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).
Properties and trials of A.C.6 alloy for die-cast main bearings, comparing it to other alloys.
| Identifier | ExFiles\Box 115\3\ scan0066 | |
| Date | 30th September 1937 | |
| -2- This A.C.6. alloy has a Brinell figure of 70-75 and its analysis is identical to A.C.7. but with 1.0% of magnesium against .55% in the A.C.7. alloy which is responsible for the increased hardness. We understand that from a casting point of view the A.C.6. alloy is more preferable than the A.C.2. which it would replace. The additional quantity of magnesium which can be regarded as the hardening element would also make for a more constant Brinell figure for the following reasons. Assuming that due to some reason or other High Duty Alloys have produced material which is .2% low in magnesium then in the case of the A.C.6. alloy, the magnesium element is .8% instead of 1.0% or 80% of the correct figure whereas in the case of A.C.2. alloy the magnesium element is .35% instead of .55% or only 43%. As quoted in memo By.Z/W.23.9.37, from the present billets of 4½ lbs. two or three 4oz. bearings are produced, which if die-cast to the approximate size of the final bearing would be an appreciable economy. In A.C.6. alloy we have run die-cast main bearings on the Bentley test bed unit and these so far as the running and the subsequent inspection, are quite satisfactory. Similar bearings are installed in G.H.IV. chassis originally assembled for 15,000 miles in April of this year. Although we are, from our results, confident of die-cast bearings as run in the A.C.6. alloy we could not standardise on account of the percentage of scrap that we have had in the bearings submitted to us for trial. This has been in the region of 50% due to porosity. We await a further batch of die-cast A.C.6. main bearings for trial on the Bentley, incorporating all the known improvements in casting to overcome the porosity troubles. The above should be cast on a production basis in order that there will be no misleading results and providing the percentage scrap is low and the bearings run through a bench test satisfactorily, we would consider standardisation. At the moment the percentage scrap with die-cast bearings is so much higher than bearings produced from the normal billet that we doubt whether there would be any saving if adopted at the present time. continued | ||