What is the process of injection molding and other processing in various types of plastic molds?
Date: October 19, 2024
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Mold injection molding: Thermoplastic injection molding is a method of melting plastic material and then injecting it into a film cavity. Once molten plastic enters the mold, it is cooled and molded into a certain shape according to the mold cavity. The resulting shape is often the final product, and no further processing is required before installation or use as the final product. Many details, such as protrusions, ribs, and threads, can be formed in one step of injection molding.
1、 The injection molding machine has two basic components:
Injection and mold closing devices used for melting and feeding plastic into molds.
The function of the mold clamping device is to: 1. close the mold under injection pressure; 2. Remove the product from the injection device and melt it before injecting the plastic into the mold, then control the pressure and speed to inject the melt into the mold.
There are currently two designs of injection devices used: screw pre plasticizers or two-stage devices, and reciprocating screws.
The screw type pre plasticizer uses a pre plasticizing screw (first stage) to inject molten plastic into the injection rod (second stage). The advantages of screw pre plasticizers are constant melt mass, high pressure and speed, and precise injection volume control (using mechanical thrust devices at both ends of the piston stroke). These advantages are required for transparent, thin-walled products and high production rates. Its disadvantages include uneven residence time (leading to material degradation), high equipment and maintenance costs.
The most commonly used reciprocating screw injection device does not require a plunger to melt and inject plastic.
2、 Extrusion blow molding
Extrusion blow molding is a method of manufacturing hollow thermoplastic parts. The widely used blow molded objects include bottles, barrels, cans, boxes, and all containers for packaging food, beverages, cosmetics, pharmaceuticals, and daily necessities. Large blow molded containers are commonly used for packaging chemical products, lubricants, and bulk materials. Other blow molded products include balls, corrugated tubes, and toys. For the automotive manufacturing industry, fuel tanks, car shock absorbers, seat backrests, center brackets, and armrest and headrest coverings are all blow molded. For the mechanical and furniture manufacturing industry, blow molded parts include shells, door frames, frames, pottery jars, or boxes with an open face.
3、 Polymer
The most common raw material for blow molded extruded plastics is high-density polyethylene, which is commonly used in milk production. Other polyolefins are also often processed through blow molding. According to their applications, styrene polymers, polyvinyl chloride, polyester, polyurethane, polycarbonate, and other thermoplastic materials can also be used for blow molding.
Recently, engineering plastics have been widely accepted in the automotive industry. The selection of materials is based on mechanical strength, weather resistance, electrical performance, optical performance, and other properties.
4、 Craftsmanship
At present, 3/4 of the blow molded products processed by plastic mold injection molding are manufactured by extrusion blow molding method. Extrusion technology forces materials to pass through a hole or mold to manufacture products.
The extrusion blow molding process consists of four steps:
1. Plastic preform (extrusion of hollow plastic tubes);
2. Close the flap mold on the embryo, clamp the mold and cut off the embryo;
3. Inflate the cold wall of the mold cavity, adjust the opening and maintain a certain pressure during cooling, open the mold, and write down the blown part;
4. Trim the edges to obtain the finished product.
5、 Polymer blending equipment
Polymer blending is defined as a process of upgrading a polymer or polymer system through melt blending.
The mixing process ranges from the addition of a single additive to the treatment of multiple additives, polymer alloys, and reactive mixing. It is estimated that one-third of polymer production in the United States goes through blending. The mixed ingredients can be customized according to the performance requirements of the final application. Mixed products have mixed properties, such as high gloss and excellent impact strength, or precision moldability and good stiffness.
The mixed polymer is usually pelletized for further processing. However, the industry is increasingly interested in combining blending with the next process, such as profile extrusion, to avoid reheating the polymer.
6、 Mixed
People use various types of melt mixing equipment, from roller mills and batch mixers to single screw and twin-screw extruders. Continuous mixing (extruder) is the most commonly used equipment because it can provide products of consistent quality and reduce operating costs.
There are two types of mixtures:
1. Distributed mixed materials can be evenly distributed without the need for high shear stress in the remarriage of ingredients. This type of mixture is called extensional mixing or laminar mixing.
2. Dispersed mixing, also known as strong mixing, in which high shear stress is applied to break down solid aggregates. For example, when the additive pellets are crushed, the actual particle size decreases. Mixing operations often require two types of mixing in one process.
7、 Rotational molding
Rotational molding, also known as rotational molding, is a processing method used to manufacture hollow seamless products of various sizes and shapes. Traditionally, it has been mainly applied to thermoplastic materials, but in recent years, the rotational molding of thermosetting materials such as cross-linked polyethylene has also developed rapidly. Due to the fact that rotational molding does not require high injection pressure, high shear rates, or precise compound meters. Therefore, both molding and machinery are relatively inexpensive and have a longer service life. Its main advantages are: high performance/price of the machine; The formation of complex components does not require post assembly; Multiple products and colors can be molded simultaneously; The cost of molds is relatively low; Colors and materials are easily changed; Less loss of scraps.
injection molding processing various types plastic molds?
The basic processing procedure is simple: place powdered or liquid polymer in a mold, heat it while rotating around two vertical axes, and then cool it down. At the beginning of the heating phase, if the powder material is used, form a porous layer on the mold surface, and then gradually melt with the circulation process to form a homogeneous layer of uniform thickness. If the liquid material is used, flow and coat on the mold surface first, and when the gel point is reached, stop flowing completely. The mold is then transferred to the cooling work area, cooled by forced ventilation or water spray, and placed in the work area. Here, the mold is opened, the completed parts are taken away, and then the next cycle is carried out.