JP2010060445A - Inert gas encapsulated sheathed thermocouple and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve an issue of a temperature measurement error increasing on the negative side over time when using a sheathed thermocouple at a high temperature of 1,000°C or more, which has housed K or N thermocouple wires in a metal sheath through intervention of an inorganic powder insulating material including magnesia, alumina, and the like, and sealed ends thereof with a resin, and the like, particularly, the sheathed thermocouple with an outer sheath diameter of ϕ3.2 mm or less. <P>SOLUTION: In the sheathed thermocouple which has housed the K or N thermocouple wires in the metal sheath through intervention of the inorganic powder insulating material including magnesia, alumina, and the like, and sealed the ends thereof with the resin, and the like, an inert gas is encapsulated among the inorganic powder insulating material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheath thermocouple for measuring the temperature of a high temperature part such as in a heating furnace and a method for manufacturing the same.

  There are two types of sheathed thermocouples: non-grounded type and grounded type. As shown in FIGS. 1 and 2, each type is a powdered inorganic insulating material made of magnesia, alumina or the like in a metal sheath 1. A pair of thermocouple wires 2 are accommodated with 3 interposed therebetween, and the end portion (the right end in FIG. 1) is provided with a seal 4 with a resin or the like in order to prevent insulation deterioration of the inorganic insulating material due to moisture intrusion. is there. In addition, the seal part of FIG. 1 is an example, and there exists a thing of another structure. Some have accommodated multiple pairs of thermocouple wires.

  The sheath thermocouple has the feature that it can be placed freely without considering the influence of the external metal potential due to the contact with the external metal because the thermocouple wire does not directly contact the external metal. Even if it is used in an oxidizing atmosphere, a reducing atmosphere, a corrosive atmosphere, etc., it has been widely used since there is an advantage that a long life can be obtained if a metal sheath material that can withstand it is used.

Since the sheath thermocouple is manufactured in the atmosphere, the conventional gas is the air present in the gap between the inorganic insulating material powders in the sheath thermocouple of FIGS.
Japanese Patent Laid-Open No. 06-260687 Published by Maruzen Co., Ltd. “High-temperature oxidation and high-temperature corrosion of metal materials”

  When a sheathed thermocouple using a K thermocouple element or an N thermocouple element is used as a measurement target at a high temperature exceeding 1000 ° C., the temperature measurement error tends to increase on the negative side with the passage of time. This increase in error is larger when the outer diameter of the sheath is thinner, and therefore the smaller the diameter of the thermocouple wire accommodated, and this is often a practical problem with sheath thermocouples with a sheath outer diameter of 3.2 mm or less. It was.

  In a sheath thermocouple in which a K thermocouple element or N thermocouple element is accommodated in a metal sheath with a powdered inorganic insulating material made of magnesia, alumina or the like interposed, and the end is sealed with resin or the like. In order to solve the problem that the temperature measurement error increases negatively over time when used at a high temperature of 1000 ° C or higher in a sheath thermocouple with a sheath outer diameter of 3.2 mm or less, the gap between the inorganic insulating powders An inert gas is sealed in. Argon gas is used as the inert gas.

  Next, the manufacturing method generally employs an argon gas at one end with respect to a metal sheath portion containing a thermocouple element by interposing an inorganic insulating material powder before processing into both ends called a MI cable to form a sheath thermocouple. The inside of the MI cable is pressurized with an inert gas such as, and injected between the inorganic insulating powders, and the air that was initially present between the inorganic insulating powders is caused to flow out of the other end by the pressure of the inert gas. After filling an inert gas between the inorganic insulating material powders, both ends are processed into a sheathed thermocouple, thereby making a sheathed thermocouple filled with the inert gas.

  An MI cable is first prepared with a large diameter, and a MI cable having a predetermined outer diameter is usually obtained by performing a plurality of times of diameter reduction by rotary swaging or cold drawing with a hole die.

  At the initial or middle stage of the diameter reduction, one end of the MI cable is pressurized with an inert gas such as argon gas and injected between the inorganic insulating powders. After filling with the active gas, it is possible to make a sheathed thermocouple filled with an inert gas by continuing to reduce the diameter and reaching a predetermined diameter and then processing both ends to finish the sheath thermocouple. .

  When a sheathed thermocouple using a K thermocouple element or an N thermocouple element was used at a high temperature exceeding 1000 ° C., it was observed by SEM that an altered layer was formed on the surface of the thermocouple element. Moreover, when it heated at the temperature exceeding 1000 degreeC, it measured that the pressure in a sheath fell.

