Ch14 Producing Rubber Goods

7/21/2019 Ch14 Producing Rubber Goods

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2007 John Wiley & Sons, Inc. M P Groover, Fundamenals o!

Modern Manu!acurin" #$e

Producing Rubber Goods

1. Rubber Processing and Shaping

2. Manufacture of Tires and Other Rubber

Products

3. Product Design Considerations


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Overvie of Rubber Processing

Man! of the production "ethods used forp#astics are a#so app#icab#e to rubbers

$oever% rubber processing techno#og! is

different in certain respects% and the rubber

industr! is #arge#! separate fro" the p#asticsindustr!

The rubber industr! and goods "ade of rubber

are do"inated b! one product& tires

Tires are used in #arge nu"bers onauto"obi#es% truc's% aircraft% and bic!c#es


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Rubber Processing and Shaping

To basic steps in rubber goods production&

1. Production of the rubber itse#f

(atura# rubber )(R* is an agricu#tura#crop

S!nthetic rubbers is based onpetro#eu"

2. Processing into finished goods&

Co"pounding

Mi+ing Shaping

,u#cani-ing


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The Rubber ndustries

Production of ra (R is an agricu#tura#industr! because latex% the starting ingredient%is gron on p#antations in tropica# c#i"ates

/! contrast% s!nthetic rubbers are produced b!

the petroche"ica# industr! 0ina##!% processing into tires and other

products occurs at processor )fabricator*p#ants% co""on#! 'non as the rubberindustr!

The co"pan! na"es inc#ude Good!ear% /.0. Goodrich% and Miche#in% a## ref#ecting thei"portance of the tire


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Production of (atura# Rubber

(atura# rubber is tapped fro" rubber trees)Hevea brasiliensis* as #ate+

The trees are gron on p#antations in

Southeast sia and other parts of the or#d

ate+ is a co##oida# dispersion of so#id partic#esof the po#!"erpolyisoprenein ater

Po#!isoprene )C3$4*nis the che"ica#

substance that co"prises (R% and its

content in the e"u#sion is about 356 The #ate+ is co##ected in #arge tan's% thus

b#ending the !ie#d of "an! trees together


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Recovering the Rubber

Preferred "ethod to recover rubber fro" #ate+invo#ves coagu#ation 7 adding an acid such asfor"ic acid )$COO$*

Coagu#ation ta'es about 12 hours

The coagu#u"% no soft so#id s#abs% is thens8uee-ed through a series of ro##s hich driveout "ost of the ater and reduce thic'ness toabout 3 "" )194 in*

The sheets are then draped over ooden

fra"es and dried in s"o'ehouses Severa# da!s are nor"a##! re8uired to

co"p#ete the dr!ing process


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Grades of (atura# Rubber

The resu#ting rubber% no in a for" ca##edribbed smoked sheet% is fo#ded into #arge ba#esfor ship"ent to the processor

t has a characteristic dar' bron co#or

n so"e cases% the sheets are dried in hot airrather than s"o'ehouses% and the ter"air dried sheet is used: this is considered to bea better grade of rubber

sti## better grade% ca##edpale creperubber%

invo#ves to coagu#ation steps% fo##oed b!ar" air dr!ing

ts co#or is #ight tan


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S!nthetic Rubber

Most s!nthetic rubbers are produced fro"petro#eu" b! the sa"e po#!"eri-ation

techni8ues used to s!nthesi-e other po#!"ers

;n#i'e ther"op#astic and ther"osetting

po#!"ers% hich are nor"a##! supp#ied to thefabricator as pe##ets or #i8uid resins% s!nthetic

rubbers are supp#ied to rubber processors in

the for" of #arge ba#es

The rubber industr! has a #ong tradition ofhand#ing (R in these unit #oads


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Co"pounding

Rubber is a#a!s co"pounded ith additives

Co"pounding adds che"ica#s for

vu#cani-ation% such as su#fur

dditives inc#ude fi##ers hich act either to

enhance the rubber


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Carbon /#ac' in Rubber

The sing#e "ost i"portant reinforcing fi##er inrubber is carbon black% a co##oida# for" of

carbon obtained b! ther"a# deco"position of

h!drocarbons )soot*

ts effect is to increase tensi#e strength andresistance to abrasion and tearing of the

fina# rubber product

Carbon b#ac' a#so provides protection fro"

u#travio#et radiation Most rubber parts are b#ac' in co#or

because of their carbon b#ac' content


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Other 0i##ers and dditives in Rubber

