Plastics Processing and Manufacturing,Process of Plastic Extrusion

Plastic extrusion is a process where plastic is melted and formed into a continuous form. This process is used for producing things such as pipe, fencing, tubing, wire insulation, window frames, and railing…

Plastics Processing and Manufacturing

Plastics are polymers with high molecular weights. Plastics are common in a wide range of products, from automotive interiors to pipes. Plastics processing and production involves three basic steps: 1) imparting certain characteristics to plastic resins with chemical additives, including lubricants, flame retardant agents, colorants and plasticizers; 2) converting raw materials (plastic granules, pellets, sheets, fluids or preformed plastics) into intermediate or final shapes; and 3) finishing the product through molding/forming processes, such as injection molding or extrusion. Injection molding involves heating granules or pellets to a fluid state and pressure injecting the fluid plastic into cold molds for setting. Extrusion involves pushing fluid plastic material through a die to create long, continuous forms, such as pipes or tubes.

The Basic Process of Plastic Extrusion

The process uses plastic resin, which are small plastic beads, fed through a hopper into the extruder’s heated barrel. There, a rotating screw, which generally turns at 120 rpm, pushes the resin through the barrel as it is generally melted at anywhere from 392 degrees to 527 degrees Fahrenheit, depending on the polymer the resin is made up of. To help reduce the risk of overheating the resin, the heat is gradually increased from one side of the barrel to the other.

At the front of the barrel, there is a screen that the melted resin is pushed through to help filter out anything that may have contaminated the resin. Once the melted thermoplastic resin passes through the screen, a feed tube sends the resin through a shaped die, which then gives the product its profile.

This shape or profile, can be made continuously, at any length.

Finally, the product must be cooled. This is usually done by means of a water bath. Plastic holds heat well, so the cooling process takes some time. Because of this, the water bath is often sealed and a vacuum is used to keep the product from losing its shape while it cools.

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