Extrusion molding is also called extrusion molding in plastic processing. It is a processing method that uses hydraulic pressure on the mold itself to extrude. It refers to the action between the barrel and the screw of the extruder, while being heated and plasticized, and being pushed forward by the screw, and continuously passing through the die to form various cross-section products or semi-finished products.
Brief description
Extrusion molding is an efficient, continuous, low-cost, and wide-adaptability molding method. It is an early technology in polymer material processing. After more than 100 years of development, extrusion molding is the molding method with the most varieties, the most changes, high productivity, strong adaptability, wide application, and the largest output in the field of polymer processing. 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 plastic products are completed by extrusion molding. At the same time, it is also widely used in the molding of chemical fibers, thermoplastic elastomers and rubber products. The extrusion molding method can produce continuous products in various forms such as pipes, rods, sheets, profiles, wire and cable sheaths, monofilaments, etc. It can also be used for mixing, plasticizing, granulating, coloring and blending and modification of polymer materials. In addition, based on extrusion molding, extrusion-blow molding technology and extrusion-stretching molding technology combined with blowing, stretching and other methods are important methods for manufacturing films and hollow products.
Extrusion molding, also known as extrusion molding or extrusion molding, mainly refers to a molding method that uses the extrusion effect of a screw or plunger to force the hot molten polymer material through the die head under pressure to form a continuous profile with a constant cross-section. The extrusion molding process mainly includes the processes of feeding, melt plasticization, extrusion molding, shaping and cooling.
The extrusion process can be divided into two stages: the first stage is to plasticize the solid plastic (that is, turn it into a viscous fluid) and pass it through a specially shaped die under pressure to become a continuum with a cross-section similar to the shape of the die; the second stage is to use appropriate methods to make the extruded continuum lose its plastic state and turn it into a solid to obtain the desired product.
According to the different ways of plasticizing plastics, the extrusion process can be divided into dry and wet processes. Dry plasticizing relies on heating to turn the plastic into a melt. Plasticizing and pressurizing can be carried out in the same equipment, and the shaping process is only a simple cooling. Wet plasticizing uses solvents to fully soften the plastic. Therefore, plasticizing and pressurizing must be divided into two independent processes. In addition, the shaping process must use more troublesome solvent removal, and solvent recovery must also be considered. Although wet extrusion has advantages in uniform plasticizing and avoiding excessive heating of plastics, due to the above-mentioned disadvantages, its scope of application is limited to the extrusion of The process can be divided into two types: dry and wet. Dry plasticization is to turn plastic into melt by heating. Plasticization and pressurization can be carried out in the same equipment, and the shaping process is only a simple cooling. Wet plasticization is to soften the plastic fully with solvent. Therefore, plasticization and pressurization must be divided into two independent processes. Moreover, the shaping process must use the more troublesome solvent removal, and the solvent recovery must also be considered. Although wet extrusion has advantages in uniform plasticization and avoiding excessive heating of plastic, due to the above disadvantages, its scope of application is limited tocellulose nitrate and a few cellulose acetate plastics.
Extrusion Equipments
1. Host
Extrusion system: It consists of a screw and a barrel and is the key part of the extruder. Its function is to plasticize the material and extrude the melt at a fixed quantity, pressure and temperature.
Transmission system: drives the screw to provide the required torque and torque
Heating and cooling system: ensure that the temperature of plastic and extrusion system reaches the process requirements during the molding process
2. Auxiliary machine
It consists of a machine head, a shaping device, a cooling device, a traction device, a winding device, and a cutting device.
3. Control system
It is composed of electrical appliances, instruments and actuators.
Function: Control the main and auxiliary motors 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; realize the automatic control of the extruder unit to ensure the coordinated operation of the main and auxiliary machines.
Related parameters
1. Temperature
Extrusion molding 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 both radial and axial directions, thus affecting the quality of the product. The strength of each point of the product is different, residual stress is generated, and the surface is dull and matte. To ensure the quality of the product, the temperature should be stable.
2. Pressure
Due to the structure of the screw and barrel, the resistance of the machine head, filter screen and filter plate, there is pressure inside the plastic.
3. Extrusion rate
The mass or length of plastic extruded from the extruder die per unit time. Factors affecting the extrusion rate: die resistance, screw and barrel structure, screw speed, heating, cooling system, plastic properties. However, when the product is fixed, the extrusion rate is only related to the screw speed. The extrusion rate also fluctuates, affecting the geometric shape and size of the product.
Temperature, pressure and extrusion rate all fluctuate. In order to ensure product quality, the screw should be properly designed, the heating and cooling system and the screw speed stability should be well controlled to reduce parameter fluctuations.
Features
Compared with other polymer molding methods, extrusion molding has many outstanding advantages.
- Continuous production can produce pipes, plates, rods, profiles, films, cables and monofilaments of any length as needed.
