Shrinkage and Stress During the Sintering Stage
(1) During high-temperature sintering, part of the fine particles undergo melting, forming a liquid phase that results in sintering shrinkage. Combined with earlier drying shrinkage, this constitutes the total shrinkage of the product. Compared to drying shrinkage, sintering shrinkage is milder, and the presence of a liquid phase partially absorbs stress, reducing damage risks to the product structure.
(2) The liquid phase introduces flexibility to the product under high temperatures, providing a cushioning effect similar to soft clay, helping to minimize structural stress concentrations.

Advantages and Risks of Rapid Cooling
1. In ceramics, the principle of "cooling while red, not while black" is applied. When the product surface exceeds 800°C, rapid cooling enhances appearance, improves glaze texture, and contributes to densification. Below 800°C, rapid cooling leads to significant shrinkage stress, potentially causing cracks or fractures.
2. In artistic ceramics like Jun porcelain, intentional rapid cooling creates decorative surface cracks (crackle glaze). However, for structural bricks, such cracks compromise strength, making rapid cooling unsuitable for large-scale brick production, especially in tunnel kilns where temperature and airflow are hard to control uniformly.
3. Furthermore, excessive cooling reduces residual heat recovery efficiency, affecting both drying systems and the energy balance of the kiln.

Physical and Chemical Stress in the Sintering Process
Prior to the kiln, stress primarily arises from physical phenomena—drying shrinkage, stacking stress, etc. Once in the sintering zone, chemical reactions dominate:
1. Liquid phase formation and solid transformations
2. Particle shrinkage and pore evolution
3. Control of open vs. closed pores
An optimal liquid phase content (2-3%) is crucial. Excess leads to over-fired bricks, while insufficient amounts cause under-fired bricks. Improving closed-pore structures enhances strength, reduces water absorption, and improves insulation properties.

Stress Management and Process Integration
1. Effective sintering relies on scientifically designed firing curves to balance liquid phase development and stress release. Burn-related defects often originate from upstream issues: raw material inconsistency, improper mixing, poor forming, inadequate aging, or uneven drying.
2. The industry maxim "master drying, master quality" emphasizes this systemic view. Modern production, especially with increased use of industrial waste in raw materials, requires precise adjustments to ensure compatibility across all process stages.
3. Relying solely on kiln adjustments to fix upstream issues is a misconception. True quality control demands coordinated management of the entire production chain.

Conclusion
High-quality brick production is a result of systematic, coordinated process management. Each stage—raw materials, mixing, aging, forming, drying, and firing—must work in harmony. Neglecting any part will compromise product integrity. Isolating kiln operation as the sole solution reflects a misunderstanding of integrated process control.