An Introduction to thermal spraying

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In many industries, including but not limited to manufacturing, aerospace and the automotive sector, the protection and restoration of solid materials is a perennial challenge. Thermal spraying technology has enabled the use of highly effective coating processes that apply sprays of finely divided droplets of a protective consumable to almost any surface, such as metals, polymers and ceramics. These molten or semi-molten substances can provide resistance to wear, corrosion, cavitation, abrasion, erosion or heat. Thermal spraying can also provide conductivity and insulation, affect levels of friction, and improve lubricity.

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Different processes

While the Thermal Spraying and Surface Engineering Association (TSSEA) clearly delineates four distinct methods of achieving the desired result, and although almost any material can be used as long as it has the appropriate physical properties, thermal plasma spray has become widespread. It has proven to be one of the most effective materials yet applied.

One of the factors that distinguish thermal spraying from comparable processes, such as arc welding and laser coating, is that the bond between the coating and the substrate is mechanical and does not involve fusion. This removes any requirement for metallurgical compatibility between the two.

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Another advantage of thermal spraying is that it allows the use of materials with a higher melting temperature than the target substrate. There is very little need for pre- or post-heat treatment, and the spraying process largely avoids any distortion to the component itself.

Applications

Many companies that specialise in the provision of protective surface treatments have evolved alongside the technology since the earliest days of nickel plating, which was invented in the US and pioneered in the UK by visionary enterprises such as Poeton. The process is routinely used on a wide variety of hard surfaces that are subjected to intense wear and heat during regular usage. It has proven indispensable in the manufacture of diesel engines, turbines, oil field machinery, and medical equipment. It also plays an important role in the reclamation and re-engineering of moving parts in machinery such as printing presses, mining equipment, power generation, and road and rail vehicles.

In addition to plasma, coating materials include steel, steel alloys, polymers, plastics, tungsten carbides, ceramics and copper. The process can be conducted manually or by mechanical means, with considerable flexibility in determining the thickness of the finished coating.

In the protection of industrial machinery and heavy plant, thermal spraying remains the leading-edge technology.

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