From PP-RCT to 7-layer pipe extrusion

• Company: Bänninger Rohrleitungssysteme, Germany
• Process: multi-layer pipe extrusion
• Material: PP-R, PP-RCT, incl. GFR (glass fibre reinforced)

Bänninger Rohrleitungssysteme is a 100% subsidiary of Bänninger Kunststoff-Produkte in Reiskirchen, Germany. For more than 20 years, these companies have been manufacturing complete PP-R piping systems. In addition to the pipes, the product range includes PVC and PE pipe couplings, fittings, fixtures, pipe tooling and other accessories. All extrusion lines have been supplied by Battenfeld-Cincinnati.

For the pipe production, the company operates four extrusion lines of different sizes, with capacities ranging from 1,000 to 6,000 t/a, on which pipes with diameters from 16 to 400 mm are produced. Various fittings and accessories are produced on 18 injection moulding machines. 80% of the manufactured pipe systems are exported, primarily to Saudi Arabia and other Middle Eastern countries, to North Africa, for example Morocco and Tunisia, as well as Latin America, for instance, Argentina and Brazil. For the Middle Eastern growth markets in particular, Bänninger built its own production plant in Dubai in 2007, which has also been laid out for four extrusion lines.

PP-RCT offers significant material savings

PP-R pipes, manufactured from a polypropylene (PP) random copolymer, are mainly used for transporting hot and cold drinking water and for heating systems. Additional applications are found in plant engineering, in greenhouses and rainwater harvesting. These pipes are characterised by their durability, good resistance to corrosion and easy laying properties. Due to their high molecular weight and thermal stability, these pipes are particularly sturdy and resistant to heat, chemicals and pressure. And pipes made of the special PP-RCT grade can be produced with even thinner walls than conventional polypropylene pipes giving the processor the advantage of less material consumption. PP-RCT is a random copolymer with improved crystalline and molecular structure which features increased strength and resistance to temperature (“R” indicates the structure of random copolymer polypropylene, “C” stands for crystalline structure, and “T” stands for improved hydrostatic strength at elevated operating temperatures).

Bänninger states that they are using the PP-RCT compound from Borealis since 2005. It allows material savings of 17% compared to the types of material they have used previously, and the pipes have been approved for a higher pressure class as well, in spite of their thinner walls. Thinner walls with the same outer diameter also offer a 17% increase in the flow volume together with a reduced sound level.

Glass fibre reinforcement brings additional benefits

The mechanical strength of PP pipes can be further improved by incorporating a glass fibre reinforced (GFR) middle layer in multilayer pipes. Bänninger is currently producing about three quarters of all their pipes with glass fibre reinforcement.

According to the company, conventional “Stabi” composite pipes could be entirely replaced by GFR pipes, as their longitudinal thermal expansion rates are almost the same. Stabi composite pipes have comparable properties, but they are much more difficult to connect, since the outer layer must be peeled off at the joints first in order to do so. By contrast, GFR PP-R pipes can be connected with each other by socket welding following simple, short heating-up. Laying glass fibre reinforced PP pipes are said to have an extremely low expansion coefficient. Due to their high stability, the distance between clamps can be increased compared to conventional plastic pipes, which saves both fastening clamps and labour.

PP-R pipe extrusion line with seven layers

All extrusion lines operating at Bänninger have been supplied by Battenfeld-Cincinnati, including a 7-layer PP-R pipe extrusion line installed at the production facility in Stassfurt, Germany. The single-screw extruder is equipped with a barrier screw with customised screw design in combination with a grooved barrel feed section. The processing unit features high wear resistance allowing the processing of extremely abrasive GFR materials.

Another vital component of this extrusion line is its helix WPO pipe die with a multilayer spiral mandrel distributor. The spiral mandrel distributor ensures high throughput, exact wall thickness distribution and a long service life thanks to low dwell times of the melt in the die. Dimensioning of the flow channels has been designed with the help of a proven flow simulation software available in-house. This enables optimal melt flow conditions with minimal loss of pressure. All surfaces which come into contact with the product are provided with a special coating to minimise wear and prevent damage to the flow areas.