the lowest price at which it was now being sold here was o-Id. per kelvin. Those costs were obtained solely by intelligently designed power houses with first costs of ;G7 10s. per kilowatt and by most economical working, and were not due to any favourable buying of by-product gases. A furnace with a high power factor would be most favourably received by the supply authorities. If large groups of furnaces were installed with a low power factor, then the price of power would be somewhat increased since the low power factor would entail the provision of rotary condensers {Le., over-excited synchronous motors) in order to correct it.Mr. Donald F. Campbell, replying to Mr. Ruthenburg, said that his remarks referred to charges consisting of nickel-chrome turnings without any addition of pig iron or other scrap, which charge could not be treated in the open-hearth furnace; whereas in the electric furnace a far greater control could be obtained and the greater part of the chromium eliminated or retained in the bath, according to the oxidising or reducing nature of the slags used. Replying to Mr. Hollis, he was aware that power could be obtained on the north-east coast at the figure mentioned, but he thought it possible that some of the companies were selling power at less than the true cost. The figure he mentioned referred to power obtained from blast furnace gases, where the blast furnaces are properly credited for the gas used and all other charges.Although many power stations claimed to produce power at o.Id. by gas engines and blast furnace gas, he considered it only proper that the blast furnaces or coke ovens should be credited with a reasonable amount as the value of the gas supplied. He stated that a properly designed and operated electric furnace might have a power factor of 0.9 and a load factor of 85 per cent., whereas the load factor on an ordinary lighting circuit was under 20 per cent., and that the electric furnace was a very desirable load for the power station. Mr. Kilburn Scott’s statement with regard to the sluggish motion of steel in an arc furnace did not appeal to him, as there was more motion than in the case of the open-hearth furnace. This, indeed, appeared in all types of electric turnace, and there was sufficient motion for the refining action, butELECTROMETALLURGY OF IRON AND STEEL 201 not sufficient to introduce any danger of oxidation, as one would expect with a furnace such as Mr.Kilburn Scott described, in which the steel some- times rose to an angle of 45'. Some criticism had been made about the trouble of electrodes, but he observed with regret that electrodes had not been eliminated in the '' Paragon " furnace. It was true that they were much smaller, but the con- sumption of carbon was not proportional to the size, because about half of the consumption was due to disintegration and pointing of the ends, and this loss would be nearly as great in the small as in the large electrodes. A further advantage in large electrodes was the more extensive slag area exposed to the arc.It had been stated that the great disadvantage of the arc furnace was the cost of roof repairs. In the case of the roof of a furnace which was removed a few days ago, eighty-six heats of 2-6 tons had been made under the one roof at a cost of only 24d. per ton of steel for roof repairs, and this was due to the fact that the roof is protected to a great extent from the direct radiation of the arc by the electrodes themselves. Mr. Morrison asked the method of arriving at the figure of 575 kilowatt hours power consumption per ton of steel mentioned in the paper. This refers to the mean kilowatt-hours per ton of steel measured on the furnace busbars, used during the manufacture of 527 tons of steel. The average kilowatts used is approximately 400 k.w. with a furnace of 2+ to 3 tons capacity. A good generator of 400 k.w. will stand any overload which may occur, as this will not exceed an instantaneous overload of 60 per cent. maximum, the duration of the variations being exceedingly short. Mr. Hardkn has discussed the question of roof repairs as being a disadvantage in arc furnaces, but in the case of a.H&oult furnace, where direct radiation of the arc is screened from the roof by the electrode itself, that is not a serious item, and will not exceed 23d. per ton of steel, even in small furnaces.

ISSN:0014-7672    

DOI:10.1039/TF9120700199

出版商:RSC    

年代:1912

数据来源: RSC

摘要:

