It mainly includes the steps of batch preparation, melting, forming, annealing and post-processing.
Batch preparation
First, the raw materials are pre-processed, including the crushing of massive raw materials, the pre-drying of wet raw materials, and the iron-removing treatment of iron-containing raw materials. The size of the crushed particles should be 0.25~0.5mm. The coarse particles are not easy to be fully melted, and residual powder stones or silicon-rich nodules will be formed in the glass; too fine particles are easy to fly or agglomerate into agglomerates. The raw materials with a certain particle size are accurately weighed according to the formula, and then mixed with a drum, paddle or disc mixer.
Melting
The glass batch material is melted and clarified at a high temperature to form a uniform glass liquid without bubbles and stones. The melting temperature of the glass batch varies with the composition, and is usually 1300 to 1600°C. The batch material undergoes a series of physical and chemical reactions at high temperature and gradually melts completely. With the increase of temperature, the viscosity decreases significantly, and a large amount of air contained therein and the gas generated by the decomposition of raw materials rise and escape from the melt, making the melt clear. While removing the bubbles at high temperature, the chemical composition of the molten glass also tends to be uniform. If necessary, mechanical external force agitation is applied. After the clarification and homogenization are completed, the temperature is lowered to make the glass liquid uniformly reach the viscosity suitable for the molding requirements.
The melting takes place in a glass melting furnace. In mass production, it is continuously melted in the kiln. The batch material is added at one end of the kiln, and the formed glass liquid is discharged at the other end. In small-volume production, it is melted intermittently in a crucible kiln.
forming
Process glass liquid into products with fixed geometric shapes. When the glass is cooled, it changes from liquid state to plastic state to solid state, which connects the production stages of glass supply and retrieval, shaping and setting. When manually picking the material, the viscosity of the glass liquid is usually 102.2Pa·s; when the material is automatically fed by the machine, it is 102～103Pa·s, which is equivalent to 10-100 times the viscosity when the glass liquid is clarified. The suitable viscosity of the glass drop into the mold is usually 103.5 Pa·s, and the viscosity should be 106 Pa·s during demolding. In this plastic range, the glass frit is subjected to shaping operations such as shearing, bonding, blowing, and calendering. If the production time is long, the glass composition must be adjusted so that the viscosity transition tends to be slow and the crystallization tendency is small, so as to avoid hardening too fast and crystallization during the molding process. Commonly used glass forming methods include blowing method, pressing method, drawing method, pouring method, calendering method and so on.
Glass tube blowing method:
used to make hollow glass products, such as drinking glasses, utensils, bottles, jars, bulbs, etc. For manual blowing, use a 1.5m hollow iron blowpipe, one end is dipped in glass liquid (material picking), and one end is a blowing nozzle. After picking the material, roll it evenly and blow on the material rolling board (bowl) to form a glass froth, which is blown into a product in the mold; it can also be blown freely without a mold, and finally knocked off from the blow tube. When forming large products, it is necessary to repeatedly pick and roll evenly to collect enough material. During mechanical blowing, the molten glass flows out from the outlet of the glass melting furnace, and is formed into droplets of set weight and shape through the feeder, cut into the preliminary mold to be blown or pressed into the preliminary shape, and then transferred to the forming mold to be blown into Products. The weighing-blowing method of blowing into a preliminary shape and then blowing into a product is suitable for making small mouth utensils and bottles. The weighing-blowing method of pressing into a preliminary shape and then blowing into a product is suitable for making large-mouthed utensils and thin-walled bottles and cans.