TWI Frequently asked questions
by Suman Shrestha
All HVOF spraying equipment uses oxy-fuel combustion to heat a coating material, usually in powder form, and to accelerate the heated particles to high velocities before impacting with the substrate.
The major differences between current commercial systems are in use of gas or liquid fuels, water or air cooling, axial or radial powder injection, combustion chamber configuration, nozzle design and length. There are operational differences in combustion pressure, fuel and gas flow rates and powder feed rates. These parameters determine powder particle heating time, velocity and temperature, and ultimately the coating quality.
Commercially available equipment includes:
| Gas fuel systems | Liquid fuel systems |
| Diamond Jet from Sulzer Metco | WOKA-Jet 400
WOKA-Star 600 from Sulzer Metco |
| HV-2000 from Praxair-Tafa | JP-5000 and TJ-4000 from Praxair-Tafa |
| Jet-Kote II from Deloro Stellite | Met-Jet from Metallization |
| G-Gun from GTV | K-Gun from GTV |
Some of the differences in design of these guns are illustrated in the diagrams below.
