91637420-Rubber-Compounding.pdf

Rubber compounding compounding Rubber

compounding

is

the

complex,

multi multidis disipl iplina inary ry scienc science e of select selecting ing and and blend blending ing the the appr approp opri riat ate e comb combin inat atio ion n of elas elasto tome mers rs and and other

ingredients

manufacturing,

to

meet

the

environmental,

performance, and

cost

requirements for rubber goods made and used in commerce. There is a wide variety of elastomers and ingredients that are available in making rubber goods, which include all of the following types of products: footwear,

tires,

innertubes,

rubber

weath eathe erst stri rip ppi ping ng,,

rolls,

O-rin -ring gs,

retreaded hoses,

sea seals ls,,

tires, belts,

diaph iaphra ragm gms, s,

tubi tubing ng,, rubb rubber er and and late latex x gl glov oves es,, ball ball bl blad adde ders rs,, medi medica call devi device ces, s, bump bumper ers, s, and and nume numero rous us othe otherr products.

“Compounding is a term that has evolved within the plast stiics and rubber industry and in many respects is a misnomer for the material science of

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modi modify fyin ing g a poly polyme merr or poly polyme merr bl blen end d thro throug ugh h additio ition n of other ther materi teria als to achie chieve ve a set set of mechanical

properties

for

a

specific

service

application.”

aw materials for a compound are generally selected in the following order: !"# polymer !natural or synthetic rubber# !$# fillers or reinforcing agent !%# antioxidants and antio&onants !'# plastici&ers or oils !(# bonding agent or adhesive !if needed# !)# tackifer !if needed# !*# vulcani&ation system +curing agent, accelerator!s#, or coagent erf erfor orma manc nce e requ requir irem emen ents ts of the the fina finall prod produc uctt often dictate which specific type of elastomer can be used. The expected usable life for the product is controlled by many factors such as end-customer













safety, and reliability. ubber products are almost always used as a functional part of another system. or exam xample, le, tires ires,, hoses, ses, belt elts, O-rin -ring gs, and numerous

rubber

components

are

used

in

manufacturing automobiles and trucks. The overall life of the vehicle as well as its performance level often relates to the service life or quality level of the rubber parts.

Equipment used for Compounding Compounding The rubber technologist/s mixing department has bags bags of powd powder ers, s, drum drums s of liqu liquid ids s and and bale bales s or granules or chips of raw gum elastomer. These are weig weighe hed d out out prec precis isel ely, y, to matc match h both both the the batc batch h weight needed and the ratio of ingredients in the formulation. 0achines are necessary to mix these













homogeneous

mixture.

1n

many

cases,

the

comp compou ound nder er and and proc proces ess s oper operat ator or expe expend nd their their ener energ gy reduc educin ing g the ela elast stiic com componen nent of the uncured rubber compound, to help it process, and then

increase

that

component

again

during

vulcan vulcani&a i&atio tion. n. 0ixing 0ixing is accom accompli plishe shed d using using mills mills and2 and2or or in inte terrnal nal mixi mixing ng mach machin ines es.. The The resu result ltin ing g compound is then preshaped by mills, extruders or calenders, to prepare it for vulcani&ation. The latter is achieved using molds !which further shape the product#, autoclaves, and sometimes ovens. That 3ust leaves finishing operations, such as removing flash !see section '.)." for an explanation of flash#, or maybe













autoclave# to a finished dimension, and then packaging the product.

Mills These were used at the beginning of the rubber industry and are still an essential piece of rubber processing equipment. 4 mill mill cons consis ists ts of two two hori hori&o &ont ntal ally ly pl plac aced ed holl hollow ow metal cylinders rotating towards each other !see igure #. The distance between the cylinders !mill rolls# can be varied, typically between 5.$( to $.5 cm. This gap between the rolls is called a nip.













igure 6onceptual view of rubber mill rolls

Operation aw gum elastomer is placed into the gap between the two mill rolls, the mill nip. 1t then bands, as a continuous sheet, onto one of the rolls. The speeds of the two rolls are often different, the back roll rota rotati ting ng fast faster er than than the the fron front. t. The The di diff ffer eren ence ce in















nip ni p to dis ispe pers rse e the the in ingr gred edie ient nts s and and to forc force e the the compound to stay on one roll, preferably the front one. 4 friction ratio of ".$(:l is common. owders, liquids, etc., are then added to the nip in a specific way. The process produces friction which creates heat. This excess heat needs to be removed, either by spraying or flooding the inside of the roll with cooling water or by passing water through drilled channels in the wall of the roll. 4 device is necessary to prevent the rubber from moving past the end of the rollers. This is













Mill processing The

following

description

relates

primarily

to

comp compou ound nds s which which us use e su sulf lfur ur as the the cros crossli slink nkin ing g agent. The key to mixing !in a 7anbury mixer or a mill# is to maintain sufficient viscosity viscosity to ensure an an adeq adequa uate te sh shea eari ring ng acti action on,, to di dist stri ribu bute te the the nonnonrubber ingredients into the raw gum elastomer, or to

force

the

raw

gum

elastomer

into

the

micr micros osco copi pic c sp spac aces es of each each fill filler er part partic icle le.. 7oth 7oth mech echanis anism ms hav have been een hyp hypothes thesi& i&ed ed and one













times to reduce its nerve !elasticity# and to lower its

high

viscosity

!low

viscosity

grades

are

avai availa labl ble# e#.. 1t then then form forms s a smoo smooth th,, more more pl plas asti tic, c, band band on the the roll roll.. 8orm 8ormal ally ly most most powd powder ers s !oth !other er than accelerators and sometimes sulfur# are then added. 1f significant heat is produced, then crosslink linkin ing g agen agents ts and and acce accele lerrator ator addi additi tion on will will be delayed to the last part of the mixing process. 1n some cases, when excessive heat is produced, it may be necessary to remove the compound from the mill before the accelerator is added, to avoid













