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Thermal Spray


Thermal Spray since its inception almost a century ago, thermal spraying has evolved from a technology designed to be a cost-effective repair of worn components and mismachined parts to a process used to provide improved part performance and longer life to OEM. As part of its growth process, thermal spray has developed from the original flame spray process the electric arc, plasma, and high-velocity oxyfuel systems. In addition, the palette of materials available for thermal spraying has expanded from metal alloys to ceramics, polymers, and carbides. One of the many industrial areas in which thermal spray has established itself is as a low-cost hardfacing alternative to weld cladding and chrome plating.

 

An Introduction to Thermal Spray

Thermal spraying, like weld cladding or chrome plating, is a coating process. In thermal spray, wire or powder is melted by a flame or electricity and sprayed onto the workpiece. During the actual process, the spray torch makes successive passes across the workpiece to produce a coating. Like all industrial processes, thermal spraying has advantages and limitations. These have to be kept in mind in order to take proper advantage of thermal-sprayed coatings.

 

The following are some of the benefits of thermal spray coatings -

Reduced Cost - In lieu of making the entire part out of an expensive material, a high-performance material is sprayed onto a low-cost base material.

Low Heat Input - Thermal-sprayed coatings do not impact the substrates' microstructure. The coating does not penetrate the base material, i.e., there is no heat-affected zone.

Versatility - Almost any metal, ceramic, or plastic can be sprayed.

Thickness Range - Coatings can be sprayed from 50 microns to more than 10 mm in thickness, depending on the material and spray system.

Processing Speed - Spray rates range from 3 to 60 lb/h depending on the material and the spray system.

Some of the limitations of thermal spray include the following -

The bond mechanism between the coating and workpiece is primarily mechanical, not metallurgical.

Thermal spraying is a line-of-sight process.

The coatings are considerably stronger in compression than in tension.

The coatings have poor resistance to pinpoint loading.

The different thermal spray processes are Flame spraying, Arc Spraying, Plasma Spraying and High Velocity Oxyfuel Spraying.