Armoured thermocouple in the application of the magnetic powder production

Thermocouples are widely used temperature sensor. With the progress of science and technology, the types of thermocouple, also have great progress, manufacturing process, from the traditional accidentally stainless steel wire, insulation porcelain tube, coat to armoured thermocouple tube structure development, its structure by heat, high insulating oxide electrode, coat stainless steel protecting tube 3, as shown in figure 1, figure 2. Armoured thermocouple has wide temperature range, stable performance, can bend, high pressure resistance, thermal response time is short and strong and durable and many other advantages. Now three chang armoured thermocouple can easily be 0. More than 5 mm to 4 mm, facilitate under solid surface, steam and gas medium is used.

1 thermocouple failure problems found

magnetic powder importance in modern life demand is more and more big, the products are widely used in computer, communications, automotive, instrumentation, automation, household appliances and other fields. I have introduced in 2012 by a university research results, to break the ndfeb alloy ingot by HDDR ( Hydrogenated & ndash; Disproportionation reaction & ndash; Dehydrogenation & ndash; Combining) Technology of preparation of high performance anisotropic NdFeB magnetic powder, in order to mass production of high quality magnets. With the magnetic powder produced by adjusting equipment commissioning and performance meets the requirements. Use of magnetic powder performance began to decline after a period of time, after six months ( In December 2012) Performance degradation, to produce waste. From the on-site inspection found no apparent problem, and recommended for all measuring instruments detection.

in January 2013, find out temperature measurement with two nickel chromium nickel silicon thermocouple data exceptions, because the production process is done under the environment of 820 ℃, so the test is 800 ℃, 850 ℃ at two o 'clock, the error value serious partial verification results, as shown in table 1.

replace JingJian qualified after the thermocouple, production test back to normal. A few months, similar situation again. Thermocouple JingJian, big error values, as shown in table 2.

in November to purchase JingJian qualified thermocouple, shorten the test cycle at the same time, at any time tracking verification. In December 2013, the test results, the error is close to or exceed the permissible error, as shown in table 3.

according to usage, magnetic powder equipment production 7 ~ 8 furnace, thermocouple cannot reoccupy. Thermocouple changed frequently, so were delayed production, waste produced in bulk, high production cost. Development into the bottleneck of production technology, large-scale production line construction in a pause state. 1 thermocouple failure reason analysis

ndfeb alloy cryogenic hydrogen absorption and disproportionation reaction in 820 ℃, disproportionation phase in 820 ℃ vacuum state to combine to generate 2 Nd Fe B hard magnetic phase. Through precise control in the process of the reaction temperature and hydrogen pressure, can be obtained with anisotropic NdFeB magnetic powder of the organization. And in the process, the ordinary thermocouple exposed hot electrode nickel chrome nickel chromium silicon in the most vulnerable to hydrogen adsorption, hydrogen atoms into the crystal lattice of the metal, aggregated into molecular hydrogen, lattice caused by twisting, produce a lot of stress, serious when metal crack, namely metal material & other Hydrogen embrittlement & throughout; Phenomenon. The internal stress of thermocouple are the important factors that affect the thermoelectric performance, is to eliminate as far as possible. Because three chang thermocouple stress in electrode materials of, make its thermoelectric properties change, in the condition of no. Extension of the internal stress increase with time, the error increase.

2 preventive measures comprehensive above factors, decided to change my strong, good sealing armoured thermocouple temperature measurement. Armoured thermocouple wire electrode is surrounded by high insulating oxide closely surrounded, with stainless steel protecting tube, protected thermoelectric highly production environment, to ensure that the thermoelectric performance is stable, accurate temperature control of production process. According to the production need to choose nickel chromium nickel silicon electrode wire, insulation materials, magnesium coat 1 cr18ni9ti stainless steel protecting tube. Armoured thermocouple purchases at the time of the test results as shown in table 4. In after thermocouple steady production, product performance meet the requirements. Using 20 ~ 30 furnace recheck, test data as shown in table 5. Three chang armoured thermocouple thermal electrode is surrounded by dense oxide powder, cut off from hydrogen corrosion of conductor, guarantee the stability of thermocouple thermoelectric performance, prolong service life. The production product inspection, gage verification results show that the magnetic powder quality controlled, trial production of magnetic powder had a breakthrough.

3 the complimentary armoured thermocouple with its strong, good sealing, corrosion resistance and other characteristics, has an irreplaceable advantage in special environment, but the price is slightly higher than ordinary thermocouple, the user can according to need to be flexible to use. Relevant product recommendations: magnetic level gauge