Alloy Steel Metal Spray Coating, For Boiler Water Walls & Tubes

Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame).
Thermal spraying can provide thick coatings (approx. thickness range is 20 micrometers to several mm, depending on the process and feedstock), over a large area at high deposition rate. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites. They are fed in powder or wire form, heated to a molten or semi molten state and accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge is usually used as the source of energy for thermal spraying. Resulting coatings are made by the accumulation of numerous sprayed particles. The surface may not heat up significantly, allowing the coating of flammable substances. Wire arc spray PrincipleThe arc spray process is based around the creation of an arc between two electrically charged metallic wires, which act as consumable electrodes, and using this arc to melt the incoming wires. Drive rolls feed the wires through the gun system to the nozzle. The contact of the wires creates the arc and melts the wire at temperatures in excess of 4000 degrees C. The molten material is atomized by the flow of compressed air through the gun and propelled towards the substrate, where the impacting particles rapidly solidify to form a coating.
The high particle velocity in arc spraying lends itself to forming a very high bond strength between the coating and the substrate, and for the production of very high spray rate coatings. Also, arc spray coatings are typically denser than their flame spray equivalents.
Another feature of this process is that it allows for the feeding of different metal wires simultaneously through each electrode to produce pseudo-alloys.
The arc wire spraying process is sometimes referred to as a cold process, because the temperature of the substrate material can be kept very low, thus avoiding any distortion or damage to the substrate. However, this also means that if substrate pre-heating is necessary, then a secondary heat source is required.