Aniline Point of Petroleum Products

Aniline point is the minimum equilibrium  solution temperature, generally given  in F although C is also used, for  equal  volumes  of  aniline  and  oil. Aromatic  compounds in oils  contribute to a low  aniline point  which  in  turn  indicates that  such  an  oil will  soften or  swell  both  natural  and  most  synthetic  rubbers. Therefore  to  insure  minimum  action  on rubber  gaskets, seals, etc., oils  with high  aniline  points  should  be  selected. Solvent refined oils  as a  rule  satisfy  such  requirements. 

Minimum action of gear oils on components of mechanisms

Well refined mineral lubricating oils have little if any action on most metals, particularly ferrous metals. It is only upon prolonged use at elevated temperatures that such oils may from compounds which will act upon metals. Since such oil changes can be retarded or almost completely arrested by the use of oxidation inhibitors and also metal deactivators or pacifiers can be included, there should be little concern about the action of straight mineral oils upon the metal components with which they come in contact.

What we are concerned with here is the action on parts made from other materials, such as paper, plastics, rubber, etc. Seals are likely to be made from rubber, either artificial or natural, and any deterioration of the compositions due to the lubricant should be at a minimum. Many seals consist of compounded materials, such as “neoprene,” and it is found that oils high in aniline points, as are most high V.I. oils, will have little effect on this compound.

Automatic transmission mechanisms may be found to contain paper and “Nylon” parts. In future devices which will require transmission fluids, a greater variety of components may be used. The safest course when supplying oils for contact with unusual materials is to have the fluids pretested to determine their suitability.