Coefficient of Friction Test

Coefficient of friction (COF) testing is used to measure the frictional qualities of a number of materials, including, films, and household objects. It’s usually defined as the ease with which two surfaces, made of different materials, glide against one another; low COF indicates that the objects glide smoothly.

What is the purpose of a coefficient of friction test?

The purpose of a coefficient of friction test is to assess friction between materials. This information can be useful when evaluating the safety and efficiency of a packaging system. 

For example, a package that does not have enough friction may slide too easily during transit, posing potential risks for accidents. However, a plastic film that has too much friction may have trouble sliding through machinery, causing jams in the equipment.

A COF test measures both static and kinetic friction by utilizing a multi-test system. The test is carried out by pulling a flat block of known mass across a flat table’s material. The coefficients are determined by measuring both the highest force required to start movement (static) and the average force required to maintain movement (kinetic).

Coefficient of friction testing leverages PC software to plot a graphical depiction of the test results and automatically calculate static and kinetic friction coefficients. This gives customers more information about the material’s surface structure and frictional qualities. With this insight, our customers can optimize processes such as machinery timing, safe handling, and more.

Typical procedures and protocols of a coefficient of friction test

To determine the starting and sliding coefficients of friction for plastic film and sheeting, WESTPAK conducts the coefficient of friction (COF) test per the ASTM D1894 test standard. The protocol allows five basic ways in which the test apparatus may be assembled. Westpak’s test setup incorporates a precision test sled apparatus, a Shimadzu or Instron load frame, and a very accurate load cell to generate test data.

Prior to testing, samples are prepared, mounted to a fixture’s base and sled, and then conditioned as per ASTM D1894. The load frame is then employed to draw the sled across the bed at a predetermined speed. Data used to determine the static (starting) and kinetic (sliding) coefficients of friction for the test specimen are obtained.

WESTPAK’s test equipment and methodology produces accurate and highly repeatable test results consistent with the requirements of ASTM D1894. Custom and/or proprietary client test requirements can be accommodated as well.

How is ASTM D1894 testing performed?

Test standard ASTM D1894 identifies the calculation of the static and kinetic coefficient of friction between two surfaces. The test is performed by pulling a sled across a horizontal plane, while the software generates data. This standard can be applied to plastic films (</=0.254 mm thick). In addition to the pulling mechanism, ASTM D1894 also considers the effect of temperature on the plane, which involves heating the plane to specific temperatures.

The coefficient of friction test method may also involve several configurations of the testing apparatus in order to better understand the object’s frictional qualities when exposed to real-world environments.

What is the difference between static & kinetic coefficient of friction tests?

• Static friction: The force that holds a stationary object back until it begins to move is known as static friction. As a result, the static COF refers to the force that prevents an object from moving while it is motionless on a reasonably smooth, hard surface. It’s computed by taking the initial peak force needed to move the sled and dividing it by the sled’s weight.
• Kinetic friction: After static friction is overcome, kinetic friction sets in, and it is this force that prevents regular motion. The force restricting the movement of an object sliding on a relatively smooth, hard surface is the subject of this kinetic COF. It’s computed by multiplying the average load during the test by the weight of the sled that bears the other material.

What are the materials and products tested in a coefficient of friction test lab?

ASTM D1894 testing is most commonly used to assess plastic film and sheeting, but it may be adapted to suit a number of different products as long as their nominal thickness is less than or equal to 0.254mm, including:

• Ceramic tiles
• Sneakers
• Flooring

Contact Westpak today to learn more about how we can help you with coefficient of friction testing and more. Our team is waiting to support with expert advice and the highest quality testing.