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).
Material selection and production processes for Bren gun springs.
| Identifier | ExFiles\Box 176\3\ img095 | |
| Date | 19th April 1940 | |
| Rm.{William Robotham - Chief Engineer}..from BY.{R.W. Bailey - Chief Engineer} Gun BY.2/HR.19.4.40. 2a SPRING FOR BREN GUN. ------------------- In regard to the use of 18/8 (18% Cr.{Mr Cra???ster / Mr Chichester} 8% Ni.) austenitic steel, this could only be used in a work hardened condition as it will not respond to heat treatment. I have used work hardened 18/8 but was not able to obtain as good results as either hard drawn high carbon steel or heat treated material. In regard to plating, we cannot plate valve springs as we did road springs, as during the hardening process a slight oxidation occurs. In fact, we produce it purposely since it cannot be avoided, as a rust preventative or as a mild rust resistant. In the case of road springs we did no cleaning by acid as we polished each plate and removed all oxide, cleaned in a Crawshawpoll (evaporation and condensation) cleaner, and then immersed in plating bath immediately following this, and switched on to plate without any recourse to etching which produces inter-crystalline corrosion and rapid failure. There is, however, another method of attacking this problem, as follows:- (a) Use either Chrome Vanadium or Silico Manganese as material. (b) After producing the springs in the soft state and before hardening plate with a minimum of .0015 of Nickel. (c) Heat treat as usual. This will provide the protection required. It also protects the spring itself against pitting or decarburisation during hardening, and the coating is still resistant and non-porous after a full heat treatment. This was my last card if I had not succeeded with Talbot's special furnace due to delay in making it. -continued | ||