GONGDA is anintegrated galvanizing solution provider in China. The oxidation-reduction type steel wire hot-dip galvanizing is a variation of the Sendzimir process. As one of the most eco-friendly and energy saving hot-dip galvanizing technologies, this type of technique is especially used for low carbon steel wire, while, at the very beginning,Sendzimir process is applied to the steel plate galvanizing. During the pretreatment of the oxidation-reduction galvanizing line, reducing gas will be used for the reduction of oxide on the metal surface before the galvanizing. This eliminates the need for acid pickling, fluxing, and drying processes.

Our R&D department spent more than 5 years in the adaptation of Sendzimir process to make it suitable for the low carbon steel wire hot-dip galvanizing. A great success was achieved after a series of hard works. The high efficiency steel wire galvanizing machines were successfully put on the market.

Advantages of the galvanizing equipment

• Environmental protection
  The oxidation-reduction method can reduce the oxides on the surface of the steel wire chemically, rather than by acid rinse and flux solution treatment. Accordingly, the production cost and pollutants are both greatly lowered.
• Energy saving
  After annealing in the reducing furnace, the 500℃ steel wire doesn’t need to be cooled, but get galvanized directly in the galvanizing kettle. The advantages of this low carbon steel wire hot-dip galvanizing include lower energy consumption, shorter galvanizing time, about one third shorter galvanizing kettle, and reduced equipment and zinc ingot investment.
• High efficiency
  The hot steel wire goes into the galvanizing kettle directly, achieving higher reaction speed between steel wire and molten zinc solution, as well as higher production efficiency.

Specification of the galvanizing equipment

• Steel wire: low carbon steel
• Wire diameter range: 1.2 – 4.5 mm
• Coating thickness: 120 – 450 g/m²
• Number of wires: 6 – 28 strands
• Drawing speed (DV value): 60 – 120 mm·m/min
• Annual output capacity: 2000 – 25000 tons

Process flow of the oxidation-reduction type steel wire hot-dip galvanizing line
Wire feeding - electrolytic alkaline rinse - hot water rinse - surface activation - oxide reducing and annealing - tempering - hot-dip galvanizing (electricity/natural gas/ liquefied petroleum gas) - wiping (nitrogen/oiled charcoal) - air/water cooling - post treatment (passivation/waxing) - wire take-up (inverted type/spool type)

Spool type wire pay-off machine
The vertical wire pay-off machine of our low carbon steel wire hot-dip galvanizing is suitable for wire with high coil weight, and comes with a damping tension control unit is available.

Ultrasonic cleaning
The rinsing bath is built with either reinforced polypropylene panels or welded 304 stainless steel, providing excellent chemical resistance and durability, and an extracorporeal circulation solution preparation tank is available, ensuring the stability of the bath solution and the convenience of the dirt cleaning.

Electrolytic alkaline degreasing tank

Ultrasonic Cleaning Bath
The ultrasonic cleaning tank is made with welded 304 stainless steel plates and equipped with a top-mounted ultrasonic vibration panel. Through ultrasonic cavitation and direct impact flow, any residual impurities on the wire surface are thoroughly removed, ensuring effective oxidation-reduction reactions in the annealing furnace.

Water rinsing bath
The rinsing bath of our low carbon steel wire hot-dip galvanizing is welded by PP plate. The overflow type circulating rinsing mechanism and an air knife are both available. Thus great cleaning performance can be guaranteed, and less sewage will be produced.

Activation bath
The activation bath is welded by reinforced PP plate. A heating device and air knife are available for getting cleaner steel wire surface.

Reducing and annealing furnace
The annealing furnace is a kind of tubular muffle furnace that could be heated by electric or gas. The high temperature resistant 2520 type stainless steel is adopted for the furnace tubes which are flooded with reducing gas (Nitrogen and hydrogen produced by an ammonia decomposition machine). Annealing furnace comprises pre-heating section, heating section, stabilizing section, and heat conservation section. A multi-point temperature control system is designed for the high precision temperature control.

Tempering Furnace
Our tempering furnaces incorporate a multi-stage water circulation cooling system to keep the wire temperature within a stable range before galvanizing. The cooling process is managed by multiple booster pumps that deliver water across several adjustable stages. Depending on the wire diameter and production speed, the cooling sequence can be precisely regulated to maintain the target temperature consistently at 450–500 °C as the wire enters the zinc bath. This design helps achieve stable process conditions and contributes to consistent coating results.

Ceramic hot dip galvanizing kettle (Zn/Galfan)
As the steel wire enters the kettle preheated to galvanizing temperature, the kettle’s heating system requires minimal operation during normal production.
The internal heating ceramic galvanizing kettle is a kind of advanced zinc-plating industry. Its heating efficiency could reach more than 80％. Limited zinc dross will be produced and the zinc consumption is also very low. The service life could be more than 20 years, while the temperature control accuracy is ±1℃. Thus the quality of the product from our steel wire hot-dip galvanizing line is quire stable.

Steel frame
The frame is made of reinforced steel which can provide great stability. A wire take-up machine is connected with the frame by bridging connection to facilitating the production.

Zinc coating wiping method of the steel wire hot-dip galvanizing line

• Nitrogen-shielded air knife wiping, designed for low-speed galvanizing applications requiring thicker zinc coatings (zinc consumption: 150~300g/m²)
  Advantage: The operation is quite simple and only a small investment is needed. Disadvantage: The galvanizing speed should be less than 25m/min. The thickness of the zinc layer can not be controlled accurately. A large amount of oil fume will be produced, causing serious air pollution.
• Nitrogen wiping
  Advantage: This contactless wiping method can precisely control the zinc layer thickness by adjusting the gas pressure. It is suitable for high speed production. The operation is quite simple, and the zinc consumption is significantly lowered. In addition, no oil fume is produced during the whole process. Disadvantage: The investment is larger than the other methods.

Cooling
In our steel wire hot-dip galvanizing line, the air cooling and water cooling are combined together to cool the steel wire rapidly. Thus we can effectively control the thickness of the zinc-iron alloy layer, and enhance the smoothness of the galvanized steel wire.

Wire take-up machine

• In our steel wire hot-dip galvanizing line, the inverted take-up machine is commonly used for low/middle carbon steel wire with regular wire diameter (1.2~5.0mm) and medium wire coil weight (500~1000kg). The production speed should be 15~80m/min.
• The spool type take-up machine is suitable for high/middle carbon steel wire with various wire diameter (1.6~8.0mm) and medium wire coil weight (above 1000kg).