EP0467798B1 - Process for making a welded connection between a flexible conductor and a contact finger, and contact finger - Google Patents

Description

The invention relates to a method of connecting by welding a flexible conductor, in particular a copper braid, to the rear end of a contact finger made of a material of good electrical conductivity, in particular copper, from of a stacking side by side of two elementary strips of identical external profiles, and joined together at the front part by a common contact pad.

The document EP-A-0 148 051 describes a multiple electrical contact device for high intensity circuit breakers, in which each contact finger comprises a pair of identical strips and joined side by side. The rear end of each strip is provided with a notch to allow the braid to be fixed. This assembly is carried out by a first mechanical hot insertion operation of the end of the braid in the two notches completely crossing the width of the finger, followed by a second brazing operation by adding tin. A third surfacing operation is then necessary to remove the unwanted particles due to soldering. This latter operation is carried out manually by means of a cleaning brush, the passage of which must be effected directly after brazing when the two opposite surfaces of the connection are still hot. The opposite end of the braid is introduced into the notches of a current supply range and then welded by resistance after local deformation of the teeth delimiting the notches.

A first object of the invention consists in perfecting the method of assembling a braid with a contact finger.

• l'extrémité de la tresse est compactée pour obtenir un bout rigide de forme complémentaire à celle d'une encoche semi-ouverte pratiquée dans la première lamelle, le bout ayant une épaisseur légèrement supérieure à l'épaisseur de la première lamelle;
• le doigt de contact est positionné à plat du côté de la deuxième lamelle sur l'électrode fixe d'une presse de soudage, l'encoche de la première lamelle délimitant un logement de réception avec la face plane juxtaposée de la deuxième lamelle;
• le bout est ensuite chauffé par résistance et incrusté par compression à chaud dans le logement au moyen de l'électrode mobile après blocage préalable des chants opposés du doigt de contact au niveau de la zone de liaison, l'effet de blocage mécanique s'exerçant perpendiculairement au sens de compression et de passage du courant de soudagepour éviter une déformation locale des lamelles (12, 14).

The method according to the invention is characterized in that:

• the end of the braid is compacted to obtain a piece rigid with a shape complementary to that of a semi-open notch made in the first strip, the tip having a thickness slightly greater than the thickness of the first strip;
• the contact finger is positioned flat on the side of the second strip on the fixed electrode of a welding press, the notch of the first strip delimiting a receiving housing with the flat face juxtaposed with the second strip;
• the end is then heated by resistance and embedded by hot compression in the housing by means of the movable electrode after prior blocking of the opposite edges of the contact finger at the level of the connection zone, the mechanical blocking effect being exerted perpendicular to the direction of compression and flow of the welding current to avoid local deformation of the lamellae (12, 14).

The assembly by resistance welding is carried out in a single operation without the addition of solder. The additional surfacing operation is eliminated, since the use of electrodes with flat bearing faces prevents local deformation of the lamellae and any excess of material in the welded connection zone.

The excess copper due to the excess thickness of the compacted end of the braid is automatically compensated for in the connection during the hot inlaying operation. The reduction of surplus is obtained either by maximum crushing of the turns of the compacted end of the braid, or by transfer of the molten copper in a discharge port made in the second strip.

A second object of the invention relates to the production of a contact finger with several lamellae and a connection braid for a high current circuit breaker. The braid is welded in a half-housing delimited by a semi-open notch in the first strip and the planar face juxtaposed with the second strip. The presence in the second strip of a discharge light in line with the notch of the first coverslip absorbs excess copper during hot inlaying of the compacted end of the braid in the receiving housing. The surface of the light is less than that of the notch. This results in an additional anchoring which strengthens the strength of the welded connection.

• la figure 1 est une vue schématique en élévation d'un doigt de contact à double lamelle connecté à une tresse de liaison;
• la figure 2 montre une vue en plan de la figure 1;
• la figure 3 représente une vue partielle de la partie postérieure du doigt de contact de la figure 1, avant le soudage de la tresse;
• les figures 4 et 5 montrent respectivement la deuxième et la première lamelles du doigt de contact de la figure 3;
• la figure 6 est une vue de profil de droite de la figure 3;
• les figures 7 à 11 sont des vues identiques respectives des figures 1 à 6 d'une variante de réalisation;
• la figure 12 illustre schématiquement la presse à souder avant l'opération de soudage de la tresse sur le doigt de contact;
• la figure 13 est une vue schématique en plan de la presse de la figure 12, au début de la phase de soudage.

Other advantages and characteristics will emerge more clearly from the description which follows, of two embodiments of the invention, given by way of nonlimiting examples, and represented in the appended drawings in which:

• Figure 1 is a schematic elevational view of a double lamella contact finger connected to a connecting braid;
• Figure 2 shows a plan view of Figure 1;
• Figure 3 shows a partial view of the rear part of the contact finger of Figure 1, before welding of the braid;
• Figures 4 and 5 show respectively the second and the first lamellae of the contact finger of Figure 3;
• Figure 6 is a right side view of Figure 3;
• Figures 7 to 11 are respective identical views of Figures 1 to 6 of an alternative embodiment;
• FIG. 12 schematically illustrates the welding press before the operation of welding the braid to the contact finger;
• Figure 13 is a schematic plan view of the press of Figure 12, at the start of the welding phase.

