CN109530848B

CN109530848B - Quick response tungsten-rhenium thermocouple welding method

Info

Publication number: CN109530848B
Application number: CN201811381362.4A
Authority: CN
Inventors: 李芝绒; 王胜强; 袁建飞; 张玉磊; 蒋海燕
Original assignee: Xian Modern Chemistry Research Institute
Current assignee: Xian Modern Chemistry Research Institute
Priority date: 2018-11-20
Filing date: 2018-11-20
Publication date: 2020-11-10
Anticipated expiration: 2038-11-20
Also published as: CN109530848A

Abstract

The invention discloses a quick response tungsten-rhenium thermocouple welding method, which takes gallium alloy as a conductive medium, controls discharge current in two thermocouple wires by adjusting resistance in a discharge loop of a thermocouple, and realizes reliable welding of a refractory tungsten-rhenium thermocouple couple. The welding method has the obvious advantages that the welding couple is firm, the problem that one couple wire is fused and the other couple wire is insoluble is solved, the yield of the tungsten-rhenium thermocouple with quick response is improved, toxic and harmful gas is not generated in the welding process, the health of operators is not damaged, and the measurement of the transient high temperature of the temperature-pressure explosion field is met.

Description

Quick response tungsten-rhenium thermocouple welding method

Technical Field

The invention belongs to the technical field of welding, and relates to a welding method of a thermocouple, in particular to a welding method of a quick response tungsten-rhenium thermocouple.

Background

The tungsten-rhenium thermocouple has the advantages of high measurement temperature, good thermal stability, low price and the like, partially replaces thermocouple manufacturing materials of precious metals such as platinum, rhodium and the like, becomes an important temperature measuring element, is widely applied to the industries such as metallurgy building materials, aviation, aerospace, nuclear energy, weapons and the like, particularly has the characteristics of high strength and high hardness of the material, can resist the effect of transient shock wave pressure of an explosion field, is applied to the test of the explosion thermal effect of a temperature-pressure explosive, and can meet the measurement of the high temperature effect of the explosion field of temperature-pressure ammunition.

At present, for the manufacture of a thermocouple, an arc discharge welding method is generally adopted, for example, chinese patent ZL201310120888.1, a thermocouple welding method and a device thereof are used, mercury and engine oil are used as conductive materials, and an arc high-temperature welding thermocouple is coupled by an instantaneous short circuit generated between a welding point of the thermocouple and the mercury surface, and when the welding method is used for welding a difficult-to-dissolve tungsten-rhenium thermocouple, the following disadvantages exist: firstly, the couple that welds into the couple is insecure to a couple silk is fused often appearing in the welding, and another does not have the phenomenon of melting, secondly because the vaporization temperature of mercury is lower, can volatilize under normal atmospheric temperature state, in the arc discharge welding process, the high temperature of production has further increased the volatility of mercury, and mercury gas is absorbed by the human body and will produce the poisoning phenomenon, and harm operator health.

Disclosure of Invention

The invention aims to provide a welding method of a quick response tungsten-rhenium thermocouple, which takes gallium alloy as a conductive medium and controls the discharge current of a thermocouple wire by adjusting the resistance of a discharge circuit of the thermocouple, thereby improving the coupling rate of the thermocouple and the coupling welding quality, generating no toxic and harmful gas in the welding process and ensuring the health of operators.

In order to realize the task, the invention adopts the following technical solution:

a quick response tungsten-rhenium thermocouple welding method comprises the following steps:

step one, melting of a conductive medium:

gallium alloy with the melting point of about 65 ℃ is selected as a conductive medium, and a water bath method is adopted to melt solid gallium alloy materials for use in welding.

Step two, butting tungsten-rhenium thermocouple wires:

taking an assembled thermocouple semi-finished product, determining the length of the thermocouple wire extending out of the end face of the shell, and bending the end parts of the two exposed thermocouple wires to enable the end heads to be in butt joint to form a circular arch butt joint shape.

