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MODELING ARC HEATING IN TWIN-WIRE-ARC SPRAY SYSTEMS

DOI: 10.1615/ICHMT.2008.CHT.2280
13 pages

Amir Pourmousa
Department of Mechanical and Industrial Engineering, University of Toronto, Canada

Sanjeev Chandra
Center for Advanced Coating Technologies, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada, M5S 3G8

Abstract

Twin-wire-arc spraying is an industrial process widely used to apply metallic coatings on surfaces of mechanical parts. Two consumable metal wires are continuously fed into the spray gun. An electric arc is struck between the tips of the two wires, melting them. A jet of high pressure gas blown over the tips of the wires removes the molten material, atomizes it into a spray of droplets and accelerates them towards a substrate where they land and freeze to form a protective coating layer.
The physical processes controlling the twin-wire-arc system are complex because the turbulent fluid flow is supersonic, the arc plasma formed between the wire-tips is unsteady, and the wire material is constantly melted and atomized. Modelling the process is therefore difficult and requires extensive validation. The presented modelling technique, however, simplifies the problem by using pictures of the arc taken with different optical filters. The arc pictures are processed using image analysis software to determine the shape (i.e. curvature, length, and radius) of the arc. Arc equations are then solved based on the known shape/current of the arc, and heating due to the arc is evaluated and modelled as an external heat-source in the fluid flow model, including radiation effects.
The presented model's prediction of the gas velocity is analyzed to evaluate shear stresses on the surface of wires and estimate the size of primary masses of molten material detaching from the wire-tips. The model predictions explain spatially-uneven particle-size-distribution in the twin-wire-arc plume and compare relatively well with experimentally measured particle sizes.

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