Extrusion
Extrusion is the method of creating continuous objects having a set cross sectional profile by forcing a substance through a tool known as a die.
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Plastics Extrusion
Plastics extrusion is a large volume production method that involves continuously melting and shaping a polymer material that has been enhanced with the necessary additives.
Granulates of the raw material (polymer) are gravity fed into the hopper through the feed mouth and onto a revolving screw. An electric motor provides screw rotation. The material and ultimate product design influence the screw design, which varies. The plastic is forced into a heated barrel by the screw’s spinning. The plastic is compressed as it passes through the barrel because the screw’s thread or channel narrows. The barrel is heated by three or more independent Proportional Integral Derivative PID controllers, which produce zones of progressively higher temperatures. Usually, the temperature at which plastic melts is higher than the temperature that the controllers are set to. Shear friction (shear heat) and compressive force work together to produce this extra heat. Once the plastic melt reaches the end of the screw, it is thoroughly mixed and forced through a screen pack that is held up by a breaker plate. This process removes the material’s rotational memory and filters impurities. The filtered melt is then forced through the die at the end. The die imparts the required form and contour to the finished product. The extrudate is extracted and chilled when it comes out of the extruder. The extrudate’s profile and form determine the cooling technique.
What Kinds of Plastic Extrusion Are There?
Different products can be made utilizing the different extrusion techniques outlined below, depending on the shape of the die:
1. Tubing Extrusion
Pipes and tubes are extruded using this technique of extrusion. Positive internal pressure air may also be used in this procedure. After leaving the die, the tubes or pipes are drawn into a cooling tank, where they are often cooled by water.
2. Blow Film Extrusion
This kind is employed in the continuous sheeting process to produce plastic film tubes. This method produces a semi-solid tube by cooling the film tube melt before it exits the die. The tube is then blown to the required size and film thickness. Products like shopping bags are manufactured with this procedure.
3. Sheet Film Extrusion
Plastic sheets or films that are too thick to be blown are extruded using this kind. The sheets are drawn and cooled by a sequence of cooling rollers as they emerge from the die; these rolls also control the thickness of the sheets.
4. Over Jacket Extrusion
Wire coating is done using this kind of extrusion. The wire is dragged into the die’s center during this procedure. Pressure tooling is utilized if adhesion between the wire and coating is necessary. Using this technique, the wire is pressured as it comes out of the die and is coated in molten plastic while it is inside. Jacketing tooling is utilized if adhesion is not needed. Using this procedure, as the wire comes out of the die, it is covered in melt.