Electric heating elements are used more and more widely in today's resistance industry. In the process of constant increase of new users, it is inevitable that there will be insufficient overall understanding of electric heating elements or less power calculation. Of course, if you contact us directly, we will definitely help you calculate, but knowledge only belongs to you if you learn it yourself. This time I will share with you this article on the design and calculation of electric heating elements. Tell about the power according to the electric heating alloy component; the wiring method of the electric heating alloy component; the surface load rate of the electric heating alloy component. A comprehensive explanation of the three aspects. I hope to be helpful.
(1) Power of electric heating alloy components:
According to Ohm's law, the power of the heating element can be obtained from the following formula:
P=U*I=I²*R= U²/ R
Where: P—electric power (W); U—voltage (V); I—current (A); R—resistance (Ω)
Generally, if the electrical resistivity (ρ) of the alloy, the temperature correction coefficient (Ct), and the surface load (W) of the element are known, the size of the element can be calculated. In order to obtain a faster heating rate and higher heating capacity, industrial resistance furnaces must comprehensively consider the requirements of various aspects when determining the total power. The power of the industrial resistance furnace and the furnace area, furnace structure, and the required productivity of the furnace It is related to factors such as heating rate. If the power is too large, the temperature of the heating element during heating will be too different from the temperature in the furnace. Unnecessarily high element temperature will shorten the life of the element. If the power is too small, the temperature of the furnace will not rise. Or the heating rate is very slow, and the process requirements are not met, the quality is affected, and the productivity is also reduced.
(2) Wiring method of electric heating alloy components:
When designing a resistance furnace, it is necessary to consider the power of the furnace, the power distribution and the voltage and the number of phases of the power supply, as well as the characteristics of the use of electric heating materials. When a lower voltage is used to prevent discharge under conditions, it needs to be implemented through a step-down transformer. Sometimes changing the wiring method of the components can completely change the power of the resistance furnace.
On the premise that the voltage of the power supply line is constant and the resistance of the electric heating element is equal, the wiring method is different, and the power in the furnace will also be different. Therefore, by changing the wiring method of the furnace element or cutting off a certain group or phase, the input can be changed. The purpose of the power in the furnace, but if this wiring method is changed incorrectly, the component will be burned. For example, when the component is working normally, the phase voltage applied by the star connection is the rated voltage and the power consumed is the rated power. If the delta connection is changed, the phase voltage will increase. If the voltage exceeds the rated voltage, the power will increase by 3 times, so the components will be burned. If you need a fast heating speed, you must have a larger power, and because the heat loss is less during the heat preservation, a smaller power can be maintained, and the phase voltage can be reduced, and the power is only 1/3 of the original, which is completely OK. To meet the requirements, this change method is correct. In addition, the original furnace design is based on the star-shaped method to obtain a reasonable cross-sectional area and length of the components. If the components are arranged in the furnace, it is unreasonable to change to the delta connection in this case. In short, the relationship between the voltage and the wiring method is closely related to the structure and process requirements of the electric furnace, and it must be used correctly.
(3) Surface load rate of electric heating alloy components:
The surface load rate of the electric heating alloy component is represented by W, which refers to the electric power emitted on the surface of the component, and the unit is W/cm². The higher the surface load rate of the component, the more heat is emitted. The higher the component temperature, the less component materials are used. However, if the surface load rate is too high, the component will shorten its service life due to its high temperature, and even severely oxidize, deform, collapse or melt. Therefore, the surface load rate should have an allowable value, which is called the allowable surface load rate.
The heat dissipation conditions of the electric heating elements in the furnace are related to factors such as furnace temperature, element structure and installation status. The lower the furnace temperature or working temperature, the better the heat dissipation conditions, and the greater the pitch of the spiral element, the better the heat dissipation conditions; the heat dissipation conditions of the corrugated resistance wire are better than the corrugated resistance tape, which is better than the spiral resistance wire; The condition of the heat dissipation element of the exposed type is better than that of the closed type; the heat dissipation condition of the electric heating element arranged on the side wall of the furnace is better than the heat dissipation condition of the electric heating element arranged under the furnace floor; the better the heat dissipation condition, the less the electric heating element is prone to overheating, and the allowable surface load The rate is also greater.
The allowable surface load rate of the electric heating element is also related to whether it is corroded. Most chemical heat treatment media corrode and destroy the oxide film on the surface of the element. Therefore, when using these media, a lower surface load rate should be adopted or the use temperature should be lowered.
