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UNIT 2 DTS Notes

The document discusses various aspects of belt drives, including their characteristics, factors affecting power transmission, and types of belt drives. It outlines the selection criteria for mechanical drives, maintenance considerations, and the materials used for belts. Additionally, it describes different configurations of belt drives such as open, crossed, and stepped drives, as well as concepts like slip and creep in belt operation.

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33 views11 pages

UNIT 2 DTS Notes

The document discusses various aspects of belt drives, including their characteristics, factors affecting power transmission, and types of belt drives. It outlines the selection criteria for mechanical drives, maintenance considerations, and the materials used for belts. Additionally, it describes different configurations of belt drives such as open, crossed, and stepped drives, as well as concepts like slip and creep in belt operation.

Uploaded by

venukumar0810
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF or read online on Scribd
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INTRODUCTION ‘The power tami fom one shaft mathe sha acompsed ser by Mele connectors or by dct ont. Owing pad crep of sch connector ‘he mea vehcy to of ving and even member stant Bek ives ai sto claications «Flat tet dive and Vb ive. V-teh dive explain i ete ee For ramming power Nenana at conde tae sft deve mont commonly wed. The centre dtance may bea age a 15 (5 sat cree my enced hi in sme cate, Ft be dive i of rteguler eer sectonconacting two pulleys which are mounted wpe two shaft. The power am om shat swans anther pulley by ton between te and pulley srices ‘he force f tc between ving pulley ad Re es the Det and tha ences ‘et an ven ply dvs the dren paey a. Ane ‘State the characteristis of Belt drives. Characteristics af belt drives : (1) They a used for eatvely centre distances (2) The angular velocity ratio between the shafts i miher constant nor cxacty equal to the ratio of pulley diameters because of slip and rep of bets (3) tt possible to obtain the clutch action when fai bets ae wed, withthe hep of the fast and loose pulleys (4) itis possible to vary the angular velocity ratio, within a range, with the help of ye drives by employing a spring louded pli alley (9) An economical means of changing the velocity ration discreet steps ean be cbained by employing stp Pues (6) Some provision to adjust the cenre distance is always required in petdrve. 02. On which factors amount of pomer transmitted depends? ‘Awa The amount of power transmited depends upon the flowing fue (1) The velociy of bet. (2) The enion under which the Be spaced on pulleys @) Trea of contact between the belt and smaller palleys. (6) The conditions under which the belts wed, sara 3. oR o “ uy ow rc) Ans, o ® ® ‘Oa whieh factors seecto Write # short note on the factors considered for selection of was) f mechanical drive depends? smechanleal drive, “The selection of proper mechanical drive for # given app depends upon a umber of factors such at centre distance, velocity rai siting arrangement, maintenance considerations and cost “Te guidelines for selection of suitable mechanical drive for the iven applcaion area follows Flat bts and rller chains are suitable for long cere distances, V- ‘ets have comparatively short centre distances. Gar drives have the mallet cent distance between wo shai tn at bet ives, the bel slips over the pulley. Therefor, the driven alley rotates a sped which i ess than that calculated by the rato of diameters ofthe driving and driven pulleys. Due to slip, the velocity ratio is not constant, Therefore, Mat belt drive is not recommended where constant speed is desirable. In case of chain ‘rives, the velocity ratio is nt constant during one revolution of the sprocket wheel due to ‘polygonal’ effect. Gear drives are preferred {in ppliations which require constant speed. In some applications, shifting mechanism is required to obtain iferent speeds such as headstock of lathe or automotive gearbox. Flat belts with relatively long centre distances can be shifted from tight to lose palleys. Spur gears can be shifted on splined sha. In ‘ase of V-belts or chain drives, i isnot possible to use the sifting mechanism ‘Maintenance of belt drives i elatively simple, I usually consists of Periodic adjustment of centre distance in order 10 compensate the stretch of the be. In chain and gear drives, Wbrication is an ‘important consideration in