3 layer pipes from random copolymer and homopolymer for use in hot water application

3 layer pipes made of PP-R with a glass fiber reinforced middle layer are being offered as an alternative to conventional heating and sanitary pipes for hot and cold water transport in the construction industry. The pipes consist of two outer PP random polymer layers and a middle layer made of PP homopolymer filled with 10-20% weight component of short glass fiber. The normal distribution of layer thicknesses in the three-layer pipes varies between 25:50:25 and 33:33:33. The main advantages of these pipes are:
• An increase in stability and e-modulus is achieved by glass fiber reinforcement.
• The glass fiber content reduces the lengthwise expansion of the pipes especially in hot water transport and consequently lessens their deflection.
• These pipes facilitate the installation of heating and sanitary pipes with larger intervals between fixtures.

The developer of the equipment for these new three layer pipes, Cincinnati Extrusion, recommends an extruder combination consisting of two single-screw extruders. The extruder for the inner and outer layers is equipped with a 30 D processing unit including a grooved feed section while the extruder for the middle layer has a length of only 25 D and a smooth processing unit with special anti-wear protection for processing PP with glass fiber content. The die, an IRIS 25-3 coex triple spiral mandrel die, is suitable for all pipe dimensions from 16-250 mm and can be adapted very easily to different layer thickness distributions. It belongs to the proven series of IRIS pipe dies featuring optimally designed spiral distribution channel geometries and flow channels. Apart from their fast and easy cleaning properties, IRIS dies stand out above all by their low pressure build-up, low shearing stress and short dwell times. In this way, they ensure optimal melt distribution and narrow thickness tolerances. A special gloss heating element in the die guarantees an absolutely smooth inner surface for the pipe. One special feature of the line concept is the downstream equipment for pipes up to 63 mm in diameter. Pipes up to 32 mm are normally cooled in a full bath. Spray cooling is used for larger pipe diameters. To cover both variants with a single downstream unit, the machine manufacturer has designed a variable water cooling bath, which, depending on the application, can be switched over from spray bath cooling to full bath cooling without any effort involved in the changeover.