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).
Bench comparative tests for dynamo bearing lubrication, comparing grease versus oil.
| Identifier | ExFiles\Box 166\1\ img129 | |
| Date | 21th April 1939 | |
| 6093. To By.{R.W. Bailey - Chief Engineer} c. to By/RD: c. to Da.{Bernard Day - Chassis Design} Rm{William Robotham - Chief Engineer}/RC.{R. Childs}1/JH.21.4.39. Dynamo Bearing Lubrication Tests. Owing to a suggestion that grease be used, as the lubricant for dynamo bearings instead of oil, we were requested by By.{R.W. Bailey - Chief Engineer} to carry out bench comparative tests with a view to deciding which was better. A theory in support of oil is that oil being thinner and less tenacious than grease allows the balls to rotate more freely. Under the weight and speed of the armature, the balls at the top of the bearing are subject to a much smaller force, producing friction and consequent rolling motion than those at the bottom. Hence those at the top tend to slow down and more so when surrounded by grease. On moving round the track however, and reaching the bottom, the balls are subjected to a greater force tending to rapidly accelerate them. Consequently, any retarding action which prevents them from quickly responding, results in increased friction and wear. The first of the two parts of the test namely that in which the bearings were lubricated with oil has now been carried out. A suitable machine was obtained and fitted with new bearings, the bearings being first washed in clean paraffin and blown out, in order to remove all grease. When the machine was assembled, but before any lubricant was supplied, i.e. with the bearings quite dry, the 'play' in each was measured by means of a micrometer clock. This was found to be negligible. Each bearing was then well supplied with oil, (motorine C) and the running commenced. It was intended to run the machine for 500 hours at 5,000 r.p.m. supplying a few drops of oil every 100 hours and measure the wear at the end of the test. The above dynamo speed corresponds to a road speed of about 63 m.p.h. on the Wraith, and about 71 m.p.h. on the Bentley. At the end of 465 hours running, however, the bearing at the commutator end seized. From an examination it was found that this bearing was quite dry, and that a fair amount of brush dust had managed to get inside. | ||