Winder (Reel) Drums
Winder (Reel) drums operate in pairs at the dry-end of a paper machine. The paper is wound around the first drum under controlled tension through differential surface velocities of the drums, the second drum having a slightly higher surface velocity than the first.
Depending on the paper type, winding speed, winding set up among other parameters, slipping may occur between the paper and the drums.Thus, the required tension is not achieved in the finished paper roll, resulting in the formation of several layers of an out-of-round paper roll. On the later stage in the re-winder (Slitter) section, this final portion of paper (usually, up to 5% of the paper machine production) cannot be re-wound and is scraped.
A traditional approach adopted to prevent the mentioned slipping is to coat the rolls with a coarse tungsten carbide composite coating. Low-velocity combustion flame spraying has been traditionally used due to this work most often being conducted on site. These coatings have been successful regarding stopping slipping, but problems regarding the initial operation, as well as long-term life, have been experienced.
These traditional tungsten carbide coatings consist of large WC powder particles (50-100 microns), bound together by a metal matrix (Cobalt or Cobalt-Chrome). Large particles tend to damage the paper initially when the drum is first operated. Furthermore, the particles are easily plucked from the metal matrix during normal operation. Thus, the coating suffers steadily decreasing performance with time until the coating needs to be stripped and replaced.
Kermetico HVAF WC-CoCr Anti-Slip Coatings
The performance of Winder drums is substantially improved by the application of tungsten carbide composite coatings with the Kermetico HVAF process.
In our process, the grain size of tungsten carbide is reduced down to about 1 micron using agglomerated and sintered WC-10Co4Cr powder, providing high binding of WC-grains in the metallic matrix. Thus, the paper is not damaged by coarse grains of carbide.
- Kermetico HVAF equipment produces WC-based coatings of the highest fracture toughness, exceeding known HVOF and flame sprayed coatings by at least 10-fold. Since the main mechanism of wear of WC-based coatings is attributed to the material brittleness, the Kermetico HVAF coating exhibits the highest wear resistance. This provides the longest lifetime of the HVAF coating.
- Finally, the required 0.05mm (0.002”) of coating thickness is applied in only one pass, eliminating defects between the layers known to affect other thermal sprayed coatings. The coating structure, and, therefore, wear during service is uniform, providing a reliable performance of the coating regardless of the remaining thickness.
Kermetico HVAF equipment is portable, providing the required possibility of applying coatings on-site. This is the equipment of the highest productivity (up to 30 kg per hour spray rate with 55-65% deposit efficiency), ensuring the quickest possible application.
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