How is the glass produced?

1. dosing, in accordance with the design of the material list, will be weighed in a variety of raw materials in a mixer to mix evenly. The main raw materials of glass are: quartz sand, limestone, feldspar, soda ash, boric acid, etc..

2. melting, will be a good match of raw materials after high-temperature heating, the formation of a uniform glass liquid without bubbles. This is a very complex physical and chemical reaction process. Glass melting is carried out in the kiln. There are two main types of kilns: one is a crucible kiln, the glass material held in the crucible, heated outside the crucible. Smaller crucible kilns put only one crucible, and larger ones can be as many as 20 crucibles. Crucible kiln is gap production, now only optical glass and color glass using crucible kiln production. Another is the pool kiln, glass material in the kiln pool melting, open fire in the upper part of the glass liquid heated. Most of the glass melting temperature in 1300 ~ 1600 ℃. Most of the flame heating, there are a small number of electric current heating, known as electric fusion kiln. Now, the pool kiln are continuous production, the small pool kiln can be a few meters, large can be as large as more than 400 meters.

3. Forming, is a good molten glass liquid into a solid product with a fixed shape. Forming must be carried out within a certain temperature range, which is a cooling process, the glass is first transformed from a viscous liquid state into a plastic state, and then into a brittle solid. Forming methods can be divided into two categories: manual forming and mechanical forming.

A. Artificial forming.
(1) blowing, with a nickel-chromium alloy blowing tube, pick a group of glass in the mold while turning and blowing. Mainly used to form glass bubbles, bottles, balls (for scratching eyeglass lenses), etc.
(2) Pulling, after blowing into small bubbles, another worker with a top plate to stick, two people while blowing and pulling mainly used to make glass tubes or rods. (3) Pressing, pick a ball of glass, cut with scissors so that it falls into the concave mold, and then pressed with a convex mold. Mainly used to form cups, plates, etc.
(4) Free forming, picking the material and then using pliers, scissors, tweezers and other tools directly into crafts.

B. Mechanical forming. Because of the labor intensity of manual forming, high temperature, poor conditions, so, in addition to free forming, most have been replaced by mechanical forming. Mechanical forming in addition to pressing, blowing, drawing, there are
(1) calendering method, used to produce thick flat glass, engraved glass, laminated wire glass, etc.
(2) casting method, the production of optical glass.
(3) centrifugal casting method, used to manufacture large diameter glass tubes, vessels and large-capacity reaction pots. This is the molten glass is injected into a high-speed rotating mold, due to centrifugal force so that the glass clings to the walls of the mold, and the rotation continues until the glass hardens.
(4) Sintering method, used to produce foam glass. It is the addition of foaming agent in the glass powder, heated in a covered metal mold, the glass in the heating process to form a lot of closed-cell bubbles which is a very good thermal insulation, sound insulation material. In addition, flat glass is formed by vertical lead-up method, flat drawing method and float method. Float method is to let the glass stream float on the surface of molten metal (tin) to form a flat glass method, the main advantage is the high quality of glass (flat, bright and clean), pulling the lead fast and large output.

4. annealing, glass in the forming over into a violent temperature change and shape change, this change in the glass left a thermal stress. This thermal stress will reduce the strength and thermal stability of the glass products. If directly cooled, it is likely to break during the cooling process or later during storage, transportation and use of their own (commonly known as the cold explosion of glass). In order to eliminate the cold burst phenomenon, glass products must be annealed after forming. Annealing is in a certain temperature range of insulation or slow cooling for a period of time to eliminate or reduce the thermal stress in the glass to allow the value.

In addition, certain glass products in order to increase their strength, can be rigidified. Including: physical stiffening (quenching), for thicker glass, desktop glass, car windshields, etc.; and chemical stiffening (ion exchange), for the watch table mask glass, aviation glass, etc.. The principle of stiffening is to create compressive stress in the surface layer of glass to increase its strength.