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ASTM D2596 – Four-ball EP (extreme pressure) test for load-carrying capacity of lubricating grease


Common Test Names: 4-Ball EP, Four Ball Extreme Pressure, 4-Ball Weld, Load Wear Index

Property Analyzed:  Load carrying ability of a lubricating grease under extreme pressure: Load-Wear Index (LWI), Last Non-Seizure Load (LNSL), Weld Point (WP).

Test Method: ASTM D2596

Unit of Measure: kg

Products Typically Tested: Grease

How Data is Used: Comparison of greases and/or additives to determine the greatest load that the lubricant can bear before welding / galling occurs between the moving surfaces.

Product Application / Market Sector: Bearing Grease for Heavy Equipment Including Mining and Construction Equipment, Industrial Equipment Where Heavy Loads are Typical i.e. Steel Mills, Pulp/Paper, Presses 

Similar / Complimentary Tests:

ASTM D2783: Four-ball EP for liquids/oils

ASTM D2266: Four-ball (wear scar) for grease

ASTM D4172: Four-ball (wear scar) for liquids/oils

ASTM D2670: Falex Pin on Vee Test

ASTM D3233: Falex Pin on Vee EP Test

ASTM D2782: Timken Method for liquids/oils

ASTM D2509: Timken Method for grease

Test Duration and Environment: 4 hours, samples are normally run at ambient temperatures.

Sample Size Requirement: 500 g


Test Overview:

The Four Ball EP test (ASTM D2596) measures the ability of grease to prevent wear during pure sliding contact under extreme pressure caused by heavy loads.

Failure Mechanism of Product Tested:

Adhesive Wear: also known as scoring, galling, or seizing. It occurs when two solid surfaces slide over one another under pressure. Surface projections, or asperities, are deformed and eventually welded together by the high local pressure. In bearings and gears the metal surfaces are actually separated by lubricating oil or grease. The lubricant is under enormous pressures which can generate temperatures in access of 2000ºF. As sliding continues, the lubricant is compromised and metal to metal contact occurs. The molecular bonds in the metal part are broken, producing surface cavities, projections, and abrasive particles, all of which contribute to abrasive wear.

Testing Specifics:

The 4-Ball Extreme Pressure (EP) test is performed by placing three ½-inch diameter steel balls in a test cup filled with the test grease.  A fourth ball is placed in the instrument chuck and brought into contact with the three lower balls.  An 80kg load is applied and the motor is turned on for 10 seconds which turns the top ball relative to the three stationary balls.

The size of the wear scar on the three stationary balls is measured and the test is repeated at a different load.  The test is typically performed 10 to 12 times at progressively higher loads until the balls weld together.

Reported Test Values:

Weld Point, reported in kg, is the lowest load at which the four balls weld together. A higher weld point indicates a more effective extreme pressure lubricant.

Load-Wear Index (LWI), reported in kg, quantifies the relative wear protection under load of a lubricant.  A higher load-wear index indicates a more effective extreme pressure lubricant.

Last Non-Seizure Load (LNSL), reported in kg, is the highest load at which elasto-hydrodynamic lubrication is in effect before the transition to boundary lubrication and metal to metal contact.  A higher last non-seizure load indicates a more effective extreme pressure lubricant.

Test Images:


For additional information on this test method or to purchase a copy of the method, please click HERE to open a new window and visit the ASTM website.