China c#a!s h!drous a#u"inu" si#icates

)#2Si2O3)O$*=* reinforce #ess than carbon b#ac'

but are used hen b#ac' is not acceptab#e

Other po#!"ers% such as st!rene% P,C% and

pheno#ics Rec!c#ed rubber added in so"e rubber

products% but usua##! 156 or #ess

ntio+idants: fatigue and o-one protective

che"ica#s: co#oring pig"ents: p#astici-ers andsoftening oi#s: b#oing agents in the production

of foa"ed rubber: "o#d re#ease co"pounds


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Mi+ing

The additives "ust be thorough#! "i+ed iththe base rubber to achieve unifor" dispersion

of ingredients

;ncured rubbers have high viscosit! so

"echanica# or'ing of the rubber can increaseits te"perature up to 15C )3550*

f vu#cani-ing agents ere present fro" the

start of "i+ing% pre"ature vu#cani-ation ou#d

resu#t the >rubber processor


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To7Stage Mi+ing

To avoid pre"ature vu#cani-ation% a to stage

"i+ing process is usua##! e"p#o!ed

Stage 1 7 carbon b#ac' and other

non vu#cani-ing additives are co"bined ith

the ra rubber The ter" "aster batch is used for this

first stage "i+ture

Stage 2 7 after stage 1 "i+ing is co"p#eted%

and coo#ing ti"e has been a##oed% stage 2"i+ing is carried out in hich vu#cani-ing

agents are added


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0i#a"ent Reinforce"ent in Rubber

Man! products re8uire fi#a"ent reinforce"ent toreduce e+tensibi#it! but retain the other desirab#e

properties of rubber

@+a"p#es& tires% conve!or be#ts

0i#a"ents used for this purpose inc#udece##u#ose% n!#on% and po#!ester

0iber g#ass and stee# are a#so used )e.g.%

stee# be#ted radia# tires*

Continuous fiber "ateria#s "ust be addedduring shaping: the! are not "i+ed #i'e the

other additives


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Shaping and Re#ated Processes

Shaping processes for rubber products can bedivided into four basic categories&

1. @+trusion

2. Ca#endering

3. Coating

=. Mo#ding and casting

So"e products re8uire severa# basic

processes p#us asse"b#! or'

@+a"p#e& tires


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@+trusion

Scre e+truders are genera##! used fore+trusion of rubber

The 9D ratio of the e+truder barre# is #ess than

for ther"op#astics% t!pica##! in the range 15 to

1% to reduce ris' of pre"ature cross #in'ing

Die se## occurs in rubber e+trudates% since the

po#!"er is in a high#! p#astic condition and

e+hibits the >"e"or!? propert!

The rubber has not !et been vu#cani-ed


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Stoc' is passed through a series of gaps ofdecreasing si-e "ade b! a stand of rotatingro##s

Rubber sheet thic'ness is deter"ined b! fina#ro## gap

0igure 13.1A Ca#endering

Ca#endering


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Co"bination of e+trusion and ca#endering thatresu#ts in better 8ua#it! product than either

e+trusion or ca#endering a#one

0igure 1=.2 Ro##er die process rubber e+trusion fo##oed b! ro##ing

Ro##er Die Process


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n i"portant industria# process for producingauto"obi#e tires% conve!or be#ts% inf#atab#e rafts%

and aterproof c#oth tents and rain coats

0igure 1=.3 Coating of fabric ith rubber using a ca#endering process

Coating or "pregnating 0abrics ith Rubber


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Mo#ded Rubber Products

Mo#ded rubber products inc#ude shoe so#es andhea#s% gas'ets and sea#s% suction cups% and

bott#e stops

#so% "an! foa"ed rubber parts are produced

b! "o#ding n addition% "o#ding is an i"portant process in

tire production


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Mo#ding Processes for Rubber

