In ceramic production, firing shrinkage significantly impacts dimensional stability and yield rates. Excessive shrinkage causes body deformation, cracking, or even scrap, thereby increasing production costs and energy consumption. Reducing firing shrinkage not only enhances the quality consistency of ceramic products but also lowers energy consumption and raw material wastage. Optimizing body formulations and firing processes are key approaches to achieving this goal.
Causes and Effects of Firing Shrinkage
Firing shrinkage primarily originates from two stages:
Physical shrinkage: The expulsion of free water and adsorbed water from the body.
Chemical shrinkage: At high temperatures, physicochemical reactions occur within the body components, including mullitization, liquid phase formation, quartz melting, and gas pore expulsion. These processes cause particle rearrangement and volumetric densification.
The core of formulation optimization lies in controlling and minimizing the volumetric changes generated during these processes by adjusting the types and proportions of raw materials.
Body Composition and Mineral Raw Material Optimization
Rational Selection of Silicate Raw Materials Traditional bodies primarily consist of kaolinite, quartz, and feldspar. Excessive kaolinite causes significant firing shrinkage, while feldspar acts as a flux to promote densification. By adjusting the quartz-to-feldspar ratio, controlling liquid phase content and sintering temperature, the body achieves densification while avoiding excessive shrinkage. | Introduction of Reinforcing Agents Adding talc promotes the formation of mullite and andalusite phases, enhancing the strength of daily-use ceramics. Nodular mullite whiskers suppress shrinkage cracking while enhancing flexural strength. |  |
III. Particle Size Distribution Adjustment
| Particle size distribution determines body density. Coarse particles form a skeletal framework, while fine particles fill voids, reducing shrinkage rates. Optimized formulations enhance body packing efficiency and stability. Reducing the proportion of plastic components is crucial, as excess clay releases structural water during firing, causing severe volume shrinkage. Minimize highly plastic clays by partially substituting them with non-plastic minerals or fluxes. |  |
IV. Process and Firing
| Adding fluxes (e.g., feldspar, talc, alkali metal salts) lowers firing temperatures, preventing excessive shrinkage at high heat. The introduction of talc and TiO₂ can lower the firing temperature by 30°C, achieving stable structure at lower temperatures for enhanced daily-use ceramics. Rapid heating or insufficient holding time can cause uneven internal stresses in the body, increasing shrinkage variation. Temperature control should be staged: dehydration phase → densification phase → holding phase, ensuring uniform shrinkage. |  |
Summary and Recommendations
Optimizing body formulations effectively reduces firing shrinkage through: Adjusting raw material ratios to moderately reduce high-plasticity clay usage; Adding reinforcing agents to promote mullite formation; Employing appropriate particle sizes to enhance body stability.
Combining these measures not only improves dimensional stability and yield rates for ceramic products but also reduces energy consumption, advancing the ceramic industry toward energy efficiency, environmental sustainability, and high-quality development.