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).
Detailed report on the metallurgy and construction of the engine, transmission, frame, and axles of the 'Golden Arrow' record-breaking car.
| Identifier | ExFiles\Box 154a\1\ scan0255 | |
| Date | 15th March 1932 guessed | |
| [Page 3] developed. In fact, in attempting to drive the machine to limits never before reached, its factor of safety must be exceptionally large, since it is almost impossible to predict accurately what stresses may be incurred, over and above those ordinary calculable, owing to chance occurrences during travelling at speed. Bearing in mind what catastrophic results even a minor failure might have, it is of interest to examine what materials the designer chose for his stressed parts. Thanks to the courtesy of Captain Irving, to Messrs. The English Steel Corporation, who supplied most of the steels, and to the firms mentioned below, we are able to give some of these details and to show how nickel alloy steels were utilised in obtaining the necessarily varied combinations of strength, toughness, hardness and resistance to shock. The illustration, Fig. 2, shows the locations in which nickel-containing steels were found to be necessary. For the purpose of our brief description we may divide these broadly into three sections, namely:—(a) the Frame, Cross Members, Axles and connected controls, (b) the Engine, and (c) the Transmission. (a) Frame, Axles, etc. Photographs which were taken of the “Golden Arrow” during the record-breaking run show that two wheels on the same side were often off the ground together, while irregularities of surface resulted once or twice in the whole car leaping into the air for distances of 40 or 50 feet. On another occasion a bad gulley in the sand caused the machine to slew sideways, the wrench damaging one of the radiators. These possibilities had naturally been foreseen and provision made for a frame which, without being unnecessarily heavy, would combine sufficient strength to carry the engine and transmission with the degree of toughness needed to withstand the effects of the inevitable sudden shocks. The whole of the main and sub-frames, including cross members, frame stiffeners, brackets, bolts and pins were made of nickel steel, containing about 3.5 per cent. nickel and 0.30 per cent. carbon, the various members being pressed hot by Messrs. John Thompson Motor Pressings Ltd. from ¼ inch thick plates. Fig. 3 gives some idea of the massive nature of the main frame, and it is of interest to record that the side members, which are 19 feet 6 inches long, were pressed in one length. Fig. 3. A front view, showing the massive Frame and Front Axle, both of which were in Nickel Alloy Steels. The Mounting and Arrangement of the Engine may also be seen. By courtesy of The Autocar. — 3 — [Page 6] twelve cylinders, arranged in three blocks of four each, as shown in the illustrations. It is capable of developing 900 h.p. at 3,300 r.p.m. and weighs only 835 lbs. Unfortunately, owing to circumstances over which we have no control, we are not able to give details of the nature of the various steels used in the construction of this engine; we are, however, permitted to state that nickel-containing steels are employed to a very great extent. (c) The Transmission. The Clutch. The engine drive was conveyed to the gear box through a multi-plate clutch made by Messrs. The British Ensign Engineering Co., Ltd. Having to transmit so great a horse-power it had to be exceptionally strong and in order to overcome the necessarily high interplate pressure a Dewandre servo motor had to be used here also. The withdrawal mechanism was made almost entirely of heat-treated nickel steel, as were also a number of details in the clutch itself. For the cover plates, clutch casing and certain small levers, a 35-ton nickel-chromium steel was specified. A steel containing about 3.5 per cent. nickel, 0.6 per cent. chromium and 0.3 per cent. carbon met the necessary conditions after hardening in oil from 830° C. (1530° F.{Mr Friese}) and tempering at 600° C. (1110° F.{Mr Friese}). After this treatment the following typical results are obtainable from this steel:— Yield Point, Tons per sq. in.: 30; Maximum Stress, Tons per sq. in.: 38; Elongation, Per cent.: 22; Reduction of Area, Per cent.: 55; Izod Impact Figure, ft.-lbs.: 60 For the clutch centre, withdrawal sleeve and several other details a high tensile case-hardening nickel-chromium steel of the following approximate composition was employed:— Carbon, Per cent.: 0.1; Manganese, Per cent.: 0.2; Nickel, Per cent.: 3.5; Chromium, Per cent.: 1.0 After carburising, the steel was generally given two after-treatments, one from 830° C. (1530° F.{Mr Friese}) and one from 770° C. (1420° F.{Mr Friese}). In some cases it was afterwards tempered at 200° C. (390° F.{Mr Friese}) in order to obtain maximum toughness. The properties obtained, of course, depended on the section of the treated part, but a 1⅛ inch diameter bar gives, after this treatment, the following figures in the core:— Yield Point, Tons per sq. in.: 55; Maximum Stress, Tons per sq. in.: 69; Elongation, Per cent.: 15; Reduction of Area, Per cent.: 45; Izod Impact Figure, ft.-lbs.: 28 The 5 per cent. nickel case-hardening steel was also employed for certain of the clutch parts. Gear Box. In order to keep the car as low as possible the drive was conveyed to the rear axle through two cardan shafts, thus permitting the driver to take up an exceptionally low position between them. It was therefore necessary to employ a gear box of some unusual design. This gave three speeds and drove the two propeller shafts through a train of spur gears. (See Figs. 8 and 9). The main and lay shafts in the gear box were made of the case-hardening nickel steel previously referred to above. For the gears themselves, use was made of a nickel-chromium-molybdenum steel with a composition similar to that mentioned on page 4, this being treated to give maximum hardness combined with toughness. The employment of this steel is interesting in that it typifies a tendency amongst some automobile manufacturers to use an oil-hardening nickel-chromium steel for gears in place of the more usual case-hardening steels. With or without the presence of molybdenum, it is possible, by quenching the steel in oil and then tempering at 200° C. (390° F.{Mr Friese}) to obtain a maximum stress of well over 100 tons per sq. inch and a Brinell hardness number up to 550, while still retaining reasonable ductility and an Izod impact figure approaching 20 ft.-lbs. Provided that the gear wheel is suitably proportioned, these figures will give quite adequate wear resistance in running while uniformly high properties are obtained throughout the component. The presence of molybdenum assists in both these directions. For certain of the selector shafts, nickel steel was employed, while for others the previously mentioned nickel-chromium steel was used. The whole box was constructed by Messrs. Gillett, Stephen & Co., to whom we are grateful for the details. Final Drive. The drive from the two cardan shafts was conveyed to the rear wheels separately through bevel and crown wheels. These latter were made of an Fig. 7. The Clutch and Control Mechanism. By courtesy of The Autocar. — 6 — | ||