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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/7/29/2019 Belt Tensioning Methods for Small Package Conveyors
2/13
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
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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
3 Belt Tensioning Methods for Small Package Conveyors 2009 Dorner Mfg. Corp.
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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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13 Belt Tensioning Methods for Small Package Conveyors 2009 Dorner Mfg. Corp.
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.