THE HERING ( L PINCH E F F E C T ” FURNACE, BY E. KILBURN SCOTT, M.I.E.E., A.M.INsT.C.E. ( A Paper read before the Faraday Society, Tuesday, October 3, 1911 Mr. F. W. HARBORD, VICE-PRESIDENT, in tlzc Chair.) The “ pinch phenomenon,” was first noticed in connection with electric furnaces by Mr. Carl Hering. It may be defined as a contraction of the cross-section of a liquid conductor through which current is passing, the contraction being due to an electromagnetic force which acts from the cir- cumference to the centre. Under certain circumstances this contraction or pinching may be sufficient to completely rupture the circuit. Mr. Hering discovered this phenomenon when working on a furnace in which it was a distinct disadvantage to have it. He therefore set to work to find out how it could be made useful, and the result has been the further discovery of a valveless electromagnetic pump.The principal patent claim (there are thirty-four claims) reads as follows :- “ For an electric furnace, a hearth for containing a mass of molten material, columns or channels connecting with said hearth and adapted to be filled with molten material in communication with said molten mass to constitute the furnace resister, and electrodes in end-on communication with said columns or channels, the square of the current transmitted through said electrodes to the molten material in said columns or channels with relation to the cross-section of said columns or channels being great, whereby said mass of molten material is automatically stirred.” Fig.I represents the cross-section of two liquid conductors A A sur- rounded by non-conducting material, BB. The current enters and leaves by water-cooled electrodes CC, D being the transformer. Assuming for the moment that each liquid conductor is made up of a number of elemental conductors, these will be attracted together in accordance with the so-called law that “ like currents attract.” Circulation of the liquid is therefore set up, as shown by the arrows, by the liquid moving from the circumference to thc centre. As one end of the hole is stopped up by the electrode any pressure set up can only be relieved by the liquid moving upwards as a fountain, and that is what actually happens. It may be interesting to note that when in Sydney the writer saw a metal pipe which had been struck by lightning.The great inward pressure due to the current travelling along the pipe had completely collapsed it. It was not simply flattened, but had crinkled all round.” Again, it may have only been an accident, but about nine years ago, when making calcium-carbide, the writer noticed that the blocks generally came out of the furnace smaller in section at the middle than at the ends. * See Pvoc. of Royal Society of New South Wales, vol. xxxix., p. 131 (19s). 202THE HERING “PINCH EFFECT” FURNACE 203 Messrs. Leeds and Northrup make an ammeter for very large currents which works by means of the pinch phenomenon on a column of mercury.* The furnace may be a tilting one (as shown in Fig. z), or there may be a tapping-hole just above the top of the resistor tubes. In any case, the resistor tubes must not be emptied, and sufficient metal must be left in the bottom of the furnace to connect them across.As Fig. 2 is drawn to scale, it shows very clearly how small the two electrodes are, compared with the bulk of the furnace. It also shows how the electrodes are inclined, this being done in order to squirt the metal FIG. I. against the blanket of slag at an angle, to produce good circulation and to expose a larger surface of metal to the slag action. Stirring Action.-Looking at the top of the charge, its appearance is some- what similar to rapid boiling of water at two spots where heat is localised, but, of course, there is no noise. Also there are no bubbles unless the charge contains gases or volatile matter.In some cases the agitation at the top of the metal charge is so great that the surface is inclined at 45 degrees. The suction down into the bottom of the resistance tubes is also considerable, and on one occasion air was drawn in through a leaky tap-hole with a whistling noise. It should be noted that the heating is entirely effected at the bottom of the charge, and the circulation from there is in a natural direction upwards. Heat is thus transferred to the whole of the charge by a vigorous stirring, and not by mere conduction. Electrodes.-The electrodes are usually made of the same metal that is * See Physical Review, June, 1907, also Journal of American Electrochemical Society, May, 1909.204 THE HERING “PINCH EFFECT” FURNACE being melted. The sections of the electrodes and the current that passes are so proportioned that the ends of the electrodes are raised to a temperature as nearly as possible equal to the temperature of the molten charge.The problem was to find conditions that give lowest heat losses, and this Mr. Carl Hering has found to be when the section and length of the electrode are such that the current heats the hot end of the electrode exactly to the furnace temperature. An electrode should be a good electrical conductor to reduce the loss of energy due to electrical resistance ; on the other hand, good electrical conductors arc as a rule also good heat conductors ; FIG. 2.-Tilting Furnace fitted with two “ Pinch Effect ” Electrodes. they thus tend to conduct heat away from the inside of the furnace where the heat is wanted. Increasing the cross-section reduces the former loss but increases the latter, while increasing the length does the reverse.In the Hering furnace no heat is abstracted by the electrodes from the charge in the furnace, the entire loss of heat energy being thus only that portion generated in the electrodes. This is the condition under which the total loss of energy is lowest, for under any other conditions the total combined losses will be greater and the electrodes will either chill the furnace product or develop excessive heat where they pass through the walls. Of the various materials for electrodes Mr. Hering’s experience goes to show that metal electrodes are distinctly cheaper and more economical in energy. Copper is the best and iron nearly as good; gas carbon is the worst, graphite being only slightly better than gas carbon.The electrodes being small and out of the way do not affect the size andTHE HERING “PINCH EFFECT” FURNACE 205 shape of the furnace, as is the case with other types of furnaces. Waste space in a furnace, and electrodes that are too large, dininish the efficiency very considerably. Refractory Lining.-As the hottest metal flows up the centre of the resistor tube, the lining does not have to withstand the greatest heat, Again, there is very little eroding action due to friction on the wall, because the pinch effect tends to pull the metal away from the lining; indeed, it tends to form a vacuum there. This is just the opposite to some furnaces, where the circula- tion of the molten metal has given trouble by eroding the lining.Alundum, which is made by fusing bauxite in the electric furnace, has been used for the lining. Magnesite powder is now employed ; it is packed in whilst in plastic condition, and forms an extremely hard and smooth glossy surface after being heated. Action of Slag.-The rapid circulation obtained in the furnace allows chemical changes to take place rapidly, and this means great economy in time. The maximum temperature at any point does not need to be much above the normal. In other furnaces where circulation is sluggish the temperatures in the charge vary a good deal. To allow for effective action of the slag it is important that the hottest metal should impinge directly on it. This is just exactly what takes place in the Hering furnace, for when it leaves the centre of the tube, the heated metal is forced up against the blanket of slag.Reaction with the slag is an essential factor in many processes, especially in steel-making. Current.-Regarding the amount of current required, it may be mentioned that a furnace having resistor tubes only 2-inch diameter and 4 inches deep, with metal about 2 inches deep over the tops of the tubes, took 3,000 amperes at 5 volts. Starting from cold, in a short while the metal was dull red, and when the current reached 5,000 amperes the squirting action was very active. For such low voltages and large currents the homopolar direct-current dynamo is excellently suited, and as an efficient and mechanical design is now available, there is no reason why this type should not be used.The pinch effect varies directly as the square of the current and inversely as the section of the conductor, Mr. Carl Hering’s formula being as follows :- C” S P = 000oooo2248 -; where- P = pounds per square inch ; S = square inches ; C = current in amperes. Power Factor.-It should be noted that the furnace will work with either direct or alternating current, because the direction of flow of the liquid in the resistor tube is independent of the direction of the current. The pinch effect is also the same. Three-phase currents can be used, there being then three electrodes instead of two and each resistor one-third shorter for the same current. With alternating current the power factor can be very high indeed, practically unity, and in this respect the Hering furnace is sharply marked out from induction furnaces, which have a low power factor.In the latter the power factor may be 0.7 to 0.8 with 25 cycles, but only by using some extraneous and expensive device, such as an over-excited motor- generator. Again, the frequency can be anything that is used in everyday practice ; it need not be specially low. As a consequence standard electrical machinery can be used for the Hering furnace.206 THE HERING “PINCH EFFECT” FURNACE Self-regulalioiz.-One feature, which may turn out to be a very important one, is that if the electrode is made of the same material as the resistor the furnace tends to be self-regulating as to temperature. Thus, when the temperature increases, the electrodes automatically become longer and the resistor column therefore shorter, whereby less heat will be generated.The reverse also holds good. The place where the electrode ends, and the resistor column begins is that plane across which no heat flows; the heat generated above this point going out to the furnace, and the heat below going to the terminal. The plane will of course move automatically up or down. The heat may be regulated with great nicety to suit the metallurgical requirements. This is not so in the arc furnace where the temperature is frequently much higher than is necessary when the melting is done in an induction furnace. Excessive Pinch Efect.-One criticism that has been made is that the pinch effect may be too great and the continuity of the liquid conductor be broken.This, however, is only a matter of correct proportioning of the size of the resistor tube and the amount of current. It may be mentioned that Mr. Hering has several times allowed the metal in the resistor tubes to cool and harden overnight, and then found that he could start up next day from the cold state. This showed that the metal had not broken apart in the shrinking. For example, in the induction furnace, aluminium, because it is light, pinches off with a current only a little higher than that required to melt it. But this only means that greater care must be exercised in proportioning the resistors and depth of metal in the Hering surface. Large versus Small Furnaces.-It is interesting to note that some inventions and developments which work well on a small scale, will not do at all on a large scale.On the other hand, other inventions give the best results on a large scale. In this respect the Hering furnace is on the right side, as it promises to give best results for large furnaces, because the resistor tubes can then be shorter and of large diameter. In furnaces where the resistor tubes are of small diameter, a slight increase in current may pinch off the column, but in furnaces with larger columns there is not that risk. Indeed, the pinching pressures may be enormous without danger of discontinuity. Melting Noiz-conductors.-But it may be asked, how are materials which when melted are non-conductors, to be dealt with ? The answer is, by means of a bath of suitable metal kept molten in the bottom of the furnace, e.g., glass, or whatever non-conductor it was required to melt, would be placed over the metal.Zinc and arsenic ores can be tackled in a similar way, and it is worthy of notice that it is not so easy to treat such materials in an arc furnace. Smelting Iron Ore.-In his patent specification Mr. Hering makes the valuable suggestion of a double furnace for making steel direct from the ore. He proposes to dissolve carbon in the iron in one part of the furnace and the oxide in another. The carbon-monoxide gas given off can also be burned to pre-heat the ore, thus making use of the total energy of the carbon. One feature which above all others will surely appeal to iron- and stcel- makers is that the furnaces are very little if any different from those they have been accustomed to. In the past, electric-furnace working has been handicapped to some extent by the unusual, not to say complicated, designs which engineers have hitherto put forward. This objection cannot be brought against the Hering pinch-eff ect furnace. So far as heat loss is concerned a section of a sphere gives the smallest Some metals pinch off more readily than others. The non-conductor does not enter the resistance tube.THE HERING “PINCH EFFECT” FURNACE 207 area from which heat can be radiated. A square-shaped bath is next, and the rectangular shape a bad third. But the worst form of all is the long, winding, narrow channel of the induction furnace. Considered from the economy of heat point of view, nothing could be worse.

ISSN:0014-7672    

DOI:10.1039/TF9120700202

出版商:RSC    

年代:1912

数据来源: RSC

摘要:

