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).
Notes on the crushing strength of ball bearings and the influence of rotational speed on carrying capacity.
| Identifier | ExFiles\Box 20\7\ Scan018 | |
| Date | 1st May 1910 | |
| W. De. C. Crushing Strength of Ball Bearings. Some notes in a recent number of a mechanical contemporary go to show that the crushing strength of balls frequently differs greatly from what is stated in makers' catalogues. The writer says that the load capacity of a ball bearing depends upon the speed of revolution as much as on the crushing strength of the ball. An ordinary (commercial) 3/8in. ball will be crushed under a load of 6,500lb., while a 3/8in. ball will withstand 30,000lb., while a "high duty" steel ball of the same size can be loaded 25 per cent. more, and even 100 per cent. if made of an uncommercial steel. The fact, however, that a 1/4in. ball will be crushed under 6,000 to 12,000lb., according to the grade of the material used, has little bearing upon its actual strength in commercial use, owing to the influence of speed. For instance, the balls in a 2in. diameter bearing will have a track of approx. 9in. circumference, and it requires 12 revolutions of a 3/4in. ball, 6 of 3/8in. ball, and 4 of a 1/4in. ball to cover the circumference once. From the speed standpoint, assuming the bearings to have a rate of 1,000 revs. per min., the 3/4in. ball will require to make 12,000, the 3/8in. ball 6,000, and the 1/4in. ball 4,000 revs. per min. The carrying capacity of a bearing is thus seen to be dependable to a large extent on its speed of rotation. | ||