Document MMR1aO1r53q1NY01EzeKX1r6L

. jfcgu tbe temperature ofthe piw* d-in* Pl, ^ l^t, tod flow and appMmm Ig^SIkaland hydraulic pramm I**, 11,,1-t.iMl darn rapidly ^"kfiiU pressure within t fracticm d*ft<r prw*ux ii fintappliad. j^iy* Um put cool* and l^mieal presses nup require to maintain dwell --are. Hydraulic prswse gener- _,*d build up pnaeuie more nurhr"1**1 puss-- hut cm. ' --~ it held throughout the no modification is ,t maintained until the put jpiffieitntlv for removal from rwll time range* from 10 to 30 , tkthicker part* requiring longer .fatal cycle tuna, which alao In.!needed to open and close the imemove finished parts, and ttht heated blank, generally ia ^,,s10and 45 see. flw temperature i* controlled to opti- wit flow, rate of coolinf, and prop pedtht stamped part. Positive diea ,oad. La., all ofthe preaa preaaure i* dlotbe material being formed and am thedie. The vertical flash, or tale- (ihetr ed(e, ahould have a clearaf00015 to 0.002 in. and be about Inltog. | Inn*the heated blank covert a large ptiftheetampins tool, relatively little Iflowaseeded to fill the die. Large, pert*atwell at very thick parte ran be formed with relative ease, eboeeee and riba ofall sixaa. Ipints ftAntpifi0 hidid phaee (tamping, the thermor eheet it formed at a temperature *Cor mort below ita crystalline meltI point Thia proceea reaulta in orientaadthe polymer chain, thua enhancing j propertiee in the direction of ation. Die deaign must make allow> for elaitic recovery which can rdhtonjon after the forming pres* a removed. The oolid phase forming ianiem k one of deformation rather llow. Ai a result, erall thickneae will atlnuntully uniform, and abrupt *C* in eras* lection cannot be formed, ^unfilled and filled thermoplattica ifaeueed for solid phaee (tamping. Wopylene and high density polyllroe are moot commonly used. Other 'oplattks such as nylon-4, PVC, and too cod be used. Fiber-reinforced atiom are very difficult to form and ,Bt normally used. rinf ofthermoplastics, like stamping, ^ w carried out either below or above *Mhingpoint Reinforced or filled used for hot forging, whereas billets normally are used for solid las?* ,,**"< Ml** orientation it aimr*")'affected by forming temperature in "j forging and (tamping. "ihil pressure is much higher for solid phase forging than for melt flow forging. For the lower-temperature pincses, the required preaaure ie reported to be between 4000and 10,000 p-S-i. For hot forging, the presaurea are in the tame range as for melt flow stamping, i^, 600 to 2000 pad. Billets for forging are very much thicker than the sheets used in stamping. Heating of billet* to avoid surface degradation and aasura temperature uniformity is there fore more difficult, and control ofthe proceas is more critical. Infrared and circulating hot-air ovena as well aa direct ` contact-heated plates or rolls are UMd to beat the billets. Polypropylene, polyethylene, and AM art the thermoplastics most commonly used for forging. Forging can also be used to form some materials, such as ultrahigh-moleculu-weight polyethylene, which an difficult to form by other methods. Melt-flow stamped thermoplastics am currently used in numerous applications. Automotive end usee, in production or In prototype tasting, include frontend fascia supports, fender liners, oil pane,' eeet components, and battery trays. Stamped shrouds and baffles are being made for lawnmowers. Stamped geu shift covers an being used an garden tractors. A variety ofcontainen am being stamped. A stamped automotive engine oil pan is an example of the coet/performanee ef- fectiveneae potential of thermopiaatic stamping. Stamped from reinforced nylon-6 sheet, such an oil pan provides TMp " malwtah, nil-tight --k against tbe engine block, rigidity te sup port the engine weight during assembly miiwtfifiyji, tmpAft rim! resistance to withstand over-the-reed use, mii< hydrpffriwn nriMnciMOMMiy to contain oil at tagiiM opmtmf tmnpm- atuma. This complex, deep-draw part can be formed rapidly at moderate premum resulting in low operating coats and low tooling rod prat invoptnMOtAutomoth* rat components require rigidity and impact resistance, a com bination readily achieved with long glass these components, a^ tbe back ofa bus eat, am luge, flat, thin parte which can be stamped in a abortcycle at moderate pressure, butwould be difficultto farm by other proteases. Automotive fender linen am currently midit Iry a trlid phase -tamping pmmm Tbaae parti art formed in a very short cycle, thereby minimising forming coats and capital investment, Forged thermoplastics am ueed for parts with heavy emm sections such m pipe flanges and gears. Mixing and compounding Continuous compoundhg By W.A. Mack The continuous compounding and mixing ofpolymers is accomplished by s variety of mechanisms tanging from single-screw to terin-serew extruders with variations in design and additional equipment to achieve a range ofend products. Tbe type ofcompounder or mixar chosen depends upon the specifications and propertiee required ofthe end product, volume re quirements, overall economics, end whether tbe compounding is done inhouse or by a custom compounder. The basic functions ofany compound ing extruder art to melt the plastic and to introduce t closely controlled amount ofsheer energy into the melt to properly disperse and distribute additives or fillers. Such properties as color, flame retardanee, impact and tenefle strength, lubricity, and uvstabflixetios) am ob tained through the addition ofone or mom additives to the basic polymer. A uniform distribution in tbe polymer mix is neces sary for a well-stabilised productand to reduce or eliminate degradation. Multi purpose or multi-additive concentrates were developed to product many char acteristics, and to properly incorporate W.A. Mao e (issues, wwnsr > Weuetei Caip-1(0 Hopesr Aw., Whom*, tu. 074(3. these into tbe bees polymer. 7T choice ofcompounding method and proems is important. There am various typm ofdegradation: thermal, mechanical, chemical, and en vironmental When polymers am me- ; chanieally degraded, a reduction ofmo lecular weight occurs. This is a function ofmechanical shear and the tuna axpoaad to that shear. Viscosity diffemnea between the poly mer matrix and the additives can be a problem with conventional compounding equipment, where conveyance in the sol ids conveying sooe it primarily dependent on frictional forces between the scikk and the betml end screw. Becauseofthe lubricity effect ofthe additives, rieocea heat generation is minimised toward the melting sons, which can lead to a nonbomoganeoui product unless modifica tions an made to obtain tbe desired ma terial. With mors sophisticated ma chinery, conveyance is nearly indepen dent offrictional forces and maltha can be adjusted to oops with the viscosity differences. A single-screw extruder may be usad far compounding colorants, masterbatch, and other additives to the resin when coat ia a major factor end when a rsletively simple deaign is an important comidera- MODERN PLASTICS ENCYCLOPEDIA 