Plasma Spray coating
The versatility of plasma coatings allows for almost unlimited applications.
Plasma Coating Technology
Plasma coating, sometimes known as thermal spray coating, is a coating application process where a metal or ceramic is sprayed onto a chosen substrate. The equipment used for the application is specialised and varies according to the desired outcome.
At Marcote our main focus is to apply the metals and ceramics to a porous layer. This porous layer is essential for top coating with a polymer or fluoropolymer, as it allows it to impregnate the metal or ceramic. This impregnation effectively creates a harder wearing topcoat.
By choosing the correct plasma layer and topcoat, Marcote can achieve properties such as high friction and non-stick, or abrasion resistance with low friction for example. An example of this would be an Aluminium roll coated in Tungsten Carbide to increase its surface hardness. The roughness or surface texture of the Tungsten Carbide can be varied. Note that when rolls are coated, we achieve very high levels of coating thickness accuracy, tolerance, and run out, which can be measured and recorded.
This ability to change the properties of the component being coated is the essence of what Marcote does.
As with all coatings, surface preparation is critical. We at Marcote use a high-grade silica to blast each individual part to a specified level of surface roughness and cleanliness. For those components that cannot be blasted, we employ various surface cleansing techniques. For more information on how we will handle and treat your components please contact us.
There are different methods of plasma or thermal spraying. The method used is dependent on the desired result. Their versatility allows for almost unlimited industrial use; for example, they are commonly used within oil and gas, aerospace, automotive, printing, converting, paper and packaging industries.
Performance Properties
- Chemical and thermal resistance
- Optimum permeation resistance
- Flame resistance
- Hard finish resistant to abrasion
- Purity
Coating thickness between 80µm and 500µm
Surface roughness (Ra) of 1.5µm to 17.0µm plus
Hardness levels of between 28 HRc and 70 HRc
Surfaces that plasma coatings can be applied to
Metallic substrates
Aluminium
Stainless Steel
Steel Alloys
Carbon Steel
Magnesium
Brass
Copper
Metallic substrates
Carbon Fibre
Glass Fibre
Glass
Plasma Coating Application Types
Thermal spraying uses the combustion of pressurised gas and oxygen to partially melt the coating material which is then propelled onto the substrate surface to form a porous metallic or ceramic layer. The coating then bonds through impact with the component with porosity typically around 38%. In most cases we apply a topcoat over and into the porous thermal coating which, for example, enables us to provide a non-stick but high traction finish.
This application method is also known as flame spraying or combustion spraying. The gas stream has a temperature of approximately 3,000°C.
Typical materials applied by this method include Aluminium, Tungsten Carbide and Chrome Oxide.
The arc spray process electrically charges two metallic wires with opposing polarity and forces them together causing the wire to get extremely hot and melt. Compressed air is then used to atomise and accelerate the molten material onto the surface; adhesion is by impact. By altering the wire feed speed and amps we can vary the surface roughness and thickness of the coating. Aluminium (known as Thermally Sprayed Aluminium or TSA), Nickel alloys and Zinc (known as Thermally Sprayed Zinc or TSZ) can be applied using this process.
TSA is commonly used for offshore applications at the splash zone for long term corrosion resistance. The Aluminium will corrode in preference to a steel substrate through galvanic action. At Marcote, we use Nickel alloys for mid-level abrasion resistance, usually in conjunction with a topcoat.
The true plasma coating process uses an inert gas such as Argon and charges it with electricity causing an arc flame which burns at temperatures approaching 20,000°C.
Ceramic powder is injected into the flame and projected by the gas flow on to a suitably prepared component to form a dense coating. Adhesion is achieved by impact of the molten ceramic. Whilst it is possible to apply Tungsten Carbide using this process, it is not usually done as HVOF is more suitable.
Different physical, thermal and electrical properties can also be achieved by varying the ceramic being sprayed.
For example, Chrome Oxide has excellent electrical properties and Aluminium Oxide has excellent thermal properties.
Because of the very high levels of UV radiation emitted, the true plasma coating process must be carried out by robot, so this may limit some components. Marcote uses the generic name of Plasma Coating for all our metal and ceramic spraying.
The HVOF process uses a combination of Oxygen and fuel (gas or liquid) mixed and then ignited in a combustion chamber to produce a high-pressure gas stream. This stream of gas is used to carry Tungsten Carbide powders at supersonic velocity (five times the speed of sound or Mach 5 is common), melting the material and causing it to hit the surface at high velocity; adhesion is by impact. This produces a very hard and dense finish (typically around 98% pore free) which can be easily ground and polished to a high specification. This application method is not suitable for impregnating polymers into the Tungsten Carbide.
Different grades of Tungsten Carbide, both in chemistry and particle size, will result in different surface properties.
Note that the supersonic velocity generates excessive heat and sound which means that the process must be carried out in a sound proofed booth, ideally without any operators present, so suitable component shape and size needs to be considered. Plus, masking and jigging can be an issue, so these need to be thought about as well.
Extraction
In all cases and with all application methods, proper, thorough, and efficient extraction of excess coating is essential. Once extracted, filtration and capture of the waste product is carried out prior to responsible disposal.
Marcote takes its environmental responsibilities seriously which is why we have invested in the latest generation of extraction equipment for our Plasma Coating processes.
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