THE HERING “PINCH EFFECT” FURNACE 207 DISCUSSION. Dr. Carl Hering (Philadelphia, USA.), wrote that he was pleased to note that the subject of his furnace was considered as of sufficient interest to bring before the Faraday Society, Concerning Mr. Kilburn Scott’s interesting observation in the calcium carbide furnace, he thought it exceedingly likely that the peculiar shape of the chunks was due to pinch effect, as it was quite a powerful force under proper conditions, and would be quite likely to give a plastic conductor such a shape as mentioned. During the summer he had worked out a modified form of furnace, better adapted to small sizes than the original one. He had also made a number of tests in which the parties who have the rights to his furnace are interested, the work being confined more to trying metallurgical processes than to the development of the furnace itself.He ran it repeatedly, day after day, without having any trouble ; in fact, it ran beautifully and gave far better results in quick melting of cold metal than he had any idea it would give. Although a poorly constructed affair, as far as heat economy was concerned, and the transformer used was for an entirely different purpose, yet he had no difficulty in melting down the charge when he filled the crucible completely to the top. He had built a number of small temporary furnaces for the purpose of getting data, trying out various metallurgical processes, and to satisfy capitalists that it was a commercial proposition, This they were now satisfied with, and they had contracted for the rights not only of the United States, but for all the foreign countries besides.This he thought would show that those supplying the money were satisfied that it was a commercial pro- position, and not merely a laboratory toy. He had melted steel without any difficulty, and gotten it very liquid ; this, in fact, was easier than many of the other metals and alloys, as the propor- tions were better for steel than for the low-resistance alloys. He had therefore been carrying out many of his tests under more unfavourable con- ditions than those for steel-making. For this reason he felt that the furnaces would run better in larger sizes for steel. In the small sizes with which he had been experimenting, the resistors were small, and at first gave rise to troubles on account of that.With larger furnaces the resistors become much larger, and when the hydraulic pressure in the crucible due to the head of the metal was sufficiently great, the operation was very smooth running. In melting steel, a carbon rod held in front of one of the squirting tubes dissolved like a stick of candy in hot water; on the other hand, iron ore placed on this carbonised iron gave off enormous volumes of gas, showing that the ore was being reduced by the carbon in the iron, just as in the open-hearth process, With this combination, he proposed to use the f uriiace for the reduction of iron ore, and it was likely that there would be advantages over the blast furnace. By placing the squirting tubes tan- gentially, the mass of molten iron may be kept in a rotary motion.Then, if the charge was divided by a partitionj which need not reach down to the liquid, the carbon being on one side and the ore on the other, the208 T H E HERING “PINCH EFFECT” FURNACE carbon would dissolve, and the ore be reduced. The carbon monoxide set free would be burnt with tuyeres in the ore chamber only, burning into carbon dioxide, thus pre-heating the ore, and giving up all of its lieat This cannot be done in the blast furnace because the carbon mixes with the ore, and reduces the COa back to CO. He was able to do it because he could keep the molten iron rotated so that every particle would come alternately under the carbon and under the ore. This process of reducing ore has not been emphasised in any publica- tion so far, although mentioned in the patent.The system approaches theoretical perfection, as there would be practically no energy in the flue gases, and therefore no expensive machinery to install to utilise such waste energy. The furnace was the best place to utilise all the heat. The next time he ran steel in his furnace he hoped to be able to try out the com- bination. He had done every operation separately, and saw no reason why they should not operate together. He was glad Mr. Kilburn Scott had emphasised that the furnace will appeal to the ordinary steel-makers, as it enabled them to use furnaces that they had been accustomed to. This he also appreciated, and he called attention to the fact that his furnace could be added to the existing open hearth furnaces to advantage.The feature which seemed to appeal most strongly to all practical steel-makers, and which they had expressed to him repeatedly, was the thorough mixing. It was not possible to accomplish this so thoroughly in any other existing furnaces, electric or fuel. Concerning the question as to the largest size furnace yet used, he could only repeat that he had been experimenting with rather small ones. He was now negotiating for large ones, and would probably soon have some in operation. He had had to determine many constants in order to design a larger one properly. Among these was the electrical resistivity of steel and other alloys, the data for which did not exist. For these experiments special furnaces had to be built and then pulled down after the constants were determined, in order to determine others.This took much time, as every furnace must be dried out. At present he had in hand the construction of several I and 5-ton furnaces, and even a 10-ton furnace, to be operated on a commercial scale. Regarding the sizes of the resistor tubes, there are, of course, an infinite number of sizes which could be given to the resistors for a given furnace, and it was thus impossible to state any fixed sizes. Nor would it be well to publish any such sizes, as others might then experiment with them, and not knowing the properties of the pinch effect, &c., might make failures, and then blame the furnace. Their size also depends greatly on the resistivity of the steel, and the value of this is only known approximately.For a furnace of I or z tons, however, the resistor tubes would probably be z or 3 inches in diameter. Concerning the material for the tubes, he had used magnesite and alundum, and while he had had good results, he was open to consider the use of other materials, He would probably use the electrically calcined magnesite for the next furnace, as suggested by Mr. Kilburn Scott. The lining of the resistor tubes is tamped in around a casting when in a plastic condition ; it thus forms part of the general refractory lining of the furnace. Any dirt in the metal is brought to the top by the upward circulation. It stays there, collecting in little whirlpools where the metal is sucked down, and it is quite surprising what a lot of such dirt will come out of apparently clean metal.Steel is apt to contain mechanically suspended impurities, such as small pockets of slag, oxides, gases, or gas-producing impurities, which tend to form blow-holes, &c. With pinch effect electrodes all these areTHE HERING LiPINCH EFFECT” FURNACE 209 rapidly brought to the surface by upward circulation, and may then be readily removed. It had been suggested to call this “boiling” the dirt out of the metal, and it was believed that such “ boiled ” metal would be entirely freed from troublesome mechanically suspended impurities. A blow-hole in the usual steel may be due to a particle of oxide of iron coming into contact with a particle of highly carbonised iron, thus developing gas. With the metal made thoroughly homogeneous it was not likely to occur, Again, some alloying metals tend to sink, while others tend to rise ; the circulation in the pinch effect furnace can be made so energetic that such segregation cannot take place.The possibility of forcing a large amount of heat into the metal quickly gives it a great advantage over arc and induction furnaces. In the arc furnace the heat received by the metal was mostly by radiation, and it dis- tributes itself through the mass by conduction, a slow process that cannot be hastened by increasing the input. The agitation produced by the sputtering of the arc aids it somewhat, but that is not a true circulation. Moreover, heat does not readily travel downwards in a liquid, yet that was what it must do in an arc furnace for molten metals. On the other hand, in an induction furnace, any forcing of the heating causes rupture of the circuit by reason of the pinch effect.Mr. E. Kilburn Scott had, without any assistance from himself (Mr. Hering), given such an able and intelligent description of the salient features of the furnace that there was little left to add. Time would show whether the furnace would turn out better than existing electric furnaces. There was certainly every promise of it. Shortening the time of the refining pro- cess was of far greater importance in an electric than in a combustion furnace, as it cuts down the energy cost in direct proportion. He there- fore believed that the cost of refining would be very materially reduced and the tonnage output of a given sized hearth be materially increased.The continuous and unavoidable losses of heat through the walls of a steel furnace are quite great, amounting, in actual tests of well-built furnaces, to about one kilowatt per square foot of metal surface exposed to the walls. Hence it was important to reduce this surface as much as possible ; and as Mr. Kilburn Scott points out, the theoretically best form of hearth is a hemi- sphere. In his (Mr. Hering’s) furnace it becomes possible to take full advantage of the hemispherical shape, whereas in the other types that cannot be done. Mr. W. Murray Morrison : It is somewhat of a relief to hear that the “pinch effect,’.’ which has caused so much trouble to many of us, has been turned to practical utility. At the same time, I doubt very much whether the effect is not manifest and of considerable use in the case of the Hkroult and similar furnaces.From the data given in the paper, I gather that the furnace described has never been tried on an important scale, There is little doubt but that very great troubles would arise with the metallic electrodes. Undoubtedly water cooling would have to be resorted to, in which case a considerable amount of energy would be abstracted from the furnace. I am afraid the advantages claimed for the “pinch effect” furnace are more likely to be apparent on paper than real in practice. Mr. Donald F. Campbell : The Hering ‘‘ pinch effect” furnace described by Mr. Kilburn Scott, and previously in the Transactions of the American Electrochemical Society, seems to present many features which would prevent it from ever bedoming a useful metallurgical appliance in its present form. The difficulty of maintaining the channels at the bottom in210 THE HERING “PINCH EFFECT” FURNACE their proper dimensions would be considerable, while the erosion on the magnesite or alundum bottom is bound to be serious, especially as there is vigorous motion in the steel bath.There will also be danger of the steel finding its way between the layers of the refractory lining at the bottom of the furnace. It would appear also that the extremely violent stirring action is a serious disadvantage rather than a point in favour of this furnace, for any agitation which would cause the surface to be at an angle of 45 degrees and causes air to be drawn through a tap-hole “ with a whistling noise ’’ would probably oxidise the steel or at least be deleterious to the conditions required.Mr. Scott states that “ in other furnaces the movement is sluggish, and that the transference of heat is chiefly due to mere conduction.” Any metallurgist who has had the privilege of seeing the principal furnaces now in commerical practice will know that in any one of these was there sufficient movement in the steel to get a complete refining reaction, and in some, such as a Rochling-Rodenhauser 3-phase furnace, it has been found necessary to take precautions to reduce this motion. His statement that zinc ores cannot be treated in an arc furnace is also incorrect, as many thousand tons have been smelted. He mentions as a disadvantage of the arc furnace that “heat is applied at the top of the charge, and thus has to travel down by slow conduction and agitation of the charge.The latter statement I cannot understand. In the Siemens furnace heat is entirely applied from above, and any other agitation except that which naturally occurs is not required, while if there is no slag no refining can occur. I have several times had to melt up masses of cold scrap frozen in the furnace up to 15 tons, and although this can be done without difficulty, it is, of course, undesirable ever to work without a coating of slag above the bath. The author states that water cooling is an objectionable feature in the arc furnace, but the amount used is very small, and there is no danger attached to the use of water above a furnace, whereas, water-cooled electrodes at the bottom of the furnace are a very serious danger, as any breakdown in the water supply may cause the steel to break through the bottom, and if there is water present there is serious danger to life and property, whereas a little water leaking from above into the furnace can at the most only damage a few bricks, and there is no risk of explosion.The furnace described does not appear in its present form to be likely to find wide application in commerce. Mr. Colin C. Gow : The principle of the Hering furnace is dependent upon two physical phenomena. The electrical energy is mainly transformed into heat in the resistor tubes, which I understand are small, namely : 33 in. diam. and 7 in. long for a 2+-ton furnace; the local heat then is likely to be intense, but owing to the pinch effect the hot metal is actually expelled into colder regions of the bath.It is evident, therefore, that thc advantages claimed for this furnace are entirely dependent upon the resistors. For any given size of furnace the dimensions of the electrodes and resistor must bear some definite relation for the effective working of the furnace to be fulfilled. From purely a steel-maker’s standpoint, it seems inconceivable that the sharp angle made by the walls of the resistor tube and the bottom of the furnace will not suffer serious erosion even supposing a bath of metal is always kept above that level. Quoting Mr.’ Kilburn Scott : ‘‘ It seems that the suction down into the bottom of the resistor tubes is considerable,” Any slag at the top interferes with working.” In short, the size of the resistor tubes must remain constant.THE HERING “PINCH EFFECT” FURNACE 211 and in consequence the risk of erosion by the metal as it is drawn down these resistors seems extremely serious.Again, it is necessary to make the electrodes of larger diameter than the tubes, consequently part of the bottom lining has to be actually built on the outer edge of the electrode, and at this point the lining would only be 7 in. thick; it would seem more than likely, if the pressure on the electrode is so great, that steel will be forced between the lining and the electrode, a fact which would again greatly minimise the possibility of the resistor tubes retaining for any length of time their original form.This risk will be seriously enhanced if the upper surface of the electrode proper should fall below the bottom limit of the resistor lining, a condition which seems highly probable in the face of the means of self-regulation of temperature as described in the Paper. I would point out that apparently any change in the length or cross- section of the resistor as caused by erosion would, besides causing trouble with the electrodes, either destroy or so moderate the pinch effect as to transform the Hering furnace into a simple resistance furnace, this being one of the types the author has so assiduously attempted to condemn when comparing them with the furnace in question. Mr. Kilborn Scott quite openly expresses the view that there may be a nigger in the fence somewhere, and in my opinion he will find a rather hard-headed one in the resistor tubes which involve a construction absolutely repellent to a practical steel-maker, though they may be essential for the production of the electrical phenomena upon which the author’s claims are dependent.Mr. J. HSrdCn thought the Hering furnace very ingenious, but he did not see that it would be possible to produce superheated slag of such refining properties as were required. If a heavy weight rested on the bottom of the channel it would be difficult to keep the steel in the furnace, especially where there was so much agitation of the molten metal. He quite admitted that the ideal electric furnace must be as simple as possible and as much like an open-hearth furnace as possible.As regards the tubes, how long would these be likely to last mechanically ? In the 3-phase Rochling-Roden- hauser furnace the rotary action of the steel was very strong, and this action where the “pinch effect” was in operation would be stronger still. With the very best lining, if the motion were not checked in the channels, the mechanical wear and tear was ruinous. It would therefore be necessary to stop the squirrel-cage action by suitable connections in order to minimise wear and tear, Further, would not the induction be so strong that a great deal of oxidation would take place? He thought that the partitions suggested by Mr. Hering in his contribution to the discussion might be ideal in conception, but were impossible in practice. Of what material would they be composed ? Dr.H. Borns : With respect to hfr. Kilburn Scott‘s paper, I am sorry that he is not here at present.