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).
Inspection report on the wear and performance of Tungsten Points AQ and AR after road testing.
| Identifier | ExFiles\Box 35\6\ scan 115 | |
| Date | 20th February 1924 | |
| EFC. PC.20. Feb. 20th .1924. TUNGSTEN POINTS. AQ AND AR. Points AQ. These have run (up to time of inspection) 5,430 miles on 7GXI. Standard condenser fitted. Screw point:- All the surface has been in contact. There is very little wear in the depth of the point. The worn surface is rough with two small cavities, but comparatively clean. (little discolouration). Lever point:- About 80% of the surface has been in contact. A little wear in the depth of the point. The worn surface is rough, but level and comparatively clean. The points generally are in fairly good condition. Points AR. These have run only 1,480 miles on 3GXII, in conjunction with a standard condenser. Screw point:- About 70% of the surface has been in contact. The point is worn down on one side to a maximum extent of about 30% of its original depth. The worn surface is badly pitted and discoloured a blue black. Lever point:- Only about 60% of the surface has been in contact. This is worn in a similar way, and to approximately the same extent as the screw point, the untouched portion of the surface being still fairly bright. The worn surface is slightly blackened and uneven. Generally, the wear on these points is heavy considering the short distance run. From a consideration of the above points and also of the AP Set (see report F.C.19) the following is suggested:- (1) Performance appears to improve with the amount of surface in contact. Larger diameter points may be an improvement. (2) Points appear unable to cope with the current after running for a time. This may be due to the blue black oxide which forms, and which in turn may be due to too high a current density. (3) The usual pip and cavity, which from observations made on the bench, together with the oxide, appear to form without any great amount of sparking taking place, suggest that a high temperature is reached at the surfaces apart from that due to sparking at the points. Contd. | ||