TYPES OF THERMOPLASTIC EXTRUSION

No matter what the end use of the plastic is, it will have undergone some form of extrusion in order for it to be shaped and moulded. Extrusion itself can be completed in many different ways depending on the use and specific application or properties of the plastic. If you’re interested in plastic extrusion, you can read our blog on the process. So what are the forms of extrusion available, and what are they best suited for? Sheet Extrusion During the sheet extrusion process, the molten plastic material (pellets, granules, flakes or powders) is extruded through a flat die and the material is then cooled by rollers. This will determine the thickness of the sheet, which can be anywhere between 0.2 to 15mm. This extrusion process is commonly used in the manufacture of trays, signage or plastic linings for various purposes. Blown Film Extrusion Typical uses for blown film extrusion mainly lie in the film family – cling film or similar wraps for food packaging, laminating film or shrink wrap. The majority of the time polyurethane plastic is used in this process. The blown film extrusion process is a lot more complicated than many other extrusion types, here is an overview of the process: Air is injected through a hole in the die centre, and the pressure causes a bubble to form in the middle of the melting plastic. The bubble is cooled whilst still inside the die, reducing the temperature of the bubble. After solidification, the film moves into a set of ‘nip-rollers’ that collapse this bubble and in turn flattens the film into two layers. The film is then passed through further rollers to ensure uniformed tension and strength. Over-Jacketing Extrusion This process allows for plastic to be extruded over a wire or cable. During this extrusion process, the wire is pulled through the centre of a die and the molten plastic will cover the wire. This is the process of extrusion commonly used for the plastic which insulates wiring. Tubing Extrusion Tubing extrusion is used when a plastic needs to be extruded with a hollow cross-section, either by applying pressure within the internal cavities of the die, or by placing a mandrel in the die to force a specific shape. This method of extrusion is used to create pipes and tubes for all number of end uses, and in an endless number of different base plastics. Coextrusion Coextrusion involves forcing two or more materials or plastics, through the same die to either combine their features to make a different type of plastic with different properties, or to make a product that requires a dual purpose. For a more detailed breakdown of coextrusion, take a look at our blog post all about this process. Extrusion Coating Extrusion coating is used to add an additional layer of plastic onto existing products. For example, to improve the water resistance of paper, a polyethene coating can be used. Generally in this process, polyethene and polypropylene are used. Extrusion coating is a great way to improve the properties of some products and make them suitable for even more uses. For more information on plastic extrusion, and what we do at Rayda, contact our team of experts.

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