* I wished to ask him whether he has made experiments of his own; the paper does not appear to contain much more information than Mr. Hering’s papers. I quite agree with the other speakers as to the difficulties which mechanical erosion would cause. If I am not mistaken, Hering said that the new system of heating was more suited for large furnaces than for small furnaces. But he describes only small furnaces, in which the difficulties appear to be sufficiently serious. Mr. M. Ruthenburg said he would make one remark with regard to the Hering furnace, and that was that a particularly high current at low voltage would be required on account of the low resistance of the metal, * Mr.K. Scott came later. VOL. VII-T10212 THE HERING ‘(PINCH EFFECT” FURNACE He considered the criticisms which had been passed on the tubes perfectly just. Mr. Ernest P. Hollis drew attention to Mr. Scott’s remark that there was a law that “like currents attract.” This, he said, was a fallacious misunderstanding of the laws of electromagnetic attraction and repulsion. The law which Mr. Scott intended to refer was that “conductors carrying like currents attract each other.” If like currents attracted each other it must follow that the distribution of the current in a conductor would be uneven and Ohm’s law would be inexact. Mr. Gow criticised the Hering furnace on the ground that the resistance of the resistance tubes would vary and thus disturb the ‘( pinch effect.” But the “pinch effect” was not dependent upon any critical value of the resistance and would only vary in amount with the resistance, and any changes in the rate of circulation of the metal would not stop or greatly interfere with the process.As to the homopolar generator, this was now a technical and commercial possibility. The Barbour machine shown at Olympia, and which was fully described in the Electrical Times of September 14, 1911 (p. 230), was a compact generator which would produce extremely high currents at low voltages without any of the sparking troubles concomitant to the use of the commutator pattern of machine. Its application to furnace and electro- plating work was further discussed in the same paper on October 19, 1911 Dr. J.A. Harker said he would like to point out that the (( pinch effect” was not simply a contraction of a column of fluid, but there was a lump on each side of the channel and a piling up of the molten metal, which oscil- lated backwards and forwards. Mr. W. A. Price and the speaker had tried to make a bath of molten salts and to heat this electrically by means of a heater of molten tin contained in a series of zigzag channels cut in a suitable fire-brick. The ‘‘ pinch effect ” manifested itself very markedly, particularly at the corners, and even under the pressure of a column of molten salt was the limiting factor in the energy which could be put in by means of the arrangement. The Chairman said on the whole he agreed with the criticism that had been made.Even if the furnace worked otherwise satisfactorily, its success must depend upon the heat generated in the resistance tubes, and these, he could hardly imagine, could remain constant in section, but must rapidly wear away, and the resistance would consequently diminish, and it would therefore be difficult to maintain the temperature required, As regards the partitions suggested for this furnace he could only say he had never known a partition to work satisfactorily in any furnace, Mr. Scott stated that zinc and arsenical ores could not be treated in the arc furnace. He, the Chairman, could say, speaking from personal experience, that some thousands of tons of zinc ores had been treated in arc furnaces, and quite recently he had supervised the smelting of some hundreds of tons of such ores in arc furnaces.Mr. E. Kilburn Scott replied as follows to the points raised in the discussion :- I am not sure that I understood Mr. Hardh’s first query, but if it refers to greater distribution of heat in a bath than it is possible to obtain with two electrodes, then there is no reason why four or more should not be used. Mr. Hard& suggests that owing to the agitation of the metal, there may be trouble with the resistor, but I would point out that the resistor is in a hole iiz a massive wall of hard refractory material, and such a hole is not easily disturbed. A steady flow of liquid metal over a hard refractory surface ought not to produce (P. 412).T H E HERING “PINCH EFFECT” FURNACE 213 “enormous mechanical wear and tear.” At any rate none of the walls of resistors have worn out as yet; it is thus impossible to say how long they would last.By merely regulating the current, the mixing action can be adjusted to any metallurgical requirement. With regard to my advocacy of direct current from homopolar dynamo Mr. Hardkn appeared to make a good point in raising the question of electrolytic action, Yet when I come to con- sider the matter I do not see a difficulty. With a metal or semi-metal bath the current will naturally flow through the bath and not (or iiot to any harmful extent) through the refractory lining. In any case, it would only flow through that part of the lining between the electrodes because of more resistance elsewhere. In his first furnace Mr. Carl Hering used direct current from storage batteries, and he did not have any electrolytic trouble with the lining.Of course, the whole question of whether to employ direct current in place of alternating depends on whether the homopolar dynamo can be made a satisfactory and cheap machine. I think it can for large outputs, and I foresce it being used extensively in future for practically all electrolytic work and for a good deal of electro-metallurgical work as well. For example, in a works where waste heat drives a steam turbine or a gas engine and the furnaces are near by, then homopolar dynamos might very well be used to generate at the exact voltage required. Dr. Harker’s description of the piling up of metal on each side of the con- traction is of special interest.The piling up appears to be a secondary effect, and in connection with this and the fact that the “pinch effect” is increased when there is another liquid over the conducting one, Mr. Carl Hering may shortly publish some interesting observations. Mr. Campbell thinks holes at bottom of a furnace objectionable, and I can just imagine the same kind of remark being made to Bessemer when his revolutionary invention came before the iron and steel world. If Bessemer converters work well with holes right through the bottom, why should any trouble be anticipated from the holes of the Hering furnace? Besides, the Girod furnace has electrodes through the bottom and no one seems to worry about them. The remark that the steel would be ‘( horribly oxidised” is absurd. In making it Mr.Campbell appears to have taken advantage of my remark that on one occasion air is said to have been drawn in through a badly plugged tap-hole. Mr. Campbell spoke of the importance of the refining action of slag as if the Hering furnace would not have any slag ; but who said it would not, and why should Mr. Campbell suggest such a thing ? Mr. Campbell’s remarks about danger of water cooling seem beside the mark. A flexible tube connection to a movable electrode over the bath of metal is very likely to leak, in which case the water must fall into the furnace. On the other hand, a water-connection to the Hering electrode can be made a more permanent job, and if the piping should leak the water drops clear of everything. As a matter of fact, it is very likely that water-cooling of the Hering electrodes will not be required in com- mercial furnaces.Mr. Ruthenburg raised the question of enormous currents being required, but the specific resistances of the materials dealt with increase very greatly at high temperatures, and the diameter of the resistors can be easily arranged to give workable values for current. One piece of fair criticism was that any wear of tubes (if it did occur) would alter the “ pinch effect ” conditions. That is so, and it is effectually met by merely increasing the current to follow the wear. There would be no trouble whatever in doing this. But why over-emphasise this question of Then plug the tap-hole !214 THE HERING “PINCH EFFECT” FURNACE wear ? Many metal furnaces in present operation have to be patched up after every run, and yet they are considered quite workable.Regarding the new process of steel smelting which Mr. Carl Hering puts forward, some speakers seemed to think that the partition might not stand up. But why not? I t could be made of the same material as the walls of a blast furnace, where it withstands a temperature very much greater than above the metal bath of the Hering furnace. Dr. Carl Hering replies as follows to the Discussion :- He regretted to see that some of the critics made very positive and unqualified remarks in the discussion, without ever having seen the furnace, and in some cases showed unfamiliarity with the features involved. In all new departures from the beaten track difficulties will naturally be en- countered ; as it has taken twenty-five years to develop the induction furnace and about thirty years to develop the arc furnace, time should be granted in developing a form which involves a new force whose properties and idiosyn- crasies must first be studied.There cannot be any “considerable use ” of the force of the pinch effect in arc furnaces, as the current must necessarily spread out the moment it reaches the liquid metal, and the force decreases with great rapidity as the current density becomes less. At most, its effect would be confined to a small surface where the arc abuts. Metallic electrodes have been used, and apparently with success, in commercial furnaces like the Girod. Of course, all electrodes necessarily involve some loss of energy in them, but if they are properly proportioned they should abstract no energy from the interior of the furnace.The proper proportioning of electrodes does not seem to have been appreciated by some of the critics. Some metallurgists hold a directly opposite opinion to that expressed SO positively by Mr. Campbell. The very active upward circulation alone is a feature which others think would make it (‘ a useful metallurgical appliance.” As a matter of fact, features which were most feared were found not to exist. Special tests were made to determine the supposed and much-talked-of wear on the resistor walls; many charges were melted in a furnace, the last one being allowed to freeze; upon breaking down the walls and measuring the diameter of the cores in the resistor holes, no measurable difference could be detected.In the case of a steel furnace it even seemed that the core had actually become somewhat smaller, which seems to be explained by the existence of a very hard, black, smooth and clean lining which forms on the walls of the holes, presumably from the impiirities or oxides in the metal. In the case of a furnace which had been run with bronze, the walls of the holes were found to be hard, clean and smooth, as though they had been sand-papered. Even a sharp edge of the refractory material was found to be intact, although for days white-hot metal had flowed past it in large quantities. Surfaces of the refractory material which are continually in contact with the metal only and not with the slag remain in very good, clean condition.The fears concerning the wear on the holes, therefore, turned out to be unnecessary and premature. Moreover, it is not essential, as Mr. Gow supposes, that the cross-section of the resistors must remain absolutely constant. It is intended to take care of any possible wear by providing for a regulation of the current, so that as the resistor increases in section a greater current at lower voltage is to be used. Another provision is to increase the length of these holes when their diameter becomes larger, by inserting bars of the right diameter into the holes after a run and then tamping a layer of the magnesite over the bottom and aroundT H E HERING “PINCH EFFECT” FURNACE 215 them. As long as the ratio of the length to the section is maintained constant, the proper amount of energy will be set free ; the pinching force is in most cases more than ample, so that its reduction by such a possible increase in section is of no importance.At first the trouble which Mr. Campbell anticipated was experienced, namely, that the metal flowed into cracks between the bricks, but this has now been entirely prevented by using practically a monolith of a certain electrically calcined magnesite which does not crack ; it is tamped into place. The sucking of air through a leaky tap-hole was cited merely to show how very strong this sucking force was. Mr. Campbell seems to have mis- understood this, as he considered this to be a normal operation, which of course it is not. As long as the iron is covered with a blanket of slag and the space above this is a neutral or even reducing atmosphere, Mr.Campbell’s criticism that oxidation would take place does not hold good, no matter how great the agitation is. Moreover, the circulation is entirely within control in the design of the furnace; it may be made to be gentle, and it is orderly and very regular. Mr. Campbell does iiot seem to appreciate the difference between the character of a regular, orderly, upward circulation of the metal against the slag and of an irregular agitation ; the one brings the suspended impurities to the surface, while the other merely agitates. The sole purpose of one of the steel furnaces now under consideration is to refine mechanically by thus “ boiling ” out the suspended impurities. He seems to have forgotten that in the “ killing ” of steel (holding it in a melted condition to allow the impurities to rise to the surface) an important amount of refining can be accomplished without any chemical action of a blanket of slag.If a steady, orderly, upward circulation hastens the bringing of the impurities to the surface, it certainly would be a gain. The furnace can of course be operated with or without slag. Water cooling of metallic electrodes extending through the bottom of the furnace has been in successful use for years by Girod. Mr. Campbell’s fears concerning this feature therefore seem to be entirely unnecessary. As the metal may be raised to any desired temperature (the danger being rather to overheat), there seems to be no good reason for Mr. Hardkn’s fear that the slag temperature will be insufficient, as the layer of slag next to the superheated metal must necessarily acquire the temperature of the latter. The “ partition” which Mr. Hard& objects to need not project down to the metal bath, nor need the very high temperature of the blast furnace exist above the metal bath ; the reduction of the ore takes place in the bath or on its surface. Recent favourable tests with small furnaces have shown that, contrary to the original opinion, the principle is applicable also to small furnaces. It is true that large currents of low voltage are required in the secondary circuit. But this is true also of induction furnaces, and perhaps to a much greater extent. Mr. Hollis is quite correct in saying that it is the conductors and not the currents which attract each other, a fact which the present writer pointed out many years ago ; the operation of this furnace is based on this distinction. Mr. Hollis is also correct in believing that the varying of the resistance would not “disturb the pinch effect.” The latter is a current phenomenon pure and simple, and it is entirely independent of the resistance. As long as the current is constant the pinching force will be constant. There is, of Mr. Campbell says: “If there is no slag no refining can occur.”216 THE HERING “PINCH EFFECT” FURNACE course, a counter electromotive force produced, corresponding to the mechanical energy set free ; this should be made as great as possible. Dr. Harker’s observation concerning the “hump” on both sides of the pinched contraction in an open channel accords with his (Hering’s) early observations” but these humps are mere secondary effects and so is the oscillation backwards and forwards. In the furnace there are humps but no oscillations. * Trans. Anzer. Electrochem. SOC., vol. 11, 1907, p. 331.

