How to precisely control the temperature curve during firing of ceramic base to avoid cracking and deformation?
Release Time : 2025-09-30
During the firing process of ceramic bases, precise control of the temperature profile is crucial for preventing cracking and deformation. The temperature profile encompasses three stages: heating, holding, and cooling. Parameter settings for each stage must be carefully tailored to the raw material characteristics, product structure, and kiln environment. Deviations in any stage can lead to thermal stress accumulation or uneven shrinkage, potentially causing cracking or deformation.
During the heating stage, differentiated heating rates must be set based on the thickness, shape, and raw material characteristics of the ceramic base. Slow heating is required in the low-temperature phase to expel residual moisture from the body and prevent a sudden increase in water vapor pressure that could lead to cracking. The medium-temperature phase accelerates oxidative decomposition to promote a thorough reaction between organic matter and carbonates. During the high-temperature phase, the vitrification reaction must be precisely controlled to prevent uneven liquid phase formation caused by excessively rapid heating. For example, a step-by-step heating method is required for thick-walled ceramic bases, with the heating rate reduced at each stage to balance heat transfer. Thin-walled products can be heated at a higher rate, but localized overheating must be avoided.
The holding phase is a critical period for the reorganization of the ceramic base's internal structure. At the peak temperature, a certain holding time is required to allow the body to complete the vitrification reaction and crystal phase reorganization. Insufficient holding time will result in incomplete vitrification, resulting in a soft core or insufficient strength; excessive holding time may cause excessive shrinkage or deformation. During this stage, the holding time should be adjusted based on the kiln structure and charge density to ensure thermal uniformity. For example, large kilns with large heat capacity require longer holding times to compensate for temperature gradients.
The cooling phase is crucial for stress relief in the ceramic base. Rapid cooling is required during high-temperature periods to stabilize the microstructure and prevent abnormal grain growth. Cooling rates should be reduced during medium and low-temperature periods to avoid cracking caused by large internal and external temperature differences. The cooling rate should be adjusted based on the body's liquid phase content and glass transition temperature. For example, a ceramic base containing high levels of quartz requires constant temperature to buffer stress during the crystal transition at 573°C to prevent cracking caused by volume expansion.
Raw material properties are the foundation for temperature profile development. Green bodies with high kaolin content require longer high-temperature holding times to promote mullite formation, while talc green bodies require shorter high-temperature holding times due to the lower liquid phase formation temperature. Furthermore, when the moisture content of green bodies entering the kiln exceeds 2%, a constant-temperature dehumidification section should be installed before 150°C to prevent rapid vaporization of the moisture and resulting in cracking. Raw material purity and particle size distribution also affect the heating rate. Green bodies with high impurities require a slower heating rate during the oxidation and decomposition phase to avoid defects.
The kiln structure and loading method directly impact the uniformity of the temperature field. Due to differences in thermal systems between tunnel kilns and shuttle kilns, the firing curve cycle for the same product can vary by 20%-40%. When loading the kiln, ensure that the distance between objects is ≥3cm. When using refractory supports, apply alumina powder to the contact points to reduce frictional stress. During vertical stacking, the angular deviation must be controlled within 2° to prevent deformation caused by tipping.
Modern kilns utilize temperature sensing modules and digital modeling to dynamically optimize the temperature profile. The set curve is compared with the actual temperature in real time, and the combustion gas ratio is automatically adjusted to compensate for heat loss. For example, oxygen-enriched combustion technology can shorten the holding time at peak temperatures by 15% while also reducing nitrogen oxide emissions. Through digital control, the ceramic base firing pass rate can be increased from 85% to over 98%, significantly reducing cracking and deformation defects.
