Timken OK Load is a qualitative measure that indicates the possible performance of extreme pressure additives (EP Additives) in a lubricating grease or oil. The units of measure are pounds-force or kilograms-force and are determined using a special test machine.
The test machine is based on a machine manufactured by the Timken Company from 1935 to 1972. It is now an industry standard test though the meaning of the qualitative measure has become less useful as the science of tribology has advanced.
The test machine consists of a bearing race mounted on a tapered arbor rotating at high speed. The race is brought into contact with a square steel test block under load. The contact area is flooded with the lubricant being tested. The Timken OK Load is the load at which the spinning bearing race produces a score mark on the test block.
Though Timken no longer manufactures the test machine, Timken OK Loads are still listed on grease and oil property charts. It was once generally assumed that the measure and the film strength of the lubricant were directly related. Today, the primary purpose of the test is to determine whether EP additives are present and functioning. A measure of 35 pounds-force (16 kilograms-force or 155 newtons) or more means that EP additives are present and working.
The Timken OK Load test specification is ASTM 2509.
