Plastics classification
According to the behavior of heating and whether it has the ability of repeated molding, plastics can be divided into two categories: thermoplastic and thermosetting plastics.
Thermoplastic melts when heated, can be processed in various forms, and solidifies when cooled. After reheating, it can be melted and processed, that is, it can be processed repeatedly.
At the same time of thermosetting plastics heating and melting, curing and cross-linking reactions occur, forming a three-dimensional network structure, which can not be melted and dissolved in organic solvents. When the temperature exceeds the decomposition temperature, it will be decomposed and destroyed, that is, it does not have the characteristics of repeated processing and can not be recycled.
Thermoplastics can be divided into general plastics and engineering plastics according to heat resistance, mechanical properties, cost and market scale. Engineering plastics can be divided into general engineering plastics and high-performance engineering plastics according to the heat-resistant grade, and the long-term heat-resistant temperature of the latter is more than 150 ℃.
General plastic mainly refers to the plastic with large output, wide use, good formability and low price. There are five main varieties, polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene copolymer (ABS)
Engineering plastics generally refer to the plastics that can bear certain external force, have good mechanical properties, high temperature resistance, low temperature performance, good dimensional stability, and can be used as engineering structures, and can be used to replace wood with plastic and steel with plastic.
It mainly includes polyamide (PA), polycarbonate (PC), POM, polyester (PBT, PET), etc.
Special plastics refer to plastics with special functions, which are used in aerospace and other special fields. For example, peek, POB, PES and so on.
In fact, in the industry, the dividing line between general plastics and engineering plastics is not so clear. For example, ABS, this material has many brands, some of which are general-purpose, and some of which are engineering.
Plastic forming method
Injection molding: it is a method that plastic melts in the screw barrel of injection molding machine to form a flowable plastic melt, and then the melt is pushed into the cavity of closed mold by reciprocating screw, and is cooled and finalized.
Extrusion molding: the method by which the plastic is heated and pressurized in the extruder to continuously flow through the die.
Foaming molding: it refers to the processing method of foaming products with small relative density, high specific strength, small amount of raw materials, sound insulation, heat insulation and other advantages. The foaming materials include PVC, PE and PS.
Blow molding: also known as hollow blow molding, it is a molding method to blow the hot thermoplastic blank or sheet in the closed mold into hollow products with the help of fluid (compressed air) pressure.
Rotary molding: also known as roll molding, rotary molding, rotary molding, rotary casting, rotary molding, etc., first add the plastic into the mold, after the mold is closed, make it rotate along the two vertical rotation axes, and at the same time make the mold heated. Under the effect of gravity and heat energy, the plastic raw materials in the mold are gradually evenly coated, fused and adhered to the entire surface of the mold cavity, forming the same as the mold cavity Shape.
Blister molding: the flat plastic hard sheet is heated and softened, then absorbed on the surface of the mold by vacuum, cooled and then formed.
Molding: also known as compression molding or compression molding, is to put the powdery, granular or fibrous plastic into the mold cavity under the molding temperature, and then close the mold to pressurize to make it form and solidify.
Injection molding is the most widely used in these plastic molding, such as automobile bumper, instrument panel, door panel, column and other parts, and other parts such as extrusion molding, blow molding and molding are widely used in the preparation of automobile parts.