ISSN:0014-7672    

DOI:10.1039/TF9120700207

出版商:RSC    

年代:1912

数据来源: RSC

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RESEARCHES ON ELECTRIC FURNACE PRODUCTS. BY DR. EDWARD G. ACHESON. {Abstract of a n Address delivered before the Faraday Society on Wednesday, November 8, 1911, Mr. JAMES SWINBURNE, F.R.S., PAST PRESIDENT, in the Chair.) Dr. Acheson said that his first carborundum experiment was made in March, 1891. He mixed clay and coke, put them in an iron bowl, and passed a strong current through by means of a rod of carbon. At the end of the experiment there was a small bright speck on the point of the carbon which was so hard that it would cut glass. His next step was to build a small brick furnace in which he made some quantity of the product. But although it turned out to be harder than diamond (though not so tough) he had great difficulty in finding a use for it. First, and naturally, he tried the lapidaries, but they would have nothing to do with it.Then he tried the emery-wheel makers : they said it was useless. Some use of it, however, was made by engineers for grinding valves. The properties of carborundum were found to be very remarkable and interesting. Although as usually made it was coloured with iron, when pure it was colourless, and it had a higher refractive index than diamond. The temperature at which carborundum forms is vastly higher than that required to fuse the walls of the furnace, which, however, are protected by the material forming the furnace charge. The carborundum forms around the core, and very accurate adjustment is required to maintain the proper temperature. If it is overheated the car- borundum crystals are destroyed, the silicon disappears, and true graphite is left behind.The manufacture of this chemically pure graphite was the second step of his investigations. This was carborundum. Last year 13,000,000 pounds of this graphite were sold. His next step was to look round for a cheap material from which to make the soft unctuous graphite that he wanted. Eventually in 1906 a suitable material was found in the waste from the anthracite coal mines of Pennsyl- vania, from which all foreign matter had to be evaporated. This was found to yield a non-coalescing graphite that was easily pulverised. He hoped it might have been useful for making crucibles, but it was not successful in this direction, not being dense enough. As a matter of fact the material expanded very much in the transformation into graphite.Dr. Acheson’s next move was to try to reduce silicon in the electric furnace. This he succeeded in doing by using an intimate mixture of fine amorphous silica and soft graphite. When these are rubbed together the graphite covers the silicon practically, and makes the mixture conductive, so that it can be smelted in a resistance furnace, although as a matter of fact an arc furnace is now employed, and silicon is made in thousands of tons. He was equally successful in reducing aluminium by passing a current 217218 RESEARCHES ON ELECTRIC FURNACE PRODUCTS through a mixture of bauxite and graphite by means of a graphite core which was surrounded by a shell of carborundum. But in his opinion his most important work had had to do with the use of his soft unctuous graphite in lubrication.He had hit upon a method of successfully utilising it, calling to mind how, in 1901, he had discovered the reason why some clays which were the same in composition as others differed considerably in physical properties. Remembering how clay could be made to suspend in water by treating it with a dilute solution of tannin, it occurred to him in 1906 to treat the graphite in the same way. The actual reagent used was a solution of gallotannic acid containing a little ammonia. This was found to render the graphite perfectly suspensive, so that it would pass through filter paper and obey all the laws of colloidal solution. He called it (‘ deflocculated graphite.” The reduction in size of the graphite particles on deflocculation was about &&h part of t h e particles that had been passed through a sieve having 40,000 meshes per square inch.A considerable number of bodies can be deflocculated ; in fact, anything that is amorphous, insoluble, non-fused and non-metallic. There are many deflocculating agents too, such as extract of straw, grass, tea-leaves and so forth ; tannin was one of the most efficient. Carbon dioxide could act as a de- flocculating agent, and Dr. Acheson threw out the suggestion that carbon might be fixed in this way in nature. Probably it penetrated the particles altogether and threw off groups of molecules or even single molecules, each of which became surrounded by an organic jelly. With regard to the practical application of the colloidal graphite there were many possible uses, for instance, in electrotyping, in the production of a perfect lead pencil ; its greatest promise, however, was as a lubricator either in oil or water.In 1908 the production of natural oil was 290 million barrels of 42 gallons of U.S. standard, one-tenth thereof distilling off as lubricating oil-roughly 100 million gallons per month. The consumption of lubricating oil is trebling every fifteen years, and a fifty-year limit would probably have to be put to the world’s supply of oil. Apart from the question of the exhaustion of the oil, however, it was at best an unsatisfactory material as a lubricator, on account of its great viscosity, which caused 50 per cent. of the energy produced to be wasted in internal friction.A suspension of colloidal graphite in water was an ideal lubricator on account of its extremely small viscosity ; moreover, the colloidal particles cannot be squeezed out from between the bearing surfaces, as is possible with a true liquid; on the contrary, they penetrate and even up the metals with a veneer of molecular graphite, until eventually a surface like glass results . To make the graphite generally available for lubricating it is best diffused in oil. This mixture goes by the name of “Oildag’’ (Oil-Deflocculated- Acheson-Graphite), while the suspension in water is know as “ Aquadag.” The aquadag is the form in which the suspension is first made. To make oildag it is necessary to transfer the graphite from the water and drive off the remaining water in a vacuum from the jelly-like organic coating on the graphite particles, as otherwise these will flocculate if acid is present in the oil. He himself had used the graphite lubricator for a motor-car for a year The deflocculating agent always became fixed to the graphite.VO L. VII-T 10-218rRESEARCHES ON ELECTRIC FURNACE PRODUCTS 219 before offering it to the public, and it was being used in all the transportation power-houses in New York with very satisfactory results. I t was interesting to note that steel was not tarnished by aquadag, but remained perfectly bright when immersed in it.

