What is the Extruder?
Before talking about the extruder, you first need to know what plastics processing is.
Plastic processing occupies a very important position in the world today as plastic has the advantages of low cost and high plasticity compared to metal, stone and wood. Continuous advancement has been made in plastic processing as some properties of plastic, for example, combustibility, affect the processing result. The processing result matters a lot due to high requirements for the look and the performance of today’s widely-used plastic products. With the development of plastics processing, many plastics machines have come out, such as extruders, injection molding machines and blow molding machines. They each have different advantages in the plastics processing segment.
The extruder is a type of plastic processing machine.
The extruder is the most essential part of the plastic extrusion line, which consists of the extruder, the mold, and other auxiliary machines. The extruder is used to extrude molten plastic through a fixed shape extrusion outlet by the action of a screw. Then, the extruded plastic will be cut after being setted and water-cooled down. The plastic extruder is an efficient, economical, and practical choice for producing plastic products.
Types of Extruders
According to the number of screws, extruders can be roughly divided into single-screw extruders, twin-screw extruders, and three-screw extruders.
The twin-screw extruder machines can also be subdivided into coaxial twin screw, conical twin-screw, co-rotating twin-screw, and parallel twin screw.
Types of screw extruder machines
According to the design improvement on the details of the extruder and the combination of different extrusions, the types of extruders are split twin-screw extruder, two-stage extruder, vented extruder, reciprocating single-screw pin-barrel extruder, planetary roller extruder, etc.
- Intermeshing and non-intermeshing twin screw
- Corotating and counter-rotating twin screw
- The parallel twin screw and the conical twin screw
- Intermeshing corotating twin-screw extruders
- Intermeshing counterrotating extruders
- Non-intermeshing counterrotating twin screw extruder
- Conical twin-screw extruder
Get to know the Triple Screw Extruder
- High shearing efficiency and good plasticizing effect
- Close training function and good dispersion effect
- High output and low energy consumption
- Good exhaust performance
- The residence time of materials in the barrel can be greatly shortened
How does a twin screw extruder work?
Twin-screw extruders are commonly used to melt and pump a polymer through a die which is designed with a required shape. The materials in a twin-screw extruder are mixed with resin and additives like color concentrate and then are transformed into smooth fusant after being subjected to heating, pressing and shearing.
Twin-screw extruder main parts include the conveying unit, the feeding unit, the barrel and the screw. Each part plays a role similar to that of the single-screw extruder. As the name indicated, the twin-screw extruder has two screws while the single-screw extruder only has one.
The twin screw extruder consists of 5 systems： extrusion system, transmission structure, feeding system, heating and cooling structure and control system.
Theoretically, the material flow process can be divided into four sections:
- feeding of the extruder
- transport of mass
- flow through the die
- exit from the die and subsequent downstream processing
During material processing, the mass is transformed mainly by the sheer force, pressure, cooling rate, shaping, and residence time.
The Applications of Screw Extruder
The extruder can be combined with various plastic forming auxiliary machines, such as pipes, films, support materials, monofilaments, flat wires, winding tapes, extrusion nets, plates, profiles, granulation, cable coating, etc., to form various plastic extrusion and forming lines to produce various plastic products.
Extruder machine used in producing PET / PLA sheets, no need pre-drying crystallization of the energy consumption and adapt to the material for the production of the second, high yield, low energy consumption, high-quality plastics characteristics.
PLA sheet production line usually adopts a single screw extruder, which generally needs to be equipped with a drying system, or vacuum exhaust twin-screw extruder can be used for direct extrusion molding.
See also： PLA Degradable Sheet Production Line