The Types of Plastic Molding and Processing
❀ Injection molding
The plastic material is first heated and melted in the heating barrel of the injection molding machine. And then the melt is pushed into the cavity of the closed mold by the reciprocating screw.
It can produce high-precision and high-quality products under high productivity. What’s more, it can process a large variety of plastics and has a large output (about 1/3 of the total amount of plastic) and be widely used. Therefore, injection molding is one of the important molding methods in plastic molding and processing.
❀ Extrusion molding
Extrusion is a method in which the plastic is continuously passed through the die in a flowing state by heating and pressing in an extruder.
It is generally used in the molding of plates, pipes, monofilaments, flat wires, films, wires and cables, etc. It has a wide range of uses and high output. Therefore, it is also one of the important molding methods in plastics molding.
❀ Foam molding
It refers to the addition of suitable foaming agents to the foaming materials to produce porous or foamed products. The foamed products have relatively low density, high specific strength, low raw material consumption, sound insulation, heat insulation and other volt points. The material usually are PVC, PE and PS etc.
Products include: films, sheets, pipes, and profiles, etc. While foaming can be divided into chemical foaming and physical foaming.
❀ Blow molding
Blowing molding (or hollow blow molding) refers to a molding method in which the hot thermoplastic parison or sheet in a closed mold is inflated into a hollow product by means of fluid (compressed air) pressure.
Plastic containers produced by this method like various bottles, square, round or flat barrels, gasoline tanks, etc. have been widely used. Besides, the various newly developed industrial parts and daily products have been applied in practice. E.g. double-walled box-shaped products, L-ring large drums, stacking boards, surfboards, seat backs and desks, as well as front spoilers for automobiles, belt covers, instrument panels, air conditioning ducts, etc.. And the processed materials are developed from daily-use plastics to engineering plastics. Nowaday, blow molding has become one of the important molding methods in plastic processing.
The basic steps of the blow molding process are:
- Melt materials.
- Form the molten resin into the shape of tube or parison.
- Melt the hollow parison in the blow mold.
- Inflate the parison in the mold.
- Cool blow molding products.
- Remove the product from the mold.
❀ Injection blow molding
Injection blow molding is a blow molding method. First, plastic is made into a bottomed parison by injection molding. And then it is moved to a blow mold and made into a hollow product.
This method can be used to produce packaging containers for daily necessities, cosmetics, medicine, food, etc.. But its volume should not exceed 1L. The commonly used plastics include polyethylene, polystyrene, and polyvinyl chloride.
❀ Extrusion blow molding
Extrusion blow molding is also a blow molding method.But it is different from injection blow molding. Its parison is made by extrusion.
❀ Stretch blow molding
Stretch blow molding is a blow molding method. It makes a parison by extrusion, injection molding and other methods. Then the parison is heated to the stretching temperature. It is stretched longitudinally under internal (such as mandrel) or external (such as clamps) mechanical force. At the same time or later, it is stretched laterally by blowing with compressed air.