ISSN:0014-7672    

DOI:10.1039/TF9120700217

出版商:RSC    

年代:1912

数据来源: RSC

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RESEARCHES ON ELECTRIC FURNACE PRODUCTS 219 DISC USS I 0 N . Dr. J. A. Harker expressed his appreciation of Dr. Acheson’s inspiring and suggestive address. He dwelt on the enormous value of graphite for electric furnace work, and showed to how great an extent advances in high- temperature work were due to Dr. Acheson’s wonderful material. It was a pity that a proper collection of electric and thermic data relating to graphite was not easily accessible, and he suggested that the Acheson Company would do well to collect and publish such information. It was of interest to note that carborundum belonged to a class of conductors which differed electrically from the other classes in that it was a conductor at ordinary temperatures and that its conductivity increased with temperature. Mr.Leon Gaster, referring to Dr. Harker’s remark, said that the data he desired was already available in a booklet issued by the Acheson Graphite Company. He referred to another material discovered by Dr. Acheson-namely, siloxicon-which was of great value for lining and making crucibles, and which he thought deserved to be more widely known. Mr. Robert Mond associated himself with the remarks made by the previous speakers, and he thanked Dr. Acheson in the name of the electro- chemists of England for placing at their disposal large electrodes, which alone enabled electrochemical processes to become practical. Only those who had tried and struggled with the old retort carbon could properly appreciate the immense service rendered by Dr. Acheson to progress in electrolytic processes.Mr. Fredrik H i o r t h said that some of those present might be interested to learn that graphite was used twenty years ago in Norway for lubricating water-wheels, wood shafts on wood bearings, &c., and it was later on used mixed with oil for this purpose. Some years ago a Swedish engineer had used molasses as the medium, but the graphite, of course, was flocculated, and this difficult problem had now been finally solved by Dr. Acheson. In Norway extensive experiments with deflocculated graphite had been carried out for lubricating guns and rifles. Each of two mitrailleuses were fired with 1,500 shots in 8 minutes, one with and the other without graphite as lubricator in the cartridges. The result was astonishing, because the powder-chamber in the one without graphite proved to have been very damaged, and the other quite undamaged.* Graphite had the further effect of sealing up the powder gases, and as a result the pressure of the gases was increased.The only fault he had to find was that the excellent Acheson graphite was too expensive in Europe, and he hoped Dr. Acheson would come and make it in Norway, where there was every facility for so doing, both in cheap water-power and cheap raw materials and short distances for the transport to Europe. This would be a great benefit for the users of the graphite, for Dr. Acheson himself, and for his, the speaker’s, country, which could give him cheap water-power at a cost of ten to twelve shillings the horse- power year for the waterfalls owner.showing the result of the above-mentioned shooting. * We have later on received from Mr. Hiorth two photos of split gun-barrels, (See Fig. I.)220 RESEARCHES ON ELECTRIC FURNACE PRODUCTS Dr. H. Borns, referring to Mr. Hiorth’s remarks, mentioned that the fact that there was usually a discharge of powder in f r a t of the bullet had recently been confirmed with the aid of instantaneous photography by C. Cranz at Charlottenburg. Dr. T. M. Lowry said that the deflocculating effect of colloids, which Dr. Acheson had applied so successfully to the graphite industry, was probably a factor of very great importance in agriculture. At the Rothamstead experimental station there were plots of ground which had remained unmanured, or had received only mineral manures during many years, but year by year better crops were obtained from plots which had received dressings of farmyard manure over thirty years ago than from those which had not received this dressing.The difference was probably due to the altered texture produced by deflocculation by organic colloids in the dressing. The Chairman, in moving a Vote of Thanks to Dr. Acheson for his interesting and suggestive discourse, remarked on his great qualities as an inventor, an inventor who, starting work on one subject, followed that subject up step by step, perfecting at every stage some new and useful discovery. Dr. E. G. Acheson, in reply, expressed his thanks to the speakers for the kind way in which they had received him. Referring to the use of the graphite for gun lubrication, as mentioned by Mr. Hiorth, he said that it was quite popular in the United States. I t was found that its use enabled a nickel- steel barrel with which a steel covered bullet was used to last much longer. There was, in fact, practically no wear at all inside the rifle, which took a very high polish. With regard to the cost of graphite, he hoped it would be reduced in the near future, and the question of manufacturing it in Norway was being considered. At the present time, however, it was doubtful whether the consumption was great enough for more than one factory in the world to be economically operated. About four grains of graphite were used in each cartridge.

