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).
The materials and construction of ignition condensers, commutators, and electrical connections.
| Identifier | ExFiles\Box 24\2\ Scan076 | |
| Date | 21th December 1920 | |
| Contd. -3- Qy2/G21.12.20. (Mica is still used for magneto condensers, however, because of its higher dielectric strength.) Ignition condensers are often assembled in pressed metal containers which are afterwards soldered up to seal them from dust, (This latter point seems worth our consideration) It was explained that Mica is not used, not simply because it is more expensive, but because however carefully it is inspected it is liable to cracks and faults, which make for a large percentage of rejections, breakdown in service, etc. Bakelite is looked upon as more commercially practicable. (I may mention here that we have had two or three cases of internal breakdown of condensers on postwar cars, which seems to confirm this view, as we know them to have been carefully inspected at Derby). Commutators: X.3966. X.3348. X.3945. Mr. Royce is familiar with the building up of commutators on a Bakelite foundation. This has now been standard with the Westinghouse Co. for eight years. Mr. Hives is bringing a sample to England. The Westinghouse Co. no longer use any metal rings imbedded in the Bakelite base of the commutator to reinforce the vees. This having been found unnecessary for speeds up to 8000 a minute, or more. They simply assemble the copper segments with astrips of Micarta in between, slip them into a mould with a central steel ferrule, across-knurled on the outside to hold the Bakelite, and press in the Bakelite powder, with a sawdust base, between the ferrule and the segments, using steam-heated dies in the ordinary way. The whole thing comes out as one block and the ferrule is then pressure into knurled longitudinal serrations on the armature spindle, which transmit the torque to the commutator. The cost of these operations is so small that the commutator can be sold for a dollar or two, representing chiefly the cost of the copper. Connections: X.1925. Mr. Clark has remarked on the fact that terminal posts are largely made on American machines in such a way that electrical connections are made by pressure on the insulating material. I am assured by Mr. Belnap, who has long been connected with electrical engineering over here, and by the Westinghouse people, that this practice is usual even in larger electrical work, and that it is quite sound now that non-hygroscopic materials, such as the Bakelite materials, are available. Experience with these extending over eight years or so has proved that they can be considered just as unchangeable as metal for | ||