WO2020221634A1

WO2020221634A1 - Apparatus for tape lamination

Info

Publication number: WO2020221634A1
Application number: PCT/EP2020/061190
Authority: WO
Inventors: Thomas Braun; Andre Zimmermann; Michael Baecker; Lukas EWALD; Jan Kunert; Ansgar KAESTNER; Julian FRITZEN
Original assignee: Basf Se
Priority date: 2019-05-02
Filing date: 2020-04-22
Publication date: 2020-11-05

Abstract

The present invention is in the field of apparatuses for tape lamination, in particular for laminating superconductor tapes. The apparatus for laminating tapes comprises a solder bath, a first alignment unit containing slits having different widths to align the tapes separately and a second alignment unit containing a slit to bring the tapes in contact to each other.

Description

Apparatus for Tape Lamination

Description

The present invention is in the field of apparatuses for tape lamination, in particular for laminat ing superconductor tapes.

Laminates containing several tapes of different materials are widely used in different technology areas. One example is superconductor tapes of the second generation. The superconducting material is usually deposited onto a metal tape which is then sandwiched between conductive tapes, such as copper tapes, held together by a solder, as for example disclosed in

WO 01 / 08 234 A2. Apparatuses for laminating tapes together are known from prior art.

US 5 121 869 discloses an apparatus for laminating tapes by bringing the tapes in contact to each other within a solder bath. However, the apparatus only yields laminates with high preci sion if the individual tapes have the same width. In particular for superconductors, the central tape is often narrower than the outer ones and it is important that the central one is precisely aligned central to the outer tapes to avoid damages, for example by ingression of cryogenic agent, such as liquid nitrogen, at the sides.

It was therefore an object of the present invention to provide an apparatus which can laminate tapes of different width with high alignment precision. The apparatus was aimed to be suitable for producing laminate at high speed without compromising the precision of the laminate. It was further aimed at an apparatus which is flexible and allows different lamination geometries. It should be possible to adapt the apparatus to different geometries with little effort, i.e. short down times. Furthermore, the apparatus should cause as little damage to the tapes as possible, even if the tapes are very sensitive.

These objects were achieved by an apparatus for laminating tapes comprising

a solder bath,

a first alignment unit containing slits having different widths to align the tapes separately and a second alignment unit containing a slit to bring the tapes in contact to each other.

The present invention further relates to a process for laminating tapes comprising

separating the tapes by a first alignment unit containing slits having different widths,

moving the tapes through a solder bath and

bringing the tapes in contact to each other by a second alignment unit containing a slit.

Preferred embodiments of the present invention can be found in the description and the claims. Combinations of different embodiments fall within the scope of the present invention.

According to the present invention, the apparatus comprises a solder bath. A solder bath in the context of the present invention is any container which can be filled with liquid solder. The sol der bath should withstand the solder thermally, chemically, and metallurgical^. Therefore, the solder bath is typically of robust materials, for example titanium or nitrogenated steel. According to the present invention, the apparatus comprises a first alignment unit containing slits to align the tapes separately. This means that the alignment unit contains one slit for each tape, for example 2 to 10 slits, preferably 3 to 5 slits. If one tape is placed in each of the slits, the tapes are spatially separated directly before and after the alignment unit. The slit has a form which resembles the tape, typically rectangular in cross-section. Preferably, edges around the slit are rounded such that the tape is less likely damaged.

The width of the slits is chosen to match the width of the corresponding tape, which preferably means that the slit is 5 to 200 pm wider than the width of the corresponding tape, more prefera bly 10 to 150 pm, in particular 20 to 100 pm, for example 50 pm. The slits can have various widths, for example 1 to 500 mm, preferably 2 to 100 mm, in particular 3 to 25 mm. According to the present invention, the slits have different widths. If the alignment unit contains more than two slits, this means that at least one slit has a different width than the other slits which can have the same or different widths. Preferably, the widths of the narrowest slit is 1 to 50 % less than the width of the widest slit, more preferably 5 to 35 %, in particular 10 to 25 %.

The height of the slit is preferably significantly more than the thickness of the tape, for example 3 to 10 times the thickness of the tape. The slits can have various heights depending on the thickness of the tape, for example 0.1 to 10 mm, preferably 0.5 to 5 mm, in particular 1 to 2 mm. The additional space above and below the tape in the slit is typically filled with solder during operation such that the tape moves with very low friction through the slit on a cushion of liquid solder. The slits in the first aligning unit are spaced apart far enough to allow for a stable sepa ration, but close enough together to minimize bending of any tape in the solder bath. Preferably, two neighboring slits are separated by a distance of 1 to 10 mm, in particular 2 to 5 mm, for ex ample 3 mm.