  From these results, the altered layer on the surface of the thermocouple wire is a combination of oxygen and nitrogen contained in the air between the inorganic insulating powder and the thermocouple wire component, and the same is true for the metal sheath. It can also be concluded that the pressure drop occurs due to the consumption of air due to these oxidation and nitridation.

  According to Non-Patent Document 1, aluminum, silicon, and chromium in the components of the K and N thermocouple strands are easy to change to oxides and nitrides because the free energy for formation of oxidation and nitridation is small.

  Among these elements, aluminum and chromium have a role as a thermoelectromotive force generation source of thermocouple wires, and the concentration reduction in thermocouple wires due to oxidation and nitridation exceeds 1000 ° C. This is the main cause of the increase in measurement error on the negative side when used at high temperatures.

  Also, the thinner the outer diameter of the sheath and the smaller the diameter of the thermocouple wire, the greater the ratio of the surface area to the volume of the thermocouple wire. The density decrease is fast, and therefore the increase rate of the measurement error to the negative side is also fast.

  From the above, the gas existing in the gap between the inorganic insulating material powders in the sheath thermocouple in the sheath thermocouple using the K thermocouple wire or the N thermocouple wire is changed to air and used as an inert gas. Even when used at a high temperature exceeding 1000 ° C., oxidation and nitridation of the thermocouple wire does not occur, and the increase in measurement error to the negative side can be suppressed. This effect is particularly great for a thin sheath thermocouple having a sheath outer diameter of φ3.2 mm or less, which has been a practical problem in the past.

  Argon is the cheapest with respect to the inert gas used, and it is economically advantageous to use argon as the inert gas.

  Argon also has an effect of remaining between the inorganic insulating powders for a long period of time because the amount of the metal that permeates is extremely small compared to helium and the like.

  Next, an inert gas sealing method for the sheath thermocouple according to the present invention will be described.

  The inert gas is sealed by pressurizing one end of the MI cable, which is the material of the sheath thermocouple, with a high-pressure inert gas, injecting the inert gas between the inorganic insulating powders, and discharging the existing air from the other end. Can be done. The determination that the air has been replaced with the inert gas is made by collecting the discharged gas and multiplying the volume of the portion of the MI cable filled with the inorganic insulating powder by the filling rate of the inorganic insulating powder. This can be performed by sufficiently increasing the gas volume between the inorganic insulating material powders obtained in the above.

  Alternatively, the discharge gas may be collected every certain time and applied to a gas analyzer, and the determination may be made by changing the discharge gas from air to an inert gas.

  An example of the configuration at the time of injecting the inert gas is shown in FIG. At one end of the MI cable 5 (the left end of the MI cable in FIG. 3), a cap 6 provided with a tube 7 is attached to the MI cable without leakage by compression fitting or the like, and the tube 7 is attached to a high-pressure inert gas source such as an inert gas cylinder. Connect to. At the other end, the cap 8 provided with the tube 9 is attached to the MI cable without leakage by compression fitting or the like. A discharge gas collector 10 is connected to the tube 9 and the discharge gas is collected in the gas collection cylinder 12 through the water 13 in the container 11. It is determined from the volume of the collected gas or the gas component change that the air has been replaced with the inert gas.

  The MI cable, which is the material of the sheath thermocouple, is first made with a large diameter as shown in FIG. 4, and then the diameter of the MI cable is reduced by rotary swaging or cold drawing with a hole die until it reaches a predetermined outer diameter. Produced by applying multiple times. Since the MI cable 5 becomes longer as the diameter decreases, the sheath thermocouple normally cuts the MI cable having a predetermined outer diameter into a required length, and processes both ends to obtain the sheath shown in FIGS. A thermocouple is made.

  The inert gas may be injected after the MI cable 5 having a predetermined outer diameter is cut to a length necessary for manufacturing the sheath thermocouple, or at the initial stage or in the middle of the MI cable diameter reduction. Also good. The MI cable into which the inert gas is injected is processed into a sheath thermocouple shown in FIG. 1, and the injected inert gas is sealed between the inorganic insulating material powders.

  In addition, if the period from the inert gas injection to the processing to the sheath thermocouple is long, the inert gas initially contained in the MI cable in a pressurized state flows out into the atmosphere from the openings at both ends of the MI cable. Part of the inert gas at both ends is replaced with external air by diffusion. The inflow of air also causes a decrease in insulation of the inorganic insulating material due to moisture contained in the air.

  Such inflow of air and accompanying insulation decrease can be prevented by sealing the opening portions at both ends of the MI cable with a resin or the like during long-term storage after injecting an inert gas.

