Pin-on-Disk Testing

As outlined by ASTM G99-04, pin-on-disk testing consists of a rotating disk in contact with a fixed pin with a spherical top. A schematic is shown below.

F: Applied normal load
R: Radius of the wear track that is produced
d: Diameter of the spherical top of the pin
D: Diameter of the disk
w: Rotational speed
 
In these experiments, the user typically has the ability to control and measure the applied normal load, unidirectional speed or oscillation frequency, and environmental parameters such as temperature, pressure, type of gas (vacuum, air, nitrogen, refrigerant, etc.) and presence of a lubricant. Both the normal and friction forces are measured with transducers. The pin holder is attached to a fixture that is allowed to deflect slightly; the transducer measures this deflection and converts it to a force. Performance is generally characterized by friction coefficient and wear rates (wear per unit time) determined my mass or volume loss with the aid of a profilometer.
 
Although, ASTM G99-04 states that a spherical pin be used, many different specimen geometries may be employed to best simulate the operation of an actual system. The machines used to conduct this testing are called tribometers, two types of which are outlined in the following sections.

High Temperature Tribometer (HTT)
The High Temperature Tribometer (HTT) has the ability to conduct tests in the method previously explained in temperatures up to 1000°C. To achieve these high temperatures, a resistance heating element is used that is similar to the red-hot coils you may see in a toaster or electric oven. The actual contact of the pin and disk takes place inside the gold-plated chamber which helps hold in heat.

High Temperature Tribometer

Animation of the contact inside the heating chamber
(Click on the image to see animation)

High Pressure Tribometer
The High Pressure Tribometer (HPT) is very similar to the HTT, except that it has the abilities to test in environments of elevated pressures (up to 250 psi) with the use of special seals. It is primarily used for compressor simulation in which lubricants and refrigerants are used. See the images and animations below.

High Pressure Tribometer

Close-up views of the HPT pressure chamber

Animations of the contact inside the pressure chamber for (a) oscillatory and (b) unidirectional tests (Click on the images to see animations)

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