Thermal spray coating refers to a number of processes in which a substrate is coated to improve functional performance. Many types of coating materials can be applied by thermal spray processes. Coatings can range in thickness from a thousandth of an inch up to an eighth of an inch. Thermal spray coatings have been used to protect parts from wear, abrasion, corrosion, high temperatures, etc. and to build dimensions on undersized parts.
Thermal spray coating processes involve the deposition of coatings from a stream of high velocity finely divided particles in a molten or semi-molten state impinging onto the substrate. These processes use fine powdered source material or sometimes metal wire that is molten and broken into fine droplets. The coating gun adds thermal energy to bring the materials to a plastic or molten condition and accelerates these materials at high velocities toward the substrate.
There are several different types of Thermal Spray Coating processes. They differ in how they apply thermal and kinetic energy to the source material, the form of the source material (powder or wire) and the relative velocities and temperatures of the flame. Each process has advantages and disadvantages, and some are optimized for certain types of coatings.
BryCoat Thermal Spray Coatings are applied by Robot for accurate control of coating properties and thickness and for process repeatability. BryCoat also relies on advanced process control systems to ensure that the quality of the coatings is optimized. Thermal spray coatings can also be applied by hand controlled guns.
Thermal Spray Coating Technology
- Coating material starts as powder or wire form. A wide range of materials are available
- The thermal spray gun provides energy to the coating material particles and transports the coating to the substrate part. Energy can be thermal (heat) or kinetic (velocity). Several different technologies are available:
- HVOF
- Plasma Spray
- Flame Spray
- The thermal spray gun is controlled by an industrial robot for precise repeatable control of the coating
- As the particles of molten material impact the substrate, they collapse into flattened droplets and in lamellar layers forming a cohesive coating structure.
- Cooling of the substrate is used to control the temperature gain of the substrate.
Comparison of Thermal Spray Technologies
This table provides a summary of typical industry values for various thermal spray coating techniques.
| Process | HVOF | Plasma | Flame |
|---|---|---|---|
| Particle Velocity (m/s) | 800 | 300 | 40 |
| Particle/Gas Temp (°C) | 3,000 | 14,000< | 3,000 |
| Adhesion (psi) | >10,000 | >7,000 | 1,000 |
| Oxides (%) | <2 | <3 | 12 |
| Porosity (%) | <2 | <5 | <15 |
Process Control Parameters
- Powder Material
- Composition
- Geometry
- Controlled feed rate in a carrier gas
- Thermal Spray Gun
- Acceleration
- Thermal Energy to particles
- Particle exit velocity
- Molten and semi-molten particles travel to part surface
- Gas flow controls
- Robotic control of gun
- Stand off distance
- Traverse rate
- Multiple coating passes to build required thickness
- Coating angle
- Substrate surface preparation
- Cleaning
- Surface roughness
- Masking of areas that must not be coated
- Substrate temperature control
- Cooling systems
- Localized temperature changes
- Coating system controls
- Acoustical booth
- Dust collector and recycling coating materials
Process Steps
- Part Cleaning/Degreasing
- Masking
- Surface Preparation of surfaces to be coated
- Blasting
- Demasking/Cleaning
- Masking/Preparation for Coating
- Coating
- Demasking
- Secondary operations such as deburing or finishing
- Inspection & Testing
- See Also:
- Thermal Spray Coatings
- HVOF
- Plasma Spray
- Flame Spray
- Thermal Spray Coatings—Carbides
- Thermal Spray Coatings—Ceramics
- Thermal Spray Coatings—Metal Alloy Coatings
- Thermal Spray Coatings—Abradable Coatings
- Guide to Substrate Preparation for thin film coatings
- Thickness Conversion Chart
- Temperature Conversion Chart