What is the Plasma Spray Coating process?
The plasma spray process is a thermal coating process that uses high temperatures and high energy, electrically produced heat sources to melt and accelerate fine particles onto a substrate. The molten metal particles cool down after hitting the substrate and form uniform coatings.
Plasma spray is the most versatile of the thermal spray processes because of the extremely high plasma temperatures associated with the plasma plume, which makes it possible to melt or vaporize any known substance. The plasma produced has a high temperature between 10,000-15,000 degrees Celsius.
Common gases used as electric arc gases include Ar, N2, H2 and He.
The plasma spray process is commonly used in aerospace, power generation, paper, oil and gas, and semi-conductor industries.
Plasma Spray Process System
The plasma spray process has several key components; plasma torch, process control (which controls the arc current and voltage and plasma gas flow rates), power supply, gas supply, high-frequency arc starter, and material feeder.
For the plasma spray system, one of the most important components is the plasma torch. The plasma torch is constructed of a gas injector, cathode, and anode. An electric arc is formed and stretched between the anode and cathode which ionizes the gas into an extremely hot plasma which is propelled out of the torch by the gas velocity. Powder is then injected into, heated by, and accelerated by the plasma gas stream towards the substrate to form the coating.
During the plasma spraying process, powders or wires are melted in the high heat of the plasma plume. These materials form the coating that will evenly distribute onto and coat the target substrate. For the plasma spray process to get an even coating onto the substrate, and produce particles of the correct size, speed and heat temperature, several factors must be considered:
- Plasma plume temperature and velocity
- Electric arc discharge power
- Spray distance
- Speed of torch and substrate movement
- Times a substrate is sprayed
- Powder particle size
- Rate, velocity, and angle of powder injection into plasma plume
What are the advantages of the Plasma Spray Process?
- The plasma spray process enables materials that melt at high heat temperatures, like ceramics and high melting point metals and metal composites to be applied to a variety of substrate materials
- Plasma spray coatings tend to be dense, smooth, and fully melted
- Plasma spray coatings will not damage or cause changes in the substrate it is applied to
- Plasma spray offers corrosion protection, high heat and oxidation resistance, and wear resistance
Common Plasma Spray Coating Materials
The plasma spray process can be applied onto many different types of substrates. Common plasma spray materials include:
- Aluminum-Polyester materials: Plasma Aluminum-Polyester spray coating material is made from a highly concentrated blend of silicon aluminum and polyester powders. This plasma spray coating is used to provide high impact resistance and high internal strength to the substrate it is applied to.
- Chromium Oxide Ceramics materials: Plasma sprayed Chromium Oxide Ceramics Coatings provide corrosion resistant, self-mating and anti-galling properties. This plasma spray coating is the perfect choice for substrates affected by high wear and tear issues.
- Tungsten Carbide materials: Plasma Tungsten Carbide spray coatings are used for substrates that require high wear resistance. This plasma spray coating is one of the hardest and highest wear resistant coatings offered.
- Alumina-Titania Ceramics materials: Plasma spray Alumina-Titania Ceramics coatings provide high corrosion resistance and are ideal for the substrates in the marine industry.
Applications of Plasma Spray Coating
Plasma spray coatings have applications in several industries including aerospace, mechanical and marine engineering, biomedical, electronics, and household appliances. Typical applications for plasma spray coatings include:
- Industrial gas and aircraft turbine combustion chambers receive a thermal barrier coating to help resist high temperatures
- Anilox rolls receive a dense, hard chromium oxide coating for laser engraving
- Sputtering targets receive a coating of various materials for use in the glass industry for producing low radiation (low-E) glass and in the semi-conductor industry in the production of microchips, memory chips, print heads, and flat panel
- Popular cookware is sold that has a non-stick coating of Teflon material
TAFA Model SG-100 Plasma Torch
TAFA Model SG-100 is an 80 kW, multi-mode plasma spray torch that is capable of producing subsonic, Mach I and Mach II gas velocity levels. Its versatility allows you to spray a wide range of materials to produce virtually any type of plasma coating from high-density wear-resistant carbides to controlled-porosity Thermal Barrier Coatings (TBCs). The SG-100's unique design also provides the option of internal or external powder injection, further enhancing the operator's ability to tailor coating characteristics.
Model SG-100 features:
- High spray rates
- Internal and external powder injection
- Long-life anodes and cathodes
- Power levels up to 80 kW
- Self-aligning components
- Three modes of operation for tailored coatings
Optional enhancements include multiple anode/cathode/gas injector configurations, air jet cooling kit, external powder feed adapter and gun mounts.