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).
Method for recovering worn, nitrided crankshafts, including processes for lapping and regrinding.
| Identifier | ExFiles\Box 146\2\ scan0235 | |
| Date | 6th November 1936 | |
| COPY. By.2/G.6.11.36. NITRIDED CRANKSHAFTS. RE: METHOD OF RECOVERING WORN SHAFT. ----------------------------------- Referring to Rm.{William Robotham - Chief Engineer}20/MJ.2.11.36 and Rm{William Robotham - Chief Engineer}/Swd.18/JH.2.11.36., it is agreed that we cannot put back a crankshaft which has 'bowed' throughout its length into centres and regrind for a small amount of wear. The only practicable method to correct for small wear conditions is by lapping. In regard to loss of hardness with depth, there is a progressive loss over .012" depth of 25 points Vickers per thousandth of an inch, and we can therefore lap 5 thousandths before we need consider regrinding. There is a further point we wish to make clear in this connection, viz. that if the shaft has run hot and the nitriding has been softened by heat, then it is necessary to completely remove the nitrided surface before any further nitriding will 'take'. If, however, the shaft is merely worn and the nitrided surface has not been softened then it is not necessary to remove the nitrided surface which already exists, if it is re-nitrided it will take on the existing nitriding and produce depth of hardening at the same rate as if it were a new shaft being treated. When it is necessary to regrind the shaft, this should be done by selecting centres which average out the wear and the "bow" of the shaft. The shaft should then be cleaned up on these centres and re-nitrided. I am of the opinion that once a shaft has been reground in this manner no further 'bowing' will take place, as the 'bowing' is a function of forging and machine work, and is ultimately due to the effects of the machining, that is, the cutting out of large quantities of metal from certain areas relative to the main design, and once the shaft has stabilised itself further 'bowing is most unlikely. By | ||