Unidirectional sliding (pin-on-disc)

What is it?

It is a technique which enables the testing of friction and wear of surfaces and the study of the interaction between different types of materials under different conditions of use. The causes and mechanisms of wear of materials are quite diverse and must be approached in a comprehensive manner covering all the complexity of a tribological system which includes the surface, the agent of wear and the medium in which this occurs.

What is it used for?

The most commonly used laboratory test for characterisation of wear by unidirectional sliding between two bodies is the Pin-on-Disc (PoD). Standard ASTM G99 establishes the procedure for testing PoD between two materials in contact for the determination of wear and friction coefficient during the sliding process. Through this equipment it is possible to analyse a wide range of metallic, ceramic, polymeric and composite materials. It is also possible to study the influence of the various parameters that influence the contact in the causes of wear for various combinations of materials between pin and disc, or even to perform analyses to determine the most suitable lubricant for a given situation of friction.

Equipment and working conditions

This equipment consists of three modules: a module composed of mechanical motor drive, control, transmission elements and mounting test specimens; a display and interface module; and a specific hardware module with software for equipment and command processing and acquisition of information gathered during the tests. In this test the sample (disc) is placed on a rotary table and a counter body is placed on it (Pin), to which a normal force is applied. By means of a load cell placed in the equipment which restricts the movement of the arm, it is possible to measure the force of friction. Reading the output signal of the cell determines the friction coefficient of the pair of materials tested (sample and pin). The friction coefficient of a given pair of materials can be determined through the Archard equation, taking into account the normal load applied (N), the distance covered during the test (S) and the amount of wear (V):

Example of use

• Evaluation of friction between different self-lubricating materials for non-lubricated contacts;
• Study of scratch resistance of machine polished surfaces against sliding materials;
• Assessment of limit conditions for lubricated contact systems;