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).
Piston treatment process to create a dense, porous oxide skin.
| Identifier | ExFiles\Box 148\4\ scan0296 | |
| Date | 24th September 1934 | |
| Specialloid LIMITED Friern Park North Finchley, N.12. - 2 - Messrs. Rolls Royce, Ltd. 24.9.'34. 2. Owing to the porous nature of the hardened skin, it is possible to impregnate the surface with a lubricating oil which is maintained under all conditions. This of course, has a positive advantage in overcoming tendency of Piston seizure. 3. That the Oxide skin will resist corrosion from certain salts and acids. DETAILS OF PROCESS. The Pistons are completely machined before subjection to treatment, for it is proved that no appreciable change in size is made to the article, and since treatment is performed at an ordinary room temperature, no distortion takes place. The process consists of forming a dense oxide skin on the surface of the Piston. This is accompanied by immersing the article in a bath of suitable electrolyte, such as diluted sulphuric acid. The article to be treated is made the anode of an electrical circuit, of medium voltage and considerable current density. The skin formed on the surface of the Piston may be up to .003" in depth, but is usually in the region of .0015" - .002". When the article is removed from the treatment bath, it is possible, owing to the porous nature of the oxide skin, to impregnate the surface with either a mineral oil or colloidal graphite, which may be maintained in the surface by a special process. The claims as already stated above for the treatment are in respect of the very high hardness value of the Aluminium oxide, combined with the very high melting point, which means that the hardness value is not affected by engine temperatures. It is, of course, realized, that since the oxide | ||