1976-1980 347 tram. Single-screw bm my range from 2 Vi in. to 8 in. in diameter with lengths of20 to 42 L/D-One ofthe disadvantages of the eingie-acrewb the difficulty of mix ing poitially melted polymer. Difference in beet history often c*n lend to nonuniformity of the product, and the time required for cleaning screws eleo can in- ctaase costs. Very little mixint occur* inaide the channel in tingle acre* equipment To overcome thb defect, mixinc devices have been initalled to ahift the point ofxero stress to various location* in the screw channel *o a* to achieve an adequate mix. Thb require* that the equipment have sufficient proceeding length to accompliah tlm daaired degree of mixing. A number of improved mixing device* ere svaila- ble, including the EVK, the Maillefer type, and the fluted screw. A further advance in technology b the precompounding of additive* a* concen trate*, which allows their introduction in conventional equipment, with im proved compatibility ofthe additive* and the matrix. Direct addition of additive* b widely u*ed; however, there are draw back* which can be overcome by the u*e of concentrate*. For example, concentrate* eliminate tome problem* ofdkr __ caused by additive* which ere liquid room temperature. It b important, ` ever, that the concentrate level be; the range of the capability of the pi _ ing equipment to avoid problem* of dnm with high leveb of concentre' ` Such concentrate* as tlip-antiblockantioxidant can be prepared in cor: tionsofSOfe or more, but since the fi concentration required b usually I 2%, e concentration of 20 to SO'V be more feasible for proper dispersion ing single-screw equipment Th* problem of poor strum t_ in the channel ha* largely been . by advances in twin-screw extruderd* sign. Thee* extruder* are available in variety ofdesigns, including co-rota ' and counter-rotating systems with variation*. The twin-ecrowa offer pc, conveyance of the material Co- and counter-rotating screw designs can be either internie^ing or nonintermashi When they are intenneehing, they can made self-wiping, which b advanug to the operational economic* as the ecrew* require much lea* downtime for cleaning. While both counter-rotating and corotating screw design* offer positive cc*veysnee, the pattern ofconveyance dilTa In a co-rotating arrangement, the ma terial b conveyed in a figure 8-*hapad pattern from on* screw to the other, thus. increasing the degree of mixing. Nonintermeshing screws are always , open both lengthwise and crosswise. Tht design ofintenneehing screw*, however, include* variations in lengthwise and crosswise open and dosed positions,which directly affect the conveying conditions, the mixing action, arid the pressure build up capacity of the ecrew system. Co-rotat ing twin-screw* can operate at higher speeds than counter-rotating. Counter rotating screws tend to cause a propor- Physical Properties Homoaonnlty Your customers want the nxt load to run just like the last load. The Baker Perkins' MPC/V System is unique in the degree of process control tt offers. In addition to control over screw and barrel speeds, the MP System's patented "barrel valves" provide variable restrictions which allow adjustments while running to con trol melt uniformity. Lower Heat History With the capability of run ning odiabattcally. the MPC/V System allows you to process materials ranging from the most heat sensitive materials to polymers requiring high-energy compounding. The melting pro cess is accomplished in a short span and at a temperature only slightly above the melting point of the materials. The unique barrel valves help conserve energy and minimize the degradation of physical properties. 1551 BakerParidns Inc. Chemical Machinery Division Saginaw/Michigan 48601 PHONE 517/7S2-4121 CIRCLE 242 FOR READER SERVICE becauae oftheir pressure and velocity distribution. Counter-rotating systems have a maximum diameter ofabout 170 mm., and they art uaad primarily for profile extruaion at lower screw speed*. Co-rot*ting screws can be operated at higher screw speed* with greater through put, with leas wear than can counter rotating screw*, because there b no calen dering effect between the creat and flank of the screws. A co-routing, self-wiping twin-screw extruder with 300 mm.-diameter screws can process up to 35,000 Ib^br. of HDP* at 160 r.p.m. screw speed. In addi tion, there b more uniform heat and shear history and more efficient self-cleaning action. Improvements in the design ofcounterand co-routing twin-screw machine* hav* been mad* to improve the degree ofdis- portion and strut* distribution. Inter rupted flighti/ehannel* hav* bean inccrporatad in counter-routing machine* to break the material and reorient tb* layer*. Among tht variation* poaaiblt for eoroUting machines, knurling disks ar* available with the same cross section ta the corresponding screw*, to achieve a higher dap** ofplasticstion. Disks with various width* and staggered angles can 346 MODERN PLASTICS ENCYCLOPEDIA 1979-1980 be arranged along the screw shaft. Rightand left-handed acrew element* alao can be included to accommodate varying protecting requirement! and to amure complete melting in abort distance*. Various feed arrangements for addi tives can be incorporated, including tide and vertical inlet*. Vertical feeders offer advantage* for feeding materials such as glass fiber*, chopped glass, and glass beads which ate highly abrasive and cause considerable wear. Wear it minimiasd by feeding abrasive fillers into the extruder, where the base polymer k already in a molten stag*. A higher feed capacity pos sible with the vertical feeder allow* a reduction in r.pxn. and s considerable reduction in wear. The vertical feeder normally is used in conjunction with a metering system, either a weigh bait feeder or a metering screw. The removal ofvolatile* from poly mers is an important factor in extrusion technology. There is a deterioration of conveying capabilitiee as single-screw di ameter* increase, because the conveyance indevolatilization zones must be at or below atmospheric pressure to prevent vent flow. Hie conveying capabilities of th* twin screws and the renewal of sur faces by product transfer from one screw to the other help to achieve staady-stata, efficient venting. A major advantage of intermeshing self-wiping twin-screw sys tems k the elimination ofmaterial hang up in the ictew channel* in a vent area, which prevents material degradation. For compounding PVCand other beatend shear sensitive materials, two-stage systems have been developed. The use of twin-screw extruder* followed by single- eerew has proved highly effective, by separating the miring and compounding operation from the pumping, conveying, and extruding function. Interchangeable screw and kneading elements in the twin- screw extruder can be used to vary the length of kneading ion-- to maintain correct beat levels for dispersion ofadd itives without degradation ofthe addi tive* or the polymer. Another system combinM a twin-screw feed section with a large rotating cone for