The influence of the type of polypropylene and the length of the flow path on the structure and properties of injection molded parts with the weld lines

Bociąga, E.; Kaptacz, Sławomir; Duda, Piotr; Rudawska, Anna

doi:10.1002/pen.25170

Cited by 17 publications

(24 citation statements)

References 22 publications

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“…The highest shear stresses occurring in the cavity-melt boundary zone resulted in an even greater orientation of the filler in this zone. Those good results of the pore size range can be explained by minimization of the fountain effect during the melt flow [48][49][50], as well as by low shear stresses during the flow and a viscosity decrease. It was caused by a lower flow rate gradient compared to the thin-walled molded part.…”

Section: Resultsmentioning

confidence: 86%

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

2020

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The aim of the study was to detect the influence of nitrogen pressure on the rheological properties and structure of PA66 GF30 thick-walled parts, produced by means of microcellular injection molding (MIM), using the MuCell® technology. The process was monitored in-line with pressure and temperature sensors assembled in the original injection mold. The measured data was subsequently used to evaluate rheological properties inside an 8.4 mm depth mold cavity. The analysis of the microcellular structure was related to the monitored in-line pressure and temperature changes during the injection process cycle. A four-times reduction of the maximum filling pressure in the mold cavity for MIM was found. At the same time, the holding pressure was taken over by expanding cells. The gradient effect of the cells distribution and the fiber arrangement in the flow direction were observed. A slight influence of nitrogen pressure on the cells size was found. Cells with a diameter lower than 20 µm dominate in the analyzed cases. An effect of reduction of the average cells size in the function of distance to the gate was observed. The creation of structure gradient and changes of cells dimensions were evaluated by SEM images and confirmed with the micro CT analysis.

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Section: Resultsmentioning

confidence: 86%

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

2020

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“…The addition of fillers, especially fibrous ones, to the plastic results in a deterioration of the strength properties due to the placement of filler particles parallel to the fronts of the material streams, as shown in Fig. 8b [19][20][21]. A similar effect is caused by the use of a pigment whose particles, of a length or width greater than the thickness or diameter, are oriented along the flow line of the material, which results not only in the strength properties but also in the colour of part in the weld area [5].…”

Section: Properties Of the Injected Materialsmentioning

confidence: 99%

“…The chemical foaming agent added to the injected polymer can also influence the structure and mechanical strength of molded parts with weld lines [20]. It was found that the tensile strength of the porous samples from unfilled polypropylene decreased of about 17% in compare to solid ones.…”

Section: Properties Of the Injected Materialsmentioning

confidence: 99%

Characteristics of injection molded parts with the areas of weld lines

Bociąga

Skoneczny

2020

Polimery

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The weld lines in injection molded parts arise as a result of the collision of two fronts of the flowing material, which fills the mold cavity and are sometimes unavoidable. They decrease the mechanical properties and surface state of the moldings, due to insufficient connection of the fronts of melted polymer streams. The paper discusses the reasons for the occurrence of weld lines in molded parts, which have been divided into ones related to the design of the injection molded part, properties of the injected material, injection mold construction and injection parameters. The design of the molded parts should ensure even, smooth flow of the material in the cavity, but in the case of parts with many injection points, holes, varied wall thickness, complicated and irregular structure the weld lines can not be avoided. The type of material processed significantly influences the strength of the weld line area. Too high viscosity of the material, fillers and large particles of the coloring agent highly oriented in the weld line area, are the factors lowering properties of the molded part. Considering the design of the injection mold, the most important aspects in forming proper parts with weld lines are correct venting of the mold, small differences in the material temperature in all cavity areas, correctly selected injection points, avoiding jet filling of the cavity. The quality of such parts can be improved by changing the injection conditions, mainly by increasing the mold and melt temperature, also increasing the holding pressure and the injection speed. The possibilities of preventing the weld lines creation or reducing the negative effects of their occurrence have been presented, e.g. by changing the design and location of gates in injection molds, changing processing conditions or using unconventional methods of injection molding, like cascade cavity filling, push-pull and multiple live-feed injection molding, vibration process. Further examinations in the range of cyclic heating/cooling of the injection mold are suggested as the most promising regarding the quality of parts in the area of weld line, their strength and surface state.

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“…Higher cavity surface temperature can improve the part stiffness and tensile strength [ 15 ] and the functional properties as well [ 20 ]. This can be also used to minimize the reduction in tensile strength in parts, where weld lines are present [ 21 , 22 , 23 ]. Besides, the high cavity surface temperature is commonly used to improve surface quality (removal of weld lines’ presence, obtaining high-gloss surface, better replication of microstructure of the cavity surface) [ 6 , 11 , 23 , 24 , 25 , 26 , 27 , 28 ].…”

Section: Introductionmentioning

confidence: 99%

Application of Magnetic Concentrator for Improvement in Rapid Temperature Cycling Technology

2020

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The main method to improve the filling of the cavity by the polymer melt is to increase the mold temperature. Rapid temperature cycling (RTC) technologies have been used around the world for several years, improving the quality of injection molded parts with a slight extension of production time. The present work focuses on the application of induction heating technology in the injection molding process since it is the most effective and most intensively developing method of heating in modern RTC technologies. In this research, the application of the induction heating process for selected surfaces was investigated with particular emphasis on the dynamics of the process. The numerical simulations were used to study the influence of the number of coils, the distance between coils and cavity surface and the mold material was examined with and without the presence of a magnetic concentrator. According to the obtained results, several crucial conclusions were made: the efficiency of heating is directly correlated with the distance between the inductor and the mold surface, the presence of magnetic flux concentrator significantly improves the homogeneity of temperature distribution and heating efficiency, application of aluminum mold lowers the obtained surface temperature.

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The influence of the type of polypropylene and the length of the flow path on the structure and properties of injection molded parts with the weld lines

Cited by 17 publications

References 22 publications

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

Characteristics of injection molded parts with the areas of weld lines

Application of Magnetic Concentrator for Improvement in Rapid Temperature Cycling Technology

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