摘要:

AbstractUntil the present time the materials used for exhaust valve spindles for diesel engines have comprised a main body of heat resistant austenite steel with a Stellite layer covering the seat area. Recently, to satisfy increasing demands for higher efficiency of engines, a forged Nimonic 80A exhaust valve spindle has been developed. This valve spindle has higher strength and hot corrosion resistance than conventional austenite steel valves. This paper introduces a compound type Nimonic 80A–austenite steel valve spindle produced via hot isostatic pressing. Nimonic 80A powder metal is consolidated and diffusion bonded to an austenite spindle body. The seat area and the total combustion chamber side of the spindle are clad using Nimonic 80A. The compound valve spindle produced via hot isostatic pressing has the same performance as a forged Nimonic 80A spindle and in addition it has improved repair weldability and hot corrosion resistance compared with the forged Nimonic 80A spindle valve. Because less of the expensive Nimonic 80A material is used, there is an added advantage in that the cost of the valve would be cheaper. Successful engine test results are also described.MST/315B

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.993

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe potential for surface engineering solutions to increase the corrosion and wear resistance of diesel valves is examined with regard to operation in residual fuel oil combustion products. The environment in which the exhaust valve operates is discussed. The corrosion test is used to sort the 27 coating treatments and 16 hardfacing alloys examined. H ardfacing materials showing the greatest potential are also evaluated in hot wear tests. As reference materials, En 52 steel, Nimonic 80A, and Stellite 6 are included. Corrosion tests over the temperature range 500–700°C have shown that the surface treatments can be ranked in terms of their composition and expected metal surface temperature. Good corrosion resistance to residual fuel oil combustion products reflects primarily the content of the alloy, the base metal (Fe, Ni, or Co) being of secondary importance. Refractory metals (Ti, Nb, Ta, Mo, and W) and other minor alloying additions do not significantly alter the corrosion behaviour, unless they are present in large quantities. Hot wear tests (650°C, 80 MN m−2contact pressure) of candidate hardfacing alloys have also demonstrated the importance of the Cr content of the alloy. This probably results from the ease of formation of a protective glaze, lowering the coefficient of friction and therefore the wear rate. Additions of refractory metals were beneficial. Since optimum wear resistant alloys contained high levels of Mo and vv: they were poor in terms of corrosion resistance. It is therefore necessary to balance wear resistance against corrosion resistance in the selection of materials for residual fuel oil service. Two coating systems, vacuum plasma sprayed Ni–50Cr and a chromised diffusion treatment appeared to have potential as valve surface treatments for improved corrosion resistance; and two hardfacing alloys, Tristelle TS2 and Colmonoy 8, offered balanced behaviour as seat materials with acceptable wear resistance and improved corrosion performance. These materials have been evaluated in the engine tests of three different diesel engine manufacturers.MST/3157

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.1002

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractRecently the requirements imposed on parts in the valve train have significantly increased and different trends are apparent for different fuels. These fuels can be defined as conventional fuels, heavy fuels, and (natural) gas. For conventional fuels, no major differences exist between truck and marine engine applications. Owing to an increase in peak pressure and process temperature, new designs and materials are required in these fields of application. For heavy fuel applications, corrosion presents a continuing problem because of further increasing temperatures. Improved materials, surface protection, and heat transfer could reduce problems such as seat burning and corrosion on valve stems, valve heads, and guides. Varying compositions of natural gas and problems with the mixture control require the optimisation of the tribological system of valve seat–valve seat insert and an improvement in the behaviour of valve materials at elevated temperatures. Both technically and economically there are many problems to solve. This paper addresses the techniques and results of improvement and optimisation, for example, finite element analysis and test facilities, improvement and optimisation of valve steels, and the surface protection, heat transfer, design, and interactions between valve stem guide and the valve seat-seat insert.MST/3156

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.1013

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.1017

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor