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).
The development of high-duty bearings, detailing the limitations of existing alloys and the creation and success of the A.C.9 alloy.
| Identifier | ExFiles\Box 115\2\ scan0442 | |
| Date | 11th April 1939 | |
| April 11, 1939. 375 The Motor Contd. DEVELOPMENTS IN HIGH-DUTY BEARINGS in the dimensions of the existing cylinder block. In these circumstances it was found that white metal bearings, which had given admirable service for over 20 years, were no longer able to perform the work imposed on them. Measured in terms of ordinary car standards of reliability they were still satisfactory; regarded in the light of Derby standards, a mileage of between 30,000 and 40,000 miles before beginning to crack up and disintegrate was insufficient. The use of some other metal was, therefore, imperative. Difficulties With Known Alloys The majority of the alternative alloys were exhaustively tested, including lead bronze, cadmium tin, cadmium nickel, silver content and other types. None, however, was found to be altogether suitable under conditions in which cars have to operate to-day. Lead bronze is, for instance, one of the most popular alloys for high-load conditions, but it suffers from relatively poor anti-friction characteristics and is not so suitable for high rubbing speeds and slightly contaminated oil, such as may be found in a motorcar, as it is for work on buses, commercial vehicles, aeroplane engines and Diesel engines where its use is widespread. Other alloys suffer from corrosion or liability to score the crankshaft. It is known that in many cases duralumin connecting rods had been satisfactorily run direct on to hard steel crankshafts. It was, therefore, thought that development along these lines towards producing a cast light alloy bearing capable of use in conjunction with a steel rod, or, alternatively, for main bearings, might offer a solution. Research and Reward During the research work on cast light alloy bearings many accepted theories on bearing structures had to be abandoned or considerably modified. It was found, for instance, that the only successful alloy contains a variety of hard constituents forming a mosaic pattern which will not be torn out during machining, nor, on the other hand, pierce the oil film under temporary conditions of poor lubrication. It was, moreover, necessary to carry out special work to prevent seizure if such bearings were used on soft crankshafts. Eventually a bearing was evolved called A.C.9, which seems to meet all the conditions required for the ideal bearing material. It has, that is to say, fatigue resistance of lead bronze, the anti-friction qualities and freedom from corrosion of white metal, and the mechanical strength of silver. Its constitution is tin 5.5 to 7 per cent., nickel 1.5 to 1.8 per cent., copper .6 to .9 per cent., magnesium .7 to 1.0 per cent., silicon .15 to .3 per cent., and iron .2 to .45. The Brinell figure is between 55 and 75 and the specific gravity about 3. The heat conductivity of this material is three times that of steel and five times better than normal white metal. Furthermore, the Brinell hardness is only slightly reduced at 150 degrees C., whereas normal white metal figures fall from an initial low of 30 Brinell when cold to only about 5 Brinell at the same temperature. The anti-friction qualities of this material as compared with lead bronze are shown in a graph on these pages; and some photographs on another page show tests as compared with other more normal bearing materials. Racing Successes. The first public appearance of this alloy was in the Tourist Trophy Race on the occasion when Mr. E.{Mr Elliott - Chief Engineer} R.{Sir Henry Royce} Hall's car finished at a speed of 80.81 m.p.h., which is a record for any car on this circuit. At the conclusion of this race the bearings were in a perfect condition. More latterly they have been used on the E.R.A. works cars. The bearings which this company put into their engines in 1937 ran untouched through the 1938 competition season and were in such good order that they required no attention for racing during this year. A.C.9 has, of course, been standard on Bentley and Rolls-Royce cars for some time, and a licence for its construction has, under the initiative of Mr. J.{Mr Johnson W.M.} W. Howlett, been taken out by Wellworthy Piston Rings, Ltd., of Lymington, Hants. Other manufacturers, therefore, now have an opportunity of benefiting from Derby research in this matter, and many of them are carrying out active tests. I have heard most favourable opinions on the results obtained. In this article I have only been able to summarize some of the work which is being carried out at the moment at Derby. Much more is veiled under official secrets, but all of it is of great value, not only to Rolls-Royce, Ltd., and Bentley Motors (1931), Ltd., but also to the nation in giving our products supremacy on road and track, on water and in the air. (Other illustrations appear in the Photogravure Section.) Image Caption: RACE TESTED. New light alloy bearings developed by Rolls-Royce were used on the Zoller-supercharged E.R.A. works cars last year and ran the whole season, finishing in perfect condition. In view of the very high blower pressure and a developed power of well over 200 b.h.p. this is a most severe test. 'Motor' copyright 89 | ||