Coefficient of Friction Measurement for Elastomers
|Publication Date:||1 November 2011|
Note: Nothing in this standard supercedes applicable laws and regulations.
Note: In the event of conflict between the English and domestic language, the English language shall take precedence.
Foreword. This document is based on ISO 15113, Rubber - Determination of Frictional Properties. The coefficient of friction (CoF) depends on the rubber composition, test duration and type of test rig. The latter affects the CoF mostly via the contact pressure and transport of debris from the contact area (on repeat measurements).
The force to start the sled (static friction) and to keep the sled moving (kinetic friction) are both measured by the load cell, and recorded on a graphical device or stored in a data acquisition system. The acquired force data is divided by the sled weight to mathematically determine the static and kinetic coefficient of friction. Static friction is derived from the first maximum peak (force) on the load curve, and the kinetic friction is derived from an averaged force value between two defined points within the region beyond the first peak on the load curve.
Applicability. To support finite element analysis of elastomeric parts for an assembled joint.
Measured Finishes. Such as cast and machined groove, or surface finishes for static mating surfaces (e.g., engine block, head, covers, etc.) It does not represent rotating or reciprocating surfaces like crankshaft or valve stems.
Friction. The resistance between two contacting surfaces.
Static Coefficient of Friction (μs). Coefficient of friction at the instant motion between surfaces starts.
Kinetic Coefficient of Friction (μk). Coefficient of friction after motion between surfaces is established.
Coefficient of Friction (CoF). The ratio of the force required to move one surface over another to the total force applied normal to those surfaces. Coefficient of friction is dimensionless and its value is not restricted to numbers less than unity.
Stick-Slip. A condition where the actual velocity between the surfaces oscillates, resulting in corresponding oscillations in the measured frictional force.
Coating. A dry substance introduced between two surfaces to lower the coefficient of friction.
Wet Assembly Aids. Solutions used to temporarily reduce assembly force (friction) between press and interference fit stationary mating elements (e.g., hose to fitting). The term lubricant is sometimes used to describe an assembly aid; however its proper usage is to describe fluids or greases as a maintained film between moving surfaces to reduce friction and wear.
Machine Direction. The direction the machining method is applied to the work piece or the direction the work piece lead end was first fed into the finish machine (running direction).
Against Machine Direction. The 180 degree movement opposite of the machine direction.
Cross Direction. The direction perpendicular to the machine direction.