In addition to the poor strength and crack resistance of additives which can not overcome the drying shrinkage force, there are several other factors worthy of attention:
① Too fine aggregate powder or excessive bad components (such as raw bauxite, etc.)
② The shrinkage rate of aggregate powder after water infiltration is too large when drying (such as bentonite)
③ Drying temperature is not stable (for example, it is shady when exposed to the sun)
④ The coating thickness is very different (for example, the corner is piled up very thick, and the straight faces of both sides are very thin, which is similar to the hot spot shrinkage crack of the casting)
The foam is not mature enough, and the drying process has 3 deformations.
⑥ Too fast hot air flow results in different drying stress (such as strong wind in the hot sun or high temperature and strong convection in the drying room)
Crack prevention measures:
① Improve the crack resistance of additives (such as increasing the content of crack resistant fiber)
② Reduce the shrinkage of additives (adjust the formula reasonably)
③ Aggregate powder shall not be too fine or air permeability is too low
④ The temperature in the drying room is balanced, and solar energy utilization should not be simplified
⑤ The slurry at the corner of the white mold shall not flow too much or too thick (handle with soft bristle brush or change the direction of slurry flow)
⑥ White mold must be fully dried and matured
⑦ The drying temperature shall be controlled below 60 ℃
⑧ If necessary, 2-3% silica sol can be added to increase crack resistance
⑨ Do not indiscriminately choose unclear additives, binders and other materials.