POSSIBLE WAYS OF REDUCING THE NUMBER OF GEARS IN UNIVERSAL GEAR UNITS

Transcription

1 Snša Kuzmanovć Mroslav Vereš Mlan Rackov ISSN eissn POSSIBLE WAYS OF REDUCING HE NUMBER OF GEARS IN UNIVERSAL GEAR UNIS Summary UDC hs paper analyzes possbltes of reducng the number of necessary gears n the famly of unversal motor gear reducers wth helcal gears, snce both the producton and storage of a large number of dfferent gears cost a lot and mpose a great burden for any gear manufacturer, as t can be seen from lterature [1,2] that focuses on ths problem. he paper partcularly emphaszes the necessty of narrowng down the assortment of gear reducers and the possblty of changng the desgn soluton between the pnon and the electrc motor as they represent the basc possbltes for reducng the number of necessary gears. he paper also ponts out the need for a specal selecton of preferred gear ratos and correspondng gears as one of the possbltes for reducng the total number of gears. hs can certanly result n faster delvery of a gearbox wth the preferred gear rato. Key words: pnon, gear wheel, unversal motor gear reducer 1. Introducton oday, professonal lterature does not consder the problem of determnng the necessary number of gear pars or gear wheels n the famly of unversal motor gear reducers. hs s not consdered to be a serous problem whch should receve closer attenton because as many gears as we thnk are needed are accepted n a gven case. However, determnng the number of gear pars s a very mportant and nterestng ssue, whch must receve close attenton. It s not only because the number of gears serously affects the costs of producton [3] and the cost of storage of gears, sem parts and spare parts n partcular, but also because the number of gears strongly affects the delvery tme of new or rebult reducers. oday, when delvery tmes of unversal gear reducers are very short (sometmes only 72 hours) and when ther prce s very low (due to ferce competton), great attenton must be gven to ths problem, because gears often take up to 50% of the total reducer producton costs. 2. he am of the study he objectve of ths paper s to present basc possbltes and ways of reducng the number of necessary gears n the famly of unversal motor gear reducers [4, 5]. hs s essental because the producton costs of a number of dfferent gears, as well as ther storage RANSACIONS OF FAMENA XXXVIII-1 (2014) 77

2 S. Kuzmanovć, M. Vereš, Possble Ways of Reducng the Number M. Rackov of Gears n Unversal Gear Unts costs [1, 6], are extremely hgh and represent a great fnancal burden for each manufacturer of gear reducers. 3. Descrpton of the problem A very large number of dfferent factors affect the total number of necessary gear pars or gears. Prmarly, t s the company polcy of the manufacturer [7] whch defnes the segment of the market on whch the company wants to put ts gear reducer (Fg. 1). If the company wants to cover a larger segment of the market, t s necessary to produce more szes of the reducer [8], whch certanly requres a larger number of dfferent gear pars, and that ncreases the costs of producton. Dependng on the product range of gear reducers, manufacturers are usually dvded nto three dfferent categores: large manufacturers, that meet almost total demand of the market, medum manufacturers, coverng the hghest demand area as well as a very small lower demand area, and small manufacturers, that are specalzed n, for example, very small reducers, or very bg reducers, or gear reducers n the hghest demand, where they qute successfully compete wth large manufacturers, thanks to some of the benefts of ther products. max 50% 80% 100% mn Fg. 1 Demand for gear reducers on the bass of gear torque and rato mn max Fg. 2 he area of torques and gear ratos that wll be covered wth the projected famly of gears he offered supply should be constantly analyzed wthn the defned segment of the market, especally for reducers of extreme szes, and the justfcaton of ther presence n the producton programme should be observed. he reducton of a large number of gears can be acheved by elmnatng unproftable gears of extreme szes. Of course, sometmes the result of ths step s that customers cannot buy all the szes they need from the same supplers they usually want to. However, ths s not a common case, so ths soluton s mostly justfed for small and medum gear reducer manufacturers. he number of gear pars (gears) s to a large extent defned (lmted) by the range n wdth (gear rato) and n heght (output torque values), Fg. 2 [4,5,9] N / f Bmn N N / f Bmax 2 N / f Bmax Fg. 3 Applcaton felds of the unversal gear reducer accordng to torque values: 1 - the man area, 2 the addtonal area, 3 the crtcal area (used only for short drves), 4 - the area where the reducer s overszed, and 5 the crtcal area where the breakdown of the reducer happens mmedately he next factor that strongly affects the number of gears s the value of the hghest gear rato and nomnal torque. Unfortunately, there are no standards whch gve nformaton about 78 RANSACIONS OF FAMENA XXXVIII-1 (2014)

