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).
Investigation into the cause of failure of a high tension cable on a 20/25 HP chassis.
| Identifier | ExFiles\Box 168\1\ img227 | |
| Date | 13th November 1935 | |
| Br.{T. E. Bellringer - Repair Manager} at N. c. Hs{Lord Ernest Hives - Chair}/Wst. c. E c. Sft{Mr Swift}/Mr Brock WST 6117. BY.15/N.13.11.35. Re: 20/25 HP. Chassis - High Tension Cable. ------------------------------------------ With reference to the opinion you recently expressed, that our high tension cable was not as good as it used to be, we went very fully into this matter and came to the conclusion that as far as we can ascertain, the fault was not in the quality of the cable, but was probably associated with the fact that some years ago we replaced the bakelite tube carrying the cables, with a steel tube. The tube in question not being insulated, either along the length of the tubes or at the points of exit of the cable. We were somewhat surprised to find in examining the piece of cable you returned, that the fault did not occur at the point where the cable left the tube, but along the length of the longest high tension cable in the tube. From an examination of the markings, we were inclined to think the trouble was due to formation of ozone, but since the splits followed a spiral line, we were slightly puzzled as to just why this actual character was taken by the fissures. We were inclined to impute this method of manufacture, as it appeared to us that the rubber might be rolled into position by rollers giving a spiral motion. We returned the cable to the Mackintosh Co. expressing our views much as above, they carried out a test by enclosing six cables in a tube, all of which were carrying an alternating current, under pressure of 10,000 volts. On one of the cables however, they imposed four complete turns, so as to put the rubber under stress torsionally, which meant of course it is in tension on the surface. After passing alternating current through under the above voltage, the alternating being 50 cycles, for a period of 10 minutes, they removed and examined the cables. Five of them which had been slid into the tube without any twisting were perfectly satisfactory, the sixth one which they had twisted, was split all along its length, in precisely the same manner as the sample we returned. | ||