Why should the steel pipe be inclined at an angle when entering the zinc bath for dipping and galvanizing?

When a steel pipe enters the zinc bath for dipping and galvanizing, it must be inclined at a sufficient angle, especially when galvanizing small-diameter steel pipes, which sag and bend significantly in the middle, requiring a larger inclination angle. What is the reason for this? Firstly, we know that steel pipes, unlike other products, are hollow and elongated with poor rigidity (especially for small diameters ranging from 10 to 25 millimeters, or 3/8" to 1"). Without a certain inclination angle and rapid zinc dipping, the gas inside the steel pipe cannot be removed. As a result, after the two ends are filled with zinc liquid, the gas in the middle expands due to heat and ejects the zinc liquid inside the steel pipe, causing harm. Especially when the solvent inside the steel pipe 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 steel pipe. This is very dangerous and can lead to missed galvanizing and spots on the inner wall of the galvanized steel pipe. Secondly, when the inclination angle is too small, especially when galvanizing small-diameter steel pipes, the middle sagging part may come into contact with the zinc liquid surface almost simultaneously with the head end. In this case, the wall of the steel pipe in contact with the zinc liquid surface rapidly elongates and bends into an arc due to heat. As pressure pushes it downwards, the resistance of the zinc liquid prevents it from going into the zinc liquid below, causing the two ends to quickly descend and the steel pipe to roll on the zinc liquid surface. When the galvanizing turntable continues to lower it, the steel pipe enters the zinc liquid as shown in Figure 3-156. Due to the presence of air in the middle of the bent steel pipe, it expands and ejects upon heating, allowing zinc liquid to fill the inner hole of the steel pipe. If the solvent is not dried, the ejection pressure will be greater and more dangerous, leading to more severe missed galvanizing. Therefore, it is preferable to have a larger inclination angle when dipping the steel pipe into zinc. The minimum angle should prevent the steel pipe from rolling after exiting the zinc bath. The best configuration, as shown in Figure 3-15c, prevents the steel pipe from coming into large-area contact with hot zinc liquid on one side, avoiding significant thermal expansion and reducing steel pipe bending. As the steel pipe is pressed into the zinc liquid with the turntable, there will be no rolling. At the same time, the gas inside the steel pipe can smoothly escape out of the pipe in sequence. The zinc liquid is at the same horizontal level inside the steel pipe, preventing missed galvanizing. This can be better achieved on step-through turntable galvanizing machines with a large zinc dipping angle. However, on continuous turntable galvanizing machines, rolling is more pronounced, especially when galvanizing small-diameter steel pipes. Rolling of the steel pipe can lead to missed galvanizing, which should be taken seriously, especially when galvanizing in zinc liquid containing aluminum.