How is glass produced? The production process of glass includes: batching, melting, forming, annealing and other processes. They are introduced as follows:
1. For ingredients, according to the designed material recipe, weigh all kinds of raw materials and mix them evenly in a mixer. The main raw materials of glass are: quartz sand, limestone, feldspar, soda ash, boric acid, etc.
2. For melting, the prepared raw materials are heated at high temperature to form a uniform glass liquid without bubbles. This is a very complex physical and chemical reaction process. The melting of glass takes place in a furnace. There are two main types of melting furnaces: one is the crucible furnace, the glass material is filled in the crucible and heated outside the crucible. There is only one crucible in a small crucible kiln, and there can be as many as 20 crucibles in a large one. Crucible kilns are produced in batches, and now only optical glass and colored glass are produced in crucible kilns. The other is a pool kiln, in which the glass frit is melted in the kiln pool, and the open flame is heated on the upper surface of the glass liquid. The melting temperature of glass is mostly at 1300~1600゜C. Most of them are heated by flames, and a small amount of them are heated by electric current, which are called electric furnaces. Now, the pond kiln is produced continuously. The small pond kiln can be several meters long, and the large one can be as large as more than 400 meters.
3. Shaping is to transform 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. Forming methods can be divided into two categories: artificial forming and mechanical forming.
A． Artificially shaped. There is also (1) blowing, using a nickel-chromium alloy blowpipe, picking a ball of glass and blowing it while turning it in the mold. It is mainly used to form glass bubbles, bottles, balls (for scratching glasses), etc. (2) Drawing, after blowing into small bubbles, another worker sticks it with the top plate, and the two are blowing and pulling, which is mainly used to make glass tubes or rods. (3) Pressing, pick a group of glass, cut it with scissors and drop it into the die, and then press it with the punch. Mainly used to form cups, plates, etc. (4) Free forming, after picking materials, use pliers, scissors, tweezers and other tools to directly make handicrafts.
B． mechanical forming. The intensity of labor is big, because artificial forming temperature is high, the condition is poor, so, except the free forming, most have been replaced by mechanical forming. In addition to pressing, blowing, and drawing, mechanical forming also has (1) calendering, which is used to produce thick flat glass, engraved glass, and wire glass. (2) Casting method to produce optical glass. (3) The centrifugal casting method is used to manufacture large-diameter glass tubes, utensils and large-capacity reaction pots. This is to inject molten glass into a high-speed rotating mold, and the centrifugal force makes the glass stick to the wall of the mold, and the rotation continues until the glass hardens. (4) Sintering method, used to produce foam glass. It is to add a foaming agent to the glass powder and heat it in a metal mold with a cover. During the heating process, the glass will form a lot of closed bubbles. It is a very good heat insulation and sound insulation material. In addition, the forming of flat glass has vertical pull method, flat pull method and float method. Float method is a method of letting glass flow float on the surface of molten metal (tin) to form flat glass. Its main advantages are high quality glass (flat, bright and clean), fast pulling speed and large output.
4. During annealing, the glass has undergone drastic temperature changes and shape changes during forming, and this change has left thermal stress in the glass. This thermal stress reduces the strength and thermal stability of the glass article. If it is directly cooled, it is likely to break by itself during the cooling process or during subsequent storage, transportation and use (commonly known as cold burst of glass). In order to eliminate the cold burst phenomenon, glass products must be annealed after forming. Annealing is to keep warm 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.
In addition, some glass products can be hardened in order to increase their strength. Including: physical hardening (quenching), used for thicker glass, table glass, car windshield, etc.; and chemical hardening (ion exchange), used for watch cover glass, aviation glass, etc. The principle of stiffening is to generate compressive stress in the surface layer of glass to increase its strength.
Post time: Jan-06-2023