Plasma gun controls

Dr Steven Matthews is a senior lecturer in the School of Engineering and Advanced Technology at Massey University in Auckland. In this video, he describes plasma spraying as an incredibly versatile technique. It is the ability to carefully control the gun settings such as plasma temperature and velocity along with powder feed and spraying distance that gives it this versatility. 

Jargon alert
Cermet – a cermet is a metal-based framework with ceramic materials embedded in it. It is hard and often used in cutting tools. It is also high temperature resistant and used in electronics components.

Transcript

STEVEN MATTHEWS
Our plasma gases are controlled by a control console outside of the booth, and there we can control the composition of the gases. So typically, you have a primary gas, and then we have what’s referred to as a secondary gas, which we use to adjust the conditions of the plasma, particularly its temperature, thermal conductivity. So argon usually our primary gas, secondary gas is usually hydrogenhelium or nitrogen

Now plasma spraying is an incredibly versatile technique. We can spray any material as long as it will go from a solid to a liquid phase, so this means we can spray anything from low melting point polymers through to metals, alloys, cermets and also very, very high melting point ceramics.

To spray these different materials, we need to be able tailor the temperature and the velocity of the plasma to suit those different materials. And we do that by controlling, for example, the plasma gases in terms of their composition and also how much plasma gas we send to the gun, the current that the gun operates under, and we can also control a lot to do with the hardware. So, for example, the anode here, we can control the geometry of the anode to accelerate the gases, the length of the anode and the diameter and also where we introduce the powder. So, for example, in this gun here, the powder is introduced internally within the anodes, so it sees a lot higher temperatures then if we introduce the powder externally.

And the other key thing we can control is the distance from our plasma gun to our workpiece here. And that controls the residence time that the particles are in the high-temperature plasma for, so it allows them to melt and hopefully give us a high deposit efficiency on the surface.

Acknowledgements:
Dr Steven Matthews, School of Engineering and Advanced Technology, Massey University, Auckland
Aaron Martin, Holster Engineering Ltd, Tokoroa