Application of Coatings for Complex Ship Structural Surfaces Using Electrostatics
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AbstractThe US Navy utilizes several corrosion control technologies to ensure that its ships and ship systems are protected from the harsh saltwater environment in which they operate. One of the most common corrosion control technologies utilized are barrier type coatings. These coatings act on the principle that if the key components necessary to the corrosion electro-chemical reaction are eliminated and/or limited, protection of a substrate can occur. Specifically, barrier coatings prevent oxygen, moisture, and ions from reaching the surface of the coated substrate, thus preventing corrosion. However, if a barrier coating exhibits low film thickness or holidays in the coating this prevention mechanism is compromised. Barrier coatings failures typically occur in areas that are difficult to cover due to substrate geometry such as blind areas behind T-bars and stiffeners as well as sharp corners where coatings tend to pull away during cure. To combat these known problem areas, the US Navy employs a combination of high solids, edge retentive coatings, specifications that require multiple coats (including hand applied stripe coats to complex areas), and strict quality assurance (QA) by a third party inspector. These processes increase the cost of tank preservation, and the combination of these efforts to apply barrier coatings has been considered a target area for cost reduction by the US Navy. Therefore, research and development efforts have been funded to improve the coatings technology by reducing the required number of coats and the cure time of the coating system. Both of these reductions contribute to reducing the time a contractor needs to preserve a ship board system. However, by reducing cure time and the number of coats the time and opportunity for QA checkpoints are also decreased, thereby increasing the risk of low film thickness and/or holidays in the coating system. The requirement of multiple coats and QA checkpoints for dry film thickness measurements and holiday detection are aimed at improving paint coverage on complex areas of tanks and voids. Another promising approach to providing better coverage of complex areas is the use of liquid electrostatic application technology. The liquid electrostatic application technology ensures uniform coverage of the barrier coating on complex geometries, thereby increasing the corrosion performance of the coating system.
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