What are the factors that determine the outer diameter of the resistance wire coil in an electric heating tube? - Yangzhou Darui

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I. Uneven resistance drop rate

　　The resistance wire is in contact with the magnesium oxide powder around it. Through compression processing after filling with magnesium oxide powder, the porosity of magnesium oxide is reduced, and the resistance value of the resistance wire decreases by about 15~25%. In the resistance drop rate at this time, attention should be paid to the influence of the coil outer diameter. Generally, the larger the coil outer diameter, the greater the resistance drop rate, and unevenness may also occur. To reduce this unevenness, because this unevenness directly causes deviation in the rated power.

　　II. Insulation distance and insulation resistance

　　The insulation resistance between the resistance wire and the sleeve at high temperature is different from that at low temperature. However, considering the insulation distance from the insulation resistance itself, the larger this distance, the greater the insulation resistance between the resistance wire and the sleeve. There is a certain limit from the perspective of heat conduction. The insulation distance varies with the required insulation resistance and operating temperature, but if high-quality magnesium oxide powder is used as insulation, it can usually be appropriately selected as 1.5~3mm.

　　III. Heat conduction

　　The heat of the resistance wire is transferred to the sleeve through the magnesium oxide powder, and then to the heated object. Generally, the resistance wire wound into a coil is regarded as a single resistance wire with an outer diameter d. When wrapped with an insulating material with a certain thermal conductivity, what thickness is best for heat dissipation?

Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.