maintenance, Flat belt drive is the cheapest, V-belt and chain drives ave ‘comparatively costly, and gear drives are costliest ‘State the various types of belt drives ‘The belt drives ar usualy casifid into the following tee groups: Light drives : These are used 10 transmit small powers at belt speeds upto about 1On/s as in agricultural machines and small rachine tos. Medium drives: These are used to transmit medium powers a belt speeds over 10 mvs bu upto 22m, as in machine tok Meany drives: These ae used to wansits large power at belt ‘speeds above 22 mia in compressor and generators. fon o ® owing are important fom thes subject point of view Frac bett ‘The flat bel consists of «strong clastic cores eather or rubber rToUnded by come or special applications textile bes or haat bls are used Flat belts are very efficient for high speeds, they are ‘transmit large power overlong centre ite, they can tances, "They don’t require large pulleys. They can transmit power around ‘commer or between pulleys at right angles to eachother, ‘The Mat belt shown in Fig), ‘mostly used inthe factories and ‘workshops, where moderate amount of power isto be transmited, The Vetch are made of cords or strands wealy of eto, rayon or mle, snd impregnated with ber, Because of wedsing action between the bel and pulley groove, he power ‘ranamiting capacity ofa V-betisinceaed in comparison tbe. ‘These bes re wed with salle pllyand at shorer cexre anes ‘These drives area ecient han Mla belt drives bus namber of them can be ‘sed on singe pulley ‘These belts are endless which eliminates the joins used in at bets. ‘The V-belt as shown in Fig(), is mostly used in the factories and workshops, where a great amount of power is to be transmitted, from one pulley to another, when the two pulleys are very near 10 each othe, Cireular belt or rope : ‘The circular belt or rope is shown in Fig () is mostly used in the factories and workshops, where a great amount of power is to be \ransmited, from one pulley to another, when the two pulleys are ‘more than metves apart. en Circular bett anna (@) Flat belt (0) Vebett Fig. Types of belts (©) Circular bett ” @ sient In such w case, wide pulleys (fr V belts oF eirult umber of grooves are used ‘Then a bet in each groove 2 provided to transmit the required mount of power from one pulley to another Link V-betts ‘These eh are composed of large number of rubberized fabric links joined by suitable metal fasteners ‘They ae special purpose belts ‘Timing bets: “These are made of rubberized fabric and steel wire having teeth hich fit into grooves cut onthe periphery ofthe pulleys. ‘They transmit powers constant angular velocity ratio Hence they re wed in situations where constant velocity ratio is required through a exible drive. lar belts) with a Describe various material used for belts. Material ued for belts ‘The various materials used for belts are as follows: Leather tis the most commonly used material for bets ‘Leather may be either oaktanned or mineral sal-tannede g. chrome tanned. Oak-tanned leather is mostly used in ordinary application whereas {for special applications involving. damp environment, chemical ‘handing machinery and ciled surfaces, the chrome-tanned leather bets are prefered Cotton : “Mort ofthe fabric belt are made by folding canvass of cotton duck to nd to prevent injury to the fives, ‘These ae cheaper mari and suitable in warm climates, in damp mosphere and in exposed positions Rubber The ruber bel ae made of yer of fabri impregnated with rubber composition and have thin ayer of rubber on the faces ‘These belt ae vey flexible but ae quickly destroyed if allowed to ome ino contact with htt, olor grease. Rubber belts are easily made endless, na a. As. o Balata: Balai belts are made form closely ‘oven cotion duck impregnated ‘with alata gum they need not be vulcanized alata does no oxidize and does not ge in ator sung Wis waterproof, and isnot affected by acids, skais, and omit. Batata belts are 20 - 40 percent stronger than the rubber bes. ties Plate i are used a core material ofthe bes. Pht-cored tes are made from nylon canvas or hin pla shets wih 2 layer of ruber sunounding the whole el scare Pte-cored Bel can be rn at high spede and canbe weaped round very salt pulleys These tes posts high stength whichis approximately two times tht of eter bet Explain, withthe help of neat shtches, the types of varius at belt drives “Types of tlt rive ae a follows Open belt rive ‘The open belt dive as shown in Fig (1), is wed with shafts aranged parallel o tating inthe same direction. Inthis case, the driver A pals the belt rom one side (ie lower ide RQ) and delivers itt the othe side (ie. upperside LM). “Thus the tension inthe lower side bet wel e more han tha in the per side bet “The lower side belt (because of more ension) is known aight side whereas the upper side belt (because of less tension) is known as slack side, a shown in Fig.