METHOD FOR JOINING ELECTRICAL CONDUCTORS BY MAGNETOSTRICTION AND MAGNETOSTRICTION-GENERATING DEVICE

- Thales

The invention relates to a method for the joining, to a first conductor that includes a connector, of a second conductor formed by at least one strand made of aluminium or an aluminium alloy and having at least one end, the shape of which allows it to be introduced into the connector of the first conductor. The method has a step of installing the conductors, with the end of the second conductor being inserted into the connector of the first conductor. There is a magnetostriction step which has an electrodynamic force being generated in the connector so that the connector is crushed around the second conductor introduced into the connector. The subject of the invention is also a magnetostriction-generating device. In particular, the invention applies to the connecting-up of energy networks on all (for example, aerospace) carriers and equipment, with high-current and/or long links. The invention may also apply to connections suitable for information transmission on general-purpose conductors.

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Description
RELATED APPLICATIONS

The present application is based on, and claims priority from, French Application Number 06 11261, filed Dec. 22, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a method for joining electrical conductors by magnetostriction and to a magnetostriction-generating device. In particular, the invention applies to the connecting-up of energy networks on all (for example aerospace) carriers and equipment, with high-current and/or long links. The invention may also apply to connections suitable for information transmission on general-purpose conductors.

BACKGROUND OF THE INVENTION

The use of power cables comprising strands made of aluminium or an aluminium alloy has many advantages, especially a significant saving for some applications in terms of weight compared with copper strands. There are for example cables with a so-called sectorial solid core, consisting of three phase conductors, in the form of 120° circular sectors, and a layer of small circular conductors constituting the neutral. Although the manufacture of this type of cable proves to be more expensive, the economic gain is real when the laying and transport costs are taken into account.

It is known to employ on such cables bimetallic end-fittings crimped at their aluminium end. They are then joined to copper cables and other equipment via the copper side of said end-fittings. There are several types of end-fittings, suitable for each case (mid-line tapping, terminations, end-to-end connection, repair, etc.). The joint between the copper part and the aluminium part of the end-fitting is a metallurgical joint, in particular by welding. The joining procedure is the following:

    • after stripping, a tool is used to deform a 120° sector zone into a circular cylinder, the surface alumina layer is removed by vigorous brushing (for example with a metal brush) under neutral grease, this solution being compatible only with a conductor sufficiently solid to withstand such a treatment;
    • once the end-fitting has been slipped onto the conductor, the assembly is subjected to a deep punching operation (penetration of the metal of the end-fitting into the core of the metal of the conductor), creating an air-tight contact.

Although this procedure proves to be satisfactory for large cables, it is not suitable for all cables. In particular, this procedure is ill-suited to multistrand cables. Now, connections on aeronautical or aerospace carriers, in which the criterion of withstanding vibrations is particularly key, require such multistrand cables, especially for their flexibility characteristic.

SUMMARY OF THE INVENTION

One object of the invention is in particular to alleviate the aforementioned drawbacks. For this purpose, one subject of the invention is a method for the joining, to a first conductor that includes a connector, of a second conductor formed by at least one strand made of aluminium or an aluminium alloy and having at least one end, the shape of which allows it to be introduced into the connector of the first conductor. The method comprises at least the following steps:

    • a step of installing the conductors, the end of the second conductor being inserted into the connector of the first conductor; and
    • a magnetostriction step, an electrodynamic force being generated in the connector so that said connector is crushed around the second conductor introduced into the connector.
      Furthermore, the magnetostriction step may comprise:
    • a substep for heating the second conductor and the connector until their plastic deformation point is reached;
    • a substep for thermally stabilizing the second conductor and the connector; and
    • a substep for implementing the electrodynamic effect of the magnetostriction.

The method may also include a step of preparing the two conductors, comprising:

    • a substep in which the second conductor is stripped at its end;
    • a substep in which the stripped part of the second conductor and at least the internal part of the connector of the first conductor are pickled; and
    • a substep in which the stripped part of the second conductor and at least the internal part of the connector are rinsed and then dried.

