With a high temperature furnace thermocouple protection tube material do, therefore, long-term stable operation under high temperature 1800 ~ 2000 ℃. Vacuum heat treatment process to prevent the ambient air contacting parts, the need to prevent air from entering the vacuum furnace, therefore, for a vacuum furnace thermocouple leakage rate request. Usually indicators to control the pressure rise rate. Imported vacuum furnace pressure rise of less than 0.268Pa / h. 1, the use of high temperature: long-term adaptation requires high temperature thermocouple 1200 ℃, the maximum may exceed 1300 ℃ (because the measure does not necessarily end up in the bin temperature point). It is inexpensive and high-temperature alloy metal thermocouple protection tube, high-temperature insulation materials commonly used in extreme operating temperatures. 2, highly corrosive environments: Carbon roasting process heavy oil, water, gas and natural gas for heating fuel in the carbon anode baking a large number of volatile (petroleum pitch, coke impurities, etc.) to escape combustion, carbon, sulfur atmosphere of high temperature corrosion very serious, and accompanied by high temperature flue gas erosion. This has exceeded the general high temperature alloy casing can afford. 3, frequent heating and cooling: As a result of the characteristics of ring roaster, a thermocouple in the course of the need for repeated removal and insertion, frequent heating and cooling, and sometimes collide, thermocouple and bushing surface oxide protective layer is easy to fall off, accelerated the damage of the thermocouple. 4, long life: Due to the harsh environment, leading to the thermocouple life is generally short, usually only 1 to 6 months. However, due to the large amount of thermocouple, higher prices, so extend the life of the thermocouple, thermocouple price increase has a very important significance for carbon baking business. For details, see: www.ybzhan.cn/st27223/product_6639566.html