Soldered superconductor with hard insulation
A method for the fabrication of an insulated solder bonded multifilamentary superconducting wire composite. An uninsulated wire composite is prepared by using a high melting point solder to join a multifilamentary superconducting composite to a solderable metallic component. A polymer insulation film coating is then applied on top of the wire composite, and the resulting assembly is subjected to heating in a furnace at furnace temperatures and for a period sufficient to cure the insulation but insufficient to melt the solder.
1 . A method for the fabrication of an insulated solder bonded multifilamentary superconducting wire composite, comprising the steps of:
(a) creating an uninsulated wire composite by using a high melting point solder to join a multifilamentary superconducting composite to a solderable metallic component;
(b) applying a polymer insulation film coating on top of the wire composite from step (a); and
(c) subjecting the assembly from step (b) to heating in a furnace at furnace temperatures and for a period sufficient to cure the said insulation but insufficient to melt the said solder.
2 . A method in accordance with claim 1 , wherein the high melting point solder is predominately Sn, with one or more alloying metals selected from the group consisting of Sb, Ag, and Cu.
3 . A method in accordance with claim 2 , wherein the melting point of the solder is above 200° C. and less than 300° C.
4 . A method in accordance with claim 3 , wherein the high melting point solder is Sn 5 wt % Sb.
5 . A method in accordance with claim 1 , wherein the multifilamentary composite comprises Nb—Ti alloy filaments in a copper matrix.
6 . A method in accordance with claim 1 , wherein the multifilamentary composite comprises Nb—Ti alloy filaments in a Cu—Ni alloy matrix.
7 . A method in accordance with claim 1 , wherein the multifilamentary superconducting composite has a round cross-section.
8 . A method in accordance with claim 7 , wherein the soldered composite is made by wrapping Cu strip around a round wire.
9 . A method in accordance with claim 7 , wherein the soldered composite is made by the “wire in channel process” of soldering round wire into a round groove in a generally rectangular shaped channel.
10 . A method in accordance with claim 9 wherein the solderable metallic channel is pure Cu, Cu alloy, or a Cu clad metal.
11 . A method in accordance with claim 1 wherein the multifilamentary superconducting composite has a generally rectangular cross-section.
12 . A method in accordance with claim 11 wherein the soldered composite is made by soldering rectangular (flat) wire to rectangular Cu, Cu alloy, or a Cu clad metal strip.
13 . A method in accordance with claim 1 wherein the polymer coating is a Formvar® (modified polyvinyl acetal resin) varnish insulation.
14 . A method in accordance with claim 1 wherein the polymer coating is selected from the group consisting of epoxy, enamel, nylon or varnish type insulations with a curing temperature of over 300° C.
15 . A method in accordance with claim 1 , where after application of the insulation, the entire composite is drawn and/or shaped into a desired configuration.
16 . A method in accordance with claim 1 wherein the application of the polymer insulation is by extrusion.
17 . A method in accordance with claim 16 , wherein the polymer used is an extrudable one selected from the group consisting of nylon, epoxy, PVC, polyethylene and fluoro-chloro-carbon polymers.
18 . A method in accordance with claim 1 , wherein the surface solder, but not the solder bonding the wire to the channel, is removed prior to application of the insulation by electroplating off the solder.
19 . A method in accordance with claim 1 , wherein the surface solder is roughened by sandblasting, grit blasting, or embossing.