Advantageously, the step of preparing the two conductors and/or the step of installing the conductors may be carried out in a flow of inert gas.

Another subject of the invention is a magnetostriction-generating device suitable for joining, to a first conductor that includes a connector, a second conductor formed by at least one strand made of aluminium or an aluminium alloy and having at least one end, the shape of which allows it to be introduced into the connector of the first conductor. The device comprises:

    • an induction loop generating a magnetic field, the induction loop being designed to couple said magnetic field to the deformable part of the connector, the shape and the dimensions of the loop being suitable for holding the deformable part in place;
    • an inductor connected via a fourth switch to a voltage generator, to a current generator and to a third switch which makes it possible to select whether the inductor is connected to the current generator or to the voltage generator;
    • an AC current generator coupled to the inductor and to the induction loop via a transformer, a first switch being placed in parallel with the AC current generator; and
    • a circuit comprising a second switch and a capacitor in parallel with the inductor.

Advantageously, the induction loop and/or the transformer and/or the inductor may be cooled.

The device may especially be included in a coaxial toroidal envelope, said outer envelope contributing to reducing the magnetic fields due to the induction and to the transformer through the Frager turn effect.

The device may be used in the following operating sequence:

    • the first switch is opened;
    • the second switch is closed;
    • position on the third switch is selected, making it possible to supply the inductor by the voltage generator until sufficient energy for implementing the electrodynamic effect is stored in the inductor;
    • the AC current generator is implemented so that sufficient thermal energy to ensure the correct temperature has been transferred into the connector;
    • the AC current generator is employed for the time needed for the heat to diffuse into the conductor placed in the connector and position on the third switch is selected, making it possible to supply the inductor by the current generator during this time;
    • the second switch is opened and the first switch is closed; and
    • the fourth switch is opened.

The invention has in particular the advantages that it does not require the conductors to undergo a particular surface treatment: simple uncoated aluminium multistrand conductors are suitable. The invention makes it possible to reduce the production costs and to improve the quality of the joint. The connectors employed are not necessarily bimetallic.

Still other advantages of embodiments according to the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein:

FIG. 1, by means of a block diagram, a method according to the invention for joining electrical conductors by magnetostriction;

FIG. 2, by means of a block diagram, the various substeps of the magnetostriction step of the method according to the invention;

FIG. 3, by means of a block diagram, the various substeps of the step of preparing the conductors of the method according to the invention; and

FIG. 4, by means of a diagram, a magnetostriction-generating device according to the invention.

FIG. 1 shows, by means of a block diagram, a method according to the invention for joining electrical conductors by magnetostriction.

Magnetostriction is a magnetic-pulse cold-welding technique. For this, a coil, in which an electric current flows, is used to create a centripetal force in an annular connector electromagnetically coupled to said coil. A sudden change in the current flowing in the coil generates a large electro-dynamic force on the annular connector, the electrodynamic force being proportional to the derivative of the current with respect to time. Furthermore, the electric current produces, by induction, a thermal effect on the connector.

The method according to the invention makes it possible in particular to join two conductors, at least one of which is a conductor made of aluminium or an aluminium alloy. The conductors may be conductors with a multistrand core made of untreated aluminium alloy. The number of strands is defined so that the conductors achieve the desired mechanical properties, for example in terms of flexibility. The strands may be twisted (in particular so as to obtain better cohesion) or they may be straight (the strands may then have the form of a 120° angular sector). In particular, the conductors may meet the insulation requirements required in the aeronautical field.

