Early in the development of electric arc thermal spray equipment, twin wire coatings were typically coarse and porous. Arc systems were used for dimensional buildup and anti-skid coatings. Today, arc spray technology has progressed to where arc spray systems are used in numerous types of applications. This presentation discusses corrosion applications and the industries that have driven arc technology development to improve coating quality and improve production rates--up to 4 times the original rates. This paper documents recent infrastructure applications, power plant cooling towers, and oil and gas industry applications as well as several other industry applications where the equipment is used. Physical properties, costs and testing in process will be discussed. The closing includes trends, needs for equipment and material and suggestions for future actions.
Two reports and a wide variety of articles in the past two years have brought metallizing or thermal spraying for corrosion protection to the point where many owners, applicators and specifiers are considering it as a viable option. Thermal spraying is the use of a heat source such as an oxygen-fuel flame (using powder or wire), a plasma (using ionized gas and powder), High Velocity Oxygen Fuel (HVOF, a supersonic oxygen-fuel) or electric arc (utilizing short circuit electricity air and wire) to make the wire or powder plastic and propel it against a substrate. We concentrate on twin wire electric arc (TWEA) in this paper because of its portability, productivity with high production units and efficiency.
The first report is the Battelle Report? which states that of the $300 billion that corrosion costs industry in the United states each year, $100 billion is avoidable and approximately.%36 billion of that amount can be viewed as a potential for thermal spray corrosion applications. This cost is driving the development of coatings to combat corrosion.
The second report is entitled Environmentally Acceptable Materials for the Corrosion Protection of Steel Bridges.* It reported that life-cycle costing analysis can show that thermal spray coatings(TSC) can be more economical than other coatings because of TSC?s much longer life. TSC?s have a low volatile organic compound (VOC) rating that is favorable when assessing environmental impact of the protection method. This report is important for bridge owners considering TX?s as corrosion protection.
Arc Spray Equipment
Arc spray equipment is simple to set up and requires only compressed air and electricity. Two electrified wires are either pulled by a motor in the gun or pushed to the gun by a remote motor into a short circuit to form a molten arc ball. The gun utilizes air to atomize small particles from the arc ball and propel them against the substrate. The volume and velocity of the air and how the air is presented to the molten metal determine the density and size of the particles and the final integrity of the coating. Figure I shows a schematic of a typical arc gun. The two intersecting lines represent the wire, and the gray arrows in the center show the path of the atomizing air. Research at INEEL with l/16 (, 16 cm) and 2 mm (.08) diameter wire and at Vartech with l/8 c.32 cm) and 3116 c.48 cm) wire characterize the parameters and show t
