The Sequential Four Ball Test

Drew Troyer

Use it to Evaluate AW / EP Performance

The plant oil analyst is responsible for ensuring the continued effectiveness of lubricants in service and is often involved in the lubricant selection process. In the case of antiwear (AW) or extreme pressure (EP) lubricants the ability to resist scuffing is the primary concern. In oil analysis, the ability to test the depleting performance of AW/EP additives in used and reconditioned lubricants has traditionally been a daunting task. Researchers at Pennsylvania State University have developed a promising new test procedure called the Sequential Four-Ball Test (SQFBT) that could prove useful to the plant oil analyst and commercial laboratory.

The SQFBT procedure is a variation on the conventional Four-Ball Tests described in current ASTM standards. Four-Ball tests, as the name implies, employ four half-inch diameter steel balls, one ball rotating in one direction within a cradle of three stationary balls. The scar on the rotating ball is measured to determine the lubricant’s anti-scuffing capabilities. A small scar signifies good performance. The test is conducted under controlled conditions of temperature and load.

The SQFBT procedure is a three-step sequence that begins with an initial 30-minute test using the fluid of interest and the initial scar is measured and recorded. Then, the fluid is tested for an additional 30-minutes and the change in scar size is measured. This change signifies the lubricant’s anti-scuffing performance unfettered by “run-in” scarring that normally occurs. The last step replaces the test lubricant with additive-free white oil for a final 30-minute run. An AW or EP lubricant should provide lasting protection by depositing additive onto the component’s surface. This third step of the SQFBT evaluates the additive’s lasting effect. This is significant to ensure protection during start-up, lubricant starvation or when shock loading leaves the machine short of bulk lubricant supply.

To the oil analyst and lubrication engineer, this test could possibly help evaluate the anti-scuffing capacity and lasting performance of different lubricants under consideration for selection. It could also be added to the test
arsenal when comparing the residual AW or EP performance of a used lubricant to the new lubricant performance. By setting minimum performance limits, the procedure could suggest when an oil needs to be changed or enhanced. A possible application for the procedure would be when AW hydraulic fluids are reconditioned after many months of service. Before returning the fluid to service, this test could help confirm the “like new” condition as it relates to anti-scuff capabilities has been achieved.

Reference: Perez J. D. Weller, Jr. and J. Duda (1999) “Sequential Four-Ball Study of Some Lubricating Oils,” Lubrication Engineering, September, pp 28-3

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