Four-Ball Wear Test: ASTM D 2266 describes a test method using three hard steel balls in a locked position. A fourth ball is rotated against the three stationary balls, producing a wear scar on each of the three balls, the average wear scar diameter. This test is run at light loads. Seizure or welding does not occur.

Four-Ball EP Test: ASTM D 2596 describes a similar test as the Four-Ball Wear Test except that the loads are much higher. The load at which the balls weld together is referred as the weld load. EP Lubricant additives result in a high load-carrying ability.

 Calculation of the contact temperature as a result of frictional heating1.
 F N K1 W/mK
 n rpm K2 W/mK
 D mm k2 10-6 m2
   H GPa
  (default value of ball bearing steel)
 F N  v m/s  r mm
 Ar /An  rj 10-6 m    
 dTbulk C  dT'flash C  dT C
1Ashby, M.F., Abulawi, J., Kong, H.S., 1991, "Temperature maps for Frictional Heating in Dry sliding", Tribology Transactions, Vol.34, Number 4, October 1991, pp577-587.

The flash temperature in the asperity summits is found by entering a representative value for the contact radius of the junctions, i.e. rj=0.1e6/H  (Ashby

At a depth of 0.5 times the asperity radius the flash temperature is for 90% leveled out and reaches the interfacial bulk temperature.

With increasing contact pressure, Ar grows until it equals An, and the distinction between dTbulk and dTflash disappears. To achieve this dT=dTflits+(1-Ar/An)dTbulk, where Ar is the real contact area under tractive load (Johnson, 1968).

 F Load [N]
 V velocity [m/s]
  coefficient of friction [-]
 r contact radius [m]
 K conductivity [GPa]
 k diffusivity [W/mK]
 HB Brinell Hardness GPa
 dTbulk bulk temperature increase [C]
 Ar real contact area [m]
 An nominal contact area [m]
 dTflash flash temperature [C]