How to precisely control the temperature during the firing process of solid color bricks to avoid surface color differences?
Release Time : 2026-01-05
Solid color bricks are highly favored in the decoration market due to their pure and uniform color. However, improper temperature control during firing can easily lead to color differences on the surface, affecting the overall aesthetics and quality. Achieving precise temperature control requires a comprehensive approach encompassing raw material pretreatment, firing curve setting, kiln structure design, atmosphere control, cooling process optimization, equipment maintenance, and intelligent monitoring.
The uniformity of raw materials is fundamental to avoiding color differences. The raw materials for solid color bricks must undergo rigorous screening and proportioning to ensure stable chemical composition. If the impurity content in the raw materials is too high or the mineral composition fluctuates, uneven coloring can easily occur during firing due to localized reaction differences. Therefore, the raw materials must undergo thorough mixing and homogenization, and, if necessary, wet grinding or spray granulation processes should be used to improve the density and compositional consistency of the brick body, laying the foundation for subsequent precise temperature control.
The setting of the firing curve must be combined with the characteristics of the raw materials and product requirements. The firing of solid color bricks typically involves five stages: preheating, oxidation, sintering, heat preservation, and cooling. The preheating stage requires a slow temperature increase to prevent cracking caused by excessive moisture loss; the oxidation stage must ensure complete decomposition of organic matter to prevent black cores or bubbles due to incomplete combustion; the sintering stage is crucial for forming a dense structure, requiring strict control of the upper temperature limit and holding time to achieve the ideal density of the green body; the cooling stage requires phased cooling to prevent deformation or cracking due to thermal stress. The matching of temperature and time at each stage needs to be optimized experimentally to form standardized curves and reduce human error.
The kiln structure significantly affects temperature uniformity. Traditional kilns may experience large temperature differences between the top and bottom, and left and right sides, due to rising hot airflow or uneven fuel distribution, leading to color variations. Modern kilns mostly adopt roller kilns or tunnel kiln designs, optimizing burner layout and adding baffles and flow guiding devices to ensure uniform hot airflow distribution. Simultaneously, the kiln insulation layer must use high-performance refractory materials to reduce heat loss and ensure consistent temperature across all areas. Furthermore, the kiln height and width must be rationally designed according to product dimensions to avoid temperature fluctuations due to excessive space.
Atmosphere control is a key factor affecting the color of solid color bricks. In an oxidizing atmosphere, iron exists as Fe₂O₃, resulting in a reddish brick. In a reducing atmosphere, Fe₂O₃ is reduced to FeO or Fe₃O₄, resulting in a bluish-black brick. To achieve a specific color, the oxygen content in the kiln must be precisely controlled by adjusting the ratio of fuel to combustion air. For example, pearl white solid color bricks need to be fired in a weak oxidizing atmosphere to avoid excessive reduction of iron, which would darken the color. Simultaneously, it is necessary to prevent excessively strong localized reducing atmospheres, which would cause uneven color depth.
The cooling process is crucial to the final color and physical properties of solid color bricks. The rapid cooling stage requires quick cooling above the quartz crystal transformation point to prevent liquid phase crystallization and surface clouding. The slow cooling stage requires a slow passage through the 573℃ α-β quartz transformation zone to avoid cracking due to abrupt volume changes. The cooling rate needs to be adjusted according to the thickness and composition of the brick; for example, thin bricks can be cooled more quickly, while thick bricks require a longer slow cooling time. Furthermore, the cooling airflow and direction must be evenly distributed to prevent color differences caused by localized overcooling.
Equipment maintenance and calibration are prerequisites for ensuring accurate temperature control. Monitoring components such as thermocouples and pressure sensors need regular calibration to ensure data accuracy; actuators such as burners and fans need regular cleaning and maintenance to prevent control malfunctions due to carbon buildup or wear. The kiln's sealing also needs regular checks to prevent air leaks that could cause atmosphere fluctuations. By establishing equipment maintenance records and early warning mechanisms, potential problems can be identified in advance, reducing unplanned downtime and quality fluctuations.
The application of an intelligent monitoring system can further improve temperature control accuracy. By deploying multiple thermocouples and atmosphere sensors at key locations in the kiln, data such as temperature, pressure, and oxygen content are collected in real time and transmitted to the central control system. The system can automatically adjust fuel supply, combustion air volume, and cooling airflow according to preset curves to achieve closed-loop control. Simultaneously, big data analysis functions can mine historical data, optimize firing parameters, and predict potential quality risks. For example, if the temperature in a certain area remains consistently low, the system can automatically adjust the burner power in that area to avoid color differences.