Belt Tensioning Methods for Small Package Conveyors

7/29/2019 Belt Tensioning Methods for Small Package Conveyors

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BeltTensioningMethodsforSmallPackageConveyors

Whatsthebestsolution?

IndustrialWhitePaper

By:MichaelA.Hosch,P.E.

DornerMfg.Corp.

975CottonwoodAvenue

Hartland,WI53029USA

Phone:8003978664

www.Dorner.com
http://www.dorner.com/http://www.dorner.com/http://www.dorner.com/


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Overview:

Thiswhitepaperwillprovideanoverviewofthemostcommonlyusedmethodsforadjustingbelttensiononsmallpackage

conveyors.Theprimaryadvantagesanddisadvantagesofeachmethodwillalsobepresentedtoassistmanufacturersidentifythe

bestoptionfortheirspecificneeds.

Table

of

Contents:

Overview Pg. 2 BeltTensioningforSmallPackageConveyorsAnIntroduction Pg. 3 BeltTensionMethods Pgs. 48

JackScrewTension Pgs. 5

RackandPinionTension Pg. 6TipUpTailTension Pg. 7

PneumaticorSpringTension Pg. 8

AdvantagesandDisadvantages Pgs. 912 Conclusion Pg. 13

2 Belt Tensioning Methods for Small Package Conveyors 2009 Dorner Mfg. Corp.


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Belt

Tensioning

for

Small

Package

Belt

Conveyors

An

Introduction:

Smallpackagebeltconveyorsareusedforthousandsofapplicationsincountlessindustrialmarkets.Theseconveyorsmove

individualproductsthroughprocessingapplicationswherefunctionssuchasforming,molding,machining,gluingandassemblyare

performedonmetalorplasticproduct.Theseproductsthenmovetopackagingapplicationswheretheyareinsertedintotheir

individualpackageandsealed,wrapped,heatshrunk,orbandedbeforebeinggroupedandloadedintotheirshippingcontainer.The

useofsmallpackagebeltconveyorsforalloftheapplicationspresentedabovehasseveralbenefits.

Typically,these

conveyors

have

end

rollers

between

1

and

2

in

diameter.

This

allows

smooth

transfer

from

process

to

process

for

smallandoftenoddlyshapedproducts.Inaddition,smallpackagebeltconveyorsgenerallyhaveathinprofileandhaveatightbelt

widthtooverallwidthratio.Thisprovidestheabilityfortheconveyortofitintotightspaces,whichmaximizesavailablefloorspace

whileminimizingprotrusionsthatmayinterferewithoperators.

Althoughtheseconveyorsaresmall(astheirclassificationwouldimply)andtheirloadsaregenerallylight,theystillpresentsomeof

thesametechnicalandmaintenancechallengesasmuchlargerconveyorsonesuchchallengeisbelttensioning.ForboSiegling,a

leadingmanufacturer

of

light

material

handling

belts,

notes

the

following

relative

to

belt

tensioning;

the

contact

pressure

of

the

belt

onthedrivedrumrequiredtotransmiteffectivepullisproducedbyelongatingthebeltwithatensiontakeup.Withoutatension

takeupdevice,therewouldbenopressureonthedrivedrumandtheconveyorbeltwouldstop.Whilethisconceptissimple,how

thetensiontakeupmechanismisdesignedtocarryoutthisprocesscanbequitecomplicated.And,ifnotdoneproperly,canleadto

avarietyofresourcedrainingmaintenanceproblems,including:

Poororinconsistentbelttracking

Over

tensioning,

causing

poor

belt

life

Overtensioning,causingpoorbearinglife Undertensioning,causingbeltslippage Confusiontomaintenancestaffontensioningprocedures Mechanismsthataredifficulttoaccessoradjust



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Alloftheissueslistedpreviouslycouldeasilyleadtoconveyorbeltshutdown,whichoftenforcesmachineandproductiondowntime

something

that

obviously

needs

to

be

avoided

in

todays

busy,

24/7

production

facilities.

