GRP pipe

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GRP - pipes consist of G las f aserverstärkten K unststoffen (synthetic resin). As a result, their mechanical resilience increases significantly compared to pure plastic pipes, which ensures them a wide range of applications. GRP pipes are used, for example, as a compressed air supply or for water supply, but the main area of ​​application is any kind of sewage transport , as sewage pipes in the sewer system . In the area of ​​pressure pipelines, there has been around 50 years of experience with GRP pipes. They meet different requirements, depending on the manufacturing process and the raw materials and additives used . GRP pipes are manufactured in various nominal sizes , ranging from DN 25 to DN 8000 (for double-walled pipes), and are offered in standard lengths of 6 m, 12 m, 18 m especially for sewer pipes. GRP pipes are superior to HT pipes or KG pipes in terms of heat resistance, expansion behavior and rigidity, which enables, for example, larger spans.

As with any fiber composite material , the properties result from a “division of labor” through the choice of materials, the orientation of the fibers and the manufacturing process. The mechanical properties such as tensile strength , compressive strength and modulus of elasticity result from the amount and type of glass . The choice of resin results in the chemical resistance and temperature behavior of the composite.

A rough distinction can initially be made between sewer pipes (reinforcement only in the circumferential direction, fillers) and pressure pipes (reinforcement in circumferential and axial direction, no fillers).

According to the type of manufacture, GRP pipes are further subdivided into centrifugal pipes, spiral pipes and pulling pipes.

production method

Centrifugal process

In the centrifugal process, reinforced fabric or scrim is first introduced into a hollow mold in the longitudinal and / or circumferential direction and then impregnated with unsaturated polyester resin, which is fed to the rotating mold (die) by a feeder. The wall construction takes place under high centrifugal forces (up to 70 g) from the outside to the inside. This process was first used by the HOBAS company in 1957 .

  • GRP pressure pipes

GRP centrifugal nozzles without additives meet the highest demands in terms of chemical resistance and abrasion resistance. Only with this manufacturing process can a 100 percent pure resin layer be produced. An excess of resin adjusts the thickness of the inner protective layer made of pure resin, which effectively prevents any hydrolysis of the glass. As a result, GRP centrifugal nozzles have a very high resistance to chemical stress.

  • GRP sewer pipes

If sand or other fillers are added to the synthetic resin during the production of centrifugal pipes, the strength values ​​drop extremely, but this is not decisive for underground pipes, since the wall thickness is entered here with the power of four, while the modulus of elasticity is only a power of one. Due to the lower use of synthetic resin, the material costs and thus the price also decrease considerably.

Winding process

Here, endlessly long glass threads ( roving ) are guided over a wide comb onto a core mold, where they are wetted with resin and wound onto the mold. There are also variants in which the mold is wetted and the thread is inserted into the resin. This technique can be refined by varying the winding angle and adapting it to the requirements (e.g. with pressure pipes at a winding angle of 54 ° to the pipe axis). With this production method, too, efforts are made to achieve the highest possible resin content inside the pipe. For this purpose, at the start of production of the pipe, a fleece or mat is introduced as a carrier for the resin.

Sewer pipes are also manufactured using the winding process, in which the components resin, quartz sand, glass (as short fibers) and glass roving (a glass thread) are dosed on a fully automatic winding machine and applied to the core. The wall thickness is built up by metering the quantities. A variant of the winding process is also known as the Flowtite process .

Drawing process

GRP pipes can also be manufactured using the extrusion process . GRP draw pipes are not designed for internal pressure due to the nature of the structure . Due to their good mechanical properties (high glass content), they are mainly used in construction .