Extrusion International 2-2026

31 Extrusion International 2/2026 mono- or multilayer heads as for the low- and high-output versions. The tolerances for layer thickness are excellent. There are two differ- ent types of coating: the pressure coating and the tube coating. Pres- sure coating is no longer common place due to its many disadvantag- es. Therefore, there is almost only tube coating, with which a large di- ameter range can be covered in the under drawing process. This means that in the smaller dimensions, four pipe diameters can be processed with one nozzle, while the range is smaller for pipe diameters over 630 mm. Similar considerations ap- ply to the coating thickness and the nozzle gap. Typically, only a larger dimensioned gap is needed, which is then gradually reduced for thin- ner layers. The PO XX CR series (CR stands for Cross Head) has small increments, but thanks to the me- chanical design, each head covers a large range. The PO 630 CR is used for the coating of pipes with a di- ameter of 630 to 90 mm. A special feature of CONEXTRU moulding heads is the mounting of the man- drel and the nozzle – both from the front – in the moulding state. The position of the extruder can be realised according to customer requirements and can be mounted from the left or right at any angle, or from above. The head is xed to the base, while the extruder is mounted on wheels to allow move- ment to accommodate length ex- pansion and reduce tension. Under pressure is required for the tube coating process, which is generated via a small side channel compressor and regulated via PLC using motor speed. Small cross heads are used for bundling small pipes for optical bre protection. Multilayer cross heads The applications of multi-layer coating heads are rare and are lim- ited to the following areas: Two-layer tools for steel pipe coating with primer and polyeth- ylene, applying adhesive strips between PP and PE for improved adhesion and get easy peel ability, applying multilayer with barrier on drinking water pipes, under oor heating pipes with coating of an oxygen barrier, jacketing pipes on PU-insulated pipes with barrier materials to reduce gas exchange keeping isolation properties, coat- ing of high- lled barium sulphate to increase the sink ability of pipes and many others. To distribute the melt (low- or high-viscosity & output) the tried- and-tested standard spiral distribu- tors from CONEXTRU are used. An accurate distribution of the layers guaranteed also for this heads. For particularly thin layers, such as ad- hesion layers and for smaller pipe dimensions, the radial distributor is also used. As the use of multi-layer tools is limited, all these construc- tions designed so that they can easily be converted to mono-extru- sion. An example of this is the PO 4 400 CR EVOH, which can be used as a single-, double- or 4-layer system with EVOH, either with PP or PP/Ad or PP/Ad/EVOH/Ad. The nozzle con- struction, design, vacuum control, sealing and assembly are identical to those of the mono crossheads. The PO XX CR EV IL series starts at 10 mm with each variant currently being a special order. A special variant of Cross Head is used in the pipe-in-pipe production of fuel lines, where another multi- layer pipe surrounds a pre-existing multi-layer pipe without touching it, as a protective pipe. In this case, the production of a 3 layer (PE/Ad- hesive/EVOH) protection pipe over a 4 layer PE pipe for fuel transporta- tion in petrol stations: Pipeheads with rotating mandrels and or dies For special applications, pipes can have spiral ribs on the inside. For ex- ample: Vertical drainage pipes have spiral ribs on the inside to put the water into rotation. This allows it to ow faster with less noise. Simi - larly, cable protection pipes have spiral ribs to reduce friction. This is achieved by rotating the mandrel that creates these ribs. Summary The trend of multilayer pipes will continue with new polymers and new applications, larger sizes. Espe- cially technical polymers with high chemical resistance and high tem- perature use such as Fluoropoly- mers, PA, PPS, Polyketon and oth- ers. This trend requires exibility in engineering and new individual design of pipeheads By Josef Dobrowsky CONEXTRU Klosterstarsse 19, 3011 Irenental, Austria Dobrowsky.j@conextru.eu Picture 20: Cross section PE//Ad//EVOH layer Head PO 3 180 CR Picture 21: Crosshead for pipe in pipe making protection pipe 3 layer Picture 22: 4 layer fuel pipe with 3 layer protection pipe with ribs