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).
Investigation into broken rollers, detailing material specifications, hardness tests, and supplier discussions.
| Identifier | ExFiles\Box 153\1\ scan0320 | |
| Date | 27th June 1939 | |
| - 2 - 27th. June 1939. Robert Armitage, Esq., boat (the chassis we despatched en route for Paris). This caused us to immediately impose an overload test by letting down the tyre pressures and increasing the load on the front wheels about 30%. It was then brought home to us that none of the rollers were up to the standard of those originally passed by us before the manufacturing of the part was handed over to the Hoffmann Co. Examination of the broken rollers returned from Paris showed that the part had been :- (a). Heavily over-carburised. (b). The core brinell should fall between 341/400. The first roller actually tested had a core brinell of 651/652, and the second 571/618, which led us at first to the conclusion that a wrong type of material had been used. Further investigation however, showed that the type of material was correct i.e. it was a nickel chrome case hardening steel to S.82, but it was at the end of the composition for hardness, having a Manganese content of .48. In regard to specification, the information conveyed to us in Messrs. Hoffmann's letter is correct, but any material specification of this type covers a wide range, no steel maker should roll into small diameter bars material at the upper limit of composition, and therefore hardness. We ourselves have bought this material from Messrs. Firths for years, and have never had to return any material in small bars because it would not meet the conditions specified on our drawings - in this case a core brinell range of 341/400. Following trouble we pointed out to Messrs. Hoffmanns that it was advisable to keep the Manganese down to a minimum of .24 for this size of bar, but this is information which should have been supplied to them by the Steel Maker as obviously one would not expect a manufacturing concern to be au fait with steel making conditions, so as to be able to specify accurately a maximum content for an alloy steel marketed under British Standards Specification. I enclose herewith a blueprint of the roller in question showing how completely the information as to requirements and how to obtain them by treatment is specified on the drawing. As a result of the discussion at our Works with Hoffmanns representative, it was agreed that the material was wrongly treated, and that the Hoffmann Co. should replace the rollers free of charge, which has been done, but the cost of this is nothing compared with the expense that this Company has been put to in replacing the rollers in cars in customers hands. | ||