imparting high shear and a singk- acrew extruder for final extrusion through a pelletising die. Thk system k designed for tba compounding and palletising of flexible pvc formulations. Material, usual ly a premix bom a ribbon blender, k fed into an agitated hopper and then to a abort twin-screw extruder for pukatioo- free conveying to the shear cone. Th# sheer cone k a ribbed conical screw that rotates in a corresponding conical housing or barrel The diameter of th* cone in crease* in th* direction ofmaterial flow and the space between the cone and th* bousing can be varied from 0.3 to 6.0 mm. during operation. When the material k forced between the cone and housing, it k plasticated, gelled, end homogenized. No ad ' energy i* required to melt tha material becaust ofthe high sheer force by the rotating cone. Even tem: _ distribution k obtained because oftU relatively small material imae'sertimi. There k a wide variety ofcommercial pelletiring systems available today, fail into two general categories: hot dk face cutting and cold cutting systems. The basic processingstep* involved hot die face cutting are; 1) Extrusion of theplacticatad through a dk plat*. 2) Immediate cuttingofth* strands ofmelt by rotating knives. 3) Transportation ofth* pellets outf th* pelletiser hood. 4) Cooling or quenching ofth* pellets in air snd/or water. 6) Drying ofthe pellets. Cold cutting involves: 1) Extrusion oftha plasticated nmdiun through a strand or strip dk. 2) Transportation ofthe extruded strands or strips (band or ribbon) thresh a cooling medium to the cutting ap paratus. 3) Cutting ofthe cooled strands or strips in granulators. 4) Drying ofth* pellet*. Tba strand* or strips alao can be dried plastic powders & pellets National Conveyors now has hundreds of pneumatic sys tems in producing and converting plants all over the world. Capacities run up to 340,000 lbs. per hour. Continuous association with the industry over a 25-year Aperiod keeps National Conveyors up to date on cur Nationalrent practice. For full facts, mNa write for Bulletin P-79B. rCnOsMa/VefVOWS COMAUW. SVC. Fairvkw, New Jersey 07022 201-246-9136 CIRCLE 244 FOR READER SERVICE 350 MODERN PLASTICS ENCYCLOPEDIA 1979-1960 advanced technology is making new Thoreson McCosh HIGH EFFICIENCY AUTOMATED resin handling a preparatior equipmer lowerIn cost, less expr less expensive to mat' more efficient in op? hiqh vnciir AUTOMATED PftlT HIQH EFFICIP*. HIQH EFFICIENCY*. Cftac* Ms Ihomasii SteCosa a*aa. syslsaw. MSaleokal way teemyaw*aa . FOR MOMMPOMMTOM C> S' "JMcCOSHINC UttnundMblFl, Tn>r,SNcMgaa4*0*4,p*Mt-yts^a* % v\vv vy % %% <0 <O V CIRCLE 245 FOR READER St UCC 035056 % before they ar* cut by means ofan air knife. The shape ofthe pellet required for spe cific applications hai a direct bearing oc the cutting method (elected. Final proceasmg efficiency end throughput retee ere directly effected by pellet characteristic* such bulk density, pelietuniformity, eurfaee structure, end surface moisture. Strand cutting the meet efficient and economical method for many poly, mere at retee of up to 4000 lbVhr. Strip dicing lyatem* are available which can accommodate rate* up to 11,000lbVhr. and, where cube-ahaped pellets are re quired, the pmreel offart advantage*. A unique cold euttinf ayetem is a self* attending forced conveyance palletirer for difficult-to-strand material* which elimiaatea stoppage and binding which are common for certain plastics. This is accomplished hy forced conveyance tfarou(h the water hath in an up-and- down path. Throughput rentes between 2000and 15.000 lbVhr. an possible for many dif ferent materials, with hot die face cutters. The water ring pelletiser it ef fects for production rates of7000 to 16.000 lbVhr. The water ring pelletiier can be used effectively for almost any thermoplastic, including all olefin bomopolymen and copolymers, FS, aBS, PUMA, and pc. It is eleoreliable with thedifficult-to-handl* highly filled thermoplastic*. In water ring pelletizing, the extruded polymer is cut immediately after discharge by rotat ing cutting blades. The freshly cut hot pellets ere thrown into a spirally rotating water stream ofapproximately H -in. depth. Theyare then quenched and spirallyconveyed through the pelletimr hood, end after rotation ere discharged into a water pre-separatorand then to a subsequent drying operation. For higher-volume polymer production, new developments in underwater pelletis ingsystems have allowed higher throtghput rate* with the main application being the polyolefin*. Cutting techniques have been developed for relatively low-viscosity polymers such a* polyamide, PC; and nou. The basic design difference in underwater pelletizing systems i* the ar rangementofthe die plate and water chamber. A split die plate design providee insulation to prevent froese-up of the polymer in the nozzle and mini mize* heat lose in the dia plate. Discontinuous compounding ByJ.K.L. Bajaj In the plastics processing industry, batch or discontinuous mixers are extensively used at various stages ofoperation. In many instances they are used as part of a continuous system. Hand* types Ribbon blendtrt are used for the mixing ofpowders, pastes, end liquids. They ere workhorses for pvc compounding, cooling, standardization, color blending, and reclaim scrap blending. Nominal capacities range from about 1 to 2500 cu. ft Typically a ribbon blender consists ofouter and inner spiral ribbon* supported on a shaft which runs longi tudinally through the center of the blender tank. The arrangement ofthese ribbons provides a triple mixing action. First, as the agitators rotate, the material is tumbled and carried radially around the ineide of the blender. Second, the pitch of the outer ribbon moves the mate rial towards the discharge opening. Third, the inner ribbon which has an opposing pitch moves the material ewey from the discharge opening. Widths ofthe inner end outer ribbons are carefully balanced to provide an even movement of material in both directions and to prevent tha load from building up at any spot in the blender. Differenttypes and designs and even different numbers of agitator blades ere . .used for various application*. Two or more agitators in the lame tank are nor mally used for unusually large capacities. J-K.l. Be* a PraCuct Manager. Day Mona. S32 Besot St. Cmamm. One 4SZ1Z. Conical mixer with orbitingscrew it ideal for solid/aolid blending and paste dispersion. It is very effective for intimate blending ofmatsrials ofwidely varying densities, shapes, and particle sixes. Large batches can be handled and pre cision additions can be made--as little as 50 pert* per million. Typical capacities range from about 1 to 1A50 cu. ft. Three distinct mixing actions are involved. A screw agitator turning an its axis produces a lifting action as it spirals the materials in an upward flow in tha tank. At the same time, while orbiting the tank, the screw removes material away from the wall and deflects it into the center ofthe tank, setting up a sec ond, wider spiral current throughout the