Effect of lubricant base stock on rolling-contact fatigue life Page: 4 of 29
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NACA TN 4161
APPARATUS
In the interest of brevity, only brief descriptions of the apparatus
and procedure are given here. A more detailed presentation can be found
in references 1 and 6 as well as in appendix A. Figure l(a) is a cutaway
view of the rolling-contact fatigue spin rig. Air jets caused the two
test balls to revolve in a horizontal plane on the bore surface of a
hardened tool-steel cylinder (fig. 1(b)). The loading on the balls was
produced by centrifugal force, and the stress was calculated according to
the methods of reference 7. Approximately 15 milliliters per hour of
lubricant were introduced in droplet form into the drive airstream between
the two guide plates above and below the air jets. The fast-moving airstream
had an atomizer effect, and the lubricant was reduced to a fine mist that
adhered to surfaces to provide a lubricating film.
Orbital speed was measured by counting the pulses from a photoam-
plifier on an electronic tachometer; a pulse was generated each time a
ball interrupted a light beam. A ball or race failure resulted in in-
creased vibration and hence the generation of an increased signal from a
velocity pickup attached to the rig. This signal, when amplified, actuated
a meter relay that shut down the system.
Temperature was controlled by mixing heated air with the normal drive
air supply. The test temperature and temperature-control signal were
taken from thermocouples on the top and bottom of the race cylinder.
All ball test specimens were from the same heat of AISI M-1 air-melt
tool steel and had a nominal 1/2-inch diameter. The running track on the
balls was predetermined by grinding two diametrically opposed 3/16-inch
flats on the ball surface. Race cylinders were AISI M-1 vacuum-melt tool
steel.
PROCEDURE
Before the test all race cylinders were given dimensional surface-
finish and hardness inspections. All test balls were weighed and given a
surface examination at a magnification of 36. A record was kept of any
abnormalities in surface conditions at the running track. Prior to
inspection and use, test specimens were flushed and scrubbed with 100
percent alcohol and clean cheesecloth. During storage they were protected
by a corrosion-resistant-oil film. Care was taken during assembly not to
scratch the running surfaces. The bore surface and test balls were coated
with the test lubricant during assembly.
The rig was brought up to operating speed as rapidly and as smoothly
as possible. About 3 minutes were required for the hot airstream to heat
the test cylinder to the test temperature when running at 1000 F. Speed,3
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Carter, Thomas L. Effect of lubricant base stock on rolling-contact fatigue life, report, February 1958; (https://digital.library.unt.edu/ark:/67531/metadc56829/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.