ISSN:0014-7672    

DOI:10.1039/TF9120700219

出版商:RSC    

年代:1912

数据来源: RSC

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A REDETERMINATION OF THE DENSITY AND COEFFICIENT O F LINEAR EXPANSION OF ALUMINIUM. I Silicon . . . . . . . . . Iron . . . . . . . . . Aluminium . . . . . . BY F. J. BRISLEE, D.Sc., &c., Chief Chemist, British Insulated and Helsby Cables, Ltd. S.E.M.F. Per Cent. 0.26 0.26 99'48 ~00'00 ( A Paper read before the Faraday Society, Wedizesday, December 6, 1911, Dr. J. A. HARKER, F.R.S., in the Chair.) The increase in the use of aluminium for many technical purposes has rendered a redetermination of some of its physical constants necessary. The metal, as now placed upon the market, is in a high state af purity ; but many of the earlier determinations of its physical constants were made upon specimens of aluminium of doubtful purity and unknown composition, which probably contained considerable quantities of iron, silicon, carbon, and oxide of aluminium, the oxide being mixed through the metal as an emulsion.Aluminium absorbs certain gases, when molten ; hence the difficulty of obtaining sound castings; and blowholes would cause too low a value for the density to be obtained. The aluminium used in the determinations of the density and coefficient of linear expansion, described below, was obtained from ( I ) the Sociktk Electrom6tallurgique FranCaise, La Praz, Savoy, and from ( 2 ) the British Aluminium Company. A few specimens of remelted scrap metal were used in one or two of the density determinations. All the metal used was carefully analysed, and the iron, silicon, the chief impurities present, were estimated. The iron was estimated by dissolving 10 grams of the metal in caustic soda.The solution was allowed to stand and the clear liquid syphoned off, water was then added, the precipitate again allowed to settle and the clear solution removed by a syphon. The precipitate was then filtered off, thoroughly washed with water, dissolved in hydrochloric acid, precipitated with ammonium hydrate after oxidation, and weighed as oxide, or the hydrochloric acid solution was reduced and titrated with a N/IO solution of potassium dichromate. Repeated determinations, made upon the same sample, showed a good agreement between the two methods. The silicon was determined by the method of Otis-Handy." The analyses of the aluminium gave, as a mean of many determinations :- British Aluminium C o . Per Cent.0.25 0.23 99'52 100'00 * Described in Lunge, Chemisch-Techliische Unt€rsuck;tln~sntefltocEen ii. p. 789 221222 REDETERMINATION O F DENSITY AND COEFFICIENT Weight of Aluminium. 31.3720 29.8970 29.8770 31.3570 15.3250 THE DENSITY OF ALUMINIUM. The specific gravity was determined upon the cast metal, as received, upon hard-drawn rod in. diameter, and upon soft annealed rod Q in. diameter. The determinations were made by both the ordinary method of weighing in air and water, and by employing the displacement method, using a IOO C.C. flask, the latter method being employed for fine wire. The cast aluminium was cut into rectangular blocks, weighing from 20 to 30 grams each ; the round rod was cut into cylinders of about the same weight. The fine wire was cut into small pieces about an inch long ; the weight used for a single determination was from 10 to 30 grams.The aluminium was care- fully cleaned with petroleum ether, in order to remove grease, &c., which might have been taken up by the metal during working. The temperature of the water was taken at the time of weighing. The results obtained were :- ___- Specific Gravity. Weight of Source and Condition Tempera- - I ture, OC. Uncorrected. Corrected.* Water displaced. of Aluminium. . 11.5630 S.E.M.F. cast I3 2.7131 2'7094 I 1.0070 ,, >, I3 2.7131 2.7094 I I ~0040 ,, ,J I7 2.7151 2.7098 11'5670 J, 9 ) I7 2.71 I I 2.7057 5.6500 J, 9 , I7 2'7116 2'7051 24'4570 27'5290 26-83 10 23.5180 28.6890 26'6040 9.0 I 30 9.8850 8.6660 10.5700 9.8020 10' I440 22 22 22 22 22 22 2'7137 2.7135 2'7143 2'7137 2'7143 2.7141 Mean Specific Gravity = 2,7139 uncorrected ; 22 6 4 = 2'7052 corrected.8.5220 7.5130 8'4930 14.9350 28.3230 23'6630 20.4970 24'4386 25'3810 25.3820 25'7370 25'7374 3.1330 2.7610 3.1 160 5'5090 10.4656 8'7490 7'5570 9-0320 9'3 560 9.3610 9'4860 9'4904 S.E.M.F. 8 Rod J, 0.08 wire J, ,J 9 , 2, 1, ,, 6:A. RodJwire Wire B.A. Hard rod Ar&ealed Yod ) > J > I7 I7 I9 16 16 16 I 4 I4 I9 18 I9 18 2.7207 2-72 I I 2.72 j6 2-71 I I 2.7063 2.7046 2.7123 2'7057 2.7128 2-71 15 2.7131 2.7119 2.7153 2.7158 2.7152 2.7060 2.6996 2-70 I 8 2.7064 2'7057 2.706 I 2'7013 2'7084 2'7067 Mean Specific Gravity, t 6 4 + = 2.7080 corrected. The density of remelted aluminium is lower than the above, due probably to the fact that a certain proportion of iron and silicon are taken up during melting, and also to the fact that gases are absorbed while molten.The value found for the density of remelted aluminium was 16616=2*687, or 16 64 = 2.6821. The most probable value for the density of aluminium is 2.708 for cast metal, and metal upon which a large amount of work has not been done. The worked metal reaches 2-72, in some of the above instances, but this value was obtained in only three determinations, and was not found for hard- drawn wire.: * Corrected for water at 4" C. and vacuum weighing. t t 6 4 is the density at room temperature referred to water at 4" C. 1 The effect of work upon the density of aluminiuni is being further investigated.OF LINEAR EXPANSION OF ALUMINIUM 223 The above values differ from the valued recorded in the literature, e.g.in Landolt and Bornstein," and in a paper by Wilson,+ in which a large amount of data are collected. 2). h THE COEFFICIENT OF LINEAR EXPANSION OF ALUMINIUhf. The coefficient of linear expansion was measured directly by determining the increase in length of a rod of the metal, about I metre long, when it was heated from I o O C . to I O O O C . It consists of a stout mild steel tube A , made of hydraulic tubing, which carries The apparatus is shown in the figure. * Plzysiknlisch-Clzemisclae Tabellen. t Jownal Irzst. Elect. Engineers, 31, p. 332, 1901.224 REDETERMINATION OF DENSITY AND COEFFICIENT two heavy bronze clamps B,, B,, which can be moved at will, and rigidly fixed in any position by means of clamping screws.B, carries a mild steel stop D, against which the end of the aluminium bar G rests when the deter- mination is being made; the other (BJ carries a micrometer head C for measuring the change in length. The tube A is supported by the bronze supports M , N , which in turn were screwed on to the wooden blocks and base W,, W,, W,. A steady stream of water was kept flowing through A . the temperature of which was measured by the thermometer T,, placed in the glass vessel F. The temperature of the water did not vary more than 0-2' C. during the measurement, and the slight error caused thereby can be neglected. The aluminium bar was placed inside the water jacket K, and supported by a half tube, ie., a brass tube cut out so as to form a shallow tray underneath the aluminium rod, the tube being complete only at the ends which carry the stop D and the stuffing-box H.The temperature of the bar was measured by the three thermometers TI, T,, T3. The change in length was measured by the micrometer C. Two micrometers were used, made by Messrs. Brown and Sharpe, and measured to 0.001 mm. and 0-0001 inch respectively. The increase in length of the bar G pushed the piston P through the stuffing-box H, and the change in length was them measured by the micrometer head C, the temperature remaining constant during the measurements. The deter- minations were made in the following way :- The aluminium rods were cut so as to be approximately I metre in length. The ends were then turned up in a lathe, exactly at right angles to the long axis.The exact length was determined by comparison with a Whitworth standard steel bar, I metre long, the difference being measured by a micro- meter. The rod was then placed in position in the water jacket K, which was well lagged with asbestos, the stop D, and the piston and the stuffing-box, P and H, fixed in position. Cold water was allowed to flow through the apparatus until the thermometers showed that the temperature was constant to within o'IOC. The thermometers were calibrated from time to time so as to check the constancy of their indications. The thermometers showed that the temperature was practically constant during the actual determinations. The micrometer was then screwed down until the piston P pressed upon the end of the rod and a reading of the position of the micrometer was then taken.A series of readings were taken of the thermometers and the micro- meters, over a period of half an hour, so as to ensure that the temperature and other conditions of the bar were constant. The cold water was then run out, and a steady current of steam was maintained, until the thermometers showed that a constant temperature was reached. The micrpmeter C was again screwed down on to P, and the reading taken. A series of readings were taken of both micrometer and thermometers. The bar was kept at the temperature of the steam for half an hour, and comparative tests showed that temperature equilibrium between the steam and metal was established in ten to fifteen minutes. At the completion of the measurement the steam was shut off, and cold water circulated through the apparatus.When the initial temperature was reached, the first readings of the micrometer were checked. The readings at the higher temperature were repeated by again heating to the temperature of steam. It was found that successive determinations made with the same bar agreed to within 0.2 to 0.3 per cent. During the whole of the measurements the temperature of the tube A was kept constant by a steady current of water, and the bronze clamps B, and B, were shielded from radiant heat by thick asbestos screens. The temperature of the bar, as indicated by the thermometers TI, T,, T3, showed that a constant temperature was maintained in the jacket to within o'IOC.OF LINEAR EXPANSION OF ALUMINIUM 225 Length of Bar in cm.=Z.100-2664 100'1 700 I 00.2664 I 00.2664 100*1920 100~1920 100. I 692 I 00' 1692 100- 1900 100.1 900 100*2560 100*2560 100*2560 100~0j60 100~0560 100.2498 100.2498 Hard-drawn Aluminium. Temperature Rise, OC. =( t2- tI). 87'5 88.1 88.3 88.0 89'4 89'9 89'3 98.02 91.0 88.7 87.8 90.6 90'5 89'3 90. I 89'5 91'4 Increase in Length in mm.=Al. 2.117 2.1 19 2.130 2-167 2.175 2.225 2.175 2.167 2.162 2.207 2.197 2.173 2.180 2.185 2-225 2'2 I 0 2'220 These results give- p = 2.432 x 10-5 & 0.0036 x 10-5 as a mean of the above seventeen determinations. The mean probable error was calculated from the formula- zrd2 N (N - I)' where Ed* is the sum of the squares of the differences between the mean and each determined value of p, and N is the number of determinations.Annealed Aluminium. Length of Bar in cm.=l. 100' I055 100-2543 I 00.2591 100*2405 100*2405 100'2405 100*1075 I 00- 1075 100*1075 100-1075 100*2403 100.08 10 100*08IO 100*2498 100.2498 100'2543 Temperature Rise, oc. = (t2 - t,). 88.6 88.7 88.5 89.8 90'4 89.2 88-5 88.7 88.7 89.2 89.6 89.0 90.0 89'5 90'5 89'7 Increase in Length in mm.=AJ. 2.190 2'187 2.187 2-2 I 7 2.216 2-225 2.193 2.170 2.185 2.190 2.180 2.205 2.197 2'200 2'202 2'210226 REDETERMINATION O F DENSITY AND COEFFICIENT Length of bar in cm. ... ... Temperature rise ... ... Increase in length in mm. ... P = The general mean of the above determinations, sixteen in number, is- p = 2.454 x 10-5 & 0.0028 x 10-5. From the two series of measurements above the variation in length of an aluminium rod can be calculated from the formula+- I 00.2403 IOO*IO75 896" C.8 8 ~ 5 ~ C. 2'202 2.170 2-452 x 10-5 2.450 x 10-5 H a rd-drawn A 1 u miii ium . Li = L( I - 0'00002432t) Annealed Aluminium. Lt = L( I - 0'00002454f) between the limits of temperature oc to 100' C. Sources of Error iiz the Determinations. The measurements above recorded could all be reproduced by repetition of the heating and cooling to within 0.2 to 0.3 per cent. Since the micro- meters were capable of being read to 0-0025 mm., and since the total expan- sion measured was about 2.2 mm., the maximum error of measurement was 0'13 per cent. The correction of the thermometers was effected by checking their indications by substances of known melting and boiling points. The corrected temperature differences were used in calculating p.The errors due to the slight expansion of the stop D and the piston P were found to be negligible by varying the length of these two parts. The length of D and P together was 3 cm. in one series of measurements, and 15 cm. in another series. The results were practically identical, as will be seen from the following figures :- The error in the temperature readings was not greater than 0.1' C. 1 Shorter Ends. 1 Longer Ends. -___ I I The temperature rise of these parts was only small, and, owing to the shortness of the ends, the error caused was not greater than 0.003 mm. The results obtained are somewhat higher than the recorded values of P. Fizeau* found 2.313 x 10-5 up to 40° C. and 2.336 x 10-5 up to 50' C., while Le Chatelier,f. working with much purer aluminium, found 2.46 x 10-5 up to 63' C. The coefficient of linear expansion was invariably found to be slightly higher for annealed aluminium than for hard-drawn aluminium, but the third significant figure is somewhat uncertain, owing to the errors of the deter- mination. The mean value for p, calculated from forty-eight determinations made upon hard and annealed aluminium, was- p = 2.450 x 10-5 per degree Centigrade, or 1'36I' x 10-5 per degree Fahrenheit. results were reproduced several times before they were considered reliable. * C. R., 68, 1125 (1869) ; Pogg, AiJfz., 138, 28 (1869). t C. R., 108, 1096 (1889). The above measurements were made upon twelve different rods, and theOF LINEAR EXPANSION OF ALUMINIUM 227 The accuracy of the expansion apparatus was tested by measuring the expansion of a bar of pure high-conductivity copper. The value obtained was 1 - 7 9 x 10-5, a value which is practically identical with that given by Zakrzewski," who found 1.753 x 10-5. CHEMICAL LABORATORIES, BRITISH INSULATED AND HELSBY CABLES, LTD.

