Common electric heating materials and characteristics of box furnace

Common electrothermal materials
The electric heating elements of box furnace are made of electric heating materials, which can be divided into metal and non-metal, of which metal is divided into alloy and pure metal. Each type of electric heating material has its maximum use temperature, recommended use temperature and application environmental conditions. In principle, electric heating elements are not allowed to exceed the recommended operating temperature, otherwise the service life will be shortened, and in serious cases, they will be damaged quickly. All electric heating elements shall be used at appropriate temperature. There is a temperature difference between the surface temperature and the working temperature in the furnace, which depends on the characteristics of electric heating materials and the requirements of heating process in the furnace. Generally, the following values can be referred to: in a 650 ℃ resistance furnace, the temperature of the electric heating element is 750 ~ 900 ℃; In an 800 ℃ resistance furnace, the temperature of the electric heating element is 850 ~ 1000 ℃; In a 1000 ℃ resistance furnace, the temperature of the electric heating element is 1050-1100 ℃; In a 1200 ℃ resistance furnace, the temperature of the electric heating element is 1250 ~ 1300 ℃.

Characteristics of electrothermal materials
As a heat source that converts electric energy into thermal energy, electric heating elements are required to reach the required temperature, and the materials used to make them are also required to have the following properties:
(1) Higher resistivity. When the current through the electrothermal element is constant, the greater the resistance, the greater the power obtained, the more the electrical energy is converted into thermal energy, and the faster the furnace temperature rises. Using high resistivity materials to process electric heating elements with short growth and large cross-section can not only save materials but also prolong the service life of electric heating elements.
(2) Smaller resistance temperature coefficient. The resistance temperature coefficient refers to the value of the resistance of an electrothermal material changing with temperature. The resistance of the electrothermal element with positive resistance temperature coefficient gradually increases with the increase of temperature. Too large a temperature coefficient is not conducive to the stability of heating power, and it is easy to cause temperature fluctuations.
(3) Good heat resistance and high strength at high temperature. The temperature of the electric heating element itself is higher than the normal operating temperature of the furnace, generally 50 ~ 100 ℃. In order to prevent it from serious deformation, melting and fracture, the electric heating materials used should have good heat resistance and high temperature strength.
(4) The coefficient of linear expansion should be small. The electric heating element with large linear expansion coefficient will become thicker and longer when the temperature rises, which may damage the fixed element and cause the electric heating element to fall off or short circuit. Therefore, the electric heating material with small linear expansion coefficient should be selected.
(5) Good processability. When selecting materials for electric heating elements, we should take into account its workability, that is, it is convenient for processing and molding, winding and installation.