模具外文文獻(xiàn)翻譯-注塑成型中顆粒填充物聚丙烯的冷卻情況【中文4060字】【PDF+中文WORD】

模具外文文獻(xiàn)翻譯-注塑成型中顆粒填充物聚丙烯的冷卻情況【中文4060字】【PDF+中文WORD】,中文4060字,PDF+中文WORD,模具,外文,文獻(xiàn),翻譯,注塑,成型,顆粒,填充物,聚丙烯,冷卻,情況,中文,4060,PDF,WORD Cooling behaviour of particle filled polypropylene duringinjection moulding processBernd Weidenfellera,*,Michael Ho ferb,Frank R.SchillingbaInstitute of Polymer Science and Plastics Processing,Technical University of Clausthal,Agricolastrasse 6,D-38678 Clausthal-Zellerfeld,GermanybGeoForschungsZentrum Potsdam,Section 4.1 Experimental Geochemistry and Mineral Physics,Telegrafenberg,D-14473 Potsdam,GermanyReceived 25 June 2004;accepted 4 July 2004AbstractThe effects of thermal properties of various fillers(magnetite,barite,copper,talc,glass fibres and strontium ferrite)in various proportionson the cooling behaviour of polypropylene matrix composites are investigated in an injection moulding process.A thermocouple in the cavityof the mould records the temperatures at the surface of the composite during injection moulding.From the slope of the cooling curves thethermal diffusivities of the composites are estimated and compared with thermal diffusivities at room temperature and elevated temperaturesmeasured with a transient technique.The cooling curves show different merging sections affected by the after pressure,the diffusivity of thecomposite and the diffusivity of polypropylene matrix.The cooling behaviour depends on the anisotropic thermal diffusivity of the usedcomposite,which is caused by the alignment of filler material due to the injection moulding process and the interconnectivity of the fillerparticles.The thermal diffusivity shows the highest value for 30 vol%talc filled polypropylene,whereas the shortest cooling time was foundfor 35 vol%copper filled polypropylene.The knowledge of the systematic variation of thermal transport properties of composites due todifferent filler material andfiller proportionsallows to optimizethe mould process and tocustomize the heat flow properties.Furthermore,thestrongly anisotropic thermal transport properties of talc filled polypropylene allow the design of composites with a predefined maximum heatflow capability to transport heat in a preferred direction.Keywords:A.Polymermatrix composites(PMCs);B.Thermal properties;E.Injection moulding;Particulate filler1.IntroductionCommonly used plastics,such as polypropylene andpolyamide,have a low thermal conductivity.However,newapplications,mainly in automotive industries,e.g.forsensors or actuators,require new materials with anenhanced or high thermal conductivity 1.By the additionof suitable fillers to plastics,the thermal behaviour ofpolymers can be changed systematically up to significanthigher thermal diffusivity of O1.2 mm2/s from 0.2 mm2/sfor unfilled polypropylene 2,3.Such filled polymers withhigher thermal conductivities than unfilled ones becomemore and more an important area of study because ofthe wide range of applications,e.g.in electronic packaging46.The higher thermal conductivity can be achieved bythe use of a suitable filler such as aluminium 1,carbonfibres and graphite 7,aluminium nitrides 6,8 ormagnetite particles 2.Also,the cooling behaviour in themould of the injection moulding machine is influenced bythe thermal properties of the polymer-filler composite.However,published values of thermal conductivities of thesame filler materials in different polymer matrices varydrastically and a comparison of different materials isdifficult or at least impossible 2.Therefore,polypropylene samples with different com-mercially available fillers(Fe3O4,BaSO4,Cu,glass fibres,talcandSrFe12O19)werepreparedbyextrusionandinjectionmoulding using various volume fractions(050%).Magne-tite and barite are generally used to increase the weight ofComposites:Part A 36(2005)345351*Corresponding author.Present address:Institute of Metallurgy,Robert-Koch-Str.42,D-38678 Clausthal-Zellerfeld,Germany.Tel.:C49-5323-723708;fax:C49-5323-723148.E-mail address:bernd.weidenfellertu-clausthal.de(B.Weidenfeller).polypropylene,e.g.for