In the manufacture of superconducting conductor lengths, tubes of a metallic base material are often used, which tubes are filled with a superconducting powder material such as a ceramic powder that may, following a given process, be formed to constitute a core of superconduct- ing material in the metallic tube. As a part of the manu- facturing process, deformation of the metallic tube is often effected to obtain a tape or a thin wire, ia with a view to obtaining adequate density, and that the individ- ual grains in the superconducting powder material are orientated such as to allow optimal utilisation of the superconducting properties of the powder material.

Tests have shown that in the production of short lengths of superconducting conductor lengths, such deformation yields the optimal effect provided the superconducting conductor length is subjected to a substantially planar pressing influence by a press piston intended therefor, since this does not to a significant extent cause unde- sired material shifting in the conductor length during the pressing operation.

However, a problem encountered in connection with the planar pressing arises when the conductor length has such length that it cannot be pressed in one single pressing operation which means that individual sections of said

conductor length have to be subjected successive pressing operations. This causes undesirable edge effects in those areas of conductor length that are situated at the edge of the press piston, which edge effects may result in re- duced superconducting properties.

In order to reduce or avoid such undesired edge effects, an apparatus has been developed which, in stead of using a planar piston as described above, uses a piston having a curved piston surface with a vary large radius of cur- vature, and which, by use of a drive mechanism intended therefor, is caused to follow a movement which takes the piston surface across the conductor length in a stepwise process. Use of this apparatus reduces the undesired edge effects while simultaneously a deformation process with substantially planar pressing is accomplished.

However, it is a drawback of the above-described proc- esses that they do particularly readily lend themselves for use in the production of long superconductor lengths, the course of the process being - as described - discon- tinuous.

Therefore, today's efforts are aimed at utilising conven- tional rollers for the rolling of the superconducting conductor lengths as described in the introductory part.

Since a continuously running deformation of the conductor length is hereby accomplished, a process obviously re- sults which is more suitable for large-scale production of long conductor lengths compared to the processes de- scribed above.

However, practice has shown that this rolling process may result in an uneven distribution of the superconducting powder in the longitudinal direction of the conductor length, since - in some cases, and in particular in case

of relatively large tube diameters - the superconducting powder material has a propensity to being distributed such that alternately a large amount and very little pow- der material is found along the conductor length, despite the fact that the outer cross section of the conductor length is completely uniform throughout the entire length of the conductor. This adverse effect is designated by the technical term "sausaging", since in principle the superconducting material is distributed like in a series of sausages. Of course, apart from such uneven distribu- tion of superconducting material resulting per se in re- duced power capacity, this undesired effect may ia also mean that the orientation of the individual grains in the powder material is not nearly to the same extent the same, which further reduces the power capacity of the conductor and deteriorates its mechanical strength.

In the light of this it is the object of the present in- vention to provide a method of manufacturing supercon- ducting conductor lengths whereby the conductor lengths can be worked in a continuous rolling process in a given roller apparatus, said process simultaneously yielding superconducting conductor lengths with improved supercon- ducting properties.

This is obtained by the method according to claim 1. The use of at least two annular or tubular roller bodies, and the two annular or tubular roller bodies being pressed against each other by means of a pressure device intended therefor which abuts on respective tracks arranged on each their roller body, said pressure device being con- figured and arranged in such a manner that it touches the roller bodies only along a fraction of the track, means that, other things being equal, a relatively large radius curvature is obtained compared to a conventional roller

device of the same dimensions as the one described herein.

Hereby a deformation process is obtained which is con- tinuous and comparable to a planar pressing, since a uni- form cross section can hereby be obtained as well as an even distribution of the materials throughout the conduc- tor length. It should be noted that this is obtained en- tirely without the occurrence of edge effects of the kind described above in connection with other, discontinuous deformation processes.

Compared to a conventional roller device with massive rollers, the roller device described herein is flexible with regard to effective roller radius. Large radius modifications of up to above factor-three radius modifi- cations can be obtained simply by exchanging the annular rollers. In a conventional roller apparatus, such modifi- cation would entail significant structural modifications.

Small modifications in the roller radius can be obtained by deforming the annular rollers elastically to accom- plish an elliptic shape. This can be obtained by mounting additional rollers, cf Figure 3. This is not an option in a conventional roller apparatus.