1f the rolls of a mill are twisted to produce a corkscrew effect !they would now be called rotors#, and then a block of steel is placed over the mill nip with the block connected to a steel rod above it, this would be called a ram. The ram would move up, to allow addition of ingredients to the nip, and it would move down to force the compound ingredient ents into the nip. 1f the whole thing is surrounded in a heavy metal 3acket with a chute at the top to put ingredients in and a door at the bottom !underneath the rotors#,













1n "9") 0r. ernley . 7anbury, improved on an ;internal

mixing

machine/

built

by

=

fle f leid ider erer er + "" by desi design gnin ing g the the 7anb 7anbur ury y mixe mixer. r. The 7anbury mixer had modified rotors and the addi additi tion on of a floa floati ting ng weig weight ht. The internal mixer rapi rapidl dly y beca became me an esse essent ntia iall part part of the the rubbe ubberr industry. 4t the present time, mixers are available in si&es ranging from those capable of mixing a kg or so, to those that can mix more than (55 kg per load, equivalent to many large mills. The internal mixer is faster, cleaner, !produces less dust from















vari variab able le ni nip p open openin ing g on a mill mill,, pl plus us imme immedi diat ate e visual feedback of the state of the mix, allows a good good mill mill oper operat ator or a hi high gh degr degree ee of cont contro roll and and consequently dispersion. The internal mixer has a fast fast mixi xin ng cap capabilit ility, y, fro from arou aroun nd two two to ten ten minu minute tes, s, and and thus thus requ requir ires es an effi effici cien entt cool coolin ing g system. This is provided by drilled channels in the walls of the mixing chamber, through which water













power !amperage or watts# and time.













rotors. The ram, pressing on to the rubber mixture, is forced down by a pneumatically or hydraulically controlled cylinder, whose pressure is ad3usted to give the best control of the mixing process. Oil may be poured in from the hopper, or in3ected through a valv valve e in the hop hopper wall 3u 3ust st above the the mix ixin ing g cham chambe ber, r, 0ixi 0ixing ng can can occu occurr betw betwee een n the the roto rotors rs !intermeshing

rotors#

or

between

the

mixing













!varia !variable ble interm intermesh eshing ing clear clearanc ance# e# design design,, where where the distance between the rotors can be varied.

Non-black fillers and other compounding compounding ingredients ilica There are two types of of silica, natural and precipitated. 8atural silicas like diatomaceous diatomaceous earth 1mpart stiffness and give a very dead compound which will extrude without swelling. These are not considered considered among reinforcing reinforcing fillers.













procedures ordinarily ordinarily used for other reinforcing fillers should be followed. 1f mill mixing is following for silica loaded 8 compounds, some productions should be taken to ensure good properties properties and hence the complete batch should mixed and cut from the mill as quickly are possible. 1t is also preferable to mix rubber and silica alone and then to complete the mixing after maturing for one or two says. The probable reason for the improvement improvement in properties properties is that in the absence of any other material, the rubber penetrates more into the filler and thus causes better filler-rubber interaction. >ubsequent addition of other materials does not interfere with any existing rubber-filler















quantity of accelerators or else to use certain activators like ABC of triethanolamine. 1n silicafilled 8 compounds thia& 5"- thiuram combinations combinations are not satisfactory as these are scorchy and are not flat coming. Thia&ol-guanidine combinations combinations are found to be more satisfactory. owever in silicas filled >7 compounds both these combinations combinations are satisfactory. >ilicas are generally













prosecutable buty" stocks with good physical properties by using precipitated silica as filler. recipitated silicas are suitable as filler for translucent compounds based on 8, >7 and nitrile rubbers.

!illers of minor importance"













#rganic fillers

". 6ork: 8atural cork, ground to various degrees of fineness gives compounds with a high degree of resilience and compressibility and is used in flooring, gaskets etc.













$lasticisers $lasticisers and Extenders lasticisers are added in rubber compounds with the following ob3ectives. ". 1ncrease plasticity and workability of the compound. $. 4id in wetting and incorporation of fillers













conditions are right for maximum activity of the plesticiser d# The cost is favourable favourable in comparison with other methods of getting the same effect. hysical plasticisers are used when: a# 0odification of the vulcanisate properties is also desired















). 6ertain petroleum sulophenol, especially its &inc salt, is powerful in 8 and at high temperature in >7.













aromatic, naphthenic and paraffin Oils. 4ll these are available in various grades of viscosity and staining power.












compounds in lage quantities so that the cost of the compound can be reduced, without seriously affecting the final properties. 1mportant 1mportant among the













processing, reduced swelling and shrinkage, higher cure rate, minimised reversion, good ageing etc.













the colours brighter important among the common white pigments are titanium dioxide and lithophone.



























91637420-Rubber-Compounding.pdf

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