Tundish Coating Mixture

Tundish Coating Mixture Introduction

Tundish coating mixture is also called steel liquid purifying coating mixture, it is alkaline magnesia calcia refractory coating material used for the coating of continuous casting tundish working lining. Why it has steel liquid cleaning function is because it contains CaO, which can adhere impurities in steel liquid, for example, oxides(Al2O3, SiO2, Fe2O3), P, S, etc, therefore, nonmetal impurities in the steel liquid is reduced in large scale, and the steel liquid is cleaned.

The raw material of magnesia calcia tundish coating mixture is composed of  dolomite or sintered magnesite calcia, sintered or fused magnesite, binder, additives(dispersant, plasticizer, sintering agent) and organic fibers. Dolomite is compound salt which is consisted of CaCO3 and MgO3, its theoretical CaO content is 30.4%, MgO content is 21.9%. Calcined dolomite contains 58% CaO and 42% MgO. But dolomite clinker is easy to be hydrated, it is difficult to be used for preparing coating mixture, so usually adopts dolomite sand and sintered( fused) magnesite or anti-hydration magnesia calcia sand and sintered magnesite for the making of tundish coating mixture.

Tundish Coating Mixture Physiochemical Index
 

 
Binders For Tundish Magnesia Calcia Coating Mixture

There are two kinds of binders suitable for the preparation of magnesia calcia coating mixture, one is silicate series(different modulus of sodium silicate), the other is polyphosphate(different polymerization sodium phosphate), the second is most often used. The functions of organic fiber in coating mixture are: avoiding cracking during drying or rupture during roasting, reducing thermal conductivity of coating mixture. Additive used for tundish coating mixture is usually plasticizer, which includes plastic clay, bentonite, silica micro powder, slaked lime and so on. The additives not only has adding plasticity function, but also play the role of sintering agent.

The Service Life of Tundish Coating Mixture

Generally speaking, the higher the CaO content is, the better the cleaning effect of tundish coating material will be. But there is no definite value of CaO content, and the high CaO content coating material is hard to produce.
   
The service life of magnesia calica tundish coating material is correlated with the thickness of the coating layer. Generally speaking, the continuous casting times  is between 8 and 10 if the coating thickness is 35~40mm, while the continuous casting times is over 10 if the coating thickness is 40~60mm.