Shuttle kiln, as a cutting-edge roasting equipment, has been widely used in many industries in my country, including the production of electrical ceramics and grinding wheels in the machinery industry, the manufacturing of sanitary ceramics in the building materials field, and the environmental protection and refractory materials industries. Its unique advantages - low energy consumption, temperature uniformity, short firing cycle, high degree of automation and flexible production, have brought revolutionary technological improvements to the above industries. This not only significantly improves production efficiency, but also brings huge economic benefits. Because of this, traditional inverted flame kilns and even tunnel kilns are gradually being replaced by shuttle kilns. Looking to the future, with the continuous breakthroughs in my country's science and technology and the continued development of related industries, we foresee that more energy-saving and highly automated shuttle kilns will be more widely used in various industries.
Structural features of shuttle kiln
The shuttle kiln has a structure similar to that of a trolley-type heating furnace and a heat treatment furnace, and is very popular in the ceramics and refractory materials industries. This kind of kiln is named after the movement of the kiln car, which is like a "shuttle" that can be flexibly pulled out and pushed in the kiln, so it is also called a drawer kiln. As an intermittent firing equipment, the shuttle kiln will undergo heating and cooling processes in each firing cycle, which makes the heat storage and heat dissipation performance of the kiln body and kiln cars have a direct impact on the thermal efficiency of the kiln.
In order to improve thermal efficiency, shuttle kilns mostly use lightweight refractory materials in design to minimize heat storage and heat dissipation losses. At the same time, it is also equipped with a temperature-adjustable high-speed burner to ensure that the temperature difference between the flame temperature and the product to be burned will not be too large, thereby avoiding defects in the product. In addition, the disturbance and entrainment of high-speed airflow in the kiln also increase the convective heat transfer efficiency. The flat-top structural design of the shuttle kiln allows the kiln roof and kiln wall to be independent of each other and freely expandable, which not only provides the possibility for the kiln body to be lightweight, but also makes full use of the space inside the kiln. It is worth mentioning that the shuttle kiln adopts the bottom exhaust method, which not only helps to uniform the temperature in the kiln, but also simplifies the workshop floor facilities.
These characteristics together constitute the key advantages of the shuttle kiln in terms of energy saving, small temperature difference, and short firing cycle, and also distinguish it from other equipment such as heating furnaces and heat treatment furnaces. At present, the firing chamber volume of domestic shuttle kilns is flexible and variable, ranging from a few cubic meters to nearly 200 cubic meters, and can be customized according to user needs. Next, we will focus on the structural characteristics and related design requirements of large-volume shuttle kilns.
A large shuttle kiln is a complex system, which consists of multiple key parts: the stable steel structure of the kiln supports the entire kiln body; the kiln body made of refractory materials withstands the test of high temperatures; the kiln door opening and closing system ensures that the kiln door The flexible switch; the kiln car and the entry and exit car system are responsible for the smooth transportation of products; and the kiln foundation, flue, combustion system, smoke exhaust system and control system are all indispensable parts to ensure the efficient and stable operation of the shuttle kiln .
The kiln refractory material structure of the shuttle kiln is quite delicate, mainly including the kiln wall masonry above and below the car table, the kiln door, the kiln roof masonry, and the kiln car table masonry. The material selection and design of these components have been carefully considered to ensure efficient operation and long life of the kiln. The kiln walls below the car table are usually built with heavy refractory bricks to withstand the weight of the kiln car and products. The kiln walls, kiln doors and kiln roofs above the turning table are made of lightweight refractory materials with good thermal shock resistance, small thermal conductivity and small expansion coefficient, which can not only reduce the weight of the kiln body, but also help improve thermal efficiency.
It is worth mentioning that these lightweight refractory materials are carefully matched according to the operating temperature of the kiln. The combination of high-strength lightweight bricks and insulating fiber materials, or the use of composite refractory fiber modules such as polycrystalline mullite, are designed to provide the best thermal insulation effect for the firing space of the kiln.
The refractory materials on the kiln wall and roof are closely integrated with the steel structure of the kiln body. This special structure not only ensures the stability of the refractory materials, but also enhances the overall strength of the kiln body. The design of the kiln steel structure cannot be ignored either. It must have sufficient strength and rigidity to support the weight of the entire kiln body and refractory materials. Depending on the height and width of the kiln, the steel structure will be accurately manufactured using different specifications of steel sections and steel plates to ensure the stability of the kiln under various working conditions.
