COLLOIDAL GRAPHITE

Evening Post, Volume CXIX, Issue 134, 8 June 1935, Page 30

COLLOIDAL GRAPHITE

PROPERTIES AND USE

ENGINE LUBRICATION

The following is taken from an.article .published in a British trade publication, "Modern Motoring":— > ' To understand the use of colloidal graphite in oil for the' lubrication of engines it is necessary to refer to the nature of graphite itself. Most people are familiar with this material, which is black, lustrous, and has an unctuous feeling to the touch. While graphite from any source has fundamentally the same nature, that

is, the same properties, it is necessary to distinguish between mined graphite and that used in automobile practice, which is made in the electric furnace. The latter is a very pure product, as opposed to the mined product, which usually contains impurities. . ... ■"■ - . Graphite made in.the electric furnace, however, must not be regarded as ah artificial product. The one stands in relation to the other as manmade ice to natural ice, the two being ■ identical in composition, but the former having the advantage of controlled purity. Purity must be the primary • object in preparing a material for a machine of such delicate strength as the internal combustion engine. A detailed examination of graphite will show it to have a laminated or plate-like, structure. It is this structure which gives graphite its lubricant properties, the minute plates sliding over one another easily when subjected to pressure. This slippery quality, it might be added, continues on down to the smallest particles of graphite. The reduction to minute particles is the next requirement for practice. This is accomplished by a process known as defloccttfation when the graphite is reduced to the colloidal state. The particular method of deflocculation was discovered by Acheson, and by "colloidal" is meant a state of fineness where the individual partisles of graphite, when in /suspension, are invisible even under the ordinary microscope. The term "colloidal graphite" thus has a strict scientific meaning, and implies a material so finely divided that when! it is suspended in, say oil, its state lies between that of a dissolved substance and that of suspended particles of minute size. Sugar dissolves in water and is lost trace of visually; French chalk suspends in water and can be seen in strong light floating about. Colloidal graphite would occur in a state intermediate between the two. The implication' of this is important. It means that colloidal graphite when incorporated in a suitable oil will lose its identity for the oil to behave as though it contained no solid matter. Such an oil will flow through any. constrictions, jets, and filters in the; engine without difficulty. This, ability on the part. of colloidal graphite; to bury its identity is illustrated by the fact that it can, in suitable circumstances, pass up a wick with, the oil holding it. ! When an oil containing colloidal graphite is circulated in the engine the | faces of the bearings, cylinder walls, and piston rings > attract the, particles of colloidal graphite. The molecules lof the metal at the surface cover themselves, as it were, with the molecules ;of colloidal graphite, and the result is that a new face with new characteristics is formed. This has been termed the "graphoid surface," the colloidal graphite having been "absorbed,"'and research work has shown that the new surface is of extreme thinness. It has unique properties, which are of great assistance in the lubrication of working faces which move over one another at highspeed. Firstly it has a lower co-efficient of friction than the original metal face, and so it develops less heat when the engine is working. The utility of this will be seen in running-in a new engine, where the relative roughness of the working faces develops much heat ■ which thins the lubricating oil and reduces the strength of the oil film, which is then liable to be squeezed out from between 'the opposite faces. A graphoid surface will tend to maintain the "body" of the oil. A valuable property is its ability to increase the spreading power of the oil over the working faces. The graphoid surface is more easily "wetted" by oil than is a plain metal surface. For this reason it can hold oil. on itself with greater facility, and tends to counteract the reduced spreading power of lubricant that is cold and relatively vicious. Both these qualities can be regarded as cardinal advantages in the lubrication of an internal combustion engine where the alleviation of friction and the preservation of a stable oil film are of firstrrate importance.' i Experiments, have shown that the graphoid surface cannot be removed except by taking off the metal with which it is combined. The above, what might be called primary characteristics, are summarised by a test carried out at the Natjonal Physical Laboratory. A bear- | ing was lubricated with plain oil, the supply of which was then discontinued, when the bearing was observed to seize within 36 minute's. The experiment was repeated, using a colloidal graphited oil in place of the plain ! lubricant, and at the end of 27 hours

the bearing still gave no indication of seizing.

Upper cylinder lubricant containing colloidal graphite forms a graphoid surface oh the cylinder walls, the piston rings, the valve stems, and guides. It is eminently suitable for this work, inasmuch as the graphoid surface is stable at the usual tempeiatures in the combusion chamber at which oil is burnt up.

Colloidal graphite is an inert material, and the graphoid surface in consequence offers a greater resistance to corrosion and oxidation than the plain metal face. Furthermore, it is unaffected by the washing action of petrol and consequently is a considerable asset during the starting up of ■an engine. An examination of the cylinder walls of an engine using a colloidalgraphited oil will show them to be very smooth, with a high polish. This polish, while assisting lubrication, offers no key for the adherence of carbon and helps to reduce the frequency of decarbonising.

Mention has been made of the property of the graphoid surface in promoting a good oilspread. This is due to a reduction in what is called surface tension between the lubricating oil.and the graphoid surface, and the property, is. utilised in penetrating oils containing colloidal graphite. These

oils can percolate or penetrate with considerable efficiency and have a wide application in automobile practice, while the surface formed by the colloidal graphite will remain to lubricate a metallic face when oil has been squeezed out by excessive pressure.