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 discussing the comparison and testing of insulators and collector gear designs, including German samples.
| Identifier | Morton\M6\ img083 | |
| Date | 23th November 1927 guessed | |
| recently received a very good report of a filling consisting of bitumen and powdered glass, as against sulphur and powdered glass. The preliminary high tension break-down tests we have already carried out on these insulators, indicate that they are preferable to the types of insulator we have been using recently, and a lot of further development work with porcelain as an insulating base is advisable. The German sample insulators have come to hand, and on opening one of these we find that they have filled their recesses with a more or less fluid bitumen, and if the top plate is removed, this bitumen is sufficiently fluid to flow out in ordinary office air temperature of about 65/70 degrees, and on high potential test, this particular insulator flashed over on 23,000 volts, but the bitumen did not carbonize in this case, and I presume that owing to the fluid nature of the bitumen, the insulator, 24 hours after breakdown tests, shews an insulation resistance of 40 megohms. All these breakdown tests have been taken with plain paper washers between porcelain and metal parts, and there is not the slightest doubt that if we contemplated the use of say bakelite varnished fabric, that we should obtain higher figures still if necessary. On a further comparison of the German insulators with our own, we find that whilst they are the same size of screw and practically the same tapping, their metal plates are only 3/8" x 3/16" as against our 3/8" x 5/16", so that I think we might very safely, for future use, reduce our size of top plate to 3/8" x 5/16"; their 1/8" plate is somewhat on the narrow side and the tapping holes 1/4" diameter come in some of the pieces very close to the edge, almost breaking through. I enclose three copies of proposals, B.168, B.168a and B.168b, shewing proposed collector gears using our standard porcelain insulators. These collector gears are largely modelled on the German designs and I thought you would like to have a look at them. In the past we have arranged the runmetal pulley to swivel as well as the arm, but in a short collector of this type, I am doubtful as to the wisdom of making the collector pulley to swivel. You will see that I have arranged the sliding shoe to swivel, but a swivelling collector pulley means a very heavy head. Perhaps you would let me have your ideas about these collectors. We have received one or two further copies from Germany of their previous circular, and I am sending you herewith one copy of their form No.444, shewing their different examples, and you are at liberty to retain this copy. I have passed on your remarks contained in your letter of the 19th, re. pulley blocks, to Mr.Coley. Motors and lubrication of bearings. I have written to the various ball bearing makers on the lines indicated in your letter of the 24th October, and I am having copies made of their replies, which I will send on to you in the course of a few posts. I Remain, Yours faithfully, FOR AND ON BEHALF OF ROYCE LIMITED, [Signature] (JOINT GENERAL MANAGER) B/HB.{C. E. Harcombe} | ||