What a pin-on-disk test tells you
A pin-on-disk test measures how a material pair behaves in continuous sliding: the coefficient of friction throughout the test and the specific wear rate at the end. Because the pin keeps passing over the same circular track, the friction record also shows run-in, the approach to steady state, and transitions such as a coating wearing through.
It is used to rank materials, coatings and lubricants, to qualify production batches against a reference, and to study wear mechanisms under controlled load, speed, temperature and environment.
How the test works
- The sample is mounted on the rotating stage. The pin or ball is clamped in the holder at a set distance from the centre of rotation, which fixes the track radius.
- A controlled normal load is applied: by dead weights on the T50, or by regulated pneumatic loading on the T200 and T2000.
- The stage rotates at the set speed for a set number of revolutions or a set sliding distance. Friction force is measured continuously, alongside depth, acoustic emission or electrical contact resistance if fitted.
- After the test, the wear track on the disk and the wear scar on the pin are measured in 3D to obtain worn volume and wear rate.
More than one way to rotate
The rotational module is not limited to a single constant-speed circle:
- Arc tests oscillate back and forth over a set angular range, a rotational form of reciprocating motion.
- Spiral tests move the pin radially during rotation at constant linear speed, so it always meets fresh surface. This is the approach used for abrasion against abrasive paper.
- Speed ramps sweep speed continuously, which is how a complete Stribeck curve is obtained in one run.
- Friction versus position maps friction around the track (0° to 360°) at any cycle, using the 16-bit external position encoder. This reveals local defects or uneven coating thickness that an average would hide.
Speed range and low-speed friction
Speed is controlled by a 20-bit internal encoder. The standard motor runs from quasi-static rotation at 0.01 rpm up to 5,000 rpm and goes from 0 to 1000 rpm in 0.23 s; high-speed motors reach 10,000 rpm on the T50 and 15,000 rpm on the T2000, with a minimum of 0.05 rpm. At the low end, breakaway friction and stick-slip can be studied directly. NANOVEA’s extreme low-speed study used this range to show rubber’s friction rising with speed between 0.01 and 5 rpm. At the high end, sliding speeds above 10 m/s are possible, which matters for brakes, seals and high-speed bearings.
Speed can also be changed during a test, either in steps or as a continuous ramp. A ramp from high to low speed under lubrication traces the transition from hydrodynamic to mixed and boundary lubrication, the basis of the continuous Stribeck curve method.
Load control and vibration
How the load is applied affects the result. Dead weights are transparent and simple, and they remain the reference for many standard tests. At high loads and speeds, though, a mass on a lever can bounce on a rough or wearing track and add uncontrolled vibration. Regulated pneumatic loading on the T200 and T2000 holds the set load in closed loop as the track wears, with the air medium damping vibration. The load is measured directly, with no spring between load cell and contact.
The T2000 can also impose a controlled load oscillation to simulate vibrating service conditions. In NANOVEA’s dynamic load study, a 5 N oscillation amplitude raised the worn volume of copper about 2.7 times compared with a constant load.
From wear track to wear rate
Wear is reported as worn volume, normalised by load and sliding distance:
K = V / (F × s)
where V is the worn volume, F the normal load and s the sliding distance (2πr per revolution at track radius r), usually in mm³/(N·m).
NANOVEA measures the wear track by chromatic confocal 3D non-contact profilometry, which works on metals, ceramics, polymers and coatings, including transparent and highly reflective surfaces. On the T2000 the profiler can be integrated on the tribometer, so the track is measured in place and can be re-measured at intervals during a test. Otherwise a standalone NANOVEA profilometer is used. The 3D map gives worn volume, track depth and width, and the track morphology that helps identify the wear mechanism.
Choosing test parameters
- Counterbody. Match the real counterface material where possible. Ball diameter sets the initial contact pressure.
- Load, speed and radius. These set contact stress and sliding velocity. Track radius and rpm together define the linear speed.
- Duration. Run past run-in to steady-state wear, or to a defined failure such as coating breakthrough.
- Environment. Temperature, lubricant, humidity or gas often change friction and wear more than load does.
- Repeats. Repeat each condition to show the scatter, so you can judge whether a difference between materials is real.
