Knowledge Centre

Coefficient of Friction Testing

Coefficient of friction (COF) testing is a measurement of surface friction i.e. the force required to pull a material sample, at a specified speed, for a specified distance over a horizontal surface, is covered in the same material.  In COF testing, the sample is normally wrapped around a metal block of specific dimensions and mass - called a 'sled', and another sample of the material is attached to a horizontal table.

When a universal test machine, such as the Mecmesin MultiTest 1-i is used for COF testing, a pulley wheel is used to transfer the tensile force applied by the stand to a horizontal force on the sled.

Two distinct calculations are then made to ascertain the coefficients of friction:

• Motion initiation force / sled weight = coefficient of static friction. This is the maximum (peak) force required to initiate movement of a material
• Motion maintenance force / sled weight = coefficient of kinetic friction.  This is the average force required to maintain movement of the material

Coefficient of friction values are particularly important within the packaging industry, where materials go through various processes in order to produce a final product. 

A wide variety of packages are produced by converting bulk plastic film or sheet, paper or foil. Form-fill seal converting machinery needs to move, feed, shape, stretch, cut, weld, fold and apply tensile load to raw material, and to do all this at high speed.  Finished packaging products must move quickly and efficiently along the production line.  Each surface has its own distinct frictional value, which determines if they have the tendency to adhere or slide apart from one another.

Benefits of COF Testing

These include:

• Optimising production levels
• Minimising problems caused by misfeeds
• Removal of need for guesswork / trial and error
• Compliance with industry standards

Standards

Common standards used for determining coefficient of friction values include:

• BS EN ISO 8295:2004 Plastics, Film and Sheeting. Determinations of the coefficients of friction
• ASTM D1894-0 Standard Test Method for Static & Kinetic Coefficients of Friction of Plastic Film and Sheeting

To find out more about Mecmesin's range of coefficient of friction testers see our test solutions section.