Thermal Spray Process
All methods of thermal spraying involve the projection of small molten particles onto a prepared surface where they adhere and form a continuous coating. To create the molten particles, a heat source, a spray material and an atomisation/projection method are required. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, firstly onto the roughened substrate and then onto each other as the coating thickness is increased. As the heat energy in the molten particles is small relative to the size of the sprayed component, the process imparts very little heat to the substrate. As the temperature increase of the coated parts is minimal, heat distortion is not normally experienced. This is a major advantage over hot-dipped galvanising.
Stages in the Process
1.) Firstly the surface of the metal is prepared by abrasive blast cleaning to ensure it is cleaned and roughened. Cleaning and grit blasting are important for substrate preparation. This provides a more chemically and physically active surface needed for good bonding. The surface area is increased which will increase the coating bond strength. The rough surface profile will promote mechanical keying.
2.) The thermal sprayed coating is applied using a Wire Arc Spraying method. Arc Spraying is a process in which an arc is produced between two wire electrodes of either the same material or to form a composite coating or alloy, two different materials. After the D.C. arc is struck, across the two feed wires, which have opposite charges, a spray stream is created that proceeds to the substrate for coating. The resulting corrosion resistant coating is achieved by the accumulation of numerous sprayed particles in a molten or semi-molten state.
3.)The final stage of the process is to seal the thermal spray coating to ensure longterm integrity
Also depending on customer requirements iwe can apply a coat of architectural grade polyester powder, which is initially green baked so as it is not fully cured, before applying a topcoat of the same powder and finish bake both coatings. The finished thickness of the overall coating is in the region of 250-300 microns. As per the European standard EN ISO 14713, this coating system has an expected life to first maintenance of 25 years.