machinery | Wear protection
specialist Carbodeon with German metal finishing specialist CCT Plating. Although developed for sliding wear applications, Carbodeon says it also considers the technology to be suitable for applications in extruder screw and barrel protection as it overcomes the traditional susceptibility of electroless nickel coatings to adhesive wear. Electroless nickel coatings provide good corrosion
Figure 2: Hardness values for the Carbodeon/CCT Plating hard coat against standard electroless nickel finishes Source: Carbodeon
particle size, higher coating density, and 2.5 times greater application velocity is claimed to provide a stronger bond with the parent metal of the screw and improved resistance to wear. Compared with standard HVOF tungsten carbide coatings, the 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. Compared with nitride case hardened screws, Nordson estimates that MPS coatings provide three to four times longer abrasive wear life. And in terms of corrosion resistance, the Xaloy MPX coating survives more than 1,000 hours of salt fog testing, which the company attributes in part to its near-zero porosity. Nordson recommends the Xaloy MPX technology for
protection from abrasion in compounds with medium (15 to 35%) filler loadings and for resisting corrosion from halogenated materials, including flame retardants and PVC. The 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. Nordson recommends MPX coated screws are used either with a barrel lined with its Xaloy X-800 nickel/ tungsten carbide alloy or with a comparable inlay. For compound filler contents above 35%, the
company offers its high-hardness Xaloy X-8000 coating. This is a nickel-based alloy with a high tungsten carbide content that is applied in an HVOF process then fused to the parent metal of the screw to form a metallurgical bond. Like the MPX and standard HVOF coatings, Xaloy X-8000 is suitable for service temperatures of up to 480°C (performance of Nordson’s three coating types is compared in Figure 1). Another new development in the field of wear
protection is the NanoDiamond electroless nickel plating technology developed by Finnish material
72 COMPOUNDING WORLD | August 2017
and abrasion resistance and allow an even coating thickness to be applied to complex geometries at relatively low cost, the company says. However, they do not perform well in tribological applications involving moving metal parts, where adhesive wear and galling tend to lead to rapid wear or failure. Carbodeon claims that incorporating its NanoDiamond materials into the coating overcomes this problem Carbodeon’s spherical diamond nanoparticles are
treated to carry a positive electrical charge to help them disperse. This means that during the plating process the diamond particles behave similarly to the positively charged metal ions and co-deposit onto the component surface with them. The resulting metal-diamond composite surface treatments have already shown their value in abrasion resistant coatings, but optimisation of the process is said to have resulted in a new generation of coatings that combat the adhesive wear that occurs when plated parts are in sliding contact with other metals. The developers say the coatings can be used “as
plated”, which does not affect the substrate’s heat treatment condition, or can be annealled for maximum performance. Abrasive wear is said to be three times better than standard electroless nickel, while adhesive wear rate is reduced by 30% in the “as plated” form and by 85% in the annealed state. The coating hardness is also significantly increased when annealed, reaching a maximum Vickers hardness of 1030 (Figure 2). Carbodeon and CCT Plating say that the improved
abrasive and adhesive wear does not make the coating more abrasive or increase the surface friction. In addition, they say that as the nano-diamond content in the plated layer is less than 1wt%, the technology is also affordable.
Click on the links for more information: ❙
www.kraussmaffeiberstorff.com ❙
www.centuryextrusion.com ❙
www.coperion.com ❙
www.feddem.com ❙
www.lesunscrew.com ❙
www.extremecoatings.net ❙
www.nordsonpolymerprocessing.com ❙
www.carbodeon.net ❙
www.cct-plating.com
www.compoundingworld.com
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