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).
Failure of tungsten contact points in battery ignition systems, exploring causes and detailing ongoing experiments with new designs and suppliers.
| Identifier | ExFiles\Box 35\6\ scan 421 | |
| Date | 4th May 1928 | |
| HS.{Lord Ernest Hives - Chair} RHC.{R. H. Coverley - Production Engineer} EFC. ---------- X2894 BY2/G.4.5.28. TUNGSTEN CONTACT POINTS. ------------------------ Immediately we tried to introduce as standard the tungsten contact points on our battery ignition we discovered that quite a big percentage of the levers fitted with contact points were faulty in one or two directions :- (1) In the first instance the tungsten contact broke away where it was welded to the steel base. (2) The unit consisting of the steel base and the tungsten point welded to it worked loose in the lever. We instructed the Works to abandon riveting which undoubtedly was the cause of the tip coming off, although at the same time faulty welding must have been present. We suggested spinning and swaging, but without any beneficial results, so far as the point working loose in the lever is concerned. Since then we have tried two outside makers, one of whom was Reynolds. Although we gave them all the advice we could and suggested several methods of doing the work they completely failed to solve the problem. We therefore had to cancel the instructions to use the tungsten points and replace them with platinum until we are satisfied that we can produce the point and fix it in the lever without fear of failure. In the meantime we are trying the Tungsten Mfg. Co. We ordered in the first instance 50 but 2 of these came loose, we then ordered a further 100, pointing out the defect, and we are trying these at the moment. 10 of these we have instructed to be handed over to EFC. for special long duration testing. We appreciate the fault is a mechanical one, and not necessarily anything to do with the Electrical Department or the Experimental, but I want the position to be clearly understood so that no misapprehension will arise betwixt ourselves and Mr. Royce. As the amount of material in the pin as originally designed for riveting over seemed to me to be inadequate, some time ago I had a number of designs got out for increasing the pin in order to allow bigger areas, and at the same time to increase the diameter of the pin passing through the lever I added a collar so that there is a real adequate surface gripping the lever. We are having some of these made as I am certain from the results we have so far got that in order to get reliability we shall have to modify the design of the contact. BY.{R.W. Bailey - Chief Engineer} | ||