Extrusion is a manufacturing process where a material is drawn through a die of required cross section. The main advantage of extrusion over other processes is that it can create very complex sections and also can be used for brittle objects since shear and compressive are the only stresses that are acting on the material. Additionally, the process also provides excellent surface finishes.
Various types of plastic material can be extruded e.g. PVC, UPVC, ABC, PE, PP, PC, etc. In plastic extrusion generally the pellets are fed to the hopper and they are heated by heating elements and the shear heating is done by the screw. Then, the molten resin is forced through the die by the screw giving it the required shape. The extruded plastic solidifies as it is pulled through the die or water tanks.
If required various additives can be added to the pellets and dried before inflicting them to the hopper. After the hopper is passed through, the pellets enter the screw through feed throat and are pushed through the barrel by the rotating screw. The melting of the pellets is
done by the heating elements in such a way that the temperature increases gradually from the hopper end to the other end of the barrel allowing the pellets to melt gradually too. Some heat is also generated by the intense pressure and friction inside the barrel as well.
Then the melted pellet passes from the end of the barrel to the screen pack where any contamination in the melt is removed. The screen pack is reinforced with breakers plate and this assembly plays an important role to create a back pressure to the barrel which facilitates to melt and mix the polymers uniformly.
Then onwards the melt is subjected to the die where the melt gets it final shape but care should be taken that the design would let the molten plastic flow evenly and let the cylindrical profile take the final shape. Any uneven flow at the stage can lead to uneven stresses over the profile. Using an appropriate die any continuous profiles may be produced.
Normally, after all these processes the substance is cooled pulling it through a water tub. Pullers are also often used to pull it uniformly from the die. Since plastics are good thermal insulators it takes some time to cool the extruded material.
Various types of plastic material can be extruded e.g. PVC, UPVC, ABC, PE, PP, PC, etc. In plastic extrusion generally the pellets are fed to the hopper and they are heated by heating elements and the shear heating is done by the screw. Then, the molten resin is forced through the die by the screw giving it the required shape. The extruded plastic solidifies as it is pulled through the die or water tanks.
If required various additives can be added to the pellets and dried before inflicting them to the hopper. After the hopper is passed through, the pellets enter the screw through feed throat and are pushed through the barrel by the rotating screw. The melting of the pellets is
done by the heating elements in such a way that the temperature increases gradually from the hopper end to the other end of the barrel allowing the pellets to melt gradually too. Some heat is also generated by the intense pressure and friction inside the barrel as well.
Then the melted pellet passes from the end of the barrel to the screen pack where any contamination in the melt is removed. The screen pack is reinforced with breakers plate and this assembly plays an important role to create a back pressure to the barrel which facilitates to melt and mix the polymers uniformly.
Then onwards the melt is subjected to the die where the melt gets it final shape but care should be taken that the design would let the molten plastic flow evenly and let the cylindrical profile take the final shape. Any uneven flow at the stage can lead to uneven stresses over the profile. Using an appropriate die any continuous profiles may be produced.
Normally, after all these processes the substance is cooled pulling it through a water tub. Pullers are also often used to pull it uniformly from the die. Since plastics are good thermal insulators it takes some time to cool the extruded material.
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