Principa# "o#ding processes for rubber are

1. Co"pression "o#ding

2. Transfer "o#ding

3. nBection "o#ding

Co"pression "o#ding is the "ost i"portant

because of its use in tire "anufacture

Curing )vu#cani-ing* is acco"p#ished in the

"o#d in a## three processes% this representing

a departure fro" previous shaping "ethods%

a## of hich use a separate vu#cani-ing step


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hat is ,u#cani-ation

Treat"ent that acco"p#ishes cross #in'ing ofe#asto"er "o#ecu#es% to "a'e the rubber

stiffer and stronger but retain e+tensibi#it!

On a sub"icroscopic sca#e% the #ong chain"o#ecu#es of rubber beco"e Boined at

certain tie points% the effect of hich is toreduce the abi#it! of the e#asto"er to f#o

t!pica# soft rubber has 1 or 2cross #in's per 1555 units )"ers*

s the nu"ber of cross #in's increases%

the po#!"er beco"es stiffer and behaves"ore and "ore #i'e a ther"osettingp#astic )e.g.% hard rubber*


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0igure 1=.= @ffect of vu#cani-ation on rubber "o#ecu#es& )1* ra rubber%and )2* vu#cani-ed )cross #in'ed* rubber. ,ariations of )2* inc#ude& )a*soft rubber% #o degree of cross #in'ing: and )b* hard rubber% highdegree of cross #in'ing.

@ffect of ,u#cani-ation


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,u#cani-ation Che"ica#s and Ti"es

hen first invented b! Good!ear in 143E%

vu#cani-ation used su#fur )about 4 parts b!

eight of S "i+ed ith 155 parts of (R* at

1=5C )2450* for about hours

,u#cani-ation ith su#fur a#one is no #onger

used toda!% due to #ong curing ti"es

,arious other che"ica#s )e.g.% -inc o+ide% stearic

acid* are co"bined ith s"a##er doses of su#fur

to acce#erate and strengthen the treat"ent

Resu#ting cure ti"e is 1 25 "inutes


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Tires and Other Rubber Products

Tires are about A6 of tota# rubber tonnage Other i"portant products&

0ootear

Sea#s

Shoc' absorbing parts

Conve!or be#ts

$ose

0oa"ed rubber products Sports e8uip"ent


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Pneu"atic Tires

0unctions of pneu"atic tires on vehic#e & Support the eight of the vehic#e%

passengers% and cargo

Trans"it the "otor tor8ue to prope# the

vehic#e bsorb road vibrations and shoc' to provide

a co"fortab#e ride

Tires are used on auto"obi#es% truc's% buses%

far" tractors% earth "oving e8uip"ent% "i#itar!vehic#es% bic!c#es% "otorc!c#es% and aircraft


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Tire Construction

tire is an asse"b#! of "an! parts Passenger car tire has about 5 individua#

co"ponents

arge earth"over tire has as "an! as 1A

The interna# structure of the tire% 'non as the

carcass% consists of "u#tip#e #a!ers of rubber

coated cords% ca##edplies

The cords are strands of n!#on% po#!ester% fiber

g#ass% or stee#% hich provide ine+tensibi#it! toreinforce the rubber in the carcass


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0igure 1=. Three tire constructions& )a* diagona# p#!% )b* be#ted bias%

and )c* radia# p#!.

Three Tire Constructions


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Tire Production Se8uence

Tire production is su""ari-ed in three steps&

1. Prefor"ing of co"ponents

2. /ui#ding the carcass and adding rubber

strips to for" the sidea##s and treads

3. Mo#ding and curing the co"ponents into one

integra# piece

0o##oing descriptions of these steps are t!pica#

,ariations e+ist in processing depending on

construction% tire si-e% and t!pe of vehic#e on

hich the tire i## be used


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Prefor"ing of Co"ponents

Carcass consists of "u#tip#e co"ponents% "ostof hich are rubber or reinforced rubber

These co"ponents and others are produced b!

continuous processes

Then pre cut to si-e and shape for

subse8uent asse"b#!