The first of the two conductors includes an annular connector. For example, the annular connector is a connection end-fitting of the connector pin type, terminated by an approximately tubular cavity. The cavity may be made of aluminium, an aluminium alloy or any other conducting material suitable for magnetostriction. The approximately tubular cavity of the first conductor may be made of a material that is ductile at a defined temperature, having an expansion coefficient substantially the same or higher than the metal making up the first conductor. The latter feature makes it possible in particular during cooling to clamp the first conductor around the second. The dimensions and the shape of the cavity are matched to those of the first conductor, in particular in the case in which the conductors do not have a substantially circular shape. The thickness of the annular connector is especially defined so as to reconcile its ductility during implementation of the magnetostriction, its mechanical strength and its capability of being inserted into an insulator. The second conductor has at least one end, the shape of which allows it to be introduced into the connector of the first conductor.

The method according to the invention optionally includes a step 1 of preparing the two conductors. Shown in the block diagram of FIG. 3 are various substeps of step 1 of preparing the two conductors. Thus, in a substep 10, if necessary the second conductor is stripped at its end so as to expose the strands of which it is composed. Next, in a substep 11, the stripped part of the second conductor and at least the internal part of the connector of the first conductor are pickled. For this, it is possible to employ a triacid to remove the alumina from the various parts. Next, in a substep 12, the stripped part of the second conductor and at least the internal part of the connector of the first conductor are rinsed. The rinsing operation may be carried out with pure water. Substep 12 is completed by a drying operation. The drying may be carried out using a flow of inert gas, such as argon, or a reducing gas, optionally heated.

The method according to the invention includes a step 2 of installing the conductors. The end of the second conductor is inserted into the connector of the first conductor. The assembly formed by the two conductors thus positioned is introduced into the magnetostriction-generating device. Alternatively, the annular connector of the first conductor is introduced into the magnetostriction-generating device before the end of the second conductor is inserted into the annular connector. To increase the reliability, these operations may be carried out under a flow of inert gas, so that the inside of the annular connector is in contact with oxygen as little as possible. This operating method reduces the risk of creating an alumina film when the connector undergoes a temperature rise during the magnetostriction.

The method according to the invention includes a magnetostriction step 3. An electrodynamic force is generated by the magnetostriction-generating device in the annular connector. The force produced on the annular connector by the magnetostriction crushes the annular conductor around the second conductor introduced into the annular connector. This technique makes it possible to obtain a metallurgical weld between the conducting strands and the annular connector with the external layer of the conducting strands, the assembly being airtight. Shown in the block diagram of FIG. 2 are various substeps of magnetostriction step 3. Magnetostriction step 3 includes a first heating substep 31. Heating substep 31 may be carried out by induction heating. In heating substep 31, the second conductor and the connector are heated up to their plastic deformation point. The plastic deformation increases the reliability of the joint avoiding the risk of a crack or crack initiator appearing. The curve representing the rise in temperature is a relatively slow ramp compared with other sequences carried out during magnetostriction, on which a high-frequency AC signal may be superimposed, in particular to improve the induction heating. Magnetostriction step 3 includes a thermal stabilization second substep 32. Thermal stabilization substep 32 allows the thermal wave to reach the surface of the conducting strands. The curve showing the rise in temperature then has an approximately constant plateau, on which a high-frequency AC signal may be superimposed. Magnetostriction step 3 includes a third substep 33, for implementing the electrodynamic force of the magnetostriction. Substep 33 has a maximum duration of a few tens of milliseconds. If necessary, substep 33 is followed by a cooling step, which may lead to work-hardening of the connector, optionally supplemented by an annealing operation.

FIG. 4 illustrates by means of a diagram a magnetostriction-generating device according to the invention. The elements identical to the elements already presented in the other figures bear the same references. The device is especially suitable for implementing magnetostriction step 3 of the method according to the invention.

The device includes an induction loop 100 generating the magnetic field. The induction loop 100 couples said magnetic field to the deformable part 102 of a connector, the stripped part of a conductor 110 (the conductor 100 moreover being within an insulator 109) having been introduced into the deformable part 102. The shape and the dimensions of the loop 100 are furthermore suitable for holding the deformable part 102 in place. The deformable part 102 may be pinched, for example by means of an opening loop, or else may be slipped thereinto. The induction loop 100 may be cooled, especially by a coolant 101. The cooling operation makes it possible both to guarantee the mechanical integrity of the induction loop 100 and a temperature that can be withstood by the operator handling the device.

