Thermal Spraying: spray coating processes and thermal spraying

Thermal Spraying: What it is and how it is applied

Thermal spraying is an industrial coating process which relies on a heat source to melt a powdery material or wire into tiny particles. The particles are then spread evenly on a surface using a high-speed spraying technique.

This operation gives the coated materials greater hardness and high resistance to scratches and wear, as well as ensuring excellent smoothness. Thermal spray coatings can be applied using different processes. Starting with its research and development department, Argos has created PlasmaCoat coating, a one-of-a-kind in thermal spray coatings.

The primary methods of thermal spray application

Plasma spraying using ionized gas to create the coating: Plasma coating

With this technique, an inert gas, such as argon, is energized by means of an electric arc and partially ionized, thus generating a flow of gas at a temperature of about 16,000°C. Ceramic powders and mixtures such as aluminium oxide, zirconium oxide, chromium oxide or tungsten carbide are then released into the plasma torch, fusing to create a dense coating for application on the metal surface.

Thermal spraying by combustion: Flame spraying

This thermal coating technique uses the heat generated by the combustion of a gas (acetylene, propylene, propane or hydrogen) and an oxygenated mixture to melt a powdery material or wire, which is then applied to a surface by means of thermal spraying. A porous coating forms, which can then be impregnated with a polymer.

This process is cost-effective. The gas flow creates a temperature of about 3,000°C.

Electric arc spraying: Arc spraying

Also known as arc spraying, this is a very popular method for thermal spraying applied to metals. An electric arc is used to generate a heat source that melts the material, a wire, turning it into the coating compound.

The metals that can be used include nickel, aluminium and zinc alloys, the choice of which depends on individual needs and experience. The two electrically charged wires have opposite polarity and are released into a speed controlled torch.

When the wires come into contact, the opposite charges create an electric arc that continuously melts the tips of the wires. Compressed air is used to ionize and accelerate the molten material. Compared to the flame spraying technique, this thermal spraying method yields a greater spraying speed and better resistance.

HVOF: High-Velocity Oxy Fuel Spraying

This is one of the latest spray coating techniques. It uses the heat and pressure generated by the combustion of a liquid or gas mixed with oxygen. The compound is burned in a chamber, heats and expands, pushing the exhaust gas out of the torch at supersonic speed. This process yields dense coatings with reduced porosity.