New Bharat Refractories Ltd.

Alipore, Kolkata, West Bengal

Acid & Alkali proof bricks are specially made for regions which require acid and alkali proofing. The acid attack may take place where there is use of sulphur based materials which causes wear of ferrous lining of furnaces and tanks.

The refractories used require good mechanical strength, thermal shock resistance abrasion resistance, volume stability and in the upper section good hot strength. Fireclay and silica are the principal refractories used with the latter in the upper section.

Silica with very carefully controlled granulometry and tridymite and quartz content are essential to withstand the severe operational requirement of the coking and combustion chambers as coke ovens, with the appropriate repairs are expected to have a life of >30 years.

As blast furnaces and converters have become larger and more efficient, the use of torpedo cars has increased as it prevents heat loss from hot metal and the cost of construction as well as maintenance is comparatively low

The torpedo car was originally used for transportation and storage of hot metal. But now hot metal pre-treatment (i.e. desiliconisation, desulphurization and dephosphorisation) has been separated from decarburization processing (done in a converter) and it is done in the torpedo car.

Based on the need for corrosion resistance against FeO, Na2O and CaF2, Al2O3-SiC-C bricks have been developed comprising of alumina as the main aggregate, graphite which provides resistance to spalling and slag penetration and SiC which protects graphite from oxidizing.

If water cooled panels are not used magnesia-carbon bricks are installed in the hot spot area, with metal used unfired chrome magnetite brick in the other wall areas.

The slag line area blow the water cooled panels is lined with Refractories that well withstand slag and molten steel and resist opening of brick joints and spalling. In former times, fusion cast magnesia chrome bricks and fired dolomite & magnesite bricks were used but at present, magnesia carbon bricks are widely used.

The following factors are considered to be most influencing ones for the lining life of steel ladles:

Slag basicity and fluidity of molten steelLong holding time of high temp. molten steelStirring action of molten steelThermal spalling from tem.Fluctuation Ladle handling method Ladle structural deignProcess constraintsTap conditionsLining/repairing method, etc.

Lining of steel teeming ladle is divided into several zones including slag zone metal zone and bottom zone. The required characteristics of Refractories for each zone are as under

0 - Most important$ - ImportantX - Moderate

For metal zone, high alumina bricks were widely used. However, it has many problems such as structural spalling by slag penetration, damage to joints by slag & metal and shrinking after 25-30 campaigns.

Alumina-magnesia spinal bricks show batter performance than high alumina brick in this area due to high corrosion resistance, slag resistance and tight brick joints.

Recently, Alumina-magnesia graphite (AMG) bricks are used successfully. The opening at the brick joints is overcome by combining MgO in Al2O3-C bricks to provide a controlled/gradual continuous expansion of brick by spinal formation. With this combination, the joints will bot open during thermal cycling of the ladle, thus reducing pre-mature wear at the joints and avoiding steel & slag penetration to the cold end and consequently unexpected ladle break through MgO addition also improves corrosion resistance. However, excessive addition of MgO causes excessive expansion of the bricks, which may cause peeling.