Thermal Spray - Here's A Second Look

Sure, hard facing relates to thermal spray, though it's really more about depositing 'filler' materials onto a metal surface for repair or dimensional restoration. And, normally, these improvements relate to promoting wear resistance, alone.

But did you know these 'overlays' of material may also contribute to corrosion prevention, low friction, anti-fretting or galling, even release (non stick) properties? What was formerly developed for rebuilding worn parts or those with machining errors is now extending into many fields of surface engineering.

The principle of applying thermal spray is quite basic. That is, molten or semi-molten metals, alloys, or ceramics, atomized, are fed toward the work piece by a jet stream of air.

As these particles impinge the working surface, they dissipate their heat, quickly cooling, building up, fusing into a cast-like structure described as highly cohesive. Resultant surface finishes, as-sprayed, typically range between 100 and 400 micro inch. So, depending on requirements, finish grinding or polishing may be required. (Values under 10 micro inch are very much attainable.)

What types of materials can be applied by thermal spray? The answer is most metals, ceramic, cermet(ceramic-metal combinations), tungsten carbide, even organic-based compounds like polyesters.

Adhesion, largely mechanical (versus metallurgical), is excellent. Grit blast, as a means of surface preparation, is typical to best promote adhesion. Though tensile strength can be sometimes improved upon with higher temperature processes, depending on choice of material, through micro-welding or diffusion.

Common methods of application include HVOF (high velocity oxygen flame), which is similar to the combustion powder thermal spray process (LVOF), though with increased density, stronger bonds and lower residual tensile stress. Plasma spray and vacuum arc spray are also popular.

Applications continue to grow with this technology. Food processing, packaging, molding, plastics, paper and chemical processing, are just some of the newer, relevant applications. (Many materials are regarded non-objectionable with FDA.)

Ideally, look for thermal spraying processes with minimal heat transfer to your work piece. Just to be certain your surfaces are free of warping, surface distortion. Latest versions include 'higher kinetic energy systems' to ensure highest density, particle-to-particle cohesive bonding. The result is long-lasting, cost-effective, surface performance.

Want to create a new dimension to your surface? Take a second look at Thermal Spray!

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