Square plastic tubes immediately distinguish themselves from most other tubing products in that they are not cylindrical. There are not many applications in which a square tube would be necessary instead of a cylindrical tube.
Square tubes could be chosen because of an aesthetic preference or because of compatibility issues with other tubing. Like cylindrical tubes, they can be found in point of purchase displays, healthcare settings, in children’s toys and in many other applications. Tubing in general is used in countless industries for many purposes.
Depending on the industry and the application, a given piece of plastic tubing could be made of High or low density polyethylene (HDPE and LDPE), polystyrene, PET, polypropylene, nylon, ABS, polyurethanes or any other of the many varieties of plastic materials used to create plastic tubing. Each variety features unique qualities of strength, reactivity and transparency.
Acrylic tubing of this form, for example, could be used in a healthcare setting to monitor the flow of fluid between laboratory equipment. Other plastic materials like PVC or HDPE are opaque and are valued more for their qualities of durability and impact resistance.
There are several processes by which square and cylindrical tubing can be formed; the process of making a square tube and the process of making a round tube are identical. Cell casting involves pouring molten plastic materials into molds and allowing them to harden. This is a fairly effective method, but the most effective and efficient method for plastic tube fabrication is plastic extrusion.
Plastic extrusion is a thermoforming process, which means it uses heat to melt a plastic in order to shape it into a useful product. The plastic extrusion process begins with a collection of raw plastic material called stock. The stock is loaded into a hopper suspended above a conveyance channel. The stock is released into the channel, and a large shearing screw within the channel forces the stock toward a die at the end of the channel. A die is a specially designed tool that is used to shape a material.
The die in a plastic tube extruder is a hole and pin in a metal plate. The turning screw causes friction that, combined with heat generated by heating elements along the channel, causes the stock to reach a molten state. At this point the stock is forced through the die and takes its shape. It emerges on the other side of the die as plastic tubing. The tubing is allowed to cool, is cut to length and is prepared for shipment or additional processing.