Glass raw material - broken glass
In the production process of flat glass, the leftovers, broken and unqualified glass plates and flat glass with similar compositions recycled in society can be used as raw materials for glass, collectively known as cullet or clinker.
Cullet can not only be used as waste, but also if used reasonably, it can also accelerate the melting process of the batch and reduce the energy consumption of glass melting, thereby reducing the production cost of glass and increasing the output.
The test proves that for every 1kg of glass liquid, the use of broken glass can reduce the heat energy consumption by about 42% compared with the use of batching. For every 10% increase in the amount of cullet used, 2.5%-4.5% energy can be saved when melting.
For soda-lime silicate glass, the incorporation of cullet glass should not exceed 40%, too much will make the glass brittle and reduce mechanical strength.
It is recommended that during normal production, the amount of broken glass should be stably controlled at 15%~18%, and under special circumstances, it can be controlled at about 25%.
For example, the Na2O after remelting ison average 0.15% lower than before remelting, and the difference is even greater for volatile components such as clarifiers, oxidants, and decolorizers.
Compared with the compound of the same composition, cullet lacks some alkali metal oxides and other volatile oxides. Therefore, when the amount of cullet is used in large quantities, clarifiers must be appropriately added and certain volatile oxides must be supplemented.
During the melting process of glass, due to the erosion of glass liquid on the refractory material,Fe2O3 andAl2O3 in the glass are produced The content increases. There are also some glass with poor chemical stability, which has a difference in the composition of the inner and outer layers due to surface dissolution.
Due to the above reasons, the use of broken glass is easy to cause uneven glass liquid, which makes the glass brittle.
When cullet glass is remelted, some of its components will be thermally decomposed and oxygen will be released to diffuse into the surrounding bubbles, and the oxygen will escape the glass liquid with the bubbles, resulting in the lack of oxygen in the glass, so the remelted glass liquid has reducing properties, for the glass produced on the basis of variable valence ions, the lack of oxygen will cause the color of the glass to change, such as thermal decomposition will make Fe203Change to Fe0, causing a change in the color of the glass.
When colored glass is remelted, due to the volatilization of coloring components, the color of the glass will become lighter, and the change of some variable ion electricity will also cause the color of the glass to change.
The proportion and block size of cullet in the compound have an important impact on the melting time. It has been proved that with the increase of the amount of cullet, the melting time of the batch is shortened, but the addition of too much cullet will prolong the clarification time. Generally, cullet with a block size of 5-60mm and uniform size melts faster.
When the block is too large, it is difficult to homogenize the glass liquid, which affects the quality of the glass plate surface, and in severe cases, it will produce wave bars on the glass plate. However, it cannot be powdered, if it is powdered, it will bring in too much gas and increase the difficulty of clarification. Considering factors such as the processing of cullet, a block size of 5-60mm is usually used, and it is forbidden to mix impurities such as soil, bricks, and stones.
When using cullet, in addition to determining the block, dosage, addition method and reasonable melting system of cullet to ensure the rapid melting and homogenization of the glass, it is also necessary to supplement the volatilization loss and adjust the formula to keep the glass composition unchanged.
When using foreign broken glass, it is also necessary to screen, clean, and classify to remove impurities, and at the same time, chemical analysis should be carried out to batch according to its chemical composition.
Low-iron cullet and high-iron crushed glass should be stacked separately, and the two types of cullet should not be mixed with each other. The broken glass yard should be managed by personnel.
