There are a few different manufacturing processes for producing plastic piping systems. The right choice depends on the material used.
Pipes are first and foremost produced through an extrusion process. The raw material is feeded into the extruder via a hopper and a gravimetric or volumetric control system. Inside the extruder barrel the material is heated up to the melting point around 200°C by electricity and the friction in the screw system. The melted material is pushed through a cavity, called a die-head and thereby formed into a pipe. The pipe is then calibrated to correct size in a vacuum box and thereafter cooled by water in spray boxes. Extrusion is a continuous process and pipes can in principle be produced in infinity lengths. In the end of the production line pipes are cut into lengths and socketed or coiled according to the intended use.
The process described above is the for producing the so-called solid wall pipes consisting of one layer of a homogeneous material.
Next to the process for solid wall pipes other variants of production processes are used, e.g. for structured wall pipe. Structured wall pipes have an optimized design to achieve the physical, mechanical and performance requirements, using less materials at the same. Twin wall is a typical structure for pipe wall construction. Another variant is the so-called co-extruded pipes where the layers can be made of different materials. A typically a 3-layer coextruded sewer pipe consists of an outer skin and an inner skin of new (virgin) material where the middle layer is post-consumer recycled material. In this way the discoloration of the recycled material in the middle layer can be hidden inside the pipe.
Multilayer pipes for plumbing are a construction of PE or PEX with an aluminum layer inside the pipe wall. The aluminum has two purposes: To improve the longitudinal stiffness and to act as an oxygen barrier. The barrier is important in cases where the pipes are used for heating applications. The barrier can also be made with a polymer called EVOH.
Pipes can be connected in a variety of ways to form reliable and leak-free pipe systems. They can be connected by either welding, a push fit joint with rubber seal or by a solvent cement system.
Generally, fittings such as joints, elbows or T-pieces are produced by injection-moulding. Also production of storm water boxes uses the injection moulding process.
In injection-moulding, the plastic material is fed from a hopper into the melting section of the injection-moulding machine. After melting via electric heating and friction in the screw system, the material is transported forward and homogenized before being injected into the mould to form the shape of the desired product. After cooling the mould is opened and the product is ejected.
The rotational moulding process is a low-pressure process where the mould is rotating around all three axes inside a furnace. The plastic material in the form of powder, located inside the mold, melts with the contact to the hot inner surface of the mould. A hollow, one-piece product is formed. In the plastic pipe industry, this process is typically used to make large inspection chambers, and water and septic tanks in polyethylene (PE) or polypropylene (PP).
Fittings in small numbers and large sizes can be fabricated in small series. This is a manufacturing method with low investments but also with a relatively high amount of manual labor. The process is widely used for special products and can be tailored for repairing of any pipe system.