Nanoparticle coating for plasticating screws features higher wear resistance than standard thermal-spray tungsten carbide

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  • Thermal spray coating made up of particles only 5 microns in diameter
  • 61% less mass loss in abrasion tests
  • Applications: from filler compounds to halogenated materials

A technology that uses exceedingly tiny tungsten carbide spheres barely larger than the particles in cigarette smoke has yielded a coating for single and twin plasticating screws that resists abrasive and corrosive wear better than standard coatings applied by high-velocity oxygen fuel (HVOF) thermal spray.

Thermal spray coating made up of particles only 5 microns in diameter

The new Xaloy MPX thermal spray coating from Nordson is made up of particles only 5 microns in diameter. Consisting primarily of tungsten carbide, the particles are six to seven times smaller than those in standard HVOF coatings and more densely packed owing to a uniform spherical shape produced in a controlled plasma process. The combination of ultra-fine particle size, higher coating density, and a 2.5 times greater application velocity results in a stronger bond with the parent metal of the screw and improved resistance to wear.

Wear-resistant MPX Coating on screw flight

Wear-resistant MPX Coating is shown on cross section of screw flights (source: Nordson)

61% less mass loss in abrasion tests

Compared with standard HVOF tungsten carbide coatings, the Xaloy MPX technology exhibits 61% less mass loss in ASTM G65 abrasion testing, 18% less mass loss in ASTM G77 sliding wear testing, and 8.5% greater bond strength in ASTM C633 bond testing. As an example of corrosion resistance, the Xaloy MPX coating survived more than 1,000 hours of salt fog testing, in part because of its near-zero porosity.

Spherical nanoparticles of coating

Greater wear resistance of Xaloy MPX screw coating results from spray coating process that applies tungsten carbide particles only 5 microns in diameter, six to seven times smaller than those in standard HVOF coatings and more densely packed owing to a uniform spherical shape produced in a controlled plasma process. The combination of ultra-fine particle size, higher coating density and a 2.5 times greater application velocity results in a stronger bond with the parent metal of the screw and improved resistance to wear (source: Nordson)

The Xaloy MPX technology can be employed across the full range of screw diameters and may be applied to the entire screw or to specific areas. Standard layer thickness is 300 microns, with variations depending on the area of the screw. The MPX screw coating should be used with a barrel lined with Nordson’s Xaloy X-800 nickel / tungsten carbide alloy or a comparable inlay.

Applications: from filler compounds to halogenated materials

Nordson recommends the Xaloy MPX technology for resisting abrasion from compounds with medium (15 to 35%) filler loadings and for resisting corrosion from halogenated materials, including flame retardants and PVC. For filler content above 35%, the company supplies the high-hardness coating Xaloy X-8000.

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