Friction is a force that obstructs the motion of two surfaces coming in contact with each other. In earlier days, film and sheet producers used off-line friction testers that had a manual operation. They were either computer-operated machines or stand-alone machines. This problem is now overcome by a single machine. A coefficient of friction tester measures stacking capacity of the sheet-like base for example plastic film, paper, corrugated board etc.
Coefficient of friction (COF) can be defined as the force to move two sliding surfaces upon each other divided by the force that holds them together. Coefficient of friction test helps the manufacturer to analyse whether materials are suited for their grip requirement. Tests are performed in two ways either static or dynamic coefficient of friction. The static test is based on the amount of momentum required to get movement between two surfaces. The dynamic test can be used to analyse the effort needed to reduce friction between two surfaces.
A variety of materials such as films, lubricants, household items include the coefficient of the testing method to assess the frictional characteristics. A low value of COF signifies that the surface is smoother. Many factors influence the evaluation result of the coefficient of friction tester such as printing, humidity, coatings etc.
The coefficient of the friction test method is done by cutting two samples of plastic films. One sample is kept on the movable track and the other on the platform. The movable block is connected to a pulley. The samples are kept facing towards each other. The test begins with the block moving upon the sample. The machine records the resistance due to the block and displays the coefficient of friction on the screen.
The formula to calculate COF is (µs) = As / B
A = Reading on the load monitor at the time the block slides on the plane and,
B = Weight of the block.
The test can be performed on three types of the sample they are a sample to metal, sample to glass and sample to sample.
Presto Coefficient of Friction Tester is a tool to define the starting and sliding friction of sheets and films upon each other or any other substance at specific test condition. The equipment has a strong metallic base with bright zinc plating to resist corrosion. The purpose of using this machine is to determine the abuse level of plastic films that it can bear without causing any damage to the contents. Chip based display, separate display for dynamic and static friction, slider block to conduct tests, no slippage of samples etc. are the basic features of this equipment. Standards are ASTM D 618, BS 2782, ASTM D 1894 and ASTM D 883.
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