Design of Roller Chain Drive theory by Prof. Sagar A. Dhotare

This covers following Points
1. Introduction.
2. Advantages and Disadvantages of Chain Drive over Belt or Rope Drive.
3. Terms Used in Chain Drive.
4. Relation Between Pitch and Pitch Circle Diameter.
5. Velocity Ratio of Chain Drives.
6. Length of Chain and Centre Distance.
7. Classification of Chains.
8. Hoisting and Hauling Chains.
9. Conveyor Chains.
10. Power Transmitting Chains.
11. Characteristics of Roller Chains.
12. Factor of Safety for Chain Drives.
13. Permissible Speed of Smaller Sprocket.
14. Power Transmitted by Chains.
15. Number of Teeth on the Smaller or Driving Sprocket
or Pinion.
16. Maximum Speed for Chains.
17. Principal Dimensions of Tooth Profile.
18. Design Procedure for Chain Drive.

1. Design of
Roller Chain Drive

2. Introduction
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Inbeltandropedrivesthatslippingmayoccur.Inordertoavoidslipping,steel
chainsareused.Thechainsaremadeupofnumberofrigidlinkswhicharehingedtogether
bypinjointsinordertoprovidethenecessaryflexibilityforwrappingroundthedrivingand
drivenwheels.Thesewheelshaveprojectingteethofspecialprofileandfitintothe
correspondingrecessesinthelinksofthechainasshowninFig.1.Thetoothedwheelsare
knownassprocketwheelsorsimplysprockets.Thesprocketsandthechainarethus
constrainedtomovetogetherwithoutslippingandensuresperfectvelocityratio.
Fig. 1. Sprockets and chain.
Thechainsare
mostlyusedtotransmit
motionandpowerfromone
shafttoanother,whenthe
centredistancebetweentheir
shaftsisshortsuchasin
bicycles,motorcycles,
agriculturalmachinery,
conveyors,rollingmills,road
rollersetc.
Thechainsmayalsobeusedforlongcenterdistanceofupto8meters.Thechainsareused
forvelocitiesupto25m/sandforpowerupto110kW.Insomecases,higherpower
transmissionisalsopossible.

3. Advantages and Disadvantages of Chain Drive
over Belt or Rope Drive
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Advantages:-
1.Asnosliptakesplaceduringchaindrive,henceperfectvelocityratiois
obtained.
2.Sincethechainsaremadeofmetal,thereforetheyoccupylessspacein
widththanabeltorropedrive.
3.Itmaybeusedforbothlongaswellasshortdistances.
4.Itgivesahightransmissionefficiency(upto98percent).
5.Itgiveslessloadontheshafts.
6.Ithastheabilitytotransmitmotiontoseveralshaftsbyonechainonly.
7.Ittransmitsmorepowerthanbelts.
8.Itpermitshighspeedratioof8to10inonestep.
9.Itcanbeoperatedunderadversetemperatureandatmospheric
conditions

4. Advantages and Disadvantages of Chain Drive
over Belt or Rope Drive
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Disadvantages:-
1.Theproductioncostofchainsisrelativelyhigh.
2.Thechaindriveneedsaccuratemountingandcarefulmaintenance,
particularlylubricationandslackadjustment.
3.Thechaindrivehasvelocityfluctuationsespeciallywhenunduly
stretched.

5. Terms Used in Chain Drive
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thefollowingtermsarefrequentlyusedinchaindrive.
1.Pitchofchain:-
Itisthedistancebetweenthehingecenterofalinkandthecorrespondinghinge
centeroftheadjacentlink,asshowninFig.2.Itisusuallydenotedbyp.
Fig. 2. Terms used in chain drive.
2.Pitchcirclediameterofchainsprocket:-
Itisthediameterofthecircleon
whichthehingecentresofthechainlie,whenthe
chainiswrappedroundasprocketasshownin
Fig.2.ThepointsA,B,C,andDarethehinge
centresofthechainandthecircledrawnthrough
thesecentresiscalledpitchcircleandits
diameter(D)isknownaspitchcirclediameter

6. Relation Between Pitch and Pitch Circle
Diameter
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
AchainwrappedroundthesprocketisshowninFig.2.Sincethelinksofthe
chainarerigid,thereforepitchofthechaindoesnotlieonthearcofthepitchcircle.The
pitchlengthbecomesachord.ConsideronepitchlengthABofthechainsubtendingan
angleθatthecentreofsprocket(orpitchcircle),

7. Velocity Ratio of Chain Drives
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.

8. Length of Chain and Centre Distance
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
An open chain drive system connecting the two sprockets is shown in Fig.3.
Fig. 3. Length of chain.
Let T1=Numberofteethonthe
smallersprocket,
T2=Numberofteethonthe
largersprocket,
p=Pitchofthechain,and
x=Centredistance.
Thelengthofthechain(L)mustbeequaltotheproductofthenumberofchainlinks(K)and
thepitchofthechain(p).Mathematically,
L=K.p
Thenumberofchainlinksmaybeobtainedfromthefollowingexpression,i.e.

