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).
Pros and cons of die castings versus sand castings and the use of cheaper alloys.
| Identifier | ExFiles\Box 142\4\ scan0049 | |
| Date | 25th November 1936 | |
| J 1202 To Rm.{William Robotham - Chief Engineer} from Hl. (For circulation if desired) DIE CASTINGS AND LESS COSTLY ALLOYS. R.R.50 alloy actually only costs us about £120.ton (£10. is deducted subsequently) We agree that die castings may be better than sand castings but there are a number of points that should be taken into account. (1) Big die castings made elsewhere - Leylands for instance - are much thicker in section and heavier than ours. (2) To obtain good castings in large dies would necessitate careful control of alloy composition and it is essential to have castings with some ductility. The cheaper or secondary commercial alloys containing high Zinc or Copper are lacking in this respect, either cold or at normal crankcase temperature and our experience suggests that they are more liable to cracking either in their mould or if stressed to any serious extent in service than is the case with RR.50. We have seen die castings in Birmal special which shewed both cracks and shrinkage cavities, at changes of section and the alloy is liable to suffer from crystal grain reversion (if fluxing effect "dies out" owing to delay in pouring?) Big die castings are difficult to produce owing to contraction effects and it is likely that dies would want repeated modification before apparently perfect castings could be produced, even in a high Silicon alloy such as Birmal Special. A thing to be noticed also is that we can remelt RR.50 runners and risers etc. even for production of casting as thin as .100" (Kestrel rocker cover for instance) Hl. | ||