Plastic Extrusion Machinery Stretches the Imagination

Plastic extruder machines are used to manufacture a wide range of consumer, industrial and agricultural products. But, no matter what the end use, the basics of the different plastic extrusion machinery remain the same.

The Extrusion Process

All plastic extrusion equipment is made up of a hopper, a barrel and a die. To break the process down, plastic resin is first fed into the hopper. Depending on the application, the resin may have previously been mixed with additives like UV inhibitors or colorants.

From the hopper, the resin is fed into the barrel, where a screw moves the material down the barrel to the die. The screw not only moves the resin, but it also mixed the resin and heats the material up, allowing the resin to melt along the way.

Heating bands on the outside of the barrel help it reach the appropriate temperature for the specific resin being extruded. Temperatures can range between 400° and 530° F. The temperature rises progressively along the length of the barrel through three or more independent heater zones, allowing the resin to melt at an appropriate rate. The barrel temperature must be carefully monitored to prevent overheating, which can degrade the resin. In some instances, cooling devices may be used to reduce the temperature.

Before the melted resin reaches the die, it passes through a screen pack to remove any possible contaminants. The screens and a reinforcing breaker plate help create sufficient back pressure in the barrel to ensure the uniform melting and mixing of the resin.

After the resin passes through the die, the resulting shape is air or water cooled to reach its final temperature. The shape then can be rolled or cut to length.

Types of Plastic Extrusion Machinery

While they all work on the same premise, different types of plastic extruders are used for different processes.

• Profile extrusion can create a wide range of shapes, from simple T-, I-, U- and L-shapes to complicated window frame assemblies. Specialty processes include:
• Tubing extrusion, which is similar to traditional extrusion, except there are interior pins or mandrels in the die to facilitate the production of hollow forms
• Coextrusion, in which several layers of material are extruded at the same time by having two or more extruders feed different types of plastic into a single extrusion head
• Overjacketing, which coats a part like wires or cables in a protective plastic coating
• Sheet extrusion, which is often a preparatory process before thermoforming
• Blown film, which uses a vertical, rather than horizontal die, to create plastic film products like grocery bags

Types of End Products

Plastic extrusion machinery is used to manufacture a wide range of products, such as:

• Drinking straws
• Weatherstripping
• Refrigerator seals
• Garbage bags
• Window frames
• Gutters and downspouts
• Fencing
• Body side moldings for cars
• Bumper strips
• Drainage tubing for farmland
• Interior and exterior finishing and accent trim
• Vertical blinds
• Medical tubing for blood and IVs
• Resealable strips on plastic bags

Depending on the application, plastic extrusion machinery usually processes resins like polyethylene, polypropylene, acetal, acrylic, nylon, polystyrene, PVC, ABS and polycarbonate.

Companies that use plastic extruders include ProVia, which makes vinyl siding and replacement windows, and Champion Plastics, which produces polyethylene packaging.

Visit polysort.com for a list of plastic extrusion machinery manufacturers.