Statistical Process Control: Friction - Slide Angle, Technical Information Paper TIP 0304-34 (2002)

Friction of corrugated board ensures that boxes made from that board will not slip from a load. Some newer methods of material handling rely on a certain friction between the boxes, so it is important for the boxmaker or his linerboard supplier to control the amount of friction. The angle of inclination at which one box on top of another will just begin to slide is a measure of the coefficient of static friction between the two surfaces of the two boxes in contact. Derivation will show that the coefficient of friction is equal to the tangent of the angle of inclination from the horizontal. The coefficient, hence the angle itself, is independent of the force applied between the two surfaces. Therefore, the coefficient of friction or slide angle is not dependent on the weight of the box and its contents.

The test covered in this technical information paper was devised to measure the coefficient between two box surfaces. It can also be used to measure the coefficient of friction between two paper surfaces prior to fabrication of the box. The test can be applied to linerboard before corrugating, to corrugated board after combining, and at any point up to and after box fabrication. Subsequent treatment, rubbing, or abrasion of that surface can alter the coefficient significantly. This is especially true if frictionizing materials have been applied to the surface. Subsequent processing could remove the frictionizing material, thereby lowering the coefficient.