Galvanized steel pipes feature strong corrosion resistance as well as high strength and rigidity, and are widely used in pipelines for gas, heating and water supply.
The production process is as follows:
Black pipe → Caustic washing → Water rinsing → Acid pickling → Clean water rinsing → Flux dipping → Drying → Hot-dip galvanizing → External air wiping → Internal air wiping → Air cooling → Water cooling → Passivation → Water rinsing → Inspection → Weighing → Warehousing
The specific name is:
1.Pre-galvanizing Process
It consists of five processes: caustic washing, acid pickling, rinsing, flux dipping and drying.
1)Some steel pipes have oil stains on the surface and require caustic washing.
2)Hydrochloric acid is used for pickling to remove oxide scale on the surface of steel pipes.
3)To remove residual acid and iron salts attached to the surface of steel pipes, the pipes need to be rinsed twice.
4)The purpose of the flux is to remove all impurities from the surface of the steel pipe, ensure clean contact between the steel pipe and the molten zinc, and form a high-quality coating.
5)To prevent splashing or explosion when the steel pipes are immersed into the zinc pot, the flux-coated steel pipes must be dried at a temperature of 120–200 ℃ for no less than 150 seconds.
2.Hot-dip Galvanizing Process
1)The temperature of the molten zinc in the zinc pot is strictly controlled at 450±5℃
2)The dried steel pipes are removed one by one from the drying furnace conveyor, fed into the furnace roller table, then transported to the galvanizing furnace, and rolled into the three zinc-dipping spirals inside the galvanizing machine.
3)The three spirals have different phases, causing the steel pipes to be inclined on the spirals. As the spirals rotate, the steel pipes move downward while forming an inclination angle, then enter the molten zinc and continue to move downward.
4)The steel pipes automatically drop onto the slide rails inside the zinc pot, are pushed to the outer side by the material shifting mechanism, and then lifted out of the molten zinc by the pipe extractor.
5)When the steel pipes are lifted to the surface of the magnetic rollers, they are attracted and transferred to the exit roller conveyor.
3.Post-galvanizing Process
The post-galvanizing process includes: external air wiping, drawing out, internal air blowing, water cooling, inspection, passivation and marking.
1)The steel pipes pass through an external air wiping ring equipped with a row of small holes. Compressed air is used to blow off excess molten zinc from the pipes, resulting in a smooth and clean surface.
2)While meeting the production tempo, reducing the drawing speed can control the coating weight and lower zinc consumption.
3)Internal wiping can remove excess molten zinc from the inner surface of steel pipes to achieve a smooth internal surface. The removed zinc forms zinc dust, which is then recycled.
4)The temperature of the cold water tank is controlled at 80℃. The cooling water is pumped to the cooling tower for cooling and then recycled.
5)After water cooling, the steel pipes are moved out of the water cooling tank and placed on the inspection stand. After inspection, pipes with bare spots (uncoated areas) are placed into the scrap bin, while finished pipes are sent to the output roller conveyor.
6)During conveying, finished pipes pass through a passivation solution spraying ring for surface passivation. After passing through the external air wiping ring, excess passivation solution is blown off using compressed air.
7)During conveying, the pipes pass through a drying rack equipped with steam-heated pipe bundles. After drying, they are marked and packaged.
