Proceedings of SerbiaTrib '13

Figure 7 shows the scuffing on wheel toothflanks for different material variants. Withexception of S1, scuffing occurred on all materialvariants. On wheels made from materials S2 andS3, under load of T 2 = 16 Nm and T 2 = 20 Nm, thephenomenon of scuffing and significant increase ofwear surface and gear forces were observed. Underoutput torque of T 2 = 28 Nm, and input speedn 1 = 5000 min -1 scuffing occurred for S4 and S6.Gear loads rose and, suddenly, the failure of wormshaft occurred. On material variant S6 “2% copperaddition”, scuffing occurred on tooth root in trialswith input speed n 1 = 5000 min -1 and output torqueof T 2 = 28 Nm, and a very short running time of ca.10 minutes. Scuffing also occurred on wheel toothflanks with speed n 1 = 5000 min -1 and output torqueof T 2 = 36 Nm for material variant S5 sinterhardening.7. MAXIMUM OUTPUT TORQUEFigure 8. Comparison of maximum transmissible torquewith critical damage type for different materials andinput speed n 1 = 5000 min -1 [8]Figure 8 shows maximum transmissible torque,as well as the type of critical damage, in a bar chart.With an output torque of T 2 = 20 Nm, materials S2(case hardening) and S3 (case hardening and shotpeening) were damaged due to scuffing. MaterialsS4 (pyrohydrolysis) and S6 (2 % copper addition)were damaged by pitting when output torque wasT 2 = 24 Nm, and by scuffing at the value ofT 2 = 28 Nm. Without an additional treatment, S1had the most critical wear and some pitting atoutput torque of T 2 = 28 Nm. The wheels S5(sinter-hardening) had the greatest load carryingcapacity, its maximum transmissible torque being32-36 Nm, and the scuffing being the mostdangerous damage form in this case.8. CONCLUSIONSThe research in this paper shows thattribological parameter of worm-and-gear has greatinfluence on working characteristics in exploitationconditions. The material characteristics likemicrostructure, wear load capacity and damagetypes of molded parts can be significantlyinfluenced by additional treatments for sinteredsteel.The Hertzian contact stress of teeth in contactdepends on the choice of lubricants. The smallestwear occurred in experiments with synthetic oilwhen Hertzian contact stresses were largest.Synthetic oil can resist the pressures of 1400N/mm 2 at sliding velocity v gs = 2.53 m/s.All experiments with different material variantsshow that additional treatments have significantinfluence on wear. Under identical experimentalconditions, the maximum wear δ wn occurred in thetrials with wheels of material variant with casehardening (115 µm) and the minimum with wheelswith sinter-hardening (7.8 µm).The pitting was observed in wheels of materialvariants S4, S5 and S6 by output torque from 16 to32 Nm. The initial pitting on the tooth flankoccurred on material variant without additionaltreatment (trials with T 2 = 20 Nm; t = 120 h; n 1 =5000 min -1 ; lubricant: synthetic oil). Destructivepitting on tooth flank occurred in material variantsinter-hardening (T 2 = 20Nm; t = 120h; n 1 = 5000min -1 ; lubricant: mineral oil).With exception of S1, scuffing occurred on allmaterial variants. The scuffing was the critical typeof damage for wheels from material variants S2 andS3 under the output torque of T 2 = 20 Nm withn 1 = 5000 min -1 and by S5 under the output torqueof T 2 = 36 Nm. For wheels of material variant S6,scuffing occurred for trials with n 1 = 5000 min -1and output torque of T 2 = 20 Nm. For wheels ofmaterial variants S4 and S6, the critical type ofdamage was the combination of pitting andscuffing.Lubrication with synthetic oil is the mostfavorable from the aspect of wear and in terms ofachieving hydrodynamic lubrication. Optimalworking lubrication was obtained for the rotationspeed n 1 = 5000 min -1 or sliding velocity v gs = 2.53m/s.REFERENCES[1] M. Hochmann: Tragfähigkeit vonZahnradpaarungen bei Schmierung mitGetriebefetten, Forschungsbericht, DGMK, 2007.[2] DIN 3990: Tragfähigkeitsberechnung vonStirnrädern, 12/2002.[3] S. Dizdar, P. Johansson, A.B. Höganäs, 263 83Höganäs, Sweden: P/M Materials for GearApplication; EURO PM2007, Tolouse October 16,2007.326 13 th International Conference on Tribology – Serbiatrib’13