Dimensions And Specifications Of Refractory Bricks For Heat Treatment Furnaces

Dimensions and specifications of refractory bricks for heat treatment furnaces

Heat treatment furnace is the basic equipment in the heat treatment workshop of metallurgical factories and mechanical manufacturing factories.

In metallurgical factories, the target of heat treatment is metal ingots, plates, pipes, wires, profiles, rails, wheels, etc. In mechanical manufacturing plants, the objects of heat treatment are various parts, cutting tools, measuring tools, forgings, castings, etc. The types and properties of refractory bricks used in heat treatment furnaces should be determined according to the process and practical application requirements of the heat treatment furnace.

1, Heat treatment process requirements

The requirements for heat treatment process are as follows:

(1) Modify the mechanical and processing functions of the workpiece, or obtain a certain application function.

(2) Make the internal components of the workpiece uniform and eliminate internal stress.

(3) Chemical heat treatment can alter the surface composition of the workpiece, thereby endowing it with special functions.

Heat treatment processes include quenching, annealing, normalizing, tempering, and chemical heat treatment. Regardless of the type of treatment, from a thermal perspective, it consists of three stages: heating, insulation, and cooling. The only difference is the combination of heating temperature, heating speed, cooling speed, and furnace atmosphere.

2, Classification of heat treatment furnaces

Due to the variety of heat treatment processes and the complexity of workpiece shape standards, various types and structures of heat treatment furnaces have emerged. So, there are also many classification methods for heat treatment furnaces. There are several classification methods available:

According to temperature, there are high-temperature heat treatment furnaces with a furnace temperature greater than 1000 ℃; Medium temperature heat treatment furnace, with a furnace temperature of 650? 1000℃; Low temperature heat treatment furnace, with a furnace temperature below 650 ℃.

According to the heat source, there are coal fired furnaces, oil fired heat treatment furnaces, and gas fired heat treatment furnaces that use fuel as the heat source. There are resistance furnaces, induction heating equipment, etc. that use electrical energy as a heat source.

According to the homework method, there are periodic operation heat treatment furnaces and continuous operation heat treatment furnaces.

According to the heat treatment process, there are quenching furnace, tempering furnace, annealing furnace, normalizing furnace, and carburizing furnace.

According to the heating process, there are direct heating heat treatment furnaces and direct heating heat treatment furnaces such as muffle furnaces, radiation tube furnaces, etc.

According to the heating medium inside the furnace, there are those that use gas as the heating medium. Such as air, smoke, controlled atmosphere, vacuum, etc; There are liquid based heating media, such as molten salt and lead furnaces; There are also solid heating media, such as active particle furnaces.

According to the mechanization method, there are trolley furnaces, roller bottom furnaces, chain furnaces, rotary bottom furnaces, vibrating bottom furnaces, hood furnaces, etc.
3, Selection of refractory materials for heat treatment furnaces

If the temperature of the steel heat treatment furnace is less than 1300 ℃, high alumina and alumina silicate fired products or amorphous refractory materials can be used to build the furnace lining.

If controlled atmosphere operation is carried out in the furnace, the furnace lining should not undergo chemical reactions with the controlled atmosphere at high temperatures. It is recommended to use anti carburizing bricks with a particularly low content of Fe2O3 as the furnace lining, and the content should be less than 1% at this time.

Due to the influence of the heat treatment furnace process, at the same productivity, the area and volume of the heat treatment furnace lining are larger than those of the heating furnace. Therefore, the heat dissipation and heat storage losses of the furnace lining are much larger. For example, the heat dissipation loss of a continuous heating furnace accounts for 3% of the total heat? 5%, generally accounting for 20% in heat treatment furnaces; Continuous heating furnace does not consider the loss of heat storage. Does the abnormal loss of heat storage in the heat treatment furnace during periodic operations account for 30% of the stored heat? 40%. Therefore, reducing the loss of lining heat in heat treatment furnaces plays a very important role in improving furnace thermal efficiency.

To reduce the loss of heat storage while meeting the working temperature and furnace atmosphere, furnace lining materials with low bulk density and specific heat should be selected; To reduce heat loss, furnace lining materials with low thermal conductivity should be selected. For example, a 300kW electric hood furnace can save 38.3% energy by replacing lightweight clay bricks (with a density of 1.3t/m3) with aluminum silicate refractory fibers.


4, Shape standard for refractory bricks used in heat treatment furnaces

The furnace standard should strive for compactness to reduce useless space inside the furnace, in order to facilitate uniform temperature inside the furnace and improve thermal efficiency. For example, cylindrical furnaces are often used instead of square furnaces for well furnaces.

When using controlled atmosphere heat treatment, the thickness of the furnace lining should be thicker than when the furnace is filled with air, because the thermal conductivity of controlled atmosphere is higher than that of air. If the thermal conductivity of air is 1, NH3 decomposition gas is 5.5, and H2 is 7. We can follow the principles of minimizing waste, maximizing economic benefits, and shortening the payback period. We can list relevant thermal and economic functions and use optimization methods to obtain the optimal thickness of the furnace lining.