PTA Coating for Minimum Wear and Long Service Times

KraussMaffei Berstorff is now offering even more efficient wear resistance for all parallel and conical twin-screw extruders with the plasma powder arc welding process (PTA) for coating the top-root edges of counter-rotating twin screws. PTA coating for minimum wear and long service times "By using the plasma powder arc welding process, we can minimize the naturally occurring adhesive wear in counter-rotating twin-screw extruders and therefore increase the machine service times enormously", stressed Dr. Liebhold, Head of Extrusion Technology at KraussMaffei Berstorff. "A software developed specially for this application permits continuous welding even with incline changes in the flights to be coated and welding of the runouts depending on the selected screw geometry", explained Dr. Liebhold. The system is designed for machining screws with diameters ranging between 43 and 184 millimeters. Counter-rotating twin-screw extruders transport (as a result of the principle of movement) the material almost completely in the axial direction in an enclosed chamber system. In the comb-out area of the screws, the speed and pressure conditions caused by the system result in a so-called calendar effect with flow conditions. In both the solids and melt handling areas, this calendar flow under high surface pressures leads to adhesive wear effects resulting from the screw shafts being pushed apart, and the screw shafts can only support themselves on the barrel. As a result of this abrasive wear mechanism, permanent damage can be caused during manufacturing to screws and barrels, which can sometimes lead to a complete failure of the system. Molybdenum-based PTA hardfacing for standard applications KraussMaffei Berstorff applies wear-resistant molybdenum-based PTA hardfacing as standard to the top root-face edges of all parallel and conical twin screws. Optimized welding process parameters such as, for example, the current in relation to the screw outer diameter and the customized composition of the flux powder ensure the production of PTA-molybdenum hardfacing that is practically free of cracks with the lowest possible dilution especially in the outer areas of the weld. The machines are therefore ideally protected against partial damage such as localized breakages. Additional tungsten-carbide-based PTA coating KraussMaffei Berstorff is also offering a PTA-produced high-wearing surface coating for all parallel twin-screw extruders with tungsten-carbide reinforcement. Tungsten-carbide coatings are used for heavy adhesive wear, for example for the processing of natural fiber composites for decking profiles. As a result, the KraussMaffei Berstorff twin-screw extruders for WPC processing achieve much higher service times compared with standard machines which, depending on the formulation and correct operation of the machines, can add between 12, 000 and 20, 000 operating hours. Even in the event of use of PVC formulations with high filler content (up to 30 parts) and medium filler particle size distributions (larger than 10 μm), tungsten-carbide-coated process units are increasingly being utilized in KraussMaffei Berstorff extruders. Source: kraussmaffei.com