Zn Spray Coating on ERW Tube Seam


A roll forming machine draws hot or cold rolled steel through successive stations and shapes the material into a tube. Electric resistance welding closes the seam left by the butted edges. Although no filler metal is added that would change the chemical compositions, the welding process applies temperatures high enough to sacrifice some corrosion resistant properties of the base metal. The process may also vaporize aluminium or galvanized coatings previously applied to the rolled steel.

The thermal spray process applies coating of zinc to reinstate the corrosion resistance properties of the tubing. Applying the spray while the weld seam is hot assures a metallurgical bond of the sprayed material with the substrate, improves both the deposit efficiency and density of the sprayed material, and allows the coating to blend, thereby helping to hide the weld seam. Arc spray is the most user-friendly and, in terms of operating cost, the least expensive of the thermal or metal spraying processes used for applying metal coatings to base materials. Any electrically conductive material in wire form can be arc sprayed.

Wire pulling system by DC Motor, fitted in the gun which ensures precision wire feed speed. The wires meet at the head of the gun and melt in the electrical arc. The molten mass is atomized and blown on to the substrate with compressed air. The particles cool to ambient temperature and coalesce into a high quality metal coating.

The distance from the arc to the tube seam is an important measurement on tube mill installations. Standard arc spray air caps provide conical spray patterns. Straight extensions provide elliptical patterns. A small spray width minimizes over-spray and precisely controls material usage.

Installing the arc spray gun in an enclosed box ventilated to a dust collector ensures environmental and personnel safety. Dust,fumes,and overspray must be removed from the spray zone quickly. Over-spray can contain particles of less than 2 microns in size, and can constitute to 4 to15% of the over-spray by weight. If not properly ventilated, this could cause a hazardous breathing zone or impede mill operations downline hence efficient dust collection system is necessary.

Metallzing Equipment Co. Pvt. Ltd. (MEC) Have supplied the complete automatic Zn spray coating on tube seam system to several well known tube mills in Indian as well as foreign territories. MEC’s manufactured arc spray system is easy to use & maintain a repeatable quality work.

Source: Metallizing Equipment Co. Pvt. Ltd.

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