bottle closures(cosmetics industry,cf.Ref.10),strontium ferrite is used in polymer bondedmagnets,glass fibres are used for the reinforcement ofmaterials,and talc is an anti-blocking agent.However,copper was chosen as additional filler because of its highthermal conductivity compared to the other materials.The thermal properties of these injection mouldedsamples and the injection moulding behaviour wereinvestigated and correlated to the amount and the kind offiller material.2.Theoretical considerationsThe Fourier law of heat transport in one dimension isgiven byvTvtZav2Tvx2(1)withtemperatureT,timet,positionxandthermaldiffusivitya.In an homogeneous body,thermal diffusivity a andthermal conductivity l are interrelated by specific density rand specific heat capacity cpaccording tol Zcpra(2)Assuming an injection moulding process with anisothermal filling stage for a polymer with a temperatureTPand a constant temperature of the mould TMas well as atemperature independent thermal diffusivity a,an analyticalsolution of Eq.(1)results in 9T ZTMC4pTPKTM!XNnZ012nC1exp Ka2nC12p2ts2?sin2nC1pxs?(3)In Eq.(3),s denotes the wall thickness of the injectionmoulded part and T the temperature of the moulding aftertime t after injection.Neglecting higher order terms,Eq.(3)can be reduced for the position xZs/2 toT ZTMC4pTPKTM expKap2ts2?(4)Eq.(4)gives a relation between cooling rate and thermaldiffusivity in an injection moulding process,where highthermal diffusivities result in a higher cooling rate andshorter process cycles.3.Experimental3.1.MaterialsTest materials were supplied by Minelco B.V.(TheNetherlands).Minelco B.V.prepared in cooperation withRTP s.a.r.l(France)several polypropylene(PP)compoundswith various fillers(Fe3O4,BaSO4,Cu,glass fibres,talc andSrFe12O19)in an extrusion process similar to that describedin Ref.2.The filler materials are commonly used materialsin industrial products.The filler particles do not have asurface coating which can affect thermal properties.Someselected properties of the filler materials are listed inTable 1.Table 1Selected properties of filler materialsMagnetite,Fe3O4Barite,BaSO4Talc,Mg3Si4O10OH2Strontiumferrite,SrFe12O19Copper,CuGlassfibresThermal conduc-tivity(W/(m K)a:4.61G0.42,a:5.10,l11:9.7l11:2.07G0.02,l33:2.92G0.07,a:1.72G0.04l11:1.76G0.00,l33:10.69G1.35,a:2.97,a:3.00G0.10,a:6.10G0.90l11:401l:1.21.5Reference1313131415Mean particle diam-eter(mm)91.52.01.51511Particle shapeIrregularIrregularPlateletIrregularIrregularFibreDensity(g/cm3)5.14.482.785.118.942.58a denotes measurements on monomineralic aggregates.Directions of anisotropy are specified by the thermal conductivity tensor(l11,l22,l33),where l11,l22and l33are parallel to the crystallographic axes a,b and c,respectively.Fig.1.Photograph of the used mould for the injection mouldingexperiments.The mould consists of a standard tensile test sample and atest bar for the measurement of thermal diffusivity.B.Weidenfeller et al./Composites:Part A 36(2005)3453513463.2.Thermal diffusivity measurementsThe thermal diffusivity of the polymers is measured by atransient method 12,closely related to laser-flash experi-ments 11.The used transient technique is especiallyoptimized for measurements of polyphase aggregates.Atemperature signal is transferred to the upper side of thesample and registered by a thermocouple.The transferredtemperature signal starts a thermal equilibration process inthe specimen,which is recorded by a thermocouple as thedifference between samples rear surface and a constanttemperature in a furnace and which is used for theevaluation of thermal diffusivity.A least squares algorithmis used to determine the thermal diffusivity,while varyingsystematically the thermal diffusivity value in an especiallydesigned finite-difference scheme.A detailed description ofthe apparatus is given by Schilling 12.The accuracy of themeasurements of the polyphase aggregates is 3%.For thermal diffusivity measurements,small cylinders of10 mm diameter and 56 mm height were cut out of