Industrial Plastic Pipe manufacturing

Plastic pipe is a commodity manufactured in many countries throughout the world. Due to the different processes involved between pipe and fittings manufacture they are rarely carried out by the same company.

Pipe manufacture is carried out by extrusion machines. The granular plastic media is fed from a hopper at one end of the machine and supplied into an enclosed auger. The auger is enclosed in a heated tube which is electronically controlled to ensure the plastic is heated to it optimum molten temperature. If the plastic is too hot it will burn or be extruded too fast through the machine resulting in a weak pipe structure. If the molten material is too cool, the auger will struggle to push enough through the die at the end, resulting in the plastic pipe having a cavitated structure, which will significantly weaken the end product. Temperatures depend on the material, colour and other additives in the plastic mix. ABS pipe is typically extruded at temperatures between 215 and 230 degrees centigrade. PVC pipe is extruded at slightly lower temperatures, typically between 190 and 220 degrees centigrade. The auger typically rotates at 120rpm and pushes the molten plastic towards a screen that removes any unwanted particles and ensures that only smooth, molten plastic is used for making the pipe. The screen and plate assembly has a secondary purpose on the plastic, and transforms the rotating direction from the auger, to a linear one, which is more suitable for the die. The pressure at this point is very high, in the region of 340 bar and so additional reinforcing plates need to be used to ensure the integrity of the screen is maintained.

The die is the part of the system that gives the end product of plastic pipe its shape. All plastic pipe is manufactured to an outside controlled diameter. The outside diameter is the critical diameter for most pipe systems as the method of system construction requires that the pipe is pushed into moulded sockets. In this way, the wall thickness can be increased and decreased for different pressure ratings, but all pipes of all pressures will fit all fittings. The internal diameter of the pipe will vary slightly, the amount depending on the quality of the manufacturing process and the quality of the raw materials. The internal wall of the pipe is not as smooth as the outside. Pipe that is well manufactured will have only a slight, barely noticeable difference, but poorly manufactured tube will sometimes display ripples in the internal bore. The atmosphere in the room where the pipe is manufactured is very carefully controlled to ensure that the plastic is uniform. After extrusion, the plastic needs to be cooled, in a controlled manner, to ensure both the retention of accuracy of he dimensions and the uniformity of quality. This process usually uses long water, temperature controlled baths, where the fluid is kept moving and the pipe cools slowly as it travels along the length of the bath.

At the end of the process, the pipe is cut to length. Some pipes are manufactured with a socket end, and this is achieved after extrusion and cooling, by reheating the end of the pipe and flaring it with a special tool, before once again, cooling it.

Metric plastic pipe is usually manufactured in 5m lengths whereas imperial is more often in 6m lengths. The 5m lengths are often preferred as they can fit in a standard iso container, where the 6m cannot.