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 advocating for the use of colloidal graphite in running-in compounds and upper-cylinder lubricants to reduce engine wear.
| Identifier | ExFiles\Box 145\3\ scan0039 | |
| Date | 14th May 1937 | |
| AS AN AID TO LUBRICATION The Case for COLLOIDAL GRAPHITE by the Technical Editor [Boxed Text] Twelve months ago Dr. A.{Mr Adams} H.{Arthur M. Hanbury - Head Complaints} Stuart explained in "The Light Car" the value of colloidal graphite as an aid to lubrication. His remarks, as our correspondence pages have shown, aroused very great interest—and a few doubts. In this article we set the doubts at rest and summarize the uses of colloidal graphite. Why a Graphoid Surface Reduces Wear—The Use of Running-in Compounds and Upper-cylinder Lubricants THE amount of interest which is being shown by readers upon the question of colloidal-graphite lubrication, first brought prominently to their notice by Dr. A.{Mr Adams} H.{Arthur M. Hanbury - Head Complaints} Stuart in *The Light Car*, is particularly gratifying. There still seems to be doubt existing, however, with regard to the suitability of colloidal graphite in an engine or in other parts of the car. In order to crystallize the position, therefore, we have been in close touch with E.{Mr Elliott - Chief Engineer} G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Acheson, Ltd., the main producers and suppliers of concentrated colloidal graphite for use by the various oil blenders. This article, therefore, will be of assistance both to users and potential users. Graphite lubrication is by no means a new idea; it has been used for many years in machines which have to operate under conditions of extreme temperature and pressure. Ordinary graphite must not, however, be confused with that which is manufactured under the Acheson process by which particles of graphite of such exceptional fineness are produced that they do not depend upon the viscosity of their carrier for suspension. The ability of the particles to act independently of the force of gravity is due to the fact that each acquires an electrical charge of the same sign during the colloidalizing process. The extreme fineness of Acheson colloidal graphite not only enables it to be thoroughly mixed with oil, but ensures also that it will pass through the finest orifices. It is not stopped by felt or similar filters, whilst, furthermore, colloidal graphited oil can be used perfectly satisfactorily in wick feeds as the graphite particles pass the capillaries of the wick unharmed just as if they were in true solution. Another advantage of the extreme fineness is that the graphite has an extremely large covering power on the metal to which it becomes attached by adsorption, a term which implies the adhesion of colloidal particles to a metal surface. The main use of colloidal graphite is in running-in an engine where its value lies in the fact that it not only in itself, but, in addition, it adds enormously to the spreading power of oil on the metal surfaces. After a very short period of running a graphoid surface is formed on the metal, and this, although of infinitesimal thinness, is sufficient to prevent metal-to-metal contact. No matter how finely ground may be the cylinder bores, pistons, crankshaft bearings, and so on, the surfaces are, in actual fact, appreciably rough when viewed under a microscope and they will adsorb a certain amount of lubricant. The adsorption is hastened by the use of colloidal graphite, and once this has taken place further adsorption of the oil to what is then called a graphoid surface proceeds more quickly, as the graphite has a strong affinity for oil. It will be clear from this that the infinitely small particles of graphite become lodged in the irregularities of the surfaces. If, therefore, during the running-in period the fluid film of lubricant breaks down there is the self-lubricating property of the graphoid to prevent seizure or scoring, but the graphite on the metal helps to provide lubrication. Furthermore, the oil film is rapidly restored owing to the affinity of the graphite for oil, as already mentioned. To obtain the greatest advantage from the use of colloidal graphite, the engine should be assembled with it already on the working surfaces, and many car manufacturers are now adopting this course. Where, however, the car is delivered to the owner in an "un-graphoided" state, use of one of the advertised brands of colloidal graphite running-in compound during the first 2,000 miles or so will prove to be a distinct advantage. THE CASE FOR COLLOIDAL GRAPHITE Continued. It has been shown by careful tests that an engine properly run-in with colloidal graphite is able to safely develop its maximum horse-power in the shortest possible time. There is absence of any tendency for the pistons to "pick up" and thus to score the cylinder bores. It will be found, in all probability, that an engine even when new will run more smoothly and usually at a lower temperature, whilst the normal feeling of stiffness or harshness should be absent. There is another aspect of the case which may