Selection of heating tube resistance wire (electric heating wire)

Selection of heating tube resistance wire (electric heating wire)

Selection of resistance wire (heating wire)

Resistance wire is the heating element of an electric heating tube, whose function is to convert electrical energy into heat energy. It is normally divided into two series: iron chromium aluminum and nickel chromium (iron). The performance of resistance wires produced by different manufacturers varies, and there is still a significant gap compared to foreign resistance wires.

① The heating wire of the high-temperature electric heating tube is Ni Cr wire, with a temperature resistance of 1400 º C;

② The heating wire of the medium and low temperature electric heating tube is Fe Cr wire, which has a temperature resistance of 1500 º C. The disadvantage is that it is easy to oxidize and has a short lifespan.

③ The watt density at the R corner of the electric heating tube is lower than that of the straight part, and the temperature difference between the two will be around 20 º C during heating. After oil pressure treatment, it will be controlled at around 10 º C.

④ The diameter of the heating wire is between ø 0.12 and ø 0.6.

3、 Magnesium oxide powder MgO

Magnesium oxide powder refers to the electrical melting crystallization of magnesium oxide blocks, which are crushed and mixed with different particle sizes or numbers in a certain proportion, and are directly or modified to be used as insulation media for conducting heat at high temperatures in tubular electric heating components. In the electric heating tube, it mainly plays a role in fixing the center position of the resistance wire, ensuring that the metal shell is not electrified (insulated), and exporting the heat generated by the resistance wire. According to production methods and main purposes, it can be divided into the following four categories:

1. Ordinary classification code P

2. Classification code D for low-temperature moisture-proof type

3. Medium temperature and moisture-proof classification code Z

4. High temperature classification code G

Performance requirements for magnesium oxide powder:

1. At working temperature, MgO powder should have high thermal conductivity in order to quickly transfer heat to the surface of the tube, making the resistance wire closer to the temperature of the tube wall;

2. When the working temperature is within 1100 ℃, MgO powder should have good insulation performance;

3. MgO powder must have a certain particle size, and its shape is generally circular rather than flaky, as the circular powder has high density, good fluidity, and a certain percentage of particles. When adding powder, it is not easy to damage the heating wire, ensuring no difficulty in powder filling;

4. MgO powder should have no corrosion on heating wire materials and pipes under normal or high temperature conditions.

5. The water absorption rate of magnesium oxide powder shall not exceed the following regulations:

1. Ordinary type ≤ 1.5%

2. Low temperature moisture-proof type ≤ 0.05%

3. Medium temperature moisture-proof type ≤ 0.10%

4. High temperature type ≤ 0.10%

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