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).
Cylinder materials, lubricants, and the effects of heat on piston ring design and performance.
| Identifier | ExFiles\Box 132\4\ scan0028 | |
| Date | 19th November 1936 guessed | |
| -2- Cylinder Materials. The following materials can be made to give satisfactory service without excessive wear:- (1) Plain carbon steel. (2) Chromium - molybdenum. (3) Nitrided steel. Smooth bores essential with hard cylinder materials to avoid excessive ring wear. Grinding and lapping the best finish. For chromium-molybdenum bores ring with two projecting strips of bronze were used in top grooves and gave particularly good results. These rings are no good in nitrided bores. Lubricants. Oils of the type like Castor oil give best results from wearing point of view of rings and cylinders but present considerable difficulty with gumming up. High cold viscosity oils may not be best oils for good cylinder wall viscosity in fact reverse is frequently true. Effect of Heat on Rings. Four various makes of rings with initial tension varying from 7½ lbs. to 12 lbs. were fitted in short section of cylinder barrel and heated for 5 hours at each of following temperature 400, 450, 500, 550, 600, 700, 800 and 900° F.{Mr Friese} after each 5 hours rings were cooled and removed and tension and hardness measured. Through the whole test average hardness remained same (i.e.) 102 Rockwell B., and tension only dropped from room temperature to 600°F.{Mr Friese} by about 8%. 600°F.{Mr Friese} seems to be limit of piston ring operating temperature loss of ring tension is therefore due to other sources than heat and may be due to high frequency vibration of ring against cylinder wall or piston rocking and slap. Ring Design and Arrangement. Step-cut, wrap round, lap joint, two piece, three piece, multi piece and all manner of highly involved designs, including ring expanders seem to be largely useless. Even diagonal slot ring has been exposed as highly over-rated. continued. | ||