The influence of knit‐lines on the tensile properties of injection molded parts

Criens, R.M.; Moslé, H. G.

doi:10.1002/pen.760231011

Cited by 43 publications

(22 citation statements)

References 2 publications

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“…Weld lines are also present when the mold cavity contains inserts around which the flow front is divided and then recombined at the opposite side of the insert (2)(3)(4)(5). Weld lines are characterized by poor mechanical properties (3, [6][7][8][9][10][11][12]. There are different manners to partially solve this problem.…”

Section: Introductionmentioning

confidence: 99%

Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends

Brahimi

Aı̈t-Kadi

Ajji

1994

Polymer Engineering & Sci

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In this article, we investigate the effect of weld lines on the tensile mechanical properties of unmodified and copolymer modified high density polyethylene (HDPE) and polystyrene (PS) blends. The homopolymers were melt blended in the proportion of 20 wt% HDPE and 80 wt% PS using a twin screw extruder at a temperature of 200°C. The results show that the mechanical properties are generally lower when weld lines are present. The decrease of the mechanical properties is much more pronounced for the blends. The addition of small amounts of a commercial styrene/butadiene copolymer significantly improves the strength and the elongation at break of this blend. An optimum copolymer concentration was observed at 3 wt%. This value coincides with the interphase saturation concentration of the copolymer obtained from the analysis of the DMTA (dynamic mechanical and thermal) properties of the blends. The copolymer was also found to induce important changes in the morphology of the blend. The interdiffusion of the polymer fronts in the weld region was also improved by the presence of the copolymer. It is believed that these two aspects contribute to the enhanced properties obtained with copolymer modified blends in presence of weld lines. An important effect of the injection temperature on the tensile strength and the elongation at break of welded samples with copolymer modified blends was observed. The effect of mold temperature on these properties was less important mainly at low injection temperatures. Only a slight effect of these two parameters was observed for the tensile modulus in the range of mold and injection temperatures considered in this study.

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Section: Introductionmentioning

confidence: 99%

Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends

Brahimi

Aı̈t-Kadi

Ajji

1994

Polymer Engineering & Sci

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“…One can increase the weldline strength of the molded composites somewhat by increasing the packing pressure. This is mainly due to the fact that increasing the packing pressure increases the molecular diffusion at the weld interface [4,5]. Finally the effect of melt injection pressure on the weldline strength of ABS composites is limited; as predicted by the statistic results in this study (Figures 4 and 5).…”

Section: Significance Of Processing Parametermentioning

confidence: 67%

Application of Statistic Estimation to Weldline Strength of Injectionmolded Thermoplastic Composites

Liu

Yang

2004

Journal of Reinforced Plastics and Composites

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The injection molding of thermoplastic composite materials has become an important process in industry, due to the possibility of producing near shape article having exceptional physical and mechanical properties. However there are still some problems that confound the overall success of this technology. The forming of weldlines wherever polymer flow fronts meet is one of them. In this report, an L'18 experimental matrix design based on the Taguchi method was conducted to study the effect of different processing parameters on the weldline strength of injection-molded thermoplastic composites. Experiments were carried out on a 4.1 oz reciprocating injection molding machine. The materials used were acrylonitrile-butadiene-styrene, and 20 and 30% glass-fiber-filled ABS composites. A plate cavity with an obstacle in the center was used to create a weldline. After molding, the weldline strength of the composites was determined by a tensile tester. Various processing variables were studied in terms of their influence on the weldline strength of injectionmolded composites: melt temperature, mold temperature, melt filling speed, melt filling pressure, packing pressure, and size of the obstacle. For the factors selected in the experiments, size of obstacle and melt temperature were found to be the important parameters affecting the weldline strengths of injection-molded composites. The weldline strength of virgin material increased with the distance from the obstacle, while the weldline strength of composites decreased with the distance.

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“…This difference is due to the notch sensitivity of the tensile strength of PMMA. On the surface of the weldline specimen, a V-shape notch exists (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). In the weld-line region, the V-shape notch has a structure with a fine groove on the surface (4,14).…”

Section: Fg 7 Comparison Of Weld-line Factor Of Pmma Measured By Tmentioning

confidence: 99%

“…A number of studies have been carried out on the weld-line, formed when two or more polymer melt A flows meet in a cavity, is often the weakest part of an injection molded or extruded product and thus the source of crack propagation. As a result, the presence of weld-lines reduces the mechanical strength and affects the surface appearance of the products (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The weak strength of weld-lines of amorphous polymers can be attributed mainly to the following three factors (2): the incomplete bonding at the interface of two polymer melt flows; the parallel molecular orientation of the interface caused by fountain flow (3) at the melt front; and the existence of a V-shape notch around the weld-line surface caused by entrapped air or contaminants (4).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of the weld‐line strength of thermoplastics by compact tension test

Cho

Ahn

Park

et al. 1997

Polymer Engineering & Sci

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In order to understand the relationship between processing conditions and the properties of weld‐lines on a molecular level, it is necessary to evaluate the true strength of the weld‐line that is not affected by the V‐shape notch on the surface of the weld‐line zone. In this experiment, the weld‐line strength of several brittle, ductile, or phase‐separated polymers was evaluated using the compact tension test by measuring the critical stress intensity factor, KIC, or the critical J‐value, JIC, and the results were compared with those obtained by tensile testing. For brittle polymers such as poly(methyl methacrylate) (PMMA) or styrene acrylonitrile copolymer (SAN), the value of the weld‐line factor, i.e., the strength ratio between the welded and the non‐welded specimen, is higher than that measured by tensile testing, because of the notch sensitivity of brittle thermoplastics and the notch dependence of tensile strength. On the other hand, in the case of ductile polymers such as polycarbonate (PC), the weld‐line factor is similar for both the tensile and compact tension tests. However, the dependency of the weld‐line factor on melt temperature is more obvious in the compact tension test. From these results, it seems that the compact tension test is more appropriate for measuring the interfacial adhesion strength across the weld‐line, which excludes the notch effect.

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The influence of knit‐lines on the tensile properties of injection molded parts

Cited by 43 publications

References 2 publications

Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends

Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends

Application of Statistic Estimation to Weldline Strength of Injectionmolded Thermoplastic Composites

Evaluation of the weld‐line strength of thermoplastics by compact tension test

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