theinjection-moulded rods(cf.Fig.1).3.3.Injection mouldingWith an injection moulding machine(Allrounder 320C600-250,Arburg,Germany)standard samples for measuringtensile properties together with a rod for thermal measure-ments of 10 mm diameter and 130 mm length were preparedin one mould(cf.Fig.1).Inthe cavity of the tensile test bar achromel alumel(Type K)thermocouple was applied.During injection moulding experiments the temperaturewas recorded every 0.5 s by a digital multimeter and storedin a personal computer.The position of the thermocouple atthe sample surface and its position in the cavity of theejector are shown in Figs.1 and 2,respectively.The thermocouple submerges approximately 0.2 mm intothe cavity.Therefore,a good thermal contact betweenpolymer and thermocouple even after shrinkage 10 of themoulding is ensured.For a better comparison of the recorded temperaturetime curves the same injection moulding parameters for allcomposite materials were chosen.The used injectionmoulding parameters are listed in Table 2.The resultantcharacteristic times of the injection moulding cycle aretabled in Table 3.4.Results and discussionIn Fig.3,the cooling behaviour of polypropylene withoutand with various fractions of magnetite filler are presented.Fig.2.Mold with cavity for preparing test samples in an injection moulding machine.The position of the thermocouple for temperature measurements ismarked by an arrow.Table 3Characteristic times in one injection moulding cycle starting with theinjection of the polymer into the cavity at time tiZK8.5 s until the ejectionof the mould at tfZ68 sInjection time(s)K8.52Dwell time(s)29Cooling time(s)954Open/close time ejection time(s)5468Total cycle time(s)76.5These times define the time axis(abscissa)of Figs.3 and 6.Table 2Injection moulding parameters during preparation of sample rods formeasurements of thermal diffusivity by transient techniqueMass(polymer)temperature(8C)200Mould temperature(8C)20Cycle time(s)76.5Injection time(s)10.5Dosing time(s)12.4Holding pressure time(s)7.0Injection pressure(Pa)6!107B.Weidenfeller et al./Composites:Part A 36(2005)345351347At a time t0Z0 s the temperature measured by thethermocouple reaches a maximum value around 200 8C.With increasing time the observed temperature decreases.After tZ54 s the mould opens and the cooling behaviourrecorded with the thermocouple changes because it is nolonger in contact with the injection moulded material.Dueto the large diameter of the rod,the time(54 s)until themould is opened and the injection moulded parts are ejectedis chosen relatively high to ensure that the parts are surelysolidified.It can be seen in Fig.3 that the slope of the curve changessignificantly after tz9 s,which corresponds to the timewhere the after pressure is removed.Additionally,Fig.3points out that the composite in the cavity cools down fasterwithincreasingmagnetitefraction.ToreachatemperatureofTZ60 8Ca temperature far below the solidification of thesamplethe polypropylene needs in the described exper-iment a time of tZ50.5 s,whereas cooling time ofpolypropylene with 50 vol%Fe3O4is reduced to tZ30.9 s(cf.Table 4).The reduced cooling time is in good agreementwith the increased thermal diffusivity of magnetitefilled composites due to the high thermal diffusivity oftheparticles(cf.Table1)whichleads,regardingEq.(4),toanincreased cooling rate.The temperature time dependence inFig.3doesnotfollow asimplelinear behaviour expected fortemperaturetime curves by Eq.(4)in a logarithmic plot.Only for the unfilled polypropylene the measured values canbefittedwithasinglestraightlinebetweenapproximately15and 54 s.The slope of this line leads to a diffusivity ofaz0.21 mm2/s(cf.Eq.