Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F6/00—Superconducting magnets; Superconducting coils
  • H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
  • H01F41/12—Insulating of windings
  • H01F41/122—Insulating between turns or between winding layers

Definitions

• the invention relates to a method for fixing the windings of a superconducting magnetic winding, which is initially built up from preliminary conductor products and in which the superconducting properties are generated by reaction annealing of the finished winding.
• Superconducting intermetallic compounds with an A15 crystal structure such as the two-component compounds Nb 3 Sn and V 3 Ga or the ternary compound Nb 3 Al 0.8 Ge 0.2 , have good superconducting properties and are distinguished by high critical values, ie due to a high transition temperature, a high critical current density and a high critical magnetic field.
• the superconducting intermetallic compounds are generally very brittle, so that their preparation in a form suitable for magnetic coils is difficult.
• the general procedure today is that a rod or wire made of the higher-melting element of the connection is first provided with a shell made of an alloy which consists of a carrier metal and the lower-melting element of the connection or, if appropriate, several such elements.
• a niobium wire is surrounded by a sheath made of Cu-tin bronze.
• a large number of these covered wires are then combined into a bundle.
• a wire or a strip of an alloy matrix is thus obtained, in which a multiplicity of thread-shaped cores from the higher-melting element of the connection is embedded, for example a copper-tin wire with a large number of embedded niobium filaments.
• a preliminary conductor product is then subjected to an annealing treatment in which the element or elements of the compound contained in the matrix diffuse into the cores of the higher-melting element and react with it to form the intermetallic compound (see, for example, DE-OS 20 44 660).
• Superconducting magnetic coils from such superconductors have hitherto generally been produced by two different processes (cf. e.g. DE-OS 28 37 199 and 28 40 526).
• the preliminary conductor product is wound onto a provisional winding body and then annealed to form the desired superconducting compound.
• the superconductor produced in this way is unwound again from the provisional winding body and can then be wound, for example, into a magnetic coil.
• the high brittleness of the superconducting intermetallic compounds there is a risk that cracks will occur in the intermetallic superconducting compounds due to inadvertent falling below the bending radius permissible for the completely reacted conductor and the superconducting properties will be impaired accordingly.
• the coil body of the magnet to be provided with the winding is wound with the as yet unreacted conductor preliminary product and the entire magnet thus wound is then subjected to diffusion annealing.
• the diffusion annealing is also called “in situ annealing”. This procedure avoids all difficulties in processing a brittle conductor material.
• diffusion annealing The materials present in the coil can withstand the required high temperatures for several hours, for example in the case of Nb 3 Sn around 700 ° C.
• the conductor pre-product wrapped or wound with an insulation made of glass, ceramic or quartz threads has been wound onto a correspondingly high-temperature-resistant coil body and the coil windings are finally fixed only after the diffusion annealing, by covering the finished winding with suitable curable or solidifying organic materials upon cooling , for example epoxy resins or paraffin, preferably impregnated by vacuum impregnation (cf. DE-OS 25 46 198 and 28 37 199).
• the object of the invention is to further improve the production of superconducting magnetic windings, the superconducting properties of which are generated by reaction annealing (in-situ annealing) of the finished winding.
• the method according to the invention leads to a fixed fixation of the individual turns of the coil winding even before the reaction annealing and thus avoids the shape and position changes occurring in unfixed turns due to the thermal expansion or contraction and their disadvantageous consequences. Furthermore, it has been shown that the formation of carbon bridges is also avoided by the putty introduced into the winding. It is therefore no longer necessary to remove the sizes or the binders of the insulation materials from the winding before the annealing treatment.
• Suitable putties are inorganic materials which, if necessary after prior mixing with water or other suitable inorganic liquids, can be hardened or otherwise harden or solidify and in the solidified state both at the high temperatures required for reaction annealing of, for example, about 700 ° C. at Nb 3 Sn as well as at the low temperatures required to bring about the superconducting state, for example the temperature of the liquid helium of 4.2 K, are stable.
• the putties should also have good resistance to temperature changes so that no damage occurs in the winding even when the coil is repeatedly cooled to low temperatures. For similar reasons, the putties should not differ too much from the superconductor material with regard to their thermal expansion. Furthermore, good thermal conductivity of the cement is also advantageous for effective cooling of the coil winding. Unstable connections that release metals during reaction annealing should not be included in the kit, since the insulation of the winding would be impaired by the released metal.
