The following problems will occur in the case of rapid heating and rapid cooling of magnesia-chrome bricks:

I. Thermal shock crack

Rapid heating and rapid cooling will lead to huge thermal stress in magnesia-chrome bricks, which will lead to thermal shock cracks. These cracks will reduce the strength and integrity of the brick, and then affect its service life. For example, in cement rotary kiln, if it is cooled quickly, magnesia-chrome bricks without kiln skin protection are prone to spalling damage.

II. Structural spalling

Under the condition of rapid temperature change, the surface of magnesia-chrome brick may peel off. This is because the internal and surface temperature changes of the brick are inconsistent, resulting in uneven expansion or contraction. Especially in the absence of kiln skin protection, this phenomenon is more obvious.

III. Differences in thermal shock resistance

Different types of magnesia-chrome bricks have different performances under the conditions of rapid heating and rapid cooling. The thermal shock stability of directly bonded magnesia-chrome bricks is good, while the thermal shock resistance of combined magnesia-chrome bricks is relatively poor. For example, after repeated thermal shock tests, the number and width of surface cracks will increase significantly.

IV. Thermal fatigue

Frequent rapid heating and cooling will lead to thermal fatigue of magnesia-chrome brick and make its structure deteriorate gradually. In this case, the thermal shock resistance and corrosion resistance of brick will be significantly reduced.

V. Influence of expansion coefficient

The thermal expansion coefficient of magnesia-chrome brick is large, and the uneven expansion and contraction will aggravate the damage of brick under the condition of rapid heating and rapid cooling. For example, in a cement rotary kiln, rapid cooling will cause the expansion coefficient of bricks to change too much, which will lead to peeling and damage.

VI. Shortening of service life

Rapid heating and rapid cooling will significantly shorten the service life of magnesia-chrome bricks. Especially in the equipment with frequent start and stop, the problems of thermal fatigue and thermal shock crack of magnesia-chrome brick will be more prominent.

Suggestions on avoiding rapid heating and cooling

In order to avoid the influence of rapid heating and rapid cooling on magnesia-chrome bricks, the following measures are suggested:

Slow heating and cooling: when the equipment is started and stopped, it should be heated or cooled as slowly as possible to avoid too fast temperature change.

Keep kiln skin intact: In cement rotary kiln and other equipment, keeping kiln skin intact and stable can effectively buffer temperature fluctuation and protect magnesia-chrome bricks.

Select the appropriate brick type: according to the specific working conditions of the equipment, choose the magnesia-chrome brick type with better thermal shock stability, such as directly combining magnesia-chrome brick.

The service life of magnesia-chrome brick can be effectively prolonged and the operation efficiency of equipment can be improved by reasonably controlling the temperature change and selecting suitable refractory materials.