Galvanized (G.I.) tubes and pipes from tube mills often lack corrosion resistance on welded seams due to zinc layer removal during welding, leading to rusting. Metal Coat developed a chemically safe thermal spray system for continuous inline zinc coating on G.I. tubes and pipes at the weld seam. The system has been proven and supplied to major tube mills with satisfactory performance. Zinc spray thickness ranges from 20 to 30 microns, with the ability to deposit 10 to 100 microns depending on pipe speed. Applicable on tubes and pipes from 15mm to 125mm nominal bore, without slowing tube mill production. Average output is about 10 pipes per minute with approximately 25 microns coating thickness. The system package includes a dry spray booth, twin cyclone dust collector, exhaust fan with motor, and ducting. The booth is installed immediately after welding. The arc spray gun inside the booth sprays zinc wire onto the hot weld seam, producing a dense coating with a strong metallurgical bond. Dust and fumes are sucked into the cyclone collector by exhaust fan suction; zinc particles settle at the cyclone bottom, while clean air exits through the blower, maintaining a clean environment. The Arc Spray Gun system features two-wire feed mechanisms (DC/AC power), integrated power source and control console, and wire spool stands with 15kg capacity. Wire feed is motor-driven by a pull process, with adjustable speed. Zinc spraying is a cool process producing fine, dense coatings with high bond strength and low porosity.

Arc Spraying Process

Arc spraying melts two similar or dissimilar wires (coating material) via an electric arc, then accelerates molten particles toward the prepared surface using an atomizing gas like compressed air. This wire spraying method requires the coating material to be electrically conductive. Twin wires are fed by an electrically driven motor.