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).
'Crazy Pattern Cracking' in iron brake drums and potential solutions.
| Identifier | ExFiles\Box 140\3\ scan0170 | |
| Date | 11th October 1938 | |
| -2- 11.10.38. into the trouble of 'Crazy Pattern Cracking', but we do not attribute this so much to the specification change, as to changes in the duty demanded of the brake. For instance, we can run an iron of given specification on a given car, used as a liner for an aluminium brake drum and be immune from cracking, but the same iron in the same car, but used as a solid drum, will craze readily. On the other hand, scoring is generally more noticeable on the aluminium drum. Any change in the iron which would improve its thermal conductivity should also reduce crazing, and it is quite possible that graphite content is important in this respect. We are not at present sufficiently worried by crazing to warrant any research being undertaken to prove the point. We are not attempting to check crazing by varying the specification of the iron, but by the design of the brake. We find that we get a skin temperature on the rubbing surface at least 120° above the average temperature of the drum. We cannot measure thus by a thermocouple on the rubbing surface since the heat is rapidly dissipated by conduction. We are aiming at reducing the bearing pressure either by widening the drum or by using a brake giving uniform lining pressure. Some years ago we made an iron drum with helical ribs cast in. Our Foundry made quite a good job of the casting. The ribs were unmachined and made no noise. This drum reduced the surface temperature from 325°C to 225°C. It would be perfectly suitable to use with a 4 shoe brake: it would, of course, reduce crazing. Trusting that some part of this information may be of interest, Yours faithfully, For ROLLS-ROYCE LTD. | ||