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).
Crankshaft forging, materials, and the 'Tocco' hardening process.
| Identifier | ExFiles\Box 148\5\ scan0216 | |
| Date | 12th November 1937 | |
| -3- Should the Operator fail to correctly locate the partly finished forging in the 2nd. or 3rd. die the crankshaft is distorted and rendered scrap due to the surplus metal at this stage being insufficient to fill the die cavity resulting in an undersized forging. Certain crankshafts of simple design are drop forged at one operation in a single pair of dies, and the billet can be rough forged previously almost to finished shape resulting in minimum labour and material cost. Due to the small production output it is necessary to obtain R.R. crankshafts in quantities of 200, and the total annual orders including aero would not exceed 4000, whereas the Morris group purchase 170,000 forgings per annum from E.S.C. and this fact adds to the difficulty of obtaining a really economical price. All things considered, however, the price paid for forgings is not excessive, and compares quite favourably with that paid by other manufacturers using shafts similar in design to our own after making due allowance for differences in material. Cost. MATERIAL. The majority of manufacturers in this country and America produce their crankshafts from a .40 Carbon Steel costing from £22.0.0d. per ton upwards, as compared with £43. 0. 0d. per ton for R.R. present V.C.M. material. This .40 carbon material has a tensile strength of 40-50 tons and can be treated to give a Brinell hardness of 210-250 which of course is inferior to the 286-311 hardness of the S/NCR. which was abandoned some four years ago in favour of V.C.M. The wearing surfaces of crankshafts in this material can be hardened by the American 'Tocco' process used by Packard and others to give a surface brinell of 600-650 which is equivalent to that obtainable with V.C.M.. Quotations are appended for .40 Carbon steel crankshafts hardened by the 'Tocco' process but although the actual process is essentially cheap the Royalties being based on engine capacity are almost sufficient to cancel out the economy obtained by the reduction in Cost of Material. Ambrose Shardlow & Co. of Sheffield are the only English firm at present treating crankshafts by the Tocco process and although it is understood that they do not hold sole rights the cost of equipment being £15,000 would render installation at Rolls-Royce uneconomical. Several English firms including Lagonda (V.12), Aston Martin, are running experimental engines with 'Tocco' hardened crankshafts, and we were able to witness a demonstration of the equipment in operation. The shaft after machining to the final grinding stage is mounted on a trolley and two semi-circular clamps liberally drilled in the bore are brought together, to encircle but not actually touch the pin or Journal to be hardened. A high voltage current is passed through | ||