Views: 9 Author: Site Editor Publish Time: 2023-09-26 Origin: Site
As we know,Float Glass Production Line is very important for the production of float glass. In addition to equipment, the preparation of raw materials is also a very important link in the production of high-quality float glass. As a global glass system integration service provider, we will help you analyze the preparation steps of float glass raw materials from the following five aspects:
1.Chemical composition of float glass
2.Composition characteristics of float glass
3.Oxides in float glass
4.Raw materials for float glass
5.Preparation of batch materials for floatglass
The basic system of chemical composition of float glass is the Na-Ca-Si ternary system, which meets three requirements:
(1) Product usage requirements;
(2) Production process requirements;
(3) Production cost requirements.
The chemical composition of float glass mainly includes silicon dioxide (SiO₂), sodium oxide (Na₂O), calcium oxide (CaO), magnesium oxide (MgO, aluminum oxide (Al₂O₃)), iron oxide (Fe₂O₃), etc.
Na₂O:12%~15%; CaO: 8%~~12%; SiO₂:69%~73%
After long-term production practice, people have concluded that the chemical combination of "high calcium, medium magnesium, low aluminum, and micro iron" is one of the conditions for producing high-quality float glass.
High calcium: Float glass has a fast pulling speed, and a "short" glass component with fast hardening speed must be used during molding, that is, CaO should be adjusted to 8% to 9%.
Medium magnesium: The CaO content increases, making the glass brittle and prone to wollastonite crystallization (CaO.SiO₂). Therefore, MgO is controlled at about 4% to improve the crystallization performance of glass.
Low aluminum: High aluminum will increase the viscosity of the glass, which is not conducive to homogenization and clarification, and will reduce the Al₂O₃ content to less than 1.3%.
Micro-iron: Fe₂+ with strong coloring ability is oxidized to Fe₃+ with weak coloring ability during melting, but is reduced to Fe₂+ in the tin bath, so it is strictly limited to 0.1%.
Oxides used in float glass include SiO₂, CaO, MgO, Al₂O₃, Na₂O, K₂O, etc.
Among them, SiO₂ is the most important oxide in forming float glass.
SiO₂ forms an irregular continuous network with silicon-oxygen tetrahedral structural units, becoming the "skeleton" of glass. It can give the glass a series of excellent properties, increase the viscosity of glass, and improve the thermal and chemical stability of glass; the density and thermal expansion coefficient of glass decrease as the SiO₂ content increases. Its disadvantages are high melting point and high viscosity, making it difficult to melt, clarify, and homogenize the glass and increase energy consumption.
There are many substances containing glass constituent elements in nature. Various substances used to prepare glass batches are collectively called glass raw materials. In order to obtain reasonable technical and economic indicators in production, pure oxides are rarely used as glass raw materials, and natural mineral raw materials are mostly used.
The raw materials for producing float glass can be divided into two types: raw material and clinker. Among them, raw materials can be divided into two categories: main raw materials and auxiliary raw materials according to their dosage and functions; while clinker refers to the cullet added to the batch materials in a certain proportion in actual production.
Main raw materials: refers to the raw materials that introduce various oxides into the glass. They are the main raw materials that form the glass structure. They determine the basic physical and chemical properties of the glass. After these raw materials are melted and reacted, silicates form the main body of the glass liquid.
For float glass, the main raw materials introduce oxides such as SiO₂, Al₂O₃, CaO, MgO, and NapO (or KO), which determine the physical and chemical properties of the glass.
Auxiliary raw materials: Auxiliary raw materials are raw materials that enable glass to obtain certain necessary characteristics and accelerate the melting process. Although the amount is small, its role is very important. According to different functions, auxiliary raw materials are divided into clarifiers, fluxes, oxidants and reducing agents, colorants and decolorizing agents, etc.
Siliceous raw material: Siliceous raw material is the most important and the most widely used raw material in glass manufacturing. It mainly introduces SiO₂ into the glass component. Natural silica sand is also called quartz sand. Silica sand is the most difficult to melt raw material in the batch. The particle size, particle size distribution, and even particle shape have an important impact on the mixing, segregation, melting, and homogenization of the batch materials.
Cullet: Cullet, also known as clinker, is an indispensable raw material for glass production. The addition of cullet can increase the melting rate and help clarify and homogenize. The melting of grain ingredients is mainly the melting of SiO₂. As the amount of cullet increases, the melting time of the ingredients shortens and the melting speed increases. When the appropriate amount of cullet is added, the viscosity of the glass melt will be reduced during the fluxing effect of the cullet, and the clarification and homogenization time will be shortened.
The addition of broken glass is beneficial for saving energy and extending the service life of the kiln. While saving soda ash, increasing the amount of cullet can also greatly save fuel.
However, the amount of cullet added depends on the glass composition. Generally, it should not be too much for soda-lime-silica glass. Too much glass will make the glass brittle and reduce its mechanical strength.
Raw materials used for float glass include feldspar, dolomite, limestone, calcite, soda ash, etc.
In the glass industry, raw materials that are uniformly mixed according to a certain proportion are called glass batches.
The preparation of batch materials includes the calculation of the bill of materials and the weighing, mixing, and transportation of raw materials. The quality of the batch materials directly affects the quality of the glass.
Weighing accuracy is an important factor in ensuring the quality of batch materials. Its accuracy depends on the accuracy of the scale, the amount of weighed materials and the error. When the weighing raw materials are close to the full range of the scale, the weighing accuracy of the batch materials is close to the calibrated accuracy of the scale itself, that is, the error is minimal; and vice versa.
The mixing of raw materials refers to an operation in which a variety of raw materials change their movement speed and direction under the action of external forces, so that various principle particles can be evenly distributed. It is an operation in which a variety of different materials are dispersed with each other to achieve uniform mixing.
The mixing process of batch materials is the process of mixing various weighed raw materials into uniform and qualified batch materials.
The uniformity of the batch materials is mainly affected by factors such as the type of mixer, mixing time, moisture content, the amount of various raw materials, and the particle size of the raw materials.
The mixed batch materials need to be transported from the mixer to the kiln head silo. Different transportation methods directly affect the degree of batch distribution. In order to minimize the material separation phenomenon, when conveying batch materials, the shortest distance should be selected to prevent vibration as much as possible, and try to reduce the number of mishaps and gaps.
At present, the process of transporting the mixed batch materials from the mixer to the kiln head silo is generally conveyed by belts. The belt that transports the batch materials is generally called the original melt belt.
The mixed batch materials are transported to the kiln head through the original melting belt conveyor. In order to be evenly sent to each storage silo, the belt conveyor is transferred to a small cloth belt (reversible belt conveyor). The cloth is started according to the storage situation of the silo. The belt conveyor performs reciprocating discharge.
Before the batch materials are transported to the kiln head, the cullet should be evenly spread on the batch materials after weighing. It is necessary to ensure that the batch materials on the belt are covered by the batch materials from the beginning to the end of the materials. To this end, the cullet glass scale must be controlled. The discharge speed and the discharge speed of the mixer.
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