Application of Industrial Thermocouples Introduction: In the production of ceramics, thermocouples are the measurement tools for thermal monitoring and testing and play an important role. In the current production process of various types of ceramic products, detection technology and its tools are more and more important, especially in the non-destructive abrasion, measurement and measurement of various products and components, ceramic thermocouple function is not... The thermocouple in ceramic production is a measurement tool for thermal monitoring and testing and plays an important role. In the current production process of various types of ceramic products, the detection technology and its appliances are more and more important, especially in the non-destructive abrasion, measurement and measurement of various products and components, the role of ceramic thermocouples contributed to the improvement. The quality of ceramic products and the economic benefits of enterprises are indispensable.
Thermocouple work principle is to connect two different conductors and semiconductors into a closed loop, and then the two contacts are placed in a temperature of T and T0 heat source, then in the circuit can generate thermal EMF, also known as Thermal potential, this phenomenon is called thermoelectric effect. The thermoelectric potential is a kind of thermoelectric potential generated at the two ends of the same conductor due to different temperatures. Since the electron energy at the high temperature end (T) is greater than the electron energy at the low temperature end, the number of electrons running from the high temperature end to the low temperature end is higher than that from the low temperature end to the high temperature end. As a result, the high temperature end loses electrons and has a positive charge. The end is negatively charged due to electrons, thus forming an electrostatic field. In this way, a corresponding potential difference or temperature difference potential is generated at both ends of the conductor. In this way, the wire of the third material is inserted in the thermocouple circuit. As long as the temperature of the third wire is the same at both ends, the introduction of the third wire does not affect the electromotive force of the thermocouple. According to this nature, various instruments, connecting wires, etc. are introduced in the circuit, and there is no need to worry about the influence of thermocouples, so it is also possible to use a welding method to make a thermocouple. Current figures in newspaper ads show that thermocouples are becoming mainstream.
The type of ceramic thermocouple. Platinum rhodium - platinum thermocouple, nickel-chromium-nickel-silicon thermocouple, nickel-chromium - test copper thermocouple and other types.
1 platinum rhodium - platinum thermocouple: is made of precious rare metal materials, made of pure platinum wire diameter 0.5mm and the same diameter platinum rhodium wire (platinum 90% and rhenium 10%), denoted by the symbol LB. The symbol WR refers to a thermocouple. In the LB thermocouple platinum rhodium wire is a positive electrode, and pure platinum wire is a negative electrode. This type of thermocouple can be used for a long time in the range of 1300°C or less, and can measure short-term high temperatures of 1600°C in a good use environment. Due to the development of chemical industry, platinum and platinum rhodium materials with high purity can be easily obtained. Therefore, the accuracy and measurement accuracy of the LB thermocouple are high, and it can be used for precise temperature measurement and use as a reference thermocouple. Platinum rhodium-platinum thermocouple is the most commonly used temperature measurement tool in the firing of ceramic industry, and can generally be used for the production of building sanitary ceramics, daily-use ceramics, and art ceramic products. LB thermocouples have high physicochemical stability in oxidizing or neutral media. The main drawback is that the thermal potential is weak. In a high-temperature firing environment, it is easily deteriorated by the vapor and metal vapor emitted from the reducing gas. In recent years, high-aluminum ceramic bushings and silicon carbide bushings have been used to change thermocouple protection materials, which can effectively resist the corrosion of harmful gases and prolong their service life. Because LB thermocouples are made of noble metal materials, the cost of the products is very high and they need to be taken care of during use. The selling price is based on the length of the standard. With the large number of advanced kiln lining materials used in new-type kiln furnaces and thin kiln walls, the length of thermocouples also tends to decrease. The LB thermocouples, usually 30cm to 60cm in length, sell for between 1200 and 5,000 yuan.
2 Nickel-chromium-nickel-silicon thermocouples: Made of nickel-chromium and nickel-silicon, denoted by the symbol EU. Thermocouple wire diameter is generally 1.2 ~ 2.5mm. Nickel-chromium is a positive electrode and nickel-silicon is a negative electrode. EU thermocouples have high chemical stability and can measure temperatures below 900°C for a long period of time in oxidizing or neutral media, with short-term measurements up to 1200°C. If used in reducing media, it is quickly corroded and can only be used to measure temperatures below 500°C. The EU thermocouple has the advantages of good reproducibility, large thermoelectric potential, good linearity, and low price. Its measurement accuracy is slightly lower, but it can also completely satisfy the measurement requirements of the ceramic industry. Especially in the low-temperature ceramic color firing, low temperature ceramic baking and semi-finished products drying, can become a commonly used thermocouple. At present, China has started to replace nickel-aluminum alloy materials with nickel-silicon materials. Thermocouples made of new materials have greatly improved both oxidation resistance and thermoelectric stability, but their materials are brittle and their welding performance and radiation resistance are poor. As the thermoelectric properties of both thermocouples are almost identical. Therefore, the original nickel-chromium-nickel-chromium thermocouple was gradually replaced by a nickel-chromium-nickel-silicon thermocouple.
