The basic principle of billet heating
In the production of seamless steel pipes, the heating process of the billet is actually the heat transfer process of the heat source. The temperature difference is the basic condition for heat transfer. Only when there is a temperature difference can heat spread. According to whether the temperature of the object changes during the heat transfer process, Heat transfer can be divided into two states: stable heat transfer and unstable heat transfer.
Steady state heat transfer refers to the heat transfer phenomenon in which the temperature of the object does not change with time during the heat transfer process.
Unstable heat transfer refers to the heat transfer phenomenon in which the temperature of the object is constantly rising during the heating process, and the heat is continuously transferred from the surface of the object to the interior, that is, the heat transfer phenomenon in which the temperature changes with time.
There are three ways of heat transmission: conduction, convection and radiation.
1 Guide
Conductive heat transfer is generally transferred from the high temperature part to the low temperature part of the same object, and can also be transferred from the high temperature object to the low temperature object in close contact with it. Conductive heat transfer has the following characteristics.
(1) Conductive heat transfer has only microscopic thermal motion of particles, not macroscopic motion or displacement. Therefore, conduction heat transfer mainly occurs in solids such as metals and refractory materials.
(2) The particles must collide and contact to conduct heat transfer. Therefore, when there are a large number of pores in the solid, the conduction heat transfer is greatly weakened. The heat insulation materials commonly used in heating furnaces are made according to this principle.
2 Convection
Convective heat exchange is due to the transfer of heat energy from high temperature to low temperature during the contact process when the fluid (liquid and gas) makes macroscopic movements. Therefore, the medium of this heat transfer method can only be liquid (including flowing metal melt) and gas. Convective heat exchange can occur between the fluid and the solid surface, or inside the fluid.
3 Radiation
Convection and conduction are two heat transfer methods that must be in contact with objects to transfer heat, while radiation is a heat transfer method in which objects can conduct heat from one object to another without contact between objects.
The above three heat transfer methods often exist simultaneously in industrial furnaces.
