COATINGS IN POLYMER PROCESSING - CRXN COATINGS PRODUCED BY PVD-MAGNETRON SPUTTERING (MSPVD) OPEN NEW POSSIBILITIES IN THE FIELD OF WEAR PROTECTION FOR POLYMER PLASTICIZATION UNITS

For several years hard coatings have been used in plastic processing. The reduction of adhesion and contamination effects play a more and mo re important role besides the wear protection of injection moulds and extrusion tools. Applications of hard coatings in the field of highly stressed screws and barrels of plastification units are very seldom. I n these cases the tribological effects are very intense so that the de manded wear resistance of hard coatings in the range of 10 mu m is not sufficient. Different hard coatings based on titanium and chromium we re tested according to their applicability for wear protection of scre ws in plastification units. Thickness, hardness, internal stresses and adhesion of the coatings were studied. Afterwards tribological tests in a model testing unit were investigated. Here the coatings were stud ied under tribological conditions, similar to those in a real plastifi cation unit. The CrxN multilayer coatings showed extremely better wear resistance than the titanium based coatings. For this reason the CrxN coatings were optimized by help of the deposition parameters. These o ptimized coatings have been investigated according to their applicabil ity for different polymers in comparison to other coating systems. Fir st tests of CrCN/TiCN coated screw elements in practice showed very pl easing results. The test in practice with the optimized CrxN multilaye r coating has yet to take place, but in the model tests the CrxN coati ngs showed excellent results.