What Is the Extrusion Process?

Extrusion molding is also called extrusion in plastic processing. In non-rubber extruder processing, the hydraulic press is used to press the extrusion of the mold itself. It refers to a processing method in which materials pass through the action between the barrel of the extruder and the screw, are plasticized under heat, are pushed forward by the screw, and are continuously passed through the head to make various cross-section products or semi-products.

Extrusion molding is an efficient, continuous, low-cost, and wide-ranging molding processing method. It is an earlier technology in polymer material processing. After more than 100 years of development, extrusion molding is a field of polymer processing. A molding processing method that produces the most varieties, the most changes, high productivity, strong adaptability, wide use, and the largest proportion of output. Extrusion molding is one of the most important forms of plastic material processing. It is suitable for most plastic materials except some thermosetting plastics. About 50% of thermoplastic products are completed by extrusion molding. Molding of chemical fibers and thermoplastic elastomers and rubber products; extrusion molding method can produce

1.Host

Extrusion system: Composed of screw and barrel, it is a key part of the extruder. Its role is to plasticize the material, and extrude the melt at a constant volume, constant pressure and temperature.

Transmission system: drive screw to provide required torque and torque

Heating and cooling system: ensure that the temperature of the plastic and extrusion system reaches the process requirements during the molding process

2.Auxiliary machine

Composed of machine head, setting device, cooling device, traction device, winding device, cutting

3.Control system

Consists of appliances, meters and actuators

Role: Control the motors of the main and auxiliary machines to meet the required speed and power; control the temperature, pressure and flow of the main and auxiliary machines to ensure the quality of the products; implement automatic control of the extrusion unit to ensure the coordinated operation of the main and auxiliary machines

1.Temperature

Extrusion temperature includes barrel temperature, plastic temperature and screw temperature. Generally, we measure barrel temperature. The temperature is controlled by the heating and cooling system. Due to the screw structure, unstable heating and cooling system, and changes in screw speed, the temperature of the extruded material fluctuates in the radial and axial directions, which affects the product quality. Residual stress, the surface is dull and dull. To ensure product quality, the temperature should be stable.

2.Stress

Due to the structure of the screw and the barrel, the resistance of the machine head, the filter screen and the filter plate causes pressure inside the plastic. The pressure changes are shown in the figure, and the pressure also fluctuates.

3.Extrusion rate

Mass or length of plastic extruded from the extruder die per unit time. Factors affecting extrusion rate: head resistance, screw and barrel structure, screw speed, heating, cooling system, plastic characteristics. But when the product has been determined, the extrusion rate is only related to the screw speed. Extrusion rates also fluctuate, affecting product geometry and size.

There are fluctuations in temperature, pressure, and extrusion rate. In order to ensure the quality of the product, the screw should be properly designed, the heating and cooling system and the rotation speed stability of the screw should be controlled to reduce the parameter fluctuation.

Compared with other polymer molding methods, extrusion has many outstanding advantages.

(1) Production continuity can produce pipes, plates, rods, profiles, films, cables and monofilaments of any length according to needs.

(2) High production efficiency The single machine output of the extruder is relatively high. For example, an extruder with a diameter of 65mm can produce PVC films with an annual output of more than 450t.

(3) Wide application This processing method is widely used in the processing of rubber, plastics and fibers, especially plastic products. Almost most thermoplastics and some thermosetting plastics can be processed by this method. In addition to direct molding products. Extrusion can also be used for mixing, plasticizing, pelletizing, coloring, and blank forming. If the extruder is combined with a calender, it can produce a rolled film; in conjunction with a press, it can produce various press-formed parts; and blow molding Machines can produce hollow products. In the production process of rubber products, the extrusion method is used to manufacture treads, inner tubes, hoses and various complex cross-sectional shapes and hollow, solid, rubber-covered semi-finished products. It can also be used for continuous mixing of filter rubber and raw rubber, Plasticizing and granulating applications. In the petrochemical plant, during the resin production process, the extruder can be used to remove the moisture in the resin, and the extruder can be used to complete the mixing of additives and modifiers in various resin grades to complete the resin pelletization process.

(4) One machine and one extruder can process multiple materials and multiple products. As long as different screws and heads are replaced according to the material performance characteristics and the shape and size of the product, different products can be produced.

(5) Simple equipment and less investment Compared with injection molding and calendering, extrusion equipment is simpler, easier to manufacture, lower equipment cost, and easier to install and debug. The equipment covers a small area, and the requirements for the plant and supporting facilities are relatively simple.

The above advantages determine the important position of extrusion in polymer processing. The production of plastic products that are fully used or contain an extrusion process in the process accounts for about half of the total thermoplastic products. Products formed by this method have applications in industrial sectors such as agriculture, construction, petrochemicals, machinery manufacturing, medical equipment, automobiles, electronics, aerospace and other industries.

In recent years, with the emergence and development of modern extruder technology, the theory and technology of extrusion molding have been continuously deepened and expanded, the means of research and development of new products and new processes have been continuously strengthened, and various structures and functions of extrusion equipment have been continuously produced. , Such as multi-screw extruders, reactive extruders and combined extruders, etc .; there are more and more types of materials that can be extruded, product structures and product forms; at the same time, with computer technology, IU is extruded. Applications in processing are becoming increasingly widespread, and new extrusion molding technologies such as reactive extrusion, auxiliary extrusion, extrusion foaming, coextrusion, high-speed extrusion, precision extrusion, and near-melting point extrusion have appeared. ^[1]