(). ‘Crossed oF twist bet drive : used with «Te cowed or twist bt dive, as shown in FIC) ed ing in the opposite directions shans aranged pra and rot 1 fom one side (He. RO) and «inthis ease, the driver pulls the bel deivrsitto the other side (6. LM) inthe belt “Tus the tension nthe blk RQ wl Be ae than Ha HE LM. 1s The belt RQ (because of more tension) 16 whereas the belt LM (Deeause of less tension) 18 crown as tight side, known as slack side, as shown in Fig). Fig (2) Crossed or twist bett drive +A ise consideration wil show that ata point where the belt rose, it ibs agains ach oter and there wil be excessive wear ‘and tear. 4 + Inorder to avid this, the sats shoud be placed ata maximum stance of 20, where bis the with ofthe belt andthe sped ofthe tel should be less than 15 ©) Quarter turn belt drive : The quer tum bt ive (lo known a ight angle bel rive) as ‘shown in Fig.(3), is used with shafts arranged at right angles and rousing in one definite direction ‘+ Imorder to preven the bel fom leaving the pulley, the width of the face of the pulley should be greater or equal to 1.4b, where b is width of bel. Incase the pulleys cannot be arranged as shown in Fig (3) or when the reversible motions desired, hen a quar tum bel drive with a ‘Buide pulley, as shown in Fig.(3), may be used. Fig.2) Quarter tur belt drive. Fig.3(b) Quarter turn drive with ‘guide pulley. (8) —_Retedrive wth ite pulleys: Ate hive with antler ply ao known jockey ply ive) town ini se wih shat aang pl and when an pene ie can te wl do salt of cotton he nal ply + Wisp of dive i ove w bain gh easy ao and when te ‘regret tel son ano! ect by the mea, Idler pulley Fig.4(a) Belt drive with single Idler pulley Fig.4{b) Bett drive with many idler pulleys, + When it i desired to tranemit motion ffom one shaft to several ‘shafs, ll arranged in paral a helt drive with many idler pateys, 5 shown in Fig (0), may be employed. 0 o o ‘Compound belt drive: . ‘eam we i as sawn Fe) ed when compound elt deve a8 ough amamber of pally transite from one shat 10 note Driver 3 2 Fig.(5) Compound belt drive. Stepped or cone plley drive : ‘A stepped or cone pulley dive, as shown in Fig(6) i used for hanging the sped ofthe driven shaft while the min or driving shaft constant speed. ‘This is accomplished by shiing the belt rom one part ofthe steps to heater Fig.(6) Stepped or cone pulley drive, Fast and loose pulley dive : ‘A fas and lose pulley drive, as shown in (7), is used when the ‘riven or machine shaft iso be started or stopped whenever desired ‘without interfering with he driving shat, ‘Alley which is Keyed to the machine shai ale fst pulley td rns a the same speed at hat of machin shaft ‘loopy rns feel over he machin shaft and is incapable of ‘ransmiting any power Ans, (iat nd eee af is required to be vied to ‘opped, the bet is pushed on tothe loose ple by means sing bar having be im be orks, Fig.7 Fast and loose pulley drive, Explain slip ofthe belt. Slip ofthe belt: ‘The motion ofthe Het and pulleys assuming Gr tina rp between tte ets an pulleys Pat sometimes he ction ip Becomes inucient The may cate sane Ferward mation ofthe river witout caning he be whit “Thin calles ofthe bet andi gene expressed asa percentage ‘The rent ofthe el spin ee every aif he ae {As the slipping ofthe belt i 8 common phenomenon, thas the belt should never be used where a definite velocity ratio is of importance (asin the cas of hur, minute and second arms in the wath). Ley %= ip between the driver and the bet S; %= Slip between the bet and follower. “Therefore, velocity ofthe belt passing over the driver per second v= BN, _ BANA SL. 6100 va 24M of) oo 100. [And velocity ofthe belt passing over follower per second, ate DESIGN OF MECHANIGAL weer = “Substiting the valve of v from equation ( i) 00, in i. we have 4,N3 _ ¥4) NifA) ye | i00 55, (seamen 5:15 Where, S=5)+53 ‘$= Total percentage of sip. thickness ofthe bel (is considered, then i) ‘What is velocity ratio of belt drive? Derive is expression. Mf “(1 Nast @ ‘Ans, Velocity ratio of belt drive: «+The ratio between the velocities ofthe driver and follower or driven, sealed as velocity ratio, . et 4, = Diameter ofthe diver. 4, = Diameter ofthe follower. 