(1) injection molding
Is first the plastics are added to the injection machine of the heating cylinder, the plastic is heated and melted, under the impetus of the injection machine screw or plunger, into the mold cavity by the nozzle and the mold gating system, due to the physical and chemical effects and hardening shaping become an injection molding products. Injection molding consists of injection, holding pressure (cooling) and plastic parts ejection process of cycle cycle, so the injection molding has the characteristics of periodicity. Thermoplastic plastic injection molding molding cycle is short, high production efficiency, the melt to mold wear small, bulk forming complex shape, surface pattern and clearly marked, size precision high plastic parts; but for wall thickness of plastic parts, it is difficult to avoid forming defects. The anisotropy of plastic parts is one of the quality problems, and all possible measures should be adopted to minimize the.
(2) compression molding
Commonly known as press molding, is one of the earliest methods of forming plastic parts. Compression molding is the plastic directly into a certain temperature of the open mold cavity, and then close the mold, the heat and pressure in the plastic melt into a flow state. As a result of physical and chemical effects, and so that the plastic hardening into a certain shape and size of the room temperature to maintain the same plastic parts. Compression molding is mainly used for the molding of a thermosetting plastic, such as phenolic moulding powder, urea formaldehyde and melamine formaldehyde moulding powder, glass fiber enhanced phenolic, epoxy resin, DAP resin, silicone resin, polyimide moulding plastics, can also processing molding unsaturated polyester material group (DMC), sheet molding compound (SMC), prefabricated bulk moulding compound (BMC). Under normal circumstances, the compression mode is divided into three types, which are overflow material, non overflow and semi overflow.
(3) extrusion molding
Is to make in the viscous flow of plastic, under high temperature and pressure, through a specific section shape of the die and at lower temperatures, shaping a desired cross-sectional shape continuous profiles of a molding method. Extrusion molding production process, preparation of materials forming, extrusion molding, cooling, shaping and pulling and cutting, squeezing produced after treatment (quenching and tempering or heat treatment). In the process of extrusion molding, pay attention to adjust the good extrusion machine barrel heating of each part and the die temperature, screw speed, traction speed and other parameters in order to obtain qualified extrusion profiles. Special attention should be paid to the adjustment of the rate of polymer melt extrusion by die. Because when the melt extrusion rate is low, the extrudate with smooth surface, uniform cross-section shape; but when the molten material extrusion rate reached to a certain extent, extrusion surface will become rough, dull, shark skin, orange peel, shape distortion phenomenon. When the extrusion rate further increases, the extrudate surface distortion, even fragmented and broken into fragments or cylindrical melt. So the control of extrusion rate is very important.
(4) injection molding
Casting press molding. Is the plastic raw material into a preheating feeding indoor, and the pressure cylinder into the feeding chamber lock the mold, through the pressure of the column to put pressure on the plastic, plastic melt under high temperature and high pressure in the flow state and by pouring system into cavity gradually solidified into plastic parts. This molding method, also known as transfer molding. Injection molding is suitable for lower than the solid plastic principle of compression molding, plastic injection molding method, are also available. But when the molding material is lower than the curing temperature, the molten state has good fluidity, and the curing rate is higher than that of the curing temperature.
(5) hollow molding
Is to by extrusion or injection of, is still in the plasticity state of tubular or sheet billet trend is fixed in the mold, immediately pass into the compressed air, forcing billet material expansion and paste on the surface of mould cavity, cooling and shaping after demoulding, hollow plastic products with a processing method. Suitable for hollow molding of plastic for high pressure polyethylene, low pressure polyethylene, rigid PVC, PVC, polystyrene, polypropylene, polycarbonate, etc.. According to the different molding method, hollow molding is mainly divided into two kinds of extrusion blow molding and injection blow molding hollow molding. Extrusion blow molding has the advantages of extruder and extrusion blow molding has the advantages of simple structure. The disadvantage is that the parison wall thickness is not consistent, easy to cause the plastic products of the wall thickness of the uneven. The extrusion blow molding principle diagram. Injection blow plastic hollow molding has the advantages is parison wall thickness uniform, no flash, due to the injected parison bottom, so the bottom of the hollow products shall not produced spell and seam not only has beautiful appearance and high strength. The disadvantage is that the molding equipment and the mold price is expensive, so the forming method is used for the large scale production of the small hollow articles, and the utility method is widely used in the process of the extrusion blow molding.
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