Custom Plastic Extrusion Terms- Part One

On September 29, 2017 | by Formtech | in Blog, Featured News, How Can We Help?

Every industry has commonly used terms and acronyms, and custom plastic profile extruders are no exception. The extrusion industry tends to take these terms for granted, which can lead to confusion.

Formtech is going to help you understand our industry’s terms!

Please join us in a four-part series, looking at the top extrusion terms relating to each of the following categories:

Part One– Extruders and Tooling

Part Two– Downstream equipment

Part Three– Materials

Part Four– Processing

What is “custom profile extrusion”.

Think of extrusion in terms of an everyday product that almost everyone has seen – the extrusion of pasta using a pasta making machine. These devices make a wide variety of pasta noodle shapes, each using basic extrusion principles. In reality, whether you are making pasta or custom plastic profiles, the processes are very similar. Let’s look at 9 terms related to custom profile extrusion, all related to the extruder and the tool.

  • Screw– Screws are the work-horse of the extruder.  Extrusion, screws are not the typical screws you may see at your local hardware store.  Instead, an extrusion line screw conveys, compresses, and mixes plastic compounds.  Screw design for plastic extrusion is a sophisticated science, with specialty screw designs being developed to increase output rates, increase mixing, and widen processing windows. Screw designs may vary depending on the plastic compound, output requirements, and physical property requirements of the finished product.
  • Single-Screw Extruder– As the name implies, a single-screw extruder has one screw, and was the first type of extruder developed around 1935 in Hamburg, Germany. Single-screw extruders are widely used today for processing a wide variety of plastic compounds and are considered a work-horse extruder for custom profile extrusion. Our Fairview, Pennsylvania manufacturing facility is outfitted with single screw extruders.
  • Twin-Screw Extruder– Twin-screw extruders were developed in Italy after the Germans developed single-screw machines. Custom plastic extrusions are typically made on counter-rotating twin-screw machines while co-rotating twin-screw extruders are used primarily for compounding of plastic materials.

Counter-rotating extruders are designed to have the screws turn toward one another (one turns clockwise, the other turns counter-clockwise), and the screws are intermeshed to mix and convey the material down the extruder. There are two different types of counter-rotating extruders. A parallel twin-screw extruder has two parallel screws that are the same diameter from the beginning to the end of the screw. Conical twin-screw extruders have a much larger screw diameter in the back of the machine, and the screws taper as material flows toward the die. Both types of twin-screw extruders provide a tremendous amount of mixing and compression of materials.

Twin screw extruders are used for PVC  Wood Plastic Composite materials(WPC), and other powder plastic compounds. Our Athens, Georgia manufacturing facility houses our high output, twin-screw extrusion lines.

  1. Extruder Size– Formtech has a variety of single-screw machines varying in size from ¾” to 3 ½”, which can accommodate profiles as small as 1/8” to over 8” in width. In general terms, the larger the diameter of the extruder, the more pounds per hour of output the machine provides. Twin-Screw extruders are typically measured in millimeters, and can vary widely in size depending on the extruded plastic profiles being manufactured. Formtech has twin-screw machines from mid-range up to large sizes, which can handle profiles as small as under 1”, up to 12” wide profiles that weigh more than 7 pounds per foot. The largest profiles manufactured by Formtech are used in marine applications such as a seawalls, or bulkheads. This product line is an innovative, hybrid sheet piling system made primarily of recycled PVC materials, with a prime, weather resistant capstock on all exposed areas. Check out the specifics at truline.com.
  2. Barrel– The barrel of the extruder is a hardened steel cylindrical cavity designed to house the extruder screw(s). The barrel is subjected to a considerable amount of pressure from compression of the plastic compounds during extrusion, and may either be simply hardened, or for high volume applications the barrel can be lined with harder materials such as tungsten carbide.
  3. Hopper– Plastic compounds are fed to the extruder through a hopper, which is basically a funnel to hold material as it is being either gravity or force fed to the machine. Generally, as the size of the extruder and output increases, larger hoppers are required to act as a reservoir for the plastic compound. At Formtech, our primary extruders are equipped with vacuum loaders, allowing our operators to focus on the quality of the custom extrusion instead of spending valuable time manually filling the hoppers.
  4. Adapter– Plastic materials exit the barrel and screw end, and are funneled into the extrusion die. The adapter allows the extrusion tooling to be mounted to the extruder, and transitions the material flow from the barrel & screw to a shape. The adapter can be a slide in configuration or can bolt on the head of the extruder. Slide in adapters provide ease of changeover from one extrusion die to the next, but are prone to leakage. Bolt on adapters take more time to change over, but provide a better opportunity for even pressure and reduced gate leakage. Many custom profile extruders utilize a series of standard adapters that can be used over a variety of extrusion tooling, to reduce tool costs and increase manufacturing flexibility.
  5. Die– Think of the extrusion die as the gateway to your finished profile. If you want angel hair pasta, you would not use a tool that looks like rigatoni. The extrusion tool is what determines the shape of the finished profile. Typically, a custom profile die is made up of several die plates, and will transition the general shape from the adapter to the finished shape of the extruded profile. This is called streamlining, and it is critical to the extrusion process to control tolerances. Have you ever made pasta and have certain strands not push out as quickly and evenly as others? This is due to improper streamlining, and the same holds true when manufacturing plastic extruded profiles. Many plastic materials are subject to degradation with heat, so smooth flow in the extrusion die is extremely important to eliminate burning during the production run. The streamlining in the die keeps plastic materials flowing, and helps prevent material degradation. The streamlined portion of the die feeds into the die land, which is the area of the extrusion tool where the material flows consistently across a section of the tool without streamlining. This land area stabilizes the material flow, and helps improve the surface finish of the extruded shape by “ironing” the outer surface of the profile. The point where the plastic compound exits the extrusion die is referred to as the die lip. It is important to keep the die lip flat and sharp, and this requires careful handling by the extrusion manufacturer. If this lip is damaged, it can result in irregularities in surface finish and appearance. Formtech maintains extrusion tooling at both manufacturing facilities with proper inspection, handling, and care. Formtech manufactures many of the extrusion dies we use to manufacture custom plastic products. We also utilize a global network of world-class tooling vendors for additional extrusion tooling support. To find out more about Formtech extrusion tooling, click here.
  6. Heater Bands– Precise temperature control is one of the processing musts in plastic extrusion. While the plastic material is in the barrel and screw of the extruder, a combination of friction heat and barrel heaters are used to carefully control the temperature of the extrudate. Once plastic compounds enter the adapter and die, external heaters are required to evenly control the compound temperature until the material exits the die lip. The die heaters can be as simple as strip heaters mounted to the extrusion die, or as sophisticated as custom made plates with flexible heater cords or even die inserts specially designed for the extrusion tool.

We hope the plastic extrusion terminology review will help you to understand the extrusion process. Check back for parts two, three and four of our four-part series.

We are anxious to work with you and your team on your next plastic extrusion requirement. Give us a call at 614-531-9954 or email at sales@formtech.com for more information or a quotation.