BeltTensionMethods:

Thereareseveralcommercialmethodsforprovidingandadjustingconveyorbelttension.Someconsistofstandardcomponentsthat

providethecapabilityofdesigningyourownconveyor. Othermethodsonlyexistindesignsavailableascompleteconveyorsfrom

conveyormanufactures.

In

most

cases,

these

methods

can

be

categorized

into

the

following

four

groups:

1. JackScrewTension2. RackandPinionTension3. TipupTailTension4. PneumaticorSpringTension

Letstake

amore

detailed

look

at

each

of

these

methods,

beginning

with

Jack

Screw

Tension.



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JackScrewTension

Jackscrewtensionisthemostcommonbelttensioningmechanism.Howdoesitwork?Asshowninthefigurebelow(FigureA),the

tensiononthebeltisaccomplishedbyturningthescrewattheendofaconveyor.Thispushesthebearingblocktowardstheendof

theconveyor,whichaddstensiontothebelt.Thereisanother,identicaljackscrewlocatedontheoppositesideoftheroller.The

sameproceduremustbeperformedevenlyforbothrollers.Inmostconveyorinstallations,thistensionmechanismisalsousedto

adjustbelttracking.Jackscrewtensioningissimpletouseandiscommonlyinstalled,butalsopresentsanumberofdisadvantages

whichwellreviewingreaterdetaillaterinthispaper.

FigureA: JackScrewTension



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RackandPinionTension

Rackandpiniontensionisaccomplishedbyincorporatingarackandpiniondeviceintotheconveyorframe.Anexampleofthis

mechanismisshownbelow(FigureB).Asyoullsee,tworacksareslideablymountedtotheconveyorframe.Turningthepinion

shaftthenpushesonthebearingblockstomovetherollerandaddbelttension.Generally,thepinionrunsthefullwidthofthe

frameandcontactsbothracks,whichmovesthebearingblocksevenlyandparallelwhileturningfromasinglepoint.Sincethe

bearingblocksmovetogether,anadditionaldeviceisneededforbelttracking.Thisbelttrackingdevicemaybeajackscreworcam,

whichistypicallymountedbetweentheracksandthebearingblock.Rackandpiniontensioningdoesnotdisturbbelttracking

if/whenabelt

tension

adjustment

is

necessary.

FigureB: RackandPinionTension



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TipUpTailTension

Atipuptailisaccomplishedbyplacingtheendrollerofaconveyoronapivotmechanism.Anexampleofthismechanismisshown

below(FigureC).Usingthismethod,thepivotdevicegenerallyliftstheendrollerabovetheconveyorframe.Whenplacedinthe

lowerlockedposition,thetotalrollertorollerlengthoftheconveyorislongerthanitisintheupperposition.Thisextensioniswhat

providestensiontotheconveyorbelt.Thepivotmechanismmovestheentireendrollerperpendiculartotheconveyorframeand

doesnotneedaccessoradjustmentfrombothsidesoftheframe.Atipuptailmechanismwillnotprovidefinitebelttension

adjustmentitcanonlybesettooneposition.Overtime,asbeltsstretch,theywillrequireadjustment.Toaccomplishthis,adevice

suchas

ajack

screw

will

need

to

be

added

for

incremental

tension

adjustment.

This

jack

screw

can

then

also

be

used

for

belt

trackingadjustment.

FigureC: TipUpTailTension



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PneumaticorSpringTension

Pneumaticorspringtensionistypicallyusedonheavilyloadedorlongerconveyors.Itisaccomplishedbytheadditionofatleast

threerollerstotheundersideoftheconveyor.Anexampleofthismechanismisshownbelow(FigureD).Belttensionisachievedby

aconnectionofapneumaticcylinderoraspringloadeddevicetothelowertensionroller.Thecylinderwillpullthelowerroller

down,whichplacestensiononthebelt.Generally,onecylinderisconnectedtotheendsoftherollerbyacrossbracket.Thecylinder

willmovetheendsoftherollerevenlyandparallel.Onebenefitofthismechanismisthatitautomaticallycompensatesforbelt

stretch. Themethodscoveredpreviouslyinthispaperhavebeenstaticdevicesthatrequiremanualadjustmentovertime.Seeingas

longerand

higher

load

conveyors

have

more

belt

stretch,

this

is

the

best

method

for

those

circumstances.

