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3.2 How to perform the tests
3.2.1 Conditions if the loads applied are low
If the loads are low, the balls show hardly any wear. The result is the same when you
measure and record the friction torque, i.e. the friction coefficient.
The friction coefficient will remain constant here and usually range from 0.05 to 1.0. No
friction peaks occur. When the machine is powered up, the friction rate will increase for a
short moment (see Fig 1).
Fig 1:
If the running time is 1 minute, the wear scar of the 3 balls clamped will be the same as or
minimally bigger than the wear scar diameter generated under the load applied due to the
static deformation.
The wear scar diameter can be determined with the Hertzian formula.
3.2.2 Conditions if the loads applied are high
If the load is high, the wear can be substantial. In other words, the wear scar diameter of
the 3 balls can be substantially bigger than the wear scar diameter generated by the
corresponding static deformation.
The anti-wear properties of the lubricant to be tested, i.e. the lubricant's behaviour in this
load range, play a pivotal role here.
The specific load applied to the contact surfaces does indeed correspond to the values
present at, e.g., the teeth of gears subjected to heavy wear.
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