Extrusion International 1-2025

31 Extrusion International 1/2025 PIPE EXTRUSION Extrusion System for ABS Foam Core Pipes The foaming of thermoplastics is a process known to the state of the art, in which a fundamental distinction is made between chemical and physical foaming. This article deals with chemical foaming, in which it is possible to achieve dense reductions of up to 40 % with the aid of blowing agents in powder or granules form. Applications can be found in pro- le, sheet and pipe extrusion. Foam core pipes are used in the pipe ex- trusion sector. PVC foam core pipes have a market share of almost 100% in the segment of non-pressurized drainage pipes with a diameter of up to 400 mm. Applications for PE, PP and ABS- foamed pipes exist on the market for non-PVC pipes, albeit to a much lesser extent. Foamed pipes have a lower overall density, which leads to weight and cost savings. This ar- ticle deals with the extrusion of ABS foam core pipes. ABS pipes are used as a PVC re- placement in certainmarkets as they have high impact strength, even at lower temperatures, and are more chemically resistant. Extruders With regard to the extrusion of ABS, it should be noted that pre- drying at 80 °C for four hours with dried air is essential, regardless of the type of extrusion. In sheet ex- trusion, a variant with a smooth feed zone and degassing zone in the barrel has proven itself, espe- cially for higher outputs of well over 1,000 kg/h. However, this process has certain disadvantages. How- ever, the process has certain disad- vantages. For example, degassing extruders require a melt pump and the disposal of residues from the de- gassing zone often proves to be dif- cult. Extruders without degassing are therefore used for outputs of up to 800 kg/h, whereby raw material manufacturers recommend the use of extruder barrels with a smooth feed zone. One disad- vantage of these barrels, however, is their poor feed be- havior with all sty- rene polymers, in- cluding ABS, which leads to uctua - tions in pump and output behavior. CONEXTRU, on the other hand, takes a different approach and uses grooved feed zones. These are stable and do not exhibit any feed uctuations. The high coef cient of friction be - tween the screw and the grooved feed zone results in a high speci c output (kg/RPM). The resulting forc- es are reduced by reducing the com- pression in the infeed compared to PE and warming up the grooved bushing. For this purpose, an ex- ternal temperature control unit is used, which works with silicone oil and enables temperatures of up to 200°C. Although such high temper- atures are possible, they are not ab- solutely necessary and it is usual to operate the feed zone at 80 °C. The necessary pre-drying at 80 °C heats