As a manufacturer of piping, tubing, insulation, or any other plastic composite product, you likely already know what an extrusion machine is, but may be wondering if it’s right for your high-volume manufacturing process. Whether you are about to purchase a plastic extruder or already own one, Leverwood Knife Works understands how important it is to keep your process flow moving.
The cutting blade on your extrusion machine should always be able to handle the precision converting expectations you have for it, which is why we are here to lay out the process in more detail. From beginning to end, understanding how plastic extruders work will help you make a more informed choice when it comes to your converting blades.
What is Plastic Extrusion Machinery?
To put it simply, plastic extrusion is a “high-volume manufacturing process” in which raw plastic is melted and formed into a continuous profile.” Plastic extrusion machinery is useful for speeding up workflow and volume. It’s also great for ensuring consistency through your products, which are made exactly to your specifications every time.
How Does the Extrusion Process Work?
Extrusion machines are simple—raw plastic materials go in, your product comes out and is cut to size. But let’s break it down into a little more detail.
As material gets fed into one end of the plastic extruder (a hopper), it is gradually melted by the heat and energy created from turning screws. These screws are located along the barrel of the machine where the raw materials are melted down. Most types of screws have three different zones to move along the extrusion process:
- Feed Zone: This is where the plastic composite material gets fed into the extrusion machine.
- Melting Zone: The next section in the screw design is where the plastic gets melted.
- Metering Zone: Finally, the metering zone is where the last bits of plastic are melted and mixed to create a uniform temperature and composition.
To ensure that the final materials won’t degrade or become weakened, it’s essential to maintain a consistent temperature inside the extruder’s barrel. Overheating the materials should be avoided to reduce imperfections, so typically the barrel is heated gradually from rear to front. The temperature is also maintained using a series of fan and water cooling systems before your product is extruded into a die mold.
A die mold is useful in plastic extruders because they can create one continuous extrusion that can then be cut into parts. Unlike with injection molding, which injects the material into individual molds, die molds will allow your product to be continuously made at whatever size (or sizes) you need. Depending on the type of product being manufactured, there are various types of dies that can be implemented into your process.
- Blown Film Extrusion: In blown film extrusion, typically used to manufacture plastic film or shopping bags, there are three types of dies used—annular, spider, and spiral. As the plastic leaves the die, it creates a semi-solid tube and is slightly cooled as it leaves. Air pressure is then used to rapidly expand the tube and then is drawn upward where the plastic gets stretched over rollers.
- Sheet/Film Extrusion: When plastic sheets need to be thicker, sheet/film extrusion is used employing both a t-shaped and coat hanger die. Both of these dies help to guide the plastic composite into a flat, planar output rather than a rounded tube.
- Tubing Extrusion: Similar to blown film extrusion are the dies used for tubing extrusion. You’ll typically see this type of die for products like PVC pipes.
- Over Jacketing Extrusion: When wires or cables get an outer layer of plastic for insulation and protections, two types of dies are used—tubing (or jacketing) and pressure. Depending on what is needed for the wire, the dies will either allow the plastic to touch the wire right before the end of the die process, or long before to ensure good adhesion of the materials.
Plastic Extrusion Converting Knives
At the end of the extrusion process, you’ll always want to ensure your product is being cut exactly to size without any malfunctions. Converting knives from Leverwood only use the highest quality materials to give you the best blades possible. When you use Leverwood blades with your machines, it is guaranteed that the blade will exceed your converting expectations saving you money in replacements blade down the road.
For over 25 years, Leverwood Knife Works has taken pride in being part of the cutting tool industry. With a competitive edge over the rest, we can assist you with modifying any existing designs and specifications to improve virtually any blade application. Contact Leverwood for more information about our converting blades or other products and applications.