OIL FILTRATION

Te Awamutu Courier, Volume 72, Issue 6238, 5 June 1946, Page 4

OIL FILTRATION

CRANKCASE CARE REMOVAL OF SLUDGE - Crankcase oil in vehicles never off city streets will show effects of considerable oxidation in a few thousand miles. The most apparent effect of oxidation is in| the appearance of those oxidation products consisting of resin-like material which normally remain in solution in the oil. This material can be removed partly, at least, by absorption or precipitation. Tests indicate that if a filter contains any substance active enough to remove resin-like material from solution, it will also remove additives to about the same degree, even from new oil. However, finely-divided carbon is present. These solids can and do absorb upwards of 30% of their own weight of resin-like material, which adheres so tightly that it cannot be washed off with hot naphtha. This can be demonstrated by the following method: Put some clean oxidised oil in a glass bottle. Introduce some finelydivided material such as oil-free solids from old crank-case oil (from either a gasoline or diesel engine). Allow the solids to settle by gravity and decant the supernatant liquid. In one cycle this top oil will be found to contain less than one-half the original amount of soluble resins. The remainder will adhere to the precipitate and can be removed only by such solvents as chloroform, acetone and alcohol. If the cycle is repeated several times the soluble resins can be reduced to practically zero. This is what happens when the same oil is filtered through active material such as Fuller’s earth. However, solids begin to form in the crankcase oil as soon as the engine is started, and since these solids contain large amounts of resin, nothing is gained by leaving them in the oil. If finely-divided solids are introduced into new oil containing additives, the additives Will adhere to the solids just as resins do. If the solids are left in and dispersed by stirring, an oil analysis will naturally show no additive depletion. Oil samples are commonly analysed for additive content with the solids left in. It would seem that the oil should first be strained because any additive adhering to a particle of solid material will not leave that particle to do a new job. If it could, soapy water would not lose its cleansing qualities by repeated use.

Resin-like material can be partially precipitated from oil by petrol or fuel oil dilution, or by the addition of new oil to the crankcase. Clean used oil often contains upwards of 3% by weight of resin-like matter in solution. Part of this is readily curdled by petrol. Inasmuch as there is always some dilution this curdling process is probably continuous, although it can be filtered out.

Checks on a large number of motor vehicles in winter revealed that the crankcase oil (solids free) often contained 2% by weight of soluble resins. Thus oxidation takes place to a marked degree even in cold weather. When new oil is added some curdling takes place. Appreciable amounts will settle out of oil that appears clear. This resin not in solution can be readily filtered out whether it is attached to solids or not. In cold weather, there is almost always some water in crankcase oil, which can be filtered with almost any filter. When water emulsions are formed in used oil, a sticky mass is formed, which is caused by curdling due to water. This material, when separated from the water, oil and carbonaceous matter, is soluble in chloroform. Without water, this sticky mass is not nearly so apt to form. An examination of the cleaning rate of filters of minimum size, designed for long life, discloses the following fact: Under normal conditions, for which they are recommended, they will keep the oil clean, but will not remove undissolved material rapidly enough. The obvious remedy is to increase filter size and cleaning rate.