• a putty made from water glass (sodium silicate solution) and talcum (soapstone powder) has proven to be particularly suitable. This putty solidifies into a hard mass made of double silicates, which very well fulfills the aforementioned requirements.
• a mixture of about 60% by weight of water glass and 40% by weight of talcum is preferably used, which can still be processed well even after a long standing time.
• This two-stage heat treatment can be combined with reaction annealing to form a three-stage heat treatment.
• a particularly stable winding structure can be obtained by first applying an insulating mat made of high-temperature resistant material, for example a glass fiber mat, to a high-temperature-resistant coil former, for example made of stainless steel, and then impregnating it with the putty, then applying the successive layers of the conductor winding and in each case with the putty are coated and finally the finished winding is surrounded by another high-temperature-resistant insulating mat, which is also to be impregnated with putty, and finally the putty is cured at elevated temperature.
• further high-temperature-resistant insulating mats can also be inserted between the individual layers of the winding.
• a strip-shaped, 1 mm wide and 0.3 mm thick conductor pre-product made of a copper-tin matrix with 1159 embedded niobium filaments was assumed.
• the preliminary conductor product was provided with a glass fiber covering on which an organic size was applied.
• a water glass-talcum mixture with about 60% by weight of fresh water glass and about 40% by weight of talc was used as the putty. If the water glass remains open for a long time before mixing with the talcum powder, it becomes thinner. It is then advisable to increase the proportion of talcum to increase the viscosity of the putty.
• the bobbin used to wind the bobbin was made of non-magnetic stainless steel and was equipped with two disk-shaped side flanges and a central bore with a diameter of 25 mm.
• the inner winding diameter was 30 mm, the outer winding diameter 50 mm, the winding length 40 mm.
• the coil was first heated to about 37 ° C for a few hours. This is sufficient if the water vapor can escape from the winding, for example through holes provided in the disk-shaped side flanges or in other ways. This drying step prevents cracks from appearing in the putty during subsequent curing.
• the putty was then given the required strength by a second heat treatment at 117 C for several hours.
• the coil was finally wrapped in a serving as a getter and zirconium foil long subjected to about two days under argon, the reaction heat at about 700 0 C.
• the coil was cast with resin in a protective trough. Instead of the casting resin, an inorganic putty can also be used.
• the finished coil was then inserted into the bore of a larger superconducting magnet and tested in its magnetic field. With a magnetic induction of 7 Tesla generated by the outer coil, a magnetic inductor was found in the bore of the inner coil tion of 9 Tesla reached. A training behavior of the coil produced according to the method according to the application could not be determined. In an external field of 2 Tesla, the critical current density was of Nb3Sn conductor of the inner coil about 90 000 A / cm 2, in an external field of 7 Tesla about 45 000 A / cm 2.
• the method according to the application has proven itself in the same way for larger coils of up to 177 mm winding length and 119 mm outer winding diameter.
• the packing density of the winding could be increased even further by omitting the insulating mats between the individual winding layers. In this case, putty is applied to each winding layer and the next winding layer is wound directly over it. However, omitting the layer insulation is only recommended if the actual conductor insulation consists of a fiber wound. If the pre-products for insulation are only wrapped with glass fiber, for example, the insulating mats should be retained to insulate the winding layers from each other.
• the putty applied to the previous winding layer is not sufficient to impregnate the insulating mat, putty is expediently applied to it again before the next winding layer is applied.
• organic binders for example with polyvinyl butyral
• there were no difficulties in the process according to the application there were no difficulties in the process according to the application.
• the thermal decomposition of the polyvinyl butyral during the Heating of the coil for reaction annealing released carbon prevented by the putty from forming conductive bridges between the turns. Carbon-releasing substances therefore do not need to be removed or at least not completely removed before the reaction annealing when winding the coil.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Manufacturing Cores, Coils, And Magnets (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6113026

Family Applications (1)

Country Status (2)

Cited By (2)

Citations (3)

• 1980
  • 1980-09-27 DE DE19803036536 patent/DE3036536A1/de not_active Withdrawn
• 1981
  • 1981-09-14 EP EP81107230A patent/EP0048880B1/fr not_active Expired
  • 1981-09-14 DE DE8181107230T patent/DE3166043D1/de not_active Expired

Patent Citations (4)

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