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).
Optimal temperatures and procedures for stress releasing valve springs after shot blasting.
| Identifier | ExFiles\Box 178\2\ img063 | |
| Date | 22th March 1940 | |
| Serial No 37 Rolls-Royce Ltd. Derby, England Rm{William Robotham - Chief Engineer} Valve Springs Received your cable: "After shot blasting valve springs at what temperature is stress releasing carried out. Our present practice 350 degrees centigrade. Robotham" Replied today: "Valve springs stress released 225 centigrade higher temperatures lose all benefit from shotblast. Zimmerli recommends 30 to 40 thousandths shot and 12 minutes operation in wheelabrator or 40 minutes with 80 lb. air. Writing. Have you sent vulture drawing. Olley 6" Here is a record of conversation just had with Zimmerli. 1) 350°C (660°F) gives a great reduction in the benefit obtained from shotblasting. 2) B.G.R.'s standard is to stress release at 425-450°F, i.e. approx. 225°C, as cabled. 3) Attached sketch chart is only rough, from telephone conversation. It represents his experiences with hard drawn swedish carbon steel wire, and represents a very large number of tests-several hundred. A lesser number of tests have been made with Chrome Vanadium wire which go to show that endurance results are so similar to carbon steel that duplication of tests was unnecessary. Zimmerli is sending me a copy of his endurance chart, which I will forward. His opinion is that Chrome Vanadium wire is only justified in case valve springs run excessively hot. Sam Heron holds the same view. 4) He finds that some stress release after shotblasting is necessary to get uniformity of load in the finished springs. Without it the springs were not uniform in load within working tolerances. With 425-450°F stress release he gets loads within +-4lbs. (four pounds) Without stress release there is no sign of brittleness. The springs will run the same endurance limit. 5) A little bit of trial and error comes into the picture. For Chrome Vanadium wire he assumes that spring is wound from annealed wire. He would proceed as follows:- | ||