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).
The construction and testing of composite brake drums and their liners.
| Identifier | ExFiles\Box 85\1\ scan0032 | |
| Date | 4th March 1936 | |
| -3- Turning now to the construction of these composite drums, our first step was to collect as much information as possible on the subject of light alloy drums, and we tried on our test rig two different types of Aston-Martin drums. (We have still to try a Hispano-Suiza drum). We weighed up carefully the probable effect of using different types of material, such as Elektron, R.R. aluminium alloys, low-expansion high silicon aluminium alloys, austenitic steel and iron liners, cast-iron and high carbon steel liners, having due regard for their ultimate strengths, Young's modulus, specific heats and conductivities, coefficient of expansion and Brinell figures, and cost, and our choice was for R.R.53 (cast) and liners made from austenitic cast-iron, ordinary cast-iron and high carbon steel. Between these last three we have still to decide. We also considered various types of construction. We have heard of drums with a very rigid iron liner, and we have also heard of such drums bursting. We had tried drums with shrunk-in liners riveted in position, and with these have experienced distortion, rivets standing proud and failure of the aluminium (L.8). We also know of drums with the aluminium cast round the liner, and have seen how these liners crack. However, after deciding on the reason for these various troubles, we made a numberof very rigid aluminium housings and have shrunk into these various types of liners with various interference fits, becoming more daring with the latter in order to use cheaper materials as our first efforts proved successful. We have not so far built a drum which it would be unsafe to use on the road, or which we have succeeded in bursting or distorting badly, even under the most severe treatment. We have evolved fixings for the liners which do not spoil the smoothness of the rubbing surface (as rivets do) and which at the same time leave the fitter free to drop the liner into the aluminium in any position. This is important, as is the fact that the outside of the liner must be ground circular and free from any projections. The latter would prevent perfect contact between liner and aluminium and would therefore hinder heat transference from one to the other. We think these fixings must be able to take the full braking torque, although this is normally taken by the interference fit. | ||