batch. Material lifted upward by tb* screw move* downward, thoroughly inter mixingwith the material being spiraled upward. These three actions in on* screw result in the most intimate and thorough intermingling ofall ingredients. Horizontal itationary cylindrical mixers have mixing elemente attached to arm* ac e shaft centrally mounted in the mixing container. The mixing elements impart intensive axial and radial movement to the material. Extremely fast lateral movement cause* the mast of material to be propelled from on* sDd of the tank to the otto, retting up strong impact currents, violent collisions, and particle interaction at the center of the vessel. This it ideally suited for blending dry powders, moist solids, solids and liq uids, together with pasty substance* up to end including high-viscoejty dough matte*. Some of the application are** are edmixing oftree* element* rapid ing ofhighly filled pvc pastas and sensitive bot-melt adbeaives; " polyurethane, natural end synthetic ben; end preparation of bulk molding compound, and rvcdryWeods. These machine* ire commonlyavail.able up to about 700 cu. ft. in size. Double-arm mixer* are characterized as medium-to-high energy procereing machines. Two interacting heavy duty agitators do the intense shearing, ing, knaading, and folding <n trouglh shaped chamber. This machine is used for compounding a wide range of heavy pot**, metrics, caulks, end othw' hard-to-mix highly viscous materials re silioons elastomers, filled epoatire. ben, hot-melts, and bulk molding campounds. The materials can be fed in sheets or chunks to the machine. Diffi types ofagitator*arecmployed, upon the application. Tbs sigma-type agitator blade it beet for all-around im. It may be used either with tangential or overlapping action. These machines are available up to 1000gal capacity. Banbury-type mixer* utilise two hori zontal epimtotaped agitator* rotating $ in opposite direction at a differential speed, and working together with vertical ' ram to develop very high shear. Prims applications art for rubber and rvccoaspounding. There machines are also being used for processing polyolefin*, ABB, and polystyrene, along with tbermoaeta such at melamines and urea. Maximum ca pacity h about 1000 lbV batch, and de pending upon material the production rates can be as high as 40 batch**/hr. Physical states of mbM In MoUd-tolid mixing, whan product is dry and flowable, eom* of the more im portant properties ofsolids that affect mixing performance are specific gravity BussCt and bulk density, surface area, interparti- de friction, angle ofrepo**, and cohesion offine powders and granules. Three mechanisms postulated for mixing of dry solids ere diffusive miring, Pelletiz for: sheer mixing, and convective mixing. Different types of mixers have one, two, or *11 three mechanism* effective at on* time. The difference* in particle size, density, shape, electrostatic properties, PVC Extrusion, SMi PVC Bottle, Wire, C PVC Continuous Ca PhenoMcs, Pilled Pol and resilience are the properties of mate- PolyoWin*. LDPE, K riel that cause segregation. When pigment particle* are mixed with plastic pellets J the very fine pigment will usually adhere j and form a coating cm the pellet*. Hence, there will not be any segregation during and aftar mixing. Mssterbeteh, Modifi Polyester*. Potyamic Thermoplastic Rufat* EPDM, EPM, NBR, S Powder Coating Fort AeryUc. Thermoplasti Ribbon bbnden, vertical com mixers with an orbiting screw, and air mixers have been tanned nonsegragativ* beceuss they rely mainly on convection current*. Rotating drum* end mixer* which rely on tumbling end stirring, such as doublecon* and twin-shall mixers, are aegrtg*' tive because In three machines the mixing mechanism it predominately diffusive or shear mixing. For segregating type* of materials, discharge, conveying, end storage should be looked into closely after the product* have been mixed. Liquid-eolid mixing and ditptnion. Special f Continuously working throughputs from 60- Unique hot die-face pi Cylindrical, freo-flmrin Precise control of fluxi Sturdy single-screw m shear advantages offei lengthwise -- opena in t A complete, building bl for the optimal solution 352 MODERN PLASTICS ENCYCLOPEDIA 1979-1900 9 UCC 035057 CBtCLE 247 POP REAPER REDUCE open mold laminating COSTS! Th> Vwiu choppy gun min- m W> imizes mist and fumes. How? With the only low pressure air less system in the industry. Since low mist and fumes means less wasted material, you reduce the cost of every part you make. Plus, because of the cleaner environment, we are able to build machines for large volume applications based on mechanization of the basic chopper gun. The sheet machine is de signed for volume pro duction of flat parts. With one op erator, the Venus sheet ma chine can gel coat, chop, and roll a sheet 16' wide and 100' long in 1% hours. The bridge crane impregna- torcan layup to 1000 lbs. of saturated woven rov- ing/mat laminate per hour--4 tons in 8 hours. Laminate is laid in mold from overhead Impreg nating unit capable of traveling in any direction by moving a joy stick control, information about these and other machines, plus papers on mechanized open mold lamination techniques are available from: PRODUCTS, inc. less IVES AVENUE KENT. WASHINGTON 98031 (206) 854-2660 Telex: 32-8488 CIRCLE 251 FOR READER SERVICE where the product i* liquid. The factors effecting mixing-dispersion here an the turbulence, interparticle attraction, the viscosity end density of liquid*, and their natural affinity to solids. The viscosity parameter is important for most plastic* proceeeed because it it not only effected by temperature but by (bear rata. Circu lation ofthe liquid* i* absolutely essential for satisfactory performance. To obtainagOodmixitienece--arytodiapero the aolid* so that all surfaces of th* particle* are coated with the liquid. Plaatiaola and abed molding compound pre mia** are two of the many ana* when liquid* are mixed with eolida end when the final product also if a pourable liquid. High-speed diaperaen, ribbon biendera, and conical mixen with an orbiting acrew and top entering dieeolver are being uaed for tuch application*. Liquid-solid mixing where the product ia dry. In PVC compounding the liquid plasticizer is absorbed by the resin, reaulting in a dry product Medium-intenaity vertical mixer* and jacketed ribbon blender* are all uaed. Paste mixing. In a put* the physical propertiea of the mixture are quite dif ferent from that of it* aolid and liquid constituent*. Internal dynamic abaar ia the method uaed for good dispersion. When mixing high solid*-low liquids, the atiffer the put* the greater the inter nal dynamic shear. Diffusion is an im portant process in the early stage* of dispersing s solid phase in liquid me dium. Machines for this dispersion are characterised by high power require ments and low speed, and the mixer is designed for slow, large-scale distributive movement ofthe mixture as well aa intense local mechanical action. Prepara tion ofbulk molding compound, high viacoaity