Shrinkage Alteration Induced by Segregation of Glass Beads in Injection Molded PA6: Experimental Analysis and Modeling J.G. Kova ´ cs Department of Polymer Engineering, Budapest University of Technology and Economics, Budapest, Hungary The segregation effect of glass beads along the ﬂow path during the injection molding process was eval- uated. Experiments were carried out on injection molded polyamide 6 (PA6) composites with solid glass bead (GB) depends on both the diameter and the con- centration of the glass beads. A model is suggested to describe the observed variations. In addition, segrega- tion affects the distribution of volumetric shrinkage along the ﬂow path, playing a major role in the dimen- sional accuracy of the part. A model is also proposed to include the effect of glass beads segregation in shrinkage calculations. POLYM. ENG. SCI., 51:2517–2525, 2011. ª 2011 Society of Plastics Engineers INTRODUCTION The mechanical properties of injection-molded polymer composites are determined by their macro structure (ge- ometry, concentration, distribution, orientation) and their micro structure (morphology, properties of the compo- nents and their impact on each other) [1]. During product design the engineer chooses the material—reinforced or ﬁlled—based on the future use of the product, assuming that the properties of the material at any point of the geometry are identical to its nominal values. The mechanical and other properties of the product (such as conductivity) are signiﬁcantly inﬂuenced by the ﬁller and reinforcing agent average and local content. However, it has been noted that the distribution of the solid particles is inhomogeneous in both transversal and longitudinal directions in the case of injection molded products containing ﬁllers or reinforcements. This effect is called segregation and is inﬂuenced by many material-, process-, or mould geometry-related parameters. The Effect of Filler or Reinforcement Shape on Segregation Researchers dealing with the inhomogeneous distribu- tion of ﬁllers or reinforcements during injection molding studied the phenomenon in the case of various types (l/d) of ﬁller or reinforcements, diameter and concentration. Their experiments will be summarized below ordered by type, size, and concentration of them as well as by the applied gate design. Hegler and Mennig [1, 2] studied segregation by pro- ducing glass ﬁber and glass bead ﬁlled thermoplastics (Polyamide6 (PA6) and Syrene Acrylonitrile (SAN) dumb-bell sample). They observed that in the direction of ﬂow the distribution of the ﬁller and reinforcement is a function of its geometry, i.e. function of the aspect ratio (l/d). In the case of glass beads (156 lm, 45 wt%) where the value of l/d is small (1) by the end of the ﬂow the ﬁller content exceeded its nominal value by 4 wt%. In contrast, using short glass ﬁber where the value of l/d is large, the reinforcement content did not differ from its nominal value. Kamal and Singh [3] studied the morphological proper- ties of injection molded specimens with polypropylene matrix containing 30 wt% short glass ﬁbers. For their experiments they used a 100 3 60 3 3 mm 3 specimen with a 7.8 mm wide semicircular cross-sectional gate on the shorter side. They observed that the ﬁber content devi- ation from the nominal value is no more than 65 wt% in the direction of the ﬂow. Near the gate, the ﬁber content decreased whereas at the end of the ﬂow higher density of ﬁbers was observed. This effect in the cross-sectional area at the edge of the product was less signiﬁcant than in the direction of the gate. O’Regan and Akay [4] studied the variation in ﬁber length and content distributions (50 wt%) in the direction of the ﬂow and the thickness. They used injection molded PA66 samples. They concluded that the ﬁber length was signiﬁcantly inﬂuenced by the type of nozzle (open or Correspondence to: J.G. Kova ´cs; e-mail: kovacs@pt.bme.hu Contract grant sponsor: New Hungary Development Plan; contract grant number: TA ´ MOP-4.2.1/B-09/1/KMR-2010-0002; contract grant sponsors: Ja ´nos Bo ´lyai Research Scholarship of the Hungarian Academy of Scien- ces, Technology Cooperation Programme, further Jedlik A ´ nyos Pro- gramme of Ministry of Economy and Transport of Hungary. DOI 10.1002/pen.22025 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2011 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2011