The vertical atmosphere furnace with bottom loading and unloading is an advanced furnace type. Thermocouples are installed into the furnace from the bottom of the furnace. Pay attention to the following aspects when using:

1. At high temperatures around 2000 degrees Celsius, thermocouples can use protective tubes such as MgO, BeO, Al2O3, etc. At high temperatures, the MgO protective tube evaporates quickly and becomes thinner and thinner. Therefore, a protective sleeve with a thicker pipe wall can be selected.

2. After measuring the temperature field, the hot end of the thermocouple moves to the edge of the uniform temperature zone, and the hot junction is placed in a temperature field of 2000 degrees, while the rest works in a lower temperature zone to extend its service life.

3. In the atmosphere furnace, there is a protective atmosphere, and it is required that the thermocouple be well sealed from the furnace body. There are two ways to protect the sealing device:

A、 Increase the thermal resistance of refractory insulation materials inside the kiln, such as using carbon felt insulation in areas above 1700 degrees Celsius and hollow alumina spheres insulation in areas below 1700 degrees Celsius. According to the principles of heat transfer, calculate a reasonable length to reduce the temperature at the sealing point of the furnace body to the temperature accepted by the sealing ring.

B、 Install a water-cooled jacket at the sealed area. However, using a lower loading and unloading system makes the design of the water cooling area more complex. If scale forms, the water flow gradually decreases, the cooling water flow rate decreases, and the cooling effect is poor.

The above two methods can also be used simultaneously.

4. After using the thermocouple for a period of time, it gradually becomes brittle. If there is sometimes no thermoelectric potential during temperature measurement, it usually indicates that the thermocouple has been disconnected and should be remade.

5. Sometimes thermocouples need to be bent when measuring temperature fields,. At this time, the insulator in this part should not be too long, generally 10-20mm is better to prevent the thermocouple wire from breaking.

6. At high temperatures, MgO protective tubes should not be used in vacuum, hydrogen, or carbon atmospheres. For electric furnaces that sinter high-temperature structural ceramics, graphite heating elements and carbon felt insulation are commonly used, and it is best to use BeO protective sleeves.

7. When the furnace temperature exceeds 2000 degrees and there is a lack of corresponding protective casing, bare wire temperature measurement should be used. Expose the hot junction at the edge of the temperature field above 2000 degrees Celsius. The two wires below the hot junction should be separated by an appropriate distance to prevent deformation and short circuit at high temperatures. The length of the thermocouple extending into the high temperature zone should take into account the thickness, strength, and high temperature deformation of the thermocouple wires.

8. Measure the temperature of an atmosphere pressure furnace at around 1800 degrees using a tungsten rhenium thermocouple. Under high nitrogen atmosphere pressure, the service life of the thermocouple is 15-30 furnace cycles. The main reasons for thermocouple damage are corrosion caused by the carbon atmosphere inside the furnace and embrittlement of the thermocouple at high temperatures.

9. After use, tungsten rhenium thermocouples have a brittle texture and should not be moved frequently during operation, otherwise their service life will be reduced.