The device includes an inductor 103 connected to a ramp generator 106. The ramp generator 106 is shown in FIG. 4, especially for better understanding, by a voltage generator 104 and a current generator 105, and a third switch K3 for selecting one or other of them. However, the switched ramp generator 106 may consist of a single generator provided with two operating modes. It may furthermore include a dynamic protection device, protecting it against external overvoltages, for example by means of a cut-off voltage regulator. The inductor 103 is connected via a fourth switch K4 to the ramp generator 106.

The inductor 103 can therefore be connected to the voltage generator 104 or to the current generator 105 via the third switch K3 which makes it possible to select whether the inductor 103 is connected to the current generator 105 (with the third switch K3 in position a in FIG. 4) or to the voltage generator 104 (with the third switch K3 in position b in FIG. 4). When the inductor 103 is connected to the voltage generator 104, it stores the energy delivered by the voltage generator 104. This is because a current delivered by the voltage generator 104 flows through the inductor 103, which current increases linearly with time. The energy thus stored increases quadratically with time. When the inductor 103 is connected to the current generator 105 delivering a constant current, the inductor 103 maintains the energy that it has stored previously.

When the inductor 103 is short-circuited by means of the fourth switch K4, it restores the energy that it has stored, causing a sudden change in the current. To maximize the change in current, especially to maximize the electrodynamic force on the induction loop 100, the ohmic resistance of the circuit must be as low as possible. In particular, the inductor 103 must have the lowest possible ohmic resistance. However, in order for the energy stored within the inductor 103 to be maximized, it is necessary for the inductance of the inductor 103 to be as high as possible: the inductor 103 must therefore have the largest number of turns possible. To reconcile these two contradictory requirements, it is possible for example to cool, or even refrigerate, the inductor 103. The inductor 103 will for example be of the toroidal type and/or coiled on a magnetic circuit, both to maximize the inductance and to minimize the magnetic losses.

The fourth switch K4 is subject to large electrical, mechanical and thermal stresses, and consequently must be designed accordingly. Furthermore, an aid to rapid switching may be added to the fourth switch K4. For example, an electromechanical circuit breaker of the magnetic or gas blast type may meet these requirements.

The device includes an AC current generator 111. The AC current generator delivers power intended for heating the deformable part 102 of the connector. The AC current generator 111 is coupled to the inductor 103 and to the induction loop via a transformer 108. A first switch K1 is placed in parallel with the AC current generator 111 so as to be able to short-circuit the transformer 108 to the primary or to the secondary, depending on the relative dimensions of the elements. The first switch K1 makes it possible in particular to protect the AC current generator 111 from the current pulse during the magnetostriction. The magnetic circuit of the transformer 108 may be saturable (by decoupling between the primary and the secondary caused by the saturation resulting from the passage of the pulse generated during the magnetostriction), improving the protection of the AC current generator 111 at the cost of a slight loss of energy. In particular, the transformer 108 must have the lowest possible ohmic resistance. It is possible for example to cool, or even refrigerate, the transformer 108. The AC current generator 111 is adjustable as regards at least two power levels (one level suitable for heating and one level suitable for maintaining temperature) and for values that vary according to the type of the deformable part 102 of the connector.

The inductor 103 forms a parallel circuit with a second switch K2 and a capacitor 107. The capacitor 107 makes it possible in particular to short-circuit the inductor 103 when the AC current generator 111 is used for heating the deformable part 102. When the inductor 103 stores energy, the spectral content is too low for the current in the inductor 103 to be stored in the capacitor 107.

The connection method employed by the device according to the invention must be optimized in terms of radiation and electrical resistivity. In one embodiment, one method of eliminating the parasitic inductance induced in the circuit is to duplicate each connection segment by its identical copy, while reversing the direction of the current therein. In another embodiment, the connection is produced using a coaxial cable consisting of two tubular conductors, which is cooled by circulating a coolant. Such an embodiment may also apply to the inductor 103, to the transformer 108, to the fourth switch K4 and to the ramp generator 106.

