Are You Playing the Clean Manufacturing Game?
A 10 part blog series discussing important aspects of clean manufacturing technology and implementation strategy.
Cool and Clean Under Fire – Part 7 of 10
Thermal spray coating uses a spray gun of one form or another to deposit finely divided and molten materials onto a substrate. Various materials, including metals and alloys, carbides, polymers, lubricants, ceramics, cermets and composites, can be thermally sprayed onto a substrate to protect critical components, rebuild worn surfaces and to reduce friction. For example, sprayed coatings are widely used to rebuild worn machine parts or to re-manufacture used equipment.
Precision surface preparation is a critical step prior to most thermal coating applications. The majority of coating failures occur at the coating-substrate interface. The reason for this is the discontinuity in the materials system (i.e., mismatched cohesion energies) and/or an improperly prepared bonding surface (i.e., cleanliness and surface area). Proper surface preparation insures that the adhesion between the first splat layer and substrate is strong. Oxides, microscopic particles and hydrocarbon films on bonding surfaces will reduce or prevent local bonding. Surface roughening with microabrasive grit blasting, for example using aluminum oxide particles, removes surface oxides while increasing the bonding surface area for the purpose of providing mechanical keying or anchoring of the first layer of solidified coating. A follow-on precision cleaning operation is used to remove ablated surface and microabrasive particles which typically populate newly formed surface topography.
Besides microscopic particles, oxides and hydrocarbons, another thermal coating process contamination is heat. During thermal spray coating processes such as flame spray, electric-arc (wire-arc) spray, plasma spray and detonation gun spray, substrates are subjected to very high and localized spray temperatures. Under continuous treatment, the temperature of a substrate will increase as the molten coating contacts and heats the surface. It is believed by experts in the field of thermal coating that if thermal migration and build-up is not managed, coating adhesion is greatly affected by the mismatch in thermal expansion or temperatures between a coating and substrate surface. For example, related to adhesion is splat formation during the application of a thermal sprayed coating.
Finally, following thermal coating of precision components, machining of coated surfaces to dimension the coating may be performed. As discussed above, machining heat must be managed properly to increase tool life, improve surface finish and increase the productivity of the machining operation.
A CO2 composite spray uniquely manages the variety of contamination present in a thermal spray coating operation, eliminating the need for separate cleaning fluids, cooling agents and machining agents.
David Jackson is President/CEO of Cleanlogix LLC and serves as the Chief Technology Officer for Cool Clean Technologies, Inc, based in Eagan, MN. He may be reached via e-mail at david.jackson@coolclean.com.
Part 8 of this series discusses a new surface inspection CleanTech called Optically Stimulated Electron Emission (OSEE).
1 comment:
You definitely know how to bring an issue to light and make it important.
I cant believe your not more popular because you definitely have the gift.
Cleantech Network
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