Extrusion or calibration die for production of thermoplastic extrudates has die inserts forming the die orifice wall made of a sintered material harder than steel

摘要

A wall(10) of the die orifice(8) along which extruded material flows under pressure includes a wear resistant sintered material with a hardness either greater than that of steel and/or not less than20GPa according to the Vickers scale. The Vickers hardness is preferably 20-26GPa, and more preferably 22-25GPa. A sintered material employed has high corrosion resistance and shows no change after 100hrs in contact with 36% HCl or 65% HNO3 or 96% H2SO4 or 85% HP3O4 at 90degreesC. Sintered material hardness and/or material type are selected to allow machining of the wall or die orifice using wire erosion. Heat conductivity is 100-150W/mK, preferably 110-130W/mK. Material thickness in the direction of heat extraction, particularly for a calibration die is either set to ensure adequate heat extraction and/or is 0.1-15mm thick. The sintered material may form a complete insert or forms several inserts(4-7) which are mounted in the die body(2). Mean particle size of the sintered material is 3-12 microns, preferably 5-10 microns and compression strength is 2500-3800MPa, more preferably 2700-3600MPa and even more preferably 3000-3500MPa. Open porosity approaches 0%.