Coal Preparation » Dewatering
The main objective of this project was to improve the wear resistance properties of coal dewatering centrifuge baskets through investigation into alternative coatings applied to the 304 stainless steel wedge wire. Adding a thin coating (~300μm) to the surface of the wedge wire does not compromise its properties but it does increase the hardness and, in turn, improve its wear resistance properties. The process of coating application is novel and requires optimisation. Coated coupons and dewatering baskets sections were wear-tested in a specially designed rig and then analysed for their durability in the simulated plant conditions.
The main findings and conclusions from the testing:
- The optimisation of process conditions was required to first apply the powder as a coating to the surface of the wedge wire, and then, secondly, to optimise the heat input conditions during coating consolidation. A balance was required so there would be sufficient input for consolidation and not excessive dilution producing a reduction in the hardness of the coating and the underlying substrate.
- Two materials were chosen for investigation: Stellite 6 and Metco 1030B, what they showed is detailed within the report
- The duration of the accelerated wet slurry testing was limited by the coating thickness of the Metco 1030B on the wedge wire basket sections. The low deposition of Metco 1030B coating thickness was problematic and the short testing time for the accelerated wear test meant there was not statistically significant variations between coatings and substrate for conclusive findings. Further work is required to improve the deposition thickness. An alternative to spraying on a curved surface would be to spray the wedge wire while flat and then form the basket shape.
- A Metco 1030B coating is recommended for improved wear erosion, however, under impact erosion the Stellite 6 coating performed slightly better than the 304 substrate.
The improved wear resistance of the coated centrifuge basket sections could be extrapolated to repairs of existing baskets. The accelerated wet slurry test used in this project used garnet, which is significantly harder than coal. A complete basket with surface coating as a true in-service test with coal is recommended to know the true performance of the coated wedge wire.
This study had a single data point and for improved confidence duplication would be advised. For future research tasks, a complete centrifuge basket, rather than assembled sections, is recommended and an 'in-service' test performed. It is also recommended that flat wedge wire plate be coated and then formed to shape of the dewatering basket. The aperture size is critical to the dewatering process and was beyond the scope of this project. Liaison with an existing supplier/ builder would allow their expertise to better manage apertures.
While wear testing and hardness testing provided indications of wear performance, the laser treatment altered the surface profile of the wedge wire, effectively opening the apertures of the wedge wire. The efficiency of the treated wedge wire was not assessed during this project.