mastics, and some plestisol* fall in this category. Fluxing of compounded polymer sys tems. Fluxing results in an extreme inti Motionless mixers By-Annette Comeau Any stationary baffle installed in a pipe aril] utilise the energy of the flowing fluid to produce mixing. The baffle represents a simple motionless mixer. Industrial motionless mixer* have programmed flow patten* that create progressive mixing action by: 1) flow division, and exponen tial increase in the number offlow striatione, and 2) radial circulation of the processed fluid around its own hydraulic center. Energy required to pro mote mixing is simply the differential pressure drop between product Inlet and outlet. Motionless mixer* are designed to pro duce a melt having almost no random character in viscosity, temperature, or mass. In essence, they are processing aid* that eliminate melt nonunifonnitiea In Aentes Comesu e MerSeMg Cdnwonewenuanuvf, Ksncs Com,. sum Cftsmmeei me. Kenct Pan,. Norm Andaw. Mass DIMS 356 MODERN PLASTICS ENCYCLOPEDIA 1979-1980 mate blend ofthe additives with that man to produce a eemimolten compounded polymeru a finished produqj Color concentrates and rvccomp are fluxed prior to further processing.. The Banburytype, high-speed fluxing mixer, and the double-arm mixer-ex truder sre all used for such application] When selecting a mixer, careful cxmaid-^ eralion should be given to the sice oft unit required. The full cost per pounds the maximum daily or hourly produ rate must be eetabliabed to determine* suitable batch six*. Ue* ofseveral smal mixen rather than one Urge unit ueua%J will increase labor costs and initial ij investment. i The need to control or change the trael perature and pressure during prnrxming ( should also be considered. Some types ef ] ewaiiAttia equipment are not suited to use beating ;SsS!SStiSm or cooling device* and others may pot la operated under vacuum or with internal pressure. Purchase of a light-duty mix* should not be overlooked ifthe materiel will be dispersed at a high temperature. - NLtuilEMiMI Also, thoughtshould be given to the ' material* which will come in contact witk | the final product Although a product may not be contaminated by plain steel, a polished stainless steel unit is easier to dean. Labor that is saved may more thu justify the additional coat of e rteinleee steel unit Other constructions tuch as the use ofhigh manganaet steel and chrome plating may be considered. The flexibility ofthe unit is also worth a long look. Can the mixer be readily cleaned to change from one product to War .STwdMl .Scam c n another and adapt to future production demands? Or, ifanother piece of equip ment in the plant breaks down, can the mixer be pressed into temporary service? Pretesting pilot-scale equipment is an extremely useful way of evaluating the various dispersers available. critical tolerance or appearance applica tions and where a machine, even under optimum condition*, cannot meet product quality requirements. -EcCMHMlW*1 .tayWlMHeMM IMiiX* Types of proeweaing Motionless mixer* have a place in all areas ofextrusion: wire and cable coating, - blow molding, foam sheeL sheet, pip* and w profile, and extrusion coatu*. Mixer ' units com* complete with hardened toolsteel housings, mating flanges, heater bands, and transition pieces for adapts- tion to the extruder barrel and die. Mixar installation in extrusion processes ~4 tenues near perfect cdtor/additive diatrih- ? utive mixing and uniform melt tempera- tura* for thermoplastics, including nylon, polyethylene, polystyrene, acrylic, celluloeie, and vinyl resins. The motionless mixer will virtually eliminate melt stream temperature gra dients created either by tba extruder or ucc 035058 Uttieford Utfieford inter, any plastics pn efficient fluldte duaasmHngtir and hold tempt imlts; thorough widely differing consistent resui continuous^. They're easyto ( CHCLE2sarorif ther proem equipment A thermally homogenized melt stream with no radial temperature gradient* provide* uniform viscosity, predae gage control, and increased output Specifically, in-line unita have bean found toe 1) Virtually eliminate pcattioodependent variationa aa well aa effect up toe 10 to 20% improvement in short-term, time-dependant variationa before melt reaches tha dl*. 2) Allow the (crew to be run at hither r.p m.. meaning greeter output without aacrifice in product quality. 3) Saw raein by reducing thicknsa* variationa in both machine and tranaverae direction*. 4) Inarea*# output matched by im- provementa in gage control. 6) Reduce additive loading*, up to 25% inaome typee ofcolorants, facilitate rapid color change*, andprovideimproved aurface gloaa. 6) Aaaure uniform distribution in the melt of a primary blowing agent. Motionleaa mixeri installed on an infec tion molding machinewill eliminate color noounifarautiee and reduce temperature yariationa in the melt stream. Incorporation ofa motinnlaaa mixer will prevent over or under loadings in the molded part, eliminate color streaking and therefore aaw concentrate# or dry color. Reein savings are pnaaihle, line* better flow maena lew packing ofthe add. The mixing oocxlee are deeigned to replace standard nozzles <m all eziatinf injection aquipmant Mixars come with standard removable tips, either ata nylon or general-purpose design. Maximum operating pteaaureia approximately 20,000 pad. at 600* P. Unlike ao-ca&ed dispersion nozzles which create thouaanda ofpoundaofback praaaure, aetanderd motionleaa mixer node operatee with a differential preeaure drop in the range of 200to500pei- Computer color matching By D.L. Alston A typical computer color matching ayatern, in addition to the main computer, include* a epectrophotometer and periph eral devicea auch aa tine printer* for hard copy record* of computer output and video icreena for rapid visual diiplay of output. Bwential to the operation of the system i* the spectrophotometer, which supplies color information to the computer on the color standard. The instrumentacana the visible spectrum (rainbow colors) to deter mine the spectral curve, Le., the quantity of each spectrum color in the measured sample. Utilising this information, the computer mathematically calculates the amounts to be selected ofeach pigment to provide the beet match to a color stan dard. Some system* allow many pigments to be considered to provide the least costly, least metameric match. The data on pigments which the com puter uses in it* calculation* usually is D.L. amba a Appbeatiom Snaewat AopfceO Cotar System* ine.. P.0. Bos MOO. Prstcaion. NJ. 0*5*0. stored on some type ofbulk storage devict for easy access to the system. Thee* de vices generally incorporate s magnetic medium similar to a tape recorder and vary in capacity from small to almost infinite depending on the specific need. Curve plotter* also may be interfaced with a color control systam to automati cally plot spectra] curves, or the spectra] curve may bs displayed on video terminal screena with graphic* capabilities. In a typical color matching routine, a system operator