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COMBUSTION WIRE & POWDER THERMAL SPRAY

The Combustion Wire Thermal Spray Process formerly known as Metallizing, Flame Spraying and Metal Spraying Processes was first invented in 1910 by Schoop in Switzerland.

The flame spraying process is basically the spraying of molten metal* onto a surface to provide a coating. Material in wire form is melted in a flame (oxy-acetylene flame most common) and atomized using compressed air to form a fine spray. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating.

This process carried out correctly is called a “cold process” (relative to the substrate material being coated) as the substrate temperature can be kept low during processing avoiding damage, metallurgical changes and distortion to the substrate material. This flame spraying process has been extensively used in the past and today for machine element work and anti-corrosion coatings.
*Ceramics and cermets can be used in rod or composite wire form.

Common materials for flame spraying:

  • Zinc and aluminium for anti-corrosion cathodic coatings on steel
  • Nickel/aluminium composite wire for bond coats and self-bonding coatings
  • Molybdenum for bond coats
  • Molybdenum for hard bearing applications, excellent resistance to adhesive wear, used on piston rings, synchromesh cones and journals
  • High Chromium steel for many applications requiring hard and wear resistant coating
  • Bronzes, babbitt for bearing applications
  • Stainless steels, nickel and monel for anti-corrosion and wear
  • Aluminium, nickel/aluminium for heat and oxidation resistance

Process Advantages:

  • Low capital investment
  • Simple to operate
  • Wire form cheaper than powder
  • Deposit efficiency very high
  • Possibly still best for applying pure molybdenum coatings for wear
  • Portable system
  • Preheating facility built in, unlike arc spraying
  • Possible to use system in areas without electricity supply

Process Disadvantages:

  • Limited to spraying materials supplied in wire or rod form
  • Not capable of the low oxide, high density and high strength coatings of plasma and HVOF

Also known as Powder Flame Spraying and LVOF (Low Velocity Oxygen Fuel Process). This flame spraying process is basically the spraying of molten material onto a surface to provide a coating. Material in powder form is melted in a flame (oxy-acetylene or hydrogen most common) to form a fine spray. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating. This flame spraying process carried out correctly is called a “cold process” (relative to the substrate material being coated) as the substrate temperature can be kept low during processing avoiding damage, metallurgical changes and distortion to the substrate material.

The main advantage of this flame spraying process over the similar combustion wire spray process is that a much wider range of materials can be easily processed into powder form giving a larger choice of coatings.

Disadvantages – The flame spraying process is only limited by materials with higher melting temperatures than the flame can provide or if the material decomposes on heating.

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