Cold Spray vs Thermal Spray – an overview
What is cold spraying?
To apply a cold spray, powdered material is increased to a speed that can reach the level of Mach 3. You can deposit a powder via cold spray onto various surfaces.
The first type of cold spray, high-pressure cold spray, often uses helium and nitrogen as carrier gases to assist powders in reaching maximum velocity. It can spray tough alloys and metals at 300 to 1000 psi.
As optimum speed is achieved and the particles collide with the surface, a plastic anamorphosis adheres them to the substrate. A robust bond is created with a recrystallised connection between the substrate and the deposited particles.
The second type, low-pressure cold spray, can also use gases but at a pressure below 300 psi. This method is preferred when working with softer metals and a hybrid of metal and ceramic powder.
Reaching these speeds is possible by passing the gas and powder via a de Laval nozzle. Kinetic energy is produced by converting the heat energy generated through an asymmetrical metronomic object.
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What is thermal spray?
One of the most popular methods of depositing a coating is thermal spraying. Its popularity can be attributed to its versatility and ability to work with any material – including polymer, metals and ceramics – that either turns to plastic or melts when heated.
Plasma spray can coat substrate materials using heat and electricity. The coat plus inert gas can quickly broaden to produce a strong and fast particle-based plasma spray from the jet.
The arc spray method is similar to plasma spray but launches an electric arc between the source materials, at which point they both melt. The air compression causes the coating to atomise and directs the particles at the substrate surface.
Another option is to flame spray using a chemical method. Fuel gas, hydrogen or propane mixes with oxygen to increase the temperature of the coating as a powder or wire. The source material is then coated as the mixture is launched using inert gas.
Similarly, high-velocity oxy fuel spray generates heat by mixing and then combusting a fuel and oxygen blend. The droplets heat up then swell in the chamber until the exhaust gas is propelled at a supersonic speed at the source material.
The substrate material needs to be spotless and then coarsened before any of these thermal spray processes can be used to coat it.