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).
Article from 'The Autocar' magazine discussing engine friction, lubrication methods, and oil viscosity.
| Identifier | ExFiles\Box 76\4\ scan0124 | |
| Date | 19th August 1911 | |
| THE AUTOCAR, August 19th, 1911. 333 Friction and Lubrication. By Robert W. A.{Mr Adams} Brewer, A.M.I.C.E., M.I.M.E., M.I.A.E., F.S.E. (Concluded from page 291.) THE questions of the temperature and viscosity of the oil have been touched upon, and, considering these points, the facilities for cooling or radiation from the bearing itself play an important part in the ultimate result. If a bearing be so placed that the heat generated by the friction set up can be rapidly carried away, such a bearing can be more heavily loaded than one less favourably placed. When a machine is working, the rate of dissipation of the heat from the bearings should be equal to the rate of heat generation, when a normal temperature is reached; but if this be not so continual trouble through hot bearings may be expected. With regard to the method of oil supply, this has been already referred to briefly. In modern motor car practice three methods are adopted—first, forced lubrication; second, trough or spray lubrication; and third, splash lubrication. With regard to the first two, there has already been a great deal of controversy as to which is the better method, and there are many points in favour of each, but up to the present one cannot state that either one of these methods is far superior to the other. Each one has its favourable points and its drawbacks, but it is outside the scope of this article to go deeply into these matters. Suffice it to say that the lubricant should be supplied to the engine clean and cool, and that its supply should be continuous and adequate, and that after the oil has passed through the bearings it should not be allowed to be thrown up into the cylinders in such quantities as to cause smoking at the exhaust. This latter point has caused a considerable amount of trouble to some of the firms of highest repute, and many small devices have been tried to prevent the oil creeping past the pistons into the combustion chamber. From the earliest study of engineering problems the question of the most suitable materials to be used in contact for bearing surfaces has been well considered. In motor car practice, for heavily loaded bearings, there is a considerable amount of favour bestowed upon what might be termed “spongy alloys” to work in contact with steel shafting. It is obvious that when a more or less spongy material is in the presence of an oil film, a certain amount of the lubricant will always be retained in the pores of this material even when a high loading is adopted. Such materials, however, fuse at a comparatively low temperature, but this may be a point in their favour in some respects, as before damage can be done to a shaft by heated bearings the metal usually runs out and can be easily replaced. The nature of lubricant for any particular purpose depends upon the physical conditions to which it is subjected, and lubricants are usually tested in the following six ways. 1. By chemical analysis. 2. For specific gravity. 3. For relative viscosity. 4. For gumming action or quick oxidation. 5. For flashing and burning points. 6. In a testing machine for lubricating properties. With regard to viscosity, the method of testing generally adopted is the observation of the time taken for oil of a measured quantity to drop from the end of a fine tube, and the following table gives the viscosity of various oils as tested by Price’s Patent Candle Co., in which the viscosities are given in relation to that of sperm oil at 70° Fahrenheit, which is taken as unity. [Table Title] Relative viscosity of various oils. Sperm at 70° F.{Mr Friese} = 100. Oils., Viscosity at 70° F.{Mr Friese}, Viscosity at 212° F.{Mr Friese}, Viscosity at 350° F.{Mr Friese} [Table Headers] Actual., Sperm at 70° = 100, Actual., Sperm at 70° = 100, Actual., Sperm at 70° = 100 Sperm ... 323, 100, 88, 27.2, 68, 21.0 Gas engine ... 845, 261.6, 89, 27.6, 68, 21.0 Heavy gas engine ... 2430, 752.3, 110, 34.1, 74, 22.9 Motor oil (water-cooled) ... 5003, 1548.9, 178, 55.1, 88, 27.2 Motor oil (medium) ... 6655, 2060.4, 181, 56.0, 94, 29.1 Motor oil (air-cooled) ... 9200, 2848.3, 220, 68.1, 96, 29.7 A study of the table will reveal the fact that oils which are very viscous when cold, rapidly lose their viscosity when heated to 212° Fahrenheit, which is however, a higher temperature than should be prevalent in the base chamber of an engine. Many engines work at temperatures in the neighbourhood of 180° to 200° Fahrenheit, but the table gives sufficient indication of what takes place when the oil is heated in actual practice. We see, therefore, that the oiling arrangements of a motor car should be such, and the pipes and passage of sufficient diameter, as to allow a viscous oil to pass when the engine and the oil are cold. If a forced feed lubrication system be used we also see that when the engine is heated up an enormously greater quantity of oil will travel through the same sized pipes, and at the same time a hot oil will much more easily squeeze out from between two surfaces in contact than would the same oil at a lower temperature. [Image Caption] A 15 h.p. Argyll, the first in New Zealand, and imported by the Scott Motor Agency of Wellington. The car has been imported to the order of Mr. T. Horton, who is the part proprietor of the largest nursery gardens south of the equator. | ||