9. Length of Chain and Centre Distance
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.

10. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
The chains, on the basis of their use, are classified into the following three groups:
A.Hoisting and hauling (or crane) chains,
B.Conveyor (or tractive) chains, and
C.Power transmitting (or driving) chains.
A. Hoisting and Hauling Chains :-
Thesechainsareusedforhoistingandhaulingpurposes
andoperateatamaximumvelocityof0.25m/s.Thehoistingandhaulingchainsareofthefollowing
twotypes:
1.Chainwithovallinks:-
Thelinksofthistypeofchainareofovalshape,asshowninFig.4(a).The
jointofeachlinkiswelded.Thesprocketswhichareusedforthistypeofchainhavereceptaclesto
receivethelinks.Suchtypeofchainsareusedonlyatlowspeedssuchasinchainhoistsandinanchors
formarineworks.
2.Chainwithsquarelinks:-
Thelinksofthis
typeofchainareofsquareshape,as
showninFig.4(b).Suchtypeofchainsare
usedinhoists,cranes,dredges.The
manufacturingcostofthistypeofchainis
lessthanthatofchainwithovallinks,but
inthesechains,thekinkingoccurseasily
onoverloading.
Fig.4. Hoisting and hauling chains.

11. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
B. Conveyor Chains :-
These chains are used for elevating and conveying the materials continuously at a
speed upto 2 m / s. The conveyor chains are of the following two types:
1. Detachable or hook joint type chain, as shown in Fig. 5 (a),
2. Closed joint type chain, as shown in Fig. 5 (b).
Fig. 5. Conveyor chains.
The conveyor chains are usually made of malleable cast iron. These chains do not have
smooth running qualities. The conveyor chains run at slow speeds of about 0.8 to 3 m / s.

12. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
C. Power Transmitting Chains :-
These chains are used for transmission of power, when the distance
between the centresof shafts is short. These chains have provision for efficient lubrication. The power
transmitting chains are of the following three types.
1.Block or bush chain :-
AblockorbushchainisshowninFig.6.Thistypeofchainwasusedintheearly
stagesofdevelopmentinthepowertransmission.Itproducesnoisewhenapproachingorleavingthe
teethofthesprocketbecauseofrubbingbetweentheteethandthelinks.Suchtypeofchainsareused
tosomeextentasconveyorchainatsmallspeed.
Fig. 6. Block or bush chain.

13. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
2.Bushrollerchain:-
AbushrollerchainasshowninFig.7,consistsofouterplatesorpinlinkplates,
innerplatesorrollerlinkplates,pins,bushesandrollers.Apinpassesthroughthebushwhichis
securedintheholesoftherollerbetweenthetwosidesofthechain.Therollersarefreetorotateonthe
bushwhichprotectthesprocketwheelteethagainstwear.Thepins,bushesandrollersaremadeofalloy
steel.
Fig. 7. Bush roller chain.
Abushrollerchainis
extremelystrongandsimplein
construction.Itgivesgoodserviceunder
severeconditions.Thereisalittlenoise
withthischainwhichisduetoimpactof
therollersonthesprocketwheelteeth.
Thischainmaybeusedwherethereisa
littlelubrication.Whenoneofthese
chainselongatesslightlyduetowearand
stretchingoftheparts,thentheextended
chainisofgreaterpitchthanthepitchof
thesprocketwheelteeth.
Therollersthenfitunequallyintothecavitiesofthewheel.Theresultisthatthetotalload
fallsononeteethoronafewteeth.Thestretchingofthepartsincreasewearofthesurfacesofthe
rollerandofthesprocketwheelteeth.

14. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
The roller chains are standardized and manufactured on the basis of pitch. These chains are
available in single-row or multi-row roller chains such as simple, duplex or triplex strands, as shown in
Fig. 8.
Fig.8. Types of roller chain.

15. Classification of Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
3.Silentchain:-
Asilentchain(alsoknownasinvertedtoothchain)isshowninFig.9.
Fig. 9. Silent chain.
Itisdesignedtoeliminatetheevileffectscausedby
stretchingandtoproducenoiselessrunning.Whenthechain
stretchesandthepitchofthechainincreases,thelinksrideon
theteethofthesprocketwheelataslightlyincreasedradius.
Thisautomaticallycorrectsthesmallchangeinthe
pitch.Thereisnorelativeslidingbetweentheteethofthe
invertedtoothchainandthesprocketwheelteeth.When
properlylubricated,thischaingivesdurableserviceandruns
verysmoothlyandquietly.
Fig. 10. Silentchainjoints.
The various types of
joints used in a silent chain are
shown in Fig. 10.

16. Characteristics of Roller Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
AccordingtoIndianStandards(IS:2403—1991),thevariouscharacteristicssuchas
pitch,rollerdiameter,widthbetweeninnerplates,transversepitchandbreakingloadfortheroller
chainsaregiveninthefollowingtable.

17. Factor of Safety for Chain Drives
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.

18. Factor of Safety for Chain Drives
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thefollowingtableshowsthefactorofsafetyforthebushrollerand
silentchainsdependinguponthespeedofthesprocketpinioninr.p.m.andpitchof
thechains.

