What do Plastic Extrusions Consist of?

Posted By: Tony | Date: 27-07-2015

When it comes to the extrusion process, the most commonly used material is aluminum. However, other metals are also used such as copper, steel, and iron. There are even plastic extrusions, which involve much the same process but with distinct differences.

As part of the plastic extrusions process, resin or a raw thermoplastic material is fed via gravity through a hopper that goes into the extruder barrel. From there, UV inhibitors and colorants are typically added either in pellet or liquid form. If wanted, these can be added to the resin or thermoplastic material prior to going into the hopper.

Plastic extrusions and plastics injection molding are similar although the primary difference is that extrusions are typically continual. Keep in mind the injection molding can produce like profiles in continuous lengths but for this, added reinforcement is usually required. In addition, instead of the finished product being extruded from fluid resin or thermoplastic through a die, molding involves the product being pulled from a die directly.

Specific to plastic extrusions, once the material goes into the feed throat toward the rear section of the barrel, it encounters the screw, which offers rotating force the pushes the material forward and into the barrel itself. The barrel is heated to an exact melt temperature based on the exact type of resin or thermoplastic.

In general, a heating profile is set for a barrel that uses at least three independent proportional integral derivative controllers (PID) controlled heat zones. These zones are designed to increase the barrel’s temperature gradually at the point where the resin has been placed in the front. Because of this, plastic melts slowly as it is forced through the barrel. In exchange, risk of overheating that could cause polymer to degrade is eliminated.

At the front portion of the barrel, the resin or thermoplastic material leaves the screw and goes through a screen that is reinforced as a means of eliminating contaminants. Because the pressure at this point can easily exceed over 5,000 pounds per square inch (PSI), reinforcement typically comes from a breaker plate.

It is then that the material goes into the die, giving the finished product is completed shape or profile. In order for the plastic extrusions process to work, the molten material must be able to flow evenly from its original form to the final profile shape.

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