When you think of “plastic” you might think about the keyboard at your fingertips, the dashboard in your car, or virtually anything in between. It is no exaggeration to say that plastic is everywhere. However, when you think “plastic” you probably don’t think about the hundreds or even thousands of tiny plastic components we constantly rely on. Many of those came about thanks to plastic extrusion. So, what is it?
Plastic extrusion, responsible for plastic parts like tubes, wire insulation, and so much more, is a technology dating back to the late 18th century – but it continues to impact us daily. In 1797, Joseph Branmah was the first to actually patent the process as it was first used to actually create lead pipe. Similar to the process for plastic, this process involved heating the metal, forcing it into a die to create a shape, and then allowing it to harden. Before long, plastics entered the equation, giving rise to the plastic extrusion process we depend on today.
Plastic extrusion typically takes advantage of tiny plastic pellets or chips, which are melted at high temperature and slowly poured into a mold. While the early version of extrusion developed by Branmah involved forcing the material into the mold by using a plunger, modern plastic extrusion is slightly different. Today, modern plastic extrusion takes advantage of a heated screw feeder which quickly and efficiently forces the plastic pellets from the hopper, through the barrel, and into the die.
Various forms of plastic extrusion exist to accomplish different goals. While there are many different types of extrusion, the main methods include sheet extrusion, tubing extrusion, and coextrusion.
Sheet extrusion (otherwise known as film extrusion) is used for products that are a plastic sheet or film. After the extrusion is created it is cooled by pulling it through sets of cooled calendar rolls. Many times, the technique known as coextrusion is used to add more than one layer on top of the base extruded layer. Coextrusion is simply a process where multiple extruders are used to melt and steadily add different plastics to a single extrusion die. This allows for an extrusion to have a number of specific properties, including for example a softer touch, a gripped surface, matted finish, and much more.
Many times, the extruded sheet also undergoes thermoforming, which involves the sheet being heated until it is once again soft, and then formed into another shape by using a mold. Many times, a vacuum is used to force the sheet into the mold (this is known as vacuum forming). This process takes extruded sheets in their more basic orientation and bends them to create complex shapes like computer housings, displays, common plastic products, and more.
While plastic extrusion is used to produce an extremely wide variety of products ranging from tubing, pipes, and seals to sheets, rails, rods, and profiles, a large number of plastics are used to create extrusions with the proper properties. For example, extruded tubing to be used in high-temperature or potentially corrosive applications might call for a much different plastic than general-purpose tubing. Given the sheer amount of plastics available on the market today that provides an extremely diverse number of solutions for plastic components, parts, and products just about everywhere.