It is a further advantage of an annular roller system that it is possible to modify the rigidity of the system by the choice of material for either the annular rollers or the pressure device by which the roller effect is ac- complished.

The rigidity of the annular roller system described herein can also be increased far more than a conventional roller apparatus having the same roller radius. This is due to the substantially reduced distance between the two

pressure devices by which the roller effect is accom- plished.

Tests in practice have thus yielded good results with an- nular rollers having an outer diameter at the roller sur- face plane of more than 200 mm with rollers that have been considerably smaller than the diameter.

According to a preferred embodiment, the pressure device used is at least one roller which abuts on the track, and wherein the track faces towards the axes of rotation of the roller bodies.

In this context, at least one pressure device is particu- larly advantageously operated with a view to rotating the roller body which is in abutment on the pressure device, since the pressure device hereby also serves as operating wheel for the annular or tubular roller body.

According to the invention, the pressure devices can be arranged in different manners in accordance with the track on the annular or tubular roller bodies. However, particularly advantageously one pressure device is used for each roller body, said pressure device being arranged to be in abutment on the track on the roller body at that level of the roller surface plane which abuts on the su- perconducting conductor section during the rolling proc- ess proper. This enables use of a conventional roller ap- paratus that can readily be adapted for use in connection with the annular or tubular rollers.

Furthermore, the invention relates to a roller apparatus which is particularly suitable for rolling elements of even thickness and which is thus particularly suitable for use in the above described method wherein the roller apparatus comprises two roller bodies that are arranged

opposite each other whereby the roller bodies form op- posed roller surface planes, and wherein the two roller bodies are driven around in such a manner that the ele- ment to be rolled is drawn in between the roller surface planes by the friction generated between the element to be rolled and the roller surface planes.

GB patent No 1 251 916 discloses a roller arrangement for rolling elements of varying thickness. This roller device uses roller rings with a roller surface plane which is excentric relative to the point of rotation of the roller ring which disqualifies such arrangement for rolling ele- ments of even thickness.

It is a problem with known roller arrangements for roll- ing elements of even thickness that it is relatively dif- ficult in connection with eg the rolling of superconduc- tors of the above-described type to simultaneously obtain a large rolling diameter and a high abutment pressure without this having adverse effects in the form of unde- sired deformations in the roller. The undesired deforma- tions in the roller can thus be in the form of flexing of a relatively wide roller whereby there is a risk that the roller surface planes meet before a satisfactory roller pressure is obtained, or in case of relatively short, substantially disc-shaped rollers where there is a risk that the roller flexes sideways and out of the disc plane. This is inexpedient since it renders control of the rolling process more difficult, and in particular it may result in an uneven thickness being imparted to the element being rolled at the two side edges of the rolled conductor.

This problem has been solved by the present invention in that the roller bodies according to the invention com- prise at least two annular or tubular roller bodies of

substantially even thickness; and wherein the annular or tubular roller bodies are further provided with surface planes that form a track which is concentric relative to the roller surface plane; and wherein the roller appara- tus has a pressure device which is intended for abutment on the track in such a manner that the roller surface planes are pressed towards each other; and wherein the pressure device is configured and arranged in such a man- ner that the pressure device is in abutment on only a fraction of the track on the annular or tubular rollers.

Hereby rollers can be used the length of which is very short while, simultaneously, very large rolling diameters are obtained; and wherein the distance from the centre of the operating shaft may still be substantially smaller than the radius of the roller body. Since far more rigid- ity is hereby obtained with regard to undesired deforma- tions in the roller proper, a more even distribution of the material in the finished superconductor is hereby ob- tained.

Furthermore, it is also accomplished with the present in- vention that roller bodies can readily be exchanged in the roller apparatus with a view to rolling with differ- ent diameters, the nature of surfaces, etc, while simul- taneously enabling ready use of conventional roller appa- ratuses in such rolling processes, despite the fact that such roller apparatuses are usually provided with rollers having relatively small diameters and are structurally modified or adjusted only with difficulty to rolling with rollers having relatively large diameters. As it is, ex- change of the annular or tubular roller bodies can often be carried out without necessitating adjustment of the roller apparatus.

