Hot Dip Galvanizing Process — Step-by-Step Guide to GI Wire Manufacturing

The Hot Dip Galvanizing Process — How GI Wire Is Made

Hot-dip galvanizing is a highly specialized metallurgical process in which iron or steel is coated with a protective layer of zinc. For wire, this is performed in a continuous galvanizing line where steel wire is pulled at high speeds through successive chemical baths and a bath of molten zinc. This guide details the 8-stage manufacturing process employed at our state-of-the-art facility in Jaipur.

Step 1: Raw Material Selection (MS Wire Rod)

The process begins with low-carbon mild steel (MS) wire rods, typically conforming to IS 7887 or IS 2830 standards. These rods undergo strict chemical analysis to verify carbon, manganese, phosphorus, and sulfur content before processing.

Step 2: Cold Wire Drawing

The heavy wire rods are pulled through a series of tungsten carbide dies on automated continuous drawing machines. This reduces the raw rod's diameter (typically 5.5mm) down to the target wire gauge (such as 1.6mm or 2.0mm) while increasing its tensile strength due to work hardening.

Step 3: Inline Thermal Annealing

Drawing makes carbon steel hard and brittle. To restore ductility and make the wire flexible (soft grade), it is passed through an annealing furnace operating at 800°C–900°C. This recrystallizes the grain structure of the steel, making it pliable enough to be easily bent or twisted.

Step 4: Acid Pickling

The annealed wire is passed through an acid bath (dilute Hydrochloric Acid or Sulfuric Acid) to strip away all surface iron oxides, scale, and rust. Clean, unoxidized steel is vital because molten zinc will not chemically bond to contaminated steel.

Step 5: Rinsing and Chemical Fluxing

After pickling, the wire is washed with water and passed through a flux solution (Zinc Ammonium Chloride). The flux acts as a drying agent and catalytic barrier, preventing the raw steel from re-oxidizing before it enters the zinc bath.

Step 6: The Molten Zinc Bath

The clean, fluxed wire is submerged in a zinc bath containing 99.99% pure molten zinc maintained at 450°C–460°C. A series of metallurgical intermetallic reactions occur, creating layers of zinc-iron alloys topped by a layer of pure zinc.

Step 7: Coating Wiping & Sizing

As the wire exits the zinc bath, it passes through specialized wiping pads (such as charcoal or asbestos wipes) to control the thickness and weight of the zinc coating. This dictates whether the finished wire meets light, medium, or heavy coating standards.

Step 8: Testing & Coiling

The finished galvanized wire is cooled, batch-tested for diameter, tensile strength, and zinc weight, and wound into coils (usually 25kg to 150kg) using continuous take-up coiling frames.