Hot-dip Galvanizing

Hot-dip Galvanizing by Delta Coat Industries

Hot-dip galvanizing stands as one of the most preferred solutions in the realm of metal protection, offering unparalleled benefits in terms of durability, sustainability, and economic viability. At its core, galvanizing is a process that involves the application of a protective zinc coating to steel or iron to prevent corrosion. This method, particularly hot-dip galvanizing, has established itself as an environmentally-friendly finishing process that surpasses many other coating techniques.

Degreasing

Degreasing is the process of cleaning Grease Oil from the material to be galvanized. Aqueous alkaline or acidic degreasing agents are usually employed.

Pickling

The surface must be cleaned prior to galvanizing. Pickling removes rust and scale which are the most common products contaminating the surface of steel fabrications.

Pickling is usually done in dilute hydrochloric acid (8-15%). The pickling time depends on the degree of rust on the article.

Rinsing

After chemical cleaning by pickling, the material is again washed in a water bath to minimize the transfer of any acid residue to the next stage. Soft water is used for this. The water quality used in the whole process shall be de-ionized water.

Flux Treatment

The application of flux immediately follows the pickling and rinsing stages. Flux serves to remove any remaining traces of impurities and provides a final intensive cleaning of the steel surface. It serves to increase the wettability of the surface of the steel to the Molten Zinc. The Flux usually consists of an aqueous solution of chlorides, principally a mixture of zinc chloride and ammonium chloride, material to be galvanized will be dipped into it.

Drying

After immersion in the flux tank, the material for galvanizing is dried and becomes coated with a thin film flux. The waste gases from the furnace are generally used for heating drying ovens.

Galvanizing

The galvanizing operation takes place in a hath of molten zinc. The temperature of molten zinc is controlled at range of 440°C – 450°C.

Zinc Used: Zinc SHG-99.995 % Confirming to ASTM B6 SHG

The galvanizing process causes the formation of a coating consisting of layers of Zinc Iron alloy caused by the reaction of zinc and steel.

Sampling will be done if the coating achieved is less, it is dipped more time in Zinc Kettle to achieve required microns DFT average coating as per standard and the same dipping time will be followed during the galvanizing process. Aluminum added to the bath shall never be more than 0.15%.

Based on the size of the material. it is dipped either vertical or inclined Lower width material will be dipped vertically and wider ones horizontally inclined. Time, the material to be kept in the bath shall be calculated and recorded in the report prior to material loading.

Quenching

The Galvanized steel, which by now is very hot, is either left to cool in the air or is immersed in a quenching bath.

Inspection

Galvanized surfaces shall be free from nodules, blisters, roughness, uncoated areas, and sharp points. Minimum 5 magnetic test readings shall be taken on 1000 sq. mm of coated areas DFT measured shall be as per the required standards. Crosshatch tests shall be carried out on the galvanizing surface when required.

Dispatch

If the material processed meets the quality requirements, it will be ready for dispatch.