3 Possble Ways of Reducng the Number of Gears n Unversal Gear Unts S. Kuzmanovć, M. Vereš M. Rackov these data, so the manufacturers of unversal gear unts defne ther own nomnal torque (Fg. 3) and the hghest values of the gear rato wthn the standard recommended shaft heght, 3 takng care to meet q ql f Bmax 2, where q s the factor of ncrease n torque, q L the factor of ncrease n lnear dmensons (shaft heght n ths case) and f Bmax the hghest value of the servce factor. he solutons of leadng manufacturers (for example SEW [10]) are usually adopted as a standard and almost all manufacturers comply wth t n order to provde mutual nterchangeablty of ther gear reducers. hs standard has a relatvely hgh load capacty and medum gear rato (Fg. 4) [4, 11]. Smaller manufacturers of gear reducers have mmedately notced the weakness of such an order and developed a gear reducer wth a lower nomnal torque and a hgh gear rato, so that n certan market segments they can successfully compete wth large manufacturers of gear reducers. Of course, shortly after that, the majorty of large manufacturers responded by provdng two sets of gears wthn the same housng, one set wth hgh load capacty - low gear rato and the other wth small capacty - hgh gear rato. Although ths dramatcally ncreased the number of gears for those manufacturers, t prevented the competton from offerng somethng that the leadng manufacturers dd not have. P em1 max P em2 max P em3 max N1 N2 N3 P em1 mn P em2 mn P em3 mn Fg. 4 orque and gear rato areas covered by partcular manufacturers of gear reducers Introducton of a mddle sze of gear reducers ( NM ), whch s between two standard szes of gear reducers, s a specal reason that nfluenced the ncrease n the number of gears (Fg. 5) [5, 9]. P em1 max P emm max P em2 max N1 NМ N2 P em1 mn P emm mn P em2 mn Fg. 5 orque and gear rato areas covered by certan szes of gear reducers by ntroducng an addtonal sze here s a recommendaton that the shaft heght of the unversal gear reducer should be adopted from the numbers of the standard R20 seres. Snce t s a very dense seres, n the begnnng, the numbers from the R10 seres, whch was not as dense as the R20 seres, were adopted as the shaft heght. However, the R10 seres was soon abandoned and a bt larger shaft heghts were adopted. hese were from the standard R20/2 seres, whch had the same growth factor as the R10 seres. Wth ths new soluton, the housng became a lttle hgher and RANSACIONS OF FAMENA XXXVIII-1 (2014) 79

