Last Updated on Mar 18, 2022
Spray arc welding is best used in non-positioned butt and fillet style welds due to efficiency. There are multiple types of spray welding technique – all which share a similar process of converting a electode rod, metal powder, or metal wire into a molten material that is then sprayed on the weld metal (substrate) via gas.
As we mentioned earlier, it’s best to avoid this type of welding technique on positioned welds due to the way it works (essentially creating metal droplets). Several of the common processes that are talked about when you hear the term “spray welding” are as follows:
- Flame & Arc welding (otherwise know as TSZ, TSA, TWAS) – commonly uses acetylene or electric arc to produce the required heat
- Plasma trasferred arc welding (otherwise known as PTA) – commonly uses ionized gas and powered metal
- High Velocity Oxyfuel welding otherwise known as HVOF) – commonly uses pressurized gas alongside power
- Detenation Gun Spray Weld- commonly uses a mix of oxygen, gas, and powder that is then ignited in a specialized gun barrel for spraying
- Cold Spray Weld – only used with plastic, this technique utilizes a preheated gas
The Spray Welding Process
The process is fairly straight forward, but be aware that it requires high voltage and high amp levels.
Step 1) Wire placed near base metal.
Step 2) Current is produced, and melts the wire.
Step 3) Molten metal from the wire then travels via the arc as metal droplets (hence where the name “spray” comes from).
A couple of things to keep in mind for this to work successfully:
- Current levels must be higher than the transition current
- This is what differntiates the droplet process from pure melting
- High voltage levels are required to keep spatter to a minimum, and produce as clean of weld as reasonable possible
Plasma Spraying (PTA)
PTA welding has a single use, to weld ceramics. The process has been through several iterations, resulting in a technique that effective can weld metals and plastics. It utilizes several gasses including helium, nitrogen, and hydrogen argon alongside an electric arc that ionizes the gas.
Step 1) You’ll need a powered alloy along with a constricted arc to begin the weld
Step 2) As you begin, the mixture in step 1 travels towards the plasma torch, along with argon gas
Step 3) The powered then runs to the effuent arc directly from the plasma torch
Step 4) It is then melted and placed onto the base material
PTA generally requires at least two passes to produce an effective weld. You’ll need to be extremely careful and make sure you have appropriate welding safety gear because PTA operates at significantly higher temperatures than many metals.
High Velocity Oxyfuel (HVOF welding)
Combines oxygen, hydrogen, propylene, air, and kerosene for successful welds applied via very high pressure via a combustion chamber. The welding powder is places directly into the flame during application, making for less than 1% porosity during the coating process.
It’s a more environmentally friendly process than other welding techniques.
How it works:
- Produces a gas stream via a fuel and oxygen within a high pressure combustion chamber
- Torch is then heated
- The gas stream produced in step 1 is then used to apply the coating onto the target material resulting in very a very thin weld