The ceramic drying process plays a vital role in the entire production process of ceramic sanitary ware, so today, as a professional manufacturer of sanitary ware, let us understand the function and process of the following ceramic drying process.
1. The role of drying in ceramic production
In addition to being as universal as other ceramic products, the drying of sanitary ceramics has its own particularity. Due to the large size and complex shape of the device, when the general factory adopts the gypsum mold grouting process, there are often two ways of hollow grouting (one-sided grouting) and solid grouting (double-sided grouting) for the same green body. The thickness and compactness of each part are affected by various factors such as mold, mud performance, gypsum performance, etc., and it is difficult to achieve consistency, and there are large differences.
Therefore, in the drying process, the heating at each stage, the internal migration of moisture and the external diffusion to achieve balance are often not consistent, and it is easy to produce differences in shrinkage of each part. This is because the drying of the sanitary ceramic body is difficult and prone to cracking, deformation, etc. The cause of the defect.
In order to improve the strength of the green body after molding, ceramic manufacturers need to dry it. After drying, the green body loses its plasticity and has certain elasticity and strength. On the other hand, the water content in the green body is high, and its ability to absorb glaze slurry is poor. Therefore, in order to improve the ability of the green body to absorb the glaze layer, the water content should reach a certain level (for example, for daily-use ceramics, the green body needs to be dried when glazing. to moisture content of 2%~4%).
In addition, after drying to remove most of the free water in the green body, the green body seldom shrinks, so that the green body can be heated up quickly during the firing stage without deformation or cracking of the product, so that ceramic manufacturers can ensure that The firing quality can also shorten the firing cycle, ultimately improving the utilization rate of the kiln and reducing energy consumption. Usually the moisture content of the green body should be dried to below 2% before entering the kiln.
Many ceramic products need to be wet repaired, inlaid or dry repaired after molding, and they all have their own suitable water content of the green body. According to the requirements of each processing procedure in molding, drying is carried out in stages, and finally dried to the final moisture content suitable for entering the kiln.
2. Scientific drying system
The drying system refers to the determination of the drying method and the drying speed of each stage in the drying process and the parameters affecting the drying speed according to the quality requirements of the product. These include: the temperature, humidity, type, flow and velocity of the drying medium.
To ensure good drying quality for sanitary ceramics due to the following reasons, an appropriate drying speed must be selected to achieve a scientific drying system.
First of all, as mentioned above, sanitary ceramics are large, thick-walled and uneven, and have complex shapes. There are single-sided and double-sided slurry-absorbing green bodies in the same green body, and the shrinkage rates of each part are often inconsistent, so each section is dry. The choice of speed is very important, otherwise it is very easy to produce destructive stress.
Secondly, due to the high amount of clay used in the green body of sanitary ceramics, the shrinkage of the clay is relatively large, that is, drying sensitivity-that is, the tendency to crack during the shrinkage stage during the drying process is relatively large.
Thirdly, due to the complex shape and inconsistent size of sanitary ceramics, not only the drying uniformity of different parts of the same body of sanitary ceramics is different, but also the drying balance of different types of green bodies in the same dryer is quite different. Therefore, the influencing factors are very complex.
3. Drying process
So in order to improve the hardness and quality of the ceramic body, what drying processes do ceramic sanitary ware manufacturers need to carry out? Let’s take a look!
3.1. In the drying stage, a large amount of water is discharged during this stage. When the temperature and humidity of the surrounding environment remain unchanged, the discharge rate of water is approximately constant, so it is called the constant-speed drying stage. In addition, the evaporation of water only occurs on the surface of the ceramic, and the drying speed is equal to the evaporation speed of water, so any speed that affects the evaporation of the surface can affect the drying speed.
3.2. In the deceleration drying stage, as the drying time increases, the moisture in the ceramics decreases, the effective evaporation area in the green body decreases, and the drying speed gradually decreases. In addition, the speed of water evaporation from the surface exceeds the speed of diffusion from the inside of the body to the surface, so the drying speed is less affected by the temperature, humidity and movement speed of the air.
3.3. In the equilibrium drying stage, the drying speed gradually approaches zero at this time, and finally the moisture in the ceramic will no longer decrease, and the moisture remaining in it is equal to the equilibrium water absorbed by the solid particles. The content of equilibrium water depends on the nature of the material, the particle size and the temperature and humidity of the drying medium.
To sum up, the drying process of ceramics needs to go through the above three stages. Different drying stages have different displacements, but their function is to evaporate the water in the product, dry it, increase the hardness and prolong the use time.
