From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article on solving automotive manufacturing problems through metallurgy.
| Identifier | ExFiles\Box 53\1\ Scan043 | |
| Date | 5th March 1927 | |
| 372 Automotive Industries March 5, 1927 Metallurgist Called Upon to Solve Increasing Number of Automotive Problems Service department troubles frequently eliminated in the metallurgical laboratory, which also does research work, tests various materials and helps with new shop processes. WITH the development during recent years of highly-organized metallurgical work in automotive plants, the industry has found an increasing number of important manufacturing problems which can be solved in this department. Among the problems which are regularly routed through the metallurgical laboratories of most plants at present are those relating to— 1. Certain lines of research work. 2. Testing of materials (non-metallic as well as metallic). 3. Shop processes which reduce production cost without affecting the quality of any fabricated parts involved. 4. Efforts of the service department to correct certain faults which cause complaints from the field. Service department problems are frequently referred to the metallurgist. All service departments keep records of the number of failures of different parts. The reputation of a car depends largely upon its freedom from premature failures of parts, and if any part fails in considerable numbers at an early stage of the normal useful life of a car, it is a matter that deserves the most serious attention on the part of the engineering department. Many such failures can be prevented either by increasing the dimensions of the part in question or by using a better or more suitable grade of material. Unless the part is entirely inadequately dimensioned, which is a rather rare occurrence in this advanced state of the art, the better plan is to use a higher grade of material, at least if this can be done without materially increasing the cost. Increasing the size of the part not only adds directly to its weight and cost, the increase in weight being particularly objectionable if the part is a high speed reciprocating one, but in many cases it would be necessary to change or increase the sizes of adjoining parts. A Rear Axle Problem A good example of this sort of problem came to light some years ago when a prominent maker of motor trucks had trouble from the breaking of rear axle shafts. An increase in the diameter of the shaft would have meant an increase in the size of the bearings supporting it and an increase in the diameter of the axle housing which would have been objectionable on account of [illegible] to the unsprung weight aside from the increased cost of the larger bearings, the greater capacity of which did not seem to be required. The trouble was completely overcome by choosing a high-grade chrome nickel steel for the shafts and treating them so as to obtain a high tensile strength and elastic limit in the completed shaft. Trouble with drop forgings sometimes occurs if the metal is worked under the hammer at too low a temperature. The metal then does not flow so well and there is a risk of imperfections at points of the section toward which the metal must flow in the operation. Another cause of imperfections is that in a rolled bar the material at the center of the bar is not of as good quality as that near the surface which latter has been improved by the hammering and rolling process. Cracks and spongy spots may be visible at such parts of the section if the part is cut in two and the surface etched. Trouble With Connecting Rods In one particular case where trouble had been experienced from breakage of connecting rods in greater numbers than could be tolerated and where a so-called micrographic examination showed porous spots at the junction of the web with the flanges, where the section of the metal is the greatest, the trouble was overcome by the use of a special steel containing about 1 per cent more manganese than the steel ordinarily used for this part. Manganese has the effect of increasing the tensile strength of steel, its effect in this respect depending upon the carbon content; that is, an increase of, say, one hundredth of 1 per cent in the manganese content will increase the tensile strength of the steel the more the greater the carbon content, at least within the limits of carbon usually employed in structural steels. Manganese, however, also tends to render the steel more brittle, and it is generally considered that if the manganese content is increased to more than 1 per cent, water quenching becomes impracticable, owing to the danger of cracking. Little improvements in details are constantly being introduced in the heat-treating department as well as in the machine shop and elsewhere, to improve results obtained and cut down costs. In case hardening parts there are usually a number of surfaces which it is desirable to keep in the normal condition, without having the surface layer highly carburized. There are two general methods in use for eliminating a case on these surfaces. One consists in leaving, say 1/16 in. of stock for machining on these surfaces while the parts are going through the carburizing process, and machining it off—thereby removing the case—after carburizing. | ||