75. Why do thin-walled pipes and thick-walled pipes exhibit different zinc patterns under identical manufacturing processes and operating conditions?

Under identical hot-dip galvanizing conditions and cooling parameters, thin-walled pipes and thick-walled pipes exhibit distinct zinc flower patterns after galvanizing. The former displays larger zinc flowers while the latter forms smaller ones. The cooling rate of zinc liquid on steel pipe surfaces is directly proportional to the wall thickness of the pipe substrate. During standard "solvent method" galvanizing, the temperature of steel pipes immersed in zinc liquid (150-230°C) remains lower than the zinc liquid temperature (470-510°C). Consequently, thin-walled pipes absorb less heat, whereas thick-walled pipes absorb more. However, under identical process conditions, when thin-walled pipes reach uniform internal and external surface temperatures after immersion, the center of thick-walled pipes may still be below the surface galvanizing temperature. After removing the zinc liquid, the thin-walled pipes 'zinc liquid solidifies solely through air cooling, while the thick-walled pipes' zinc liquid must dissipate heat from the low-temperature core of the pipe wall in addition to air cooling, accelerating solidification. This explains why slow-cooled thin-walled pipes develop larger zinc flowers, whereas fast-cooled thick-walled pipes form smaller ones.