Pulsed Semiconductor Diode Lasers as an Environmentally Efficient and Affordable Decoating Method for Shipbuilding and Ship Maintenance

Abstract

Coating removal during new ship construction or ship maintenance has traditionally posed environmental and production issues. Coating removal results in a large amount of waste, and other trades cannot work in or near areas where coating removal operations are going on. Hydroblasting, an environmentally friendly method, has significantly decreased in recent years; it cannot be used on interior compartments. The dilemma has been to find a surface-preparation method that is effective yet environmentally acceptable and one that can work on the outer hull as well as on the inside compartments. Further, a method is needed to remove coatings from the new "soft" substrates. Laser devolved over the years from expensive CO2 and Nd:YAG lasers to the recent innovation of using affordable semiconductor diode lasers for coatings removal. Semiconductor diode laser decoating is a nonintrusive, nonkinetic energy process that has successfully removed coatings from a variety of substrates, such as composites, fiberglass, metal, and plastics, in a controlled manner, layer by layer, without damage, leaving the surface ready for immediate repainting. The process is very rapid (up to 400 sq ft per hour), 6 to 10 times faster on average than the present manual hand-sanding methods, and involves a minimal increase in temperature, because the energy is mostly absorbed and utilized in coating decomposition (i.e., instant pyrolization and evaporation). The only waste associated with this process is the ablated coating that is vacuumed from the surface and captured in particle filters, approximately one-third of the amount of coating originally on the surface. Diode lasers are compact, durable for shipbuilding and repair industry use, and present low operating costs. Due to delays in receiving test panels from Navy and commercial ship sources, this paper will highlight data from tests of removal of coatings similar to military epoxy/polyurethane coatings from thin-skin metallic, composite, and fiberglass structures, radome material, and for removing powder coatings. Pulsed high-energy diode laser decoating technology is now commercially and economically available for ship corrosion control and maintenance, can reduce the overall environmental impact of decoating, and can increase productivity of all the ship trades.