In shuttle kilns in the electric porcelain industry, the configuration of kiln wall refractory materials is particularly critical. The combination of lightweight mullite bricks and aluminum silicate refractory fibers, or the combination of lightweight mullite bricks, lightweight high alumina bricks and aluminum silicate refractory fibers, all reflect the industry's high requirements for the performance of refractory materials. However, refractory fibers may face problems such as shrinkage, aging, and fiber powdering and peeling during use. These problems may have a negative impact on the appearance and performance of electrical porcelain and ceramic products. Therefore, manufacturers usually take great care when selecting refractory materials to ensure long-term stable operation of the kiln.
In addition, the "floating anchor" structural connection between the lightweight bricks and the kiln wall steel plates further enhances the stability of the kiln wall. This structural form not only ensures the tight combination of refractory bricks and steel plates, but also effectively prevents the refractory materials from falling off and being damaged.
When building kiln walls, kiln roofs and kiln doors, the selection of air-hardening refractory mud is also a science. This kind of mud needs to have good masonry properties, not only to maintain appropriate viscosity during construction, but also to harden quickly after construction to produce sufficient bonding strength. At the same time, it also needs to maintain good performance within the temperature range of 1000~1600°C to meet the needs of shuttle kilns at various operating temperatures.
On the kiln walls on both sides of the shuttle kiln, several temperature-adjusting high-speed burners are carefully arranged at each fire channel. The flame gas ejected at high speed from these burners not only provides a stable heat supply to the shuttle kiln, but also becomes the power source for air flow disturbance and entrainment in the kiln. Unlike traditional industrial furnace burners, which are mainly arranged at the lower part of the furnace wall, the burner arrangement of the shuttle kiln pays more attention to the air flow circulation in the vertical section and horizontal plane. This design plays a vital role in uniforming the temperature field in the kiln. .
The design of the kiln door of a large shuttle kiln is also exquisite, and is usually composed of a combination of steel structure and lightweight refractory materials. The refractory material part is generally composed of lightweight mullite bricks and aluminum silicate refractory fibers, which not only ensures the fire resistance of the kiln door, but also effectively reduces the weight. The opening and closing mechanisms of kiln doors are flexible and diverse, including rotary, translation and lifting. Most of them have been driven automatically through electric mechanisms, and a very few manufacturers still use manual operation. But no matter which way, ensuring the sealing between the kiln door and the kiln body is the core point of the design.
The kiln bottom of the shuttle kiln is composed of the kiln car and the table masonry, which together with the kiln wall, kiln roof and kiln door form a complete firing space. The design of the kiln car is also full of ingenuity. It is composed of a strong steel frame, wheels and carefully constructed refractory materials. When selecting the structural form and material of the refractory material for the car table, it is necessary to ensure its load-bearing capacity, enhance the heat insulation effect, and at the same time reduce the heat storage and heat dissipation losses of the kiln car masonry as much as possible. The wide application of lightweight kiln cars provides an effective way to reduce product heat consumption.
In terms of smoke exhaust methods, except for a few shuttle kilns imported from abroad that use upper smoke exhaust due to special reasons, most large domestic shuttle kilns have chosen the lower smoke exhaust method. This design complies with the vertical gas distribution law, allowing the high-temperature airflow in the kiln to flow from top to bottom, thereby ensuring horizontal temperature uniformity in the kiln. At the same time, the shuttle kiln is equipped with high-speed burners above and below the vertical section, and together with the lower smoke exhaust method, it achieves the goals of uniform temperature distribution in the kiln and rapid firing. This structural feature has been fully verified in heat treatment furnaces and other equipment in the machinery industry.
In terms of kiln infrastructure construction, considering the geological conditions of the location where the kiln is built, such as high groundwater levels, the flue is mostly designed to be waterproof. In order to completely avoid the impact of groundwater on the flue, some kilns even adopt a design plan of spreading multiple shallow flues. For flues with heat exchangers placed inside the flue, seepage wells are also provided on the deeper sides as auxiliary waterproofing facilities to ensure the stable operation of the kiln.
Finally, in the construction of the kiln foundation, concrete with a grade of C-15 or above is used for pounding. Depending on the soil quality and ground endurance, most kiln foundations are designed as reinforced concrete structures to provide sufficient stability and load-bearing capacity. The kiln car track is installed on a solid kiln concrete foundation, and light rail with a specification of 22kg/m or above is usually used to withstand the load conditions of the shuttle kiln. These meticulous design considerations jointly ensure that the shuttle kiln can operate efficiently and stably.
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