4 S. Kuzmanovć, M. Vereš, Possble Ways of Reducng the Number M. Rackov of Gears n Unversal Gear Unts a slghtly hgher gear rato could be acheved. In addton, stronger electrc motors (wth a larger flange dameter) could be mounted n ths housng. Wth ths new desgn, large manufacturers of gear reducers tred to get rd of the competton that was not able to nvest n new tools. oday, n the area wth the hghest demand some manufacturers are ntroducng addtonal szes (from the R20 seres) n order to be able to offer a cheaper soluton n certan market segments. Unfortunately, ths new soluton ncreases the number of necessary gears even more. he adopted conceptual soluton of the unversal gear unt has a certan mpact on the necessary number of gear pars. Namely, unversal gear reducers can be produced n varous ways: as sngle-stage, two-stage, three-stage and mult-stage gear reducers. Sngle-stage reducers are usually made n a sngle gear housng. wo-stage reducers can be produced n a specal housng for two-stage gear pars, or n the unversal housng for two-stage and threestage gear pars. hree-stage reducers can be produced n a specal housng for three-stage gear pars, or n the unversal housng for two-stage and three-stage gear pars, or by combnng two-stage and sngle-stage housngs, etc. Some manufacturers do not produce sngle-stage gear reducers, snce there s a relatvely small demand for them on the market. However, there are some manufacturers that produce sngle-stage reducers wth a hgh gear rato the value of whch overlaps wth the area of two-stage reducers, and thus they can successfully compete wth two-stage reducers n a certan segment of gear rato. Of course, there are some manufacturers that do not produce four-stage and mult-stage gear reducers. Regardless of the desgn, every mult-stage reducer has the frst gear par, the second gear par, etc., so the number of gears does not depend on the concept much, but t depends a lot on the hghest gear rato,.e. the nomnal torque of the gear par. If the gear rato s hgh (and the capacty low), there s a larger varety of dfferent gear ratos on offer, whch s good and justfed, but unfortunately t also results n a hgher number of necessary gears. he desgn soluton of the gear reducer has great nfluence on the number of necessary gears. he number of gear pars for the same shaft heght of the housng greatly depends on the space avalable for the gears. herefore, wder housngs are used now, as they enable larger shaft dstances for the same mountng dmensons of the housng. Addtonally, the way of mountng the pnon onto the electrc motor shaft also has a great nfluence on the number of necessary gears. oday, pnons are often ether mpressed nto the shaft of the electrc motor n order to obtan a hgh gear rato, or they are placed on a specal bushng mounted onto the electrc motor shaft. he number of necessary gears also depends on the avalable technology. A hgher gear rato can be acheved wth modern technology so that the pnons can have less than 10 teeth. Also, the concept of the parallel gear unt has been abandoned, and hgh and slow runnng gear chambers have been opened so that bg gears can be placed nsde, etc. 4. How the problems can be solved he most mportant task, regardless of whether a manufacturer produces only snglestage gear reducers, s to defne the magntude of gear ratos and the number of gears (Fg. 6) of the frst gear par. he values of gear ratos are typcally adopted from the standard R10 seres. If the R20 seres were to be appled, there would be too many frst gear pars, especally the pnons, whch are made wth varous openngs (so that they could be mounted on dfferent szes of electrc motors) [12]. he hghest value of the gear rato s adopted dependng on the avalable technology (the pnon wth the smallest number of teeth) and the adopted way of mountng the pnon on the electrc motor shaft. he pnon s usually 80 RANSACIONS OF FAMENA XXXVIII-1 (2014)

5 Possble Ways of Reducng the Number of Gears n Unversal Gear Unts S. Kuzmanovć, M. Vereš M. Rackov mounted on the shaft of the electrc motor. Such an approach lmts the sze of gears and thus the value of the gear rato as well. If we want to use smaller pnons (at a hgh value of the gear rato), the pnons must ether be mpressed n a specal bushng mounted on the electrc motor shaft, or n the shaft of the electrc motor, or the electrc motor shaft must be made as a gear shaft (whch s the most complex and the most expensve soluton). Untl recently, the hghest values of the gear rato of the frst gear par were between 6.3 and 7.1 and nowadays they have ncreased to 8 and even up to he choce of the hghest gear rato to be adopted depends on the adopted gearng concept (hgh gear ratos and a smaller load capacty or vce versa). However, as t has already been sad, t s qute common that two sets of gears are offered for the same shaft heght of the housng. 1 2 Gear rato number Gear rato number Gear rato number 1x Number of gear pars 1x 2x Number of gear pars 1x 2x 3x Number of gear pars Fg. 6 Gear rato dstrbuton for one-stage reducer Fg. 7 Gear rato dstrbuton for two-stage reducer Fg. 8 Gear rato dstrbuton for three-stage reducer For two-stage and multstage reducers, the gear rato s offered accordng to the R20 seres. Gear ratos for two-stage gear reducers are usually obtaned n the combnaton wth two second gear pars (Fg. 7). Gear ratos for three-stage reducers are obtaned n the combnaton of one second and two thrd gear pars (Fg. 8), but t can also be done dfferently. 2 = < 3 em 1x 3x wo-stage reducer 1x 2x 3x hree-stage reducer Fg. 9 Necessary load capacty of gear reducers for partcular gear ratos of reducers Based on the dagram of torque (Fg. 9), certan gear pars of three-stage reducers are dfferently loaded. If we use the concept that two-stage reducers are manufactured n the specal housng for two-stage reducers, and three-stage reducers are manufactured by combnng a two-stage and a sngle-stage reducer, t follows that the frst smaller sze of the sngle-stage reducer wll have to be used for the frst gear par of the three-stage unt, whch s not usually a problem. However, the stuaton changes when the same housng s used for manufacturng two-stage and three-stage gear reducers (whch happens more often),.e. when the same output shaft and gear wheel are used for two-stage and three-stage unts n order to ratonalze ther structure. hese output shafts and gears wll not be used ratonally n the twostage gear unt (f the frst couples from the three-stage reducer are kept), or stronger frst RANSACIONS OF FAMENA XXXVIII-1 (2014) 81