19. Permissible Speed of Smaller Sprocket
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thefollowingtableshowsthepermissiblespeedofthesmallersprocketor
pinion(inr.p.m.)forthebushrollerandsilentchaincorrespondingtodifferentpitches.
Thechainvelocityfortherollerchainsmaybeashighas20m/s,ifthe
chainsareproperlylubricatedandenclosed,whereasthesilentchainmaybe
operatedupto40m/s.

20. Power Transmitted by Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Theservicefactor(KS)istheproductofvariousfactors,suchasloadfactor(K1),
lubricationfactor(K2)andratingfactor(K3).Thevaluesofthesefactorsaretakenasfollows:
1.Loadfactor(K1) =1,forconstantload
=1.25,forvariableloadwithmildshock
=1.5,forheavyshockloads
2.Lubricationfactor(K2)=0.8,forcontinuouslubrication
=1,fordroplubrication
=1.5,forperiodiclubrication
3.Ratingfactor(K3)=1,for8hoursperday
=1.25,for16hoursperday
=1.5,forcontinuousservice

21. Power Transmitted by Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
The power rating for simple roller chains depending upon the speed of the smaller
sprocket is shown in the following table.

22. Number of Teeth on the Smaller or Driving
Sprocket or Pinion
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Consideranarrangementofachaindriveinwhichthesmallerordrivingsprockethasonly
fourteeth,asshowninFig.11(a).LetthesprocketrotatesanticlockwiseataconstantspeedofNr.p.m.
ThechainlinkABisatadistanceofd/2fromthecentreofthesprocketanditslinearspeedisgiven
by
Fig. 11. Number of teeth on the smaller sprocket.

23. Number of Teeth on the Smaller or Driving
Sprocket or Pinion
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.

24. Number of Teeth on the Smaller or Driving
Sprocket or Pinion
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thenumberofteethonthesmallersprocketplaysanimportantrolein
decidingtheperformanceofachaindrive.Asmallnumberofteethtendstomake
thedrivenoisy.Alargenumberofteethmakeschainpitchsmallerwhichis
favorableforkeepingthedrivesilentandreducingshock,centrifugalforceand
frictionforce.

25. Maximum Speed for Chains
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
The maximum allowable speed for the roller and silent chains, depending upon
the number of teeth on the smaller sprocket or pinion and the chain pitch is shown in the
following table.

26. Principal Dimensions of Tooth Profile
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
ThestandardprofilesfortheteethofasprocketareshowninFig.12.AccordingtoIndianStandards
(IS:2403–1991),theprincipaldimensionsofthetoothprofileareasfollows:

27. Principal Dimensions of Tooth Profile
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Fig. 12 Profiles of Socket

28. Design Procedure of Chain Drive
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thechaindriveisdesignedasdiscussedbelow:
1.Firstofall,determinethevelocityratioofthechaindrive.
2.SelecttheminimumnumberofteethonthesmallersprocketorpinionfromTable.
3.Findthenumberofteethonthelargersprocket.
4.Determinethedesignpowerbyusingtheservicefactor,suchthat
Designpower=Ratedpower×Servicefactor
5.Choosethetypeofchain,numberofstrandsforthedesignpowerandr.p.m.ofthe
smallersprocketfromTable.
6.Notedowntheparametersofthechain,suchaspitch,rollerdiameter,minimum
widthofrolleretc.fromTable.
7.Findpitchcirclediametersandpitchlinevelocityofthesmallersprocket.
8.Determinetheload(W)onthechainbyusingthefollowingrelation,i.e.
W=Ratedpower/Pitchlinevelocity
9.Calculatethefactorofsafetybydividingthebreakingload(WB)totheloadonthe
chain(W).Thisvalueoffactorofsafetyshouldbegreaterthanthevaluegivenin
Table.
10.Fixthecentredistancebetweenthesprockets.
11.Determinethelengthofthechain.
12.Theotherdimensions.

29. Design Procedure of Chain Drive
Prof. Sagar A. Dhotare, Deparment of Mechanical Engineering, ViMEET.
Thechaindriveisdesignedasdiscussedbelow:
1.Firstofall,determinethevelocityratioofthechaindrive.
2.SelecttheminimumnumberofteethonthesmallersprocketorpinionfromTable.
3.Findthenumberofteethonthelargersprocket.
4.Determinethedesignpowerbyusingtheservicefactor,suchthat
Designpower=Ratedpower×Servicefactor
5.Choosethetypeofchain,numberofstrandsforthedesignpowerandr.p.m.ofthe
smallersprocketfromTable.
6.Notedowntheparametersofthechain,suchaspitch,rollerdiameter,minimum
widthofrolleretc.fromTable.
7.Findpitchcirclediametersandpitchlinevelocityofthesmallersprocket.
8.Determinetheload(W)onthechainbyusingthefollowingrelation,i.e.
W=Ratedpower/Pitchlinevelocity
9.Calculatethefactorofsafetybydividingthebreakingload(WB)totheloadonthe
chain(W).Thisvalueoffactorofsafetyshouldbegreaterthanthevaluegivenin
Table.
10.Fixthecentredistancebetweenthesprockets.
11.Determinethelengthofthechain.
12.Theotherdimensions.