Published: Jan 1937
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The subject of metallic wear in automobiles is such an exceedingly broad one that it cannot be covered in any detail in one technical paper. Included under this heading is the wear of gears, cylinder bores, piston rings, pistons, camshafts, tappets, valves, valve seats, bushings, ball bearings, roller bearings, crankshaft and connecting-rod bearings, brake drums and a host of other less known parts. Our knowledge of wear does not permit us to do much classifying or generalizing so that each one of these parts must be considered by itself and in some detail. It will be possible to discuss only a few of these parts rather briefly in this paper inasmuch as it is desired to include a description of a new wear test machine developed in our laboratory. The parts which will be discussed are connecting-rod bearings, gears, cylinder bores and piston rings. Before discussing the wear of these parts it might be well to indicate what we mean by wear in the following discussion. We think of metallic wear as the removal from the surface, at a relatively slow rate, of very small particles due to the rolling or sliding of one surface over the other in such a way as to leave the surfaces smooth. When the surface is not left smooth we usually call the phenomena scoring, pitting, scuffing or galling. These may be considered as various degrees of wear, but when they occur the surface deterioration is so fast that early failure usually results. When the particle size of removed metal is larger or the rate of removal of particles is faster we may call the process lapping, polishing, grinding or cutting. No very exact line of demarcation has been drawn between wear and other processes involving the removal of surface metal so that there is a lack of agreement as to just what is meant by the various terms used in connection with wear. The description just given will be adhered to in this paper.
Jominy, W. E.
Metallurgist, General Motors Corp., Detroit, Mich.