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

National Advisory Committee for Aeronautics, Technical Notes - Effective Lubrication Range for Steel Surfaces Boundary Lubricated at High Sliding Velocities by Various Classes of Synthetic Fluids

Synthetic lubricants are necessary to satisfy the physical property
requirements for future lubricants of aircraft turbine engines. Boundary-
lubrication data on the synthetic fluids are rather limited; consequently,
the effects of a wide range of sliding velocities on boundary lubrication
were studied.

Sliding-friction data and surface-failure properties show that a
number of synthetics including diesters, polyethers, a silicate ester,
and a phosphonate ester as well as a silicone-diester blend are more
effective boundary lubricants at high sliding velocities than comparable
petroleum oils. The blend of a diester in silicones, an alkyl silicate
ester, and a compounded diester (containing lubrication additives) were
more effective boundary lubricants at high sliding velocities than the
comparable diesters from which the most widely accepted synthetic lubri~
cants are made. A diester failed to lubricate nonreactive surfaces
which indicates that the lubrication mechanism for diesters may involve
chemical reaction with the lubricated surfaces.

It is currently appreciated (references 1 to 6) that new types of
lubricant must be found to replace current petroleum oils for the turbine—
type aircraft engines of the immediate future. The present lubricants
(specification MEL—O—SOBlA, grades 1010 and 1005), are not completely
satisfactory because they are either too viscous for adequate pumpability
(based on CBC studies in a simulated lubricants system) at low tempera—
tures (—650 F) or because they have marginal lubricating ability and
excessive volatility at present bearing operating temperatures (under
5500 F).

The lubricant requirements are further complicated by high
"soak back" temperatures (approabhing 5000 F at present) of the bear-
ings which cause thermal decomposition of the lubricant. New engines will
have higher bearing operating temperature and lower starting tempera-
ture (—650 F or below) operational requirements. There is no evidence
that a petroleum oil can satisfy these requirements; consequently, it has
been necessary to consider other lubricants such as synthesized fluids
for use in aircraft turbines. Military specification MEL—L-7808 is for
such a synthetic lubricant. In order to be considered, synthetic lubri-
cants must be thermally stable, be pumpable at low temperatures, and,
in addition, must be capable of providing effective boundary lubrication
under extreme conditions of temperature, load, and sliding velocity.