6 S. Kuzmanovć, M. Vereš, Possble Ways of Reducng the Number M. Rackov of Gears n Unversal Gear Unts pars must be used n the two-stage unt (whch s the most common case), so that n the threestage reducer the frst pars must be used from the frst smaller two-stage unt. Some manufacturers defne the same load capacty for two-stage and three-stage gear unts, whle the others offer smaller load capacty not only because the output pars n a twostage unt rotate faster and thus bearngs and gears do not allow such heavy load, but also because the same sze of the electrc motor and the same pnon.e. the openng dameters n the pnons, should be used wth all the stages (Fg. 10). hs s certanly a justfed soluton and t should be appled [1,4]. Determnng the number of necessary (dfferent) pnons wth varous openngs (only for those pnons that are mounted on the electrc motor shaft), for the same gear rato, s done accordng to the dagram of power shown n Fg. 11. hs procedure depends on the sze of the nomnal torque and especally on the electrc motor used (a standard IEC 1 motor or a specal reducer motor), as well as on the sze of the reducer flange. Based on ths dagram (Fg. 11), t s defned for every gear rato whch electrc motors t would be justfable to connect wth such a reducer, and also, openngs n pnons and requred flange dameters of electrc motor are specfed (f t s the case of specal reducer motors), Fg. 12 [5]. 3x 2x 1x P em max = const. N3x P em max = const. P em mn = const. P em mn = const. Fg. 10 Nomnal torque and gear rato areas of gear reducer covered by one-, two- and three-stage unts for the same sze of unversal gear reducer Fg. 11 Nomnal torque changes dependng on the sze of reducer gear rato (n logarthmc coordnates) l 1 l 2 l 3 D 1 d 1 D 2 d 1 D 3 d 1 D 1 d 2 D 1 d 3 Fg. 12 Revew of necessary nstallng dmensons of electrc motors for certan szes of gear reducers 1 IEC motors standard electrc motors covered wth IEC (Internatonal Electrotechncal Commsson standard) 82 RANSACIONS OF FAMENA XXXVIII-1 (2014)

7 Possble Ways of Reducng the Number of Gears n Unversal Gear Unts S. Kuzmanovć, M. Vereš M. Rackov Snce there s no standard n ths feld and f t s possble regardng strength, t s allowed to shft torque values up and down from the projected values. In the fnal determnaton of the torque value, the characterstcs of compettve solutons must be taken nto account, n order to provde mutual nterchangeablty of gear reducers [13]. he value of the output torque for each sze of the gear rato s defned separately, dependng on the load capacty of gears, keys, shafts, bearngs and housngs. Some manufacturers produce the output par wth a dfferent helcal angle for two-stage and threestage reducers, n order to decrease the axal force on the gear shaft of the output par, whch strongly affects the total number of gears. Other manufacturers use stronger bearngs (even cylndrcal roller bearngs), that can take much larger axal force, and n that way avod a large number of gears. he way to obtan dfferent gear ratos (the numbers from the standard R10 seres) depends on the adopted concept of the motor mountng on the reducer housng. he tendency s to have fewer output gears whch are large and expensve and more nput gears whch are small and nexpensve (although ths s not the rule). If the pnon s not mounted drectly on the shaft of the electrc motor, t s not necessary to provde the pnon (for each gear rato) wth varous openngs, whch reduces the number of gears drectly. hs s usually acheved by postonng one pnon wth dfferent bushngs, whch allows for the use of more frst gear couples and less of the other gear pars; t s usually only one or two pars n each next gear stage. hs approach can result n a reducton n producton costs, even though the costs are ncreased due to the applcaton of bushngs or adapters for IEC motors. able 1 ypcal values (R10) of gear ratos of the frst gear couple for the same sze of gear unt and possble mountng connectons (hole dameters n the pnon) wth characterstc szes of electrc motors Szes of electrc motors x x x x 1.60 x x x x 2.00 x x x x 2.50 x x x 3.15 x x x 4.00 x x 5.00 x x 6.30 x 8.00 x Pnon of the nput gear par otal number of gears 100% 100% 61.5% 37.5% Present soluton New proposed soluton Present soluton New proposed soluton Fg. 13 he number of pnons of the nput gear par and the total number of gears n the present soluton and n the new proposed solutons for three-stage gear reducers RANSACIONS OF FAMENA XXXVIII-1 (2014) 83

