Radiation Resistant Gear Oils

Some oils, both natural and synthetic, are more resistant to the effects of ionizing radiation than others. However, according to  Gordon and  Weir^22  resistance  to  such  action  is  increased  by  the  addition of 0.1 to 10  per cent  of  asphalteness . For best results the base oil should contain less than 0.1 per cent of asphalt. Thus, a bright  stock  containing  0.75 per cent  of  asphaltenes was  exposed to  radiation until  it  had  adsorbed  2 *10^8   rads  causing  a viscosity  increase of 31 per cent. The unmodified oil under   the same conditions increased in viscosity 48 per cent. An  oxidation  inhibitor  such  as 5  per cent  dialkyl  selenide is also  effective  in such  lubricants as  is a metal  deactivator consisting of 0.05 per cent  of  quinizarin.   

Power Steering Gear Fluids

As a base for such a fluids, a solvent refined oil of about 250 viscosity SUS at 100 degree F may be used. While , as Johnson and Mortensen state, the major requirements are shear  stability  and high  V.I., the oil should  also  be  resistant  to oxidation and  have no  adverse effects on both metals  and  seal and  hose  materials. Likewise the blended oil should have a low pour point. All of the above point to a solvent refined oil which will have the desired high V.I. and aniline number.

Chrysler MS 3590 “Hydraulic Steering Fluid with Rust Preventive”, summarizes the composition requirements as follows:

“Well refined oil with admixture of proper rust preventive additives. Small amounts of oxidation inhibitor and pour depressant may also be used to meet the details requirements. The use of   detergents and V.I. improvers is prohibited. The additives small be selected to have a minimum effect on the seal and hose materials”.

Therefore, additives may  include up to 0.5 per cent  of an  oxidation inhibitor, such as  can be  recommended  by  an  additive supplier, or  may  be  phenyl  alpha napththylamine , 2,6-ditertbutyl – 4- methyl  phenol, mixtures  of these  two  types, or  an oil-soluble  organic thiophosphate salt of certain  metals, such  as zinc  methylphenyl  dithiophosphate.

If the pour point of the oil is above -20 degree F, from 0.2 to 1 per cent of a pour depressant, such as “Acryloid  150”, “Paraflow”, or “ Santopour C”, can be added.

Suitable rust inhibitors, used in concentrations of 0.5 to 2 per cent, include petroleum or synthetic sulfonates, such as “Petronate” or barium dinonyl naphthalene sulfonate. A combination oxidation and rust inhibitor, which is usually used in a concentration of 1 per cent or less, is “Vanlube 76”.