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Episode Synopsis "It is difficult to achieve consistency in injection molding"
The main task of the hot runner plate is to thermostatically feed the melt from the main flow path to each individual nozzle. During melt transfer, the melt pressure drop should be as small as possible and no material degradation is allowed. The flow of the melt to each nozzle should be as uniform as possible. In order to save heating power, the volume is small, but if it is too small, the heat capacity is too small and the temperature is not stable. The hot runner plate should be processed in a thick plate. The surface of the runner that is in contact with the melt is drilled and then re-polished with a reamer. The end points of the flow path are not allowed to have blind holes, and the shape of the corner should be smoothly transitioned with the flow path. The hot runner plate should be made of a material that is smaller than heat and has a high thermal conductivity. Hot runner plates are typically fabricated from steel and nozzles are made of beryllium copper or copper to maintain a uniform temperature. In recent years, it has been recommended to use a finished, high-quality stainless steel tube with an inner wall to make a hot runner for a large product mold, which is fixed with cast copper around it. A support pad having a high strength contact area is used at the support portion or an air gap is used between the hot runner plate and the fixed plate. The hot runner system is generally divided into two categories according to the heating method of the hot runner plate: 1. Heating type: The heating channel system also has two designs: an inner heating channel and an outer heating channel: 1. an inner heating channel: an inner heating stream The road features an internally heated annular flow path. Heating is provided by a probe in the flow channel and a heating shuttle (also known as a distributor tube). This system utilizes the insulating effect of molten plastic to reduce heat transfer and loss elsewhere in the mold. Despite the annular heater in the distributor tube, there is still a condensation of material between the heating shuttle and the flow channel wall. The material must flow between the insulation wall and the heating shuttle, which, combined with the annual flow effect, causes a drop in pressure within the system, so the importance of balance is critical. In view of this problem, the internal heating system is most suitable for Thin-wall injection molding processing a wide range of materials and equidistant flow paths to the gates. This system is not suitable for the use of heat sensitive plastics. Internal heating provides improved heat distribution relative to the insulation system, but the system is more costly and more complex to design. Such systems require careful balancing and complex thermal control. 2, external heating system: Another design of the hot runner is the external heating system. This design consists of an annular heating header with internal flow channels. The header is designed with a variety of insulation configurations that are isolated from the rest of the mold. The advantage of this system is better temperature control, but the cost is higher and the equipment is complicated. The latest technology development has reduced the size of the header and made the installation easier. The external heating system can also be balanced by diameter rather than by length. Second, the heat insulation type: the heat insulation flow channel mold has an excessively large flow path composed of a template. The flow channel is not heated, but the size of the flow channel is large enough to be combined with the heat generated by the plastic that is condensed on the flow channel wall under working conditions to maintain the melt in the flow channel. Unblocked. This kind of system is earlier and simpler in two categories. The advantage is that the design is not so complicated and the manufacturing cost is low. The disadvantage is that condensation sometimes forms at the gate; in order to maintain the molten state, a very fast duty cycle is required; in order to achieve a stable melting temperature, a long preparation time is required. Another major problem is that it is difficult to achieve consistency in injection molding, or it cannot be guaranteed. Also, because there is no heating in the system, a high injection pressure is required, which often causes deformation or bending of the cavity plate.
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