Introduction to the hottest non-metallic electric

Introduction to non-metallic electric heating elements

I. silicon molybdenum rod (mosio2) rod or tube

1. Recrystallization temperature: 1800 ℃

2. At normal temperature: high hardness, brittleness, high temperature resistance

3. Small deformation in high temperature state, common horizontal installation

4. Good temperature sudden change resistance (sudden change resistance)

5. Stable chemical properties, not reacting with acidic materials

6. But at high temperature, It will react with alkaline earth metals or low melting point acid salts

7. Contact with hydrogen will produce hydrogen embrittlement

8. The resistance coefficient is large

9. Because the resistance of each is different, it should be selected when using to make the current three-phase balance, It must be equipped with a voltmeter (the capacity of the voltmeter is 3 times of the working voltage)

10. Resistance characteristics: the resistivity is the lowest at 800 ℃ or 900 ℃

11. Surface load: the design is generally 5w/cm2

12. At the outlet port of the heating element, it is generally at the sealing device to reduce the heat loss

13. Electrical performance: there is a large specific resistance. When heated to 1200 ℃ in the air, the error reaches plus or minus 50 degrees, Generally, dense emission during assembly is adopted, and the error is reduced by radiation

14. atmosphere influence:

a. there will be influence if there is water vapor

b. when used in hydrogen, the temperature should be less than 1200 degrees

c. when used in chlorine, the elements decomposed in NH3 will react with it at 500-600 degrees

d. when used in nitrogen and hydrogen mixture, the temperature should be less than 1250 degrees

e. when used in ammonia, sin will be produced at 1350 degrees, affecting the service life

f. purchase after detailed consultation. In sulfur, SO2 will be produced at 1300 degrees, and SO3 will corrode SiC, Therefore, it should be less than 1200 degrees

g. in CO, free carbon will be produced, react with silicon carbide, increase the current, and burn out the transformer

II. Silicon carbide rod (SIC): (mainly used in experiments and industrial electric furnaces)

1. Oxidation resistance, high temperature resistance (1200-1650 degrees)

2. The shape is "U", so there is enough expansion space at the bottom during installation

3. At room temperature, it has high strength and brittleness. When it reaches 1350 degrees, Begin to soften. Low temperature oxidation will occur at 400-800 ℃

4. I believe this is the most reliable way to apply When it is used in air, nitrogen and inert gas, but cannot be used in reducing atmosphere

5.1350 ℃, sulfur and chlorine atmosphere should be avoided as far as possible. The refractory material is acid or neutral material

material

6. Compared with silicon carbide rod, the service temperature is high, and it can be used to 1200-1650 degrees in the atmosphere of air, steam, nitrogen and carbon dioxide

III. rhenium chromate (LaCrO3)

is used more abroad, and in recent years, China has also begun to use

IV. Carbon electric heating elements (graphite tube, graphite rod, graphite cloth)

1. Generally used in vacuum oil quenching furnace (1400 ℃), gas quenching furnace (1350 ℃), carbon tube furnace

2. Graphite (melting point: 3600 ℃) is commonly used at 1400-2500 ℃

3. High temperature resistance, good processing performance, low price; The service life mainly depends on its graphically beneficial

speed of oxidation and volatilization

4. In the protective atmosphere (hydrogen, nitrogen, carbon dioxide, argon), the maximum temperature can reach 3000

degrees

5. The conductivity of graphite: decreases with the increase of temperature

6. The tensile test of temperature resistant plastic tensile testing machine shows good denaturation

v. electric radiant tube

1. The heat transfer speed is slow, The surface load should be smaller. Temperature difference inside and outside the radiant tube: 120-140 degrees

2. selection of surface load:

sealed box furnace: 1.5w/cm2

continuous furnace: 1.3-1.5w/cm2

periodic furnace: 2.02w/cm2

continuous carburizing furnace: 1.4-1.97w/cm2

3. Selection of radiant tube material: good heat resistance, corrosion resistance and chemical stability. Good heat resistance and fatigue resistance (end)