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).
Valve spring fatigue failure, surface decarburization, and the quality of Swedish wire, including a table of stress ranges.
| Identifier | ExFiles\Box 96\2\ scan0159 | |
| Date | 23th September 1936 | |
| September 23rd 1936. We agree with Mr J.D.Pearson's letter of September 7 that surface playes a most important part in fatigue failure of valve springs. Surface decarburization is also an extremely vital factor. In our estimation about ninety percent of valve spring failures can be traced to either one or the other of these causes with surface conditions the predominating factor. At the present time, the American valve spring wire market is held by Swedish Wire Manufacturers. The reason for this condition is excellent surface and freedom from decarburization. We would recommend to Mr Pearson that he investigate "Oteva" wire made by A-B Garphytte Bruck, Garphytten, Sweden. He should write to Mr Ekstrand and may use our name should he so desire. I do not know whether this company has an English representative, but it may be advisable to check this point. Typical American design on maximum stress and stress range may best be illustrated by example. Corrected Stresses. Valve Open. Valve Closed. Stress range. A 80,000 49,600 30,400. B 73,000 41,000 31,900 C 85,000 46,100 39,900 D 84,000 59,600 24,400 E 76,900 29,300 47,600 F 76,000 28,800 47,200 P.III 73,500 30,500 43,000 These springs are all production springs and have operated with satisfactory results. Solid stress conditions vary but under no circumstances should the solid stress go beyond the point where trapped stresses due to pressing cause the spring to creep upon standing. This point changes for kind of material, size of wire, and manufacturing operations so we would not like to go on record unless we had more data. However, for a specific item, such as one valve spring, we make from Oil Tempered .148" diameter Swedish Wire, the "set" point is 155,000 psi. We believe that valve springs should be | ||