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 design, cold-pressing techniques, and testing methodologies.
| Identifier | ExFiles\Box 178\2\ img065 | |
| Date | 22th March 1940 | |
| -3- 7) Furthermore, to judge by results on torsion rods, I think the spring makers generally have not studied sufficiently the effects of the cold-pressing. A cold-press which only settles the spring .015" is obviously not enough to do what we did on torsion rods. 8) My recommendation, which Eaton Mfg. Co. are considering, is to build the spring more overlength than present practice, perhaps 3/16" to 1/4" in the case of a valve spring. A vertical stroking machine is then built in which the stroke is adjustable so as to compress the spring thru its designed range plus 5%. The pedestal on which the spring sits is arranged like a large hydraulic tappet, so that it will always exert the same low load on the spring at the upper end of each stroke. Then the strokes are repeated rapidly until the hydraulic tappet ceases to creep up. Probably 30 strokes are necessary. The original spring length is, of course, controlled by the necessity of having correct free length or compressed load when the spring has been thoroughly cold-settled as above. And coil clearance must be such as to allow 5% overstress without striking solid. When springs are cold settled in this way, I think the Wahl stress distortion is pretty nearly washed out of them and still higher endurance limits could be obtained (to judge by torsion rods). G.M. have done some work on these lines. I must talk to Zimmerli about it. Copies to: Bailey Lessels OY | ||