Thermal Spray is an industrial coating process consisting of a heat source and a material feedstock - either in powder or wire form - that results in a surface modifying coating. Typically applied to metal surfaces, thermal sprayed coatings impart desired properties to these surfaces that result in a wide range of component improvements.In this way, the component can be rebuilt if worn or damaged, or a wide variety of qualities can be given to the surface, depending on the material to be used.
Classification of Thermal Spary Processes
Initially thermal spray processes were classified according to the type of heat source. For example, processes were classed as flame, plasma or detonation gun spraying. Modifications to the heat source environment further classed these materials into the precise category by which these processes are known today
What Processes are called Thermal Spray Processes ?
- Cold spraying
- Flame spraying
- Arc spraying
- High velocity oxy fuel (HVOF) spraying
- Plasma spraying
- Detonation gun
Materials that can be plastically formed either in the solid or liquid state can be deposited. Where heating is involved, only those materials that remain stable upon heating can be sprayed. Instability may refer to oxidation or decomposition of the material. These materials may, however, be deposited in the form of composites where a secondary material is used to protect the unstable or reactive material. Spraying into a special atmosphere, use of a metallic or polymeric binder to form a composite, or encapsulation of these powder are means of protecting the thermally sensitive materials
Forms of Thermal spray Meterials
Thermal spray feedstock can take several forms which are suited to various materials such as:
- Powder - plastic, metal, composite, ceramic
- Wire - metal, composite
- Rods - ceramic
Use of Thermal Spray
Thermal spraying is used to produce flattened particles, spherical particles (either hollow or dense) and coatings. The most common application is the production of coatings. Coatings can be deposited to such dimensions that free forms can be produced.
Common Applications of Thermal Spray Coatings
- Wear and abrasion resistance coatings - mining
- Biomedical - orthopaedics (e.g. hydroxyapatite), dentistry, cancer therapy
- Thermal barrier coatings - combustion engines
- Anticorrosion coatings - infrastructure and marine environments
- Abradables - aviation industry
- Ink transfer rolls - printing industry
- Reclamation of worn components
- Art - glass colouring, bronze application
- Electronic applications
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.
Due to high processing temperatures, is Oxydation a problem?
Oxidation can be overcome by the use of a shroud placed onto the torch or by placing the thermal spray process into a chamber with a controlled atmosphere. With plasma spraying, the controlled atmosphere most commonly is a vacuum.
Are thermal stresses in thermally sprayed coatings a problem?
The residual stress remaining within the deposited particles mostly influences ceramic coatings. The cooling of such materials needs to be optimised to avoid excessive residual stress levels.
What's the advantage of using thermal spray?
By giving your product the advantages of a thermal sprayed surface, you can achieve advantages over your competitors.
Reduce the costs of your products by using basic materials chosen for their strength, cheapness, lightness or ease of manufacture. Then coat them with more exotic materials to achieve the required effects.
Solve problems such as corrosion fretting wear conductivity oxidation and much, much more!
Give your products longer life Reduce maintenance costs on your products or extend the time between maintenance and replacement. Give your customers greater product satisfaction!