Discussion on the causes and solutions of cracks in sintered brick blanks | Brick and tile technology

1 The basic reason for the cracking of the billet in the drying process.

The characteristics of the preheating section, air supply section and cooling section of the drying chamber and the requirements for the drying process are not fully understood and understood. The supply of hot air is insufficient, and the preconditions for the full drying of the body are not met. The drying temperature curve is unreasonable and fails to meet the requirements of the temperature curve of the green body during the drying process.

The moisture emission control of the brick is not good, the moisture emission efficiency can not meet the requirements, the air humidity in the preheating zone of the drying kiln is saturated, and the surface of the brick expands after absorbing the moisture in the air, resulting in network cracks. Incoming hot air and uneven moisture discharge result in a large temperature difference in the drying kiln and thermal shock in some places. Therefore, the body is heated unevenly, the drying is uneven, and the dehydration speed of the brick is unstable, resulting in inconsistent shrinkage inside and outside the brick, and the resulting thermal stress will destroy the body and cause cracking.

The residual moisture content is too high, the higher the moisture content of the brick, the greater the shrinkage rate in the drying process. When the brick in the middle of the brick is affected by the shrinkage pulling force of the adjacent brick exceeds its own mechanical strength, the brick will be cracked.

Ventilation is too large, too high ventilation will take away a lot of water, will make the relative humidity of the air in the kiln becomes smaller, the brick will accelerate the dehydration, resulting in dry crack.

Kiln car table temperature is too high, the bottom of the brick due to rapid drying and causing serious cracks.

2 The basic method of solving the billet crack caused by drying.

The temperature distribution, the condition of the hot air flow and the size and direction of the air flow all play a key role in the drying effect. Increase the temperature in the front section of the drying kiln. In general, the temperature of 2~3 parking spaces in the drying kiln should be controlled below 100 ℃, and the temperature difference of the cross section in the drying kiln should be controlled within 15 ℃. The smaller the temperature difference between the upper and lower, the better, the drying temperature rise should be stable, generally should be slightly positive pressure is appropriate.

The air inlet gate valves on the top of the drying kiln and on both sides of the kiln should adjust the temperature difference at any time according to the drying temperature curve to prevent and overcome the direct impact of hot air on the brick billet. The heating curve in the whole drying process should be relatively stable, except that the temperature of the 1~2 temperature points in the front section is different from that of the 1~2 temperature points in the back section, the temperature of the remaining temperature points is relatively close. The drying time should be controlled in the middle and rear sections of the drying kiln.

Control the moisture content of brick molding, improve the vacuum of the extruder, improve the plasticity of raw materials, and improve the mechanical strength of brick. Take effective cooling measures on the kiln car table to increase the cooling time. Reasonable control of ventilation, the drying system to establish a complete set of humidity detection system, in order to accurately judge.

3 mechanical crack and non mechanical crack difference

In general, the directional and location characteristics of mechanical cracks are obvious and intuitive, and the cracks are longer and clearly visible. Mechanical cracks are generally caused by collision, vibration or heavy pressure on the blank.

The manifestations of non-mechanical cracks can be described as diverse, and in general, the crack directionality is not so obvious. However, in some cases, the location of non-mechanical cracks is also relatively regular. Therefore, it cannot be simply considered that as long as the directionality is obvious, it is a mechanical crack.

4 Two dry crack types and their performance characteristics

"Peripheral crack": when the temperature in the drying kiln is not enough, the brick is prone to peripheral cracks, especially when the temperature difference between the section of the drying chamber is large and the temperature on both sides of the drying kiln is low, the probability of occurrence is more. However, if the gate valve of the hot air pipe on both sides of the drying kiln is not properly adjusted, the inlet air is too strong, resulting in a large thermal shock, which will also cause peripheral cracks. Some areas in the drying kiln temperature is too fast, the temperature is too high will also cause the surrounding crack.

"Heart crack": Brick core crack caused by too low temperature in the front section of the drying kiln and too fast tide discharge. Because the reasons for the billet crack are more complex, various reasons are intertwined, influence and cover up each other, it is difficult to distinguish which type of billet crack, often wrong judgment, take measures easy to go into the misunderstanding, difficult to solve. Therefore, when the blank crack occurs, it is necessary to carefully understand and observe the nature of the crack, analyze and find the root causes, and adopt different treatment measures according to different types of blank cracks to prevent the improper measures taken due to wrong judgment, which will cause great losses. This is a problem that must be paid attention.