not be apparent at the end of the running-in period, but will probably be noticed later. This is that an engine run-in with colloidal graphite will not suffer from the same amount of wear. It is more than likely, in fact, that a very greatly additional mileage than normal will be covered before cylinder grinding becomes necessary. With regard to the question of carbon formation in the cylinder heads, it is generally known that this arises from the burning of the oil which has passed the pistons and from incorrect fuel/air mixtures. It must not be forgotten, also, that road grit drawn in through the carburetter where no air filter is used, has also a considerable bearing upon carbon formation, but there is no evidence to show that the amount of carbon is increased by the use of colloidal graphite. A large number of motorists has, in fact, reported that their engines remain much more free from carbon when run with colloidal graphite in the oil and in the petrol, in the form of a graphited upper-cylinder lubricant. Even if the use of colloidal graphite has no effect upon the actual amount of carbon formed, it will be found that the low adhesion between the carbon and the graphoid surface on the heads and piston crowns prevents the carbon from becoming attached to form a hard deposit. Some motorists have found it difficult to understand why, when every effort is made in the ordinary way to reduce carbon formation in the cylinder heads, the introduction of carbon in another form should be beneficial. It must, however, be realized that there is as much difference between graphite and the carbon formed by the lubricating oil and petrol as there is between carbon and diamonds, which are only the same element in crystalline form. With regard to the method of using colloidal graphite running-in compound, the proper course with new or re-bored engines is to mix the lubricant with the crankcase oil in the proportion of one pint of the compound to each gallon of oil. If the crankcase is drained and refilled with fresh oil before the running-in period has been completed, a further pint of running-in compound should be added to each gallon of oil. [Graph 1 Caption] This graph shows how the use of colloidal graphite (full lines) materially reduces the coefficient of friction. The dotted lines refer to plain oil. It is unnecessary to mix the compound with the make-up oil used to maintain the proper level in the sump. For this purpose plain oil only should be used. After the running-in period has been completed there is still great advantage to be found in using the compound, but the quantity should be reduced by half—that is, half a pint to the gallon. It is believed by some motorists that the graphoid surface is indestructible; this is not quite the case. There is every reason, therefore, for continued use of colloidal graphite during the life of the car, as the fresh supplies will have the beneficial effect of preserving the graphoid surfaces and thus reducing the rate of wear. It must be made clear, too, that the use of colloidal graphite does not mean that the engine oil may be used for a longer period than usual, as it is well known that the oil becomes contaminated with road dust and the products of combustion. Therefore, the normal sump draining and refilling periods should be the same as when only plain oil is used. Motorists will, of course, adopt the recommendations of the manufacturers of their cars upon this point. "Carrier" Oil Quality. Questions have been asked from time to time regarding the quality of the oil used as the "carrier" in colloidal graphited running-in compounds. It can be stated authoritatively that those compounds advertised in *The Light Car* are manufactured from high-quality engine lubricating oils and that they contain the correct proportion of colloidal graphite as specified by E.{Mr Elliott - Chief Engineer} G.{Mr Griffiths - Chief Accountant / Mr Gnapp} Acheson, Ltd. The oils used have been selected having regard to the fact that the running-in compound will be mixed with various brands of motor oil and, in consequence, they may be used with every confidence. Turning now to the use of upper-cylinder lubricants in general, it may be said first of all that these are now almost universally used, or at least approved for use, by car manufacturers, and are, of course, becoming increasingly popular amongst private motorists, although there still appear to be some who raise objections to them. One of the objections, based upon earlier experience, is that the oil has a tendency to form carbon in the cylinder heads. This, of course, may be the case where unsuitable oils have been used, but the type now sold for this purpose has very little carbon-forming tendency. This is particularly the case with upper-cylinder lubricants containing Acheson colloidal graphite as these may be used in quite small quantities and their nature is such [Graph 2 Caption] In a special test an ungraphitised bearing seized in 36 mins. (curve A), but when lubricated with colloidal graphite it ran freely for 27 hours (curve B), after which the test was discontinued. | ||