3 Nickel-chromium—copper thermocouple: Consisting of nickel-chromium materials and nickel and copper alloy materials, the symbol EA is used. The diameter of a thermocouple wire is generally 1.2mm to 2mm, nickel-chromium is a positive electrode, and copper is a negative electrode. Suitable for reducing or neutral media, long-term use temperature can not exceed 600 °C, short-term measurement up to 800 °C. The EA thermocouple is characterized by high thermoelectric sensitivity and low price, but its temperature range is low and narrow, and the copper alloy wire is easily deteriorated due to oxidation. Furthermore, due to the hard texture of the material, it is not easy to obtain a uniform wire diameter. This type of thermocouple can be used in ceramic body dryers, ceramic heat exchangers and other places, in order to obtain more accurate temperature parameters, improve drying and energy saving effects.
4 platinum crucible 30 - platinum crucible 6 thermocouple: platinum crucible 30 wire (including platinum 70%, crucible 30%) as the positive, platinum crucible 6 wire (94% platinum content, 铑6%) as the negative electrode. It can be used for long-term measurement of temperatures up to 1600°C, and can measure ultra-high temperatures up to 1800°C in the short term. LL thermocouples have stable performance and high precision and are suitable for use in oxidizing and neutral media. However, it generates a small thermal potential and is expensive. At present, the firing temperature of special ceramics, especially high-temperature structural ceramics (such as zirconia ceramics and 99 alumina ceramics) is as high as 1600°C to 1800°C. It is entirely feasible to use LL thermocouples. With the expansion of special ceramic product series, various ceramic thermocouples suitable for firing in high-temperature and ultra-high-temperature kiln furnaces will gain greater utility.
While the use of conventional thermocouples in the production of ceramics continues to expand, special thermocouple products with better features continue to emerge. Such as tungsten-based thermocouple, it is a good ultra-high temperature thermocouple material, the maximum use temperature is limited by the insulating material, generally can reach the use conditions of 2400 °C. Higher temperatures can be used as measured in vacuum in bare wires. At present, tungsten crucible thermocouples produced in China use tungsten crucible 5 as the anode and tungsten crucible 20 as the cathode. The use range is from 300°C to 2000°C and the indexing accuracy can reach ±1%. At present, the sintering temperature of certain silicon nitride ceramics in the world has reached 1800°C or more, and it is entirely feasible to use a tungsten-rhenium thermocouple for temperature measurement. In addition, gold-iron-nickel-chromium low-temperature thermocouples, rapid-response thin-film thermocouples, and non-metal thermocouple materials used in the production of superconducting ceramics are used, and thanks to their various advantages, low prices and abundant resources, gratifying progress has been achieved.
Thermocouple work principle is to connect two different conductors and semiconductors into a closed loop, and then the two contacts are placed in a temperature of T and T0 heat source, then in the circuit can generate thermal EMF, also known as Thermal potential, this phenomenon is called thermoelectric effect. The thermoelectric potential is a kind of thermoelectric potential generated at the two ends of the same conductor due to different temperatures. Since the electron energy at the high temperature end (T) is greater than the electron energy at the low temperature end, the number of electrons running from the high temperature end to the low temperature end is higher than that from the low temperature end to the high temperature end. As a result, the high temperature end loses electrons and has a positive charge. The end is negatively charged due to electrons, thus forming an electrostatic field. In this way, a corresponding potential difference or temperature difference potential is generated at both ends of the conductor. In this way, the wire of the third material is inserted in the thermocouple circuit. As long as the temperature of the third wire is the same at both ends, the introduction of the third wire does not affect the electromotive force of the thermocouple. According to this nature, various instruments, connecting wires, etc. are introduced in the circuit, and there is no need to worry about the influence of thermocouples, so it is also possible to use a welding method to make a thermocouple. Current figures in newspaper ads show that thermocouples are becoming mainstream.
The type of ceramic thermocouple. Platinum rhodium - platinum thermocouple, nickel-chromium-nickel-silicon thermocouple, nickel-chromium - test copper thermocouple and other types.
