Original Date: 04/24/2007
Revision Date: / /
Best Practice : Plasma Cleaning Process
The University of New Orleans, College of Engineering evaluated Cathodic Atmospheric Plasma using foam plasma processes for cleaning rust, scale, hydrocarbon, and other forms of contaminants from conductive metal surfaces, allowing them to accept paint or coatings. The technology is ready for commercialization, with its first full-scale application in the cleaning and preparing of wire, rods, and tubing.
The University of New Orleans, College of Engineering (UNO COE) is developing and evaluating electro-plasma technology as a source for cleaning and coating metal surfaces for maritime applications. The scope of its work involves the study and comparison of flow-through electro-plasma processes with Cathodic Atmospheric Plasma (CAP) using foam plasma processes for cleaning rust, scale, hydrocarbon, and other forms of contaminants from conductive metal surfaces, allowing them to accept paint or coatings. The technology is ready for transfer to industry, with its first full-scale application in the cleaning and preparation of wire, rods, and tubing. The development and evaluation work was accomplished in partnership with CAP Technologies, LLC. Commercialization of the technology is being pursued to meet the needs of shipbuilding and other industrial markets.
Existing processes for removing rust and scales from steel and other conductive metals include grit or shot blasting, acid pickling, electrolytic cleaning, electroplating, and plasma processing in a high vacuum. The UNO COE’s original study evaluated the cost effectiveness, long-term performance, and environmental considerations of each process compared to the flow-through electro-plasma process. This first-generation technology was soon superceded by the CAP foam process, which has fewer critical parameters and achieves more reliable results without the use of a vacuum system. The CAP foam process consists of a foam-aqueous electrolyte comprised of at least 30% gas/vapor. The workpiece is then positioned in a sealed chamber and filled with foam (Figure 2-2). A pad of discrete hydrogen bubbles form within the liquid layer on the surface of the workpiece. The conductive path becomes the walls of the foam bubble. The key to this process is that the distance between the anode and the workpiece is less critical than the flow-through process. Tap water and baking soda can be used to create a denser foam material to remove stubborn materials from surfaces.
The UNO COE and its partner CAP Technologies, LLC, built prototype equipment and evaluated the cleaning of carbon, stainless, duplex, silicon steels, copper, titanium, and aluminum. Zinc, copper, lead, nickel, copper/nickel, copper/zinc, and zinc/aluminum were deposited using the process. Evaluations of cleanliness, corrosion resistance, and adhesion properties were based on data accumulated from polarization resistance tests, ultraviolet weathering tests, surface profiling, and others. Analysis shows that CAP plasma cleaning provides superior cleaning and corrosion resistance and offers good adhesion properties at a fraction of the cost of traditional cleaning and coating methods. As a result, the CAP plasma cleaning system is being repackaged for use on a production scale to clean metal pipes, rods, and tubes for sale to shipyards and commercial markets. Future plans call for broader commercial applications on metal surfaces and conductive metal coatings.
Figure 2-2. CAP Foam Process Chamber
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