The gases commonly used for blowing and wiping the unsolidified zinc liquid on the inner wall of galvanized steel pipes include superheated steam, compressed air, pressurized hot air, and saturated steam, among which superheated steam is most frequently applied. This is because superheated steam can be heated above the solidification point of zinc under specified process pressures and contains minimal moisture. When used to blow and wipe the zinc liquid on the inner wall of galvanized steel pipes, it does not cool down the zinc liquid but rather slightly increases its temperature. This is beneficial for smoothing the zinc liquid on the inner bore wall. Additionally, superheated steam equipment is relatively simple and can be easily implemented in most factories. In contrast, saturated steam contains more moisture and has a lower temperature, which can actually absorb heat from the zinc liquid and accelerate its solidification. Compressed air, despite containing less moisture, can also accelerate the solidification of zinc liquid, increasing the resistance when passing through the inner bore of galvanized steel pipes and impeding the blowing and wiping process. The use of pressurized hot air for internal blowing and wiping of zinc is less common due to difficulties in achieving the required high temperature, pressure, and flow rate, as well as higher equipment costs and energy consumption.
If compressed air is first used for external blowing and wiping, it becomes even more necessary to employ superheated steam (or pressurized hot air) at higher temperatures and pressures for internal blowing and wiping of zinc.