1 platinum rhodium - platinum thermocouple: is made of precious rare metal materials, made of pure platinum wire diameter 0.5mm and the same diameter platinum rhodium wire (platinum 90% and rhenium 10%), denoted by the symbol LB. The symbol WR refers to a thermocouple. In the LB thermocouple platinum rhodium wire is a positive electrode, and pure platinum wire is a negative electrode. This type of thermocouple can be used for a long time in the range of 1300°C or less, and can measure short-term high temperatures of 1600°C in a good use environment. Due to the development of chemical industry, platinum and platinum rhodium materials with high purity can be easily obtained. Therefore, the accuracy and measurement accuracy of the LB thermocouple are high, and it can be used for precise temperature measurement and use as a reference thermocouple. Platinum rhodium-platinum thermocouple is the most commonly used temperature measurement tool in the firing of ceramic industry, and can generally be used for the production of building sanitary ceramics, daily-use ceramics, and art ceramic products. LB thermocouples have high physicochemical stability in oxidizing or neutral media. The main drawback is that the thermal potential is weak. In a high-temperature firing environment, it is easily deteriorated by the vapor and metal vapor emitted from the reducing gas. In recent years, high-aluminum ceramic bushings and silicon carbide bushings have been used to change thermocouple protection materials, which can effectively resist the corrosion of harmful gases and prolong their service life. Because LB thermocouples are made of noble metal materials, the cost of the products is very high and they need to be taken care of during use. The selling price is based on the length of the standard. With the large number of advanced kiln lining materials used in new-type kiln furnaces and thin kiln walls, the length of thermocouples also tends to decrease. The LB thermocouples, usually 30cm to 60cm in length, sell for between 1200 and 5,000 yuan.
2 Nickel-chromium-nickel-silicon thermocouples: Made of nickel-chromium and nickel-silicon, denoted by the symbol EU. Thermocouple wire diameter is generally 1.2 ~ 2.5mm. Nickel-chromium is a positive electrode and nickel-silicon is a negative electrode. EU thermocouples have high chemical stability and can measure temperatures below 900°C for a long period of time in oxidizing or neutral media, with short-term measurements up to 1200°C. If used in reducing media, it is quickly corroded and can only be used to measure temperatures below 500°C. The EU thermocouple has the advantages of good reproducibility, large thermoelectric potential, good linearity, and low price. Its measurement accuracy is slightly lower, but it can also completely satisfy the measurement requirements of the ceramic industry. Especially in the low-temperature ceramic color firing, low temperature ceramic baking and semi-finished products drying, can become a commonly used thermocouple. At present, China has started to replace nickel-aluminum alloy materials with nickel-silicon materials. Thermocouples made of new materials have greatly improved both oxidation resistance and thermoelectric stability, but their materials are brittle and their welding performance and radiation resistance are poor. As the thermoelectric properties of both thermocouples are almost identical. Therefore, the original nickel-chromium-nickel-chromium thermocouple was gradually replaced by a nickel-chromium-nickel-silicon thermocouple.
3 Nickel-chromium—copper thermocouple: Consisting of nickel-chromium materials and nickel and copper alloy materials, the symbol EA is used. The diameter of a thermocouple wire is generally 1.2mm to 2mm, nickel-chromium is a positive electrode, and copper is a negative electrode. Suitable for reducing or neutral media, long-term use temperature can not exceed 600 °C, short-term measurement up to 800 °C. The EA thermocouple is characterized by high thermoelectric sensitivity and low price, but its temperature range is low and narrow, and the copper alloy wire is easily deteriorated due to oxidation. Furthermore, due to the hard texture of the material, it is not easy to obtain a uniform wire diameter. This type of thermocouple can be used in ceramic body dryers, ceramic heat exchangers and other places, in order to obtain more accurate temperature parameters, improve drying and energy saving effects.
4 platinum crucible 30 - platinum crucible 6 thermocouple: platinum crucible 30 wire (including platinum 70%, crucible 30%) as the positive, platinum crucible 6 wire (94% platinum content, 铑6%) as the negative electrode. It can be used for long-term measurement of temperatures up to 1600°C, and can measure ultra-high temperatures up to 1800°C in the short term. LL thermocouples have stable performance and high precision and are suitable for use in oxidizing and neutral media. However, it generates a small thermal potential and is expensive. At present, the firing temperature of special ceramics, especially high-temperature structural ceramics (such as zirconia ceramics and 99 alumina ceramics) is as high as 1600°C to 1800°C. It is entirely feasible to use LL thermocouples. With the expansion of special ceramic product series, various ceramic thermocouples suitable for firing in high-temperature and ultra-high-temperature kiln furnaces will gain greater utility.
While the use of conventional thermocouples in the production of ceramics continues to expand, special thermocouple products with better features continue to emerge. Such as tungsten-based thermocouple, it is a good ultra-high temperature thermocouple material, the maximum use temperature is limited by the insulating material, generally can reach the use conditions of 2400 °C. Higher temperatures can be used as measured in vacuum in bare wires. At present, tungsten crucible thermocouples produced in China use tungsten crucible 5 as the anode and tungsten crucible 20 as the cathode. The use range is from 300°C to 2000°C and the indexing accuracy can reach ±1%. At present, the sintering temperature of certain silicon nitride ceramics in the world has reached 1800°C or more, and it is entirely feasible to use a tungsten-rhenium thermocouple for temperature measurement. In addition, gold-iron-nickel-chromium low-temperature thermocouples, rapid-response thin-film thermocouples, and non-metal thermocouple materials used in the production of superconducting ceramics are used, and thanks to their various advantages, low prices and abundant resources, gratifying progress has been achieved.
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