Other factors affecting glass whiteness

(1) Melting temperature When the melting temperature is increased at a certain iron content and selenium powder dosage, the decolorization quality of the glass will decrease. The reason is that increasing the melting temperature will cause the selenium powder to volatilize and increase the dosage. According to practical experience, when the melting temperature is above 1450℃, the selenium powder dosage will increase by about 5% for every 10℃ increase.

(2) Annealing temperature When using selenium powder to decolorize glass, if the annealing process is not well controlled, the product quality will be affected and even discoloration may occur. During the production process, a certain company found that the glass bottles were light rose red after annealing, but the bottles taken directly from the bottle feeding machine did not have this color. Later, by looking for the cause, it was found that the annealing temperature was too high. After adjusting to the normal annealing temperature, the discoloration phenomenon disappeared immediately.

3) Fuel properties In addition to raw materials, fuel is also an important part of the production of high-white glass. Many companies use electric

furnaces or natural gas to reduce pollution to the glass liquid when producing high-white glass. Some enterprises have used ground oil and crude oil to reduce costs. However, due to the ash content of 0.3% in the ground oil and 1% in the ash content of Fe2O3, and the excessive moisture content in the oil, the oil pressure is unstable, the flame is sometimes long and sometimes short, the material color is always unstable, and the decolorizer must be adjusted frequently, which brings many adverse effects to production.

(4) Melting furnace atmosphere From the perspective of glass decolorization principle, the furnace is in an oxidizing atmosphere, which is conducive to the conversion of Fe2+ with strong coloring ability into Fe3+ with weak coloring ability under the action of oxidant, thereby enhancing the decolorization effect. At the same time, the amount of selenium powder is reduced and the cost is reduced. However, when the oxidizing atmosphere is too strong, the purple elemental selenium will be oxidized to colorless SeO2}, thereby weakening the decolorization ability. Generally, it is advisable to control the atmosphere in the furnace to a weak oxidizing atmosphere.
The combustion air volume, the moisture content of the batch material, the fuel properties and the atomization pressure will all have an impact on the furnace atmosphere. According to practical experience, when natural air intake or small air volume is used, the furnace atmosphere fluctuates greatly and is prone to reduction, which will reduce SO2 and SO3 in the glass to sulfides, and then react with iron and selenium in the glass material to form iron sulfide and selenide sulfide, thereby reducing the whiteness of the glass. The combustion-supporting air volume is set to the maximum to make it highly oxidizing, avoiding the defects of large fluctuations and strong reduction of the gas furnace atmosphere, and the color effect is pure and stable.

(5) Influence of discharge volume When the discharge volume is reduced, the volatilization of selenium powder increases due to the extension of the time the batch material stays in the tank kiln. Therefore, when the discharge volume increases, it is beneficial to the color development of selenium powder, and the stable discharge volume is beneficial to the stability of decolorization. When the discharge volume fluctuates by no more than 5%, the impact on decolorization is small, and there is no need to adjust the amount of decolorizer.

(1) Bubbles Bubbles are a common problem in high white glass, mainly small bubbles with a diameter of less than 1mm. Larger bubbles occasionally appear. The reasons for their occurrence are very complicated, mainly due to process reasons and the influence of external factors.
In the glass tank kiln, compared with colored materials, the temperature difference between the upper and lower parts of the high white glass liquid is small, the bottom temperature is relatively high, and the viscosity is relatively much lower. Therefore, it is much easier to discharge bubbles in the high white glass liquid. However, it is much more difficult to absorb bubbles, which is mainly caused by the solubility of gas in the glass liquid being inversely proportional to the temperature. Therefore, when considering the elimination of bubbles in high white glass, do not ignore the role of the bubble "absorption method". Take the method of appropriately lowering the melting temperature, increasing the solubility of gas in the glass liquid, and controlling the discharge amount at the same time, so that the bubbles that affect the appearance quality of the product can be absorbed by the glass liquid and eliminated. Of course, the lower the temperature, the better. When the temperature is reduced to a certain level, the problem will go to the opposite side. Not only will the bubbles not be reduced, but stones will also appear. In addition, the gas rate and melting rate of high white glass production should also be properly controlled and should not be too high. According to production experience: Large bubbles or surface bubbles are generally not related to glass melting, and are mostly produced in the feeding process.

(2) Crystallization Glass crystallization is also a common defect in production, and it is more serious in high-white glass, which often leads to long-term product failure and causes great losses. In glass production, internal and external factors such as glass composition, batching process, production process control, and kiln design should be comprehensively considered to avoid glass crystallization.