Which Type Thermal Spray Coating Is Best For Your Component?

February 26, 2020

What is thermal spray coating?

Thermal spray coatings are typically used in the aerospace, automotive, power generation and oil and gas industries. Curtiss-Wright offers a wide variety of coatings including HVOF (High Velocity Oxygen Fuel), plasma, flame and arc spray coatings. The range of thermal spray coatings offered by CWST means that it’s possible to achieve a cost effective and high performing finish that protects metal components from heat, wear, corrosion, fatigue and oxidation. HVOF coatings are a viable alternative for hard chrome plating.

Our thermal coatings can repair damaged and worn components- such as gas and steam turbines- to original specification.

Types of thermal spray coating

HVOF

High velocity oxy fuel thermal coating is a process that propels semi-molten powders at supersonic velocity onto the substrate. The semi-molten powder then cools and solidifies in a fraction of a second to form a strong mechanical bond with the surface of the component.  HVOF coatings tend to be extremely dense with low porosity, good thickness control and strong bond strength.

Plasma

The plasma coating process involves spraying molten or semi-molten powders onto the surface of a component to provide a coating. The selected coating is injected in powder form into a high temperature plasma flame, where it is rapidly heated and propelled against the component surface using a carrier gas. Plasma sprayed coatings typically utilise higher temperatures and lower velocities (compared to HVOF) allowing a larger variety of coatings including ceramics to be applied.

The component surface is usually roughed by grit blasting to provide a key for the coating.  The hot material impacts on the roughened substrate   where it cools rapidly shrinking against the roughened peaks of the surface forming a strong bond and foundation for the final coating. When this plasma spray coating process is carried out correctly is known as a “cold process” as the substrate temperature can be kept low during the process to avoid material damage.

Flame

Flame spray coating is widely considered the original method of thermal spraying and has been commonly used across a wide range of industries for over 100 years. The flame spraying process utilises an oxy-acetylene flame to apply the thermal coating. The heat from the flame melts the chosen coating material and compressed air propels it onto the product that is being coated. The flame spraying process is also another form of “cold process” due to the relatively low working temperature during the process.

Arc spray coating

The arc spray coating process provided by CWST is not only a cost effective and efficient service, but also a fast one. This type of thermal spray coating uses a twin wire feedstock that uses an electric arc to melt the feedstock and compressed air to propel the molten particles against the substrate.  Arc wire coatings provide strong bond strength, low substrate temperatures and high coverage rates making them very suitable for large areas.    There are many coating applications for this process (wear resistance, corrosion resistance, component repair and anti-fretting).  This system also has the advantage of being portable and it can be used for on-site applications.

Benefits of thermal spray coatings

Versatility in choice of performance enhancing coatings

Almost any material that melts and re-solidifies when cool can be applied as a thermal spray coating (pure metals, alloys, ceramics and carbides are amongst the most common).

Component protection

Coatings can be selected to:-

Increase temperature tolerance (thermal barrier coatings – TBCs)

Increase temperature conduction

Increase resistance to wear (Hard face Coatings)

Increase electrical conduction

Increase electrical insulation

Increase corrosion resistance

Increase chemical resistance

Increase resistance to fretting

Provide accurate clearance control (abradable coatings)

Metallisation of polymers and composites

Accurately controlled temperature of bulk substrate to 150°C or less

CWST has the ability to accurately control the temperature of the substrate during the coating process.  -This prevents any change in the properties of the substrate and allows coating of low melting point polymers or composite materials.

Coating thickness is easily controlled

Matching optimum coating selection with robotic application the coating thicknesses can be accurately controlled to ensure that the optimum depositions are achieved.

Complex shapes can be coated

Even components with complex shaped surfaces can be coated effectively using robotically manipulated application of the thermal spray coating.

Excellent Coating Properties

The final coating is optimised using data from the lab; hot and cold mount of coating samples, micro-graph image analysis, tensile bond testing, hardness checking, surface finish checking, thickness and evenness checking.

Pre and Post Processing

CWST can offer pre-thermal spray services such as shot peening to manage residual stresses and improve fatigue life as well as post-thermal spray services such as liquid coatings, grinding, polishing and impregnation both internally and through a trusted network of processing partners.

Find out more

To find out more about Curtis Wright or the thermal spray coating services provided by CWST get in touch with a member of our skilled team today.