1.Blank has insufficient bonding force and can’t resist shrinkage stress.
2. Stickiness of Mud is too strong, not only makes the mud body shrink too large, but also easy to cause cracking due to the difference in shrinkage; and then because the mud is sticky and the water permeability is poor, resulting in a large difference in the humidity gradient of the body in the thickness direction. The shrinkage stress causes cracking. In addition, too much viscosity will hinder the ion exchange between the mud and the mold to affect the die release, and if the drying is uneven, it will crack.
3. Mud storage time too short, and didn’t complete to hydration process of the billet. The fluidity is poor because of mixing uneven.
4. Mud particles are too big, especially the large and medium particles increase, and when the fine particles are reduced, the mud performance will be unstable.
5. Dispergator type chose not properly or used.
6.Bad quality of the plaster model. It have various defects during the manufacturing process make difference water absorption speed of model, which causes the mud body to shrink and crack. There will have difference quality in the same batch of models, the old and the new are inconsistent, the degree of wet and dry is inconsistent or the demoulding time is improper that also will cause crack.
7. Improper grouting operation, formation of air interlayer, stress, and uneven drying.
8. Before grouting, the mud is not evenly stirred and has not been sieved; when grouting, a slurry of water, a coarse subdivided layer, a slurry with agglomerates or a thick consistency is used.
9. Due to the temperature and ventilation of the grouting chamber, the thickness of the product is not the same, or the grouting is not possible, resulting in the deposition of the bottom of the grout. The formation of the blank is too thick.
10. In the process of forming, the blank is damaged, or drilling, bonding water control are improper controlled, resulting in stress.
11. Grouting chamber is poor in windproof, there is a wind in the hall, or the indoor temperature is uneven, resulting in uneven drying of the blank.
12. Particle size of the raw material is large and small, and the mixing is uneven.
13. Water content of the green body is too large or uneven of the water distribution .
14. Drying speed is too fast, causing the surface of the blank to shrink too much.
15. Various parts of the blank are unevenly heated during drying, or the airflow is uneven, so that the blank shrinks unevenly.
16. When drying, the water vapor in the gas stream condenses on the cold billet, and when dried, it tends to crack the billet.