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Commonly used electric heating materials and characteristics of box furnace

Commonly used electric heating materials

    The electric heating elements of the box furnace are made of electric heating materials, which are divided into two categories: metal and non-metal. Among them, 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 severe cases, it will be quickly damaged. The electric heating elements should be used at the appropriate temperature. There is a temperature difference between the surface temperature and the working temperature in the furnace. This temperature difference depends on the characteristics of the electric heating material and the requirements of the heating process in the furnace. Generally refer to the following values: in the resistance furnace of 650¡æ, the temperature of the electric heating element is 750~900¡æ; in the resistance furnace of 800¡æ, the temperature of the electric heating element is 850~1000¡æ; in the resistance furnace of 1000¡æ, the temperature of the electric heating element The temperature is 1050-1100¡æ; in the resistance furnace of 1200¡æ, the temperature of the electric heating element is 1250~1300¡æ.
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Characteristics of electric heating materials for box furnaces

    Electric heating elements are used as heat sources to convert electrical energy into heat. In addition to requiring the heating elements to reach the required temperature, the materials used to make the heating elements are also required to have the following properties:

    (1) Higher resistivity. When the current through the heating element is constant, the greater the resistance, the greater the power obtained, the more electrical energy is converted into heat energy, and the faster the furnace temperature rises. Using high-resistivity materials, processed into electric heating elements with short length and large cross-section, which not only saves materials but also prolongs the service life of the electric heating elements.

    (2) Smaller temperature coefficient of resistance. The temperature coefficient of resistance refers to the value that the resistance of an electrothermal material changes with temperature. An electric heating element with a positive temperature coefficient of resistance gradually increases in resistance as the temperature increases. Too much temperature coefficient is not conducive to the stability of heating power and easily causes 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 working temperature of the furnace, generally 50~100¡æ. In order to prevent serious deformation, melting and fracture, the electric heating material used should have good heat resistance and high temperature strength.

    (4) The coefficient of linear expansion should be small. The heating element with a large linear expansion coefficient will become thicker and longer as the temperature rises, which may damage the fixed element and cause the heating element to fall off or short-circuit. Therefore, electric heating materials with a small linear expansion coefficient should be selected.

    (5) Good processing performance. When selecting electric heating element materials, it is necessary to consider its ease of processing, that is, easy to process and shape, easy to wind and install.

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