The Reason for Inclining Steel Tubes at an Angle When Dipping Them into the Zinc Bath for Galvanizing

When steel tubes are dipped into the zinc bath for galvanizing, they must be inclined at a sufficient angle, especially when galvanizing small-diameter tubes which sag and bend significantly in the middle. Why is this necessary? Firstly, we know that steel tubes, unlike other products, are hollow and slender with poor rigidity (especially for small diameters of 10 to 25 millimeters or 3/8" to 1"). Without a certain angle of inclination and rapid immersion in zinc, the gas inside the tubes cannot be removed. When both ends of the tube are filled with zinc liquid, the gas in the middle expands due to heat and ejects the zinc liquid inside the tube, causing harm. Especially when the solvent inside the tube is not fully dried, water evaporates into steam, increasing in volume by hundreds of times, resulting in a strong ejection of zinc liquid from inside the tube. This is very dangerous and can lead to missed plating and speckling on the inner wall of the galvanized steel tube. Secondly, when the angle of inclination is too small, especially when galvanizing small-diameter tubes, the middle sagging part may come into contact with the zinc liquid surface almost simultaneously with the head end. As a result, the wall of the steel tube in contact with the zinc liquid surface rapidly elongates and bends into an arc shape due to heat. The pressure then pushes it downwards, but the resistance of the zinc liquid prevents it from moving further down. Consequently, both ends of the tube move down rapidly, causing the tube to roll over on the surface of the zinc liquid. As the zinc-plating turntables continue to lower it, the steel tube enters the zinc liquid as shown in Figure 3-156. Due to the presence of air in the middle of the bent tube, it expands upon heating and ejects out, allowing the zinc liquid to fill the inner hole of the tube. If the solvent is not fully dried, the ejection pressure will be greater and more dangerous, leading to more severe missed plating. Therefore, it is better to have a larger angle of inclination when dipping steel tubes into zinc. The minimum angle should prevent the tube from rolling over after emerging from the zinc bath. The best configuration is as shown in Figure 3-15c, which prevents the steel tube from coming into large-area contact with the hot zinc liquid on one side, thus avoiding significant thermal expansion and minimizing tube bending. As the tube is pressed into the zinc liquid with the turntable, there will be no rolling. At the same time, the gas inside the tube can escape smoothly and sequentially. The zinc liquid is at the same horizontal level inside the tube, preventing missed plating. This is more effectively achieved on step-through turntable galvanizing machines with a large dipping angle. However, on continuous turntable galvanizing machines, rolling is more pronounced, especially when galvanizing small-diameter tubes. Rolling of steel tubes will result in missed plating, which should be taken seriously, especially when galvanizing in aluminum-containing zinc liquid.