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).
Options for reducing car unit costs and weight through cheaper alloys and die casting.
| Identifier | ExFiles\Box 142\4\ scan0039 | |
| Date | 23th November 1936 | |
| Rm.{William Robotham - Chief Engineer} from Smth. Rm{William Robotham - Chief Engineer}/Smth4/R.23.11.36. CAR UNIT WEIGHTS & COSTS. We have been looking into the possibilities of saving cost and weight on our car units by altering either foundry procedure or material. Taking our existing designs, there are two ways of reducing the cost of aluminium pieces, viz:- (1) by using cheaper alloys. (2) by die casting. (1) Cheap Alloys. There are about 150 lbs of aluminium castings in the 25/30 & Bentley engine and gearbox units. We use RR.50 alloy throughout which costs £130 per ton. This is very rarely used by other manufacturers on account of its high price. On discussing the matter with the Birmingham Aluminium Casting Co., we find that with the possible exception of the crankcase top half (the only piece in which strength is a consideration) all these castings could be made in their 'No.6' secondary L.5 material, costing £74 per ton. We propose to test a crankcase in this material without delay, and are confident that even if it is not strong enough with the present design, very slight modifications will make it so. By using this alloy we ought to save about £3/10/- on the Bentley and 25/30 units. Owing to the slight extra density of the cheaper alloy, the weight would increase by 10 lbs. On P.III the bulk of the aluminium is in the cylinder heads, and the crankcase monoblock for which L.5 would not be suitable as it is not free from corrosion when exposed to water. The cheapest alternative alloy to RR.50. which we know of for this application is Birmasil special at £110 per ton. Using this where necessary, and L.5 for the other castings, we could save about £3/10/- on this unit also. (2) Die Casting. Owing to the great saving in Foundry labour cost (usually about 75%) we could save money by die casting a number of our pieces. We have discussed the matter with the Birmingham Aluminium Casting Co., and they are of the opinion that it would be possible to die cast all the big aluminium pieces on the 25/30 unit. Neglecting the cost of the dies, and assuming the following savings:- | ||