Colloidal Graphite in Lubrication
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GRAPHITE has, for many years, used in various ways for purposes of Jubricaticrn, but the natural product, even when powdered to the finest degree possilde, possesses certain disadvantages. It is often impure, and has a tendency towards deposition in oil pumps, behind piston rings, in filters, etc., where it may cause failure of the oil supply. For these reasons many engineers and users of commercial vehicles are inclined to look with suspicion upon any, form of graphite lubricant ; but they need have no fear of other than excellent results from the employment of artificially produced graphite as used in the manufacture of Oildag, which is a special oil carrying in suspension colloidal graphite prepared under a special process discovered by Dr. E. G. Acheson, and manufactured and marketed by E. G. Acheson, Ltd., 40, Wood Street, London, S.W.1.
The Acheson-graphite is obtained by heating pure carbon in an electric furnace, and its conversion at a temperature of about 7,500 degrees F. into a grit-free graphite having a purity of over 99.9 per cent. The resulting material is, however, too coarse to be used for lubrication, , but by a colloidalizing process the particles are reduced to such an extent that they are visible only by reflection under a powerful microscope.
During the process through which the graphite passes, these particles receive equal and like charges of static electricity. Consequently, they continually repel each other, resulting in that state of agitation known as the Brownian Movement. This permits substances in the colloidal state to remain indefinitely suspended in fluids, although the latter may be of lower specific gravity than the suspended bodies.
There is ample proof that the most valuable benefits derived from oil containing colloidal Acheson-graphite are obtained after some of the-graphite particles remove themselves from the oil and become attached to the 'rubbing surfaces of the metal. This adhesion of the graphite results from surface energy, and the absorbed graphite cannot be removed from the metal by any ordinary cleansing process. A surface of this nature, irrespective of its thickness, which may be too small to measure, offers ideal anti-friction qualities.
Forming a "Graphoid" Surface.
In the practical use of Oillag, the particles are removed from the oil when they come into contact with the surfaces of the journals and bearings while the machine is in operation, and in course of time sufficient is transferred to form what is termed a "grapboid" surface. Whilst such a surface, once established, is capable of functioning efficiently for a time even in the absence of oil, it is slowly removed, and for this reason the lubricant should constantly carry a small percentage of the graphite in order to maintain the surfaee.
It is claimed that oil or petrol engines develop more power, run More smoothly and require less overhauling when lubricated with Oildag ; piston rings function more freely and cylinder wear is reduced. In many instances, it is found possible to reduce the oil consumption by its use, and these points are well borne out by tests carried out by the National Physical Laboratory.
In one N.P.L. test, bearings were run with a full oil supply for a short time, in the one case plain mineral oil being employed, and in the other oil graphited with Oildag, and the supply of oil was then cut off. The average of four tests gave 36 minutes as the time for seizure to take place in the case of the plain mineral oil, whereas with graphited oil, under similar conditions, the time was 261 hours.
A similar test carried out to see how the oil supply could be reduced showed that if a bearing be run-in with a surplus of graphited oil, the feed can afterwards be reduced to a quarter of that required for ungraphited lubrication, although, of course, this was a laboratory test, and it would not be advisable to reduce to such a great extent the oil feed on an engine in service.
The material is excellent for runningin on the bench, as it results in minimum clearances and enables the full power to be obtained more rapidly, as the risk of seizure is greatly reduced.
Colloidal Acheson-graphite forms the basis of many ,commercial preparations, such as penetrating oils, upper-cylinder lubricants, running-in oils, graphited greases, graphited lubricating oils, etc. Concentrated Oildag is a graphited oil containing approximately 10 per cent. of Acheson-graphite, and it is sold in tins numbered to represent the quantity of oil in gallons which can be treated.