Heating Furnace What You Need to Know

1. Heating furnace's purpose

The heating furnace is to heat the billet to a uniform temperature (austenite structure) suitable for rolling. After the temperature increases, the first thing is to improve the plasticity of the steel and reduce the deformation resistance, so that the steel is easy to deform. For example, the deformation resistance of T12 steel is about 600 MPa at room temperature, and it decreases to about 30 MPa when heated to 1200 ℃, which is only one twentieth of that at room temperature.

For the steel with proper heating temperature, a larger reduction can be used during rolling, which can reduce the equipment accidents caused by wear and impact, improve the productivity and operation rate of the rolling mill, and reduce the rolling energy consumption. Secondly, heating can improve the internal structure and properties of the billet. The inhomogeneous structure and non-metallic inclusions are homogenized by the diffusion of high-temperature heating. The heating temperature and uniformity are the marks of heating quality. The steel with good heating quality is easy to obtain the finished product with the correct section shape and accurate geometric size.

2. Heating furnace's heating process

The heating temperature of the billet includes surface temperature, temperature difference along with section and temperature difference along billet length. The final heating temperature of the billet in the furnace is determined after considering the actual situation of the rolling process, structural characteristics of the rolling mill and heating furnace. The time required for heating to the specified temperature depends on the billet size, steel grade, temperature system adopted and some other conditions.

The billet gets heat by convection and radiation in the heating furnaces. The former is that the furnace gas washes the billet surface, while the latter is that the furnace gas and hot lining radiate heat. Along the length direction, our furnace is divided into three sections: preheating section, heating section and soaking section. When the billet enters the preheating section of the heating furnace, the heat flux increases gradually. When the billet reaches the second heating section, the heat flux basically remains unchanged. When the billet reaches the soaking section, the heat flux decreases gradually.

In the soaking zone, the surface temperature of the billet remains basically unchanged, while the temperature difference of the cross-section decreases gradually, and the heat from the billet surface diffuses to the interior in the way of heat conduction. The smaller the heat flux to the billet surface, the larger the heating area, the smaller the section size of the billet and the greater the thermal conductivity of steel, the smaller the section temperature difference. Generally, the heating time of billets with large section is longer than that of billets with small section, and that of alloy steel is longer than that of carbon steel.

3. Heating furnace pressure system

The size and distribution of the heating furnace pressure are an important means to adjust the temperature field, control the flame and atmosphere in the furnace. It affects the heating speed and quality, and also affects the utilization of fuel. In particular, the furnace pressure at the discharge section of the furnace is particularly important.

The heating furnace pressure should be set at 0 ~ 30Pa higher than atmospheric pressure. If the furnace pressure is too high, the charging port, discharging port, observation hole and other opening parts will be exposed to fire. The results are as follows: (1) the furnace gas loss increases, which increases the heat loss; (2) SO 2 and other harmful gases enter the workshop, which pollutes the working environment; (3) the furnace wall, nearby steel structure or mechanical equipment at the burning part are damaged or deformed. On the contrary, if the furnace pressure is too low, the absorption of cold air in the workshop will make (1) the furnace temperature decrease and the fuel consumption increase; (2) the cooling of billet by low-temperature air will lead to uneven temperature; (3) the increase of oxygen content in the furnace gas will lead to the increase of burning loss.

4. Heating furnace combustion system:

The basic requirement is to ensure that the fuel is completely burned in the heating furnaces and the air coefficient α is small. Excess air leads to a large amount of flue gas and more heat carried away; insufficient air leads to incomplete combustion in the furnace, which also increases heat loss.

Inquiry about heating furnaces, please mail at marketing2@hanrm.com.

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