Matrix coatings on endless flexible metallic belts for continuous

Abstract

A unitary-layer partially metallic, suitably adherent, mechanically and thermally durable, non-wetting, fusion-bonded matrix coating on endless, flexible metallic casting belts for continuous casting machines is described. This fusion-bonded matrix coating is also advantageous for coating other molten-metal-contacting surfaces, in continuous casting machines, such as edge-dam blocks that define moving side walls of a mold cavity. The fusion-bonded matrix (or reticulum) coating provides advantageous accessible porosity throughout the coating and comprises a nonmetallic refractory material interspersed substantially uniformly throughout a matrix of heat-resistant metal or metal alloy, for example nickel or nickel alloy, which is fusion-bonded to the grit-blasted surface of the belt and anchors and holds the nonmetallic material. The coating is applied by thermally spraying a powdered mixture directly on the roughened surface. The result is to insulate and protect the underlying belt from intimate molten metal contact, from heat stress and consequent distortion and from chemical or stress-corrosive action by the molten metal or its oxides or slags. The nonmetallic material may be present, at least partly, in the form of isolated particles encased within the metallic reticulum and/or in the form of a second reticulum intertwined with the metallic reticulum. The life of the coated belts is dramatically increased, and the surface quality and properties of the cast product are significantly improved. The coating controls and renders more uniform the rate of freezing of the metal being cast, resulting in improved metallurgical properties. Formulations are described and a method of forming such coatings by thermal spraying.