Munich, Germany - Machinery specialist KraussMaffei Berstorff (KMB) is now offering complete systems for the continuous production of PU-insulated pipes. In this process, a plastic pipe is extruded and then coated with an insulating polyurethane layer, followed immediately by coating the PU foam with a protective polyethylene sheath.
KMB claims to have many decades of experience in pipe extrusion and in PU processing which allows it to develop such complete solutions - ones which, "successfully integrate different plastics processes."
KraussMaffei Berstorff says it can now quote on complete, precision-planned systems to make the media pipes and to applying the insulating layer and protective sheathing. The company claims that, in contrast with other systems on the market, its technology is characterised by sharply reduced wear on all system components, high system reliability and a high-quality end-product.
The inner pipe -- made of various types of polyethylene or polybutadiene -- is produced on a conventional pipe extrusion line, and a barrier layer can be applied. As the pipe comes off the line it is wound onto large steel drums, KMB says.
A second unit unwinds the pipe from the steel drums, heats it if necessary, and feeds it under tension into a shaping conveyor. A PU mixing head dispenses the polyurethane mix at the inlet throat, while aluminium shaping jaws define the outer diameter of the insulation layer by limiting the foam volume. A film prevents the foam from adhering to these jaws.
Once the PU insulation layer has cured, a PE outer sheath is applied, using a single-screw extruder with a sheathing die. This outer sheath is cooled, and the complete composite pipe is wound onto a drum. KMB points out that this system allows integration of anti-diffusion barrier layers and/or wires to monitor leakage.
The standard version of this system can make pipe with an outer diameter of between 20 and 110 mm. For pipe diameters from 20 to 63 mm, a complete pipe element usually contains two pipes (outflow and return pipes) -- see photo. The exterior diameter of the pipe element will then be between 75 and 180 mm, depending on the diameter of the pipes and the thickness of the insulating layer.
KraussMaffei Berstorff claims that the "outstanding mixing performance of its PU mixing head produces an insulation layer with very low thermal conductivity," - between 0.02 and 0.03 W/m*K, depending on the type of foam.
Such efficient insulation makes these pipes valuable when users must maintain a significant temperature differential between the fluid flowing through the pipes and the ambient temperature.
In some cases, KMB points out, the medium being transported is hotter - in supply lines for combined heat and power plants or geothermal plants, or in hot water pipelines in general. Insulated pipes are also sometimes used for potable water if there is a risk of the pipes freezing.
In other cases, users need the medium to be cool, for example, in air conditioning or refrigeration systems, or in pipes for transporting liquefied gas. KMB concludes that "With the current focus on energy savings, strong growth in demand can be expected in all these application areas."