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).
Machining, nitriding, and steel selection for car cranks, including comparisons with American manufacturing practices.
| Identifier | ExFiles\Box 178\2\ img106 | |
| Date | 5th January 1940 guessed | |
| The matter is still in the air. If it goes through our forging price will increase about $1.50 per crank. Machining. We put up to W.G. and Republic that there were three things we had to watch-- 1. Distortion of crank during rough machining, making finish machining impossible. 2. Distortion after nitriding, making finished cranks unacceptable. 3. Inclusion lines revealed after nitriding. Mr. Wood explained that the first was largely controlled by grain flow, which in turn was controlled by the forging practice. If the grain flow was uniform and arranged lengthwise of the crank sections, the distortion in roughing should be small. Also careful quenching in heat treat was necessary. The second was largely a matter of thorough stress release after roughing, support of crank in nitriding etc. The third was a matter of doubt, but with steel as nearly perfect as shown by magnaflux tests, it was difficult to see where the inclusion lines after nitriding were to come from. Car Cranks. The print PL.72 had been studied by Mr. Wood. He agreed to send us a forging drawing, or at least a drawing representing the typical forging around each individual crank throw ( the drawing as received not being fully dimensioned). This will represent standard American practice. He will quote on forgings in standard 1045 "resulphurized" steel as commonly used, in 1050 "Tocco" steel, and in 4135 steel, as representing moderate alloy steel practice suitable for nitriding. 1045. This is standard American practice. GM on Cadillac and Olds, control the sulphur to near the maximum (.055) for ease of machining with smooth finish, freedom from scoring, etc., along the lines represented by the free-cutting steels of the 1100 and 1300 series. Heat treated to a range of 241-269 the steel runs well for a trouble free life of at least 100,000 miles, as proved by average American car practice, provided correct (thin) oils are used and white metal bearings preferably of the new steel-backed thin white-metal type. In some exceptional cases, a hardness range of 269-302 is used, but this gets close to the limit of machine ability of the steel. | ||