the influence of overhung and axial loads at output shaft of universal ...

2 / 3 3( ν n) d−7M0 = 10 f0m(7) P 1 – the load determining the frictional moment, N forparticular bearing and load:if ν n ≥ 2000 or usingP 1 = 3 F Aa perm – 0.1 F R perm (11)−73M0 = 160 × 10 f0dm(8) Frictional moment (M 2 ) which depends mostly on theif ν n < 2000, where:axial load can be calculated as follows:d m – mean diameter of bearing (for particular bearingM 2 = f 2 F Aa perm d m (12)d m = 0.5 (d + D) = 0.5 (30 + 72) = 51 mm)where:f 0 – a factor depending on bearing type and lubrication f 2 – a factor depending on bearing design and(for particular bearing f 0 = 1)lubrication (for particular bearing design andν – kinematic viscosity of the lubricant at the lubrication f 2 =0.006)operating temperature, mm 2 /s (for usual operating The frictional moment (M 3 ) of the seals for a sealedtemperature Θ = 40°C)bearing can be estimated and for particular bearing itTable 1. Results of calculation of a typical worm gearreducer without a fan with shaft height 80 mmThermal capacity – P Q , W 1500 920 280Permissive overhung forceof output shaft – F R perm , N3260 5370 5300Permissive axial force ofoutput shaft – F A perm , N5520 7800 7800Actual permissive axialforce when overhung andaxial loads simultaneously 1304 2148 2120acting on output shaft – F Aaperm, NSpeed ratio – u 5.4 26 79Revolution number ofoutput shaft – n, min -1 259 54 18Mean diameter of bearing –d m , mm51 51 51Kinematic viscosity of thelubricant at the operating 53,6 210 544temperature – ν, mm 2 /sLoad independentfrictional moment – M 0 , 7.66 6.7 6.07NmmLoad-dependent frictionalmoment – M 1 , Nmm68.62 148.73 145.74Axial load-dependentfrictional moment – M 2 , 399.02 657.29 648.72NmmFrictional moment of seals– M 3 , Nmm18 18 18Total frictional moment ofbearing – M, Nmm493.3 830.71 818.53Additional power losses ingear reducer – P L , W13.41 4.71 1.55Percent ratio of powerPLlosses – ⋅100, %0.89 0.51 0.55PQThe load dependent frictional moment (M 1 ) arisesfrom elastic deformations and partial sliding in thecontacts and predominates in slowly rotating, heavilyloaded bearings. It can be calculated from:M 1 = f 1 P 1 d m (9)where:f 1 – a factor depending on bearing type and load forparticular bearing and load:0.55⎛ FRperm ⎞f1 = ( 0.0006K 0. 0009)⎜ ⎟(10)⎝ C0⎠is calculated as M 3 = 18 Nmm.For a smaller size of gear reducer (with shaft height h= 80 mm) orientation values of frictional moments andadditional losses of power in worm and helical-wormreducer are calculated and shown in Table. 1.Based on carried out calculation it follows that theadditional power losses in the gearbox, with themaximum permissive overhung and axial loads of theoutput shaft, amounts about 1%, so that they can becompletely ignored. On the basis of this, it is quitejustified that manufacturers of gear reducers, whenmake the instruction for selecting gearbox, ignore theinfluence of external loads on the thermal capacity ofgear unit and thus considerably simplify their selectionof gear reducer.CONCLUSIONBased on the conducted analysis it can be seen that theexternal overhung and axial loads of the output shaftof worm and helical-worm gear reducers have a smallinfluence on the change of thermal capacity, about 1%,so that manufacturers of gear reducers ignore it with afull right, i.e. they do not take external forces intoaccount when selecting gearbox and do not makecorrection in thermal capacity. Also, it would beinteresting to see what influence has only axial forceat the output shaft, because in this analysis axial loadis 0.4 of permissive overhung load, but when just axialforce is applied, it can be much bigger.REFERENCES[1] KUZMANOVIĆ, S., Universal Gear Reducers withCylindrical Gears, University of Novi Sad, Faculty ofTechnical Sciences, Novi Sad, 2009. (in Serbian)[2] Catalog SEW Eurodrive, Movimot Gearmotors, Edition04/2004[3] SKF General Catalogue, 2007[4] Catalog Nord, Constant speeds, G1000/2008,Getriebebau Nord, Hamburg[5] Catalog Siemens, Flender Gear Units, Catalog MD 20.1-2009AUTHORS & AFFILIATION1. Siniša KUZMANOVIĆ,2. Milan RACKOV1-2. UNIVERSITY OF NOVI SAD, FACULTY OF TECHNICAL SCIENCES,NOVI SAD, SERBIA58