Channels can attach, hold, guard, seal and direct the flow of liquid. Common types of profiles include J-channels, H-channels and U-channels, although much more complicated profiles are often extruded for applications such as window insulation, which requires multiple internal gaps and chambers for heat and sound insulation.
Construction industries use plastic channels quite extensively, not only for window trim and insulation, but for outdoor siding, indoor and outdoor trim, outdoor gutters (commonly known as U-channels), indoor drains and gutters, door frame trim and insulation and for guards and bumpers around sharp corners and edges.
Appliance manufacturers use flexible PVC and vinyl channels for refrigerator and stove door sealant, while automotive industries use many profiled channels for interior and exterior trim and bumpers.
Commercial manufacturers extrude plastic channels into curtain rods, drinking straws, picture frames, partition holders, point of purchase displays, shelving and guards. Channels are often coextruded, combining hard plastic with softer plastic or rubber to create soft sealing channels with hard fixtures.
Plastic channels are produced by the plastic extrusion process. Extrusion is very well suited to the production of channels and other long plastic products because the process is continuous.
The extrusion process begins with a collection of raw plastic material in a hopper suspended above a conveyance channel. The raw plastic is released from the hopper into the channel. In the channel is long shearing screw that forces the plastic down the channel. The friction caused by the turning of the shearing screw heats the plastic and causes it to become molten.
Some plastic extruders also feature electronic heating elements that aid in the melting of the plastic. By the time the plastic reaches the end of the channel, it is completely plasticized.
At the end of the channel is a die, which is a specialized tool designed to shape raw materials into useful products. In the case of plastic extrusion, a die is a metal plate cut with a hole through which the plastic passes.
When the plastic is forced through the hole, it takes its shape, emerging on the other side of the die as newly-extruded plastic. The extruded plastic is allowed to cool and harden and is then cut and prepared for shipment or sent for additional processing.