- High production efficiency: The single-unit output of the extruder is relatively high. For example, an extruder with a diameter of 65 mm can produce polyvinyl chloride film with an annual output of more than 450 tons.
- Wide range of applications This processing method is widely used in the processing of rubber, plastics, and fibers, especially plastic products. Almost all thermoplastics and some thermosetting plastics can be processed by this method. In addition to directly molding products, extrusion can also be used for mixing, plasticizing, granulation, coloring, and blank molding. For example, when an extruder is combined with a calender, it can produce calendered films; when combined with a press, it can produce various pressed parts; when combined with a blow molding machine, it can produce hollow products. In the production process of rubber products, the extrusion method is used to manufacture tire treads, inner tubes, hoses, and various products with complex cross-sectional shapes, as well as semi-finished products such as hollow, solid, and rubber-coated products. It can also be used for continuous mixing, plasticizing, and granulation of filter rubber and raw rubber. In petrochemical plants, during the production of resins, an extruder can be used to squeeze out the moisture in the resin, and an extruder can be used to complete the mixing of additives and modifiers in various grades of resins, and complete the resin granulation process.
- One extruder can process a variety of materials and products. Different products can be produced by replacing different screws and die heads according to the material performance characteristics and the shape and size of the product.
- Simple equipment and low investment. Compared with injection molding and calendering, extrusion equipment is relatively simple, easier to manufacture, lower in equipment cost, and more convenient to install and debug. The equipment occupies a small area and has relatively simple requirements for plant and supporting facilities.
The above advantages determine the important position of extrusion molding in polymer processing. The production of plastic products that are completely used or contain extrusion process in the process accounts for about half of the total amount of thermoplastic plastic products. Products molded by this method are used in agriculture, construction, petrochemical, machinery manufacturing, medical equipment, automobile, electronics, aerospace and other industrial sectors.
Applications
Extrusion molding technology is a versatile manufacturing process used in various industries to create products with a consistent cross-section. Here are some common applications of extrusion molding technology:
Plastic Extrusion:
- Pipes and Tubing: Extrusion is widely used to manufacture plastic pipes and tubing for applications in plumbing, irrigation, and construction.
- Profiles: Extrusion is used to create plastic profiles such as window frames, seals, and trim.
- Sheeting and Film: Extrusion is employed to produce plastic sheets and films used in packaging, agriculture, and construction.
Aluminum Extrusion:
- Construction: Aluminum extrusion is used to create structural components for buildings, such as window frames, curtain walls, and door frames.
- Transportation: Aluminum extrusions are utilized in the automotive and aerospace industries for components like structural frames and interior trims.
- Consumer Goods: Aluminum extrusion is used in the production of consumer goods like furniture, shelving, and appliances.
Rubber Extrusion:
- Seals and Gaskets: Rubber extrusion is commonly used to manufacture seals, gaskets, and weather-stripping for automotive, construction, and industrial applications.
- Tubing and Hoses: Rubber extrusion is employed in creating rubber tubing and hoses used in fluid transfer applications.
- Profiles: Rubber extrusion is utilized to produce custom profiles for various applications, including window seals and automotive components.
Food Extrusion:
- Snack Foods: Food extrusion technology is used to produce a variety of snack foods like puffed snacks, breakfast cereals, and extruded bars.
- Pasta: Extrusion molding is employed in the production of pasta shapes like spaghetti, macaroni, and penne.
- Pet Food: Extrusion is used to manufacture pet foods in various shapes and formulations.
Composite Extrusion:
- Fiber-Reinforced Composites: Extrusion technology is utilized to manufacture fiber-reinforced composite profiles and structures for applications in aerospace, automotive, and construction.
- Wood-Plastic Composites: Extrusion is used to create wood-plastic composite products like decking, railing, and fencing.
- Thermoplastic Composites: Extrusion molding is employed to produce thermoplastic composite parts with customized properties for specific applications.
Medical Extrusion:
- Catheters and Tubing: Extrusion is used to manufacture medical tubing and catheters for various medical procedures.
- Medical Profiles: Extrusion technology is employed in creating custom profiles used in medical devices and equipment.
These are just a few examples of how extrusion molding technology is applied across different industries to create a wide range of products efficiently and cost-effectively.
Development Trend
In recent years, with the emergence and development of modern extruder technology, extrusion molding theory and technology have been continuously deepened and expanded, the means of researching and developing new products and new processes have been continuously strengthened, and extrusion equipment with various structures and functions has been continuously produced, such as multi- screw extruders, reaction extruders and combination extruders. The types of materials that can be extruded, the structure of products and the form of products are also increasing. At the same time, with the increasing application of computer technology in extrusion molding, new extrusion molding technologies such as reaction extrusion, auxiliary extrusion, extrusion foaming, co-extrusion, high-speed extrusion, precision extrusion and near-melting point extrusion have emerged.
