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).
Bulletin on the benefits and applications of colloidal graphite lubricants for engine run-in, upper cylinder, and gear lubrication.
| Identifier | ExFiles\Box 145\3\ scan0013 | |
| Date | 13th February 1934 guessed | |
| No. 42.2 TECHNICAL BULLETIN under more severe conditions than is usually the case after it has been run for some time under load; during which time bearing surfaces have become bedded down and working clearances established. For this reason the use of a Colloidal Acheson-Graphite ‘Running-in’ Compound mixed with the ‘Running-in’ oil generally employed lessens the risk of metal to metal contact. Due to the initial tightness of the bearings or irregularities of the surface, heat is generated which tends to lower the viscosity of the oil thereby reducing its load-carrying capacity. For this reason to avoid excessive wear, particularly in the cylinders of an engine, it becomes more important for Colloidal Acheson-Graphite to be used; for when the viscosity of an oil has been reduced the Graphoid Surfaces which have been formed, carry the load, prevent metal to metal contact, and minimise wear. By this means the engine is enabled to reach its rated capacity in the shortest possible time, and is a tighter ‘run-in’ job than is possible when ordinary low viscosity running-in lubricants are used. When the engine is taken off the test-bed it is the usual practice to run it on the road at a moderate speed and load for sufficient time to allow the ‘running-in’ process to be completed. During this period it is advisable to mix with the usual lubricating oil a ‘Running-in’ Compound containing Colloidal Acheson-Graphite. By following this course Graphoid Surfaces will be established which provide a second line of defence so to speak, in the event of such circumstances as temporary failure of the oil supply or sudden excessive loading. UPPER CYLINDER LUBRICATION The object of lubricating the upper or top end of the cylinders is to supplement the lubrication provided by splash from the crank-case. As is well known the temperature of the upper end of the cylinder is considerably higher than that of other parts. This is, of course, due to the fact that combustion takes place in a confined space at a time when the piston is practically at the top of its stroke. On the power stroke whilst the piston is descending, the explosion flame tends to burn off the cylinder walls any oil which clings to them so that on the remaining strokes the piston and rings are operating on more or less dry surfaces. To overcome this there is a growing tendency for oil lubricants to be mixed with the fuel. These, whilst offering certain advantages, do not give the same good results as can be obtained when they carry a small proportion of Colloidal Graphite, which forms a Graphoid Surface at the upper end of the cylinders. Not only does Colloidal Graphite assist cylinder lubrication but it :— (1) Prevents wear and delays the time when re-boring of cylinders becomes necessary. (2) Tends to prevent the formation of carbon on piston and cylinder heads. (3) Lubricates the inlet and exhaust valve stems, etc. In addition the use of Upper Cylinder Lubricants containing Colloidal Graphite reduces wear, due to the fact that the Graphoid Surface is not affected if the oil is washed off the cylinder walls by the fuel when the air strangler is used for starting in cold weather. It also reduces oil and fuel consumption as a result of a better seal between the piston rings and cylinders. The use of Upper Cylinder lubricants is now becoming almost universal, and some motor car manufacturers not only use these lubricants whilst testing their engines, but recommend their customers to follow the same practice during service. It has been found that Colloidal Graphite added to the light oils employed as upper cylinder lubricants increases their value appreciably, particularly when it is understood that Colloidal Graphite is not affected by the temperature of combustion. TECHNICAL BULLETIN No. 42.2 Long after the oil carrier has been completely destroyed by the high temperatures produced by combustion, the graphite film formed by using Colloidal Graphite remains inert and continues to function as an anti-friction surface on the valve mechanism and those engine parts located directly in the combustion zone. GEAR LUBRICATION To maintain the high efficiency of new gears and to keep them running smoothly and silently after many years of service is the aim of both of Manufacturers and Users and to a large extent the careful selection of lubricating oils and greases has a bearing on this. As the intensity of pressure on gear teeth is far more severe than on bearings, some reinforcement to the oil is advisable if gears are to continue running silently. This extra protection, it has been found, is provided by using lubricants containing a suitable proportion of Colloidal Graphite. As has been explained in connection with the improved lubrication of bearings and cylinders, the use of a small proportion of Colloidal Graphite forms a protective graphite film on bearing surfaces. In the case of gearing this takes place on gear teeth protecting them from wear and so increasing their life. Whereas lubricants containing ordinary graphite powder may not be advisable for use in gear boxes fitted with ball or roller bearings, the use of Colloidal Graphite in oils or greases can be safely recommended since their power to form Graphoid Surfaces protects these bearings from corrosion and promotes perfectly free action. Tests carried out at the National Physical Laboratory in the Lanchester Worm Gear Testing Machine have shown that the addition of a small percentage of “Oildag”* (Concentrated) to the usual gear oil raises its critical temperature; in other words it enables the lubricant to work efficiently at higher temperatures than would otherwise be the case. As a general rule gear lubricants are relied upon to give fairly long service without renewal and in view of the improvement which follows its use, the addition of Colloidal Graphite is more than justified. * A ‘Graphoid Surface’ may be defined as an adsorbed film of graphite held to the surface of the metal by its surface energy. † REG. TRADE MARK Oildag† is the brand of Colloidal-Graphited Oil manufactured by E.{Mr Elliott - Chief Engineer} G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Acheson, Ltd. Additional copies of this Bulletin may be obtained from E.{Mr Elliott - Chief Engineer} G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Acheson, Ltd., 40 Wood St.{Capt. P. R. Strong}, London, S.W.1 THAMES HOUSE, MILLBANK, LONDON, S.W. 1. | ||