Abnormal overheat damage of the hottest electric h

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Abnormal overheating damage of electric heating element connector

fault phenomenon

the electrical connectors of electric heating elements, such as broken outgoing lines, burnt and corroded crimping bolts and nuts, are abnormally overheated and damaged, resulting in abnormal operation of electric heating equipment

reason analysis and elimination

the main reason for this abnormal overheating damage is that the wiring method of electrical installation is incorrect. Different from the requirements of conventional electrical equipment and component circuit connectors (contacts), the electrical connectors of electric heating elements require not only correct and reliable wiring and small contact resistance, but also certain heat dissipation characteristics and high anti-oxidation and corrosion capacity. In addition to the serious corrosive gas and liquid (such as constant temperature water bath and salt bath) in the workplace of electric heating elements, high-temperature oxidation corrosion is the most common direct cause of damage to the joints of electric heating elements. Measures can be taken from the following aspects to reduce the working temperature at the electric connector of the electric heating element and improve the working reliability of the electric heating element connector

(1) enhance the contact pressure between crimping connecting conductors: within a certain pressure range, the greater the pressure, the smaller the contact resistance. However, if the pressure exceeds a certain limit, the contact resistance will no longer change significantly with the increase of pressure. One of the purposes of fitting the bolt and nut of the crimping wire with the metal spring pad of corresponding specifications is to ensure that a moderate and constant contact pressure is always maintained between the connecting conductors, so as to reduce the auxiliary contact nozzle between conductors such as oxide skin and metal debris. Because most of the outgoing connecting wires of the electric heating elements belong to the heating conductor, and the temperature fluctuation of the joint workplace is very large. The deformation sizes of thermal expansion and cold contraction between the wiring contacts are different, resulting in a gap between the contacts, resulting in an increase in contact resistance and an increase in contact temperature when the current passes through. Adding spring pads between the contacts can compensate the gap between the connecting conductors during thermal expansion and cold contraction, maintain the contact pressure and push it into the next clamping device to keep the gap between the contact surfaces constant, and ensure the constant contact resistance between the contacts from one foil rolling production line

(2) reduce the resistance value of the outgoing wiring of the electric heating element: usually, the electric heating element directly leads out the internal electric heating wire (resistance wire) as its connecting wire (this is the most common in the general electric heating furnace). Part of the heating capacity at the electrical connector is generated by the contact resistance of the connector itself, and the other part is generated by the resistance of the lead out wiring of the electric heating element. For the latter, the new experiment proves that the contact heating is reduced by reducing the resistance value of the outgoing wiring. When making the outgoing terminal of the electric heating element (such as the electric furnace wire connector and the electric iron electric heater connector) at the production site, according to the distance between the main heating area and the wiring terminal (set it as 1), the electric heating wire with a length greater than 2L or 3L is reserved and straightened, and then its 2 or 3 strands are twisted in parallel to make it an integral whole, The joint shall be bent or crimped according to the actual situation. In this way, due to the increase of the contact area, the resistance value of the outgoing line of the electric heating element will drop to 1/3 ~ 1/2 of the original value, and the corresponding heating capacity will also drop to 1/3 ~ 1/2 of the original value. If the diameter of the heating wire is very small, the number of strands of the outgoing line of the electric heater can be increased correspondingly

(3) enhance the heat dissipation and ventilation effect at the electrical joints of electric heating elements: for high-power equipment, due to the large number of electric heating elements and corresponding electrical connection points, the heat generated by the contact resistance and lead resistance at the connection points is also large. If the heat is not dissipated in time, local overheating will occur near the electrical contacts and around the leads, resulting in overheating, high-temperature corrosion and damage of the leads and contacts of electric heating elements. Therefore, for the wiring of high-power electric heating equipment, the connection between the main power line and the branch lines of heating elements generally does not adopt the method of direct crimping or splicing, but should be equipped with an intermediate transitional connection terminal with certain thermal conductivity and heat dissipation effect. The terminal can be copper bar with large surface area, stainless steel plate or galvanized (drilled) flat iron. Avoid the formation of high-temperature area of heat accumulation, so as to overcome the local overheating phenomenon

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