CN115274212A

CN115274212A - High-pressure heat treatment end sealing method for multi-strand twisted Bi-2212 conductor

Info

Publication number: CN115274212A
Application number: CN202210925515.7A
Authority: CN
Inventors: 杨东昇; 于敏; 秦经刚; 周超; 金环; 高鹏
Original assignee: Hefei Institutes of Physical Science of CAS
Current assignee: Hefei Institutes of Physical Science of CAS
Priority date: 2022-08-03
Filing date: 2022-08-03
Publication date: 2022-11-01

Abstract

The invention discloses a method for sealing the high-pressure heat treatment end part of a multi-strand twisted Bi2212 conductor, which comprises the steps of Bi-2212 round wire surface treatment and sealing structure design, a heating mode and control parameter setting. According to the invention, the aerogel thermal insulation coating is sprayed on the outside (5 mm away from the port) of the Bi-2212 superconducting round wire, the silver-magnesium alloy wire with the thickness of 1.0mm is wound on the surface of the cable, and the end of the cable is finally covered to form an oval structure, so that the external temperature is higher when the cable is sealed at high temperature, the internal temperature is firstly melted, and the internal temperature is lower when the silver-magnesium alloy wire is melted and falls along with gravity, and the silver solution covers the end of the superconducting wire to complete sealing.

Description

High-pressure heat treatment end sealing method for multi-strand twisted Bi-2212 conductor

Technical Field

The invention relates to the field of superconducting strands in a CICC (common integrated circuit chip) armored conductor, in particular to a method for sealing the high-pressure heat treatment end part of a multi-strand twisted Bi-2212 conductor.

Background

The CICC armored conductor (cable-in-conductor) is the first conductor which is recognized internationally and used for manufacturing large superconducting magnet coils, because the coolant in the structural conductor is in direct contact with the cable in a fluid form, the wet surface area is large, the heat exchange efficiency is excellent, and the outer armor can provide support for the inner cable, so that the structural strength of the cable is improved. The CICC conductor is widely applied to large scientific devices such as an accelerator, a fusion reactor and the like at present, such as an international cooperation ITER device which is being built, a CFETR device which is to be built in China in the future and the like.

Currently, conventional Nb-based superconducting materials such as Nb ₃ Sn and NbTi are subjected to their upper critical field (Hc) ₂ ) Has gradually failed to meet the high field requirements in the future. Therefore, people gradually turn attention to high-temperature superconducting materials with high critical fields, such as Bi-2212, YBCO and the like, which have higher upper critical fields and have great development prospects. Bi-2212 can be made into isotropic round wires, thereby being beneficial to developing CICC conductors. The current general preparation method of the Bi-2212 round wire is a powder tube-filling method, namely, raw materials for forming the superconducting phase are filled into a silver-based sleeve and are subjected to multiple annealing and drawing to form a wire, and finally the wire is subjected to high-temperature heat treatment to form the superconducting phase. The Bi-2212 round wire preparation process and the Bi-2212 phase ceramic structure determine the characteristic of poor mechanical property of the prepared strand, and the mechanical strength is only about that of the traditional Nb ₃ Half of the Sn material. In the manufacturing and practical application of the CICC conductor, the superconducting material may deform due to the action of acting force in the stranding process, lorentz force in the operation process, thermal stress in the temperature raising and lowering process, and the like, so that the critical current of the conductor is degraded. In the future, with the development of magnet technology, people will have higher and higher requirements on magnetic field strength.

The Bi-2212 high-temperature superconducting material can reach the high critical current performance meeting the engineering application only by a special heat treatment process, namely a high-temperature high-pressure heat treatment process. The high-pressure heat treatment (3-10 MPa) needs to carry out sealing treatment on two ends of the Bi-2212 superconducting wire, so that the high external pressure is ensured, the pressure in the superconducting wire is low, and the pressure difference is formed, thereby achieving the purpose of high pressure. The Bi-2212 superconducting wire sealing process has been studied, and several thousand CICC conductors of superconducting wires are required to be sealed at present.

