Hot galvanised steel sheet or strip for deep drawing - with extremely thin coating of iron-zinc alloy on one or both surfaces obtd. by abrasion after steel leaves zinc bath

摘要

The steel travels vertically upwards out of a molten bath of Zn, and the excess Zn on both sides of the steel is removed via streams of air or rakes. Mechanical action is then used on at least one side of the steel at a point where the zinc is in a semisolid state and is easily crushed, so that all the non-alloyed Zn is removed leaving only a very thin layer (I) of Fe-Zn on the steel. The semisolid Zn is pref. removed by a rotating wire brush, where the base of the wires is cooled to below 50 degrees C while the steel in contact with the at 410-450 degrees C. Layer (I) is pref. 0.3-4, esp. 1-2 mu m thick, i.e. 2-30, esp. 7-15 g/m2. The thin coating provides lubricating properties during deep drawing and also increases the corrosion resistance of painted steel sheet or strip.