According to the present invention, the apparatus comprises a second alignment unit containing a slit to bring the tapes in contact to each other. In the context of the present invention, two tapes are in contact to each other if there is only a thin solder film between them which remains after applying a gentle force. Typically, this solder film has a thickness of 0.1 to 50 pm, prefera bly 0.5 to 20 pm, such as 2 to 5 pm. The slit has a form which resembles the stack of tapes, typically rectangular in cross-section. Preferably, edges around the slit are slightly rounded such that the stack of tapes is less likely damaged. The width of the slit is chosen to match the width of the widest tape, which preferably means that the slit is 5 to 200 pm wider than the width of the widest tape, more preferably 10 to 150 pm, in particular 20 to 100 pm, for example 50 pm. The slit can have various widths, for example 1 to 500 mm, preferably 2 to 100 mm, in particular 3 to 25 mm. The height of the slit is preferably significantly more than the thickness of the stack of tapes, for example 3 to 10 times the thickness of the stack of tapes. The slits can have vari ous heights depending on the thickness of the tapes, for example 0.1 to 10 mm, preferably 0.5 to 5 mm, in particular 1 to 2 mm.

The first and the second aligning units are arranged relative to each other in a way that the tapes experience a minimum bending. This is usually achieved by arranging them such that the central-most tape is not bent at all, i.e. follows a straight line through the first and the second aligning unit. The other tapes are slightly bent as a consequence of the fact that they are sepa rated from each other in the first aligning unit and come in contact to each other in the second alignment unit. The bending typically occurs around the aligning units. The bending radius should be as large as possible to avoid damages such as cracks. The bending radius can be decreased by increasing the distance between the first and the second aligning unit, by de creasing the distance between the tapes in the first aligning unit as well as the geometry of the aligning units. These can, for example, be rounded where the bending of the tape occurs. Pref erably, the bending radius of the tapes is 0.25 to 10 mm, in particular 0.5 to 5 mm. The angle between two tapes coming in contact at an aligning unit should be small, preferably less than 20°, more preferably less than 10°, more preferably less than 5°, in particular less than 3°.

Preferably, the first and the second aligning units are placed apart from each other by at least half the size of the solder bath with respect to the moving direction of the tape, more preferably at least 70 % of the size of the solder bath, in particular at least 90 % of the size of the solder bath. The distance between the first and the second aligning unit can be 5 to 100 cm, more preferably 10 to 50 cm. In particular, the first aligning unit is integrated into one wall of the sol der bath and the second aligning unit is integrated into an opposite wall of the solder bath. This ensures optimum wetting of the tapes with solder.

The first and the second aligning units are generally made of a material which withstands the temperature and the chemical composition of typical solders, which means in particular that nothing of the material should dissolve into the solder. Examples for suitable materials are tita nium or nitrogenated steel. Preferably, at least one of the first and the second aligning unit con tain a stack of individual pieces having recesses forming the slits, more preferably both the first and the second aligning unit contain a stack of individual pieces having recesses forming the slits. Figure 3 shows an example for a first aligning unit which separates three tapes, wherein the central tape is narrower than the outer tapes. The aligning unit is shown from a perspective with a viewing direction along the moving direction of the tapes. The four pieces (21 1 , 212, 213, 214) each have recesses which mutually form the slits (215, 216, 217). The pieces can be held together for example by screws, bolts, clamps or a guiding rail. An aligning unit containing sepa rate pieces has the advantage that the aligning unit can easily be adapted to different geome tries, i.e. different numbers of tapes and different widths, by simply stacking the required pieces. Also, it is easier to produce each piece separately rather than the whole aligning unit in one piece. In addition, the tapes can be mounted more easily into the aligning unit with potentially less damage to the tapes.

In order to achieve best results, the first and the second aligning unit need to be exactly kept in place. Preferably, the first and the second aligning unit are fixed by a plate which is placed above the solder bath. This has the advantage that the plate remains at about room tempera ture independent of the temperature of the solder bath, which may be adjusted to a certain sol der material or the desired process conditions. Hence, any thermal expansion which changes the relative position and orientation of the first and the second aligning unit relative to each oth er is minimized.

Preferably, the apparatus comprises a third aligning unit in between the first and the second aligning unit. A third aligning unit is particularly useful if more than one narrower tapes are lami nated between wider tapes. In this case, the narrower tapes can be brought in precise contact to each other by the third aligning unit while the wider tapes are separated and only brought in contact to the narrower tapes in the second aligning unit. Therefore, the third aligning unit pref erably contains fewer slits than the first aligning unit and more slits than the second aligning unit. The shorter the distance is between the third and the second aligning unit the lower is the probability that the tapes slip away from their desired position while at the same time the wetting of the tapes by solder is unaffected. Preferably, the distance between the third aligning unit and the second aligning unit is smaller than the distance between the third aligning unit and the first aligning unit. More preferably, the distance between the third aligning unit the second aligning unit is less than half the distance between the third aligning unit and the first aligning unit.

