Pet Preform Mould Forming Classification
Posted by preform nicole on April 18th, 2019
(1) Injection molding
The plastic is first added to the heating barrel of the injection machine. The plastic is heated and melted. Under the push of the screw or plunger of the injection machine, the nozzle and the mold casting system enter the cavity of the Pet Preform Mould and harden due to physical and chemical effects. Shaped into an injection molded product. Injection molding consists of a cycle consisting of injection, pressure holding (cooling) and plastic part demolding, so that injection molding has periodic characteristics. Thermoplastic injection molding has a short molding cycle, high production efficiency, and low wear of the melt on the mold. It can form large-sized plastic parts with complex shapes, clear surface patterns and high mark precision; but for plastics with large wall thickness changes. It is difficult to avoid molding defects. Plastic anisotropy is also one of the quality issues and should be minimized by taking all possible measures.
(2) compression molding
Commonly known as press molding, it is one of the first methods of molding plastic parts. Compression molding is to directly add plastic to an open mold cavity with a certain temperature, and then close the mold, and the plastic melts into a flowing state under the action of heat and pressure. Due to physical and chemical effects, the plastic is hardened into a plastic part having a constant shape and constant shape and size. Compression molding is mainly used for molding thermosetting plastics, such as phenolic molding powder, urea-formaldehyde and melamine formaldehyde molding powder, glass fiber reinforced phenolic plastic, epoxy resin, DAP resin, silicone resin, polyimide, etc. It is also possible to mold and process unsaturated polyester dough (DMC), sheet molding compound (SMC), pre-formed molding compound (BMC), and the like. Under normal circumstances, the compression mold is often divided into three types: the overflow type, the non-overflow type, and the semi-overfill type according to the matching structure of the upper and lower molds of the compression film.
(3) Extrusion molding
It is a molding method in which a plastic in a viscous state is passed through a die having a specific sectional shape at a high temperature and a certain pressure, and then shaped into a continuous profile of a desired sectional shape at a lower temperature. The production process of extrusion molding is to prepare molding materials, extrusion molding, cooling setting, drawing and cutting, and post-processing of extrusion products (tempering or heat treatment). In the extrusion molding process, it is necessary to adjust the process parameters such as the temperature of the heating section of the extruder barrel and the die of the machine head, the number of revolutions of the screw, the traction speed, etc. in order to obtain a qualified extruded profile. Particular attention should be paid to adjusting the rate at which the polymer melt is extruded from the die. Because when the rate of extrusion of the melt is low, the extrudate has a smooth surface and a uniform cross-sectional shape; however, when the extrusion rate of the molten material reaches a certain limit, the surface of the extrudate becomes rough and tarnished. , shark skin, orange peel, shape distortion and so on. As the extrusion rate is further increased, the surface of the extrudate is distorted, even fragmented and broken into melt fragments or cylinders. Therefore, the control of the extrusion rate is crucial.
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