You might have already heard plasma spray coating but not truly understand what it means. In order to use this form of spraying, you need to ensure that you have a working environment that is both safe and regulated, as this will enable you to create a plasma spray coating jet. It is difficult to create this working environment due to the way in which a gas mixture is passed through an electrical arch.
The process is one that requires planning and the right environment so that the spray coating is suitable for use in industrial applications. Achieving the discharge is formed in a gap located between the cathode and anode. What this creates is a rapid release of energy that increases the heat of the gas mixture to 14,000k high-temperature plasma.
It is clear to see that this form of spray coating is very intricate but it doesn’t prove useful in many instances such as those pans that have a Teflon coating. However, there is a variety of thermal coatings available that can be used in a range of applications.
So, the process involves a combination of high temperature, a high energy heat source, an inert spraying medium, argon and high particle velocities, this makes it possible to create a high-quality coating.
As a result, plasma spray coating can be applied to a variety of surfaces such as metallic or ceramic. It also offers exceptional bond strength.
So, let’s look in more detail at Plasma Spraying.
How does Plasma Spray Coating work?
In order to create a high-temperature flame to directly treat an industrial part, there are several elements involved in the process. Do the elements include?:
- A plasma gun that is used as the source of the flame
- The spray gun receives a source of plasma gas and this is used as the heat source
- An electric charge is used to create plasma
- An external powder supply is used to provide a powder coating
- A special anode nozzle is used to allow the plasma to exit where it interacts with the powder
- The plasma spray gun creates an ultra-hot flame that is then used to coat the part
Plasma Spray Coating Process
Preheating and Preheating Parameters
Preheating is a crucial step in the plasma spray coating process that involves heating the substrate before the coating is applied. The preheating parameters, such as temperature and duration, are carefully controlled to optimize adhesion and coating quality. By preheating the substrate, it, becomes more receptive to the molten particles sprayed during the coating process. This enhances the bond between the coating and the substrate, resulting in improved coating adhesion, reduced residual stresses, and enhanced overall performance of the coated component.
Powder Injection and Melting
Powder injection and melting are integral stages in the plasma spray coating process. Fine powder particles are injected into a high-temperature plasma jet, where they rapidly melt and become molten droplets. The plasma jet provides the necessary heat to melt the powder particles, transforming them into a semi-fluid state. The molten droplets are propelled toward the substrate, where they solidify upon impact, forming a coating layer. This technique allows for precise control over coating thickness and composition, enabling the deposition of various materials for diverse applications.
Coating Build-up and Thickness Control
As the molten droplets impact the substrate, they solidify and accumulate, gradually building up the coating layer. By controlling the spraying parameters, it makes it possible to control the coating thickness. This includes the spraying distance as well as the spray angle and traverse speed. When these parameters are adjusted, the operator can precisely control the deposition rate and ensure uniform coating thickness across the substrate’s surface. This control allows for tailored coating thicknesses to meet specific design and performance requirements.
Cooling and Solidification
After the plasma spray coating is applied, the molten droplets that impinge on the substrate undergo cooling and solidification. This determines the microstructure and properties of the coating. Proper cooling is imperative to prevent defects like cracks and promote strong adhesion between the coating and substrate. Various techniques, including post-spray heat treatment and controlled cooling rates, can be employed to optimise the mechanical properties, density, and overall performance of the coating. These processes ensure a high-quality and reliable coating for the intended application.
Materials Used in Plasma Spraying
Plasma spraying opens up a world of possibilities when it comes to coating materials. The range is vast, spanning metals, ceramics, polymers, and composites, each with unique attributes. Need sturdy and corrosion-resistant coatings? Metals like stainless steel, aluminum, or titanium alloys step up to the plate. When high-temperature stability and wear resistance are paramount, ceramics such as alumina, zirconia, or tungsten carbide shine. Seeking lubricity or electrical insulation? Polymers like polyimides or polytetrafluoroethylene (PTFE) step in. And for that extra edge, composites blending different materials, like metal-ceramic combinations, offer enhanced wear and erosion resistance. So, depending on your specific needs, the plasma spraying process provides a plethora of materials to choose from, ensuring tailored and reliable coatings for various applications.
Plasma spray coatings can be used in a range of industrial applications, making it extremely useful and flexible. The coating then helps to provide protection for a range of equipment and material when it is applied to the surface. Therefore, this can be used in a range of industries including:
- Culinary and cooking
- Marine and Boating
- Engineering, and more
There are specific applications targeted within each of these industries.
It is possible to use a plasma coating in a range of applications, making it versatile and highly functional. Therefore, you can find it used in:
- A range of personal care items that could include the likes of blow dryers and hair straighteners will use these coatings
- A range of pet toys that use a Teflon coating
- The compressor area where aero-engine turbine seal ring grooves are used will use spray coatings
- The car industry where it is often found in piston rings, bypass shafts and carburettor parts
- Medical and dental implants where you can find a plasma spray coating of hydroxyapatite.
- Energy industries and solar panels while turbine combustion chambers will also use zirconia-based thermal barrier coatings
These industries use plasma coatings because of the way in which they can be adapted. It can be applied in thin layers that are micrometres in thickness or it can be applied so that it is millimetres thick. Plasma spray is a widely used material that offers many different benefits.
Benefits of Using Plasma Spray Coating
Plasma coating is designed to treat industrial parts that are exposed to many different elements such as heat or wear and tear. When parts are passed through the spray coating process, they will become more durable and their lifespan will be extended. However, the benefits of using this process include:
- Thermal Insulation
- Preventing Wear and Tear
- Protects from Corrosion
- Resistant to Oxidation
Types of Thermal Spray Coatings
Plasma spray coating is one type of thermal spray coating from a total of five. They are used in a range of industries although they are designed to help materials remain durable and usable when they are exposed to high temperatures, chemicals and a range of environmental conditions.
Combustion Flame Spraying
Combustion flame thermal spray coatings are designed to be used on materials that are not capable of handling extreme stress even though they will be exposed to them. This coating doesn’t use a high flame velocity and that ensures that the coating does not adhere to the material as solidly as other methods. Furthermore, this is also one of the lower-priced coating options.
Plasma coating uses the plasma torch to heat and spray. Plasma spray coating is adaptable and that means that this coating can be used in a range of industries. The coating that is produced is thin and can be used on a range of substances while it is an extremely reliable plasma spray.
High-Velocity Oxy-Fuel (HVOF)
This is one of the more commonly used spray coating options. This also uses the torch and this means that the coatings can be applied that are strong and provide a high level of adhesive.
This coating process has to be used in an environment that offers a high level of control, despite it using a low temperature. However, the controlled environment for this coating is required due to the combinations of gas that are used as part of the process. This ensures that the correct pressure can be used to apply the thermal spray coating.
Two-Wire Electric Arc
The Two-Wire Electric Arc spraying process involves using the arc point that is created between two wires that conduct an electrical charge. This takes place when the wires connect and then the coating is applied using compressed air. This is a processes that is extremely popular as it offers a high level of effectiveness while the base materials commonly used are aluminium and zinc.
Plasma spray has a wide range of uses and is commonly used in a wide range of industries. There are a number of different coatings available depending on the industry and use. However, thermal spray coatings come with a range of benefits dependent on the type of coating used. The thermal spray coating process is one that requires expertise and an understanding of the correct environment and uses, only then is the process complete making it possible to apply the coating.