Extrusion International 1-2026

26 Extrusion International 1/2026 PIPE EXTRUSION, EXTRUSION TOOLING Status Report and Outlook of Pipeheads for Polyolefines (Part 1) Since 1985, CONEXTRU and its founder, J. Dobrowsky, have been involved in the continuous development of new pipe heads. This means that over 3,500 pipe heads designed and built during this period are currently in operation worldwide. I t all starts with the core compo- nent: the spiral distributor. It is the most effective melt distribu- tion system available. It is the most widely used system in extrusion applications, including the pro- duction of smooth and corrugated pipes, as well as in blow moulding, blown film and cable production. CONEXTRU uses both helical and radial spiral distributors for pipe applications. Two different spiral geometry designs are used for monolayer heads with high or low through- put. Both designs produce a spiral- shaped layered structure in the pipe with the least possible eccen- tricity. These geometries are also used for technical polymers such as PA, ABS, PVDF, PMMA and others. In addition to the standard spiral geometries, there are two more geometries for low-viscosity melts. These four basic geometries can be used to design a multilayer pipe head for all possible pipe layer con- structions. Technical background The spiral distribution system re- quires the flow channel to be calcu - lated. No other distribution system depends so much on calculations as the helical spiral. This calcula- tion also requires the viscosity data of the polymer over shear rate. Ge- ometry optimisation based on mak- ing small changes to a starting ge- ometry. After each calculation run, the result to be analysed is the leak flow. The leak flow curve shows the amount remaining within the spi- ral channel and the amount going out of the spiral channel into an axial flow. This curve, showing ax - ial flow over channel length, is the leak flow, which should resemble a Gaussian distribution with a maxi- mum in the middle. Once the best distribution has been achieved, the optimisation process is complete. The leak flow of the final spiral ge - ometry is also calculated at high and low throughput rates. It is observed that the maximum position changes little at high and low throughput, meaning the quality of the distribu- tion is independent of the output. Scale up As the calculation is based on one channel along its length, a new pipe head is initially generated by the number of channels. Therefore, we can predict exactly how the distribu- tor will behave in terms of melt dis- tribution when it has X spiral chan- nels. At the same time, we can calculate the output based on the diameter because the throughput is propor- tional to the number of channels.If such a geometry defined, it will be used for all the heads, so there is no need to make this calculation for each new head. Over the years, it has emerged that only four geometries are need- ed for mono and multilayer heads, for high and low output, and for high and low viscosity materials.In pipe extrusion, we work with poly- Pic. 1: Spiral shaped layer structure of pipe made by spiral distributor Pic. 2: Function of helical spiral