Aging And Storage of Enamel Slurry
The grinded enamel slurry must be stored in a container for a period of time. This process is called aging. Its purpose is to adapt the enamel slurry to the requirements of enamelling:
1. The temperature of the enamel slurry rises during the ball milling, and the puffing phenomenon is serious, which brings difficulties to the enameling operation. After aging, the temperature of the enamel slurry decreases, and the puffing phenomenon subsides to a normal state.
2. A large amount of air will inevitably be mixed into the enamel slurry during the ball milling process, which will adversely affect the coating quality (bubbles appear on the surface of the porcelain layer). Through aging, the gas mixed in the enamel slurry will gradually escape.
3. Due to turning, friction and other reasons, the enamel slurry that has just been ground will accelerate the hydrolysis of the enamel, and the precipitation of soluble alkali will increase the pH of the enamel slurry (this phenomenon is particularly obvious in antimony enamel), thereby affecting the gloss of the enamel surface. Through aging, the enamel slurry will have a certain degree of sedimentation, and the surface layer solution can be removed to reduce free substances, which is beneficial to improve the quality of the enamel surface.
4. Soluble salts will also be liberated during the grinding process of colored enamel, if these soluble salts are not removed. After being burned (or decorated with flowers), the porcelain surface will show uneven color and shadow. After aging, skimming the upper layer of solution will help improve the quality of the colored enamel surface.
The aging of the enamel slurry is not absolute, and various enamel frits have different requirements for aging. Generally speaking, the base enamel and side enamel can be used directly without aging and grinding; the titanium enamel can be aged for 1~2d; The aging time of antimony enamel needs to be longer, generally 5~7d. The storage time of the enamel slurry should not be too long, otherwise, coarser particles will be deposited and the enamel slurry will be stratified. At present, the aging time of each enamel factory is different. Therefore, the above aging time data is for reference only.
The freshly ground enamel slurry should be stored for at least 12h to have a stable consistency. High temperature will increase the water solubility of enamel surface ions and cause excessive aging of the enamel slurry. Therefore, the enamel slurry should be stored in a place with a lower temperature as much as possible, especially not beside the firing furnace. The storage time of the enamel slurry should not be too long. Do not exceed 3 months.
The storage equipment of enamel enamel slurry generally uses a slurry tank lined with ceramic tiles, and the surface of the pool must be covered to prevent dust from invading and contaminating the enamel slurry. Small batches of enamel slurry can also be stored in plastic drums with lids or stainless steel drums.