The device according to the invention may be constructed so as to be included in a coaxial structure. Thus, the device according to the invention may be included in a coaxial toroidal envelope. Said outer envelope may contribute to reducing the magnetic fields due to the inductor 103 and to the transformer 108, through the Frager turn effect.

The operating sequence of the magnetostriction-generating device according to the invention is the following:

    • initially:
      • the first switch K1 is opened and the AC current generator 111 is then connected to the circuit; and
      • the second switch K2 is closed and the capacitor 107 is then charging.
    • in a current-rise/heating phase corresponding in particular to substep 31 of the method according to the invention:
      • the inductor 103 is supplied by the voltage generator 104 (with the third switch K3 in position a), a current flowing through the inductor that increases linearly until sufficient energy for implementing the electrodynamic effect (substep 33 of the method according to the invention) is stored in the inductor 103 (the time having moreover to be chosen to be long enough to prevent too large a current drift resulting in premature deformation of the connector 102); and
      • the AC current generator 111 delivers power so that, at the end of the current rise, sufficient thermal energy for ensuring the correct temperature has been transferred into the end-fitting 102;
    • in a thermal-diffusion/current-maintaining phase corresponding in particular to substep 32 of the method according to the invention, the energy needed for the correct temperature being in the end-fitting 102 but poorly distributed (too close to the surface because of the skin effect),
      • the AC current generator 111 delivers, during the time needed for the heat to diffuse into the conductor placed in the connector 102, the power needed to maintain the temperature of the connector 102, designed to compensate for the thermal losses; and
      • the current generator 105 supplies the inductor 103 with constant current (position b of the third switch K3) so as to compensate for the losses due to the ohmic resistance of the circuit;
    • the AC current generator 111 is protected by:
      • turning the AC current generator 111 off;
      • opening the second switch K2 in order to protect the capacitor 107 and prevent it from diverting some of the energy intended for the induction loop 100; and
      • closing the first switch K1 in order to protect the AC current generator 111;
    • in a crimping phase corresponding in particular to substep 33 of the method according to the invention, the fourth switch K4 is opened so as to break the current in the inductor 103 as suddenly as possible; and
    • in an optional phase of cooling and annealing the connector 102, corresponding to step 4 of the method according to the invention, the fourth switch K4 remains open.

It will be readily seen by one of ordinary skill in the art that embodiments according to the present invention fulfill many of the advantages set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.

Claims

1. A method for the joining, to a first conductor that includes a connector, a second conductor formed by a strand made of aluminium or an aluminium alloy and having at least one end, the shape of which allows it to be introduced into the connector of the first conductor, comprising the following steps:

a step of installing the conductors, the end of the second conductor being inserted into the connector of the first conductor; and
a magnetostriction step, an electrodynamic force being generated in the connector so that said connector is crushed around the second conductor introduced into the connector.

2. The method according to claim 1, wherein said magnetostriction step comprises:

a substep for heating the second conductor and the connector until their plastic deformation point is reached;
a substep for thermally stabilizing the second conductor and the connector; and
a substep for implementing the electrodynamic effect of the magnetostriction.

3. The method according to claim 1, including a step of preparing the two conductors, comprising:

a substep in which the second conductor is stripped at its end;
a substep in which the stripped part of the second conductor and at least the internal part of the connector of the first conductor are pickled; and
a substep in which the stripped part of the second conductor and at least the internal part of the connector are rinsed and then dried.

4. The method according to claim 1, wherein said step of preparing the two conductors and/or step of installing the conductors are carried out in a flow of inert gas.