Preferably, the apparatus comprises a second solder bath. The second solder bath is preferably arranged beneath the first solder bath. Preferably, the apparatus further comprises a pump to pump liquid solder from the second solder bath to the first solder bath. In this way, solder can flow from the first solder bath through the aligning units, exit the first solder bath and flow to the second solder bath. From there, the pump pumps the solder up to the first solder bath. This has the advantage that the solder is distributed very evenly between the tapes to be laminated and friction between any tape and parts of the apparatus is reduced.

Preferably, the apparatus comprises a housing means to fill the housing with an inert gas, such as nitrogen or argon. This avoids chemical reaction of the liquid solder with oxygen forming side products which deteriorate the laminate need to be removed. More preferably, the apparatus comprises a housing adapted to contain an inert gas at an elevated temperature.

The tapes can be moved through the apparatus according to the present invention by various ways. Preferably, the apparatus comprises a supply spool for each tape to be laminated and a receiver spool to collect the laminated tape. Preferably, the apparatus comprises a strain con troller for each spool in order to maintain a constant stain on each tape. The apparatus is pref erably adapted to move the tapes at a speed of 0.05 to 2 m/s, more preferably 0.1 to 0.5 m/s through the solder bath. The spools should have a sufficient radius such that bending of the tapes does not cause any damage. Preferably, the supply spools exert bending on the tapes at a bending radius of at least 25 mm, more preferably at least 50 mm. As the laminate are gener ally more sensitive towards bending, the receiver spools exert bending on the laminates at a bending radius of at least 80 mm, more preferably at least 150 mm, in particular at least 250 mm.

Preferably, the apparatus further comprises a stripper to remove excess solder from the lami nate. Preferably, the stripper contains two dies with a low-friction material on their surface, for example PTFE (Teflon^®). The dies can be pressed onto the laminate by a certain set pressure, preferably 0.05 to 0.5 N/mm². Preferably, the apparatus further contains means to keep the lam inate at a temperature above the melting point of the solder between the second aligning unit and the stripper, for example a fan blowing hot air or nitrogen onto the laminate and the dies.

Preferably, the apparatus further comprises a cooling section for solidifying the solder in the laminate. Typically, the lower the temperature is in the cooling section the faster the apparatus can operate. Preferably the cooling section is capable of blowing nitrogen at a temperature slightly above the boiling point of nitrogen at ambient pressure. This can, for example, be achieved by expanding nitrogen from a gas container or by using nitrogen which just evapo rated from a liquid nitrogen bath.

Preferably, the apparatus further comprises a coating section for coating the tape with a flux agent. Typically, the coating section contains a bath or a spray unit for the flux agent and a dry ing section. Preferably, the apparatus comprises one coating section for each tape. Figure 1 illustrates an example of an apparatus adapted to laminate three tapes. The supply spools (11 , 12, 13) provide the tapes which are aligned to each other by the first aligning unit

(21) which is integrated into the side wall of the solder bath (31). The second aligning unit (22) is integrated into an opposite side wall of the solder bath (31) and brings the tapes in contact to each other. The first aligning unit (21) and the second aligning unit (22) are kept in place by a plate (25) outside the solder bath (31). Beneath the solder bath (31), there is a second solder bath (32). A pump (33) pumps solder from the second solder bath (32) to solder bath (31). The solder flows towards the first aligning unit (21) and the second aligning unit (22), exits through the aligning units (21 , 22) and flows into the second solder bath (32). A stripper (41) removes excess solder from the laminate and the cooling section (42) cools the laminate below the melt ing point of the solder. The receiver spool (15) collects the finished laminate.

Figure 2 illustrates an example of an apparatus adapted to laminate four tapes. The supply spools (11 , 12, 13, 14) provide the tapes which are aligned to each other by the first aligning unit (21) which is part of the side wall of the solder bath (31). A third aligning unit (23) brings together the two central tapes while keeping the outer tapes separate. The second aligning unit

(22) finally brings them in contact to the central tapes. The first aligning unit (21), the second aligning unit (22) and a third aligning unit (23) are kept in place by a plate (25) outside the sol der bath (31). Beneath the solder bath (31), there is a second solder bath (32). A pump (33) pumps solder from the second solder bath (32) to the solder bath (31). The solder flows towards the first aligning unit (21) and the second aligning unit (22), exits through the aligning units (21 , 22) and flows into the second solder bath (32). A stripper (41) removes excess solder from the laminate and the cooling section (42) cools the laminate below the melting point of the solder. The receiver spool (15) collects the finished laminate.