instructs the computer to run a color match program. The opera tor then answer* questions concerning pigment selection, match criteria, ate., and presents the color standard tothe spectrophotometer for measurement. After measurement, the match program considers all the pigments entered and give* all formulas which maet the speci fied color criteria. Present technology has dewloped to the point where computer systems can control not only the matching and correc tion ofcolors but the actual dispensing of liquid colorants. Plastisol processing By G.R. Crane A vinyl plastisol is a dispersion ofPVC res in in a liquid plasticiser. Since it is a fluid, it can be formed by dipping, rotational casting, spreading, or spraying to produce a wide variety of molded items or coated good*. As heat is applied, the plastisol compound gel* and subsequently fuses to become a homogeneous melt Upon cool- 0 R Crane s Stolon Head. Goodyear Tee a RuMef Co i tee E Mina SI . Asian. Ohio *43 is ing.it become* a solid with good physical properties and chemical resistance, Sine* the liquid plasticiser becomes part of the final fused compound, plastisol* are con sidered to be 100% solid* systems. At times, to achieve lower viacoaity or to work at a very low plasticizer level, volatile organic thinner* may be incorpor ated. Such compounds are known as or ganosol*. While this technique aids in producing hard finish coatings, extra care is required to assure that the thinner* are evaporated before fusion. Too rapid tkm and fusion may result in bubbling the finish coating*. The kroer the sohm | content, the mar* costly an otguoMl coating will be, sine* the thinner is kat1 and extra energy is required tovoiatih . iaait. Pvc roain* uaad in plastisol cmapoundtag ar* generally known as dispersion tsria Tbs primarydispersion main* ar*ipso- duosd by highly sophisticated tsi which yields carefully controlled _ is* distributions with avaraga diam*t in the neighborhood of 1 micron. High- ; molecular-weight homopaiymsn an pm- farted fee moat mating and molding sppg cations. Copolymers ofvinyl acetate with vinyl chloride are employed in specialty - areas requiring lower fusion tampamtaen A number oflow- and mediuro-moieeular- weight homopolynwr* also are produced to satisfy special property tequiramsula, PLastitol blending resin* often around to replace 10 to 00% ofthe dispersion min. Blsnding resins contribute versatility to the formulating schema a* they offer " viscosity reduction, cost savings, giro* v oontrol, air release improvsmant, and pi retardation. Modam blending reams ar* available in well-oontrolled particle si** range* averaging 20 to 20 micron*. A ranp ofmolecular weight* permit* selection at a blsnding resin to match the dispersion resin. When uaad at moderate level* they may fuse as well as the primary dispersiaa I resin and in some caae* may actually im prove physical propertiesPlasticisers for pvcdispersions mint be chosen for their effect* upon viscosity as well as fusion properties. Moat com monly used ar* th* monomeric eaters, with dioctyl phthalat* ths basis for tbs . majority ofapplications. Tha longer chain, linear phthalate* offer improved viacueity control, low temperature flexi bility and permanence at a modest cost increase. High-solvating type* such as butyl benxyl phthalat* at* employed to enhance fusion properties and for special properties, eg., stain resistance in coatad flooring wear layer*. Adipate and assist* eaten, substituted for a minor proportion of the total plasticiser system, greatly re duce the plastisol viscosity while improv ing low-temperature performance and hand or rubbery quality. Least common an tha polymeric types, whose high cost and high viacoaity must bejustified by * need for exceptional extraction resistance Plastisol*, lilt* other PVC compounds, re quire stabilization against degradation by heat and light. Barium-cadium-sinc bq- . uida are most commonly used because of their favorable balance ofstabilizing effi ciency, air release, and viscosity control effects. Calcium-zinc liquids maybe J**- fsrTed for low toxidty and stain rseist- anct. Epoxidized oils which an often in cluded in the plasticiser system act syner- gistically with tha mats) stabilizers. Special requirement* may call for tin or lead stabilizers. Auxiliary component* of plastisol* in clude fillers, used chiefly for cost reduc tion, color pigments, blowing agents, aur- 358 MODERN PLASTICS ENCYCLOPEDIA 1979-1980 UCC 035059 k mlxtr atandi blanc diaper timam tariai* dsnaiti particle for sta batch* tromely age, Ct 1,400 CL Plus ga! aaa _e ragn t dtetf high mixer Ideal! production c SMC prami and/or pigrr Iona. Capai BOO gallon*. 2S3 FOR Re factant*, mold relearn agent*, and adbeion promoter*. Any ofthese may ba com bined with a variety ofrain*, plasticizers, and stabilizer* to achieve specific end-use properties. Fabric coatinf. Leather-like, vinyl-coated fabric* are widely used in automotive in terior*, furniture, upholstery, ahoa producto. luggage. and handbap. Knife coating offabrics was one ofthe earliest appli cations of p'aatian'i Relatively highvi*co*ity compound* can be uaed and tbe rbaolo(y can be adjusted to permit tba ooeting oflooae weave fabric* without exeeMiva penetration or strike-through. Reverie roll coatera are uaed for high speed. high-volume coating*. Plastisol rbeolofy ia critical on a revere* roll coater. Use high speed and extremely high shear demand low vi*co*ity and near-Newtonian flow properties. In return for a relatively high capital investment, the reverse roll coeter enable* the processor to produce high yardage ofhigh-quality coated fab ric* with good gage control. Another approach to coated fabrics i* baaed on the uae of emboaaed release pa per. The paper, embossed with the desired grain pattern, i* the carrier medium through the oven. A *kin coat ofsolid plastisol is cast first, then gelled in a abort heating zona. One or more inner layers are cast next and also gelled. Tbe inner portion may be a foamable plastisol, containing a chemical blowing agent such as azodicarbonamide. Finally, the fabric backing is applied and gently pressed into tbe last semi-gelled layer with a kiss roll, and the entire construction passes through the fusion oven where the multi ple layer* are fused, bonded securely to gether, and the foamable layer expand* to give a cellular core. This method produce* coated fabrics combining a luxurious soft hand, a tough abrasion-resistant skin, and a permanent, molded-in grain that cannot be obtained by poat-emboaaing. Tbe re lease paper is rewound and reused a* many times aa possible for economy. A wide variety offilm and/or foam con struction* is produced without supporting fabrics. These can include place mats, tape, various upholstery items, and cer tain apparel items. Production ofsuch items usually is accomplished by casting on release paper or stainless steel belt. The film or film and foam construction may be cast as described above, fused, separated from the carrier medium, and cooled before being wound on a