8 S. Kuzmanovć, M. Vereš, Possble Ways of Reducng the Number M. Rackov of Gears n Unversal Gear Unts If we take nto consderaton only one sze of the three-stage gear reducer desgned for nstallng only four szes of electrc motors (able 1), t s evdent that the pnon has to be made wth dfferent openngs for partcular gear ratos n order to be nstalled wth certan electrc motors. In the analyzed case, ths means there should be 24 dfferent pnons. If the pnons were made only wth the largest hole for each gear rato, t would mean that only 9 pnons would be enough. hat s to say, the number of the pnons would be reduced by approxmately 62%, or the total number of gears would be reduced by 33%, whch s a sgnfcant reducton (Fg. 13). Of course, ths approach requres havng four shafts and four adapter flanges for IEC motors. However, the number of specal reducer electrc motors wth dfferent flanges would be reduced,.e. only four standard IEC motors would have to be kept n stock, whch justfes ths new approach. An obvous example of the justfcaton of ths approach s the company PUJOL whch apples t [10]. As t has been mentoned before, motor gear reducers can be produced wth specal reducer motors (whch are characterzed by specal flanges, specal dameters of the shaft end and stronger shaft bearngs), but they can be also produced wth standard IEC motors, whch are mounted to the housng drectly or through an adapter for IEC motors. Large manufacturers usually use specal motors snce they have many advantages (smpler, cheaper and more compact desgn, the possblty of achevng hgher gear rato, the possblty of heaver loadng of the motor shaft and better tghtness). Snce large manufacturers buy large quanttes of specal motors, they get them quckly and at the cost of standard motors, so ther way of manufacturng completely pays off. Also, large manufacturers usually have ther own electrc motor factory, so they usually do not have a problem wth buyng specal motors. Smaller manufacturers are forced to use standard IEC motors, manly due to the prce and the delvery tme, and they try to compensate for all the advantages of the specal motor by attachng the motor wth a reducer n a sutable way. Snce t s very dffcult to compensate for all of the advantages of the specal motor, we can see very dfferent desgn solutons n practce. Fg. 14 A characterstc soluton for the two-stage gear reducer wth an adapter for IEC motors, manufacturer PUJOL A successful example s the manufacturer PUJOL [10] whose producton program has only gear reducers wth an adapter for IEC motors and the classcal output shaft (Fg. 14), but they also delver motor gear unts,.e. they nstall standard IEC motors on ther reducers wth an adapter for the IEC motor. hs soluton provdes fast delvery of cheapеr standard IEC motors and the number of pnons s largely reduced (only one hole sze s used n the gear), whle specal flanges, specal bushngs and a par of bearngs are always delvered wth the standard IEC motors. Of course, all ths complcates the producton, but for smaller manufacturers t s a secure way to reduce the number of gears and thus smplfy the producton. 84 RANSACIONS OF FAMENA XXXVIII-1 (2014)

