Different Plastic Molding

(1) Injection molding
Injection molding is to send granular or powdery plastics from the hopper of the injection machine to the heated barrel, and then melt and plasticize it into a viscous fluid melt under the action of the plunger or scroll of the injection machine. A large flow rate is injected into the mold cavity through the nozzle. After a certain period of pressure maintaining, cooling and setting, the shape given by the mold cavity can be maintained, and then the mold is opened to obtain the molded plastic part. Injection molding can be used in all types of plastic manufacturing processes, especially suitable to produce thermosetting plastics with good fluidity. There are also certain differences in the types of machines and equipment commonly used in injection molding. The common ones are vertical, angle, rotary and horizontal types according to their characteristics of appearance. According to the different plasticizing forms of injection molding equipment, the equipment can be divided into two types: the screw type and the plug type.
 
The injection molding process can be divided into the preparation stage, injection stage, plasticizing stage and post-processing stage. The preparation stage is the basic guarantee to ensure the smooth progress of the entire injection molding process, and it is also a key stage that affects the quality of the entire plastic molding. The injection process is the process in which plastics are transformed from powdery or granular substances into plastic products. The plasticizing stage and the post-processing stage are the processes of eliminating the internal stress in the plastic by using the demoulding machine, the purpose of which is to improve the performance of the plastic and stability of the plastic. There are three main necessary conditions for plastic injection molding. First, it is necessary to ensure that the control barrel, mold and nozzle are in an appropriate temperature environment; second, it is necessary to ensure that the plasticizing pressure and injection pressure are maintained at an appropriate level during injection molding; master the molding cycle, and the time required to complete an injection molding process is called the molding cycle or the total cycle.
 
(2) Compression molding
Compression molding is to add raw plastic into the corresponding compression molding model, and then use the heating and pressure of the mold cavity to melt the plastic, and then fill the entire mold cavity, and produce cross-reaction in the cavity. Then, it is solidified, and the required plastic part is obtained. The compression molding includes steps such as feeding, mold closing, exhaust, solidifying, demoulding and mold cleaning. Several conditions that have an important impact on the entire molding are pressure, pressure time and mold temperature. In the compression molding process, if the product insert is required to be sealed into the mold, the corresponding insert should be placed before feeding. The main equipment used in the implementation of compression molding is a press and a mold. The function of the press is to apply pressure to the raw material using the mold. The common parameters of the press are nominal tonnages, sizes of platen, working strokes and diameters of plungers, which can have a direct impact on the height, thickness and size of the plastic product, and directly determine its maximum pressure.
 
(3) Extrusion molding
Extrusion molding is to use the screw rod to push the granular material in the hopper to the barrel. Under the action of the external heat of the heater and the heat generated by the screw in the extrusion friction or stirring process, in the forward direction of the screw shaft, the material melting occurs due to the action of heat, showing a state of fluidity, and then gradually being extruded to the machine head to complete extrusion molding. Extrusion molding is a relatively common process used in plastic molding in China. The molding equipment machinery includes two parts: the main machine and the auxiliary machinery. The main engine is the core of the equipment, and the operation quality of the main equipment will have a major impact on the quality of the entire plastic molding, and the auxiliary equipment is mainly other equipment.
 
There are four main points in plastic extrusion molding: first is the temperature control of extrusion molding, which can directly have an important impact on the plasticizing effect and quality; the second is the extrusion screw speed, which can affect the size and shape of extruded plastic products; third is the extrusion pressure of the machine head. The increase in the extrusion pressure can provide a guarantee for the product texture, but it will reduce the product output to a certain extent; fourth is the traction speed, which requires maintaining a uniform and stable traction speed during the process of pulling the product, and it is necessary to ensure that the traction speed is consistent with the extrusion speed of the main machine.
 
(4) Other moldings
Several other common plastic molding includes blow molding and vacuum molding. Vacuum molding mainly uses a heater to heat the thermoplastic material and fix it on the corresponding mold, and then evacuate the air between the mold and the plastic sheet to let the plastic sheet fit well with the mold and finally realize plastic shaping.
 
Development trend of plastic molding
At present, China's plastic molding has made great progress compared with the last century. The main development trends of the plastic molding in the future can be summarized as the following four aspects: the first is the development of precision. High crystallization, molecular orientation and other molding processing methods are adopted, such as laser discs, computer discs, optical fibers and plastic watch gears that require ultra-micro instructions. The second is the development of high performance. The so-called high performance refers to the further development and utilization of new performance based on the original performance, and in the process of high-performance development, it is possible to reduce costs, simplify procedures and save raw materials. The third is high-quality development. The development of quality mainly integrates some technologies at the present stage, that is, the cross-use of different plastic molding. For example, several plastic moldings are currently widely used: injection molding and extrusion molding. Combining the two technologies, molded plastics can have the advantages of two kinds of molding technologies at the same time.
 
The fourth is the development of parameterization. Under the influence of the dispersed nanometer size effect, there are large specific surface areas and good interfacial bonding that make nano plastics have excellent properties that general engineering plastics do not have, including high strength and good heat resistance. The integration of the rigidity, stability and thermal stability of inorganic materials with the toughness and dielectric properties of polymer materials. In addition, good barrier properties and self-extinguishing properties can also be achieved by controlling the orientation of nano pile layers.