According to a particularly preferred embodiment, the roller apparatus can be configured such that the annular or tubular roller bodies have an outer diameter at the roller surface plane which is at least three times larger than the width of the roller surface plane. Hereby the roller apparatus provides the advantages obtained with long roller bodies as well as short disc-shaped roller bodies, and this is obtained without the above-mentioned drawbacks of these roller types.

Moreover, the annular or tubular roller device can have an outer diameter at the roller surface plane which is at least three times larger than the outer diameter of the pressure device.

The invention will now be described in further detail with reference to the drawings, wherein: Figure 1 is an explanatory sketch of a roller device ac- cording to the invention, seen in a lateral view; Figure 2 is an explanatory sketch of the roller device shown in Figure 1, seen in a front view; Figure 3 is an explanatory sketch showing an alternative embodiment of the invention Thus, Figure 1 illustrates a roller apparatus 1, said roller apparatus 1 consisting of a motor housing 2 in which a motor is arranged for driving the functions of the roller apparatus 1.

Additionally, the roller apparatus comprises a gear hous- ing 3 in which a gear is located which is operated by the motor in the motor housing 2 and thus drives two driving shafts 4,5 around. The driving shafts are connected to

two rolls 6,7 that are rotatably embedded about the axes of symmetry 19,20 in two frame parts 8,9 that are perma- nently mounted on the roller apparatus 1.

The above-mentioned structure corresponds essentially to the principle of a conventional roller apparatus and therefore these parts are not shown in detail. In accor- dance with the invention, an upper and a lower annular roller body 10,11 are also shown, in sectional views, these roller bodies being circular and having the axes of symmetry designated by the reference numerals 12 and 13.

The annular roller bodies thus extend around the rolls 6,7, and the annular roller bodies have tracks 14,15 at their internal periphery whereby the rollers 6,7 will, when driven round via driving shafts 4,5, be caused to abut on the tracks 14,15 provided an element to be rolled is introduced between the roller surface planes 17,18 that delimit the area 16.

In this manner it is accomplished that there is a very small distance between the roller surface planes 17 and 18 and the axes of symmetry 19,20 for the rolls 6,7 rela- tive to the diameters of the annular roller bodies 10,11 while it is simultaneously enabled that very short, annu- lar rollers can be used without significant risk of ad- verse deformations in the roller bodies in case of ele- vated roller pressures.

Now, Figure 2 illustrates the same roller arrangement as in Figure 1, only in a front view, from which it will ap- pear that in this embodiment only one roll 6,7 is ar- ranged for each of the annular roller bodies 10,11. This configuration is particularly convenient since it allows for the use of an entirely conventional roller apparatus 1 which can, without structural modifications, be pro- vided with the two annular roller bodies 10,11. It will

be understood from this that the rolls 6,7 can be conven- tional rollers and that the tracks 14,15 on the annular roller bodies 10,11 can be substantially smooth surfaces.

It should be noted that, in accordance with the present invention, a conventional roller apparatus which has been provided with annular roller bodies 10,11 retains its usual options for adjustment, in particular with regard to regulating the distance between the roller surface planes, substantially without limitations.

It will be obvious for the person skilled in the art that the rolls 6,7 can be provided with eg toothed wheels or other driving wheels provided the tracks 14,15 on the an- nular roller bodies are provided with suitable surfaces for abutment on the rolls 6,7.

Now, Figure 3 illustrates an alternative embodiment in which several rolls 6,7,6a,7a are arranged at each of the annular roller bodies 10,11. However, this presupposes a modification of a conventional roller apparatus which is, of course, to be provided with suitable journalling means for the extra rolls.

With the embodiment shown in Figure 3 it is obtained that the annular roller bodies 10,11 are to a higher degree fixed in their position during the rolling process com- pared to the embodiment shown in Figure 2. Thus a more uniform rolling of eg a superconductor is obtained de- spite variations in the process due to eg unevenness in the dimensions of the element to be rolled which may en- tail unevenness in the roller pressure.

Moreover, it is obvious for the person skilled in the art to arrange several rolls with a view to pressing the an- nular roller body towards the element to be rolled, or with a view to driving the annular roller body around, or to support this. Besides, it is obvious that separate rolls can be arranged with a view to driving the annular roller bodies around with a view to pressing them towards the element to be rolled.

It will also be obvious for the skilled person to suggest other locations for the individual rolls as well as for the track on the annular roller bodies.