Frequently Asked Questions

1. What is Thermal Spray?

Thermal Spray is a group of coating processes in which metallic, ceramic, cermet and some polymeric materials in the form of wire, powder, or rod are fed to a gun which results in heating to near or somewhat above their melting point. The resulting molten or nearly molten droplets of material are then accelerated in a gas stream and projected against the surface to be coated. When the hot energetic particles impact the surface of the part being coated, they rapidly solidify. As subsequent particles impact the surface, a deposit thickness is built up. The droplets flow into thin lamellar particles adhering to the surface, overlapping and interlocking as they solidify. The total coating thickness is usually generated in multiple passes of the coating device. Thermal spray devices used to accomplish this work are commonly called as guns or torches.

2. How are thermal spray processes classified?

Thermal spray processes are mainly classified into five main categories. They are:

• Wire Flame spraying
• Combustion Powder Flame Spraying
• High velocity oxy fuel (HVOF) spraying
• Electric Wire Arc spraying
• Plasma spraying

3. What forms of materials can be used for thermal spraying?

Thermal spray feedstocks can take several forms which are suited to various materials such as:

• Powder – plastic, metal, composite, ceramic
• Wire – metal, composite
• Rods – ceramic
• Liquid

4. What are some common applications of thermally sprayed coatings?

• Wear and abrasion resistance coatings
• Thermal barrier coatings
• Corrosion Resistant (Anticorrosion) coatings.
• Abradable
• Reclamation of worn components.
• Art – glass colouring, bronze application.
• Electronic applications

5. What advantages does thermal spraying have over other coating techniques?

• It allows to deposit high melting temperature materials.
• It is a fast coating deposition process.
• Wide variety of materials can be used to make a coating. Virtually any material that melts without decomposing can be used.
• Most of the thermal spray processes apply a coating to a substrate without significantly heating it. Thus, materials with very high melting points can be applied to finally machined, fully heat-treated parts without changing the properties of the part and without thermal distortion of the part.
• Ability to strip and recoat worn or damaged coatings without changing the properties or dimensions of the part.

6. How are thermally sprayed coatings created/built up?

A molten particle or a particle able to deform plastically is transported at high speeds within a heat source towards a surface upon which deposition occurs. The droplet or particle undergoes spreading and may create a chemical bond with the underlying surface. With materials that are not able to produce a chemical bond, the substrate is roughened to create a mechanical bond. Each droplet or particle impacts a roughened surface and mechanically interlocks with the asperities on the underlying surface.

7. How thick are typical coatings deposited by thermal spray processes?

The coatings thickness is dictated by the size of the feedstock for powders, the size of the droplets for arc and wire spraying. Typically, flattening of the material by factor of three of the particle sizes can be expected. To create thin coatings, one requires a very fine particle size, usually at sizes between 10 and 20 microns. It is not uncommon to find coatings as thin as 30 microns. Softer metals can typically be applied very thick. In some cases, as thick as ¼”.

8. What is Wire Flame Spray Process?

Please see our detailed description on Wire Flame Spray Process.

9. What is Combustion Powder Flame Spray Process?

Please see our detailed description on Combustion Powder Flame Spray Process.

10. What is Electric Arc Spray or Twin Wire Arc Spray?

Please see our detailed description on Electric Arc Spray process.

11. What is High-Velocity Oxy Fuel Spray or HVOF process?

Please see our detailed description on High-Velocity Oxy Fuel Spray.

12. What is plasma spray process?

Please see our detailed description on Plasma Spray Process.

13. What kind of Thermal Spray systems are available?

Below is a list of available Metal Coat Thermal Spray systems:

• Combustion Wire – Oxy/Acetylene or Oxy/Propane fuelled torch that uses wire form material.
• Combustion Powder – Oxy/Acetylene or Oxy/Propane fuelled torch that uses powder form material.
• Electric Wire Arc – A dual wire system using electricity to melt wire form material.
• HVOF – High Velocity Oxy Fuel delivers powder form material at supersonic speeds.

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