The apparatus according to the present invention is well suitable for laminating tapes. There fore, the present invention also relates to a process for laminating tapes. The description of the apparatus and the preferred embodiments also apply to the process.

Preferably, the process comprises laminating at least one metal tapes onto at least one super conductor tapes, for example two metal tapes onto one superconductor tape. The metal tapes can contain copper, bronze, brass, or stainless steel. The superconductor tape can contain a substrate, for example a nickel substrate with cubic texture, one or two ceramic buffer layers, a layer containing REBa2Cu3C>7-_x, wherein RE stand for one or more than one rare earth metals, and a layer containing silver. Details of a superconductor tape and the way it is produced are for example disclosed in WO 2016 / 150 781 A1. Preferably, the metal tapes and the superconduc tor tapes have a width of 2 to 100 mm, more preferably 3 to 25 mm. Preferably, the metal tapes and the superconductor tapes have a thickness of 0.01 to 1 mm, more preferably 0.03 to 0.15 mm. Preferably, the superconductor tapes are narrower than the metal tapes, preferably 0.1 to 5 mm narrower, more preferably 0.2 to 3 mm narrower.

Preferably, the two outermost tapes have the same width, more preferably, the two outermost tapes have the same width which is wider than the width of the remaining tapes.

The solder bath contains a solder above its melting temperature. Preferably, the solder layer has an electric conductivity of at least 10² S/m, more preferably at least 10³ S/m, in particular at least 10⁴ S/m. Typical solder materials can be used, preferably tin or indium alloys such as Sn- Pb, Sn-Ag, Sn-Cu, Sn-Bi, Sn-Ag-Cu, Sn-Ag-Bi, In-Sn, In-Ag, In-Pb, In-Pb-Ag. Examples are 60 wt.-% Sn - 40 wt.-% Pb or 52 wt.-% In - 48 wt.-% Sn. Preferably, the solder layer contains silver, more preferably the solder layer contains 0.4 to 4 wt.-% Ag. The melting point of the sol- der is preferably not more than 300 °C, more preferably not more than 250 °C, in particular not more than 220 °C.

The process of the present invention can comprise the step of moving the tapes through a sol der bath once. This is useful if all tapes should be soldered together with the same solder com- position. It is also possible that the process comprises the step of moving the tapes through a solder bath more than once, for example twice or three times. Preferably, each time the tapes are moved through the solder bath, the solder bath contains a different solder composition. As an example, two tapes are moved through a solder bath containing a solder with a high melting point. This laminate is then once again moved through a solder bath containing a solder with a lower melting point and brought in contact with further tapes to build up a more complex lami nate.

Claims

1. An apparatus for laminating tapes comprising

a solder bath,

a first alignment unit containing slits having different widths to align the tapes separately and

a second alignment unit containing a slit to bring the tapes in contact to each other.

2. The apparatus according to claim 1 , wherein the angle between two tapes coming in con tact at an aligning unit is less than 10°.

3. The apparatus according to claim 1 or 2, wherein the apparatus comprises a housing means to fill the housing with an inert gas.

4. The apparatus according to any of the claims 1 to 3, wherein at least one of the first and the second aligning unit contain a stack of individual pieces having recesses forming the slits.

5. The apparatus according to any of the claims 1 to 4, wherein the first and the second aligning unit are fixed by a plate which is placed above the solder bath.

6. The apparatus according to any of the claims 1 to 5, wherein the first and the second aligning units are placed apart from each other by at least half the size of the solder bath with respect to the moving direction of the tape

7. The apparatus according to any of the claims 1 to 6, wherein the apparatus comprises a third aligning unit in between the first and the second aligning unit.

8. The apparatus according to claim 7, wherein the distance between the third aligning unit and the second aligning unit is less than half the distance between the third aligning unit and the first aligning unit.

9. The apparatus according to any of the claims 1 to 8, wherein the apparatus comprises a supply spool for each tape to be laminated and a receiver spool to collect the laminated tape.

10. The apparatus according to any of the claims 1 to 9, wherein the apparatus comprises a stripper containing two dies to remove excess solder from the laminate.

11. A process for laminating tapes comprising

separating the tapes by a first alignment unit containing slits having different widths, moving the tapes through a solder bath and

12. The process according to claim 11 , wherein the process comprises laminating two metal tapes onto one or two superconductor tapes.

13. The process according to claim 12, wherein the superconductor tape is 0.2 to 3 m nar rower than the metal tapes.

14. The process according to claim any of the claims 11 to 13, wherein the superconductor tape contains a substrate, a ceramic buffer layer, a layer containing REBa2Cu3C>7-_x, where in RE stand for one or more than one rare earth metals, and a layer containing silver.

15. The process according to claim any of the claims 11 to 14, wherein the solder bath con tains a solder containing silver.