Part Two: Examination of the Main Causes of Cracking in Ceramic Tile Bodies

In the first part of the previous article titled "Causes of Cracking in Ceramic Tiles During the Production Process," we comprehensively examined the causes of glaze cracking. As mentioned, cracks are divided into three main categories: glaze cracks, body cracks, and cracks between the glaze and the body. In this second part of the article, we will focus on the issue of body cracks and explain the main reasons for their occurrence during the production process.

Main Causes of Body Cracking During the Production Process

Cracking in the ceramic tile industry is one of the most common and challenging problems encountered during the production of these products. These cracks can form at various stages of production, from shaping to the final firing of the product. The cracks that occur during the production of ceramic tiles are among the most significant defects that can affect the quality and durability of these products, ultimately reducing their lifespan. Below are some of the most important factors contributing to body cracks in ceramic tiles.

Raw Material Properties

If the raw body strength is low, cracks can occur due to contact with mechanical dryer parts. There is also a type of very fine crack that starts from one side of the tile and extends to the other side. This defect can occur for two reasons, which sometimes happen simultaneously. The first is the presence of excess quartz in the fired piece, and the second is a high thermal gradient that may occur during the cooling process of the piece.

Pressing and Molding Variables

Proper pressing and the use of suitable molds in the production of ceramic tiles are critical to preventing body cracks. Incorrect pressing processes, such as uneven pressure or mold challenges like rapid ejection of tiles, poorly designed mold slopes, or worn-out molds, can cause microcracks at the edges of the tiles. These microcracks can later develop into larger, visible cracks after firing. To prevent this issue, it is essential to design and maintain molds properly and ensure correct pressing settings.

Drying Variables

Drying refers to the stage in which the moist tiles gradually lose their excess moisture after shaping and molding, preparing them for firing. If the edges of the tiles dry faster than the center, cracks can occur at the edges. Additionally, if the dry strength of the body is low, cracks may occur due to the tiles colliding with each other or passing through the production line and coming into contact with equipment.

Firing Variables

The firing time, kiln temperature settings, and cooling speed after firing are crucial variables that can affect the quality of the tiles and prevent cracking. For example, if the temperature in the pre-firing or nidling stage is too high and the firing curve settings are incorrect, it can lead to issues such as cracking or reduced mechanical strength in the tiles. Moreover, if the insulation at the ends of the rollers is damaged or inadequate during firing, cold air may enter the kiln, causing cracks in the tile edges. Overall, thermal shock and a significant temperature difference between the upper and lower rollers are major causes of cracking during the firing stage.

Conclusion

Ceramic tile body cracks result from a complex interaction of various factors, including raw material properties, pressing pressure and settings, mold type and condition, and drying process conditions. Each of these variables can create stresses within the body structure that lead to cracking. To prevent these issues, precise control of each production stage is essential. These cracks can affect the quality, strength, and appearance of the product and ultimately lead to increased waste and reduced production efficiency.