What Thermal Sprays Do for Corrosion Resistance
Corrosion is a massive problem for many industries in the UK, with millions of pounds spent on replacing parts and rectifying engineering failures due to corrosion. By applying the right thermal spray coating a significant portion of these failures can be avoided.
How the Coating Blocks Corrosion
A thermal spray coating forms a barrier on a surface by creating a dense layer of material. This layer of material will act to prevent moisture, oxygen and other corrosive chemicals from coming into contact with the substrate material. The particles that are sprayed at the surface will flatten and lock together, forming a strong barrier. The density of the coating is critical to the life of the coating, as a less dense coating with pores and voids in it will allow corrosive media to penetrate the coating, resulting in early coating failure.
Choosing the Right Coating Material
Zinc and aluminium are two of the most commonly used thermal spray materials for corrosion resistance. As sacrificial coatings on steel they will corrode in preference to the substrate, and will provide adequate protection even where the coating has been locally damaged. Pure aluminium is particularly suitable for use in marine environments and in the protection of equipment operating in chemical environments. However, a zinc-aluminium alloy provides a suitable compromise between the two materials, for use in environments where there is a risk of salt spray as well as high humidity.
Thickness, Porosity, and Salt Spray Performance
Spray coatings that have been applied to the correct thickness for corrosion protection are typically around 150 to 250 microns in thickness for most severe industrial applications. For less severe environments, coatings can be applied at a thinner thickness; however, it is always best to apply a thicker coating and ensure that the coating has low porosity as thinner coatings that have high porosity will deteriorate quickly in continuous salt spray testing.
Sealing the Coating After Application
Post treatment sealing of thermal spray coatings can improve the life of a coating significantly. Penetrating sealers are typical for the post treatment of thermal spray coatings and are available in various types of resin and silicone. A useful reference for Thermal Sprays is https://www.poeton.co.uk/surface-treatments/thermal-metal-sprays/.
Get the specification right for initial coating application to avoid early coating failure.
