Classification of crucible kilns
Crucible kiln, also known as crucible furnace, is a small intermittent glass melting furnace that melts glass batch materials in the crucible in the kiln. Place a single or multiple crucibles in the kiln, put the batch materials into the crucible and melt them into molten glass.
The various stages of glass melting in the crucible kiln (melting, clarification, homogenization, cooling) are performed sequentially in the same crucible over time, and the temperature system in the kiln changes over time. During molding, materials are manually taken from the mouth of the crucible, and then blowing, pressing, pulling, pouring, etc. can also be supplied from the bottom of the crucible, or the entire crucible can be removed to take out the materials. There are two types of crucible shapes: open mouth and horizontal mouth (closed mouth). The crucible mouth of the open-mouth crucible faces the kiln chamber, which can directly obtain the heat energy radiated and transmitted by the kiln wall and heat source; the crucible mouth of the horizontal-mouth crucible faces the outside of the kiln, and heat is obtained indirectly through the crucible wall, avoiding the influence of the atmosphere in the kiln on the glass liquid. and pollution.
Compared with pool kilns, crucible kilns have simple structures, lower costs, fast construction speeds, and are suitable for rapid production; the operating system is easy to adjust, and methods such as mechanical stirring (such as melting optical glass, etc.) and extended heat preservation time can be used to achieve uniform production. It is a glass with good properties and high quality; it has strong adaptability to the process, can change materials at any time, and can melt several glasses with similar properties and melting systems in different crucibles at the same time. However, the crucible kiln operates intermittently, has small output, low thermal efficiency, is not easy to mechanize, and has a low utilization rate of glass liquid, so the production efficiency is not high. The manufacturing of the crucible itself is also complicated, and the labor intensity is high when replacing the crucible. Nonetheless, crucible kilns also have their advantages, and are especially suitable for producing glass products with small output, many varieties, high quality requirements or certain special properties, such as optical glass, colored glass, crystalline glass, lead glass, instrument glass and Special glass, etc., are also suitable for scientific research or trial production of new varieties of glass.
According to different classification methods, crucible kilns are classified into many categories:
According to the waste heat recovery method, it is divided into regenerative kiln and heat exchange kiln. The multi-crucible regenerator kiln has a large capacity, high furnace temperature, high thermal efficiency, and can use low-quality coal. However, this kind of kiln requires all crucibles to be charged, melted, cooled, and formed at the same time, and additional ancillary equipment such as a gas generator is required, making the kiln structure more complex. Regenerative multi-crucible kilns existed in China in the early 1960s, but because they were difficult to popularize, only a handful of factories now use these kilns to produce instrument glass and electric vacuum glass. The heat exchange multi-crucible kiln uses closed crucibles and is widely used in daily glass production. The heat exchanger can be a metal heat exchanger or a ceramic heat exchanger. Metal heat exchangers have good air tightness and good heat transfer effect, but the materials used need to be resistant to high temperatures and corrosion. Although the air tightness of ceramic heat exchangers is not as good as that of metal heat exchangers, they are widely used because of their high temperature resistance and corrosion resistance. At present, there are two types of ceramic heat exchangers mainly used in China: standard brick heat exchangers and cylindrical brick heat exchangers.
According to the heat source, it is divided into flame kiln using fuel as the heat source and electric kiln using electric energy as the heat source.
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 open crucible and closed crucible. Most single crucible kilns use open crucibles to facilitate mechanical stirring, and can be used for products with strict melting system requirements and high glass quality requirements. Most of them use electric heating elements (such as silicon carbon rods or silicon molybdenum rods) as heat sources to produce optical glass, filter glass and some special glasses;
According to the flame flow direction, it is divided into inverted flame kiln and flat flame kiln. The flame of an inverted flame crucible kiln is injected from the center of the kiln bottom and discharged from the periphery of the kiln bottom. This type of kiln has a relatively uniform temperature distribution along the height of the crucible, and the molten glass liquid is also relatively uniform. However, the bottom of the kiln and the bottom of the crucible are often at High temperature, easy to damage. The flame of a flat-flame crucible kiln is injected from the top of the crucible and discharged from the bottom of the kiln. The temperature difference at the height of the crucible is large, which often makes artificial forming operations difficult. Therefore, it is only suitable for products that require high-temperature melting and short forming time. For example, casting method is used to form optical glass products.
According to the shape of the heat exchanger, it is divided into round furnace and square furnace. Round furnace and square furnace refer to the shape of the heat exchanger. The heat exchanger with a round shape is commonly called a round furnace, and the heat exchanger with a square shape is commonly known as a square furnace. The square furnace developed from the round furnace. Compared with the round furnace, the square furnace has a larger heat exchange area and longer heat exchange time. The preheated air temperature is higher, so the heat exchange effect is obvious. Square furnaces are easy to build, have tight brick joints and strong masonry, which can reduce the thickness of the partition wall between air and flue gas and further improve heat exchange efficiency. Therefore, they are more widely used than round furnaces.
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