Injection molding is the most commonly used method in plastic molding. The reason is that as long as the mold is made, even complex shapes can be produced in large quantities. In Dalian injection molding, various products are produced by changing the mold, from small to large, from simple to complex, which not only reduces the production cycle, but also saves the cost.

In plastic molding, the molding methods of many products (second only to injection molding) include extrusion molding and blow molding. In the case of extrusion molding, the equipment is usually large, and because they are kneaded with various additives, they are usually manufactured by large companies (such as material manufacturers).

The forming method will be explained below.

Injection molding:

Melt the plastic at a high temperature of about 200 ° C, push it into the mold, then cool and solidify. The injection molding machine consists of two main equipment. Push the syringe and other equipment into the molten plastic and lock the "injection device" and "clamping device" to prevent the mold from opening.

injection molding machine

The injection device is composed of an injection mechanism such as a syringe and a "plasticizing mechanism" for melting the plastic. The clamping device has a clamping mechanism for opening and closing the mold and an ejection mechanism for taking out the finished product.

Injection molding schematic diagram

The method of melting plastics usually uses screws. A heater is wound on the outside of the metal round tube (cylinder) for heating. The plastic particles are put into the pipe. After rotating the screw, the particles are transported to the front end along the threaded groove, heated and melted. When the screw is rotated counterclockwise, molten plastic accumulates in the front of the cylinder.

Dalian injection molding

Injection mechanism

Dalian injection molding factory next, tighten the mold with the clamping device. Then, the part of the syringe outlet connected to the top of the cylinder (called nozzle) is firmly pressed against the hole at the inlet of the die. When you press the screw, the accumulated plastic is pushed into the mold, cooled and cured. Plastic shrinks as it hardens, so add a little molten plastic after all filling.

The pressure during injection molding is 2000 kgf / cm2 and the pressure in the mold is 200-500 kgf / cm2. The die requires a clamping force of about 150 tons, so it cannot be opened easily. The large mold weighs 50 tons, and the clamping force of the molding machine is about 3000 tons. Injection molding is characterized by efficient production of high-precision products. However, machines and molds are very expensive. Therefore, this method is suitable for mass production.

For mixed metal and plastic products, first put the metal parts into the mold, and then inject the plastic around the mold. This method is called insert molding.

Extrusion:

It is called extrusion because plastic is pushed out from the extrusion (die) part. The typical product is vinyl chloride pipe. This kind of mold is a kind of mold. According to the shape of the product, there are various cross-sectional shapes, such as circle and square.

Extrusion molding principle

Most of the raw materials are not particles for injection molding, but plastic powder. The formed plastic just coming out of the extrusion port has not been cooled and is easy to deform. Therefore, in order to suppress the deformation, it is recycled after extrusion.

The bellows on the washing machine can also be made by extrusion. After extrusion, it is transported to Caterpillar by compressed air for molding. In addition, by designing extrusion holes, drilling holes inside and outside the die, rotating and pushing the internal and external dies away from each other, a grid shape can be formed.

T-die extrusion:

In GB, a sheet with a thickness of more than 0.25mm is called a sheet, and a sheet with a thickness of less than 0.25mm is called a film. The extrusion die head has a slender shape. It is called T-die extrusion because it expands T-shaped in the extrusion direction.

The process of increasing the winding speed and stretching the sheet in the length direction is called stretching. The plastic is reinforced by stretching the plastic in the longitudinal direction. By performing a process called biaxial stretching, which is stretched not only in one direction of flow, but also in the left and right directions, a strong film in the length direction and perpendicular to it can be manufactured.