AGMA 90FTM8-1990 pdf free.Investigations on the Scuffing Resistance of High – Speed Gears.
In many test runs the temperature in the center of one pinion tooth was measured. It is known, that temperature strongly affects the scuffing resistance. Some factors, necessary for the calculation of surface and bulk temperatures have to be extrapolated to high speed, because there are no measured data available, for example the coefficient of friction and the coefficient of heat transfer from the gear to the oil.
To determine, whether this extrapolation is valid for the used test gears, Fig. 7 shows the measured tooth center temperature and the calculated bulk temperature according to Iso 633614 [9]. Because of the good correlation it is possible to use I] to calculate the bulk temperature at high speed.
The bulk temperature increases with speed in a degressive curve (Fig. 8) and nearly linear with load (Fig. 9). At high speed the bulk temperature is nearly independent of the speed.
6 Factors influencing the Sculling Load
6.1 011 Temperature
The scuffing load is found to be directly dependent on the gear temperature and only indirectly dependent on the load at low and at high speed (Fig. 9). When the oil inlet temperature is increased, the scuffmg load decreases. The critical bulk temperature at scuffing conditions is independent of the oil inlet temperature.
Obviously, the critical temperature is not the same at different speed. In the test, the critical bulk temperature at 51 m/s was about 50% higher than at 23 m/s pitch line velocity.
6.2 Lubricant
All test lubricants are commercial oils. Some are compounded with commercial EP-additives. The main lubricant data are given in table 1.
The results of all tested lubricants show the same scuffing load-speed characteristic: the scuffing load decreases with speed in the medium speed zone and increases at high speed.
6.2.1 VIscosity
A comparison of the results of two non-EP turbine oils shows, that the scuffing load of lub’icants without EP-additives increases as expected with viscosity. This influence is independent of speed (Fig. 10).
The same turbine oils were compounded with 0.4 percent in weight of a commercial ZnDDTP-additive package (oils Z22, Z49). Now the scuffing load greately increases and the shape of the curves is different from that of the the non-EP oils. But there is no significant difference in the scuffing load between both EP-containing oils of different viscosity. The lower vircosity oil shows an even steeper increase of scuffing load with speed than the higher grade oil.AGMA 90FTM8 pdf free download.