Classification by molding method
(1) injection molding
Was added to the injection machine put plastic heating cylinder, the molten plastic is heated, the injection machine screw or plunger, driven by the nozzle and mould gating system into the mold cavity, due to the physics and chemistry hardening shape become injection molding products.Injection molding consists of the cycle of injection, pressure protection (cooling) and molding process, so injection molding has the characteristics of cycle.Thermoplastic injection molding molding cycle is short, high efficiency, wear small to mold, melting can bulk forming complex shape, surface design and legible, high dimensional accuracy of parts;However, it is difficult to avoid forming defects for the plastic parts with large thickness changes.It is also a quality problem that the plastic parts are different from each other. All possible measures should be adopted to minimize them.
(2) compression molding
Commonly known as pressing molding, it is one of the earliest methods of molding plastic parts.Compression molding is to add plastic directly into an open mold cavity with a certain temperature, then close the mold, and the plastic melts into flowing state under the action of heat and pressure.Because of the physical and chemical action, the plastic hardening becomes the constant temperature of a certain shape and size.Compression molding is mainly used for thermosetting plastics molding, such as phenolic molding powder, urea formaldehyde and melamine formaldehyde moulding powder, phenolics, epoxy resin, glass fiber increases DAP resin, silicone resin, polyimide, such as mold plastic, can also processing unsaturated polyester material group (DMC), mold (C), the overall prefabricated plastic mold plastic (BMC), etc.In general, the compression mould can be divided into three types: spillage type, non-spillage type and semi-overspill, according to the fit structure of the compression film and the lower mould.
(3) extrusion molding
Is made in the viscous flow state of plastic, under high temperature and pressure, through a specific profile is the mouth of the mould, and then at low temperatures, finalize the design become continuous profile of the cross section shape of a molding method.Extrusion molding process is preparation of materials, extrusion molding, cooling styling, traction and cutting, extrusion aftertreatment (tempering or heat treatment).In the process of extrusion molding, the temperature of each heating section of the extruder and the die of the die, the screw rotation and the traction speed are adjusted so as to get the qualified extrusion profile.In particular, it is important to adjust the speed of the polymer melt extruding from the die.Because when the melt extrusion rate is low, the extruder has a smooth surface and uniform section shape;But when the extrusion rate of molten material reaches a certain limit, the surface of the extruder will become rougher and lose, and there will be the phenomenon of shark skin, orange peel and shape distortion.When the extrusion rate increases further, the extrusion surfaces appear distorted and even fractured and fractured into molten fragments or columns.Therefore, the control of extrusion rate is critical.
(4) injection molding
Also known as cast pressure forming.Is to add plastic raw materials to preheat the indoor feeding, and then put pressure column in the charging chamber lock mould, through pressure column pressure on plastic, plastic melt under high temperature and high pressure as the flow state, and through pouring system into the cavity gradually solidified into plastic parts.This kind of forming method, also called transfer molding.The injection molding is suitable for all plastics below solid plastic, which can be compressed and molded in principle.However, the molten state has a good flow when it is lower than the curing temperature, and the curing rate is higher than the curing temperature.
(5) hollow forming
Is brought by extrusion or injection system, is still in a state of plasticizing tubular or fixed PiCai trend in molding, immediately into the compressed air, forcing PiCai expansion and post them on the mold cavity wall, after waiting for cooling to finalize the design, mold release, a quick needed a processing method of hollow products.Suitable for hollow molding plastics for high pressure polyethylene, low pressure polyethylene, hard polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, polycarbonate etc.According to the different shape method, hollow molding is mainly divided into two types: extrusion blow molding and injection blow molding.The advantages of extrusion blow molding are simple structure of extruder and extrusion blow mould, and the disadvantage is that the wall thickness of the slab is not consistent, and it is easy to cause the wall thickness of plastic products to be uneven.The right image is the schematic diagram of extrusion blow molding principle.The advantage of injection blow molding is that the wall thickness is uniform and no flying side, because the injection mold has a base surface, so the bottom of the hollow products will not produce spline and seam, not only beautiful but also high.The disadvantage is that the used molding equipment and the mold price are expensive, so this kind of forming method is mainly used in the mass production of small hollow products, in the use of no extrusion blow plastic hollow forming method is extensive.