JP2685910B2 - Manufacturing method of oxide superconducting conductor - Google Patents

Description

The present invention relates to a method for producing an oxide superconducting conductor, and more particularly to a method for producing a tape-shaped oxide superconducting conductor.

[Prior Art] Filling a sheath metal tube with powder of oxide superconductor,
A method of reducing the diameter of this to form a wire rod is generally known as a method of easily forming a wire rod.

Particularly in recent years, in order to improve the critical current density of the wire rod, it is better to roll the thin plate into a tape shape than to the cylindrical shape, so that the final processing is mostly performed by rolling.

A feature of the tape-shaped wire rod is that by rolling in one direction, the major axis (C axis) of the crystal of the superconductor inside the metal sheath is oriented in the same direction as the rolling direction. Therefore, the bonding area between each crystal grain is increased as compared with the non-oriented material, and so-called weak bonding is improved. Therefore, the thickness of the interfacial phase can be reduced.

On the other hand, it is necessary to supply oxygen in performing the sintering heat treatment after processing the oxide superconductor into a wire, and as the metal for the sheath, silver and silver alloy having oxygen permeability are generally used.

In addition, oxide superconductors, especially those having a composition containing rare earths, are accompanied by absorption of oxygen during the sintering process to the cooling process.
Even if the composition has the following phase transformation, and even if the composition does not contain a rare earth, it is necessary to supply oxygen during the sintering and the subsequent heat treatment process. No reducing metal was used.

[Problems to be Solved by the Invention] However, silver and silver alloys used as the metal for the sheath have small deformation resistance and excellent plastic workability, but have a difference in mechanical strength from the oxide superconductor inside. Since it is large, when it is rolled between a pair of or a plurality of rolling rolls, it becomes impossible to perform uniform processing in the length direction as the thickness of the tape becomes thinner, and the cross-sectional area of the oxide superconductor layer in the length direction becomes longer. Non-uniformity, that is, a so-called sausaging phenomenon occurred.

According to the present invention, the cross-sectional area of the oxide superconducting ceramics portion inside the metal tube for the sheath is long when the linear body coated with the oxide superconductor with a metal having a small deformation resistance such as silver or a silver alloy is rolled. The purpose is to improve the unevenness in the depth direction.

[Means for Solving the Problems] In the method for producing an oxide superconductor according to the present invention, the oxide superconductor is rolled together with the sheath metal tube in a state where the oxide superconductor is filled in the sheath metal tube. In the method for producing an oxide superconductor, the wire rod is heat-treated after the wire rod is subjected to a pre-rolling step of previously rolling the sheath metal tube filled with the oxide superconductor, and this pre-rolling step. The metal tube for the sheath that has passed through is sandwiched by a pair of metal strips having a larger deformation resistance than the metal tube for the sheath from opposite sides in the rolling direction, and a sandwich for applying a reduction to the metal pipe for the sheath via the pair of metal strips. And a rolling process.

Further, preferably, the method further comprises a step of peeling the pair of metal strips immediately after the sandwich rolling step, opposite to the rolling direction.

Further, preferably, an infinite loop metal strip is used as the metal strip.

[Operation] In the present invention, when rolling a sheath metal tube filled with an oxide superconductor, metal strips having a larger deformation resistance than the sheath metal tube are provided on both sides of the sheath metal tube in the rolling direction. Since it is sandwiched and rolled by interposing,
When the oxide superconductor is coated with a metal such as silver or silver alloy with low deformation resistance and rolled into a tape-shaped conductor, the cross-sectional area of the oxide superconducting ceramics part inside the sheath metal tube is Non-uniformity is improved.

That is, when the oxide superconducting powder is filled into the metal tube for the sheath of silver, silver alloy, etc. and the rolling process is performed, at the initial stage when the packing density is low, due to the mutual slip of the powders, the apparent plastic deformation occurs. Is done easily.

However, as the number of times of rolling increases, the packing density increases as the total processing rate increases, and not only slippage between powders but also crushing due to shearing force between powders increases.
The deformation resistance of the apparent powder is significantly increased. as a result,
In a metal tube for a sheath having a small deformation resistance such as silver or a silver alloy, the oxide superconducting powder inside cannot be uniformly deformed over the entire length, so that the cross-sectional area in the longitudinal direction becomes nonuniform.

As a means for solving this, a metal strip having a larger deformation resistance than that of the sheath metal, such as stainless steel, is arranged on both sides of the sheath metal tube, and sandwiching rolling is performed with the metal strip interposed. The rigidity of the metal tube for the hanging sheath has increased, and it is possible to perform processing involving crushing of the oxide superconducting powder inside, and the rolling force is applied to the surface, so the oxide superconducting powder is uniformly filled in the length direction. It will be possible to carry out rolling processing with a defined cross section.

