Extrusion International 2-2026

28 Extrusion International 2/2026 PIPE EXTRUSION, EXTRUSION TOOLING Status Report and Outlook of Pipeheads for Polyolefines Technical requirements and features of pie heads High throuput at low pressure L ow pressure in uences pump - ing energy of extruder, the me- chanical design, i.e. the number and size of screws. This in uences the time required for maintenance and mounting. Low pressure also affects the melt temperature in the extruder. If the pressure at the screw tip is high, the melt temperature will increase. Low pressure has no negative in- uence on plastication because the extruder achieves plastica- tion by shearing and not by pres- sure. That’s why the calculation of pressure build-up is important, as shown before. Finally, the total pressure of the entire system, from the extruder ange to the end of the die, is the sum of the sections. The target is for it to be below 250 bar. Adapters play an important part because, in space-based extru- sion, adapters are sometimes long and can create high pressure if the cross-section diameter is too small. Optimised ow with a minimum of eccentricity and thermal centring Equal circumference owwith the lowest possible eccentricity of the wall is needed to reduce weight and save raw materials. This is especially important for heavy wall pipes. To- day's pipe tools, which are based on spiral distributors, are optimised to the extent that automated me- chanical die centring systems have disappeared from the market. New PE polymers with high strength now have a ow behaviour that causes less sticking to the steel ow chan - nel. This effect improves the ther- mal centring effect, which is well known in PVC processing. The front part of the die is seg- mented into eight or twelve sepa- rate heating zones, and the ow can be in uenced by temperature – a higher temperature in a given segment leads to more ow in that segment. Melt cooler for pipes with high wall thickness Sagging occurs due to the weight of the wall thickness and is a ow effect that occurs outside the die head. This is a polymer behaviour: the higher the viscosity at very low shear rates and the lower the melt temperature, the less the sagging effect. However, there are limits to extruding wall thicknesses over 100 mm. In this case, the head can be equipped with a melt cooler to reduce the melt temperature in the head. This concept also requires the ability to operate the head at a low- er temperature than usual. Inner pipe cooling Higher output rates require a lon- ger cooling time. Up-to-date tools should offer the possibility of cool- ing the pipe from the inside as well, which not only impacts the cooling length, but also the roundness, ec- centricity and internal stress of the tubing after cutting, as well as ex- hausting some evaporated waxes of PE, which would otherwise con- dense on the inner surface. Inter- nal pipe cooling reduces the ther- mal load on the material, as can be seen in the OIT value. High-pressure blowers with an air ow of up to 30,000 m³/hour are used to suck air from the pipe end through the pipe and out of the building. Depending on the SDR ratio, this cooling effect reduces the cooling length by between 5 and 30%. Ad- ditionally, in some cases, the spray tank can be removed from the cool- Picture11 a+b: Internal head cooling PO 250 ABS Picture 10: Thermal centered die (Part 2)