Selection basis of refractory bricks for roller kiln

According to the use of lightweight refractory bricks for roller kilns abroad and the production and use experience of domestic lightweight bricks, the following points shall be considered when selecting lightweight refractory bricks:

Operating temperature, i.e. the long-term use temperature.

It is related to the maximum use temperature of thermal insulation refractory bricks. In foreign standards, the maximum use temperature (i.e. the classification temperature) refers to the experimental temperature under the condition that the change range of reheating line is less than 29 for 24 hours continuously, but this temperature cannot be used as the operating temperature of heat-insulating refractory bricks. The usual foreign practice is as follows: the operating temperature is equal to the classification temperature minus 10% of the classification temperature and then minus 40 °C. For example, the operating temperature of JM26 (°C)=1430-10%×1430-40=1247°C.

As the experimental method for the change of reheating line in China does not exactly indicate that the holding time is 24h, when selecting materials to test the change of the reheating line of lightweight bricks, the time shall be marked as 24h and the test shall be performed according to ASTMC210.

Compressive strength

Refractory materials usually generate strength based on liquid phase, and high strength means that a large amount of liquid phase is generated in the green body at the firing temperature. Most of these liquid phases are cooled to room temperature in the glass phase, which is brittle and reduces the thermal shock stability of the material. Therefore, no high requirements shall be proposed for the compressive strength when selecting materials for lightweight bricks.

For flat-ceiling roller kiln, the lightweight brick on the wall mainly bears its own weight. For example, for a kiln wall with a height of 1.5m, lightweight refractory bricks will bear maximum pressure of 0.15kg/cm², which will increase at high temperature. In order to facilitate transportation and construction, based on foreign experience, the compressive strength of lightweight bricks at the grade of 0.8g/cm³ and 1.0g/cm³ is about 15kg/cm2 and 20kg/cm² respectively.

Thermal shock stability

There are no requirements for lightweight bricks in domestic and foreign standards, and there is no inspection standard. This indicator can comprehensively reflect the material properties and has an important impact on the service life of the kiln. Practice has proved that the damage of lightweight bricks mainly involves cracking, broken ends and corners. Based on the measured indicators of thermal shock stability of lightweight refractory bricks at home and abroad, the number of cycles from 950°C to air cooling mode shall be greater than 15 times for the lightweight bricks in the working layer of the high temperature part of the roller kiln.

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