Laboratory wear testing method

An apparatus for wear testing is termed as wear tester, tribotester or tribometer. The prefix of "tribo-" refers to wear, friction and lubrication. Many, probably more than several hundreds, different wear testing arrangements and procedures are used in laboratories around the world and described in technical literature. However big difference of one arrangement as compared with another, a wear tester will always involve two components loaded against and relatively moving each other. The movement can be driven by a motor or by an electro-magnetic device. For convenient purpose, the material or component being investigated is normally referred to as specimen, the other termed as counterface. As examples, the working principle of three most widely used laboratory wear testers are given below.

An abrasive wear tester
Fig. 1 is a schematic of an abrasive wear tester, in which a wheel or a ball is driven by a motor, rotating and sliding against a fixed sample in the presence of abrasive particles. The specimen is in the form of a plate or a block. Contact pressure is controlled by dead weight through a loading lever. The abrasive particles, such as silica, are added through a nozzle connecting to a hopper above, giving a three-body wear situation. After a set time of running, the sample is removed, and wear loss is measured. The parameters to be controlled include contact load, sliding speed, type of abrasive particles and its flow rate.

A rolling sliding wear tester
Rolling-sliding wear tester is the most popular tribometer for investigating wear as well as frictional behaviour of a materials under conditions of rolling, sliding, or a combination of both. Two discs (wheels), as show in Fig. 2a), are fixed to two parallel shafts and pressed against each other under a constant contact load. Driven by a motor through a train of gear, the specimens are rotating along with the shafts. The rotating speed can be controlled, so that when the linear speeds of two wheels are equal at the contact point (V1=V2), a pure rolling contact is achieved. When V1 and V2 are different (V1 ? V2) and both wheels are rotating, a combined rolling-sliding can be realised. Whilst when one of the specimen is fixed, and the other is rotating, then wear is a pure sliding. In this case, the fixed specimen can be a block, so that a name of block-on-wheel is used. Abrasive particles may be added to the contact area, achieving a three body abrasive wear testing.

A pin-on-disc wear tester
In a pin-on-disc wear tester, a pin is loaded against a flat rotating disc specimen such that a circular wear path is described by the machine. The machine can be used to evaluate wear and friction properties of materials under pure sliding conditions. Either disc or pin can serve as specimen, while the other as counterface. Pin with various geometry can be used. A convenient way is to use ball of commercially available materials such as bearing steel, tungsten carbide or alumina (Al2O3) as counterface, so that the name of ball-on-disc is used.

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