摘要:

AbstractMost research in elastohydrodynamic lubrication has concentrated on the immediate contact area between the two elements. In the case of ball or cylindrical roller bearings, the finitely separated rolling elements may have, between them, a free‐surface lubricant film on each of their races. This film, formed by the wake emanating from one pair of elements, becomes the inlet boundary condition for the following pair. Its possible variation in shape with time is thus important when estimating the lubricant film thickness.With this practical situation in mind, the variation with time of the wake formed behind a ball sliding in a thin viscous lubricant layer on a plate has been studied. Using thin‐film theory and an initial wake cross‐section similar to those observed experimentally, the Navier Stokes equations are solved to yield solutions which describe the subsequent alteration in the wake shape with time. It was found that the track centre of the wake remains at, or slightly below, its chosen initial height for some time before commencing rebound towards the undisturbed layer condition.This behaviour is confirmed by some simple experiments carried out on a ball‐and‐plate machine which also indicate that the track centre height, measured just downstream of the ball, is initially less than the minimum film thickness under the ball and remains at or near this condition for some time before rebound commences.The experiments have also shown that time taken for the track centre height to regain the minimum height under the ball is found to depend on the lubricant properties, the undisturbed layer thickness and the depth of immersion of

ISSN:0954-0075    

DOI:10.1002/ls.3010120102

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

摘要:

AbstractMethacrylate polymers are much used as additives in lubricating oils, as pour‐point depressants and viscosity index improvers. Although the mechanism of such pour‐point depression is still controversial, it is thought to be related to the length of the alkyl side chains of the polymethacrylates, and to the nature of the base oil. In this paper, work is reported on: (a) the depressant activity of polymethacrylate copolymers in relation to the content of short alkyl methacrylates and styrene, and the average side‐chain length of the basic methacrylate constituents; (b) the pour point of the base stock; and (c) the additive concentr

ISSN:0954-0075    

DOI:10.1002/ls.3010120103

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

摘要:

AbstractSignificant savings can be made by the correct use of lubricants in terms of energy consumption, replacement parts, maintenance costs and the reduction of machinery downtime, because the service life of machines is one of the most important aspects of engineering. Planned preventive maintenance means the minimisation of failures and of maintenance costs; the technology should allow identification of the tribomechanical systems in all operating conditions and of the tribological regime and duration of operation. Despite the enormous advances that have been made over the last thirty years in the theory of rolling bearing lubrication, the successful operation of rolling bearings remains highly dependent on empirical knowledge. The aim of the present study is to investigate the influence of lubricating grease on rolling bearing failure; the experimental work was carried out at a metalworking factory.

ISSN:0954-0075    

DOI:10.1002/ls.3010120104

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

摘要:

AbstractFriction and wear tests were used to evaluate a partially stabilised zirconia (PSZ) disc rubbing against a PSZ pin in a high‐vacuum sliding tester. The surrounding atmosphere contained an organic compound vapour (either benzene, acetone, methane or methanol) at a reduced pressure. In order to understand the mechanism of the tribochemical reaction, the sliding conditions, velocity, and load were varied. During the sliding test, the friction coefficient, surface electrostatic voltage, and adsorption behaviour were measured dynamically. After the sliding test, the worn surfaces were analysed with EPMA and TOF‐SIMS to characterise the components and the molecular weight of the reaction products. The formation of sticky reaction products was observed on the sliding surface in benzene and acetone vapours. These products acted as lubricants, reducing the friction coefficients and wear rates. Analysis suggested that such sticky reaction products contained molecules up to 1000 atomic mass units (A

ISSN:0954-0075    

DOI:10.1002/ls.3010120105

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

摘要:

AbstractAn oil‐soluble compound containing aluminium and boron has been synthesized. The tribological properties of the compound in SN500 oil were evaluated on a four‐ball and block‐on‐ring test apparatus. The results showed that the wear resistance and load‐carrying capacity of the oil were improved, and the friction coefficient was decreased. Evidence of deposition was found in the wear scar by SEM. It is concluded that this deposition provided the oil with its good wear resistance p

ISSN:0954-0075    

DOI:10.1002/ls.3010120106

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

摘要:

AbstractPetroleum waxes are mainly derived from paraffinic crudes. These waxes must be removed from lubricant base oils through a dewaxing process to avoid affecting oil performance at low temperatures. The waxes themselves have uses.This paper describes successful attempts to select the optimum conditions for sulphonation and/or hydrogenation of local waxes to obtain medicinal macro‐ and microcrystalline waxes suitable for use in petroleum jelly blends that meet medicinal specifications.Deoiling was carried out to separate the oil from the wax samples. Concentrated and fuming sulphuric acids were used as sulphonating agents. Sulphonation processes were carried out at different temperatures, stirring speeds, and digestion times. The optimum sulphonation conditions, which give 0.007 UV absorbance at 290 nm and the highest yield, were achieved using 28% concentrated sulphuric acid.The optimum hydrogenation conditions were achieved using a Ni/Mo catalyst at 105°C and 60 bar for paraffin wax and 180°C and 100 bar for petrolatum, for 30 min for both types of waxes.Analysis and field trials of the blended petroleum jelly showed that these blends meet British Pharmacopoeia specificati

ISSN:0954-0075    

DOI:10.1002/ls.3010120107

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY

ISSN:0954-0075    

DOI:10.1002/ls.3010120101

出版商:John Wiley&Sons, Ltd    

年代:1999

数据来源: WILEY