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1. What is Thermal Spray?
Thermal spray refers to a collection of coating techniques where materials such as metals, ceramics, cermets, and certain polymers—provided in the form of wire, powder, or rod—are delivered into a device (commonly called a gun or torch). Inside this device, the material is heated to a temperature close to or slightly above its melting point. The molten or semi-molten particles are then propelled by a high-velocity gas stream toward the target surface. Upon contact, the particles cool and solidify rapidly. As more particles land and solidify, a layered coating begins to form. These flattened particles—often referred to aslamellae—adhere to the surface, overlapping and interlocking with each other. The complete coating typically requires several passes of the spraying apparatus to achieve the desired thickness.
2. How are thermal spray processes classified?
Thermal spray methods are generally divided into five primary types or 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 feedstock materials are available in multiple forms, each adapted to different applications and process requirements. 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 or plastically deformable particle is propelled at high velocity by a heat source toward a target surface for deposition. Upon impact, the particle flattens and may form a chemical bond with the surface. When a chemical bond is not feasible, the surface is roughened to enable a mechanical bond. Each particle adheres by interlocking with the microscopic peaks and valleys (asperities) of the prepared surface.
7. How thick are typical coatings deposited by thermal spray processes?
The thickness of the coating depends on the feedstock particle size in powder-based methods, and on droplet size in arc and wire spraying. Generally, the particles spread to about three times their original diameter upon impact. Producing thin coatings requires very fine particles, typically ranging from 10 to 20 microns. Coatings as thin as 30 microns are quite common. Softer metals, on the other hand, can be deposited in much thicker layers—sometimes up to ¼ inch.
8. What is Wire Flame Spray Process?
Kindly refer to our comprehensive explanation of the Wire Flame Spray Process.
9. What is Combustion Powder Flame Spray Process?
Kindly refer to our in-depth overview of the Combustion Powder Flame Spray Process.
10. What is Electric Arc Spray or Twin Wire Arc Spray?
Kindly refer to our comprehensive explanation of the Electric Arc Spray process.
11. What is High-Velocity Oxy Fuel Spray or HVOF process?
Kindly refer to our in-depth overview of the High-Velocity Oxy Fuel (HVOF) Spray process.
12. What is plasma spray process?
Kindly consult our comprehensive explanation of the Plasma Spray Process.
13. What kind of Thermal Spray systems are available?
Below is a selection of Thermal Spray systems offered by Metal Coat:
- Combustion Wire – A torch powered by Oxy/Acetylene or Oxy/Propane that applies material in wire form.
- Combustion Powder – A flame spray torch using Oxy/Acetylene or Oxy/Propane and material in powder form.
- Electric Wire Arc – A system that melts wire feedstock using electric current between two wires.
- HVOF (High Velocity Oxy Fuel) – A process that uses high-speed combustion to apply powdered materials at supersonic velocities.