Role of Plastic Extruders in Different Extrusion Techniques

What is a Plastic Extruder?
Plastic extrusion refers to the conversion of a thermoplastic polymer to a certain shape and/product. Pipes and sheets are the common products of extrusion. The part of the machine that melts solid polymer fed into it before the melt is taken to form a product is known as a plastic extruder. The plastic extruder is only part of the plastic extrusion machinery and has other roles apart from forming a plastic melt. It can mix the plastic polymer with one or more additives, including mineral fillers and colors, for example. In other cases, reinforcing fibers can be added into the mixture. The extruder ensures that these and/or other additives and ingredients are evenly distributed in the mixture.

A plastic extruder must supply the die with a melt of consistent temperature and pressure as it moves to the die for shaping. In plastic extrusions machinery, plastic extruders are of various sizes, described by barrel or screw diameter.

Different Types of Plastic Extruders and their role in various extrusions methods

In extrusion of plastic, extruders can either be single-screw or twin-screw/multiple screw. A screw rotates to transport and compress the polymer from feeder base into the extruder for melting, and then to the adapter and die. It has the mixing, compounding and metering sections. In single-screw plastic extrusion machinery, only one screw is used while two/many are used in twin-screw plastic extrusion machinery. The single-screw type is useful in production of films, sheets and other products from pre-compounded pellets. In multiple-screw type of plastic extrusion machinery, the screws that are arranged together could be rotating in the same (co-rotating) or different (counter rotating) directions.

In co-extrusion, molten polymer emanating from multiple extruders is combined such that the product has more than one layer of the extrudate. In most cases, co-extrusion is helpful in surrounding recycled resin with virgin resin. A profile die receives the extrudate from twin or single-screw extruders in profile extrusion machinery. Profile extrusion machinery can produce flat, flexible, rigid, HIPS and Vinyl siding profiles.

Offset extrusion works mostly with profiles and the person works with planes. Offset extrusion refers to creation of special profiles using a extrusion software where a second plane is created off the main plane, the two differing in measurements. Cold extrusion is where the temperature kept low during extrusion process. They can be parallel or conical. Ram extruders in ram extrusions machinery are used to manufacture continuous profiles from high molecular weight polymers using pressure. Ram extruders in ram extrusions machinery uses pressure-sintering technique like in sintered metal production because of high melt viscosity possessed by the polymers being extruded.


The demand of extruder & plastic extrusion machinery in Local & Global Market

Most plastic products are cheaper than metal products. This alone has made the local and global demand for plastics continue to increase, with global demand set to increase at 6.2% annually through to 2017. This has forced more manufacturers into the business, hence the demand for extruders and plastic extrusion machinery is high. The global demand for plastic processing machinery will increase by 6.0 percent annually to 2015, with Extrusion equipment recording the largest gains, according to projections. Besides, plastic products are more common because they are lighter, easier to handle and use, as well as easier to recycle compared to metals.


Conclusion

There are different types of extruders used in melting polymers and mixing them with various ingredients before the melt is taken for shaping in the die. These include the single-screw and multiple-screw. In addition, various methods of extrusion employ various techniques in manufacturing plastics, including co-extrusion, offset extrusion, overcoat extrusion, cold extrusion and ram extrusion. The global and local demand for plastic extrusion machinery is increasing because of increasing demand for plastic products.