Disclosure of Invention

The Bi-2212 conductor is composed of hundreds of dozens to thousands of superconducting round wires with different quantities, only by a method of sealing superconducting single wires, more time is needed for a large-size conductor and can be months, the risk of single wire sealing failure is increased, a new reliable integral sealing means is needed for rapidly sealing a large-size cable and a conductor, therefore, the invention provides a high-pressure (3-10 MPa) heat treatment end sealing method of a multi-strand twisted Bi-2212 conductor, and the problem that the CICC conductor in the prior art can be treated by only one Bi-2212 round wire and cannot be rapidly sealed in a large quantity is solved.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for sealing the high-pressure heat-treated end of a multi-stranded twisted Bi-2212 conductor, comprising the steps of:

(1) Removing the armor 5-10cm away from the front end of the Bi-2212 conductor before sealing the conductor, winding the silver-magnesium alloy wire after scattering the cable, and using SiO to ensure that the distance between the outer surface of the Bi-2212 round wire and the end is within 5mm ₂ Aerogel spray coating is used as the insulating layer. Wherein, the Bi-2212 conductor is formed by twisting a Bi-2212 round wire. SiO 2 ₂ Aerogel material SiO ₂ The content is more than wt90%, and meanwhile, the insulating layer can not contain easily oxidized metal powder such as copper, iron and the like, and the thickness of the insulating layer is 5-20 mu m;

(2) Then, winding 3-7 circles of silver-magnesium alloy wires at the front end of each superconducting wire in the cable by 5-10mm, and finally winding silver sheets for 2-4 weeks for fastening; obtaining a cable wound with the silver-magnesium alloy;

(3) Heating the end part of the cable wound with the silver-magnesium alloy by adopting electromagnetic induction; the electromagnetic induction heating device and the sample are vertically installed, and the sample clamping part is controlled by a stepping motor and a PC end to move upwards for a certain distance (0.5-1 cm) at a constant speed of 5-10mm/5 seconds. The sample is the cable wound with the silver-magnesium alloy.

Further, the end part of the cable wound with the silver-magnesium alloy is heated by adopting electromagnetic induction, the power of an electromagnetic induction coil is kept between 1500Hz and 5000Hz, and the heating time is 0.5-10 seconds, so that the sealing of the cable or the conductor is finished.

Further, no superconducting phase (black phase) and voids can occur around the bottom superconducting wire after the cable is sealed. And (3) digging out the superconducting phase flowing out of the surface of the cable end closure by using a graver, heating for 5-10 seconds by using a flame gun at the temperature of more than 1500 ℃, and determining whether the superconducting phase flows out again. If a gap appears in the middle of the superconducting wire at the bottom, the superconducting wire is filled with molten silver solution and then is rapidly cooled by alcohol.

Compared with the prior art, the invention has the advantages that:

the invention solves the problem that the superconducting wire sealing of the prior art is intelligent and single sealing, and a large number of superconducting wires cannot be intensively sealed without influencing the critical current performance of the superconducting wire. The structure is simple in form and simple and convenient to operate, is beneficial to large-batch engineering realization, and increases the possibility for the application of the Bi-2212 CICC conductor in the future.

Drawings

FIG. 1 is a schematic view of the construction of the conductor sealing device of the present invention;

in the figure, 1-computer, 2-stepping motor, 3-slide rail, 4-clamp, 5-conductor, 6-high frequency induction heating melting machine.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention without inventive step, are within the scope of protection of the invention.

Fig. 1 is a schematic view of the structure of the conductor sealing device of the present invention. The device comprises a computer 1 (PC), a stepping motor 2, a slide rail 3, a clamp 4, a conductor 5 and a high-frequency induction heating smelting machine 6. The conductor 5 is removed and thickened to be wrapped by silver alloy, and the stepping motor 2 is arranged on the sliding rail 3. Then, fixing the workpiece in the vertical direction by using a clamp 4 on the stepping motor 2; and (3) starting a program at the (PC) end of the computer 1, controlling the high-frequency induction heating smelting machine 6 to reach the required heating power within 2 seconds by the program, and starting the stepping motor 2 to move the conductor 5 upwards to finish the conductor sealing.

As shown in figure 1, a Bi-2212 CICC conductor end sealing process aims to solve the problem that a Bi-2212 round wire used for a CICC conductor in the prior art can only be processed by one wire and cannot be rapidly sealed in a large quantity. The Bi-2212 conductor is made by twisting Bi-2212 round wires.

Firstly, removing 5-10cm of armor and wrapping tape at the front end of a Bi-2212 conductor cable, scattering the cable, cleaning each superconducting wire by alcohol, and using SiO to ensure that the distance between the outer surface of a Bi-2212 round wire and the end head is within 5mm ₂ Aerogel spray coating is used as the insulating layer. Aerogel material SiO ₂ The content is more than 90wt%, and simultaneously, the copper powder, the iron powder and other metal powder which are easy to oxidize cannot be contained, and the thickness is 5-20 mu m.

Each superconducting wire is wound with a silver-magnesium alloy wire, each superconducting wire in the cable is wound by 3-7 circles of silver-magnesium alloy wires, and finally, silver sheets with the thickness of 0.1mm and the width of 2cm are wound for 2-4 weeks. And after the winding is finished, extruding by using two semicircular dies, wherein the final size is not more than 120% of the original diameter of the cable.