1N, =Speed of river in rpm, Na = Speed ofthe follower in rpm. : Length ofthe belt that pasts over the driver in one minute =naNy Similatly, length of belt that passes over the follower, in one minute =14,N; Since the length of belt that pases over the diver in on minute is equal to the length of the belt that pases over the follower in one minut, therefore ad\Ny = 2dNy on erecta, Nea ™ "When the thickness ofthe belt is considered, then velocity ratio ‘where, = Thickness ofthe belt. ee ote: o @ The velocity ratio of a belt deve may also be obtained as discussed below . ‘We know that peripheral velocity ofthe Belt onthe driving pulley, Vetere i © ‘And peripheral velocity ofthe belt on diven pulley nN Vy = MANS mis . ‘when there iso slip, then Vy = Vp w Ne In case of a compound belt drive, the velocity ratios given by, Na dxdy Nr axe __ Speed of last driven ‘Speed of first driver Na. _ Product of diameters of drivers Ny Product of diameters of drivers Explain the term creep of belt Creep of bet: ‘Wen thee ses fom the lick 1 gt ie, wer pation of the tet exends and i conrcs agin when the Bel pases fromthe tight ie 10 the sack ie ‘Dac tothese changes of length there is a relative motion between the elt ant the ply mete “Thi relive motion is ermed as ee, “The tl fleet rep is rece shy the peed of he driven pulley oF folower ‘Considering crep, the velocity ratio is given by. E+ fer Bs Je, Where, 01 and os = Stes in the belt on the tight and slack side Nd respectively [E= Young's modulus forthe materia of the shaf. Ams, Met jo ‘O.11. Mow are ends of belts ole? xhout any joint and in such ihe belt material strength, a lt ou be made ees tat case ie srng of joint How 1008 ita setts ay n cme eens mn eames rome a epee of feedom in eh te edo, th ons bo wold voice sn ite 0 seranmor, ot cratengng pani of ee Sd EY removable bearings ‘The varius type of joint are given a Flows Cemented joint: “Te cemented joint shown in Fig, made bythe manufacture 10 form on endless bet, s preferred than other joints ‘The high performance belis have only such joints resulting in efficiency of 98%, (Eeegaeeeessseeees (@) Leather : (b) Rubber Fig{1) Cemented joint Laced joined “The laced joined is formed by punching holes in line across the belt, Jeaving a margin between the edge and the holes ‘A raw hide stip is used for lacing the two ends together to form 2 Jit (0) Stralght-atitch raw hide laced joint Ready to Finished drive in joint (0) Meta ace joint Fig.(2) Laced joints Fieve Meal wed nt hown Fie Yim he nal Te pint even og, teh sid he and enced 0 te ini Hinged joint: Sometimes, metal hingss may be fastened to the bel ends and connected bya see! or fibre pin a shown in Fig) Fig.(3) Hinged joint [ANALYSIS OF BELT TENSION” en Ans. Prove that the ratio ofthe driving tensions on the two sides of & % where T; = Tension inthe tight side of belt. = Tension in the slack side ofthe belt. 1 =Coefficient of friction between the belt and pulley. 0 = Angle of contact in radians. Consider a driven pulley rotating in the clock wise directions as shown in igure Let, = Tension in the bet on the right side “Ty = Tension inthe belt onthe sack side 6 Ange of contact in radian (i, angle subended by the ae AB, long which the belt touches the pulley athe certs). ‘Now consider a small portion of the belt PQ, Sublending an angle 0 a the centre ofthe pulleys as shown in figure. nsopt htt tana ggg 8 siden vm ea 0) @ ° ” DESIGN Ur meveenen=: F Ta, Fig, Ratio of driving tensions for flat belt. “The belt Pisin equibviom under the allowing foees ‘enson The belt a P Tension (T+ 8T in the bet tQ Nomalreston Ry Frisina force F= Wx Ry where = coeficien of ction between Blt and pulley Resolving al the forces horizontally, we have 8 sin 8 Ry=(T+arpsin a tain 0 Since the angle 60 is very small, therefor putting sin 52. 58 i a 2 ‘uation (), we have Ry Tao eglecting STM) yy "Now Resolving the forees vertically, we have mem octsamendt rel 8 «iy Since the angle 80 very small, therefore puting cos 2. in 2 equation (i), we have WARY T+ BT Te ST oF iw) Equaing the values Fauaine he values of Ry fom equation (i) and (iy), we get 50. 0 ” a ® r= Imceraing the above equation betven the mis T, and) and om 0100, we have [f-fo "Note: We cn also denote tension by lte F. So that Teh Tek Tek eu, efi centrifugal tension for belt drive and prove that Tem! ‘where T,= Centrifugal Tension = Mase of the belt per unit length ing Y= Linear velocity of belt in mis ‘Ans. Centrifugal Teaton : JN OF MECHANICAL wre: ere ‘he lt continnny ame over t= the tensions ceniituga force x caused, whane fet sw ierenne

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