The production process of glass includes processes such as batching, melting, forming, and annealing.
1. Ingredients: According to the designed ingredient list, weigh various raw materials and mix them evenly in a mixing machine. The main raw materials for glass include quartz sand, limestone, feldspar, soda ash, boric acid, etc.
2. Melting: The prepared raw materials are heated at high temperatures to form a uniform, bubble free glass liquid. This is a very complex physical and chemical reaction process. The melting of glass is carried out in a furnace. There are two main types of furnaces: one is a crucible kiln, in which the glass material is held inside and heated outside the crucible. Small crucible kilns only hold one crucible, while larger ones can hold up to 20 crucibles. Crucible kilns are used for intermittent production, and currently only optical glass and colored glass are produced using crucible kilns. Another type is a tank furnace, where the glass material is melted in the furnace and heated by an open flame above the glass surface. The melting temperature of glass is mostly between 1300 and 1600 ° C. Most of them are heated by flame, and there are also a few that are heated by electric current, called electric furnaces. Nowadays, tank kilns are all continuously produced, with small ones reaching several meters and large ones reaching over 400 meters.
3. Forming refers to the transformation of molten glass liquid into a solid product with a fixed shape. Glass first transitions from a viscous liquid to a plastic state, and then to a brittle solid state. Forming methods can be divided into two categories: manual forming and mechanical forming.
A. Artificial forming.
(1) Blowing, using a nickel chromium alloy blowing tube, pick a ball of glass and blow it while rotating in the mold. Mainly used for forming glass bubbles, bottles, balls (for eyeglass lenses), etc.
(2) Drawing, after blowing into small bubbles, another worker uses a top plate to stick, and the two of them blow while pulling, mainly used to make glass tubes or rods.
(3) Press, pick a ball of glass, cut it with scissors to drop it into the concave mold, and then press it with the convex mold. Mainly used for forming cups, plates, etc.
(4) Free form, pick materials and use tools such as pliers, scissors, and tweezers to directly make handicrafts.
B. Mechanical forming.
Due to the high labor intensity, high temperature, and poor conditions of manual forming, most of it has been replaced by mechanical forming, except for free forming. In addition to pressing, blowing, and drawing, mechanical forming also includes
(1) Rolling method is used to produce thick flat glass, engraved glass, metal wire glass, etc.
(2) Casting method for producing optical glass.
(3) Centrifugal casting method is used to manufacture large diameter glass tubes, vessels, and large capacity reaction pots. This involves injecting glass melt into a high-speed rotating mold, and due to centrifugal force, the glass adheres tightly to the mold wall. The rotation continues until the glass hardens.
(4) Sintering method is used to produce foam glass. It involves adding a foaming agent to glass powder and heating it in a covered metal mold. During the heating process, the glass forms many closed bubbles, which is a good insulation and sound insulation material.
In addition, the forming of flat glass includes vertical upward method, flat pulling method, and float method. Float method is a method of allowing glass liquid to float on the surface of molten metal (tin) to form flat glass. Its main advantages are high glass quality (flat and smooth), fast pulling speed, and large output.
4. Annealing, glass undergoes intense temperature and shape changes during forming, leaving thermal stress in the glass. This thermal stress will reduce the strength and thermal stability of glass products. If directly cooled, it is likely to self rupture during the cooling process or during subsequent storage, transportation, and use (commonly known as cold explosion of glass). In order to eliminate the phenomenon of cold explosion, glass products must undergo annealing after forming. Annealing refers to holding or slowly cooling within a certain temperature range 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 undergo hardening treatment to increase their strength. Including: physical hardening (quenching), used for thicker glass cups, tabletop glass, car windshields, etc; And chemical hardening (ion exchange), used for watch glass, aviation glass, etc. The principle of stiffening is to generate compressive stress on the surface layer of glass to increase its strength.
