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 use of magnesium castings for engine components, comparing them to aluminum in terms of production, cost, and weight.
| Identifier | ExFiles\Box 140\3\ scan0054 | |
| Date | 25th August 1936 | |
| -2- We were rather surprised to see the matter of fact way in which castings were being produced on a production scale, because we have always had such difficulty in getting castings and have been given to understand that the material was exceedingly awkward to handle. We discussed their future policy with regard to magnesium. The present situation appears to be that the weight regulations have been altered and therefore the use of exceptionally light alloys is not so imperative. Therefore it is questionable whether in the future the additional cost of the castings, which is of the order of 15%, will be justified from their point of view. Additionally, when they come to use magnesium crankcases on compression ignition engines, where the stresses due to the high explosion pressures are very high, they have run into trouble with crankcase distortion. They are at present carrying out a test comparing magnesium and aluminium, to ascertain whether this trouble can be attributed entirely to material, or whether design is partly responsible. As they have been using magnesium crankcases for long periods, it cannot be assumed from their recent trouble that the metal is entirely unsuitable for this class of work. However, they are letting us know what they find out on completion of the present series of tests. It has been said that the weight saving to be achieved by the use of magnesium is in no way what one would expect from the low specific gravity of the material, due to the casting difficulties making thin sections impossible. As Leylands do not seem to agree with this we got some further confirmatory evidence from Crossley Motors, who are also using magnesium for induction pipes, valve covers, oil sumps, and crankcases, and they confirm that as a general rule their magnesium castings weighed 60% of the same casting made in aluminium. They also confirm that the approximate increase in cost of the castings is 15%. This means that if we made every aluminium piece on the Bentley in magnesium, the increased cost would be £5. 15. 0d. | ||