Step three, connecting the welding device lines:

the components are connected according to the circuit shown in fig. 1. Putting the electrode plate into a glass vessel containing a liquid conductive medium, and connecting a 220V power supply with the input end of an alternating current transformer through a control switch by a lead; one output end of the alternating current transformer is connected with the electrode plate through a lead, and the other connecting terminal is connected with the positive end of the thermocouple signal output signal wire through a lead on one hand and is connected with the rheostat and the negative end of the thermocouple signal output signal wire through a lead on the other hand.

Step four, adjusting the resistance of the discharge circuit of the tungsten-rhenium thermocouple to achieve the equality:

measuring the resistance of the end of the thermocouple wire connected from one output end of the AC transformer to the positive wire of the thermocouple output signal, measuring the resistance of the end of the thermocouple wire connected from the output end to the negative wire of the thermocouple output signal through the rheostat, comparing the results of the measured resistance values, and when the resistance values are not equal, adjusting the resistance of the rheostat until the resistance values of the two wires are equal.

Step five, assembling and fixing a tungsten-rhenium thermocouple:

the thermocouple wire is fixed to the support with the clamp with the end portion of the thermocouple wire facing downward. A glass vessel containing conductive medium liquid is placed below the thermocouple. And adjusting the clamp to enable the thermocouple wire butt joint point to be close to the liquid level of the conductive medium.

Welding a tungsten-rhenium thermocouple:

and adjusting the output voltage of the alternating current transformer, pressing the control switch to quickly release after the output voltage meets the requirement, generating high discharge temperature between the thermocouple wire butt joint and the gallium alloy surface, and melting the thermocouple butt joint into a thermocouple.

The beneficial benefits of the invention are as follows:

(1) according to the welding method, the resistance of the discharge circuit of the thermocouple is adjusted, so that the discharge current passing through the end parts of the two thermocouple wires is equal, and therefore, the butt joint ends of the two thermocouple wires are melted into a thermocouple under the action of high temperature of arc discharge, a thermocouple junction with small volume and firm structure is formed, the phenomenon that one thermocouple wire is heated and melted or even fused and the other thermocouple wire is not melted in the discharge process of the thermocouple wires is avoided, the yield of the thermocouple is improved, the labor, the material resources and the time are greatly saved, and the manufacturing cost is saved;

(2) in the welding method, gallium alloy is used as a conductive medium, the gallium alloy material not only has excellent heat conduction and electrical conductivity, but also has firm coupling of the welded tungsten-rhenium thermocouple, low melting point and high boiling point, the conductive medium hardly exists in the coupling in the arc discharge heating process, the purity of the coupling material is high, and the measurement precision of the tungsten-rhenium thermocouple is ensured;

(3) the welding method does not generate toxic and harmful gas, and does not harm the health of operators compared with the common mercury conductive medium;

(4) the welding method is simple and convenient to operate and implement.

Drawings

FIG. 1 is a schematic diagram of a welding circuit of the present invention.

FIG. 2 is a graph of explosive fireball temperature measured by a tungsten-rhenium thermocouple welded by this welding method.

Detailed Description

The present invention will be further described in detail with reference to the accompanying drawings and examples.

Referring to a welding circuit diagram shown in fig. 1, according to the above technical solution, the fast response tungsten-rhenium thermocouple welding method provided by the invention comprises the following steps:

step one, melting of the conductive medium 8:

putting the glass vessel 7 containing the conductive medium 8 into an open container filled with boiled water, and taking out the conductive medium 8 for later use after the conductive medium is completely dissolved.

