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).
Letter detailing the manufacturing process for valve springs, including heat treatment and shot blasting.
| Identifier | ExFiles\Box 158\4\ scan0033 | |
| Date | 8th June 1936 guessed | |
| -3- In Canada the Steel Company of Canada, Hamilton, Ontario, produce an acceptable product. You of course are familiar with the wires which are produced in ENGLAND, and which are probably as good as those made in other countries. In manufacturing valve springs we use Sleeper & Hartley coilers, which are rigged up with a wheel rather than the usual coiling point. We then coil the springs at a fairly low rate of speed not to exceed 800 an hour. The springs after coiling are ground, and heated to 750 degress F.{Mr Friese} for at least 30 minutes at heat. They are then pressed and shot blasted. This shot blast is done in the ordinary barrel sand blast machine, but we use round steel shot which, as we purchase it, is about 1/32" in dia. and it is blown against the springs with an air pressure of between 65 and 75 pounds. It takes about twenty minutes to completely clean the springs and cold work the surface of the wire. After this treatment the springs, which are clean and bright, are again put through the Heat Treat Department, this time receiving 550 degrees F.{Mr Friese} for twelve minutes. This not only gives the springs a blue coating of oxide, which is resistant to corrosion, but relieves some of the strain of tumbling in the barrels and the effect of the impingement of the steel balls. The springs are now again pressed solid and scale tested for load. We find that this shot blasting in addition to cleaning also increases the fatigue life of the springs a small percentage. This percentage, however, might make a difference between success and failure, as it is the percent of the fatigue limit over which failure is certain to occur, and under it, to the best of our knowledge, barring corrosion and metallurgical defects, failure is not to be looked for. If there is any other way we can be of service to you we will be glad to have you write us and we will try to give you to information you desire. Your very truly, BARNES-GIBSON-RAYMOND-INC. F.J. Zimmerlie, Chief Engineer, FPZ:T | ||