The extreme pressure version of the four-ball rig, ASTM D2783 for oils and D2596 for greases, run at 1760 rpm with a fresh set of balls for each 10-second step of rising load. It reports the weld point, the load in kgf at which the spinning ball seizes and welds to the others, and the load wear index averaged over the steps before welding. Plain oils weld around 120 to 160 kgf, while good EP greases reach 250 kgf and beyond.
Four-ball EP on the moly grease welded at 400 kgf, the plain lithium let go at 160.
Also heard as
- four-ball EP
- weld load test
- 4-ball EP
Related terms
Four-ball wear test
Bench test that spins one steel ball against three clamped balls in a lubricant and measures the wear scars.
EP
Extreme pressure: additives or oils that react with metal under heavy load to prevent welding and scuffing.
Scuffing
Sudden, severe adhesive damage where the oil film fails and sliding surfaces locally weld and tear.
Moly
Shop name for molybdenum disulfide, the black solid lubricant, or for any grease that contains it.