Plastic Extrusion: The Building Blocks of Today and Tomorrow

Ever wondered why plastic products are numbered in the millions and found everywhere? Take low cost and fast production times for starters, paired with exceptional durability and flexibility, and the fact that the materials are lightweight, versatile and easy to handle and transport. 

Production processes are also relatively straightforward and good for high-volume turnover. It ranges from injection moulding in automotive parts and consumer electronics, thermoforming in bins, trays and sporting goods and extrusion in window frames, doors and wire insulation.

The Basics of Plastic Extrusion

Plastic extrusion is one of the more widespread plastic manufacturing processes. It’s existed for nearly a century and remained virtually unchanged. Extruding involves pushing granulated plastic particles through an extruder that heats and pressurises the molten material through different sections of the extruder and shapes it into distinct profiles using dies. It is then cooled and solidified into the desired shape. 

A more detailed description is that granulated raw materials or polymers are first fed into a hopper. This granulated mix drops through a feed throat by way of gravity and onto a barrel for further processing. The barrel heats the material, and temperatures steadily rise as it is pushed through the machine by way of a rotating screw.

Along with rising temperatures, the pressure acting on the heated plastic increases as the screw thread decreases. When the plastic has reached the end of the screw it is filtered of contaminants in a screen pack, then pushed through a die. This is what gives the end product its final shape and profile. After being pulled through the die, the plastic is cooled and takes on a permanent, solid form. 

Types of Plastic Extrusion Processes

The die determines shapes and profiles and leads to different extrusion processes in which varied plastic extrusions are formed. This ranges from pipes and tubes produced with tubing extrusion and everyday products such as shopping bags, wraps and packaging made using blown film extrusion. 

Sheet film extrusion is similar but produces plastic items that are thicker such as cups and utensils. And insulation sheaths in wires are made with a process called over-jacket extrusion. 

• Tubing Extrusion – tubes and pipes are formed with air and positive air pressure. Common items produced this way are PVC water and sewer pipes of varying diameters (some exceeding 150cm/60 inches in diameter) to exceptionally detailed medical tubes measuring a minute 0.01 inches/0.025cm.

• Blown Film Extrusion – this is used in the production of plastic film tubes through continuous sheeting. The melted film tube is cooled inside the extruder before leaving the die. creating a semi-solid tube which is then blown to the desired shape, size and thickness. 

• Sheet Extrusion – involves plastic sheeting that is too thick to be blown but instead is pulled out of the die and cooled with a system of cooling rollers which determine the end-products thickness.

• Jacket Extrusion involves wire being pulled through the die and insulation extruded around it. Adhesion can be added by using pressure tooling with molten plastic added while the wire is still in the die. Uncoated insulation is achieved with jacket tooling and molten plastic added to the wire as it exits the die.