Belt

tracking

is

typically

accomplishedbyaddingadevicesuchasajackscrewtothesnubrollersjustabovethetensionroller.

FigureD: PneumaticTension



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AdvantagesandDisadvantagesofTensioningMethods:

Nowthatyouhaveabetterunderstandingofthemostcommonlyutilizedtensioningmethods,welltakeamoredetailedlookatthe

generaladvantagesanddisadvantagesofeach.

JackScrewTension

Advantages:1. Lowcost. Thismethodhastheleastamountofcomponentsandthecomponentsaresimpleandreadilyavailable.2. Familiarity. Thisisthemostcommonmethodoftensioningandmostmaintenancecrewsarefamiliarwithitsoperation,soit

cangenerallybefixedquickly.

Disadvantages:1. Addedmaintenancetimeforbelttracking.Becausethejackscrewistheonlymethodofadjustment,itmustbeusedfor

bothtensioningandtracking.Onceaconveyorbeltrequiresretensioning,thejackscrewswillbeadjustedandthetracking

settingswillbedisturbed.Therefore,atrackingadjustmentmustbeperformedeventhoughitwasntrequired.Thiscauses

muchhighermaintenancetimesastrackingadjustmentcantakesubstantiallylongerthansimpletensioningalone.

2. Highriskofovertensioning.Inmostcases,thejackscrewadjustmentdeviceisasimplethreadedbolt.Threadedboltsaredesignedtoapplyextremeforcetoclamporholddevices.Belttensionadjustmentsmadewithjackscrewsaredone

manually.And,withtheshallowpitchangleofthejackscrewthread,thereisverylittlefeedbacktotheoperatormaking

the

adjustment.

They

are

often

unaware

of

the

extreme

forces

they

are

placing

on

the

belt

and

the

bearings.

Unfortunately,

intime,thisovertensioningwillresultinreducedbearingandbeltlife.

3. Difficulttoaccessformaintenance.Inmanyconveyordesigns,thejackscrewislocatedattheendoftheconveyorrolleralongthesideoftheconveyorframe.Unfortunately,inmostapplications,theendoftheconveyorisplacedupagainst

anotherconveyorrollerorpieceofequipment,makingitnearlyimpossibletoaccesstheendofthejackscrewfor



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Disadvantages:1. Requiresanaccurateframe.Sincethepremiseforthismechanismistomovethetwobearingblocksevenly,itiscriticalforit

tobeinstalledaccuratelyandparalleltotheroller.Customconveyorsgenerallydonotusethismethodforthatreason.

However,standardconveyorsthatusequalityengineeringandconsistentmanufacturingmethodsareabletoaccomplishthe

accuracyneeded.

2. Requiresperiodicretensioning.Thismechanismdoesnotcompensateforthebeltstretchthatwillhappenovertimeduetowearorheavyloads.Ifbeltslipoccurs,therackandpinionwillneedtoberetightenedtotensionthebelt.

TipUpTailTension

Advantages:1. Quickaccessforcleaning.Tipuptailtensionmechanismsaremostoftenutilizedonconveyorsusedinfoodapplications. For

theseapplications,itisimportanttohavefastandtoollessaccesstotheinsideoftheconveyorforcleaning. Tipuptails

providethis

function.

2. Doesnotaffectbelttracking.Tipupmechanismsswingthebearingblocksevenlyintopositionfromasinglepoint.Movingthebearingblockstogetherensuresthatthetrackingadjustmentthathasbeenpreviouslysetdoesnotgetdisturbedbythe

needtoretension.

Disadvantages:1. Requiresanaccurateframe.Sincethepremiseforthismechanismistomovethetwobearingblocksevenly,itisrequired

thatitisinstalledaccuratelyandparalleltotheroller.2. Onlysetsinitialtension.Atipuptailtensionsystemisasinglepositionsystem.Thepivotarmrotatestherollerintoone

positiononly.Therefore,thistensionsystemcanonlysetinitialtensionandcannotcompensateforbeltstretchovertime.

