Plastic extrusions are produced by a process known as plastic extrusion. Plastic extrusion is a manufacturing process where raw plastic materials are melted down and then formed into a continuous profile. Plastic extrusion produces all types of different items and is particularly useful for manufacturing window frames, tubing, pipes and weather stripping.
To extrude plastic into various forms, raw thermoplastic material called resin in the extrusion industry, and in the form of small beads, are loaded into a gravity fed hopper which is mounted onto the top of an extrusion barrel. UV inhibitors and additives such as colourants are very often mixed into the resin before it is loaded into the hopper.
The resin drops down into a barrel which contains a screw which can rotate from anything up to 120 rpm. The screw forces the resin or plastic beads along the barrel which is heated to the desired temperature, and this can range from 200 degrees centigrade to around 275 degrees centigrade. The barrels temperature is controlled along its length so as the beads move along it the temperature will increase. This gradual heating of the resin allows it to melt gradually and more evenly as it is forced along through the barrel and minimises the risk of overheating which in turn can cause the polymer to degrade. Cooling fans may be used to lower the temperature of the barrel if too much heat is generated.
The plastic leaves the screw at the front end of the barrel and passes through a screen pack to remove any contaminants which may be present in the melted plastic. The screens are strengthened by a breaker plate which also helps to create back up pressure in the barrel which is required for uniform mixing and melting of the polymer.
When the molten plastic has passed through the breaker plate it enters a die. The die gives the product its final shape or profile, and must be designed to allow the molten plastic to flow evenly from a cylindrical profile, to the products final profile form. A vast number of different shapes and forms can be created using this process, as long as it is a continuous profile.
The final heated product is then cooled by being pulled through a water bath. When compared with some metals, plastic conducts its heat away approximately two thousand times more slowly, because plastics are very efficient thermal insulators. As soon as the product is cooled it may be cut into manageable lengths or spooled for later use.
There are quite a few different types of material used in plastic extrusions and some of these may include:
o Polystyrene: Polycarbonate: Acrylic: Nylon: Acetal: Acrylonitrile Butadiene Styrene.