Analysis of bursting causes the bursting of castables

Source: | Author:ChangXing Refractory | Published time: 1548 days ago | 1166 Views | Share:

Baking of refractory castable before use is an important part in its production process. Whether the baking system of castable is reasonable or not determines the baking quality of its green body, and then directly affects its service performance, production process and economic benefits of manufacturers. The traditional baking schedule for castables usually emphasizes the control of two nodes: 100~150℃ and 250~350℃, that is, the free water is excluded from the crystal water. However, the baking schedule established according to this will often cause the castables to peel off or even burst during baking. Therefore, the designation of the baking schedule for castables needs to reasonably analyze the physical changes of castables during baking and strictly formulate the baking schedule.

Analysis of Bursting Causes The bursting of castables is caused by two reasons, one is the steam pressure generated inside during baking, and the other is the bursting of internal thermal stress caused by temperature gradient.

1.1The mechanism of steam pressure-induced bursting is mainly that free water and bound water in refractory products evaporate during baking, and pressurized gas is generated inside the green body. If the product has poor air permeability, or the heating rate is too fast, the generated steam cannot be eliminated in time, and the pressure formed by aggregation exceeds the ultimate strength of the product, it will lead to mechanical damage and even smash cracking of refractory products. The formation of internal steam pressure of refractory castables during baking can not be simply explained by the temperature-pressure relationship between water and steam.

The reasons are as follows: (1) The mechanism of internal steam pressure rise of refractory castables: there is a saturated steam barrier wall effect in the refractory castables during baking, which is blocked by the saturated layer, and the steam can not migrate inward quickly, but only enters the heating layer, and is further heated to increase the temperature, and the volume increases sharply to thousands of times, thus forming a very high steam pressure inside the castables;
(2) Influencing factors of steam pressure burst mechanism: the pressure of water vapor formed, the way of water (gas) removal, the strength of green body, internal structure and air permeability.

1.2 The mechanism of internal thermal stress in the baking process of thermal stress-induced blowout castables can be understood as two-dimensional or three-dimensional thermal stress around the internal particles during baking. Because castables are a complex heterogeneous system, the thermal stress increases with the increase of temperature gradient, and then tiny cracks with higher energy are formed in the particles or the weak places around them. When reaching a certain value, or combined with other factors such as pore steam pressure, tensile stress with higher tensile strength than the products themselves is formed, resulting in damage.

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