ASTM D2596-20 Standard Test Method for Measuring Extreme Pressure Properties of Lubricating Grease (Four Ball Method)

The ASTM D2596-20 standard, developed by the American Society for Testing and Materials (ASTM), describes a test method (four-ball method) for determining the load-bearing properties of lubricating greases. The following three values are determined by this test method:

Load wear index (previously called average Hertz load)
Welding point via four-ball extreme pressure tester
Last non-seizure load

Used as a standard in the industry, this test method distinguishes between lubricating greases with low, medium and high extreme pressure characteristics. Results are not necessarily related to results from the service. Lubricating greases with silicone, halogenated silicone or a mixture of silicone fluid and petroleum oil as fluid components are not suitable for this test method.

The four-ball method is one of two lubricant testing procedures based on the same principle:

Four-ball wear method (ASTM D2266 standard)
Four-ball overpressure method (ASTM D 2596 standard)

In these test methods, three steel balls are interlocked to form a cradle on which a fourth ball rotates on a vertical axis. The balls are immersed in the lubricant under investigation. The four-ball wear method is used to determine the anti-wear properties of lubricants operating under boundary lubrication conditions. The test is performed at a specific speed, temperature, and load. At the end of a specified test period, the average diameter of the wear marks on the bottom three balls is reported. The four-ball overpressure method is designed to evaluate performance at much higher unit loads. The load is increased in increments until the rotating ball engages and welds to the other balls. At the end of each increment, the average scar diameter is recorded. Generally, two values are reported: the load wear index (formerly Hertz load) and the weld point.

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