ISSN:0014-7672    

DOI:10.1039/TF9120700221

出版商:RSC    

年代:1912

数据来源: RSC

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OF LINEAR EXPANSION OF ALUMINIUM 227 DISCUSSION. Dr. R. Seligman : I think the thanks of this Society are due to Dr. Brislee, not only for putting the matter contained in his paper before it, but for having set an example which might profitably be followed by others of the scientists attached to the large metallurgical establishments. In the second instance, I wish to support Dr. Brislee’s contention that the physical proper- ties of aluminium should be redetermined with the accuracy of which modern methods are capable, for there can be no doubt that many of the figures still given in text-books and literature are far from correct. A good deal of pro- gress has been made in this direction of late years, but there is still room for much work in this field. For instance, we are still without any satisfactory data as to the thermal conductivity of aluminium and its strength under com- pression and other properties, which I venture to hope will engage the atten- tion of Dr.Brislee and the chemists of other companies dealing with aluminium, and having the same opportunities as he has. Deaiing now with the particular properties examined by Dr. Brislee, it must come as a shock to many members that the most salient, if not the most important, property of aluminium, its specific gravity, should require redetermination in the year 1911. But I can assure members of the crying necessity for the work just done by Dr. Brislee on this subject. The older figures which have been used are entirely erroneous, and have in my own experience led to much difficulty and trouble.It is clear that if an engineer counts on, say, 2-67 as the specific gravity of his metal, he will be in difficulties if, when he has made a certain piece of machinery, he finds that actually the metal was much heavier. Now, Dr. Brislee’s results are materially higher than those adopted by other aluminium companies, and, in my opinion, there can be no doubt that his are the truer values. His results for cast metal being presumably done on chill castings are in good agreement with the most recent publication on the subject, his 2.708 comparing with the 2-71 obtained by Professor Carpenter for metal containing 0.25 per cent. Si and 0’14 per cent. Fe, and is probably more accurate than my own result with Mr. Willott of 2.702. Dr. Brislee’s results are also in agreement with those of Professor Car- penter in another direction, to which I have drawn attention elsewhere, It seems so incomprehensible to me that, in view of the very great differences in their mechanical properties, a rolled bar or a drawn wire of aluminium should have practically the same density as a chill casting, as both Dr.Brislee and Professor Carpenter found. The wire, for instance, may have a tenacity of about three times that of the casting, and yet they apparently have the same specific gravity. One could perhaps understand this if there were any evi- dence of the wire being in the state described by Kahlbaum, and explained by Dr. Beilby in his May lecture to the Institute of Metals. According to this explanation, wires which have been overdrawn lose both in tenacity and density, but the loss of density is restored by amzealiizg.The rods tested by Dr. Brislee showed no gain on annealing. If Dr. Brislee has considered * KvaR. A m , 1889, No. 19.228 REDETERMINATION OF DENSITY AND COEFFICIENT this point, I for one should be very glad to hear his views on what I cannot but consider an important question both to the wire drawer and others who work aluminium. I am sorry that Dr. Brislee did not find time to add some determinations on rolled sheet. I do not know why Dr. Brislee should assume that the iron taken up by aluminium during remelting would tend to reduce the specific gravity. Surely the reverse would be the case, so that the decrease in gravity on remelting should be laid almost entirely upon the gas absorbed.This phenomenon is particularly noticeable if the metal is remelted at unduly high temperatures, as the aluminium producers know to their cost. There has been a regular epidemic of occluded gas in the aluminium produced during the last twelve months, not only in this country, but also abroad, the cause of which I showed some six or seven years ago to be overheating. I am glad to say that the epidemic has shown signs of abating latterly. The result obtained by Dr. Brislee for the linear expansion of aluminium varies appreciably from the figure given by Professor Carpenter, but I do not think that in this case ProfessorjCarpenter would claim for his results anything like the accuracy of the present paper. .The range of his measurements is also quite different. Perhaps I may give an instance of the importance of accurate information on this subject.I was recently called in to examine an aluminium vacuum pan made on the Continent for a firm of oil distillers, about 10 ft. long, which had collapsed. I found that the collapse was due to insufficient allowance for the difference in expansion of aluminium and iron under the influence of high temperature. Dr. G. Senter said that according to the observations of Sieverts (Berichte, 1910, 43, 893) the solubility of gases, both in solid and fused metals, increases with the temperature. It follows that when the properties of a metal are adversely affected by a dissolved gas the effect is likely to be the greater the higher the temperature to which the metal is heated in contact with a gas.The Chairman recalled the case of a pressure pan which had steam be- tween the two walls, which turned completely inside out. Fortunately the pan was empty, and it was successfully turned back again, thus showing the ex- treme toughness of the aluminium, which showed no perceptible cracks, and after stiffening was used successfully. Dr. F. J. Brislee (communicated reply): In reply to Dr. Seligman, I wish to say that at present I am still further investigating the change of density of aluminium with work. I have made a number of experiments upon hard drawn wire and hard rolled sheet, the wire being 0.080 and 0.065 inch diameter and the sheet 0.018 inch thick, but all the figures obtained so far favour the lower figure, viz., 27080. I must confess that up to the present I am entirely at a loss to account for this, especially as the wire had been drawn cold from *-inch rod and the sheet cold rolled from 2-inch slab. I have also determined the density of cast aluminium and annealed for fourteen hours, then redetermined the density and again annealed for a further period of fourteen hours and again determined the density, but the result was a practically consistent figure. I hope to be able to communicate these results to the Society at a later date, and perhaps an explanation of the anomaly may be forthcoming. In regard to the occlusion of gases by aluminium, I have recently found a considerable amount of nitrogen in remelted aluminium, especially when the temperature has beep allowed to rise excessively above the melting-point, and there is no doubt that the absorp- tion of gas by a metal would result in a great diminution of density.

ISSN:0014-7672    

DOI:10.1039/TF9120700227

出版商:RSC    

年代:1912

数据来源: RSC