Plastic Extrusion and Molding Processes: A Comprehensive Look

Plastic Extrusion and Molding Processes

Extrusion profiles are used to create long, uniform sections. This process utilizes a specialized machine called an extruder, which operates similarly to a kitchen cutting machine. Plastic granules are poured into a feed hopper and flow into a chamber where a screw rotates. The extruder heats the plastic to between 150 and 250 degrees Celsius to soften it and force it through a die, creating the desired shape.

Extrusion and Blow Molding

Extrusion and blow molding are used for creating items like electrical lighting components, bottles, and toys. A hollow preform, called a parison, is extruded and then placed into a mold. Air pressure is then injected to expand the plastic, conforming it to the mold's shape.

Calendering

Calendering is essential in the manufacture of laminates. The process involves feeding plastic granules into a machine where they are preheated. These granules become a thick paste and are passed through a series of rollers to achieve the desired thickness. The resulting sheet is then cooled by passing it through a liquid bath and an air stream before being cut to the desired length.

Injection Molding

Injection molding is a widely used process for injecting thermoplastic plastic, typically using a machine with a mold and a reciprocating screw. The screw rotates and acts as a plunger, injecting the plastic into the mold. The mold is often cooled by circulating water to solidify the plastic, after which the part can be ejected.

Compression Molding

Compression molding is suitable for producing large, relatively simple parts from thermosetting plastics. The plastic is heated within a mold, allowing it to flow and fill the cavity under pressure from a hydraulic system. The part is then cooled sufficiently before being removed from the mold.

Transfer Molding

Transfer molding is similar to compression molding. The plastic is introduced into a heated mold, and a plunger is used to force the material to flow and fill the mold. This method is often used for producing large series of identical parts, where molds may contain multiple cavities in a cluster arrangement.

Thermoforming of Plastic

Thermoforming is a plastic forming process that starts with a pre-formed sheet or film with predetermined external dimensions. The process involves clamping the sheet to a mold. A heating element, typically an infrared heat source, softens the plastic sheet. Vacuum pressure is then applied to draw the material against the mold walls, conforming it to the desired shape.