Plastic injection molding process of thermoplastic plastic
Plastic injection molding process of thermoplastic plastic
Heating thermoplastic softened to flow, cooling hardening molding product, the process is reversible and can be repeated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastic, and other polyolefin copolymer, polysulfone, polyphenylene oxide, chlorinated polyether and so on are all thermoplastics. Thermoplastic resin molecular chains are linear or branched chain structure, no chemical bonds between molecular chains, softening flow on heating and cooling process of hardening is a physical change.
Resin is made by the polymerization. The resin is general by containing unsaturated bond, mainly is the double bond of monomer, open generated by double bond, no low molecular product release in the process of reaction. Polyolefin, halogenated olefins, polystyrene, polyformaldehyde, acrylic plastic are convergent plastic. Convergent plastic are thermoplastics. B) condensation type plastic resin is obtained by polycondensation reaction. This kind of resin is generally with some functional groups by monomer containing two functional groups) (at least, between borrow functional groups
Reaction for connecting monomer. 1.3.3 according to plastic resin molecules in the state points: a) the arrangement of amorphous macromolecule plastic resin is chaotic. This kind of plastic, due to the resin molecular chain structure characteristics, reasons, or because of thermodynamics or constraint range of molding process and molecular chain won't produce neat and orderly pile form crystalline structure, and present ruleless random arrangement. In the pure state of resin, the plastic is transparent. B) crystallization type plastic resin molecules appear orderly crystal phase. From the molten state cooling into products, in the process of resin molecular chain tight and orderly pile produce crystalline structure. Generally the so-called crystalline plastics, are actually half crystallization, not like low molecular crystals (e.g., NaCl) can produce 100% of the crystallinity. Resin macromolecule chain arrangement presents the amorphous and crystalline facies coexistence state. Had significant effect on the forming conditions on the crystallinity and crystalline structure, which has obvious influence on product performance. Crystalline structure exists only in thermoplastics.
Thermoplastic plastic injection molding is to melt the plastic material and then inject it into the film cavity. Once the molten plastic enters the mould, it is cooled and molded into a certain shape. The resulting shape is often the final product and no longer needs to be processed before it is installed or used as a final product. A lot of detail, such as a bulge. Rib, thread, can be formed in injection molding step by step. The injection molding machine has two basic components: the injection device and the fitting device for the melting and the plastic delivery mould. The function of the module is: (1) to make the die close under the pressure of the injection; (2) remove the products. The injection device melts the plastic before it is injected into the mold, then controls the pressure and velocity to inject the melt into the mold. There are two kinds of injection devices: screw preplasticizer or two-stage device, and reciprocating screw. The screw type preplasticizer USES preplasticized screw (first stage) to give the melt plastic injection rod (level 2). The advantage of the screw preplasticizer is that the melt quality is constant, high voltage and high speed, and accurate injection control (the mechanical thrust device used at both ends of the piston stroke). These strengths are needed for transparency, thin-wall products and high production rates. Disadvantages include uneven retention time (resulting in degradation of materials), higher equipment costs and maintenance costs. The most commonly used reciprocating screw injection device does not require plunger to melt and inject. Melt the powdery or granular plastic in the hopper. Through the rotating screw, the plastic fluid flows through the front end of the screw and accumulates at the front of the screw. The accumulation of molten plastic in the front of the screw pushes the screw to the back of the injection device, and the rotation of the screw, the accumulation of molten material and the movement of the back to the rear continue to form a certain amount of injection. In the next equipment working cycle, the end of the screw end is closed to prevent the material from returning along the screw. The screw tip and feed screw are used as the filling plunger, the plastic press mould. The advantages of reciprocating screw include reducing the time of the plastic, from the screw and the screw tip. These advantages are key in the processing of heat-sensitive materials and when the changes of colored materials or resin varieties are used, both the screw and the cylinder should be cleaned. The design of the widely used fitting module includes: elbow - rod - type fitting, hydraulic - fitting and hydraulic - mechanical - type fitting. It is suitable for small tonnage equipment because of its low cost in manufacturing. The characteristics include high mechanical efficiency of the closed-lock operation, the internal lock mode deceleration device, the failure of the mould and the fast closing operation.
