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 from Hoffmann Manufacturing regarding an analysis of a failed ball bearing.
| Identifier | ExFiles\Box 153\2\ scan0359 | |
| Date | 29th July 1937 | |
| HOFFMANN Registered Trade Mark BRANCHES: LONDON, BIRMINGHAM, MANCHESTER, LEEDS, GLASGOW. AGENTS IN PRINCIPAL COUNTRIES THROUGHOUT THE WORLD. BALL-AND-ROLLER-BEARINGS STEEL-BALLS-AND-ROLLERS TELEPHONE: 3151 (5 lines) TELEGRAMS: HOFFMANN, CHELMSFORD CODES USED: A.B.C. 5TH EDITION, BENTLEY PHRASE, MARCONI AND WESTERN UNION 5 LETTER. THE HOFFMANN MANUFACTURING CO. LTD. CONTRACTORS TO THE ADMIRALTY, WAR OFFICE AND INDIA OFFICE. CHELMSFORD. July 29th. 1937. YOUR REF Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer}24/AP. IN YOUR REPLY PLEASE QUOTE OUR REF. CHS/AMB. 1499. Messrs. Rolls Royce Ltd., DERBY. [Handwritten Annotation] F.J. HARDY. See me. Rm{William Robotham - Chief Engineer} Dear Sirs, For the attention of Mr. F.J. Hardy. Further to Mr. Brand's and the writer's call at your works, we thank you for sending us a summary of the results of endurance tests you have made on steering rollers. We have carefully examined the broken ball but have been unable to find any evidence which would definitely explain the isolated failure of this one ball. As you noticed, the balls on the loaded side vary considerably in size and roundness. This is undoubtedly due to crowding consequent on there being no cage, and it is interesting to note that whilst some of the balls are as much as .004" below size, others are nearly .001" above standard size, having apparently picked up metal from the adjacent balls. In this connection we would confirm that the same size of balls is invariably used in both tracks of one bearing. In the only other case where broken balls are mentioned in your summary, they were ¼" diameter as in the present instance, and you subsequently used 5/16" balls. The increase in size undoubtedly gives considerably higher load capacity and resistance to fracture, and we notice you are using a larger size in your Part No. FW.911, Hoffmann Bearing No. N.2790, although there is more space available in the section of the size under discussion, Hoffmann Bearing No. N.2784, your Part No. F.61471. We are wondering, therefore, whether this feature, combined with the higher preload which Mr. Hardy noticed, is the cause of the shorter life. We shall be interested to learn whether you have made any further running tests, and hope you have obtained better results from these. Yours faithfully, THE HOFFMANN MANUFACTURING CO. LTD. [Signature] Technical Manager. | ||