roll to pre vent distortion. Coatedflooring. Today's extra-wide roll goods flooring is produced by reverse roll coating (normally on aabaato* felt) and rotogravure printing. Designs are multi colored and almost unlimited in complex ity and artistic beauty. Many have an ex panded vinyl plastisol cushioning layer beneath the printed pattern and the dear top coat or wear layer. Embossing ofthe foam layer aids in producing a threedimensional effect in the pattern. Em bossing may be accomplished either by mechanical methods or by a patented chemical embossing technique. Ifa me chanical emboss is used, it is the last step ofthe process. Coil coating. Protective and/or decora tive amtings are applied to sheet metal or aluminum in the mill, before the coils are shipped to the forming plant. Thin coatings ofplastisol or organosol are ap plied by reverse roll coeter and baked to produce a durable finish. The metal strip may then be formed into siding or other shapes without additional decorating. Adhaaion is obtained by the uae ofa suit able primer. Clone dipping. Both unsupported and fabric-supported vinyl gloves are pro duced by dipping. In the former case, a thin coating is ftiaed on the mold after allowing the excess to drain thoroughly. The fabric type is produced bystraichiag a cotton liner over the mold farm, than dipping it briefly into the plastisol, drain ing, and fusing. Rheology ofthe plastisol is all-important as the coating weight, flexibility, and degree of panetratian must hn Iwliiuwt. Dip coating. Many metal items are given e protective coating by dipping in a plastisoL A common example is the addi tion ofcushioning grips to tools. The usual method is by hot dipping, wherein thepre heated metal cause* a certain thickness ofthe compound to be picked up through gelation. A variation ofthis proeam is dip molding, in which the mold is removed and reined while the molded vinyl be come* the complete object Small items such a* bicycle grip* may be economically produced by dip molding. Another variation ia cold dipping. The plastisol must display highly peeudoplastie flow behavior to coat an object such as a dishdrain rack. A relatively heavy coat ing ia carried on the object solely through its high viscosity and must resist sagging or running through the subsequent gela tion and fusion steps. Sluth molding. Article* such as boots and doll heads are molded by using bast to gel a plastisol coating onto the mold. The mold* may be either preheeted or cold-filled. In the Utter case, heat is ap plied to the exterior of the mold under carefully controlled condition* after fill ing. The ungelled plastisol is then drained and recycled end the mold is carried into e fusion oven. After cooling, the built up coating can be stripped. Its exterior sur face will exactly reproduce the mold interior. Rotational catting. This technique ia similar to the process used to produce hol low chocolate Easter bunnie*. Typical products include balls, toys, and automo tive ann rests. A measured charge ofplaatiaoi is delivered into halfofe split mold. The mold is dosed and mounted on tb* arm ofa rotational molding machine. As the molds are simultaneously rotated around two perpendicular axes, the plastiaol flows over and evenly coats all sur faces ofthe mold interior. This takes place edthin the funon oven, ao that on subse quent cooling and opening ofthe mold a rinsed, hollow object is produced. Cavity or in-place molding. This meth od is used to produce diverse item* includ ing automotive air filter gasket*, synthetic fishing lures, and novelty items. A sol in this application generally is or metered into tray-type mold end equently fused. Another application daeervee attention. Closure sealers that are f< in place represent a fairly important ket. In the case 6fcape, usually tlw inside area ofthe cap is coated, whil* a~ jar lids it normally is limited to a ring around the area that make* contactwtt the jar. Caulk* and sealant*. Plestieoto with, tremely high viscosity are used aa for automotive bodyjoints, drip raih, refrigerator cabinets. Rheology is tant to prevent sagging prior to fusion. Strand coating. A relatively new growing area is tb* coating offibers wiping dice. Chiefly applied to fiaas strands, the technique permits high-^w application ofthin coatings. Aftertax the strands art woven and haat-fusedfc gather to produce insect screening. Plra sol rheology end particle m control sn mini isl to successful operation. Spray coating. Plastisol* also can hi sprayed, and such has been tha csm ia many metal-coating applications. Ccwtrol ofcompound viscosity and spray am ditioos can lead to a variety ofpoasibia textures. This ana is finding new proas nence with the increasing uae in eutems ties undereoating application*. Cellular vinyl may b* used in any oftks above procmaa*. Cellular vinyl i* knows as vinyl foam, vinyl sponge, or expandri vinyl, and while some may differentiate between time according to the methodd production and/or the type ofcell struc ture, there is no universally accepted aamendature. The foam may be open caU ordoMd dll Mechanical foam it the term appliedfe foam produced by mechanical introduc tion ofair or other gate* into the plestitoL Most commonly, air is introduced ia a plastisol which indudcaafrothingagHL The gat is dissolved in tb* plastisol undo pressure ate low temperature. Wbentto plastisol is released to atmospheric pres sure, the froth is formed. The froth it tin subjected to beat for final fusion. This process produce* predominantly openid foam. Chemically blown foam is produced when a chemical blowing agent which few been mixed with the plastisol decompose to produce a gas which expands the riajl compound. This decomposition mayoecur in the plaatiaol compound at atmo spheric pressure (which is usually ths case) or in closed molds undsr pressure There ar# two general types ofprocsstas that operate at atmospheric premure: 1) Usings blowing agent that telesaw gas at relatively low temperatures, th* plastisol is heated to a point below it* gelation temperature whai* tbe gas is re leased to form a froth. The froth is than heated to the fusion temperature and cooled. This process produce* largelyeft cell foam but it finds little use beeaum of its critical nature. 