Continuous production of PU foam-insulated pipes in one system

KraussMaffei Berstorff is now offering complete systems for continuous production of PU-insulated pipes. The extruded plastic pipe is given an insulating polyurethane layer, followed immediately by the addition of a protective polyethylene sheath.

PU-insulated pipes are used to transport both hot and cold media

The pipe – made of PE-HD, PE-X, PE-RT or PB according to the application – is produced on a conventional pipe extrusion line. A barrier layer can be applied. The pipe coming off the line is wound onto large steel drums ready for transfer to the second production system unit for application of the insulation layer. Alternatively, the insulation layer can be added to bought-in pipe. In this second unit, the pipe is unwound from the steel drums, heated if necessary, and fed under tension into a shaping conveyor.

A PU mixing head dispenses the polyurethane mix at the inlet throat. The aluminium shaping jaws define the outer diameter of the insulation layer by limiting the foam volume. A film prevents the polyurethane from adhering to the aluminium shaping jaws. Once the PU insulation layer has cured, the pipe leaves the shaping conveyor and a PE outer sheath is applied, using a single-screw extruder with a sheathing die. This outer sheath is cooled, the whole composite pipe is hauled off and wound on a drum. The system allows the integration of anti-diffusion barrier layers and/or wires to monitor leakage.

The standard version of this production system can be used to produce pipe with an outer diameter 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). 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.

The PU mixing head produces an insulation layer with a very low thermal conductivity – between 0.02 and 0.03 W/m*K, depending on the type of foam. This highly efficient insulation makes these pipes the ideal solution whenever a significant temperature differential must be maintained between the medium flowing through the pipes and the ambient temperature. In some cases, the medium being transported is hotter – such as supply lines for combined heat and power or geothermal plants, or hot water pipelines in general. Insulated pipes are also sometimes required for potable water transport if there is a risk of the pipes freezing. In other cases, the medium must be kept cold or cool, for example, in air conditioning or refrigeration systems, or in pipes for transporting liquefied gas. With the current focus on energy savings, strong growth in demand can be expected in all these application areas.

Producing insulated pipe in a continuous process has several advantages compared with discontinuous production. One major advantage is the relatively high level of automation that results in lower labour costs. Furthermore, there are virtually no limits on the length of the pipe being produced. Contributing to this wide freedom is the design of the PU mixing head, which eliminates stoppages for cleaning and changing the mixing head. Longer pipe sections reduce the number of production system restarts and also the number of connections needing to be made when the pipe is laid. This in turn eliminates the risk of thermal bridges and leaks, and makes pipe laying easier and quicker.