[Examples] FIG. 1 is a schematic cross-sectional view of a rolled state in the sandwich rolling process. In the figure, a pair of stainless metal strips 1 having a high deformation resistance is sandwiched between two rotating rolling rolls 4, and between the metal strips 1 for a sheath made of silver or silver alloy. The metal tube 2 is sandwiched. The inside of the metal tube for sheath 2 is filled with oxide superconductor powder 3.

The high-strength metal strip 1 is hardly deformed by rolling.
On the other hand, the sheath metal tube 2 and the oxide superconducting powder 3 are deformed,
become thinner. Therefore, the metal strip 1 and the sheath metal tube 2 have relatively different speeds during the rolling process. In order to reduce the occurrence of wear flaws on the surface of the sheath metal tube 2 due to this speed difference, it is desirable to apply a lubricant having a high kinematic viscosity coefficient between the metal strip 1 and the sheath metal tube 2.

As a method for actually obtaining a long wire rod by the above-mentioned sandwich rolling, it is preferable to use an apparatus in which metal strips are arranged in an infinite loop.

FIG. 2 is an explanatory view showing the configuration of an apparatus in which high-strength metal strips are arranged in an infinite loop shape.

In the figure, a pair of stainless steel high-strength metal strips
11 are arranged in an endless loop by the guide roll 41. The curvature of the portion of the guide roll 41 in contact with the metal strip 11 is within the elastic limit of the metal strip 11.

A guide roll 41 is provided on the entrance side of the main rolling roll 42, and the metal strip 11 is interposed between the sheath metal tube 21 and the main rolling roll 42 with a curvature larger than the roll diameter of the main rolling roll 42.

By doing so, it is possible to prevent the bulge deformation caused by the sheath metal tube 21 being pushed by the roll at the entrance of the main rolling roll 42.

Further, a sub-rolling roll 43 is also provided on the exit side of the main rolling roll 42 to prevent the occurrence of swelling deformation of the rolled sheath metal tube 21 on the exit side of the main rolling roll 42 and to promote uniform rolling. Has become.

Also in this rolling, it is desirable to apply a lubricant having a high kinematic viscosity coefficient between the metal strip 11 and the sheath metal tube 21.

In addition, the reduction ratio of one time is more than 10%, preferably 20%.
% Is desirable. This is because if it is 10% or less, the rolling force of the high-strength metal strip is insufficiently transmitted, and a wire rod having a uniform cross-sectional area over the entire length cannot be obtained.

 An example in which a wire rod was actually manufactured will be shown below.

Example 1 An oxide superconductor powder represented by YBa ₂ Cu ₃ O _7-X (average particle size 10 μm) was filled in a silver pipe having an inner diameter of 15 mm, an outer diameter of 25 mm and a length of 150 mm, and both ends were sealed with silver blocks. After that, the diameter was reduced to 5 mm by swaging.

The wire rod manufactured in this way is 2 mm thick with a flat roll mill.
It was rolled flat as it was to obtain a tape-shaped wire rod having a thickness of 2 mm and a width of 7 mm.

A 0.5 mm thick and 10 mm wide stainless steel strip (sus304H) is placed in the endless track type on both the upper and lower sides of this tape strip as shown in Fig. 2. Through this stainless steel strip, one pass rolling reduction is performed.
Rolled to a thickness of 0.5 mm at 30%.

The obtained wire rod is divided into three parts, and rolled in the same way to a thickness of 0.1 mm with a reduction ratio of 30%, 50%, 80%, and a section perpendicular to the longitudinal direction of the wire rod is lengthened for each sample of each reduction ratio. It was cut out at 10 positions in the vertical direction, the cross-sectional area of the oxide superconductor layer portion inside the sheath was measured, and the average cross-sectional area and variation (σs%) were obtained.

The rolled tape wire was subjected to a sintering heat treatment at 900 ° C. for 5 hours in an oxygen stream, and then the critical current Ic was measured. This Ic was divided by the average cross-sectional area to obtain the critical current density Jc.

Comparative Example 1-1 The same sandwich rolling process as in Example 1 was performed, and rolling was performed from a thickness of 0.5 mm to a thickness of 0.1 mm at a 1-pass reduction of 10%. The cross-sectional area of the oxide superconductor layer inside the wire thus obtained, and Ic
Was measured in the same manner as in Example 1.

Comparative Example 1-2 As in Example 1, a silver pipe was filled with YBa ₂ Cu ₃ O _7-X oxide superconducting powder, and then swaged and rolled to obtain a thickness.
A tape-shaped wire rod having a width of 2 mm and a width of 7 mm was obtained. The obtained wire rod has a thickness of 0.1 m at a pass reduction of 30% without passing through a stainless steel strip.
Rolled to m. Example 1 of the wire thus obtained
Similarly, the cross-sectional area and Ic of the oxide superconductor layer inside were measured.

 The results are shown in Table 1 below.

