• Version
• 39 Downloads
• 1.05 MB File Size
• 1 File Count
• January 17, 2017 Create Date
• January 17, 2017 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Effects of Solvents in Improving Boundary Lubrication of Steel by Silicones

Because, of the known synthetic fluids, silicones best satisfy the
viscometric requirements for lubricants for turbine engines, a study was
conducted to establish the effect of solvents on boundary lubrication
by silicones. Bomdary—lubrication data were obtained which are con-
sidered substantiating evidence for a hypothesis that, in solutions of
solvents blended with silicones, the silicones form a closely packed
and oriented adsorbed film on ferrous surfaces. The solutions reduced
friction and prevented surface failure even when the solvent as well as
the silicone was an extremely poor lubricant. These data indicate that
satisfactory lubrication is the result of a solvation effect rather than
a lubrication additive effect of the solvent because 30 to 50 percent of
solvent was necessary for good results . The best results were obtained
with solvents having dipole moments .

Solutions of di(2-ethylhexyl) sebacate and di(2-ethylhe:xyl) adipate
in silicone fluid were found to have viscometric characteristics approach-
ing that of the silicone alone and were effective lubricants at tempera-
tures above 500° F. The temperature limit of effective lubrication could
be increased by mploying silicones of greater average chain length.

New turbine engines for military aircraft have lubrication require-
ments that cannot be met satisfactorily by available petroleum lubricants .
In particular, extremely good viscometric and thermal stability properties
are necessary for lubricating fluids,- the specific requirements are set
forth in a recent military specification, Milli-7808. Viscosity at -65° F
must be sufficiently low to allow adequate pumpability of the fluid.

Also, the fluid should be thermally stable so that harmful decomposition
and vaporization will not occur. Petroleum lubricants are not satisfactory
with regard to either low—temperature viscosity or high-temperature thermal
stability. A number of tailor-made synthetic fluids are available which
satisfy the viscometric and thermal stability requirements and, conse-
quently, have promise as lubricants for aircraft turbines .