Glass is malleable when it reaches its melting point, and just like plastic molding, it can be produced for molding using effective methods.
Forming is the transformation of molten liquid glass into a solid product with a fixed shape. Forming must be in a certain temperature range can be carried out, this is a cooling process, the glass first from a viscous liquid state into a plastic state, and then into a brittle solid state. Forming methods can be divided into two categories: manual forming and mechanical forming.
Manual forming:
1. Blowing: Using a nichrome blowpipe, pick a clump of glass and blow it while spinning it in the mold. Mainly used to form glass bubbles, bottles, and balls.
2. Drawing: After blowing into a small bubble, another worker sticks with the top plate, and the two people blow while pulling is mainly used to make glass tubes or rods.
3. Pressing: Picking a ball of glass, cutting it with scissors so that it falls into a concave mold, and then pressing it with a convex mold. Mainly used for molding cups, plates, etc.
4. Free-form: Picking the material and then using tools such as pliers, scissors, and tweezers to make crafts directly.
Mechanical forming:
Because manual forming is labor-intensive, high temperature, and poor conditions, most of them have been replaced by mechanical forming, except free forming. Mechanical
molding in addition to pressing, blowing, and drawing, there are other methods.
1. Calendering: Used to produce thick flat glass, etched glass, laminated wire glass, etc.
2. Casting method: Used for the production of optical glass.
3. Centrifugal casting method: Used for the manufacture of large-diameter glass tubes, vessels, and large-capacity reaction pots. This involves injecting molten glass into a mold that rotates at high speeds, and due to centrifugal force the glass is pressed against the walls of the mold and the rotation continues until the glass hardens.
4. Sintering method for the production of foam glass. It is a foaming agent added to the glass powder and heated in a covered metal mold, the glass is heated to form a lot of closed-cell bubbles This is a good insulation, sound insulation material. In addition, flat glass is formed by the vertical lead-up method, flat drawing method, and float method. The float method is to let the glass liquid stream on the surface of molten metal (tin) to form a flat glass method, its main advantage is the high quality of the glass (flat, smooth), pulling the lead speed, and large output.
Raw materials for glass containers：
The raw materials used to make glass are silica sand and soda ash, limestone (added to lower the melting temperature of the mixture), and magnesium oxide and aluminum oxide (to provide better chemical durability).
Another basic and very important ingredient is the cullet. Cullet is a type of recycled glass that helps reduce the amount of raw materials and energy needed to make new glass. A glass batch can consist of 25 to 60 percent cullet by volume. Cullet is crushed glass, usually of the same composition as the mineral mixture, from regrind from previous production runs and recycling sources. It is included because of its property of melting earlier in the furnace than other minerals, which helps accelerate the batch reaction into molten glass. This is an important energy-saving ingredient that both reduces the energy required for the melting process and helps to reduce greenhouse gas emissions. The resulting glass typically contains 70 to 74 percent silica by weight.
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