Baking and bursting of refractory castables is a more complicated problem. The following are its common causes and preventive measures:
1. Causes of baking and bursting of refractory castables
1) Moisture factor: The castable contains a large amount of free water and bound water after construction. The water evaporates quickly during baking to form steam. If the steam cannot be discharged in time, the internal pressure will increase and cause bursting.
2) Heating rate: The heating rate is too fast during baking, the surface of the castable quickly dries to form a hard shell, while the internal water is still evaporating, and the steam cannot be discharged through the hard shell, thereby accumulating pressure and causing bursting.
3) Material ratio: Improper ratio of aggregate to powder in the castable, excessive or insufficient amount of binder, etc., will affect its structure and performance, resulting in poor air permeability or insufficient strength, increasing the risk of bursting.
4) Construction problems: Uneven mixing and loose vibration during construction will cause gaps or local water concentration inside the castable; the formwork is removed too early, the castable is not fully solidified, and it is also easy to burst during baking.
2. Preventive measures for baking and cracking of refractory castables
1) Control moisture: Ensure that the raw materials are dry before construction and strictly control the amount of water added; after construction, appropriately extend the natural curing time to allow some of the moisture to evaporate naturally and reduce the moisture content during baking.
2) Optimize the heating system: formulate a reasonable baking heating curve, and adopt a slow and uniform heating rate according to the characteristics and thickness of the castable, such as heating at a rate of 5-10℃/h in the low temperature stage to give enough time for the moisture to be discharged.
3) Adjust the material ratio: According to the use requirements and environment, accurately design the material ratio, select appropriate aggregates, powders and binders, and strictly control their dosage to ensure that the castable has good air permeability and strength.
4) Standardize construction operations: Use mechanical stirring and ensure sufficient stirring time to mix the materials evenly; vibrate densely to ensure that the internal structure of the castable is uniform; remove the formwork at the specified time to ensure that the castable is fully solidified.
5.)Set exhaust holes: For thick and large-volume castables, appropriate exhaust holes can be reserved during construction to provide a discharge channel for steam and reduce internal pressure.
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