A screw extruder is a type of pump used in a plastic injection machine to pump
molten plastic. Screw extruder is among the common machinery used in improved plastics and polymer plants. There are mainly two types of extruders: single screw extruders and twin screw extruders. These extruders work differently, and they both have their own strengths and weaknesses.
Different Types of Screw Extruders
Single Screw Extruder
A single screw extruder is a plastic injection pump that uses a screw that rotates inside a heated barrel. It’s one of the widely used technological advancements in plastic extrusion. Its structure is simple to manufacture, has high processing efficiency and is cost-effective.
A single screw extruder works by using three sections; the extrusion system, the heating and cooling system and the transmission system. What describes an extruder is its diameter, length, pitch and depth.
Advantages of Single Screw Extruders
- Single screw extruders use many different types of materials in their operations.
- Have high throughput
- They are affordable hence even small business people can afford them as well as homeowners.
- It’s good for plasticizing polymer pellets for extrusion.
Disadvantages of Single Screw Extrusion
Some of the cons of the single screw extruders are;
- The sheer force of a single screw extruder is smaller than that of a twin-screw extruder.
- Feeding performance is not good since the materials are transported through plastic materials.
- They are not suitable for all processes since materials like pastes or powders are hard to mix. It doesn’t have a self-cleaning feature.
Twin Screw Extruder
A twin screw extruder has a transmission device that uses two screws. Twin extruders can be subdivided into meshing types and non-meshing types.
Advantages of Twin Screw Extruder
- You can handle multiple processing functions in this extruder since the output depends on the speed of the screw.
- It helps create products of good quality since there is better heat transfer and more controlled temperature.
- The twin-screw extruder has a self-cleaning feature. This feature helps in ensuring there is reduced material deterioration and degradation.
- The twin-screw extruder can be used with several materials and compression, which gives better results.
Disadvantages of Twin Screw Extruder
Even though twin screw extruders have many benefits for users, they also have some drawbacks.
- It has high operating costs. If you are using this type of extruder, you should expect to pay more than single screw extruders since frequent maintenance is very costly.
- The operations are more complicated than those of single screw extruders. Understanding how a twin screw extruder works can be hard.
Lab extruders are suitable for the production of small batches of material. This type of extruder is relatively small in size and can be used to meet the needs of any laboratory space or facility layout.
This machine is available in a broad range of part shapes and sizes, including spiral, barrel, screw and die configurations. Laboratory extruders are customizable to meet specific needs and for different applications.
Applications of Extruders
Twin-screw extruders can be classified into counter-rotating twin-screw extruders and co-rotating twin-screw extruders based on the different rotational directions of the two screws.
Co-rotating twin-screw extruders can be used for the physical and chemical modification of matrix resins. Co-Rotating twin-screw extruders are used for mixing, dispersing and blending all kinds of raw materials. The counter-rotating twin screws oppose each other at their shear points, resulting in a much greater mixing effect.
Powdered calcium carbonate, talc and titanium dioxide are often used for mixing and filling plastics. Fillers can typically make up 30% to 60% of the batch. Powdered fillers contain a large amount of air, but the air is dispersed into the kneading zone of the screw during the mixing process. When the material flows into the screw groove, the air flows in the opposite direction, interfering with the positive delivery of the powder and ultimately reducing the extrusion volume.
When buying extruders, you must consider the purpose you are buying them for and then look for an extruder that will help you achieve the desired results. A twin screw extruder has wide use, and’s more efficient than a single screw extruder and hence stands out as the best extruder to buy. However, you must consider factors such as cost and the purpose of the extruder before making your choice.