  Argon gas was injected into the following MI cables having outer diameters of φ1.6 mm and φ3.2 mm. Both are MI cables that have been reduced in diameter to the same outer diameter as the sheathed thermocouple to be manufactured.

Sheath outer diameter: φ1.6mm and φ3.2mm
Sheath length: 1.7m
Type of thermocouple wire: K thermocouple Metal sheath material: NCF600
The injection was performed according to the configuration shown in FIG. 3, and the argon gas pressure was 4.7 kg / cm ² G.

  The air contained between the inorganic insulating powders of the MI cable having an outer diameter of φ1.6 mm and a length of 1.7 m is 0.6 cc in the calculation. The amount of discharged gas collected by pressurization for 4 days was about 2.5 cc, and it was confirmed that the air was sufficiently replaced with argon gas.

  Moreover, the MI cable having an outer diameter of 3.2 mm and a length of 1.7 m has 2.3 cc of air contained between the inorganic insulating powders. Also about this, argon gas was inject | poured similarly to MI cable with an outer diameter of φ1.6mm, and the amount of discharged gas collected by pressurization for 3 days was about 10cc, and it was confirmed that the air was sufficiently replaced with argon gas. .

  As described above, both ends of the MI cable into which argon gas was injected were processed for 4 days for an outer diameter of φ1.6 mm, and for an φ3.2 mm for 3 days, and the ungrounded thermocouple shown in FIG. Sheath thermocouples with outer diameters of φ1.6mm and φ3.2mm, in which argon gas was sealed between the inorganic insulating powders, were fabricated. Note that the MI cable was cut when processing both ends, and the finished sheath length of the sheath thermocouple was 1000 mm for both.

  As described above in detail, when the measurement target is a high temperature of 1000 ° C or higher, a thin sheath thermocouple with a sheath outer diameter of φ3.2 mm or less has been a problem in the past due to the increase in measurement error to the negative side. In addition, even when a high temperature of 1000 ° C. or higher was measured, a sheathed thermocouple with a small increase in measurement error on the negative side was obtained.

  In the present invention, an inert gas is sealed in a sheath thermocouple, but the inert gas is sealed in the inorganic insulating material powder in the sheath used at a high temperature, so that deterioration of the electrical conductors can be prevented.

It is longitudinal direction sectional drawing of a sheath thermocouple. It is II-II sectional drawing of a sheath thermocouple. It is a structural example at the time of inert gas injection | pouring. It is longitudinal direction sectional drawing of MI cable explaining the diameter reduction process of MI cable.

Explanation of symbols

1: Metal sheath 2: Thermocouple wire (K or N)
3: Insulating material powder 4: Sealing part made of resin, etc. 5: MI cable 6, 8: Cap with compression fitting 7, 9: Tube 10: Discharge gas collector 11: Container 12: Gas collecting cylinder 13: Water

Claims (4)

  In a sheathed thermocouple in which a K thermocouple element or an N thermocouple element is accommodated by interposing a powdered inorganic insulating material made of magnesia, alumina or the like in the metal sheath, and the end portion is sealed with a resin or the like, inorganic A sheathed thermocouple with an inert gas sealed between insulating powders.   The sheath thermocouple according to claim 1, wherein the inert gas to be sealed is argon.   One end of an MI cable is treated with an inert gas such as argon gas with respect to a metal sheath portion containing a thermocouple wire by interposing inorganic insulating powder before processing both ends into a sheath thermocouple. By pressurizing and injecting between the inorganic insulating material powders, the air that was initially present between the inorganic insulating material powders is caused to flow out from the other end by the pressure of the inert gas, so that the inorganic insulating material powders in the MI cable A method for manufacturing a sheathed thermocouple in which an inert gas is sealed between inorganic insulating powders that are filled with an inert gas and then processed at both ends to be finished into a sheathed thermocouple.   In the process of manufacturing a MI cable having a predetermined outer diameter by performing a diameter reduction of a large-diameter MI cable multiple times by rotary swaging or cold drawing with a hole die, etc. One end of the MI cable is pressurized with an inert gas such as argon gas, an inert gas is injected between the inorganic insulating material powders, and the air that has existed between the inorganic insulating material powders by the pressure of the inert gas is introduced from the other end. After flowing out and filling an inert gas between the inorganic insulating material powders in the MI cable, the MI cable is continuously reduced in diameter, and after reaching a predetermined diameter, the MI cable is cut to a required length and the MI cable is cut. A method for manufacturing a sheathed thermocouple in which an inert gas is sealed between inorganic insulating material powders, which is processed into a sheathed thermocouple by processing both ends of a cable.

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