CONTACT TEMPERATURE 4-BALL

 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
µ  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 et.al.). 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).
 Symbols F Load [N] V velocity [m/s] µ 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]