Wear Scar Diameter for Lubricating Greases

Description

A fundamental tribological test to evaluate the ability of lubricating greases to prevent wear of rubbing parts under medium load and sliding conditions.

Wheel bearings, CV joints, and industrial guideways are constantly subjected to sliding friction. If a lubricating grease lacks a reliable package of anti-wear (AW) additives, metal surfaces wear down quickly, leading to backlash, vibrations, and catastrophic failure of the assembly. The analysis of the wear scar diameter of greases on a four-ball tester (FBT) at the RENA laboratory is objective proof of product quality. This test allows you to choose a grease that is guaranteed to extend the service life of your equipment twofold or threefold compared to cheap alternatives. The test according to the international ASTM D2266 standard takes place on a precision friction machine (FBT-3). Three steel reference balls are rigidly fixed in a cup and thickly covered with the lubricating grease under test (a minimum of 10 grams to ensure complete lubrication). The fourth ball, fixed in the spindle, is lowered onto them, creating a pyramidal contact. A strictly standardized load of 40 kgf (392 N) is applied to the system, and the grease temperature is maintained at 75 °C. The motor rotates the top ball at a speed of 1200 rpm for exactly one hour. During this time, intense sliding friction occurs between the balls. After the machine stops, the grease is washed off with a solvent, and the tribologist uses a microscope to measure the diameters of the circular wear scars formed on the three lower stationary balls.