Example 2 An oxide superconducting powder represented by (Bi _1.8 Pb _0.2 ) ₂ Sr ₂ Ca ₂ Cu ₃ O _x (average particle size 10 μm) was filled in the same silver pipe as in Example 1, and the thickness was increased by the same method. Rolled to 0.5 mm. The obtained wire rod was divided into three and rolled to a thickness of 0.1 mm at a reduction rate of 30%, 50% and 80%, respectively. With respect to the wire material thus obtained, the cross-sectional areas of the oxide superconductor layer portions inside 10 places in the lengthwise direction were measured in the same manner as in Example 1, and the average cross-sectional area and the variation (σs%) were obtained.

Further, after the above-mentioned rolled tape wire rod is subjected to a sintering heat treatment at 845 ° C. for 20 hours in the air, it is pressed by applying a pressure of 200 kg / cm ² , and further subjected to a heat treatment at 845 ° C. for 100 hours to obtain a critical current Ic.
Was measured. The critical current density is calculated by dividing this Ic by the average cross-sectional area.
I asked for Jc.

Comparative Example 2-1 The same sandwich rolling process as in Example 2 was performed, and rolling was performed from a thickness of 0.5 mm to a thickness of 0.1 mm with a 1-pass reduction of 10%. With respect to the wire thus obtained, the cross-sectional area of the oxide superconductor layer inside and Ic were measured for Example 2 and application.

Comparative Example 2-2 The same Bi-based oxide superconducting powder as in Example 2 was used, and the same procedure as in Comparative Example (1-2) was performed without using a stainless steel strip.
It was rolled to a thickness of 0.1 mm with a pass reduction of 30%. The cross-sectional area and Ic of the internal oxide superconductor layer of the wire thus obtained were measured in the same manner as in Example 2.

 The results are shown in Table 2 below.

As shown in Tables 1 and 2, in Example 1 product and Example 2 product having a large 1-pass rolling reduction, the variation (σs) in the cross-sectional area of the oxide superconductor layer inside was small, and therefore Ic
Was found to be high.

On the other hand, Comparative Example 1-1 products and Comparative Example 2-1 products having a small 1-pass rolling reduction ratio, and Comparative Example 1-rolled without a metal strip.
It was found that the two products and the product of Comparative Example 2-2 had a large variation (σs) in the cross-sectional area of the oxide superconductor layer inside and a low Ic.

The difference in the value of Ic beyond the variation of the cross-sectional area of the oxide superconductor layer in this example and the comparative example is that the orientation of mutual crystal grains in the wire material having a large variation in the cross-sectional area of the oxide superconductor layer. This is because the contact was poor and the current path decreased and the weak coupling increased.

[Effects of the Invention] As described above, according to the present invention, when an oxide superconductor filled in a sheath metal tube is rolled together with the sheath metal tube, the sheath metal tube is provided on both sides of the sheath metal tube in the rolling direction. Since a metal strip having a larger deformation resistance than that of a metal tube is interposed and rolled, the linear body coated with an oxide superconductor with a metal having a small deformation resistance such as silver or a silver alloy is rolled. In this case, the cross-sectional area of the oxide superconducting ceramics inside the sheath metal tube becomes uniform in the lengthwise direction, the orientation and contact of the crystal grains become better, and the current path increases and the weak coupling decreases. There is an effect of fulfilling.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a rolled state of the sandwich rolling process according to the present invention, and FIG. 2 is an explanatory view showing the configuration of an embodiment apparatus in which high-strength metal strips are arranged in an infinite loop shape. In the figure, 1, 11 are metal strips, 2, 21 are metal tubes for sheath, 3
Is an oxide superconductor powder, 4 is a rolling roll, 41 is a guide roll, 42 is a main rolling roll, and 43 is a sub-rolling roll.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A 1-258832 (JP, A) JP-A 1-206518 (JP, A) JP-A 2-8335 (JP, A) JP-A 3- 53419 (JP, A) JP-A-2-199715 (JP, A)

Claims (3)

(57) [Claims] 1. An oxide in which a metal rod for sheath is filled with an oxide superconductor and the oxide superconductor is rolled together with a metal pipe for sheath to form a wire, and then the wire is heat-treated. In the method for manufacturing a superconducting conductor, a pre-rolling step of pre-rolling a sheath metal tube filled with the oxide superconductor, and a sheath metal tube that has undergone this pre-rolling step is applied to the sheath metal tube from opposite sides in a rolling direction. A sandwich rolling step of sandwiching between a pair of metal strips having a larger deformation resistance than that of the metal pipe and applying a rolling reduction to the sheath metal pipe through the pair of metal strips. Method. 2. The method for producing an oxide superconducting conductor according to claim 1, further comprising a step of peeling the pair of metal strips in a direction opposite to a rolling direction immediately after the sandwich rolling step. 3. The method for producing an oxide superconducting conductor according to claim 1, wherein an infinite loop metal strip is used as the metal strip.