How Plastic Extrusion Works

Plastic items are becoming more and more popular due to their simplicity of manufacture, durability, and diversity. Similar to plastic injection molding, plastic extrusion is one of the most popular methods for producing large quantities of parts; it works especially well for producing continuous profiles like pipes and tubes.

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Plastic extrusion has a long history of industrial use that goes back more than a century. This method has consistently improved over time, securing its place as the method of choice for the production of plastics. Plastic extrusion is still a popular method for many tasks today due to its ease of use, effectiveness, and capacity for exact and precise outputs.

An overview of the plastic extrusion process, including its benefits and drawbacks, kinds, and typical uses in various sectors, is given in this article. Fictiv is prepared to assist you if you want CNC machining for plastic extrusions or if you would prefer injection molding services. To get started, make an account and upload your part drawing.

What is Extrusion of Plastic?

A manufacturing process called plastic extrusion, sometimes known as plasticating extrusion, is used to create huge volumes of continuous goods with a consistent cross-section. A thermoplastic material, such as powder, pellets, or granules, is taken and evenly melted. The molten plastic is then forced through a die under pressure.

This pressure is produced during screw extrusion when a screw rotates against a barrel’s walls. Melted plastic emerges from the extruder with the shape of the die’s apertures as it passes through. After that, the resultant material, called extrudate, is cooled until it takes on its final shape, frequently using cooling rollers or water baths.

Pipes, tubes, sheets, films, profiles, and other bespoke forms can be made using plastic extrusion. The apparatus in use is known as an extruder, and it is a component of a bigger system that facilitates the high-volume manufacture of plastic parts.

Parts for Plastic Extruders

The hopper, feed throat, breaker plate, barrel, feed pipe/adapter, die, and cooling system are the main parts of a plastic extruder (see below). Together, these elements enable the plastic material to melt, shape, and solidify more effectively.

Components for Plastic Extruders (Photo courtesy of Wayken Rapid Manufacturing)

The following are the roles played by the various parts of a plastic extruder:

Hopper: The initial part of the extruder, used to store and get ready for processing plastic grains.

Feed Throat: This mechanism moves plastic from the barrel into the hopper.

Breaker Plate: Preserves the pressure inside the barrel while serving as a filter.

Barrel: Melts and warms the plastic as a revolving screw moves the molten substance in the direction of the feed pipe.

The molten plastic is conveyed toward the die via the feed pipe/adapter.

Die: A metal instrument used to control the extruded profile’s form.

Cooling System: Quickly cools and solidifies the profile that has been extruded.

The Extrusion Process for Plastic

The thermoplastic raw material is supplied into the extruder via a top-mounted hopper during the plastic extrusion process. Before entering the hopper, the material—which might take the form of tiny beads or resin—can be combined with additives like colorants and UV inhibitors.

An overview of the full plastic extrusion process is given in the phases that follow.

Material Feeding: The feed throat, which is situated close to the barrel’s back, allows raw material to enter the extruder. Next, a revolving screw inside the barrel makes contact with the molten thermoplastic.

Melting and Heating: The plastic beads are forced forward in the barrel by the screw, which turns at a regulated speed of up to 120 rpm. The temperature at which the barrel must melt varies from 200 to 275°C, contingent upon the kind of polymer being extruded. The barrel usually features many PID-controlled heating zones that raise the temperature progressively from the back to the front.

Melt Formation: The plastic beads slowly melt as they are pushed into the hot barrel. Temperature controls stop polymer breakdown and overheating. Melting is further aided by pressure and friction inside the barrel. In some situations, the heaters can be switched off if the extrusion speed is high enough to maintain the melt temperature only by friction and pressure. The use of cast-in heater jackets or cooling fans helps control temperature and avoid overheating.

Filtration: To get rid of impurities, molten plastic exits the screw and goes through a screen pack. Because pressures can reach more than 34 Mpa, a breaker plate strengthens the screens. In order to provide enough mixing and consistent melting of the polymer, the screen pack and breaker plate assembly also generate back pressure inside the barrel.

Shaping: The molten plastic undergoes a precise shape-giving process in the die once it has passed through the breaker plate. The die makes sure that the molten plastic flows consistently, shaping it into the appropriate shape for the finished product instead of just a regular cylinder.

Cooling: Depending on the method of extrusion, the product is cooled by being pulled through a water bath or by employing cooling rollers. Because plastics don’t transfer heat well, regulated cooling is crucial. To keep pipes and tubes from collapsing, a vacuum is created in the water bath. A series of cooling rolls is used to chill plastic sheeting.

Plastic Extrusion Process Types: Four

Different methods of plastic extrusion are used for various applications. Tubing, blow-film, sheet film, and over-jacketing are the four main procedures.

Tubing Extrusion: This method creates internal cavities in the die by inserting a mandrel or pin. Extrusion of tubing is the best method for making hollow objects, pipes, and tubes.

Shopping bags and other goods of such kind are frequently made by blow-film extrusion. The extruded plastic is cooled and expanded using an air ring in this process, which results in a bubble that is flattened into a double-layered film extrusion by nip rollers.

Sheet Film Extrusion: This method produces flat plastic sheets, much to blow-film extrusion. Pulling and rolling are used to create the required shape and surface roughness.

Over-jacketing Extrusion: This kind of plastic extrusion is specifically used to coat wires. Depending on the needed amount of adhesion, jacketing or pressure are employed to cover the wire with molten plastic.