Basic knowledge of plastic mold
Thermoplastic injection molding is the process of melting the plastic material and injecting 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 that no longer needs to be processed before it is installed or used as a final product. Many of the details, such as the bulge, rib, and thread, can be formed in the injection molding.
The injection molding machine has two basic components: the injection device and the fitting device for the melting and injection of plastic into the mould. The function of the die device is: 1. Make the die close under the pressure of the injection. 2. Remove the product from the injection device and melt it before injecting it into the mold, then control the pressure and speed 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 utilizes the preplasticized screw (first stage) to inject the molten 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.
Extrusion blow molding
Extrusion blow molding is a method of manufacturing hollow thermoplastic making parts. The widely held blown plastic objects have containers, buckets, tanks, boxes and all containers of packaged foods, beverages, cosmetics, medicines and daily necessities. Large blown plastic containers are usually used in chemical products, lubricants and packaging of bulk materials. Other blow molding products have balls, bellows and toys. For automobile manufacturing, fuel tank, car shock absorber, seat back, center bracket and armrest and headrest cover are all blown. For machinery and furniture manufacturing, blow molding parts have shells, door frames, frames, ceramic POTS or to an open box.
The most common plastic blowing plastic material is high density polyethylene. Most milk is made of this polymer. Other polyolefins are also used in blow molding. For use, styrene polymers, polyvinyl chloride, polyester, polyurethane, polycarbonate and other thermoplastics can also be used for blowing.
Engineering plastics have been widely accepted in the automobile industry recently. Material selection is based on mechanical strength, weather resistance, electrical properties, optical properties and other properties.
3/4 of the blow molding products are made by extrusion blow molding. Extrusion process is to force the material through a hole or mold to make the product. The extrusion blow molding process consists of 5 steps: 1. Plastic type embryo (extrusion of hollow plastic tube); 2. In the type embryo, the valve is closed, clamped and cut off the mold; 3. Blow up the cold wall of the cavity, adjust the opening and maintain some pressure during cooling, open the mould and write down the parts that are blown; Trim the edges to get the finished product.
Polymer mixing is defined as a process by which a polymer or polymer system can be improved by a mixture of melt. Mixing process from single additive to a variety of additives, polymer alloys and reactive mixtures has a wide range. It is estimated that a third of all polymer production in the United States is mixed. Mixing ingredients can be customized according to the performance requirements of the final application. Mixing products have mixed performance, such as high gloss and excellent impact strength, or precision moulding and good rigidity.
Mixtures of good polymers are usually used for further processing. However, the growing interest in industry is to combine the mix with the next process, such as extrusion of profiles so as to avoid reheating the polymer.
Various types of melt mixers are used, from the roller mixer and the batch mixer to the single screw and twin screw extruder. Continuous mixing (extruding machine) is the most commonly used equipment, because he can provide products with consistent quality and can reduce operating expenses. There are two types of mixtures: extended mixing or laminar mixing and distributed mixing.
Extended mixing or laminar mixing refers to the uniform distribution of the distributed mixing materials without high shear stress. The dispersion type is also called a strong mixing, which means to apply high shear stress to break up the solid. For example, when the additive mass is broken, the actual particle size becomes smaller.
Mix and match operations often require two types of mixing in a process.
Second, rotomolding
Roll-molding is also known as rotary molding, which is a process for making hollow seamless products of various sizes and shapes. Traditionally, it has been applied to thermoplastic materials. In recent years, the rolling plastic of thermosetting materials such as crosslinked polyethylene has also developed rapidly. Since roll-rolling does not require high injection pressure, high shear rate or precise compound meter. As a result, mods and machines are cheaper and have a longer life. Its main advantages are: machine performance/high price; Complex parts are formed without post-assembly; Multiple products and colors can be formed at the same time. The cost of mold is low; Colors and materials are easy to change; There is less loss of edge material.
The basic process is simple, and the powder or liquid polymer is placed in the mold, heated and rotated around the two vertical shafts, then cooled. In the initial heating stage, if use the powder material, the mold surface porous layer, and then gradually fused with cyclic process, the formation of homogeneous layer of uniform thickness if using the liquid material, the flow and coated on the surface of mould first, when reach the gel point is completely stopped flowing. Die then turn into cooling work area, by forced ventilation or spray water cooling, and then be placed in the workspace, here, the mould is opened, the finished parts are removed, and then on to the next round of cycle.
Third, cast
The cast plastic nylon -6 has high strength, abrasion resistance, abrasion resistance and resilience. Most of the casting reactions are carried out under atmospheric pressure or very low pressure, so the nylon that is cast and moulded has an obvious advantage over extruded or moulded nylon. Compared with the nylon extruded nylon, the cast plastic nylon has high crystallinity and molecular weight, which has good dimensional stability, easy machine processing, high modulus and heat deformation temperature.
Because the size and shape of the cast nylon are not limited, they have great flexibility. Low-price tools can produce simple cast-plastic nylon and production cycle is short. Complex parts need to be produced in complex tools. Try not to use high - price casting machine in the club. The endoamide monomer reacts in the mold with anionic polymerization, which is transformed into a polymer. Therefore, the reaction of the anhydrous acid catalysis process is low and the conversion efficiency is low, so people choose a catalytic reaction to get better results. Since the 1950s, the catalyst has been developed and more effective production machinery has been developed in the late 1960s to accelerate the commercialization process of casting plastic nylon.
