[China Glass Net] The production process of glass includes: batching, melting, forming, annealing and other processes. Introduced as follows:
1. Ingredients, according to the designed material list, weigh the various raw materials and mix them evenly in a mixing machine. The main raw materials of glass are: quartz sand, limestone, feldspar, soda ash, boric acid and the like.
Second, the melting, the prepared raw materials are heated at a high temperature to form a uniform 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 kiln, and the glass is contained in the crucible and heated outside the crucible. The small kiln has only one raft, and the big one can have up to 20 rafts. The kiln is produced by gap type, and now only optical glass and color glass are produced in the kiln. The other is a pool kiln in which the frit is melted and the open flame is heated on the upper side of the glass. The melting temperature of glass is mostly between 1300 and 1600 ã‚šC. Most of them are heated by flame, and a small amount is heated by electric current, which is called electric melting furnace. Now, the pool kiln is continuously produced. The small pool kiln can be several meters, and the large one can be as large as 400 meters.
3. Forming is to convert the molten glass into a solid product having a fixed shape. Forming must be carried out within a certain temperature range. This is a cooling process in which the glass first changes from a viscous liquid state to a plastic state and then to a brittle solid state. The forming method can be divided into two major categories: manual forming and mechanical forming.
A. Artificially formed.
(1) Blow, use a nickel-chromium alloy to blow the tube, and pick a glass of glass while blowing in the mold. Mainly used to form glass bubbles, bottles, balls (for ophthalmic lenses).
(2) Drawing, after blowing into small bubbles, another worker sticks with the top plate, and the two are mainly used to make glass tubes or rods while blowing.
(3) Press, pick a glass, cut it with scissors, drop it into the die, and press it with the punch. Mainly used to form cups, plates, etc.
(4) Freeform forming, after the material is picked, it can be directly made into crafts with tools such as pliers, scissors and tweezers.
B. Mechanical forming. Because manual forming is labor intensive, high in temperature, and poor in condition, 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) Calendering method for producing thick flat glass, engraved glass, wire metal glass, and the like.
(2) Casting method to produce optical glass.
(3) Centrifugal casting method for manufacturing large diameter glass tubes, vessels and large-capacity reaction pots. This is to inject the glass melt into a mold that rotates at high speed, and the glass is pressed against the wall of the mold due to centrifugal force, and the rotation continues until the glass is hardened.
(4) Sintering method for producing foam glass. It is a kind of good heat insulation and sound insulation material by adding a foaming agent to the glass powder and heating it in a covered metal mold. The glass forms many closed bubbles during the heating process. In addition, the flat glass is formed by a vertical lead method, a flat pull method, and a float method. The float method is a method in which a glass flow floats on a surface of a molten metal (tin) to form a flat glass. The main advantage is that the glass has high quality (flat, smooth), high drawing speed, and large output.
4. Annealing, the glass undergoes intense temperature changes and shape changes during the forming process, and this change leaves 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 rupture itself during storage or transportation during the cooling process. In order to eliminate the cold explosion phenomenon, the glass article must be annealed after forming. Annealing is to heat or slowly cool for a period of time to eliminate or reduce the thermal stress in the glass to an allowable value.
In addition, some glass products can be rigidified in order to increase their strength. Including: physical rigidification (quenching), for thick glass, tabletop glass, car windshield, etc.; and chemical rigidification (ion exchange), for watch glass, aviation glass, etc. The principle of stiffening is to generate compressive stress on the surface layer of the glass to increase its strength.
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