Friction / Slip Testing Why & How To Measure Coefficient of Friction

Why Measure Coefficient of Friction?

Being able to measure the slip resistance properties of material will help predict the run ability and line speed of a product or material on a packing line, automatic gluing or automatic carton erection machine. Other examples of the need to measure COF could be the automatic feeding of banknotes, envelopes and plastic films. Another key area for measuring coefficient of friction is in the manufacture of non-slip sheets used when packing pallets. Or knowing how the package will slide when being packed.

Measuring coefficient of friction key industries / applications

  • Plastic packaging films
  • Packaging board
  • Corrugated board
  • Ink manufacture and development
  • Carton printers

What is Friction / Slip?

The frictional forces caused by a material are expressed as Coefficient of Friction. Static coefficient of friction = Fs/N Dynamic coefficient of friction = Fd/N Fs being the maximum static frictional force (force required to move the sled) and Fd is the average dynamic frictional force. N is the force of gravity acting on the sample and test sled.

Measuring Coefficient of Friction

Measuring coefficient of friction is done using a Coefficient of Friction Tester or Friction Tester / Slip Tester for short. The coefficient of friction measurement device will have a sled of a known / controlled size and weight and either a load cell or means to angle the bed. There are different types of coefficient of friction measurement device that are discussed below.

Coefficient of Friction Tester Measurement Device Types 

Horizontal Plane (flat bed) Friction Tester

Measures the dynamic Fd/N & dynamic coefficient of friction Fs/N. A flat bed is required and a sled is dragged across the bed and material being tested. There is a load cell in between sled and the motor that measures the force required to keep moving the sled over the material and the initial force required to move it.

Inclined Plane Coefficient Friction Tester

Measures just static coefficient of friction Fs/N. A simple low cost instrument where the bed raises and the angle that the sled breaks away from the material is recorded. This is either converted automatically our manually into a static COF value. AML offers three coefficient of friction testers Compact Friction Tester, a simple easy to use basic COF tester suited to shop floor and quality control laboratories. Advanced Friction Tester, an advanced COF tester with powerful software with more complex analysis of results. More suited to R&D and more demanding QC testing Inclined Plane Coefficient Friction Tester, easy, quick tests if static COF is all you need. Another option is to use a Universal Testing Machine / Tensile Tester with a flat plane coefficient of friction measurement device. This is a good option if you would like to perform other tests such as tensile or compressive strength. But the downside is the friction tests won't be as accurate or repeatable as using a dedicated COF tester. However we do see lots of companies using this type of device.

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