Thermal Spray – The All Purpose Solution For Material Challenges

Designers, engineers, and manufacturers are tasked with pushing conventional materials to their limits. Components are required to succeed in new, challenging and often extreme operating conditions.

Rhys Didcott, Flow Manager at Poeton Industries, knows how important choosing the correct surface treatment is in achieving this operational success. One such surface treatment solution that he recommends to his customers due to the range of benefits is thermal spray.

Here Rhys helps explain the choice of thermal sprays that there are on the market and why engineers should be turning to them when looking for solutions.

“It is often seen as the surface treatment of the future, but thermal spray is not a new invention. In fact, the first thermal spray patents are over 100 years old. Initial thermal spray processes were refined in the early parts of the 20th century, with use growing throughout the 1940s and 50’s before becoming a mainstream surface treatment choice in the 1980s. Today, thermal spray has been adopted as an application in a wide range of industries due to the scope of benefits it provides.”

Reducing Abrasive Wear

“The effects of wear can be a costly problem causing delays to production, machine breakdowns and component failure” states Rhys, but “using thermal spray coatings can help protect against abrasive wear, in both low-stress and high-stress scenarios.”

Low-stress abrasion often occurs in industries such as textiles, plastics, and food production, where micro-particles in the product cause abrasion of machine parts. For the best thermal spray solution to prevent machine-downtime, Rhys recommends “a plasma sprayed ceramic material, such as chromium oxide as these provide the required surface hardness to withstand the abrasive properties of the product.”

Additionally, high-stress abrasion can occur in pumps, valves, and conveyors where aggressive debris or product is heavily loaded against the contact surfaces. The solution here will need to be an extremely tough, hard, high energy thermal coating in the form of the various chromium and tungsten carbide coatings available.

Corrosion Resistance

“Nickel, chrome, and cobalt-based aluminium and zinc coatings are the best choice when looking for corrosion protection”.

“When corrosion resistance is the primary objective, we also recommend sealing the coating to close any residual porosity and maximise the protection offered”.

This corrosion resistance is particularly important in the marine, petrochemical, oil and gas sectors. Due to the nature of the products, thermal spray coatings help extend the life of these components.

Thermal Barriers

A thermal barrier coating is used to protect a vulnerable substrate from the effects of an external heat source. This is achieved by reducing the flow of heat on to the substrate and requires a coating with low thermal conductivity.

Rhys comments that he would advise on “ceramic coatings, such as alumina, MCrAlY or yttria stabilised zirconia when thermal barriers are required.” They provide a low conductive and oxygen diffusion barrier, protecting vulnerable substrates in applications including piston crowns, rocket nozzles, missile nose cones and carburising boxes.

Salvage

Thermal spray coatings excel in being able to salvage parts that have been damaged, worn or eroded and are destined for the scrap heap. In order to reclaim these parts, the damaged area is cleaned up, blasted and then coated with new material. Components are coated to an oversize condition before being machined or ground back to its final size.

The chosen coating must, in general, match the substrate regarding its composition and hardness. This includes similar machining or grinding characteristics.

Rhys describes the component shown to the right as a “perfect example of the role salvage can play.” He continues, “this high-performance exhaust manifold was going to be scrapped. Abrasion damage and corrosion meant our customer couldn’t rely on it to perform to the standard required and were faced with a high cost of a replacement.” A Poeton thermal spray coating was applied along with a polymer top layer to provide wear and corrosion resistance, enabling the manifold to remain in service.

Electrical Properties

Thermal spray coatings can provide a range of electrical properties. For example, Rhys details that “plasma-sprayed metals, like copper, allow for a highly conductive surface”, making them ideal for applications such as lightning arrestors.

Alternatively, thermal coatings can also be utilised to provide a high level of electrical resistance. Rhys explains that this is “achieved by dense, pore-free sprayed ceramics to provide the dielectric strength for insulation applications”, such as heater tubes, soldering tips and electronic componentry.

Electrical shielding can also be achieved with thermal spray coatings and are commonly used for instrument assemblies and missile systems. The sprayed material is employed to absorb and earth stray RF induction and to shield against gamma rays and thermal neutrons.

Bedding-In Applications

Rhys comments that this is “a classic application where a combination of thermal spray coatings are used on parts in turbine engines.” An abradable coating, such as nickel-graphite, is applied to turbine stators whilst an abrasive coating is applied to the turbine blade tips.

The abrasive blade tips then cut through the stator surface when rotating, creating the perfect dimensional match with the minimum blade/stator clearance. Rhys continues, “we process a lot of components for this as it allows the engine to operate to its maximum performance efficiencies, vital in meeting stringent emission targets.”

Ready to incorporate thermal spray into your plans?

If you’re now convinced by the benefits that thermal spray can offer and the range of applications in which it can be utilised, then the Poeton Thermal Spray Centre of Excellence will be able to help you on your way. Staffed by expert engineers and state of the art equipment, the team will be able to guide you in selecting the best thermal spray option to ensure your engineering success.

To find out how you and your components can benefit from the properties of thermal spray coatings, visit www.poeton.co.uk or call 01452 300 500.