Problems Solved by Oil Technologists By J. E. Southcombe, M.Sc.,
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F.Inst.Pet. (Director, GermsLubricants, Lid.) DURING World War No. I, Wells and Southcombe showed that the lubricating efficiency, or "oiliness," of mineral oils could be markedly improved by adding to them a very small amount—less than 1 per cent.—of certain fatty acids. This discovery indicated that the lubricating properties of oils could be influenced by the presence of minute amounts of chemical compounds, just as iron is converted into the much stronger metal, steel, by adding minute quantities of carbon, nickel, chromium, etc There followed a feverish search by the oil companies for so-called "additives" for lubricating oils.
In the early 'twenties the hypoid gear was introduced in the motor world and difficulties were soon encountered with its lubrication, ordinary oils causing pitting and scuffing of the teeth The oil technologist solved this problem by blending in the oil small quantities of compounds of sulphur, chlorine and metallic soaps, thereby producing oils suitable for gears carrying heavy loads, and the extreme-pressure lubricants were introduced.
Stimulated by the success which attended the use of "oiliness," and, later, extreme-pressure additives, the search continued for the improvement of other properties of lubricants. The latest arrivals are the detergent and "heavy-duty" oils. Some designs of compressionignition engine produce sooty deposits from incomplete combustion of the fuel, which, added to decomposition products of the lubricant, give rise to a dirty engine because of the accumulation of these sooty, slimy impurities on the engine parts. An effort was made to find some substance which, when added to the oil, would have a cleansing action on the engine.
Dissolving Soap in Oil It has long been known that common soap will much improve the cleansing power of water, and soap solutions are called "detergents." Ordinary soap will not mix with oil, but soaps of certain heavy metals (such as barium, calcium and zinc) can be dissolved in oil and have the effect, more or less, of cleansing the engine surfaces. Such, in the simplest case, is the detergent oil.
It must be emphasized that this type of .oil does not reduce the amount of soot and carbon produced by the engine, but simply keeps these impurities in a state Of suspension in the oil, so.that they do not separate and settle, so readily on the metallic surfaces. For thus reason' a detergent-type oil must be drained frequently to avoid too much contamination of the lubricant, which may have the effect of thickening the oil to a degree
where the freedom of flow may be seriously impeded.
The action of detergents is not fully understood, but it is known that they keep the particles of carbon and soot in a fine state of sub-division, preventing them from coalescing into larger masses which would precipitate. Unfortunately, herein lies a disadvantage. The impurities remain suspended in the oil in such fine particles that filters readily become clogged and great attention must be paid to filter cleaning. Nevertheless, there is a future for lubricants of this class for certain types of high-speed oil engine.
When Piston Rings Become "Stuck" Closely connected with detergency, but involving somewhat different phenomena, is the anti-ring stick oil. The heavily stressed high-speed oil unit suffers sometimes from a tendency for the piston rings to become "stuck" in their grooves by gummy or carbonaceous matter; under some conditions of operation it is the bottom or cooler rings which stick, whilst in others the trouble is confined chiefly to the top or second ring —cold stick and hot stick. The detergent oil is obviously helpful in the former case and is sometimes effective in the latter, but a whole host of patents has been filed for additives to lubricating oil purporting to influence hot stick. Organic sulphur compounds and metallic organic substances sometimes containing phosphorus are generally employed for this 'purpose. .
During the late war there crept into the language the expressions "heavy-duty engines" and "heavy-duty (FID) oils." What is a heavy-duty engine? Na real definition has yet been evolved. The race to increase power output of aero-engines during war imposed greater stress on the lubricant, and, further, the United States Army, recognizing the need for motor vehicles capable of withstanding the roughest usage, encouraged refiners to supply oils suitable for such duty in the minimum number of grades. These were called H.D. oils, and possessed a specified degree of detergency and anti-ring stick properties
Sonic degree of detergency may be useful where exceptionally high-speed driving conditions exist, but it is extremely unlikely that such oils will replace existing high-quality motor oils for road-transport use. In fact, the lubrication committee of the American Petroleum Institute has asked motcir manufacturers not to recammend these H.D. oils pending further experience,. because the normal type of lubricant produced .by modern methods of refining and treatment continues to give excellent service in the vast majority of engines: