Extrusion is a melt and form process where the desired material is melted and extruded through a shaping die. This process can produce pipes or components of various sizes depending on the requirement. Polyvinyl chloride (PVC) and high density polyethylene (HDPE) are the commonly used materials that employ the extrusion process for manufacturing pipes.
Twin-screw extruders are used when rigid PVC pipes are manufactured such as those used in buildings for drain and vent pipes.
Trenchlesspedia Explains Extrusion
The process of pipe extrusion is usually gravity fed and utilizes a hopper mounted on a barrel. The melting takes place in the barrel and the heating is done in multiple stages to avoid damaging the polymer by overheating. The material may be in the form of resin, pellets or any other raw form and is fed into one end of the hopper, at which point additives such as colorants can be added.
Once the material has melted, it is forced through a die which forms it into the desired shape. The flow of the melted material should be even to prevent stress on certain parts of the pipe. The finished product is allowed to cool and harden before it is removed for cutting and finishing.