Surface coatings are becoming increasingly popular as more businesses become aware of their benefits. Adding a surface coating means the items/components – referred to as the substrates – can be given new and desirable attributes or enhance existing ones. One of the most commonly used surface coating methods is plasma spray.
What is plasma spray?
Plasma spray is one of several thermal spray surface coating techniques. These techniques involve heating/melting particles, which are then sprayed onto a substrate. Plasma, in this instance, is the term used to describe the gas that ionises (due to extreme heat) and becomes electrically conductive. Plasma spray techniques can be used to spray a wide range of materials of assorted sizes with minimal distortion of the substrate.
What does it involve?
The plasma spray process involves the use of a plasma gun, plasma gas source, electric charge, an external powder, and an anode nozzle.
Stages of the process
There are four main stages to the plasma spray coating process: preheating and preheating parameters, powder injection and melting, coating build-up/thickness control, and cooling and solidification
The preheating stage involves heating the substrate to make it more receptive to the particles used for coating. This results in a stronger bond and greater adhesion.
The powder injection and melting stage involves the powder particles being injected into a high-temperature plasma jet, where they become molten.
The coating build-up and thickness control stage involves spraying the molten particles onto the substrate. This is done at high velocity to enable the particles to stick. As they hit the substrate, they gradually build up the coating layer. The thickness of the layer can be controlled using the various spraying parameters.
Once the coating is applied to the substrate, the droplets cool and solidify. The cooling process is important, as it helps determine the microstructure of the coating, prevents defects, and ensures a high-quality finish.
Applications
Plasma spray coatings are used in numerous industries and on items including hair straighteners, pet toys, car parts (piston rings, shafts), medical and dental implants, solar panels, and wind turbines.