CASE-HARDENING.

Hawera Star, Volume XLVI, 9 April 1927, Page 14

CASE-HARDENING.

MUCH- USED PROCESS. IX AUTOMOBILE INDUSTRY. The process of case-hardening, an old one in the metallurgy of steel, has come into wide use in recent years in the automobile industry. In casehardening, the outside of a soft steel article is impregnated with carbon, which makes it possible after quenching to obtain a hard wearing service while the interior remains tough and ductile. An example is a cam shaft of an automobile, which must have hard bearing surfaces to keep the wear down to a minimum to ensure smooth running of the machine. Case-hardening, or carburising, is somewhat complicated, and a good many difficulties arise. One of the most serious is soft spots. Recent work by a metallurgist of a roller-bear-ing company indicated that a type of steel which he called “abnormal” is more prone to give this trouble than another which he called “normal.” The difference between the two types of steel is revealed by microscopic examination.

The conclusion that the kind of steel used may he responsible for soft spots was at first not accepted by all metallurgists. Study of the problem has shown that the two types of steel really exist, and the abnormal steel is more prone to give soft spots. Aside from the tendency to give, soft spots, however, the abnormal type is not inferior to the nounal. and in some ways may even be superior It was shown that bv somewhat more drastic quenching it is possible to harden satisfactorily both types of steel.

To keep hydraulic brakes working efficiently, the plunger of the supply tank s’oil'd he pulled out now and again and wiped clean with a cloth. This pie ents corrosion on the plunger from mixing with the solution and reaching the wheel cylinders, where a perfect piston fit is desirable.