Then the heating device and the sample are installed in the vertical direction, and the sample holding part is controlled by a stepping motor and a PC terminal to move upwards for a certain distance (0.5-1 cm) at a constant speed. The electromagnetic induction heating method is adopted, the power of the electromagnetic induction coil is kept between 1500Hz and 15KHz, and the heating time is 0.5-10 seconds.

After the cable is sealed, a superconducting phase (black phase) and pores cannot appear around the superconducting wire at the bottom. The superconducting phase on the upper surface is removed by a nicking tool and heated for 5-10 seconds by a flame gun at 1500 ℃. Gaps appear in the middle of the superconducting wire at the bottom, and the superconducting wire is quickly cooled by alcohol after being filled with molten silver solution. If the bottom part is larger (larger than 1mm hole) after melting, cutting the end part of the cable and manufacturing the conductor seal again (in order to avoid the failure of the conductor seal).

Example 1

1. Stripping 10cm of armor of a three-level CICC conductor which is about 9mm in diameter and consists of 42 superconducting wires into a cable;

2. SiO is used for the cables with the distance of 5mm from the end head ₂ Aerogel spray coating is used as the insulating layer. SiO 2 ₂ Aerogel material SiO ₂ The content is more than 90wt%, and the thickness of the insulating layer is 15 mu m;

3. winding a silver-magnesium alloy wire on the superconducting wire;

4. winding a first silver-coated tape 3 layer with the thickness of 0.1mm and the width of 10mm on the outer layer;

5. electromagnetic heating is adopted, and the material moves upwards at the speed of 2 mm/s;

6. closing the heater, and carrying out alcohol spray type cooling from the position 10cm above the end part of the cable to the upper part to obtain a sealing part;

7. the statistical sealing success rate of the obtained superconducting conductor end socket is more than 85 percent after performance test.

The embodiments of the present invention are described only for the preferred embodiments of the present invention, and not for the limitation of the concept and scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall into the protection scope of the present invention, and the technical content of the present invention which is claimed is fully set forth in the claims.

Claims

1. A method for sealing the high-pressure heat-treated end of a multi-stranded twisted Bi-2212 conductor, which is characterized by comprising the following steps of:

(1) Removing armor 5-10cm away from the front end of a Bi-2212 conductor cable before sealing the conductor, spreading the cable, and winding silver-magnesium alloy wires, wherein SiO is used for the distance between the outer surface of the Bi-2212 round wire and the end within 5mm ₂ Spraying aerogel to form an insulating layer; wherein, the Bi2212 conductor is formed by twisting a Bi-2212 round wire;

(2) Then, winding 3-7 circles of silver-magnesium alloy wires at the front end of each superconducting wire in the cable by 5-10cm, and finally winding silver sheets for 2-4 weeks for fixing to obtain the cable wound with the silver-magnesium alloy wires;

(3) Heating the end part of the cable wound with the silver-magnesium alloy by adopting electromagnetic induction; the electromagnetic induction heating device and the sample are installed in the vertical direction, the sample clamping part is controlled by a stepping motor and a PC end, and the cable moves upwards at a constant speed of 5-10mm/5 seconds; wherein the sample is the cable wound with the silver-magnesium alloy.

2. The method according to claim 1, wherein in step (1), the insulating layer has a thickness of 5-20 μm.

3. The method of claim 1, wherein in step (1), the aerogel material SiO is ₂ The content is more than 90wt%, and copper or iron metal powder cannot be contained.

4. The method of claim 1, wherein in step (2), the silver flakes are 0.1mm thick and 2cm wide.

5. The method of claim 1, wherein in step (3), the electromagnetic induction heating parameters are as follows: the power of the electromagnetic induction coil is kept between 1500Hz and 8000Hz, and the heating time is 0.5-10 seconds; preferably, the power of the electromagnetic induction coil is kept between 1500Hz and 5000Hz, and the heating time is 0.5-10 seconds.

6. The method according to claim 1, wherein in the step (3), the upward movement is 0.5-1cm.

7. The method as claimed in claim 1, wherein in step (3), no superconducting phase and no porosity are present around the Bi2212 conductor after the cable is sealed.

8. The method according to claim 1, wherein in the step (3), the superconducting phase on the upper surface is removed by cutting with a nicking tool and then heated with a torch at 1500 to 3000 ℃ for 5 to 10 seconds.

9. The method according to claim 1, wherein in the step (3), a gap appears in the middle of the Bi2212 conductor at the bottom, and the silver conductor is filled with the molten silver solution and then cooled by alcohol.