Experiments were carried out using pin on disc apparatus (120N, 800rpm, a flat faced pin 10mm, room temperature) and four ball test(120N,800rpm , AISI 52100 balls , 75 degree C). The lubricant used was graphite added vegetable oil.
We got two different values of coefficient of friction. In fact a trend of increasing Coefficient of friction was observed in pin on disc.
The test was repeated for several load conditions.
Dear Bhaumik
Yes, COF is a tribo system property and governed by test configuration, test mode, velocity, load etc. For more information you can refer
Czizhos H. Tribology –a systems approach to the science and technology of friction, lubrication and wear, Tribology series, 1. Elsevier; 1978.
Dear Mr. Bhaumik,
Theoretically speaking, friction varies between different modes of measurement but the coefficient of friction may not be expected to vary (under same operating conditions). However experimentally due to minor reasons such as different operating environments, variation of surface roughness of the samples etc.
1. With increase in temperature (due to thermal expansion), the space between molecules is increased and so the free volume within the material becomes larger which speeds up the molecular movement . This results in variation of some of the properties , might be probably why the coefficient of friction changes with temperature
2. The increasing of coefficient of friction in the case of pin on disc tribometer may be due to increase in the frictional heat with time at the contact surface . In extreme cases this may also be due to "run over" of the materials under examination.
Hope this helps !
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