1、UNCORRECTED PROOF12Shrinkage study of textile roller molded by conventional/microcellular3injection-molding process4Shyh-shin Hwanga,Peming P.Hsub,Chi-wei Chianga5aDepartment of Mechanical Engineering,Ching-Yun University,Chung-Li,32023,Taiwan,ROC6bDepartment of Mechanical Engineering,Far-East Unive
2、rsity,Tainan,74420,Taiwan,ROC78Abstract9Oneoftheadvantagesofmicrocellularconventionalinjectionmoldingoverconventionalinjectionmoldingisthattheshrinkageofthepartcanbe10reduced.This project investigated the effect of the process parameters on the shrinkage of the textile roller by conventional/microce
3、llular injection-11molding process.Polybutyleneterephthalate(PBT)materials with 30 wt.%glass and Wollastonite fiber were used.The results showed that the12shrinkage by microcellular injection molding is less than that of conventional injection molding.Glass fiber filled PBT has more shrinkage than13
4、Wollastonite fiber filled PBT due to the non-uniform cell size of the glass fiber filled PBT.14 2008 Published by Elsevier Ltd.1516Keywords:Microcellular injection molding;Three-plate-mold;PBT;Glass fiber;Wollastonite;Shrinkage17181.Introduction19The microcellular process was first introduced by N.P
5、.Suh201,2asabatchprocessin1980.Inthisprocess,apolymersample21ishoused ina highpressurechamber.Aninert gas likeCO2or N222is introduced into the chamber,diffusing into the polymer until23saturation.Then,the pressure is rapidly reduced while the poly-24mertemperatureissimultaneouslyincreased,producinga
6、thermo-25dynamic instability that lowers the gas solubility and creates cell26growth.The disadvantage of the batch process is that a long27period of time is required for the polymer to become saturated28with the gas,due to low diffusion rates at room temperature.To29avoid this problem,microcellular
7、extrusion was developed.It30reduces the time necessary for the gas to saturate the polymer by31introducing the inert gas into the barrel while the polymer is still32molten.The diffusion rate is high because the temperature in the33barrel is high.Unfortunately,as parts become more complex,34microcell
8、ular extrusion cannot be used to produce them.35In response,microcellular injection molding was developed363 and commercialized by Trexel Co.Ltd.as the Mucell37process.The key insight of this process is the application of a38supercritical fluid.The supercritical fluid is injected during the39injecti
9、on stage cycle,creating millions of micron-sized voids in40otherwise solid thermoplastic polymer parts.41Severalstudieshaveinvestigatedtheshrinkageandwarpageof42injection molded parts.Bushko et al.4,5 studied the effect of43processing conditions on shrinkage,warpage,and residual44stresses of a therm
10、al viscoelastic melt.Their results showed that45ahigherpackingpressureresultedinlessshrinkage.Liaoetal.646investigated optimal process conditions for shrinkage and war-47page in thin-wall parts.They showed that the optimal process48conditions differ for shrinkage and warpage in injected thin-wall49c
11、ellular-phone covers.Recently,Kramschuster et al.7 studied50the shrinkage and warpage behavior of a grocery box in micro-51cellular and conventional injection molding.They showed that52the SCF level and injection speed are the most important factors53affecting the shrinkage and warpage of microcellu
12、lar injection54molded parts.In the authors last paper 8,we have showed that55the shrinkage rate of microcellular injection molding is less than56that of convention injection molding.57Thetextileroller(Fig.1)inthetextilemachinesisawornpart58whichshouldbereplacedafteracertaintime.Thematerial ofthe59ro
13、ller is PBT.PBT has good dimensional stability,mechanical60strength,stiffness,and fire retardant characteristics.To improve61the mechanical strength,most of the plastics are filled with glass62fiber.In this study,both glass and Wollastonite fiber filled PBTAvailable online at International Communica
14、tions in Heat and Mass Transfer xx(2008)xxxxxxICHMT-01731;No of Pages by W.J.Minkowycz.Corresponding author.E-mail address:stanhwangcyu.edu.tw(S.Hwang).0735-1933/$-see front matter 2008 Published by Elsevier Ltd.doi:10.1016/j.icheatmasstransfer.2008.02.011ARTICLE IN PRESSPlease cite this article as:
15、S.Hwang,et al.,Shrinkage study of textile roller molded by conventional/microcellular injection-molding process,Int Commun HeatMass Transf(2008),doi:10.1016/j.icheatmasstransfer.2008.02.011UNCORRECTED PROOF63areinvestigated.Wollastonite isacalcium metasilicate(CaSiO3)64which can improve thermal and
16、dimensionalstabilityat elevated65temperatures 9.66In this study,we have investigated the effects of process67parameters on the variation of the rim thickness(Fig.2Q1)by68conventional and microcellular injection molding.The specifica-69tion of the rim thickness is 0.02 mm.If the rim thickness70tolerance is out of specification,there is a running noise from the71roller,andthetextilerollershouldbereplacedafter a certaintime.722.Experimental work732.1.Material74The materials used were 30 wt.%glass f
