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).
Issues with chromium plated tappets for the Phantom III, specifically over-stress and chipping.
| Identifier | ExFiles\Box 96\2\ scan0112 | |
| Date | 28th April 1936 | |
| P Giles Rm{William Robotham - Chief Engineer} 354 HY{Tom Haldenby - Plant Engineer}/CS. [struck through] c. KHC. c. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} BY.W/G.28.4.36. SWDL{Len H. Swindell} PHANTOM III. CHROMIUM PLATED TAPPETS. Any Commenti? Rm{William Robotham - Chief Engineer} Mr. Wilson and his technical assistant recently paid a visit to these Works, as a result of criticisms made by myself in regard to the chipping off of the chromium plating on the edges of the tappets. It was agreed on both sides that the cause of the trouble was mainly over-stress due to building up of chromium around the edges or boundaries of the plated surfaces. As chromium has very little throwing power, and as a result of this has to a marked degree characteristics of building up on corners, this in turn sets up high internal stress, which can be sufficient when a hard plating is aimed at to tear away the deposit from the base metal. During the discussion Mr. Wilson made the suggestion that they would probably get far better results if they completely plated the camshaft, they would protect the end where the gear and the taper for the driving wheel are arranged, but would require the diameter of the bearings to be increased in order to enable us to grind away the chromium plating. Their suggestion being that they would use what they term their 'Millichrome' deposit which is a thin deposit of considerable hardness, the thickness being not more than .0005". The object of this was to avoid grinding the deposit, and also to avoid the high tension effects where the deposit petered out, as in the case of the tappet round the boundaries of the plated surface. Will BY/CS. please arrange to modify a blueprint making an allowance on all the bearing surfaces of .003" per side, so that the plating can be ground off and the usual case hardened bearing surface uncovered. Mr. Wilson particularly asked for this, as he was afraid their deposit would not be sufficiently round to be reliable as a bearing surface without grinding, and therefore the only solution was to grind off chromium on the actual diametrical bearing surfaces. The plated camshaft is intended to be used with unplated case hardened tappets. By BY.{R.W. Bailey - Chief Engineer} | ||