(4).The other measured coolingcurves of the polypropylene-magnetite composites are fittedin each case with two straight lines,for the high temperature(a1)and low temperature(a2)region.The thermal diffusiv-ities estimated from the slopes of the regression linesare a1(15 s!t!40 s)z0.24 mm2/s and a2(41 s!t!54 s)z0.19 mm2/s for PP with 15 vol%Fe3O4,a1(12 s!t!33 s)z0.29 mm2/s and a2(34 s!t!54 s)z0.19 mm2/sforPPwith30 vol%Fe3O4,anda1(9 s!t!22 s)z0.33 mm2/s and a2(28 s!t!54 s)z0.16 mm2/s forPP with 50 vol%Fe3O4(cf.Table 5).It is remarkable that the calculated thermal diffusivitiesa1of the higher temperature parts of the cooling curvesare a little bit lower than the diffusivities measured withthe transient technique,while the calculated thermaldiffusivities a2of the lower temperature parts of thecooling curves meet the measured diffusivity valuesFig.3.Comparisonof coolingcurves ofunfilledpolypropylene with polypropylene compositeswith variousfillerfractionsof Fe3O4.The symbolsare measuredvalues;the lines are regression lines(cf.text).Table 4Time t to cool down a polypropylene-filler composite from a mass(polymer)temperature of TMZ200 down to 60 8CCompositeFiller fraction(vol%)t(from 200 to 60 8C)(s)PP050.5PPCFe3O41546.4PPCFe3O43040.5PPCFe3O44534.6PPCFe3O45034.9PPCBaSO41544.3PPCBaSO43040.7PPCBaSO44535.6PPCCu1540.5PPCCu3033.8PPCCu3529.0PPCglass fibres1546.0PPCglass fibres3041.8PPCglass fibres3540.8PPCtalc1545.7PPCtalc3042.5PPCSrFe12O193040.9The cooling is measured in situ within a cavity of the mould by a K-typethermocouple.B.Weidenfeller et al./Composites:Part A 36(2005)345351348of unfilled polypropylene quite well(cf.Table 5 andFig.4).Fig.4 shows the measured thermal diffusivity data of theinvestigated samples at ambient conditions.It can be seenthat the thermal diffusivity of the magnetite-polypropylenecomposite is increased from aZ0.19 for unfilled poly-propylene up to aZ0.48(PPC50 vol%Fe3O4)withincreasing magnetite loading.Therefore,the cooling timebecomes shorter for higher magnetite filler fractions(Fig.3).One reason for the change in the slope of the coolingcurves shown in Fig.3 is a change of the thermaldiffusivity with temperature which is shown in Fig.5 formagnetite and barite polypropylene composites with45 vol%filler fraction.With increasing temperaturethermal diffusivity decreases.Therefore,the valuesderived from mould experiments should be smaller thanthe measured values of the composites at room tempera-tures.Thermal diffusivity of the PP matrix is mainlycaused by phonons and is related to the mean soundvelocity v and mean free path length l of phononsaccording toa Z13vl(5)Above the solidification temperature of the PP matrix(around110 8C,DSCmeasurements)thethermaldiffusivity of the matrix is reduced due to the loweredbulk modulus K which results in a reduced phonon velocity(vz(K/r)0.5)and reduced mean free path length of phononsin a liquid(Einstein approximation).Furthermore,abovesolidification temperature TSno crystallites in the poly-propylene matrix are present,but below TSa crystallizationin the polypropylene matrix appears,and the degree ofcrystallization as well as the bulk modulus of the compositeis dependent on the amount of filler 16.The presence orabsence of crystallites affects the bulk modulus K and thephonon free path.Other reasons for the discrepancybetween diffusivity values of the different experimentsare the non-isobaric conditions in the injection mouldingprocess and the non-isothermal conditions along thesamples thickness.The cooling behaviour of magnetite,barite,glass fibre,talc,hard ferrite and copper fillers in comparison withthe unfilled polypropylene are plotted in Fig.6.Only thecooling behaviour of the unfilled and the copper filledpolypropylene show significant differences to the othercomposites.Table 5Thermal diffusivity estimated from the cooling behaviour of injection moulded polypropylene-filler composites using the slope of the regression lines(a1,a2)(cf.Fig.3)compared to thermal diffusivity values measured by the transient method(a)CompositeRegression linesTransient methoda1(mm2/s)a2(mm2/s)a(mm2/s)PP0.21(12055 8C)0.19(26 8C)PPC15 vol%Fe3O40.24(12067 8C)0.19(6751 8C)0.27(26 8C)PPC30 vol%Fe3O40.29(12068 8C)0.19(6845 8C)0.35(26 8C)PPC50 vol%Fe3O40.33(12577 8C)0.16(6745 8C)0.48(26 8C)The temperature values in parenthesis give the temperature region of the regression