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What you need to know about thermocouple of vacuum furnace

Vacuum heat treatment technology has the outstanding advantages of no oxidation, no decarburization, good surface quality, etc. The workpiece after heat treatment has made great progress in wear resistance, corrosion resistance, etc. Vacuum heat treatment technology has been widely used in the treatment of key components of various equipment, and is a key heat treatment technology in military and civilian products. Therefore, vacuum heat treatment technology has become the main symbol of the current advanced heat treatment production technology, and has been rapidly developed in recent years.

Vacuum heat treatment furnace is a necessary condition for vacuum heat treatment. The two important indicators of vacuum heat treatment are vacuum and temperature. In vacuum heat treatment furnace, thermocouple is the key component of temperature control. Thermocouple selection includes thermocouple structure, thermocouple model, and thermocouple protection tube. Knowledge of thermocouples allows you to select and maintain vacuum furnaces.

The vacuum furnace can use different thermocouples at different temperature sections to achieve accurate temperature control.

The following describes different thermocouples from three temperature segments:

1) Low temperature section (0~300 ℃): In this temperature section, we generally choose PT100 platinum resistance. Although all aspects of the performance of PT100 platinum resistance are average, in the low temperature section, the performance of PT100 can basically meet the requirements of equipment use, and the price of PT100 platinum resistance is very low. If there are higher requirements on performance, K-type thermocouple or N-type thermocouple can also be selected.

2) Middle temperature range (300~1000 ℃): K-type thermocouple or N-type thermocouple are generally selected in this temperature range. The traditional model selection standard in China is K-type thermocouple, because K-type thermocouple can meet the needs of vacuum heat treatment furnace in temperature measurement area and all aspects of performance, and is the most widely used thermocouple at present due to its low price.

In recent years, N-type thermocouples have been greatly developed in vacuum heat treatment furnaces. The performance index of the N-type thermocouple is comparable to that of the K-type thermocouple, and it overcomes the disadvantage of unstable electromotive force of the K-type thermocouple between 300~500 ℃ and 800 ℃. In terms of price, N-type thermocouple is also relatively cheap, and has gradually replaced the application of K-type thermocouple. If the vacuum heat treatment furnace has higher requirements for temperature performance indicators in this temperature range, S-type thermocouples can also be selected, with higher prices.

3) High temperature section (1000~1300 ℃). R type thermocouples are mainly used at 1200 ℃ and 1300 ℃ abroad. The performance of R type thermocouple is better than that of S type thermocouple. However, it has not been popularized in China, and it is still dominated by the traditional S-type.

Introduction and Application of Thermocouple Protective Tube

An important part of vacuum furnace thermocouple is the thermocouple protection tube. The protective tubes for thermocouples commonly used in vacuum heat treatment furnaces can be divided into two categories: metal protective tubes and non-metallic protective tubes. In vacuum heat treatment furnace, metal protective tubes are generally used, because metal protective tubes are sensitive to temperature and have small temperature difference. The disadvantage is that it is not resistant to high temperature. The maximum use temperature is about 1200 ℃. When the temperature exceeds 1300 ℃, it should be used with caution. If you want to use it at 1300 ℃ for a long time, you need to choose non-metallic protective tubes. The non-metallic protective tube is resistant to high temperature, but the sensitivity of temperature change is slightly poor. If the vacuum heat treatment furnace has high requirements for the constant temperature zone, such as: ± 3 ℃, it is not suitable to use the non-metallic protective tube.

Thermocouple is a key component in vacuum heat treatment furnace, not only because it is the key to temperature control, but also because thermocouple is a consumable. No matter what type of vacuum heat treatment furnace, the temperature measurement accuracy of the thermocouple will decline with the increase of use time. Therefore, according to the frequency of use, we will replace new thermocouples to ensure that the temperature measurement and control accuracy of the equipment can meet the requirements after a certain period of time. This requires us to select appropriate thermocouples to reduce the production cost of the equipment.

Heat treatment equipment selection: The vacuum heat treatment furnace produced by SIMUWU is a high-quality product for vacuum heat treatment process. Our engineers choose the best accessories for customers. Good temperature control accuracy and uniformity ensure the effective implementation of vacuum heat treatment process. SIMUWU focuses on the manufacturing of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum gas quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.