WO2001026120A2

WO2001026120A2 - A method of manufacturing and using a superconducting tape.

Info

Publication number: WO2001026120A2
Application number: PCT/DK2000/000561
Authority: WO
Inventors: Peder Skov-Hansen
Original assignee: Nordic Superconductor Technologies AS
Current assignee: Nordic Superconductor Technologies AS
Priority date: 1999-10-06
Filing date: 2000-10-06
Publication date: 2001-04-12
Anticipated expiration: 2002-04-06
Also published as: KR20020035885A; WO2001026120A3; EP1222672A2; WO2001026120B1; AU7645500A; JP2003511818A

Abstract

A method for the use of a superconducting tape, especially for the winding of a superconducting tape to a coil. According to the invention, the superconducting tape is wound with a radius of curvature adapted to a specific application before it is subjected to a sintering in an oven, whereafter the sintering is carried out. Thus the sintering can be carried out before a winding to a mandrel is carried out. As a result it is possible to manufacture even small coils without the use of special mandrels and insulating layers which can tolerate high temperatures.

Description

Claims

1. A method for the use of a superconducting tape, characterised in that prior to the sintering in an oven, the superconducting tape is wound with a radius of curvature dimensioned in such a way that the curvature is adapted to a specific appli- cation, whereafter the sintering is carried out.

2. A method as claimed in claim 1, characterised in that the said radius of curvature range includes a radius of curvature being smaller than the final radius of curvature, as well as a radius of curvature exceeding said final radius of curvature.

3. A method as claimed in one of the preceding claims, characterised in that prior to the sintering, the superconducting tape is wound with a radius where the tape brittles if it is subjected to a strain after the sintering.

4. A method as claimed in one of the preceding claims, characterised in that after the sintering the superconducting tape is wound on a holder, preferably a coil holder without being subjected to a strain beyond the range of the above radius of curvature.

5. A method as claimed in one of the preceding claims, characterised in that prior to the sintering, the superconducting tape is provided with one or several bending radii, whereby it does not brittle when it is placed in the application in question after the sintering. 1

Title: A method of manufacturing and using a superconducting tape, especially when said tape is to be wound on a coil.

Technical Field.

The invention relates to a method of manufacturing and using a superconducting tape, especially when said tape is to be wound into a coil.

Background Art

US-PS No. 5,531 ,015 discloses two principles for the winding procedure.

_. Wind and react or 2_, React and wind.

The first method involves winding a superconducting tape to a mandrel with or without intermediate insulating layers followed by a sintering in an oven. This method presents high requirements to the mandrel and to the properties of the insulating layers with respect to absorption of heat, and it is suited for the manufacture of coils with a small radius.

The second method involves a winding up of the tape with a relatively large radius followed by the tape wound up being sintered in an oven. Not until now the tape is wound onto a mandrel. However, during the winding procedure a risk applies of the superconducting material of the tape brittling due to the small bending radius. The latter applies especially to the manufacture of small coils where the tape is subjected to particularly extensive deformations during the winding procedure.

Brief Description of the Invention. The object of the invention is to provide a method of manufacturing superconducting tapes with small radii of curvature, especially small coils not encumbered with the above draw-backs.

A method of the above type is according to the invention characterised in that prior to the sintering in an oven, the superconducting tape is wound up with a radius of curvature dimensioned in such a way that the curvature is adapted to a specific application, whereafter the sintering is carried out.

As a result the sintering can be carried out before the tape is wound on a mandrel. In this manner it is possible to manufacture even small coils without the use of special mandrels and insulating layers which can tolerate high temperatures.

Moreover, the superconducting tape may according to the invention be wound up or bent into one or more radii of curvature prior to the sintering, said radii of curvature being dimensioned in such a way that within a predetermined radius of curvature range said radius of curvature is adapted to a specific application, whereby the said radius of curvature range corresponds to the range defining the handling and winding extent of the tape without involving a brittling of the superconducting material.

Furthermore, the said radius of curvature range may according to the invention include a radius of curvature being smaller than the final radius of curvature as well as a radius of curvature exceeding said final radius of curvature.

Prior to the sintering, the superconducting tape may according to the invention be provided with one or more bending radii, whereby said tape does not brittle when it is placed in the application in question after the sintering.

Brief Description of the Drawings The invention is explained in greater detail below with reference to the accompanying drawings, in which

Fig. 1 illustrates a superconducting tape wound into a so-called "pancake shape" for the sintering,

Fig. 2 illustrates the sintered tape wound on a coil holder, and

Fig. 3 shows the maximum strain in a superconducting tape versus an amendment of the radius of curvature for two different values of the initial radius of curvature.

Best Mode for Carrying Out the Invention

The known "React and Wind" method involves a winding of the tape so as to allow the tape to be placed in an oven for an annealing of the superconducting material. It is, of course, not possible to place several km of tape in an oven without said tape being wound up. Such a wound up tape is ordinarily called a "pancake-shaped" superconducting tape. Such pancake-shaped tapes are for instance described in EP 0631331 in the name of Sumitomo Electric Industries. Such a wound up tape is encumbered with the draw-back that microcracks can arise in the superconducting material in case said material is bent too much or if said material is subjected to a too extensive deformation. The inventors have tried to map these circumstances, and Fig. 3 illustrates the strain versus the radius of curvature of two different initial radii of curvature. It appears that it is much easier to increase the radius of curvature without involving a too extensive strain than to reduce said radius of curvature. When a strain of for instance 0.40% , viz. a critical strain, is acceptable, the possible range of radius of curvature without exceeding the superconducting properties can be deduced from the graph with the initial radius of curvature in question. Sometimes a critical strain of up to 1 % is acceptable, cf. US-PS No. 5,531 ,015. According to the present invention the superconducting tape is provided with a radius of curvature, viz. is subjected to a deformation, prior to the annealing, and within the range appearing from Fig. 3 this radius of curvature is close to the final radius of curvature, viz. the resulting deformation. The radius of curvature can be slightly smaller or slightly larger than the final radius of curvature. In this manner it is possible to avoid a deformation of the tape to such an extent that microcracks arise during the following placing of said superconducting tape on for instance a mandrel, viz. a coil holder, with intermediate layers of insulating material, i.e. without being subjected to a strain beyond the range of the radius of curvature. In addition, the advan- tage is obtained that it is possible to use a mandrel and intermediate insulating material not tolerating the high sintering temperatures of typically 900 °C. In other words a free choice applies with respect to the material used for the mandrel and the insulating layers, which in practice turned out to be a vital factor.

However, during the manufacturing process it is important that a predetermined operating margin applies to the radius of curvature of the superconducting tape, and it is thanks to the inventor that these margins have now been mapped and quantified, cf. Fig. 3.

It appears furthermore from the curve of Fig. 3 that the initial radius of curvature should rather be too small than too large because it is much easier to carry out a strain than to carry out a further bending. However, with respect to the handling it is an advantage that it is possible to subject the tape to a strain.

In general, the superconducting tape can be wound with a radius of curvature implying that the tape brittles when it is subjected to a strain after the sintering, and according to a particular embodiment the superconducting tape is provided with one or several bending radii, whereby it does not brittle when it is placed in the application after said sintering. The tape is preferably a multi-filament tape because such tapes are more tolerant to bending than the mono-filament tapes.