Utilization of coal ash as the layer onto the steel tank protecting its walls and bottom – In the Zn coating process of steel bars in the tank

摘要

Protecting the walls and bottom of normal steel (C% high content) tanks for plating steelbars in hot-melt Zn metal is an important work, which has a great value in view of technology andeconomy. However, it requires very high technical points. The authors have proposed, studied andused two protecting layers. The main components of the outer layer are coal ash, zinc and polysilicate.The outer layer is called CAZSIPOL layer. An inner layer is the lining one. Repairing theold special steel 08KP (according to GOST 1050/88 with 0.1% C) tanks and protecting the new08KP tanks by the layers in the production conditions in Vietnam is very economical. The layershave been developed in Vietnam, especially in some key projects of Vietnam such as the 500KVhigh-voltage lines. Now the layers have been applied continuously for common steelconstructions.To improve lifetime of the 500KVpoles, the steel bars of electricity poles have to be dippedinto hot-melt Zn tank about 13m length for plating of the12.7m steel bars. In the case of ST3(according to GOST 380-71 with 0.14-0.22% C - equivalent SPHT2 steel according to JIS G3132)normal steel tanks being 30-40mm thick without protecting layers, after about 20 days for its use aremaining thick of the tank is only 3-4mm. In the case of 08KP special steel tank lifetime of thetanks may be longer. In practice because of trouble sometimes about thermal property supply, thetank is too hot. So that the authors have studied to use the layers for 08KP and ST3 steel tanks toavoid the some accidents in actual processing.When building 500KV line at North – South, Vietnam lacks 08KP special steel and has alot of ST3 normal steel plates used for rail floors being40-50mm thick. Lifetime of the first tankmade of the rail floor steel with the two layers is 7 months and its total production weight is 547tons.A special effect of coal-ash in the outer layer is a reduction of hard Zn amount. Normallywhen dipping steel bars into the hot-melt Zn tank, hot hard Zn is formed and workers must scoopthe hard Zn, however, on the face of tank walls there is a hard Zn layer being about 2 cm thick. Byusing the layers the hard Zn thickness becomes only 1-2mm, this meaning that the amount of hardZn has decreased dramatically about 10 times.