Other co"ponents inc#ude& bead coi#% p#ies%

inner #ining% be#ts% tread% and sidea##


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Carcass is traditiona##! asse"b#ed using a"achine 'non as a building drum% hose

"ain e#e"ent is a c!#indrica# arbor that rotates

0igure 1=.F Tire Bust before re"ova# fro" bui#ding dru"% but prior to "o#ding

and curing.

/ui#ding the Carcass


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Tire "o#ds are usua##! sp#it "o#ds and containthe tread pattern to be i"pressed on the tire

0igure 1=.A Tire "o#ding& )1* uncured tire is p#aced over e+pandab#ediaphrag": )2* "o#d is c#osed and diaphrag" is e+panded toforce uncured rubber against "o#d cavit!% i"pressing treadpattern into rubber: "o#d diaphrag" are heated to cure rubber

Mo#ding and Curing


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Other Rubber Products& Rubber /e#ts

ide#! used in conve!ors and "echanica#poer trans"ission s!ste"s )pu##e!s*

Rubber is an idea# "ateria# for these productsbecause if its f#e+ibi#it!% but the be#t "ust have#itt#e or no e+tensibi#it! in order to function

ccording#!% it is reinforced ith fibers%co""on#! po#!ester or n!#on

0abrics of these po#!"ers are usua##! coatedb! ca#endering% asse"b#ed together to obtain

re8uired nu"ber of p#ies and thic'ness% andsubse8uent#! vu#cani-ed b! continuous orbatch heating processes


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Other Rubber Products& $ose

To basic t!pes&1. P#ain hose )no reinforce"ent* is e+truded

tubing

2. Reinforced tube% hich consists of&

nner tube 7 e+truded of a rubberco"pounded for particu#ar #i8uid that i##

f#o through it

Reinforce"ent #a!er 7 app#ied to inner tube

as fabric% or b! spira#ing% 'nitting% braiding Outer #a!er H co"pounded for environ"ent

and app#ied b! e+trusion


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Other Rubber Products& 0ootear

Rubber co"ponents in footear& so#es% hee#s%rubber overshoes% and certain upper parts

Mo#ded parts are produced b! inBection

"o#ding% co"pression "o#ding% and certain

specia# "o#ding techni8ues deve#oped b! theshoe industr!

The rubbers inc#ude both so#id and foa"ed

0or #o vo#u"e production% "anua# "ethods

are so"eti"es used to cut rubber fro" f#atstoc'


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Processing of Ther"op#astic @#asto"ers

ther"op#astic e#asto"er )TP@* is ather"op#astic po#!"er that possesses the

properties of a rubber

TP@s are processed #i'e ther"op#astics% but

their app#ications are those of an e#asto"er Most co""on shaping processes are inBection

"o#ding and e+trusion

Genera##! "ore econo"ica# and faster than

the traditiona# processes used for rubbersthat "ust be vu#cani-ed


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TP@ Products

Mo#ded products& shoe so#es% ath#etic footear%and auto"otive co"ponents such as fender

e+tensions and corner pane#s

@+truded ite"s& insu#ation coating for e#ectrica#

ire% tubing for "edica# app#ications% conve!orbe#ts% sheet and fi#" stoc'

(o tires of TP@


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Product Design Considerations

@cono"ic Production Iuantities& Rubber parts produced b! co"pression

"o#ding )the traditiona# process* can often be

produced in 8uantities of 1555 or #ess

The "o#d cost is re#ative#! #o co"pared toother "o#ding "ethods

s ith p#astic parts% inBection "o#ding of

rubber parts re8uires higher production

8uantities to Bustif! the "ore e+pensive "o#d


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M d M ! i #$

Product Design Considerations

Draft& Draft is usua##! unnecessar! for "o#ded parts

of rubber% because its f#e+ibi#it! a##os it to

defor" for re"ova# fro" the "o#d

Sha##o undercuts% a#though undesirab#e% arepossib#e ith rubber "o#ded parts for the sa"e

reason

The #o stiffness and high e#asticit! of the

"ateria# per"its re"ova# fro" the "o#d

Documents

Ch14 Producing Rubber Goods