The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Improving Surface Quality of An Injection Molded Part By Adapting Rapid Heating and Cooling Technology
In injection molding, the cooling stage has significant impact on the overall part quality. Cooling time is a major contributor towards the molding cycle time. In conventional molding, the mold is maintained at a constant temperature for the entire duration of molding cycle. To achieve this, coolant at a constant temperature is pumped through the mold cooling channels. A relatively new molding technology called ‘Rapid Heating and Cooling Molding’ (RHCM) involves varying the inlet temperature of the coolant fluid, so as to maintain the mold temperature relatively hotter during filling stage and reduce the surface temperature to ejection temperature during the packing and cooling stages of the injection molding cycle. RHCM is best achieved with mold designs that allow for conformal cooling ofthe mold. Some of the key benefits of using RHCM are mitigation of weld line effects, improvement in the weld line strength, achievement of high-gloss surface finish, reduction of molding pressures, residual stresses and clamping force. In this paper, a comparative study is carried out between Conventional and RHCM molding to quantify the benefits of RHCM. The component chosen for this study is arepresentative center bezel part typically seen in automotive industry; a center bezel is used in the interiors of the car, and is required to be of high-quality surface finish and devoid of surface defects such as weld lines. Different materials, i.e., filled and unfilled grades from SABIC were used for this study. The molded parts were evaluated for gloss, L*, a*, b* values, visual defects, weld line appearance and its depth, scratch and mar resistance performance.
Increasing the Process Window of Single-screw Extruders Operated with Regrind
A feed zone geometry was developed which adapts the specific throughput when processing regrind to that of virgin material without adjustable means. This leads to an enlarged process window of the extruder. For this, the filling zone of a single-screw extruder was increased and a conical section was implemented in the feed zone which was designed with helical grooves. The experimental investigations with a 35mm extruder show that a complete alignment of the specific throughput is possible depending on the enlargement of the filling zone, the grooving as well as the angle of the conical section. Here, the self-adjusting compression is used which varies depending on the material’s particle shape. Additionally, approaches for the three-dimensional description of the throughput behavior using the discrete element method are shown. The uneven shape of regrind particles is transformed into so called superquadrics.
Inline Surface Activation in the Multi Injection Molding Process
Surface activation by plasma is a widely used process technology for connecting several components to each other. Usually, the activation takes place outside the injection molding machine as an additional step. With the development of the InMould-Plasma technology, the surface activation is fully integrated in the injection molding process, which eliminates an additional process step. Therefore, a plasma nozzle is directly connected to the mold. The plasma runs along a defined channel and activates the substrate surface in the closed mold. Through the technology, a strong bond of originally incompatible materials has been achieved. Without a surface activation, there is no adhesion of polypropylene (PP) and thermoplastic polyurethane (TPU). Studies on the peel strength of PP with TPU show that a treatment time of 5 s can drastically increase the material compatibility and achieve a peel strength of > 12.5 N/mm over the entire treatment area.
Reduction of Demoulding Force Through Innovative Surface Modification
Plastic parts are becoming more and more complex. Thus, the demolding of such parts is becoming more and more challenging. Meanwhile it is difficult to reproduce the conditions, appearing during the demolding of a part from a molding tool. To overcome this gap a simple and robust test setup has been developed to measure the necessary torque to demold a plastic test specimen from a defined surface of a test blank. During the test, two variables are measured and evaluated, the adhesion torque, which describes the loss of adhesion between the plastic test specimen and the metal surface of the test blank, and the sliding integral, which describes the torque needed to overcome the sliding friction between friction partner. As a result of the tests the influence of the used plastic, the influence of the process and the influence of the functionalizing of the metal surface via structuring and coating on the demolding behavior is shown.
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