Refractory firebrick

Refractories Firebrick-Specialties, Uses and Industrial Importance, The Refractories Institute, Pittsburgh, Pa., pp. 1—43. 

This cement is very resistant to attack by sulphates, sea water and acid waters. It is also used with crushed firebrick to produce refractory concrete. 

A typical large three-phase ferroalloy furnace using prebaked carbon electrodes is shown in Eigure 4. The hearth and lower walls where molten materials come in contact with refractories are usually composed of carbon blocks backed by safety courses of brick. In the upper section, where the refractories are not exposed to the higher temperatures, superduty or regular firebrick may be used. The walls of the shell also may be water-cooled for extended life. Usually, the furnace shell is elevated and supported on beams or on concrete piers to allow ventilation of the bottom. When normal ventilation is insufficient, blowers are added to remove the heat more rapidly. The shell also may rest on a turntable so that it can be oscillated slightly more than 120° at a speed equivalent to 0.25—1 revolution per day in order to equalize refractory erosion or bottom buildup. 

When heavier refractories are required because of operating conditions, insulating brick is installed next to the shell and firebrick is installed to protect the insulating brick. Industrial experience in many fields of application has demonstrated that such a hning will success-billy withstand the abrasive conditions for many years without replacement. Most serious refractory wear occurs with coarse particles at high gas velocities and is usually most pronounced near the operating level of the fluidized bed. 

Whatever the process, the steelmaking vessel must be lined with a suitable refractory material, usually bricks of calcined dolomite, (Mg,Ca)0. Silicate firebricks cannot be used in the presence of lime. 

The results of tension tests upon refractories in the hot state are not available in the literature nor are data relating to the transverse strength of bricks and tiles. This is to be regretted since in many furnace constructions transverse loads must be considered. Again, it seems very probable that the compression test of firebricks will ultimately be replaced by one involving transverse stress. 

A large class of fireclays associated with the coal measures of Pennsylvania, Maryland, Ohio, Kentucky, West Virginia and Indiana belong to the types softening between cones 28 to 32. These are useful for bonding purposes in the manufacture of firebricks and shapes. Such clays are available in enormous quantities in conjunction of the coals of these states. All of the plastic bond clays, whether of the No. 1 grade or not, fire to a buff color which may become more and more discolored through the presence of iron pyrites or iron oxide as we descend in the scale of refractoriness. 

Properties of Flint-clay Refractories.—These may be briefly summarized as follows The refractoriness of No. 1 materials as indicated by the softening point is usually not lower than that of cone 31 (about 1,685°C. or 3,065°F.). Kanolt has found the mean melting point of 41 samples of firebrick to be 1,649°C., determined in the Arsem furnace. 

In using heat-insulating materials it is necessary to realize that insulation necessarily raises the mean temperature of the wall between the surface exposed to the heat and the insulation to a point far above that applying to ordinary conditions. The damming up of the heat thus raises especially the temperature of the surface of the firebrick. It is inevitable therefore that insulation requires the use of materials which are more heat resisting. Many instances are on record where firebrick have failed soon after insulation was applied. Heat insulation may thus be said to have increased the necessity for superior refractories. 

Besides firebricks, tiles made of similar refractory material are frequently used in furnaces and similar constructive work. They are particularly useful for covering spans of more than 6 inches, such as occur in flues and small fireplaces. Thus we have seen in Chapter IY. that the bed of a blind roaster is made of tiles, the reason for this being that we are thus enabled to make the flues wider. If we were to use ordinary or fire bricks for the purpose, we could not place the side walls forming the flue more than 5 or 6 inches apart, otherwise the 9-inch brick would not rest on them securely. By using tiles we can therefore span distances which are too large to be covered by brick, and too small to be covered by arches, or where, for other reasons, it would be inconvenient to use an arch. 

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