Toaccommodatethis,anadditionaldevicesuchasajackscrewmustbeaddedtothemechanism.



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3. Operatorsafetyhazards.Theuseofatipuptailmechanismcreatestwopotentialoperatorhazards. Thefirstisthepotentialto

lift

the

tip

up

tail

into

the

upper

position

while

the

conveyor

is

running.

If

this

is

done,

the

operator

has

access

to

driven

rollersinsidetheconveyorframe.CESafetyStandardsdictatethataccesstoequipmentshallonlybedoneusingatool. Ifthe

tailismanuallyactivated,itmayviolateCEandOSHAsafetystandards.ManuallyactivatedtipuptailsarepreferredinFood

conveyorapplications.Intheseapplications,theneedforsanitationoutweighsthepotentialsafetyrisks. Thesecondsafety

hazardwithtipuptailmechanismsisthepotentialpinchpointcreatedfromloweringthetailbackdownintoitstensioned

position.Thescissorsactioncreatedfromthepivotframetotheconveyorframecreatesadangerpoint.Ifnotproperly

designedorguarded,injurycouldoccur.

PneumaticorSpringTension

Advantages:1. Automaticallytensionsthebelt.Withtheadditionofapneumaticcylinderorspringloadeddevice,thistension

mechanismmaintainsconstanttensionontheconveyorbelt.Thisisespeciallyimportantonlongerorheavilyloaded

conveyors.

Re

tension

maintenance

is

not

required

until

the

mechanism

runs

out

of

travel.

Disadvantages:1. Costly.Theadditionofthethreerollersandthetensionmechanismaddssignificantlytothecostoftheconveyor.2. Longerbeltreplacementtime.Inthistensionmethod,thereturnconveyorbeltisinterwoventhroughthethreerollers.

Whenbeltreplacementisrequired,removaloftheuppertworollersisalsonecessary. Dependingonthedesignofthe

mechanism,thiscanaddsignificantlytothemaintenancetimetoreplaceawornoutbelt.Toincreasemaintenance

efficiency,asystem

with

aquick

release

feature

should

be

utilized,

which

provides

easy

access

to

the

top

rollers.

3. Beltsurfacecontamination.Withthethreerollermechanism,thetoptworollerscontactthetoprunningsurfaceofthebelt.Theserollerscanpickupdebrisandimbeditintothebeltsurface.Insomeapplicationsthismaynotbeanissue,but

infoodorfoodpackagingapplications,thisshouldbeavoided.



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Conclusion:

So,whichmethodofbelttensioningisbest?Ofcourse,thecorrectanswerdependsonthespecificapplicationathand.But,

generallyspeaking,inasituationwhereaoneoffcustomconveyorisbeingimplementedbynonconveyorpeoplethejackscrew

methodwouldmostlikelybesufficient.Ithasreadilyavailablecomponentstoaideinthedesignanditsalsosimpleand

inexpensive.

However,whenacompanyispurchasingaconveyorfromaconveyormanufacturer,theyshouldexpectmoreutilityfortheirmoney

andhigher

quality

technology.

A

technology

that

decreases

maintenance

times,

while

prolonging

the

conveyors

life

and

improving

itsoverallfunction.ThetechnologythatmostregularlydeliversthesebenefitsistheRackandPinionmethod.

FormoredetailsaboutRackandPiniontensioning,oranyoftheothermethodspresentedinthispaper,pleasecallDornerMfg.

Corp.at18003978664orvisitDorner.com.

AboutDorner

Mfg.

Corp.

BasedinHartland,Wis.,DornerMfg.Corp.isaworldleaderinthedesign,manufactureanddistributionofhighqualityconveyors

andrelatedequipment.Since1973,companiesfromaroundtheworldhaveturnedtoDornerforgreatlyimprovedefficiencyand

productivity.AdditionalinformationaboutthecompanycanbeobtainedonlineatDorner.com.

Belt Tensioning Methods for Small Package Conveyors

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