9 Possble Ways of Reducng the Number of Gears n Unversal Gear Unts S. Kuzmanovć, M. Vereš M. Rackov Only four-poles (three-phase asynchronous) motors are consdered n defnng the requred motor power, because they have the best startng characterstcs and are the easest to purchase. Dfferent motors can be also delvered as the motor gear drve, but usually at a hgher prce. In order to reduce the number of gears that need to be kept n stock, some manufacturers emphasze the preferred rato, whch they can offer mmedately (these values are usually prnted n bold n catalogues), whle for other ratos they offer longer delvery tmes. hs practce could be a soluton for other manufacturers of gear reducers as well. 5. Concluson In the famly of unversal gear reducers, selectng the smallest possble number of gear pars and gears s of utmost mportance. Reducng the number of gears can be acheved n the followng ways: by narrowng down the range of reducers, by modfyng the method of mountng the pnon on the shaft of the electrc motor, by modfyng the way of combnng gears, by emphaszng preferred gear ratos and correspondng gears whch are used wthn certan gear ratos, by makng a more ratonal choce of the electrc motor sze (power), etc. A partcularly nterestng opton for reducng the necessary number of gears s usng adapters for IEC motors. hs soluton enables a large reducton n the number of dfferent gears and electrc motors that need to be kept n stock. hs s favourable for faster delvery and easer and faster servce (or repar) of gear reducers. In fact, nstead of three types of gear reducers, only two types are made, and nstead of fve or sx types of electrc motors (szes of flange on the motor), only one type of electrc motor s used (the standard IEC motor wth ts flange). It s certanly a great advantage that should not be gnored by smaller and medum manufacturers of gear reducers. REFERENCES [1] Kuzmanovć, S., Rackov, M. (2009). Development endences of Unversal Gear Reducers, Proceedngs of he 3 rd Internatonal Conference Power ransmssons 2009, 1-2 October 2009, Kallthea, Greece, Ed.: A. Mhalds, p [2] Nemann, J., chkewtch, S., Westkamper, E. (2009). Desgn of Sustanable Product Lfe Cycles, Sprnger Verlag, ISBN , Berln, Hedelberg [3] Anšć, Z., Krsmanovć, C. (2008). Assembly ntated producton as a prerequste for mass customzaton and effectve manufacturng, Strojnšk vestnk Journal of Mechancal Engneerng, vol. 54, no. 9, p [4] Kuzmanovć, S. (2009). Unversal Gear Reducers wth Cylndrcal Gears, Unversty of Nov Sad, Faculty of echncal Scences, Nov Sad, 231 p. (n Serban) [5] Kuzmanovć, S., Rackov, M. (2009). Usual Possble Ways of Increasng of Speed Ratons Values of Unversal Gear Reducers, Acta echnca Napocenss, echncal Unversty of Cluj-Napoca, Romana, No. 52, Vol. III, p [6] Manć, M., Mltenovć, V., Stojkovć, M., Banć, M. (2010). Feature Models n Vrtual Product Development, Strojnšk vestnk - Journal of Mechancal Engneerng, vol. 56, no. 3, p [7] Kuzmanovć, S., Ianc, S., Rackov, M. (2009). Lfe Cycle Influence on the Polcy of Product Development, Annals of the Oradea Unversty - Fasccle of Management and echnologcal Engneerng, ome VII, p [8] Kuzmanovć, S., Smonovsk, P. (2009). Justfcatons Analyss of Unversal Gear Reducer Assortment Extenson, Mechancal Engneerng Scentfc Journal, Vol. 28, No. 1, p [9] Pandev, G. (2009). Gear Rato Determnaton of a Hgh-rato Gear Reducer, Proceedngs of he 3 rd Internatonal Conference Power ransmssons 2009, 1-2 October 2009, Kallthea, Greece, Ed.: A. Mhalds, p RANSACIONS OF FAMENA XXXVIII-1 (2014) 85

10 S. Kuzmanovć, M. Vereš, Possble Ways of Reducng the Number M. Rackov of Gears n Unversal Gear Unts [10] Catalogues: Nord G1000 (2010), Lenze L-force (02, 2010), Ross ES07 (12, 2010), Semens D87.1 (2010), Bonfglol (2010), PUJOL (2010) [11] Kuzmanovć, S., Ianc, S., Rackov, M. (2010). Analyss of ypcal Method of Connecton of Electrc Motor and Gear Unt n the Frame of Unversal Motor Gear Reducers, Machne Desgn 2010, Faculty of echncal Scences, Nov Sad, p [12] Kuzmanovć, S.; Rackov, M., Veres, M. (2009). Product Lfetme, Scentfc Proceedngs 2009, Faculty of Mechancal Engneerng, SU n Bratslava, Bratslava ISBN , Palcak, F. & Horvat, M. (Ed.), p [13] Zadnk, Ž., Karakašć, M., Kljajn, M., Duhovnk, J. (2009). Functon and functonalty n the conceptual desgn process, Strojnšk vestnk - Journal of Mechancal Engneerng, vol. 55, no. 7-8, p Submtted: Accepted: Snša Kuzmanovć Unversty of Nov Sad, Faculty of echncal Scences, Nov Sad, Serba Mroslav Vereš Slovak Unversty of echnology, Mechancal Engneerng Faculty, Bratslava, Slovaka Mlan Rackov Unversty of Nov Sad, Faculty of echncal Scences, Nov Sad, Serba 86 RANSACIONS OF FAMENA XXXVIII-1 (2014)