1. Ingredients, according to the designed material list, weigh the various raw materials and mix them evenly in a mixer. The main raw materials of glass are: quartz sand, limestone, feldspar, soda ash, boric acid and so on.
2. For melting, the prepared raw materials are heated at high temperature to form a uniform and bubble-free glass liquid. This is a very complicated physical and chemical reaction process. The melting of the glass takes place in the furnace. There are two main types of melting furnaces: one is a crucible furnace, where the glass frit is contained in the crucible and heated outside the crucible. The small crucible kiln only puts one crucible, and the large one can have as many as 20 crucibles. Crucible kiln is produced in gap type, and now only optical glass and colored glass are produced in crucible kiln. The other is a tank kiln, where the glass frit is melted in the kiln, and an open flame heats the upper part of the glass surface. The melting temperature of glass is mostly 1300~1600°C. Most of them are heated by flames, and a few are heated by electric current, which are called electric furnaces. Nowadays, tank kilns are produced continuously. Small tank kilns can be several meters long, and large tank kilns can be as large as more than 400 meters.
3. Forming is to transform the molten glass into a solid product with a fixed shape. Forming must be carried out within a certain temperature range. This is a cooling process. The glass first changes from a viscous liquid state to a plastic state, and then into a brittle solid state. The forming method can be divided into two categories: artificial forming and mechanical forming.
4. Annealing, the glass undergoes drastic temperature changes and shape changes during the forming process, and this change leaves thermal stress in the glass. Such thermal stress will reduce the strength and thermal stability of the glass product. If it is cooled directly, it is likely to rupture on its own during the cooling process or later during storage, transportation and use (commonly known as the cold burst of glass). In order to eliminate the phenomenon of cold burst, the glass product must be annealed after being formed. Annealing is to keep the temperature in a certain temperature range or slowly cool down for a period of time to eliminate or reduce the thermal stress in the glass to the allowable value.