5. A magnetostriction-generating device suitable for joining, to a first conductor that includes a connector, a second conductor formed a strand made of aluminium or an aluminium alloy and having at least one end, the shape of which allows it to be introduced into the connector of the first conductor, comprising:

an induction loop generating a magnetic field, the induction loop being designed to couple said magnetic field to the deformable part of the connector, the shape and the dimensions of the loop being suitable for holding the deformable part in place;
an inductor connected via a fourth switch to a voltage generator, to a current generator and to a third switch which makes it possible to select whether the inductor is connected to the current generator or to the voltage generator;
an AC current generator coupled to the inductor and to the induction loop via a transformer, a first switch being placed in parallel with the AC current generator; and
a circuit comprising a second switch and a capacitor in parallel with the inductor.

6. The device according to claim 5, wherein the induction loop and/or the transformer and/or the inductor are cooled.

7. The device according to claim 5, wherein said device is included in a coaxial toroidal envelope, said outer envelope contributing to reducing the magnetic fields due to the inductor and to the transformer through the Frager turn effect.

8. The use of the device according to claim 5, in the following operating sequence:

the first switch is opened;
the second switch is closed;
position (a) on the third switch is selected, making it possible to supply the inductor by the voltage generator until sufficient energy for implementing the electrodynamic effect is stored in the inductor;
the AC current generator is implemented so that sufficient thermal energy to ensure the correct temperature has been transferred into the connector;
the AC current generator is employed for the time needed for the heat to diffuse into the conductor placed in the connector and position (b) on the third switch is selected, making it possible to supply the inductor by the current generator during this time;
the second switch is opened and the first switch is closed; and
the fourth switch is opened.

9. The method according to claim 2, including a step of preparing the two conductors, comprising: a substep in which the stripped part of the second conductor and at least the internal part of the connector are rinsed and then dried.

a substep in which the second conductor is stripped at its end;
a substep in which the stripped part of the second conductor and at least the internal part of the connector of the first conductor are pickled; and

10. The method according to claim 2, wherein said step of preparing the two conductors and/or step of installing the conductors are carried out in a flow of inert gas.

11. The method according to claim 3, wherein said step of preparing the two conductors and/or step of installing the conductors are carried out in a flow of inert gas.

12. The device according to claim 6, wherein said device is included in a coaxial toroidal envelope, said outer envelope contributing to reducing the magnetic fields due to the inductor and to the transformer through the Frager turn effect.

13. The use of the device according to claim 6, in the following operating sequence: the fourth switch is opened.

the first switch is opened;
the second switch is closed;
position (a) on the third switch is selected, making it possible to supply the inductor by the voltage generator until sufficient energy for implementing the electrodynamic effect is stored in the inductor;
the AC current generator is implemented so that sufficient thermal energy to ensure the correct temperature has been transferred into the connector;
the AC current generator is employed for the time needed for the heat to diffuse into the conductor placed in the connector and position (b) on the third switch is selected, making it possible to supply the inductor by the current generator during this time;
the second switch is opened and the first switch is closed; and

14. The use of the device according to claim 7, in the following operating sequence: the fourth switch is opened.

the first switch is opened;
the second switch is closed;
position (a) on the third switch is selected, making it possible to supply the inductor by the voltage generator until sufficient energy for implementing the electrodynamic effect is stored in the inductor;
the AC current generator is implemented so that sufficient thermal energy to ensure the correct temperature has been transferred into the connector;
the AC current generator is employed for the time needed for the heat to diffuse into the conductor placed in the connector and position (b) on the third switch is selected, making it possible to supply the inductor by the current generator during this time;
the second switch is opened and the first switch is closed; and
Patent History
Publication number: 20080156055
Type: Application
Filed: Dec 21, 2007
Publication Date: Jul 3, 2008
Applicant: Thales (Neuilly Sur Seine)
Inventor: Jean-Pierre DELWAULLE (Brest)
Application Number: 11/963,780
Classifications
Current U.S. Class: With Exposure Of Work To Gas, Vapor, Mist, Or Modified Atmosphere (72/38); By Application Of Fluent Medium, Or Energy Field (72/54)
International Classification: B21C 37/00 (20060101);