The conductive medium 8 is made of gallium alloy material with melting point of about 65 ℃, gallium is metal with melting point of 30 ℃ and boiling point of 2400 ℃, the metal alloy material can form a metal alloy material with melting point of 3-100 ℃ with indium, thallium, tin, bismuth, zinc and the like, the gallium alloy material with melting point of about 65 ℃ is selected, the gallium alloy material is in a solid state at normal temperature and is convenient to store, and the gallium alloy material is not combined into a couple at the butt joint end of a coupling wire under the action of high temperature generated by arc discharge, so that the purity of the coupling material is ensured, and the measurement accuracy of the tungsten-rhenium thermocouple is guaranteed. Meanwhile, the most important thing is that in the arc discharge welding process, the gallium alloy does not generate toxic and harmful gas, replaces mercury conductive materials which are easy to volatilize at normal temperature, and avoids the human poisoning and other injury events caused by the volatilization of mercury in the welding process.

Step two, butting tungsten-rhenium thermocouple 4 couple wires:

taking a semi-finished product of the tungsten-rhenium thermocouple 4, measuring and determining the length of the thermocouple wire extending out of the end face of the shell, and then bending the end parts of the two exposed thermocouple wires to enable the end parts to be in butt joint to form a circular arch butt joint shape.

For the tungsten-rhenium thermocouple wire with the diameter of the thermocouple wire being (0.1-0.2) mm, the length of the thermocouple wire is about 10 mm. The thermocouple wire with the length has high structural strength and is not easy to damage under the action of 10MPa transient shock wave overpressure, and when the thermocouple with the length is arranged on a measuring plane, the thermocouple junction exceeds an air stratosphere within a range of (1-3) mm near the measuring plane, so that the thermocouple junction is fully contacted with high-temperature explosive gas in the environment, and the temperature of the explosive gas is ensured to be accurately measured. If the diameter of the tungsten-rhenium thermocouple 4 thermocouple wire is larger than 0.2mm, the length of the thermocouple wire can be properly lengthened.

The thermocouple wire adopts a circular arch type butt joint mode, a thermocouple coupling junction with a smaller volume is easily formed in welding, the volume of the coupling junction is smaller than that of the coupling junction formed in a thermocouple wire hinge mode, thermal inertia is small, the requirement of thermocouple quick response can be met, and the measurement of the explosion heat effect of an explosion field can be met. For tungsten-rhenium thermocouple wires with the diameter of the thermocouple wire being (0.1-0.2) mm, the response time of welding the thermocouple in the mode is less than 2ms (water bath measurement method).

Step three, connecting the welding lines:

the electrode plate 9 is put into a glass vessel 7 containing a conductive medium 8, and the components are connected according to a circuit shown in figure 1: the electrode plate 9 is put into a glass vessel 7 containing liquid conductive media, and the control switch 1 connects a 220V power supply with the input end of the transformer 2 through a lead; one output end of the transformer is connected with the electrode plate 9 through a lead, and the other connecting terminal is connected with the positive end of the thermocouple signal output line 4-1 through a lead on one hand and is connected with the rheostat 3 and the negative end of the thermocouple signal output signal line 4-1 through a lead on the other hand.

Step four, adjusting the resistance of the thermocouple discharge circuit, and achieving the equality:

measuring the resistance of the end part of the thermocouple wire connected from the output end of the transformer 2 to the positive end of the thermocouple signal output line 4-1, measuring the resistance of the end part of the thermocouple wire connected from the output end to the negative electrode line of the thermocouple signal output line 4-1 through the rheostat, comparing the resistance values, and when the resistance values are not equal, adjusting the resistance of the rheostat 3 until the resistances of the two lines are equal.

For a thermocouple using a low-noise cable as a signal output line, the resistances of positive and negative leads of the output signal line are unequal, and the longer the lead is, the larger the difference is. When the thermocouple is welded, because the resistances of the two thermocouple wire discharge circuits are not equal, the currents passing through the butt joint points of the two thermocouple wires are different, the heat released by arc discharge is also different, the larger the discharge current is, the more the heat released from the end point of the thermocouple wire is, and the end of the thermocouple wire can be melted; the smaller the discharge current is, the less the heat release quantity of the thermocouple wire end is, the thermocouple wire end can not be melted, the thermocouple can not be formed, or one thermocouple wire end is fused and the other thermocouple wire end is not melted, therefore, the rheostat 3 is arranged in the discharge circuit of the thermocouple, and the resistance of the negative electrode of the thermocouple signal output line is equal to that of the discharge line of the positive electrode by adjusting the resistance of the rheostat 3 access circuit.

