Selection and characterisation of HVOF cermet coatings for volutes of high capacity pumps of opencast lignite mines

Abstract

The centrifugal pumps made of grey cast iron deployed in mining conditions encounter severe erosion and corrosion problems causing sudden failures. To combat this, the thermal spray ‘high velocity oxyfuel’ (HVOF) process was selected to provide a cermet coating, namely, WC–Co–Cr–Ni. After design investigation on coatings, erosion and corrosion experiments were conducted and characterisation studies involving microstructure, surface morphology and energy dispersive X-ray fluorescence analysis were made. The operating parameters on the different sections of impact volute surface were assessed and accordingly, the coating thickness was designed scientifically for maximum impact loads and minimum corrosion failures. The life of the coated pump casings has been improved up to 12 times by optimising the coating thickness.

Keywords:

• Erosion–corrosion
• Pumps
• Impact stress
• Coating design
• Cavitation
• Volute
• Microcutting
• Ploughing

Acknowledgements

The authors record their sincere gratitude to the Management of M/s Neyveli Lignite Corporation (A Navaratna Enterprise, under Ministry of Coal, Government of India), for their permission to publish the research work carried out at the Neyveli Lignite Mines and extending all help during the above research work. The authors also thank profusely the administration of National Institute of Technology, Tiruchirappalli, India for facilities made available.