A wide variety of industries use various types of plastic, HDPE, LDPE, butyrate, PVC, acrylic and vinyl trim in a diversity of applications, and plastic extruders are often capable of catering to multiple industries due to the versatility of the plastic extrusion process. PVC is the most common material used to form plastic trim.
Many different types of plastic trim with fairly close tolerances can be fabricated with plastic extrusion simply by changing the die through which the molten plastic is pushed.
Construction industries use plastic trim quite extensively, not only for window trim and insulation, but for outdoor siding, indoor and outdoor trim, door frame trim and insulation, and for guards and bumpers around sharp corners and edges.
Appliance manufacturers use flexible PVC and vinyl trim for refrigerator and stove door sealant, while automotive industries use profiled trim for interior and exterior trim and fenders.
In addition, furniture, marine and recreational industries use plastic trim for numerous incidentals. Common types of plastic trim includes J trim, edge trim, decorative trim, fender flare trim, brush guard trim, lip trim and drip rail trim.
In order to begin the plastic extrusion process, thermoplastic pellets or flakes are fed into a hopper placed atop a closed extruding channel. Gravity feeds the raw plastic material down into the extruding channel; running through the length of the channel is a screw conveyor that moves the raw plastic along towards the opposite end, shearing and heating the plastic through friction.
Electric heaters built into the extruding channel often help the screw conveyor to plasticize, or melt, the plastic pellets so that the plastic is completely molten by the time it comes to the end of the channel. Near the end of the channel, the molten plastic leaves the screw and travels through a screen pack in order to remove any contaminants.
The screens are reinforced by a breaker plate, which is a thick metal puck with many holes drilled through it, because the pressure at this point can exceed 5,000 PSI. The molten plastic must pass through the breaker plate before entering the die. The die is secured on the end of the conveyor channel and forms the molten plastic into a specific profile as it is pushed, or extruded, through by the screw conveyor.
The newly formed plastic profile is instantly cooled, often by pulling the newly extruded trim through a water bath, pulled through by a series of conveyors and cut to appropriate lengths. Plastic trim is often co-extruded, combining hard plastic with softer plastic or rubber to create soft sealing trim with hard fixtures.