Modern Metallurgy Aids Progressive Design
If you've noticed an error in this article please click here to report it so we can fix it.
APREDICTION that powdered metals, which, in use, are consolidated by pressure and heat, will play an important part in motorvehicle manufacture, was voiced by Mr. Frank Calvert, a Leeds metallurgist, in a lecture to the Leeds Centre of the Institute of the Motor Trade at its October meeting. Mr. .Frank Lockwood, chairman of the Centre, preaided.
Mr. Calvert said that if sufficient pressure be applied it was possible to consolidate certain metal powders without the use of heat, but the general practice was to heat to a point below the melting temperature after a preliminary pressing operation. By this process of manufacture it was possible to obtain a practically finished article which required little or no machining.
• In America, where the use of powder metallurgy probably was much more advanced than in Britain, excellent results had been obtained in the mass production of many motor-vehicle parts by the process. After the article , had been made, it was, in malty cases, possible to subject it to heat treatment; however, this was liable to cause a certain amount of distortion, according to the design of the part. To obviate this complication, the metal should be constituted so as not to necessitate heat treatment after manufacture.
In discussing other aspects of metallurgy, Mr. Calvert referred to the problem of corrosion by electrolytic action, which he explained could be set up by contact between one metal and another, especially in the presence of water. Trouble from electrolytic action in metals was a matter which called for serious consideration, both as to the choice of alloys used and as to the actual manufacture of the alloys, particularly in the case of metals for use in motor-vehicle manufacture.
Protection against electrolytic action could be obtained, in some instances, by making additions to the alloy, particularly in the case of non-ferrous metals, as was illustrated by the use of bronze containing excess lead. In contact with reagents, such as sulphuric-acid fumes, the alloy would become coated with an insoluble film of lead sulphate, protecting it against further attack.
In the same way as additions to alloys were introduced as a protection against electrolytic action, so also were they made for such purposes as rendering the structure of a metal more suitable for particular requirements. For example, the motor trade required a type of cast iron in which the flakes of graphite were so distributed as to create greater homogeneity and finer grain-; therefore, in the making of cast iron for most accessories, such as piston rings, a small quantity of chromium was added; to harden the matrix and produce a finer dispez-se phase of graphite.
Electrolytic action and the distribution of the graphite element in cast iron might have some effect on cylinderwear in motor engines. It might, for example, be that there was some electrolytic action which had not yet been -fathomed because its effect was regarded simply as abrasion. Then. again, undue wear might be due to the fact that the structure and composition of the materials used were not as suitable as they should be. The question of cylinder wear had not so far been satisfactorily solved.
A promising means for applying heat treatment to metal after casting was by means of H.F. induction heating. It was possible to harden the centre of a metal bar by so heating and quenching that part as completely to change the • metal structure there, whilst the ends of the bar remained comparatively cool and unchanged.