All That You Must Know About Single Screw Extruder

A single screw extruder will generally be used for melting continuously and then it will be compressed, extruded, and solid material will be formed within a heated barrel. 

The single screw extruder actually has been developed from the basic spiral structure, e.g., damping screw block, slotted screw barrel, exhaust screw, building block structure, pin barrel, and many other different types of structures.

Since the single screw extruder will generally occupy a small space, it has turned into the main equipment that is used in the area of compound processing as well as plastic blown film.

Extrusion is a kind of process that is used to create a product by forcing a certain material through an orifice or die to form a certain shape. Alternatively, an extruder will be used for producing semi-finished/finished products.

Structure

Basically, a single screw extruder consists of a screw, drive mechanism, barrel, resin feed arrangement, and various controls. Through a heated barrel, a constantly turning screw will move the resin where it will be heated to a suitable temperature and then blended into a certain homogeneous melt. 

Turbulent back pressure will be build-up which is going to push the melt out of this extruder in the form of the die. Sometimes the resin may not be completely melted in your basic extrusion screw. There will be a barrier screw designed for countering this problem. Often, additional flights are also attached to its transition section to separate both molten and solid plastic to certain different channels. 

As this solid pellet will move forward it will melt because of shear against the wall. Thus, it will melt and flow into the liquid channel. In this way, the solid channel will gradually narrow and the liquid channel will widen.

Over the years, the design of extrusion screws has been improving, with various new ideas and innovations. Nowadays, single screws will be available that have got secondary flights that can improve speed by allowing faster melting. 

Single screw extruders are available with many different types of accessories such as

1. Automatic gravimetric feeders
2. Heat and pressure controllers
3. Heat exchangers
4. Melt pumps
5. Microprocessor control systems
6. Static and dynamic mixers
7. Vent vacuum units

Also, they are available with a wide range of geometrics of screws for different products and materials.

Principle

• The conveying section from where the last thread of your material opening will start.

Here the material is not needed to be plasticized, rather it should be preheated and compacted. Earlier, on the old theory of extrusion, it was believed that all the material here was loose. However, later, it was finally proved that the material is actually a solid plug, and this means the material will be solid like any plug after being squeezed, hence its function will be to complete the total delivery task.

• The second section will be the compression section

The volume of the screw groove, at this time will gradually become smaller, and the temperature should reach the degree of material plasticization. The compression that is produced here will be from the third conveying section.

Here the compression will be one that is called the screw compression ratio of 3:1. Also, there are a few changes for other machines. Then the plasticized material will enter the third stage.

• The third section is going to be the measurement section

Here the material will be maintained at the plasticizing temperature, almost like any metering pump for accurately and quantitatively transporting the melt material for supplying the machine head. During this time, all the temperatures cannot be lesser than the temperature needed for plasticizing, generally slightly higher.

Mainly these single screw extruder machines are used for extruding hard and soft polyethylene, polyvinyl chloride, and other thermoplastic plastics. Also, it can process many different plastic products, like tubes, films, and plates, in combination with the corresponding auxiliary and it also can process the granulation.

How It Works

Single screw extrusion generally uses one screw that is within a certain cylindrical barrel for continuously pushing plastic through a certain constant profile die. Typically, the production rate is measured in mass/hour that is controlled by the machine’s screw speed.

Advantage And Disadvantage

The advantages of these single screw extruders are that they have an advanced design, good plasticization, high quality, low energy consumption, low noise, large bearing capacity, stable operation, and long life.

The single screw extruder can adopt a 2-stage overall design for strengthening the plasticization function for ensuring high-speed, stable extrusion, and high performance.

The special barrier complete mixing design will ensure the material mixing effect and the high shear, as well as low melting temperature will be guaranteed.

In addition, to that, a single screw plastic extruder will be quite cheap in design and offer high-performance and low-temperature low-pressure metering material extrusion so the single-screw extruder is very widely used.

There are many single screw extruder manufacturers available in China who can offer you this kind of extrusion machine.

The disadvantages are:

As the transmission of any plastic materials in a single screw plastic extruder will be through friction, hence there is a certain limitation when we consider the feeding performance.

A few materials like powder or paste possess difficulties during mixing. This will make using the machine unsuitable in some processes.

Applications

The following are a few applications of single screw extrusion machine to manufacture the following products:

1. Feedstock for Other Plastics Processes: Widely used as mixers or compounders. The output from any extruder compounder will be chopped or granulated for forming the feed for any other process like injection moulding or extrusion.
2. Filaments: Used for twine, brushes, ropes, etc.
3. Nets: Used for packaging, soil stabilization, etc.
4. Plastic Coated Paper and Metal: Generally used for packaging.
5. Plastic Film: Generally, this is used for packaging and sealed into bags.
6. Plastic Insulated Wire: In the industry as well as home it is used for appliances, electric power distribution, and communications, etc.
7. Plastic Pipe: Used for gas, water, drains etc.
8. Plastic Tubing: Used for automobiles, tubing and also hose for laboratories, etc.
9. Profile: Used for gaskets, home siding, doors, windows, tracks, etc.
10. Sheet: Used for signs, lighting, glazing, etc.