Flash temperature is indicated by AGMA as a suitable index for evaluation of the scoring resistance of gears. In the AGMA formula, flash temperature is divided into flash rise of temperature and initial temperature, and the latter is suggested to be the temperature of oil inlet. In this research, the initial temperature and its distribution of carburized spur gears were measured by using of fine thermocouples. The results show that initial temperature is much higher than the temperature of oil inlet, and it is strongly affected by rotational velocity, tooth surface roughness, rate of lubricant supply and the extent of profile modification. It is found that lower roughness, appropriate extent of profile modification and higher rate of lubricant supply are effective for decreasing the initial temperaure, which results in the improvement of the scoring resistance of gears.
