Extrusion Molding

In plastic processing, also known as extrusion or extrusion, in rubber processing, also known as extrusion. It is a kind of processing method that the material is plasticized by heat and pushed forward by the screw through the action between the barrel and the screw of the extruder, and is continuously made into various cross-section products or semi-finished products through the die.

catalogue

1 definition of words

2 extrusion equipment

3 extrusion process

4 stability control system

Extrusion

Definition of words

In the chemical fiber industry, the extruder is also used to feed the spinneret for melt spinning. Extrusion is applied to the addition of thermoplastic and rubber

It can be used for batching, granulation, rubber filtration, etc. it can be used for continuous production and manufacture various continuous products, such as pipe, profile, plate (or sheet), film, wire and cable coating, rubber tire noodles, inner tube tube, sealing strip, etc., with high production efficiency. In the production of synthetic resin, the extruder can be used as a reactor for continuous polymerization and molding.

Extrusion equipment

The main body is extruder and die, in addition to feeding, shaping, cooling, traction, cutting and coiling and other auxiliary equipment (see color picture). Vulcanization device is also included in rubber processing. In actual production, the main body and auxiliary equipment are often connected into a unit.

Extruder

——According to the number of screw, it is divided into single screw extruder and twin-screw extruder

Single screw extruder

The single screw extruder is equipped with a rotating screw in the heating barrel. The external partition of the barrel is equipped with heating and cooling devices. One end has a radial feeding port, and the other end is connected with the die axially. Screw is the key part of extruder. The main technical parameters of single screw extruder are screw diameter, length diameter ratio (the ratio of screw length to diameter), screw speed range, driving motor power, barrel heating power and machine production capacity. The screw diameter determines the production capacity of the extruder and the maximum allowable cross section of the product. Different materials require different screw shapes and length diameter ratio. Modern plastic extruders widely use combination screw, distribution mixing screw, and adding barrier or pin on screw to improve plasticization, production capacity and product quality [2].

Double screw extruder

Twin screw extruder has two screws rotating in ∞ shaped heating barrel. The screw can be divided into meshing type and non meshing type; Combination and non combination; Rotating in the same direction or in the opposite direction. The same direction meshing type and different direction meshing type are used more. The former is used for blending, filling and strengthening of plastics to produce various batch materials; The latter is used for processing UPVC products.

Head and die

The die and die are located at the front end of the barrel, which are the warm flow and molding parts of the extruder. By changing the die and die, semi-finished products with different specifications and shapes can be extruded [3].

(1) The head is located in the front of the fuselage, and is installed between the end of the screw and the die. The function of the head is to change the movement state of the rubber from the screw to the linear movement state, and form the necessary pressure and a certain shape of semi-finished products.

(2) The die is located in the front of the head, which is used for semi-finished product modeling and controlling its size. By changing the die, one extruder can produce semi-finished products of different specifications and shapes. The requirement of the die is to ensure the laminar flow of the compound, no dead point and minimum pressure drop. The main types of mouth are common and special.

There are two kinds of common die: one is steel plate with certain geometry, which is used to extrude solid and sheet semi-finished products, such as tread, rubber strip, rubber sheet, etc; The other is composed of die, core and core support, which is used to extrude hollow semi-finished products, such as inner tube, rubber tube, etc.

The special die is a new type of die design, which mainly includes double roll die and orientation die.

Extrusion process

Generally, according to the type of polymer processed and the shape of products or semi-finished products, the extruder, die and die, as well as the corresponding auxiliary devices such as setting and traction are selected, and then the extrusion process conditions such as screw speed, die pressure, material temperature, setting temperature and traction speed are determined. In the extrusion process, the material is usually plasticized, but the setting method is different. For example, extruded plastics often need to be cooled and set to cure, while semi-finished products of extruded rubber need to be further vulcanized. Different products can be obtained by different extrusion equipment and process.

1. Granular material

After mixing with various additives, the polymer is sent to the extruder for melting and further mixing. Through the porous die, a plurality of strips are formed, and then cut into granules. Cutting is divided into hot cutting and cold cutting. The former is cooled by air or water and cut off by rotary knife immediately after leaving the die. The latter is to cool all the strips and then send them to the granulator for granulation.

2. Pipe material

The material passes through the annular gap formed by the die and the mandrel to form a tube, and then through shaping and cooling, the tube with smooth surface, accurate size and geometry can be obtained. The common shaping method is to adopt the outer diameter shaping, that is, the extruded tube passes through a shaping sleeve with the same inner diameter as the outer diameter of the product, and the tube is close to the inner wall of the shaping sleeve by using the pressure difference, so that the tube with accurate outer diameter can be obtained. In order to create pressure difference, compressed air can be introduced into the pipe, and negative pressure can also be created outside the pipe.

3. Sheet and film

Flat products with a thickness of more than 0.25 mm and a length much larger than the width are called sheets; If the thickness is less than 0.25 mm, it is called film. If the film formed by flat die is cooled and shaped by a cooling drum with very smooth surface, the flat film can be made. This method is also called extrusion casting method. This is a common way to make polypropylene film. If the flat film is fed into the stretcher and stretched 4-10 times in both the longitudinal and transverse directions (or the film can be stretched first in the longitudinal direction and then in the transverse direction), the biaxially oriented film can be obtained. Due to the orientation of macromolecules during stretching, the strength of the film is very high, but the water permeability and air permeability are decreased. Commonly used in the manufacture of polypropylene and polyester film. If the foaming agent is added to the material and special screws and dies are used, low foam plastic sheets can also be made.

4. Wrapping line

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

5. Blown film

Most films are made by blowing. In this method, the tube shaped by the die is inflated with compressed air, and the formed film bubble is cooled by the air blown out by the wind ring, and then is led out through the guide roller (or splint), and then wound into a roll, and the blown film can be made. A large number of packaging bags and agricultural films are made of cylindrical film by this method, and then further welded and cut.

6. Composite products

It uses several extruders to supply several kinds of plastics at the same time, and then extrudes them through the common die to form a whole composite product. For example, CO extrusion of a, B and C plastics can produce various composite films, composite sheets, plates, profiles and pipes.

7. Rubber filtration

When manufacturing thin-walled rubber products, in order to prevent air and water leakage, the rubber compound should not contain impurities. Generally, the rubber compound should be filtered by an extruder before adding vulcanizing agent, that is, one or more layers of filter screen should be placed at the head of the extruder to filter the impurities in the plasticized materials.

8. Tire tread and tube manufacturing

The tread is divided into integral extrusion and layered extrusion. One extruder can be used to extrude a rubber compound through a flat die; Two kinds of compound (crown compound and sidewall compound) can also be co extruded by two extruders to form a whole tread in the co extruder head. Two extruders are used to extrude the two kinds of compound into crown and sidewall respectively, and then heat lamination is carried out on the transport belt, and the multi disc flexible roller is used to press them as a whole. Tube extrusion is similar to tube extrusion. After the tube is extruded, it is cut off and then joined to form.

9. Melt spinning

When some resins with high viscosity are melt spun, extruders are often used to melt the materials. The melted material directly enters the spinneret through the filter or is pumped into the spinneret by the spinneret pump.

Stability control system

Features of extrusion die temperature machine:

Pipeline explosion proof device

Air blowing and water return function (optional)

Return water temperature display table

Automatic exhaust function after power on

Heating power switching function

Instant cooling shutdown function

Isolated electrical control box. Extend the service life of electrical appliances