Flame spray: Concept, and working process

Flame spray

Flame spray

The flame spraying method is a type of thermal spray coating process, whereby, the material to be sprayed is used in two ways, either in powder or a wire form. 


First, the material to be sprayed melts in flames of oxyacetylene (natural flame) then it is sprayed onto the surface of the base metal by blowing it through a stream of compressed air.

So that it spreads around, interlocks with projections, is contained in the pits, and cools and overlaps to form a coherent structure, and joins with each other. Spraying material is usually applied in layers less than 0.25 mm thick.

Equipment used in spraying equipment

The equipment used in flame spraying system can be divided into two parts based on their processes, such as

  • Wire spray system and
  • Powder spray system.

Wire flame spraying equipment

A wire flame spraying process includes the following equipment and supplies.

  • Wire-type spray gun 

The gun resembles an oxy-fuel gas torch with a hole for the wire through the center of its tip. The gun also has the arrangement to drive a pair of rolls to feed the wire into the flame. An air cap surrounds the tip of the gun and directs an explosion of compressed air to pick up the molten metal and project it completely.

  • Wire reel and straightener
  • Fuel  (acetylene) gas cylinder and regulator.
  • Flow meters for both compressed air and acetylene cylinders.
  • Hose
  • Flame arrestors.

Roll of  Compressed Air in a wire flame spraying process

  • The compressed air forms an air envelope around the outside of the flame and the liquid metal, it atomizes the molten wire metal that has been melted by the oxyacetylene flame.
  • Compressed air cools the substrate, thus maintaining its temperature below  205 degrees centigrade.
    Compressed air accelerates the molten metal particles on its path to the base metal and thus deposits them there.

Typical data for Wire flame spraying

Pressure ofZinc25kg/hr
Weight of a manually operated gun1.35 to 2.75 kgLead45kg/hr
Weight of a machine-mounted gunup to 4.50 kgAcetylene0.7kh/cm²
Wire electrode sizeup to 4.75 mmOxygen1.12kg.cm²
Deposition rate  for steel8 kg/hrAir2.45kg/cm²

Advantages of Wire type flame spraying system

  • A wire-type metal spraying system is probably the most commonly used metalizing process employed today. Wire metalizing is a fast and low-cost method of applying a wide variety of metal coatings, such as carbon steel, stainless steel, brass, and bronze, over a grit-blasted or nickel aluminize-undercoated substrate. Such coatings are often used for shaft buildup and general restoration of worn or mismatched parts.

Powder flame spraying equipment

Flame spray

A powder flame spray system includes the following equipment and supplies:

  • Powder spray gun
  • Cylinder, pressure regulator, and flow meter.
  • Dry compressed air supply with pressure control and flow meter.
  • Powder container.
  • Hosepipe for oxygen, acetylene, and air


The metal powder is carried by compressed air from the powder container to the spray gun where it feeds through the air from the powder container orifice into the nozzle and from there into the oxyacetylene flame. As it enters the flame, the powder is melted and the resulting molten globules are blown onto the work surface.

Advantages and limitations of Powder flame spraying

  • This process has the potential to be applied to a large variety of metal, ceramic, and cermet blending materials.
  • Compared with wire flame spraying equipment, powder spraying equipment is simpler and lighter in weight.

One problem experienced in the powder spray process is the difficulty of maintaining a steady feed of powder. Also, the deposition capacity is low.

 See More–  Electric arc spraying