Extrusion, also known as extrusion molding or extrusion in plastic processing, extruders are divided into single-screw extruders and twin-screw extruders according to the number of screws.

Content Introduction

In the chemical fiber industry, extruders are also used to feed the spinneret for melt spinning. In the production of synthetic resins, extruders can be used as reactors to continuously complete polymerization and molding.

Extrusion equipment

The main body is the extruder and auxiliary equipment such as feeding, shaping, cooling, traction, cutting and winding. In rubber processing, it also includes vulcanization equipment. In actual production, the main body and auxiliary equipment are often connected to one unit.

Extruders are divided into single-screw extruders and twin-screw extruders according to the number of screws.

¢ÙSingle-screw extruders are equipped with a rotating screw in a heated barrel, and the outer partition of the barrel is equipped with heating and cooling devices. One end has a radial feeding port, and the other end is axially connected to the head. The screw is the key component of the extruder. The main technical parameters of a single screw extruder are screw diameter, aspect ratio (ratio of screw length to diameter), screw speed range, drive 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 screws of different geometric shapes and aspect ratios. Modern plastic extruders widely use combined screws, distribution and mixing screws, and add barriers or pins to the screws to improve plasticization, production capacity and product quality.

¢Ú The twin-screw extruder has two screws rotating in an ¡Þ-shaped heated barrel. Screws can be divided into meshing and non-meshing types; combined and non-combined types; co-rotating and counter-rotating. Co-meshing and counter-meshing types are more commonly used. The former is used for plastic blending, filling and reinforcement, and the production of various compounding materials; the latter is used for processing rigid polyvinyl chloride products.

The die and the mouth die are the parts of the extruder that make the extrudate form a specified cross-sectional shape. The transition part between the barrel and the mouth die is called the die. If the die and the die are an integral whole, they are generally collectively referred to as the die, which can also be called the die. The die is equipped with a porous plate and a filter screen, which is used to filter the molten material and increase the flow resistance, thereby filtering out mechanical impurities and improving the plasticizing effect. The function of the flow channel shape in the die is: ¢Ù The filtered columnar melt is transformed into a cross-section similar to the product through the die distribution cavity; ¢Ú The gradually reduced flow channel cross-section makes the melt dense; ¢Û The melt enters the die lip at a uniform flow rate, forming a cross-sectional shape suitable for the product. The straight part of the die should be of sufficient length to overcome the "memory effect" of the melt. Commonly used die heads include: die for tube extrusion, die for film blowing, and die for sheet extrusion.

Extrusion process

Generally, according to the type of polymer being processed and the shape of the product or semi-finished product, the extruder, die and die, as well as the corresponding auxiliary devices such as shaping and traction are selected, and then the extrusion process conditions such as screw speed, die pressure, material temperature, shaping temperature, traction speed, etc. are determined. During the extrusion process, the material generally undergoes plasticization, but the shaping method is different. For example, the extruded plastic often needs to be cooled and shaped to solidify, while the semi-finished product of extruded rubber needs further vulcanization. Different extrusion equipment and processes can produce different products.

After the pelletized polymer is mixed with various additives, it is sent to the extruder for melting and further mixed evenly. Through the multi-hole die, multiple strips are formed and then cut into pellets. Cutting can be divided into hot pelletizing and cold pelletizing. In the former, after the strip leaves the die, it is cooled with air or water and cut immediately with a rotating knife. In the latter, the strip is completely cooled and then sent to the pelletizer for pelletizing.

The pipe material passes through the annular gap formed by the die and the core die to form a tubular object, and then through shaping and cooling, a pipe with a smooth surface, accurate size and geometric shape is obtained. The commonly used shaping method is to use outer diameter shaping, that is, the extruded tubular object passes through a shaping sleeve with an inner diameter the same as the outer diameter of the product, and the pressure difference is used to make the tubular object close to the inner wall of the shaping sleeve, so that a pipe with an accurate outer diameter can be obtained. In order to create a pressure difference, compressed air can be introduced into the tube, or negative pressure can be created outside the tube.

Sheets and films are flat products with a thickness of more than 0.25mm and a length much larger than the width. Sheets and films are called sheets; those with a thickness of less than 0.25mm are called films. If the film-like object coming out of the flat die is cooled and shaped through a cooling drum with a very smooth surface, a flat film can be obtained. This method is also called extrusion casting. This is a common method for manufacturing polypropylene film. If the obtained flat film is fed into a tentering machine and stretched 4 to 10 times in the longitudinal and transverse directions at the same time (it can also be stretched longitudinally first and then transversely), a biaxially oriented film can be obtained. Since the macromolecules are oriented during stretching, the film strength is very high, but the water permeability and air permeability are reduced. It is often used to make polypropylene and polyester films. If a foaming agent is added to the material and a special screw and die are used, low-foam plastic sheets can also be made.

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

Most films are made by the inflation method. This method is to blow up the tubular object coming out of the die with compressed air, and the formed film bubble is cooled by the air blown out by the wind ring, and then it is led out through a guide roller (or splint), and then wound into a roll to obtain a blown film. A large number of packaging bags and agricultural films are made into cylindrical films by this method, and then further welded and cut to make them.

Composite products use several extruders to supply several plastics at the same time, and then extrude them through a common die to form an integral composite product. For example, co-extrusion of three plastics A, B, and C can produce various composite films, composite sheets, plates, profiles, and pipes.

Rubber filtration When manufacturing thin-walled rubber products, in order to prevent air leakage and water leakage of the products, the rubber cannot contain impurities. Generally, the rubber is filtered by an extruder before adding the vulcanizer, that is, one or more layers of filter screens are placed at the die to filter out impurities in the plasticized material.

The manufacturing of tire treads and inner tubes is divided into integral extrusion and layered extrusion. In integral extrusion, one rubber compound can be extruded through a flat die by one extruder; two rubber compounds (crown material and sidewall material) can also be co-extruded by two extruders, and combined into an integral tread in the co-extrusion die. Layered extrusion uses two extruders to extrude two types of rubber into the crown and sidewall respectively, and then heat-bonds them on the conveyor belt and presses them into a whole through multi-disc active rollers. Inner tube extrusion is similar to tube extrusion. After the tube is extruded, it is cut and then jointed.

Melt spinning When some resins with high viscosity are melted, extruders are often used to melt the materials. The melted materials directly pass through the filter into the spinneret, or are pumped into the spinneret by a spinneret pump.

Extruder system

Features of extrusion temperature controller:

Pipeline explosion-proof device

Air blowing and water return function (optional)

Water return temperature display

Automatic exhaust function when starting

Heating power switching function

Instant cooling and shutdown function

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

RS485 communication function to achieve automatic management. (optional)

Hot water BY-PASS pressure relief circuit

Multi-point temperature control unit can be customized

Water pump horsepower and heating power can be customized

Electrical appliances adopt OMRON. FUJI. TE. LG. MOELLER. ABB. WEST.

Temperature control range: Inlet water temperature +15¡æ¡ú120¡æ

304 stainless steel integrated pipeline to reduce pipe resistance and rust

Control method: Imported microcomputer or (optional) PLC control

Perfect safety protection, fault display, repair. Maintenance does not require professional personnel