In recent years, the cost pressure faced by manufacturers in pipe extrusion has been rising continuously. Material costs amount to about 80 per cent of total production cost and energy prices are rising. Increasingly shorter delivery times and smaller production batches are also a challenge. In addition, it can be expected that the trend towards thicker walls will also continue.
The economic efficiency of a pipe extrusion line is determined essentially by five factors:
- Output / line speed
- Energy consumption per kg of output
- Wall thickness tolerance
- Flexibility in (dimension) change processes
- Material usage.
New developments have to address these topics.
The quality of the pipe and the length of the necessary cooling section are strongly dependent on melt temperature.
A low melt temperature can only be reached with a sufficiently high specific throughput, i.e. kg output per screw revolution, as well as a screw concept that ensures the complete plastification of the material and prevents unnecessary increases in temperature.
battenfeld-cincinnati’s new solEX NG series offer reductions in melt temperature by up to 10°C thanks to a completely redesigned feed zone with a new screw and barrel concept and grooved bushing. As the load on the system is reduced, energy consumption is decreased by up to 15 per cent and outputs for each machine size increase by up to 25 per cent compared to the original solEX series.
The new plasticising concept offers a lot more possibilities than the conventional technologies, so that further improvements can be foreseen.
Beside the extruder, the tooling is the second core component of every pipe extrusion line. The pipe head is the determining factor when it comes to wall thickness tolerances and has further gained in importance in recent years due to the increase in the production of multi-layer pipes. This trend will continue over the next years.
Continuous dimension change systems will gain more and more importance as production batches are becoming smaller and smaller. This also means that colour changes increase continuously.
A significant reduction in purging times can only be achieved if the steel surface touching the melt is kept as small as possible. According to this, the design of the pipe head has to follow the principle. Outer layers should be applied just before the melt exits the pipe head.
The die set can also be optimised, if the gap has a conical shape and the position of the die can be adjusted against the position of the mandrel. By the help of such a system, the die set is suitable for a number of diameters and pressure classes and changing it is no longer necessary.
Several systems for dimension change during production have been developed. battenfeld-cincinnati’s FDC (fast dimension change) system enables fully automatic pipe dimension and wall thickness changes during running production across a range of diameters from 75 to 630 mm, which is unique in the market.
The FDC calibration sleeve operates with stainless-steel sheets that are moveable into each other. Thus, they enable flexible dimension changes across the diameter range and ensure there are no markings on the pipe surface.
Downstream equipment with FDC functions is available to offer complete, synchronised lines where dimension changes can be started at the push of a button.
Beside the above mentioned topics, new combinations of different materials, especially the use of fibres or other reinforcements, might gain in importance. The goal is on the one hand to reach higher pressure classes in order to replace steel pipes. On the other hand, it will be possible to use thinner pipes for today’s applications and therefore to reduce the material consumption dramatically. The first products are already available and it can be expected that processing technologies will be developed in the field.
Dr Henning Stieglitz, CTO, battenfeld-cincinnati