What is Powder Flame Spray ?
What is Powder Flame Spray
The powder flame spray process is similar to the combustion wire spray process with the difference, that powder and not a wire is injected into the flame. In the flame powder process, powdered feedstock materials are melted or semi-melted into the oxyfuel flame by heat of combustion and the particles/droplets are accelerated towards the substrate surface by the expanding gas flow and air jets. A powder feed carrier gas transports the powder particles into the combustion flame, and the gases transport the material towards the prepared workpiece surface. Typical choices for fuel gases are acetylene or hydrogen.
Here feedstock powders are introduced axially through the rear of the nozzle into the flame at the nozzle exit. This offers a much wider range of coating material options than the wire flame spray process.
Particle speed is relatively low (<100 m/s), and bond strength of the deposits is generally lower than the higher velocity processes. Porosity can be high and cohesive strength is also generally lower. Spray rates are usually in the 0.5 to 9 kg/h (1 to 20 lb/h) range for all but the lower melting point materials, which spray at significantly higher rates. Substrate surface temperatures can run quite high because of flame impingement.
About our Powder Flame Spray Equipment
Powder is fed into our spray torches in one of two ways which are by carrier gases or by gravity.
Gravity-fed devices have powder canisters or bottles mounted directly to, and on top of, the torch as in our 5PM-II Powder Flame Spray Gun . Powder feed rate is controlled by a pinch valve that meters powder into the body of the torch, where it is aspirated by the gases flowing through the torch.
Carrier-gas-fed units use externally mounted powder feeders as in our 6PM-II Powder Flame Spray Gun . Powder feeders, use a carrier gas stream to transport the powder from the feeder through a hose to the spray torch. Carrier gases used for flame spray are commonly air or nitrogen.
Components of Powder Flame Spray System
- The key components of a typical powder flame spray system are:
- Gas and Air supply
- Gas hoses
- Gas regulators for oxygen, fuel, and air
- Gas flow control units
- Flashback arrestors at the gun and regulators
- A powder flame spray gun either 5PM-II or 6PM-II comprising a torch body, nozzle, and atomized air cap
- Feedstock delivery system comprising a powder feeder, Powder Hopper (if required).
Features
- Micro porous lamellar structure
- Relatively high degree of oxidation in the coating
- Moderate tensile strength
- Good compressive strength
- Low elongation properties
- Versatile and with a wide choice of materials
- Relatively inexpensive thermal spraying process
- Transportable process, spraying on location is possible
Features of fused coating
- Metallurgical bond with the substrate
- Resistant to line and point loads
- Low resistance to impact loads
- Homogeneous and closed structure
Typical coatings
- Fused alloys NiCrBSi (Fusing, Self-fluxing)
- Nickel-based alloys
- Various stainless-steel alloys
- Cermet, carbides (hard metals)
- Ceramic coatings (oxides)
- Abradable coatings (abradable such as nickel graphite, AlSi polyester)
Applications
- Sealing moving surfaces to prevent seals from leaking
- Improvement of wear resistance and chemical protection of ball valves
- Boiler walls of incinerators against high-temperature erosion and chemical degradation
- Repairs and dimension corrections of worn drive shafts and bearing seatings with nickel-based alloys