2) A very high percentage ofcsllular rinyl ia produced 1 Mowing agent whi. fuuon temperatur pend th* hot melL poet commonly ua guess a mixture of put under meet coi predominate. In g< Belt viscosity at ti the more closed cel riscoaitywillrawh while too low a mel is large cells (posei toss ofgee. Melt via lams temperature, tbs molecularweig Post-1 Molded | By F.T. Osther Ibebinicdpertar sobstantially redvx grove part quality, cycle times normal latent product, a*) snm work. Tha ays sorkizy repetitive! tactions ofa aeccn can protect the pro aurface marring cai from th* molds. Co prevented a* requii parts. Equipment c die heavy, large par parts requiring ace placement. More p< control requitemee Add the obvious keeping operatorst to the savings in dh machine productiv quality, end it toes, should consider aut Automatic parts bt divided into fou: handling, unacram sad positive takem Tha beat system cation will depend, md strength, mack design, number ofc system, length ofpi material. A process vide rang* ofeophi tarn th* relatively i *eyor system* to th duplicating operate The simplestand 1* tawch, bulk handli rang* ofsmall par short production ro rnatik sines part i rial, and mold daaig handling procedure FT Omars Mamma Is. |e Srsem*, s.o. *oioc 360 MODERN PLASTICS ENCYCLOPEDIA 1979-1980 UCC Q35060 -JL- the type and amount ofplastictxer, and tba fuskm temperature. In addition, ths laa rekase temperature can b* variad to suit a particular formulation either by chmin| the Mowing agent or by changing the ftabilixer-activator ayatcm to vary the gaa relaaie temperature of a given blowing agent. Above atmospheric pressure profeaaia are uaed to produce foam withnearly 100% closed calk (sometimes called unicellular foam) aueh ee ia uaed in flotation equip ment Aa in the case ofother chemically blown foams, a blowing agent is mixed into the plaetiaol compound. Thia cowpound it then uaed to fill praaaure molds and Anion takee place in a press under sufficient pressure to contain the yea toleaned by the Mowing agent.The Anad compound it cooled while under pleasure until it is strong enough to contain the |aa when the pressure is released. When the fused pam are removed from the mold, the expansion is not complete; the parts must be heated ia a low-temperature oven (210 to 220* F.) for several hours to com plete the expansion and relieve streaeae. Sometimes steam is uaed to aid this proc ess. This is an expensive processand both formulation and past treatment ate im portant to the dimensional stability ofthe parts produced. Post-production handling Molded parts removal 0yF.T. Osther Mnairnl parts removal systems can mur`""]' reduce labor costs and Im ps* part quality. Constant machine time* normally produce e more conmmt product, especially on dose tolarmm ecrk. The systeme are capable of taking repetitively with a precision of Senicesof a second. Positive handling amprotect the product from possible effetemarring caused when dropping tsm tbs molds. Contamination can be' pneeted at required in many medicd sets. Equipment can be selected to hanArlmvy, large parts or small, delicate mn> lequiring accurate and gentle ihwmsnt. More parts may meet quality mid requirements. Md the obvious safety benefits of mping operators out ofthe platen area * thesavings in direct coats, increased mriiiwc productivity, end improved ewhty.tnd it is easy to eec why a molder meild consider automation. Automatic parts handling systems can fe divided into four main groups: bulk kwdling, unscrambling, controlled drop, wd positive takeout The best system for s particular appli**e will depend on part site, geometry ddiength, machine cycle time, mold number ofcavities, mold runner length ofproduction run, and raw ****f*tl- A processor can choose from a *<eerange ofsophisticated equipment lb* relatively simple carton and conTjwsystem to the programmable robot ^"rating operator movements. **handling ^vtitaplestand least expensive ap- bulk handling, is ideally suited to ofsmall parts, particularly in ^ Production rune. It is also the mast *< 1j ,inc* geometry, raw matemold d*gn have noeffect on ^rag procedures. ucc 035061 With bulk handling, the product is ejected from the mold and deposited into a csrton or tote bin. Ifno further process ing is required, s shipping carton may be used to collect the parts. When small parts are deposited into large cartons, operator attendance at the machine it only required every few hours to replace the carton. With larger parts, an auto matic counting or weighing system may be required which indexes filled cartons away from the loading area. Operator at tendance can be minimized by providing sufficient inventory ofempty cartons and adequate storage space for the filled containers. Runnerlew molds simplifythe use of bulk handling, since only the parts need be handled. With cold runner molds, a parts runner separator between the mold end carton loading station separates parte from the runners for regrinding. With automatic scrap regrinding and recircula tion to the machine hopper, this approach ia almost as reliabla as completely runnerlees molding. Parts uMcrembtlng Many unscrambling systems use a vibra tory bowl feeder. Stacking devices that orient end count the parte--containers, lids, drinking glsssss, etc.--ere widely used. Unscrambler* must accumulate sufficient inventory of the finiahed prod uct to enable an operator to handle the output ofseveral machine lines. With cold runner molds, a parts runner separa tor can be used betwsien the mold and the unscrambling device. While this approach ia inexpensive and reliable, it has two major limitations. Due to the vibrating action of these systems, fragile parts and component* that are sen sitive to scratching cannot he handled. Because pert geometry end center ofgrav ity ere critical, the unscrambling equip ment usually is custom designed for handling a particular product. As e re sult, often considerable on-line debug ging ia required to achieve acceptable operating efficienciee, and even rela tively minor pert design changes can obsolete the unscramble/. b^w,in^lv,Mn_Q^ flnpppng Another effective handling method is one in which injection molded parts am eject ed in the normal way, but the drop ia con trolled so as to maintain part orientation. For large shallow parts and single-cavity molds, opening the mold only a short dis tance permits the stationary mold half to guide the mold pert ea it falls. With mul ticavity molds, a special guiding mecha nism--Uide tracks or rails within the molds--usually i* required. When the mold ' is closed, the rails are shuttled by a cam mechanism to a position outside the molding surfaces. Aa the mold opens, the rails are indexed inward surrounding the side surfaces of the ejected parts. Sta tionary tracks initelled below the mold guide the parts downward and move them towards a subsequent processing or peck ing station. , While controlled drop systems ensure 100% reliability in part orientation, they are limited to relatively shallow parts (2 in. maximum depth). Round and square shapes ere handled most effectively by this means, frith at least two points of symmetry required for proper tracking. Because the nils must entrap the part, the runner system and method ofgating an critical Runnerlees molda simplify the use of guide rails. With cold runner molds, runners must be separated from the pert before the rails move into position. Either three-plate or self-degating molds (with secondary ejection ofthe runners) may be used for cold runner applications. Positive takeout The moat effective means oforienting parts is to grasp them directly ea they are ejected from the mold. A wide range of pert sizes and shapes can be handled since pickup devices can be designed to specific part configurations. Runners can be re moved simultaneously or ejected sepa-