What does extrusion mean in wire and cable production?

Extrusion in wire and cable production refers to a processing method in which materials are plasticized by heat, pushed forward by screws and passed through dies continuously to make products or semi-finished products with various sections.

Expansion: Extrusion (extrusion) process generally selects extruder, die and die, and corresponding auxiliary equipment such as setting and traction according to the type of polymer to be processed and the shape of products or semi-finished products, and then determines extrusion process conditions such as screw speed, die pressure, material temperature, setting temperature and traction speed. In the process of extrusion, materials are generally plasticized, but the solidification methods are different. For example, extruded plastics often need cooling and setting to cure them, while extruded rubber semi-finished products need further vulcanization. Different products can be obtained by using different extrusion equipment and technology.

1 granular material

After the polymer is mixed with various additives, it is sent to an extruder for melting and further mixed evenly. Through a porous die, a plurality of strips are formed and then cut into particles. Cutting can be divided into hot cutting and cold cutting. After the former one leaves the mold, it is cooled with air or water and immediately cut with a rotary knife. The latter is to cool all the strips and then send them to a granulator for granulation.

2. Pipe installation

The material passes through the annular gap composed of the die and the core die to form a tube, and then through molding and cooling, the tube with smooth surface, accurate size and geometric shape is obtained. The common forming method is external diameter forming, that is, the extruded pipe passes through the forming sleeve with the same internal diameter as the external diameter of the product, and the pressure difference is used to make the pipe cling to the inner wall of the forming sleeve, so as to obtain the pipe with accurate external diameter. In order to cause pressure difference, compressed air can be introduced into the pipe or negative pressure can be caused outside the pipe.

3. Sheets and films

Flat products with a thickness of more than 0.25mm and a length much greater than the width are called plates; A film with a thickness of less than 0.25mm is called a film. For example, a flat film can be prepared by cooling and shaping the film with a flat die through a cooling drum with a very smooth surface. This method is also called squeeze casting. This is a common method for manufacture polypropylene films. If the obtained flat film is sent to a tenter and stretched 4 ~ 10 times in the longitudinal direction and the transverse direction at the same time (it can also be stretched in the longitudinal direction first and then in the transverse direction), a biaxially oriented film can be made. Due to the orientation of macromolecules during stretching, the strength of the film is high, but the water permeability and air permeability are reduced. It is usually used to make polypropylene and polyester films. If foaming agent is added to the material and special screws and dies are used, low foaming plastic plates can also be made.

4. Envelope

When the bare metal wire passes through the T-shaped die, the molten plastic forms a coating around the bare metal wire, and after the coated metal wire is cooled and wound, various wire and cable products are obtained.

5. Blow film

Most movies are made because of inflation. In this method, the pipe molded by the mold is inflated with compressed air, and the molded film bubble is cooled by the air blown by the wind ring, and then led out by the guide roller (or splint) and wound into a roll, so that the blown film can be made. A large number of packaging bags and agricultural films are made into cylindrical films by this method, and then further welded and cut.

6. Composite products

Several extruders are used to supply several kinds of plastics at the same time, and then the whole composite product is formed by die extrusion. For example, three kinds of plastics, A, B and C, can be extruded to produce various composite films, composite sheets, plates, profiles and pipes.

7. Rubber filtration

When manufacturing thin-walled rubber products, in order to prevent the products from leaking, the rubber compound cannot contain impurities. Generally, before the vulcanizing agent is added, the rubber compound is filtered by an extruder, that is, one or more layers of filter screens are placed at the head to filter out the impurities in the plasticized material.

8. Manufacture of tire tread and inner tube

Tread is divided into integral extrusion and layered extrusion. Integral extrusion can use an extruder to extrude rubber materials through a flat die; Two kinds of rubber mixture (crown material and sidewall material) can also be extruded by two extruders and combined into an integral tread in the extruder head. Layered extrusion means that two kinds of rubber compounds are extruded from the crown and sidewall respectively by two extruders, then thermally bonded on the conveyor belt, and then rolled into a whole by multi-disc flexible rollers. Inner tube extrusion is similar to tube extrusion. After the inner tube is extruded, it is cut off and then joined to form.

9. Melt spinning

When some high-viscosity resins are melt spun, an extruder is usually used to melt these materials. The molten material directly enters the spinneret through a filter or is pumped into the spinneret by a spinneret pump.