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New production line

New machine for fabrication of thermoplastic tanks


The engineering company Krah AG, worldwide known for production lines for large diameter pipes and leading in the technology of helical extruded pipes has developed a new production line for cylindrical tanks. The new line “Solid 1” is specially designed for the market of thermoplastic tanks, apparatus and ventilation systems. This new development was mainly attributable to the high technical and commercial requirements of the market as potential customers are always looking for high quality products, maximum production flexibility and of course efficiency relating to the output.




Up to now, most plastic fabricator are predominantly using prefabricated and semi-finished products (sheets) for the production of thermoplastic tanks out of PE or PP. The sheets are formed to a cylindrical figure. The joints are welded by extrusion or butt fusion welding. A more homogenous method is to use a helical wound or extruded spiral pipe. But to obtain a helical wound pipe from a supplier, means to invest extra costs into transport and also to lose flexibility in the production process.

Therefore the best solution is to have their own slim helical extrusion process machine which makes the manufacturer of plastic tanks and apparatus much more independently and free regarding innovative and customized solutions - like inter alia multilayer pipes, double wall tanks, special wall constructions or regarding to the diameters and colours of the pipes.

This situation was the main reason for Krah to develop a new generation of machines which are designed in order to increase the efficiency even at lower quantities. The investment in a helical extrusion process machine for the production of cylinders depends on the overall market situation and company experience and is worthwhile starting from quantities of 100 tons per year. This comprises a volume of approximately 200 storage tanks in common dimensions.

The output performance of the machine is 500 kg/h. It is possible to produce 500 tons in one year with a 3-shift system, 24 hour operation and sufficient mandrels. The energy consumption is only 1,2 kW per kg plastic.

Even billets and cylinders with wall thicknesses up to 200 mm can be manufactured. As the required wall thicknesses can be produced very precise, there are enormous material and cost savings. In addition it is possible to fabricate tailor-made wall constructions, which is a huge advantage regarding competitors.
The homogenous integration of supports, stepped wall thickness, edge reinforcements and flanges is providing more flexibility in the production process. The height of one step of a stepped wall thickness is 4-5 mm, but it depends on the minimum thickness of one layer.

The helical extrusion process is providing the opportunity to produce functional layers with special properties. Some examples are mentioned as follows:

  • electro conductive inside or outside layer for PE- and PP- tanks – necessary for applications of explosive gases (environment)
  • light inner layer for PE or PP, for the inspection of inner surface of tanks and pipes
  • outside protection layer – for example against UV-radiation
  • inside layer out of polymers with a better chemical and crack resistance for the application of hazardous and aggressive liquids

Such functional layers can be integrated with the help of the optional available Co-extruder with the main extrusion flow, which reduces the production time considerably.

The cylinders were produced on special steel mandrels which are available in standard diameters from DN 800 up to DN 5000.
The tank fabrication of nominal diameters 1500, 2000, 2500, 3000 and 3500 is playing an important role. The standard lengths of the mandrels is 7 meter, so that cylinders up to a length of 6 meter can be produced.

Mandrels up to a length of 13 m, for the production of long pipes, silos or chimneys are available since 2010.

Krah offers with the new slim production machine a reasonable entry into the plastic winding technology. In addition, Krah is providing a full start-up service for the adequate implementation of the production machine at the particular market.


Stephan Füllgrabe,
Plaspitec GmbH