lines and the ambient temperature during the measurement with thetransient technique.Fig.4.Thermal diffusivity values of injection moulded polypropylenesamples with different fillers and various filler proportions measured by atransient technique at room temperature(cf.text).Solid lines are plotted toguide eyes.Fig.5.Temperature dependence of thermal diffusivity of magnetite andbarite filled polypropylene with a filler content of 45 vol%.The symbolsrepresent measured values,the lines are deduced by linear regression.B.Weidenfeller et al./Composites:Part A 36(2005)345351349The copper filled composite cools down much faster thanthe other investigated composites.The temperature of theunfilled polypropylene is during the whole injectionmoulding process higher than the temperature of the otherinvestigated materials.The cooling behaviour of the othercomposite materials does not show large differences.Thetemperatures of the magnetite loaded PP is a little bit lowerthan the temperatures of the barite filled PP at the samecooling time.The temperatures of the strontium ferritepolypropylene composite again are a little bit lower thanthose of the magnetite filled polymers.While the measured thermal diffusivity of the talc filledpolypropylene is much higher than the thermal diffusivity ofthe other investigated materials and even much higher thanthat of the copper filled polypropylene,the coolingbehaviour of talc is smaller than that of the otherinvestigated materials.Weidenfeller et al.3 report inthe talc filled composite an alignment of the talc particlesoriented along their direction of highest thermal conduc-tivity in the direction of the flow,due to the mouldingprocess.The measurements of thermal diffusivity are madeparallel to this axis of highest thermal conductivity,whereasthe temperature measurements in the injection mouldingprocess reveal the diffusivity perpendicular to the flowdirection.This implies that the talc filled PP samples have astrong anisotropy with a maximum in the flow directionand a minimum perpendicular to the flow.The anisotropy ofthe injection moulded specimens due to the geometry of theparticles is shown in Ref.3.In spite of the high thermal conductivity of the copper(cf.Table 1)compared to the other used filler materials,the cooling behaviour is relative poor and the measuredtemperatures in the cavity are not as significant differentfrom those of the other composites as could be expectedfrom the thermal conductivity which is approximately40 times higher than that of talc.This might be related tothe poor interconnectivity of the particles in the composite,which was shown by Weidenfeller et al.3.It was shownthat the interconnectivity,which is a relative measure to anideally interconnected network of high conductivity par-ticles,is for copper in a polypropylene matrix lower than 1%and very poor compared to interconnectivity of magnetitewith 55%or the interconnectivity of barite with 46%3.The authors also discussed influences of particle sizeand shape on the interconnectivity in a polypropylenematrix 2,3.The necessary time to cool down the surface of thecomposite in the cavity to 60 8C is shown in Fig.7.Fig.6.Comparison of the cooling behaviour of polypropylene matrix composites filled with filler fraction of 30 vol%in the cavity of an injection mouldingmachine.Fig.7.Dependence of cooling time(from 200 down to 60 8C)from fillerfraction for various polypropylene matrix composites.The symbols aremeasured values,the lines represent linear fits.B.Weidenfeller et al./Composites:Part A 36(2005)345351350The cooling time is linearly dependent on the filler volumefraction in the polypropylene matrix.The data ofthe calculated regression lines are listed in Table 6.It canbe clearly seen that the copper filled polypropylene coolsdown much faster than the other investigated composites.The cooling behaviour of polypropylene with barite,strontium ferrite and magnetite is similar,whereas themagnetite cools down a little bit faster than all othermaterials.5.Conclus