Extrusion and coextrusion process

Extrusion process Extrusion is one of the most common processes for producing polymer products.

This process is used to produce products that are produced uniformly and continuously (such as pipes and profiles). In general, the goal of this process is to produce a product of appropriate quality and in accordance with the taste and demand of the customer.

To achieve these goals, 5 points must be considered in the quality of the product, which are:

Appropriate polymer melting temperature
Uniform melt temperature
Constant correct melt pressure in the die
Uniform melt pressure
Constant product in the die with a homogeneous melt to optimize a process

A superficial understanding of the extrusion process, such as how it works, is not enough. Therefore, it is necessary to examine and analyze the behavior of polymer materials in different areas of the extruder. Also, to effectively eliminate defects in the production line, extrusion equipment and how they behave with polymer materials and ultimately the properties created in the product must be understood. Here, a process with an extruder is examined. The following figure (Figure 1) shows the key points of a single screw extruder. These points consist of 5 main parts:

Drive system
Feeding system
Screw system, barrel and heaters
Head and die area
Control system

Drive system: This system includes the motor, gear box, thrust bearing, bull gear and the screw feed section.

Feeding system: Includes the hopper, feed throat and screw feed section.

The screw, barrel and heaters system is where the solid resin is moved forward, melted and pumped towards the die. The extruded material is transferred and takes on the desired shape by the die and adapter.

Control system: It controls the electrical inputs to the extruder and records its electrical feedback. This control system controls all the extrusion processes in addition to controlling all the control inputs. Co-Extrusion Co-extrusion is the simultaneous extrusion of multiple layers of material.

This type of extrusion uses two or more extruders to melt the materials and deliver a fixed volume of different melts of different viscosities to a die, which extrudes the resin into the desired shape and product. This process can be used in a variety of extrusion processes (blown film, profile or sheet). The thickness of the layers is controlled by adjusting the speed and relative sizes of the amounts of each material in each extruder. There are many reasons why manufacturers use co-extrusion instead of a single-layer process.

For example, in the vinyl fence industry, co-extrusion is used to adjust the layers. Usually, a layer of expensive materials that are resistant to corrosion is extruded on the outer surface of the fence, while the materials inside have additives that are more effective against impact and structural performance of the part.

Extrusion process, the heart of polymer processes

Extrusion process?

It is a process during which plastic materials in the form of granules, powder, flakes, etc. are continuously shaped and the final product is produced in the form of tubes, solid rods, sheets, wire coatings, various types of films, etc.

The word continuous is considered a very important and inseparable feature of this process.

All of the above products can be molded and produced in short lengths by other methods.

The extrusion process finds its special application when the manufacture of long-length parts is considered. Such as hoses, water pipes, etc., which are cut into the dimensions desired by the consumer after production.

What is the function of the extruder?

The extrusion process is used to mix and blend two or more components of the formulation. This method can also be used to mix milled and fresh waste materials. The polymer obtained is converted into granules of the required dimensions by a granulator and then shaped by the usual methods of injection, extrusion, blowing, etc. The capacity of extruders is expressed in terms of the amount of material they extrude per hour. For example, one hundred kilograms per hour, the efficiency can be used to determine whether the device is large or small.

What is the most important part of an extruder?

The most important part of an extruder is its screw. Most of the active extruders in the world have one screw, some have two screws, and sometimes four. One of the important features of multi-screw extruders is their good ability to mix and blend materials. In addition, the extrusion efficiency of a twin-screw machine is three times that of a single-screw machine. The high price of these devices is a factor that has not been replaced as it should be due to their rapid expansion in production centers.

What parts does an extruder consist of?

Single screw extruders have 7 important parts:

Feed hopper: which is the location of the feed or polymer mixture (hopper).
Barrel: The screw is located in the center and in its length direction, and the heating and cooling elements are installed near the inner surface to provide the heat needed to melt the materials.
Screw: It is responsible for moving and heating the granules. Moving and compacting them while in contact with the hot surface of the barrel, it melts the materials and then passes the polymer melt through the die.59- Extrusion process, the heart of polymer processes
Motor and gearbox: To rotate the screw at the optimal speed in order to achieve maximum production.
Circular mesh screen: It is used to filter the molten fluid and create back pressure.
Die: Determines the final shape of the product. In fact, it plays the role of a mold in the extrusion process.
Thermocouples: