Analytical injection molding of thermoplastics

When the thermoplastic is heated, it becomes soft and even flows, and the cooling hardens the product. This process is reversible and can be repeated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic, other polyolefins and copolymers, polysulfone, polyphenylene ether, chlorinated polyether, etc. Thermoplastic. In the thermoplastic, the molecular chains of the resin are linear or branched, and there is no chemical bond between the molecular chains. The process of softening and heating when heated, the process of cooling and hardening is a physical change.

The resin is prepared by polymerization. The resin is generally formed by a monomer containing an unsaturated bond, mainly a double bond, which is opened by a double bond, and no low molecular product is released during the reaction. Polyolefins, polyhalogenated olefins, polystyrene, polyoxymethylene, and acrylic plastics all belong to polymeric plastics. Polymeric plastics are all thermoplastics. b) The polycondensation type plastic resin is obtained by a polycondensation reaction. This resin is generally composed of a monomer containing a certain functional group (generally containing at least two functional groups),

The reaction is formed by joining the monomers together. 1.3.3 According to the ordered state of the resin macromolecule in the plastic: a) The arrangement of the macromolecule of the amorphous plastic resin is disordered. Due to the structural characteristics of the resin molecular chain, or due to thermodynamic reasons, or the limitation of the process conditions of the molding process, the molecular chain does not produce an orderly and neatly stacked crystal structure, but presents a random random arrangement. In the pure resin state, this plastic is transparent. b) The crystalline plastic resin macromolecular arrangement exhibits an ordered crystalline phase. During the process of cooling from a molten state to a product, the molecular chains of the resin can be closely packed in an orderly manner to produce a crystalline structure. Generally, the so-called crystalline plastics are actually semi-crystalline, unlike the low molecular crystals (such as NaCl), which can produce 100% crystallinity. The resin macromolecular chain arrangement exhibits a state in which the amorphous phase and the crystalline phase coexist. Molding conditions have a significant effect on crystallinity and crystalline structure, which has a significant impact on product properties. The crystalline structure is only present in the thermoplastic.

Thermoplastic injection molding involves melting a plastic material and then injecting it into the membrane cavity. Once the molten plastic enters the mold, it is shaped into a shape by the cold cavity. The resulting shape is often the final product and no further processing is required prior to installation or use as a final product. Many details, such as raised parts. Ribs and threads can be formed in one step of injection molding. The injection molding machine has two basic components: an injection device and a clamping device for melting and feeding the plastic to the mold. The function of the clamping device is to: (1) close the mold while receiving the injection pressure; and (2) remove the product. The injection device melts the plastic before it is injected into the mold and then controls the pressure and velocity to inject the melt into the mold. There are two types of injection devices currently in use: a screw pre-plasticizer or a two-stage device, and a reciprocating screw. The screw pre-plasticizer uses a pre-plasticized screw (first stage) to deliver the molten plastic to the shot bar (second stage). The advantages of the screw pre-plasticizer are constant melt mass, high pressure and high speed, and precise injection volume control (using mechanical thrust devices at both ends of the piston stroke). These strengths are required for transparent, thin-walled products and high production rates. Disadvantages include uneven residence time (resulting in material degradation), higher equipment costs, and maintenance costs. The most common reciprocating screw injection device does not require a plunger to melt and inject the plastic. The powdery or granular plastic in the hopper is melted, and is sent to the front end of the screw through the rotating screw, and the plastic fluid flows through the front end of the screw and is accumulated in front of the screw. The accumulation of molten plastic in front of the screw pushes the screw toward the rear of the injection device, and the rotation of the screw, the accumulation of the melt, and the movement to the rear continue until a certain amount of injection is formed. During the next equipment duty cycle, the screw tip is closed and the material is prevented from returning along the screw. The screw tip and the feed screw function as a shot plunger to press the plastic into the mold. Advantages of the reciprocating screw include reduced plastic residence time, self-cleaning screw and screw tip. These advantages are key to the processing of heat sensitive materials and the cleaning of the screw and barrel when changing the color of the raw material or resin. Currently widely used mold clamping device designs include: toggle-type clamping device, hydraulic clamping device and hydraulic-mechanical clamping device. The toggle-type clamping device is suitable for small tonnage equipment because of its low cost in manufacturing. Features include high mechanical efficiency of the locking operation, built-in mold-locking slowdown, slow mold damage and fast mold clamping.

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