For a 5\ 26W-Re thermocouple wire with the diameter phi of 0.2mm, when the thermocouple signal output line 4-1 is a low-noise cable with the length of 5m, the resistance value of the circuit connected with the rheostat 3 is 2.9 omega.

Step five, assembling and fixing a tungsten-rhenium thermocouple 4:

the tungsten-rhenium thermocouple 4 is fixed to a support 5 by a clamp 6 with one end of the thermocouple wire facing downwards. A glass vessel 7 containing a conductive medium 8 is placed below the butt joint point of the tungsten-rhenium thermocouple 4, and the height of the clamp 6 is adjusted to enable the butt joint point of the tungsten-rhenium thermocouple 4 to be close to the liquid surface of the conductive medium 8 by 0.5 mm.

Step six, welding the tungsten-rhenium thermocouple 4:

the output voltage of the transformer 4 is adjusted, after the requirement is met, the control switch 1 is pressed and then quickly released, high-temperature electric arc is generated between the butt joint of the thermocouple wire and the liquid level of the electric conductor, and heat is released to melt the butt joint of the thermocouple into a thermocouple.

The output voltage of the ac transformer 2 is related to the diameter of the wire of the tungsten-rhenium thermocouple, and for a tungsten-rhenium wire with a diameter of 0.1mm, the output voltage is approximately equal to 24V.

The applicant adopts the method of the invention to weld a tungsten-rhenium thermocouple with a thermocouple wire diameter of 0.2mm, 2kg of explosive heat of certain temperature and pressure is measured in an explosion tank by applying the thermocouple, the obtained thermocouple response temperature curve is shown in figure 2, the peak value of the response temperature is 1980 ℃, 2kg of explosive heat of TNT charge is also measured, and the peak value of the response temperature of the thermocouple is 950 ℃. The test data provides support data for the evaluation of the explosion thermal effect of the thermal-pressure explosive.

Claims

1. A quick response tungsten-rhenium thermocouple welding method is characterized by comprising the following steps:

step one, putting a glass vessel (7) containing a solid conductive medium (8) into an open container filled with boiled water, and taking out the conductive medium (8) for later use after the conductive medium is completely melted;

step two, two exposed couple wires of the tungsten-rhenium thermocouple (4) are equal in length, and the ends of the couple wires are butted to form a circular arch shape;

thirdly, the control switch (1) is respectively connected with the power supply and the input end of the transformer (2) by leads; one terminal of the output of the transformer (2) is connected with the electrode (9); the other output terminal of the transformer (2) is connected with a negative electrode line (4-1) of a signal output line of the tungsten-rhenium thermocouple (4) through a rheostat (3) on one hand, and is connected with a positive electrode line (4-2) of the signal output line of the tungsten-rhenium thermocouple (4) on the other hand;

adjusting the resistance of the rheostat (3) to enable the resistances of the two coupled filament discharge circuits of the tungsten-rhenium thermocouple to be equal;

fifthly, downward facing a wire of the tungsten-rhenium thermocouple (4), approaching the liquid level of the conductive medium (8), and fixing the wire on a cylindrical rod of the support (5) through a clamp (6);

and step six, adjusting the output voltage of the transformer (2), starting the control switch (1) after the output voltage meets the requirement, generating high-temperature electric arc between the coupling wire butt joint of the tungsten-rhenium thermocouple (4) and the liquid level of the conductive medium, and melting the tungsten-rhenium thermocouple butt joint into a couple.

2. The method as claimed in claim 1, characterized in that the discharge currents passed through the two wires of the tungsten-rhenium thermocouple (4) are equal.

3. The method according to claim 1, characterized in that the conductive medium (8) is a gallium alloy and is melted by means of a water bath.