Proceedings of SerbiaTrib '13

flowable at high temperatures and very viscous atextremely high temperatures. The best oil in thissense is the Klüber GH6 1500 oil.5. HERTZIAN CONTACT STRESSThe Hertzian contact stress has a significantinfluence on the wear rate and the width of the wearsurface. The Hertzian contact stress in the crossedhelical gears can be determined as the Hertziancontact stress of globoid wheel. It should be takeninto consideration that the Hertzian contact stresson the crossed helical gear depends on the width ofthe wear surface. Therefore, a correlation betweenthe width of the wear surface b V and thedimensionless ratio p m * [5] is introduced. TheHertzian contact stress by the dimensionlessparameter of the average Hertzian contact stressp m,V * is taken into account. The new Hertziancontact stress Hm can be calculate for the averageHertzian contact stress p m,V * according to Equation1, depending on the output torque T 2 , the E-ModuleE red and centre distance a s .4 p EredHm (1)*m, VT210003asAccording to the tests for sintered steelFe1.5Cr0.2Mo with sintered-hardening (S5), thevalue of E-Module is E 2 = 203759 N/mm 2 .Therefore, for the material combination of wormmade of 16MnCr5 and wheel made of sintered steelFe1.5Cr0.2Mo, the value of the reduced E-Moduleis E red = 227288 N/mm 2 .The Hertzian contact stress that depends on thewidth of the teeth p m,V * can be calculated usingEquation 3. The ratio of the width of the globoidwheel b 2H to the width of wear surface b v takes intoconsideration the increase of the Hertzian contactstress with decreasing width [6].0,8614 b 2Hp m, V pm(2) bvFigure 3 shows the resulting Hertzian contactstress of all tests with different lubricants andn 1 = 1500; 5000 und 10000 min -1 . In the first loadstep output torque is 12 Nm, each next step outputtorque T 2 is increased by 4 Nm, and the timeduration of load level is set at 40 hours.Higher torques leads to the increase in pressure.There is no great difference in pressure values ofHertzian contact stress for lubrication with mineraland synthetic oil for the rotation speed n 1 = 1500min -1 or sliding velocity v gs = 0.76 m/s. For greaselubrication, the Hertzian contact stress is onaverage half the size in relation to mineral andsynthetic lubricating oil.There is great difference in pressure values ofHertzian contact stress for lubrication with mineraland synthetic oil for the rotation speedn 1 = 5000 min -1 or sliding velocity v gs = 2.53 m/s.The values of Hertzian contact stress with syntheticoil are for about 65% higher compared tolubrication with mineral oil. Hertzian contactstresses for lubrication with synthetic oil goes up to1400 N/mm 2 .Herzian contact stress Hm [N/mm 2 ]Herzian contact stress Hm [N/mm 2 ]Herzian contact stress Hm [N/mm 2 ]160014001200100080060040020001000900800700600500400300200100016001400120010008006004002000n 1 = 1500 min ‐18 12 16 20 24 28 32 36 40n 1 = 10000 min ‐1Output torque T 2[Nm]synthetic oilmineral oilgreasesynthetic oilmineral oil4 8 12 16 20 24Output torque T 2 [Nm]n 1 = 5000 min ‐18 12 16 20 24 28 32 36Output torque T 2 [N]synthetic oilmineral oilFigure 3. Hertzian contact stress Hm for duration of theexperiment with different lubrication and n 1 = 1500;5000 and 10000 min -1For the rotation speed n 1 = 10000 min -1 orsliding velocity v gs = 5.05 m/s up to the number ofload changes N L = 0,9×10 6 values of Hertziancontact stress are greater for mineral oil lubricationas compared to synthetic lubricating oil. Then it13 th International Conference on Tribology – Serbiatrib’13 323