High-velocity oxygen fuel spray coatings for reclamation

These coatings are produced by a spray of molten powder in a system which has recently been developed utilizing a high-velocity fuel mixture of oxygen-propylene or oxygen-hydrogen. These gases are ejected at high speed from a nozzle and then ignited externally to form a flame which envelops the spray material. A high-velocity flame of compressed air carries the molten powder to a specially prepared surface where it solidifies to form a very dense coating of high bond strength and low porosity. The composition of the coating can be varied and depends upon that of the powder, the most commonly used for reclamation being based on either iron or nickel or tungsten carbide. During coating, the substrate temperature is held below 423 K so the process is considered ‘cold’. The spray coatings have good adhesion with low porosity. The high hardness and cost competetiveness means that they are beginning to replace electrodeposited nickel and chromium which have long been used for the repair of engineering components.