Crucible kiln is a kind of thermal equipment in which a crucible is placed in the kiln, and the batch material is melted into glass in the crucible.
Compared with the tank kiln, the crucible kiln has simple structure, low cost, fast construction, and is suitable for rapid production; the operation system is easy to adjust, and mechanical stirring (such as melting optical glass, etc.) can be used to extend the heat preservation time, etc., and the production uniformity Good, high-quality glass; strong adaptability to the process, it can be changed at any time, and several glasses with similar properties and melting systems can be melted in different crucibles at the same time. The crucible kiln is an intermittent operation, with small output, low thermal efficiency, difficult to realize mechanization, low utilization rate of glass liquid, and low production efficiency. The manufacturing of the crucible itself is also more complicated, and the labor intensive when changing the crucible. Nevertheless, the crucible kiln also has its advantages, especially suitable for the production of glass products with small output, many varieties, high quality requirements or some special properties, such as optical glass, colored glass, crystal glass, lead glass, instrument glass and Special glass, etc., are also suitable for scientific research or trial production of new varieties of glass.
The classification of crucible kiln
There are many classification methods for crucible kilns: according to the waste heat recovery method, it is divided into regenerative kiln and heat exchange kiln; according to heat source, it is divided into electric heating kiln and flame kiln; according to the number of crucibles used, it is divided into single crucible kiln and multi-crucible kiln; According to the characteristics of the crucible, it is divided into an open crucible and a closed crucible; according to the flame flow direction, it is divided into an inverted flame kiln and a flat flame kiln; according to the shape of the heat exchanger, it is divided into a round furnace and a square furnace.
The flame of the inverted-flame crucible kiln is injected from the center of the kiln bottom, and then discharged from the periphery of the kiln bottom. This type of kiln has a more uniform temperature distribution along the height of the crucible, and the molten glass is also more uniform. However, the bottom of the kiln and the bottom of the crucible are often at High temperature, easy to damage.
The flame of flat flame crucible kiln is sprayed from above the crucible and discharged from the bottom of the kiln. The temperature difference in the height of the crucible is large, which often makes manual forming operations difficult. Therefore, it is only used for products that require high temperature melting and short forming time. Such as casting optical glass products.
Single crucible kilns mostly use open crucibles to facilitate mechanical stirring, and can be used for products with strict requirements for melting systems and high glass quality requirements. Most of them use electric heating elements (such as silicon carbide rods or silicon molybdenum rods) as heat sources to produce optical glass, filter glass and some special glasses.
Round furnace and square furnace refer to the shape of the heat exchanger. The shape of the heat exchanger is round, commonly known as round furnace, and the shape of square heat exchanger is commonly known as square furnace. The square furnace was developed from the round furnace. Compared with the round furnace, the square furnace has a larger heat exchange area and longer heat exchange time, and the preheated air temperature is higher, so the heat exchange effect is obvious. The square furnace is easy to build, the brick joints are tight, and the masonry is firm, which can reduce the thickness of the partition wall between air and flue gas, and further improve the heat exchange efficiency, so it is used more.
The regenerator multi-crucible kiln has a large capacity, and generally has 8 to 14 closed crucibles. Its furnace temperature is high, the thermal efficiency is high, and it can use inferior coal. However, this kind of kiln requires all the crucibles to be charged, melted, cooled, and formed at the same time, and auxiliary equipment such as a gas generator must be added. The kiln structure is more complicated. There was a regenerative multi-crucible kiln in China in the early 1960s, but it was difficult to promote. Now only a few factories use this kiln to produce instrument glass and electric vacuum glass.
Heat exchange type multi-crucible kiln adopts closed crucible, which is widely used in daily glass production. The heat exchanger can be a metal heat exchanger or a ceramic heat exchanger. The metal heat exchanger has good airtightness and better heat transfer effect, but the material is required to be resistant to high temperature and corrosion. Although the air tightness of ceramic heat exchangers is not as good as that of metal heat exchangers, it has the characteristics of high temperature resistance and corrosion resistance. So it is widely used. At present, the ceramic heat exchangers mainly used in China include standard brick heat exchangers and cylindrical brick heat exchangers.