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).
Technical memo discussing bearing wear, hardness, material properties, and testing of aluminium alloys.
| Identifier | ExFiles\Box 115\1\ scan0147 | |
| Date | 21th November 1936 | |
| 1020 Rm.{William Robotham - Chief Engineer} from Hl. Pules Sg.{Arthur F. Sidgreaves - MD} from Hl. (struck through) He. (struck through) Swadl H1.1/VL.{V. Lewis / Mr Valentine}21.11.36. c. to E.{Mr Elliott - Chief Engineer} By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} Sr. BEARING POSITION. Referring to Rm{William Robotham - Chief Engineer}6/R.19.11.36; - A.{Mr Adams} (1) Of the above memo. I conclude this is mainly due to mutual wear owing to fidget between back of bearing and housing (RR 50 crankcase) for if it were due to hammering out there would be serious increase in clearance between journals and bearing or evidence of plastic movement at junctions of bearing halves with the parting liners. It is understandable that under heavy load conditions such wear might occur at the junction of two aluminium alloys of not very dissimilar hardness. With AC1 or AC2, however, this effect might be less owing to their greater hardness. It is possible that graphitic coatings on the surfaces concerned might reduce this trouble which incidentally one would expect to be less, from relative expansion considerations, than with steel backed bearings in an aluminium crankcase. A.{Mr Adams} (2). There has been some evidence that the effect of grit or dirt is more serious from the lapping point of view, with very soft aluminium bearing alloy, owing to the fact that it gets embedded more easily therein, but unlike white metal (Babbits) is unable to sink easily out of harms way. It appears therefore that the hardness, in the case of aluminium bearing alloy, is better over 45 Brinell rather than about 40. The original AC7 bearing alloy was over 45 Brinell. On production, however, it was found that the hardness had dropped to about 40; in consequence a note was written, (BY/EM9/J.26.5.36.) to alter testing methods etc. so as to ensure a high Brinell hardness. Thus, we unfortunately have bearings of relatively low hardness on production of Bentleys' 25-30 h.p. This may explain certain variation noticed, particularly from the endurance standpoint. Some considerable time ago we concentrated on testing and comparing RR56 and several other hard aluminium alloys for their bearing properties, more particularly with Nickel-Chrome crankshaft steel, but also with V.C.M. and carburised steel. With the last named good and consistent results were obtained in the laboratory. It was concluded, however, that with softer shafts it was necessary to have alloys of greater accommodation from the friction standpoint and less liable to weld or seize on to | ||