Coated screw
A tungsten carbide ball technology that uses extremely small particles that are only a little larger than the particles in cigarette smoke has been used to produce coatings suitable for single and double plasticizing screws, which are superior in wear resistance and corrosion resistance. Standard coating formed by high temperature oxygen fuel (HVOF) thermal spraying. Nordson Corporation will introduce this technology at K 2016 (Building 11, Hall A26).
Nordson's new Xaloy® MPX thermal spray coating consists of particles with a diameter of only 5 microns. These particles are mainly composed of tungsten carbide, which is only one-sixth or even one-seventh the volume of the particles in the standard HVOF coating, and its density is also increased by the uniform spherical shape produced by the controlled plasma process. Ultrafine particle size, higher coating density, and a coating speed that is 2.5 times higher than previously increased the bond to the screw parent metal and improved wear resistance.
Compared to the standard HVOF tungsten carbide coating, Xaloy MPX technology reduces the mass loss in the ASTM G65 wear test by 61%, the mass loss in the ASTM G77 sliding wear test by 18%, and the bond strength in the ASTM C633 bonding test. 8.5%. As an example of corrosion resistance, the salt spray test of the Xaloy MPX coating has a tolerance time of 1,000 hours, in part because its porosity is close to zero.
Mark Colella, global product manager for the Xaloy brand, said: "The Nordson Xaloy MPX screw coating provides superior wear protection compared to standard HVOF coatings, and its higher bond strength eliminates the possibility of flaking. This latest technology Extends the working life of the screw in extrusion and injection molding, enabling processors to process some of today's most challenging materials."
Screw coating process
Spherical MPS coated particles
Nordson recommends Xaloy MPX technology to protect against wear from moderate (15% to 35%) fillers and from halogenated materials including flame retardants and PVC. For compounds with a filler content of more than 35%, Nordson offers a high hardness coating Xaloy® X-8000.
The new Xaloy MPX technology can be used on a variety of screw diameters and can be applied to the entire screw or specific location. The standard layer thickness is 300 microns and the difference depends on the location of the screw. The MPX screw coating should be used with a liner of Nordson Xaloy® X-800® nickel/tungsten carbide or a similarly lined cartridge.
Xaloy MPX technology extends the high-wear applications of Nordson screw packages. Xaloy® X-8000 is a nickel-based coating with a high tungsten carbide content. It is first used in the HVOF process and then sintered to the parent metal of the screw for metallurgical bonding.
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