The atmosphere of the annealing furnace is different:
The difference in the protective atmosphere is mainly manifested in the difference in hydrogen content. Galvanized hydrogen content is generally controlled at 15-30%, while the hydrogen content of galvalume is generally controlled at 25-50%. The controlled temperature when entered the zinc pot is different.
When galvanized, it’s required that steel plate temperature is slightly lower than the temperature of aluminum zinc solution. Usually 570-580 degrees, so that the heating of the zinc pot to be carried out under relatively large power consumption. There are two main aspects of the mechanism that the plate temperature is lower than the aluminum-zinc temperature:
(1) The need of the middle layer formation. The composition and requirements of intermediate layer between the aluminum-zinc alloy and steel and the zinc and steel are different.
(2) As the aluminum is relatively light in zinc-aluminum alloy, it has upward trend, and zinc pot induction body activation has the role of stirring aluminum zinc solution.