Chemistry Reference
In-Depth Information
pressure. All samples were run in duplicate and the averaged RPVOT times
in min are reported.
10.2.6 Friction and Wear Measurements
Friction and wear tests were conducted using a 4-ball tribometer (model
KTR-30L, Koehler Instruments, Bohemia, NY) following the 4-ball AW test
method in ASTM D4172-94
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under the following test conditions: load,
392
2 N (40
0.2 kgf, the force in kilograms exerted on the top rotating
ball); speed, 1200
40 rpm; lubricant temperature, 75
2 1C; test duration,
60
1 min. During the test, the torque required to overcome the friction
opposing the rotation of the ball was continuously measured and recorded
along with the spindle speed, load and lubricant temperature. The measured
frictional torque was converted into the coecient of friction (COF) fol-
lowing the procedure outlined in ASTM D5183-95.
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At the end of the test
period, the wear scar diameter on each of the three bottom balls was
measured along and transverse to the wear direction using an automated
wear scar measurement system, comprising hardware and software (Scar
View software version 2005, Koehler Instruments). The instrument load and
torque cells were properly calibrated prior to use, and freshly degreased test
balls were used in each test. In a typical experiment, the rotating ball was
first secured in the collect of the top spindle. The three stationery balls were
secured in the pot using a wrench set to the recommended pressure. The test
lubricant was then poured into the mixture until the balls were completely
submerged. The assembled mixture was then placed in the tribometer and
the load applied carefully so the top ball contacted all three bottom balls.
The test parameters (lubricant, speed, load temp, duration) were entered
into the computer and the heater turned on. The test started automatically
as soon as the test temperature was reached, and continued until the test
duration expired. At the end of the test, the mixture was removed, the oil
poured out, rinsed with hexanes and used in wear scar diameter measure-
ment. For each test lubricant, two AW tests were conducted using fresh balls
and test lubricants. The COF and wear scar diameter from the two tests were
averaged and used in further analysis.
10.2.7 Film Thickness
Lubricant film thickness was measured using the optical interferometry
method between a glass disc and a steel ball. Details regarding the basic
principles of the optical interferometry method can be found elsewhere.
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Film thickness measurement was conducted on an EHL Ultra Thin Film
Measurement System (PCS Instruments, UK). The glass disc used with this
instrument is coated with a semi-reflecting chrome layer, which is coated
with a silica spacer layer of pre-determined thickness to allow for instrument
calibration as well as for measuring very thin (ultra-thin) lubricant films. The
system has several components including: a mechanical unit; electronic
unit; optical system; and a computer with the appropriate software.
