Extrusion International 3-2026

28 Extrusion International 3/2026 CONEXTRU – always applies the concept with a grooved feed section for technical polymers such as PA, ABS, PMMA, PC, EVOH, PVDF, PFA, MFA, ECTFE, and also for PK. The screw geometries for technical polymers so often recommended by raw material manufacturers, in combination with a smooth feed zone, primarily have the disadvantage of low feed rates, uctuating feed behaviour, and non-linear feed behaviour across the speed range. In contrast, there are the characteristics of the grooved feed zone. This grooved feed zone is available in CONEXTRU standard straight-grooved design – mean- ing there is no special groove shape or number com- pared to polyole n processing of PE and PP. The dif - ference lies solely in the temperature control. While polyole ns are processed with the feed bushing kept as cool as possible, these engineering polymers are pro- cessed with a heated feed bushing – because most plas- tics are preheated and enter the feed zone at a higher pellet temperature. However, the higher feed screw temperature also results in a slightly lower conveying capacity per revolution, thereby ensuring gentle, stable conveying of solid materials. A closed-loop system us- ing silicone oil is employed for feed screw temperature control, allowing a temperature range between 20 and 250°C to be set depending on the material. Grooved feed zones offer the advantage of abso- lutely stable feeding due to the nut-spindle effect. In more technical terms, this is due to the compression and friction between the grooved bushing and the material, as well as minimal friction between the screw base and the material. Furthermore, it has been shown that a barrier screw also offers advantages; there are numerous ways to design a barrier screw. One of the most inuential parameters is the barrier gap and the length of the zone. This allows for gentle shearing over a long zone. It is recommended to start the extruder with PP – using standard processing temperatures for PP and to switch to PK once the extruder and die are lled. If unmolten particles are visible, higher temperatures should be set. These can also be raised to up to 260 °C contrary to the raw material manufacturer’s recommendation. It is important to ensure that no cross-linking or yel- low discoloration occurs. These higher temperatures are possible and necessary because the residence time in groovedmachines is signi cantly shorter than in smooth extruders for the same output. A short residence time prevents cross-linking. The extruder is shut down using the PP ushing process. Outlook for PK in Pipe Extrusion The growth of polyketone (PK) is skyrocketing as it evolves from a niche product into a genuine strategic alternative to established engineering plastics. Here are the key trends for the coming years. Annual growth is projected at approximately 5%. Another key factor in its success is its environmental pro le, as its production uses carbon monoxide and does not contain free form- aldehyde, unlike POM, for example. The extrusion concept presented here, featuring a grooved feed section and a barrier screw, enables ef - cient processing and is also suitable for higher output rates through larger machine sizes. By J. Dobrowsky CONEXTRU GmbH Klosterstarsse 19, 3011 Irenental, Austria Dobrowsky.j@conextru.eu EXTRUSION TECHNOLOGIES Specification and special kriterias for PK extrusion Alternativ supplier CONEXTRU Extruder diameter, mm 90 45 L/D 30 30 Barrel heating zones 4 heating cooling 4 heating cooling stronger heaters Intake design Smooth 0,5 D long Straight grooved 4,0 D long Feed temperature °C 20 80 Target ouput kg/h 100 100 Spec. Energy of PK Wh/kg 350 350 Installed motor power kW 90 33 Circumferance speed at output recomanded below 0,3 m/sec 0,4 0,2 Screw type 5 zone design barrier type 22 D long barrier part Mixing Elemnts no recomanded possible streamlined Material Type Extruder / max. RPM / kW max. Ampere Motor / max. RPM Motor type of feed bush Screw Heating / Cooling Zone Material Temperature after drying °C 80 Feed bush °C 100 100 E 1 °C 240 240 E 2 °C 230 230 E 3 °C 230 230 E 4 °C 220 220 Adapter °C 220 220 Throttle Valve °C 220 220 Speed Screw RPM Motor speed RPM Melt temperature in Adapter °C Melt temperature on floor °C Melt pressure Trotthle valve bar Output manual kg/h Spec. Output kg / RPM h ENERGY MOTOR Electric current Motor A Load Motor calculated from Amp % Motor power kW 27 82 55 1,25 266 225 230 793,6 Run sheet of C 45 30 Extruder 80 100,0 C 45 30 150 33 67 A / 1500 RPM HYOSUNG / POLYKETONE set / actual straight grooved M 730 R intake, transmission, barrier part, short mixing Table 1: Extruder concept comparison Table 2: Extrusion protocol