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”.
