REFRACTORY AND INSULATING FIREBRICK

ASTM 0134-95(1999), Standard Test Methods for Size, Dimensional Measurements, and Bulk Density of Refractory Brick and Insulating Firebrick, 1999. 

ASTM C-134 Size and bulk density of refractory brick and insulating firebrick... 

Refractories - In North America certain foimdry refi actories contain flint clay to give a dense, strong product able to withstand much higher temperatures than ordinary clay-based refractories. In Europe calcined ball clay (chamotte) is used in place of flint clay. China clay is used in cordierite-based kiln furniture and insulating firebrick. 

Fig. 9-11. Thermal conductivity data of high-temperature materials (o) refractory brick and (6) insulating firebrick. Courtesy of C. L, NorUm, Jr., Chem. Eng., 60(6) 216 (1953).]...

Pt 7.6 specifies the test for castable refractories. ASTM C133 and C93 specify tests for refractories and for insulating firebricks C583 specifies a test for refractories at high temperatures ... 

The RUL value of porous fireclay is not good. The conductivity of insulating firebrick is 0.3349 W/mK at 700°C, whereas it is 0.8374 W/mK for the normal one. Refractory materials such as kieselguhr, asbestos, and slag wool have lower thermal conductivity than insulating firebrick. They are useful only at temperatures lower than 900°C. 

The sidewall brick had expanded due to alkali attack to the point that they were replaced. In addition, the insulating firebrick in the crown exhibited both surface glazing and sheet spalling. Sheet spalling is well known, and it usually results from a subsurface expansion reaction caused by penetration of an agent in the gas phase that subsequently reacts with the refractory. 

In the same kilns, crown (roof) brick (insulating firebrick) in flat, suspended construction exhibited sheef spalling in seven years of service. Sheet spalling is loss of refractory thickness of about 25 mm (1 in.) over a large area (many bricks). The sheet spalling was apparently a result of expansion reactions between the IFB and the alkali in the kiln atmosphere. 

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. 

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. 

Ceramic shapes made in this way have excellent insulating characteristics and relatively low weight when compared to firebrick types of insulation. Fiber bonded refractories also have very good thermal shock characteristics. 

Thermal conductivity of castable refractories is as much as 35% less than that of firebrick, that is, castables are better insulators. High alumina castables have high abrasion resistance, and are more durable at high temperatures. 

---