5 minutes to understand the extruder

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.

Comparison table of different plastics processing machines

Plastic processing machineProcessMain parts and componentsDetailsApplication
Blow moulding machineInjection/extrusion blow MouldingInjection/extrusion machines, die heads, clamping tools and air blowing systems.The plastic is extruded/injected to form a tubular shape which is then placed in the mould while it is still hot. The mould should be immediately closed. The compressed air into the mould is used to make the plastic parison cling to the inner wall of the mould.The blow moulding machine is used to produce various types of hollow packaging containers, film, flakes, etc.
Suction molding machineSuction moldingElectric heating furnace, vacuum pump, moldsThe plastic hard sheet is heated to be soft, then vacuum-absorbed onto the mould surface, cooled and setted.The suction molding machine is used to produce basins, plates, bowls, plastic packaging, lamps and lanterns, advertising boards, etc.
Injection molding machine Die castingInjection parts, mould closing parts, machine body, hydraulic system, heating system, control system and filling device.  It is achieved by means of an injection moulding machine and a mould. The heated liquid fills the mould, which then is cooled down to set the shape.The injection molding machine can be used to produce everything you want only if you have the molds. Examples: plastic plates, chess pieces, combs, car parts, etc.
ExtruderExtrusiontransmission , charging unit, barrel, screw, head and outlet (a shaped cut).During the plastic extrusion process, the material is heated and is forced through a shaped cut in a metal plate creating a continuous form that can be stretched and then cooled to set.Plastic bars and wire, industrial piping, synthetic filaments, plastic sheeting, plastic drinking straws,plastic modification and pelletizing.

Wide ranges of the applications of the extruder

The extruder occupies an important position as either a plastic pelletizing machine or a molding processing machine.

Plastic extruders are suitable for the production of thermoplastic materials and thermosetting and reinforced plastics with good flowability. In addition, extruders can be used for color masterbatch compounding, the production of filler masterbatch and PVC compounding.

The screw extruder is not limited to plastic processing. It is also used in the food processing, pharmaceutical and chemical industries.

In the production process, the thermoplastic material is heated to melt. And, the srcew rotates to extrude the molten material out from an outlet of a required shape. Then, the extruded material is seted by a setting machine and cooled down to become firm enough. Going through these steps, the material is made into finished products.

Schematic diagram of mixing effect of extruder
Schematic diagram of mixing effect of extruder

The screw, the key part of an extruder, has 5 sections: the feeding section, the melting section, the mixing section, the air exhaust section and the homogenization section.

Diagram of the screw extruder structure
Diagram of the screw extruder structure

Types of extruders

Over time, extruders have evolved to have many types, such as single screw extruder, twin screw extruder, triple screw extruder, two stage extruder (a combination of two separate extruders and works in tandem), split type twin-screw extruder, micro extruders for laboratory use, etc.

There are many types of twin-screw extruders.

Depending on the direction of screw rotation, twin-screw extruders are divided into parallel twin screw extruders and

Depending on the direction of screw rotation, twin-screw extruders are divided into co rotating twin screw extruder and counter-rotating twin-screw extruder.

Co-rotating twin screw extrusion
Co-rotating twin screw extrusion
Counter-rotating twin screw extrusion
Counter-rotating twin screw extrusion

Depending on the whether the twin screw axis is parallel , twin-screw extruders are divided into parallel twin screw extruders and conical twin screw extruders.

Counter Rotating conical screw
Counter-Rotating Conical Screw Set

Depending on whether the two screws gear into each other or not, twin-screw extruders can be divided into intermeshing screw extruders and non Intermeshing screw extruders.

Co-rotating intermeshing screw set
Co-rotating Intermeshing Screw Set
Counterrotating non-intermeshing screw set
Counterrotating Non-intermeshing Screw Set

According to the feeding method, twin-screw extruders can be divided into extruder with the volumetric feeder and extruders with the loss-in-weight feeder.

volumetric feeder
volumetric feeder
loss-in-weight feeder
loss-in-weight feeder

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