What is Plastic Extrusion? Your Complete Guide
What is plastic extrusion, you may be wondering. In simple terms, plastic extrusion is a process of forming melted plastic into a continuous profile. Typically used for long items, like pipe or tubing, railings, or window frames, it is a high-volume manufacturing process that can create complex shapes with various cross-sections and sizes. Below we will take a deeper dive into the process of plastic extrusion.
What is Plastic Extrusion Machinery
To better understand plastic extrusion, it is helpful to understand the machinery used in the process. The machinery that produces the extrusion is called an extruder. On the surface, the process is simple, raw material goes in, and the product comes out. However, the equipment requires several parts that work together to produce the profile.
Material is fed into a hopper at one end of the extruder. The feedthroat directs the material toward the barrel, where the plastic is melted. Within the barrel is a rotating screw that forces the material to the feed pipe. The screw is the heart of the machine and can impact product quality, throughput, and efficiency. While there are different types of screws available, the 3-zone screw is the standard and what is described here. These general-purpose screws have three different zones: the feed zone, the compression zone, and the metering zone. Each zone will be at a different temperature depending on the plastic used, starting with the lowest temperature at the feed zone.
A thin film forms on the barrel wall as the plastic is melted. As the screw rotates, it scrapes away the plastic film and causes it to flow down the barrel. The circulatory flow generated by the rotating barrel causes the melted plastic to surround unmelted granules and melt them, creating a uniform melt. Some machines have a double screw, allowing compounding and increased productivity.
The melted plastic leaves the barrel through the breaker plate, which filters any foreign substances and maintains the pressure needed for the extrusion. The melted plastic moves through a feedpipe to the custom die. The die is used to create the extrusion profile. It is forced through the die, forming the custom shape. The profile is cooled to ensure the profile maintains its shape.
The Importance of the Die
Extrusion dies are designed to create different profile shapes – they are essentially the mold. They are thick metal disks with machined openings that produce the desired shape when plastic is forced through. Dies are custom manufactured for each application.
The polymer must exit the die with a uniform velocity. The flow properties of the polymer, the flow channel geometry, the flow rate, and the temperature of the die and polymer melt determine how the polymer is distributed. Polymers have different viscosity-thinning characteristics at increasing shear rates. Shear rate is the rate of change in velocity when one layer of melted plastic passes over another. As the shear rate increases, plastic becomes less viscous. So if the flow channel geometry is designed for one polymer under specific conditions, changes in the polymer of conditions impact the extrusion.
High-quality tooling is critical to achieving tight tolerance extrusions required for many industries and applications. Burrs, scratches, or scrapes on the tooling can impact precision.
Types of Extrusion
Answering the question, “What is plastic Extrusion?” cannot be answered without going into more detail about the different extrusion options that are available. The simple process described above is great if you only need one type of polymer. But sometimes applications require the use of more than one material. This is where co-extrusion, dual durometer co-extrusion, tri-extrusion, and crosshead extrusion become necessary.
These methods offer exceptional design possibilities, allowing for the creation of products with enhanced functionality, aesthetics, and performance. By understanding the capabilities and applications of these extrusion techniques, manufacturers and designers can be more creative with designing products using plastic extrusions.
Co-Extrusion: Co-extrusion is a process where multiple materials are simultaneously extruded through a single die to create a single, multi-layered product. It combines two or more plastic materials with different properties to enhance functionality or aesthetic appeal. By carefully controlling the layer thickness and composition, co-extrusion enables the production of products with distinct layers, such as weather-resistant outer layers or reinforcement layers for added strength.
Dual Durometer Co-Extrusion: Dual durometer co-extrusion takes co-extrusion a step further by incorporating two materials with different hardness levels into a single product. This technique is commonly used to produce items requiring both soft and rigid areas. For instance, dual durometer co-extrusion can extrude window or door seals and gaskets that require a soft material for effective sealing and a ridged material for structural support. Dual durometer co-extrusion allows for the seamless integration of these materials, resulting in improved functionality and user experience.
Tri-Extrusion: As the name suggests, Tri-extrusion involves extruding three different but compatible materials to create a product with multiple layers. This technique offers even greater design flexibility and allows for incorporating materials with unique properties, such as UV resistance, chemical resistance, or electrical conductivity.
Crosshead Extrusion: Crosshead extrusion is a specialized technique that encapsulates a piece of metal or wire into a plastic substrate. This is one of the most challenging types of extrusion and is used to create wires, cables, and more.
Bring your Ideas to Fruition
At Custom Profile, we design, manufacture, and deliver your custom extrusions with total cost savings in mind from product and tooling design through extrusion and in-line operations. Our in-house tool capabilities mean you get the highest quality tooling with shorter lead times. Value-added in-line operations can be performed, reducing handling and increasing operational efficiency. Whether your product requires co-extrusion, dual durometer co-extrusion, tri-extrusion, crosshead extrusion, or tubing extrusion, we can provide a solution that will meet your needs. Contact us to get started.