In the figures, a movable contact finger 10 of a low-voltage current cut-off device, in particular an electrical circuit breaker of high currents, is formed by a stacking side by side. side of two elementary strips 12,14, having identical external profiles. Each strip 12,14 is cut from a copper strip, having a thickness close to two millimeters. A circular orifice 16 is provided in each strip 12,14 to allow the mounting of the finger 10 on a transverse pivot axis. The assembly of the first and second elementary strips 12, 14 is operated by fixing a contact pad 18 to the front part, and by connecting the end 21 of a flexible braid 20 to the rear part of the finger 10. The another end 22 of the braid 20 is intended to be connected to a current supply range (not shown).

The fixing of the silver-based contact pad 18 on the lower edges of the strips 12, 14 is carried out by means of a brazing or resistance welding operation, described in detail in French patent 2,541,520.

The flexible braid 20 is made of copper, and the end 21 is shaped by a compacting and shearing operation to obtain a rigid rectangular tinned end. This compacting operation of the braid 20 is carried out by a special machine.

The rear part of the first strip 12 is equipped with a semi-open notch 24 cooperating with the juxtaposed flat part of the second strip 14 to define a housing 25 for receiving the end 21 to be connected.

The notch 24 and the end 21 have conjugate rectangular shapes, and the depth of the housing 25 corresponds substantially to the thickness of the strip 12 (see FIGS. 6 and 11). On the other hand, the thickness h of the compacted end 21 of the braid 20 (see FIG. 12) is slightly greater than the depth of the housing 25, that is to say the thickness of the strip 12.

Figures 1 to 6 and 7 to 11 show two embodiments of contact finger 10 for two different sizes of circuit breakers.

For the lower gauge of FIGS. 1 to 6, the braid 20 has a reduced section, and the entire rear part of the second strip 14 beyond the orifice 16 is massive.

For the upper gauge of FIGS. 7 to 11, the double section of the braid 20 requires a larger notch 24 in the first lamella 12. In this case, an oblong outlet port 26 (FIGS. 8 and 9) is formed between the rear end of the second strip 14 and the orifice 16, to improve the connection between the braid 20 and the finger 10 during the welding operation. The shape of this light 26 can be different, or have a plurality of holes. In the adjoining position of the two strips 12,14 (FIG. 8), the lumen 26 of the second lamella 14 is arranged in the vicinity of a plane passing through the bottom of the notch 24 of the first lamella 12. The length of the lumen 26 corresponds substantially to the width of the notch 24.

Referring more particularly to FIGS. 12 and 13, which illustrate the initial phase of the process of welding the braid 20 to the contact finger 10, it is noted that the compacted end 21 of the braid 20 is positioned between the movable electrode 30 d a resistance welding press 31, and the notch 24 of the first strip 12 of the finger 10. The second strip 14 of the latter bears flat on the fixed electrode 32, such that the axis of the orifices 16 s 'extends vertically in the direction of movement of the movable electrode 30. The complementary shapes of the tip 21 and the notch 24 allow cold or hot embedding respectively before and during the welding operation.

In the example of Figure 12, the tip 21 extends parallel to the strip 12 and is projecting above the notch 24. The downward movement according to arrow F1 of the movable electrode 30 first causes a gradual approximation of two jaws 34, 36 for clamping the welding press on the edges of the contact finger 10, then the hot inlaying of the tip 21 in the housing 25 by mechanical compression effect and electric heating by passing a welding current. The locking of the contact finger 10 by the action of the clamping jaws 34.36 on the opposite edges of the lamellae 12.14 (arrow F2, Figure 13), is carried out at the rear part of the finger 10 to avoid local deformation strips 12,14 during the welding operation. The blocking force F2 of the jaws 34, 36 is exerted transversely in a direction perpendicular to the movement of the mobile electrode 30. Resistance welding of the copper braid 20 on the contact finger 10 in copper takes place without addition of brazing metal (tin), and without annealing. The planar configuration of the two electrodes 30, 32 contributes to obtaining, after welding, smooth lateral surfaces at the level of the connection zone, requiring no additional surfacing or cleaning of the contact finger 10.

• soit par écrasement maximum des spires du bout 21 de tresse compacté (cas figures 1 à 6);
• soit par report de cuivre fondu dans la lumière 26 de la deuxième lamelle 14 juxtaposée (cas figures 7 à 11) permettant d'obtenir un effet d'agrippage supplémentaire qui améliore la résistance à la traction de la liaison soudée.

The excess copper due to the excess thickness of the compacted end 21 of the braid 20 is automatically reduced during the hot inlaying carried out by the welding press:

• either by maximum crushing of the turns of the end 21 of compacted braid (case Figures 1 to 6);
• either by transferring molten copper into the lumen 26 of the second juxtaposed strip 14 (case in FIGS. 7 to 11) making it possible to obtain an additional gripping effect which improves the tensile strength of the welded connection.

The clamping jaws 34, 36 of the welding press are advantageously made of molybdenum, and are arranged to derive a fraction of current flowing in the electrodes 30, 32.

This method of welding a copper braid on a copper contact, without the addition of solder metal, is advantageously used for multiple pole contacts above 1000A.

Claims (7)

1. A connection process by welding of a flexible conductor, notably a braided copper strip (20), to the rear end of a contact finger (10) made of a material with good electrical conductibility, notably copper, from side by side stacking of two elementary blades (12, 14) of identical external profile joined together at the rear part by a common contact pad (18), characterized in that :

   - the end of the braided strip (20) is compacted to obtain a rigid end (21) of complementary shape to that of a semi-open notch (24) made in the first blade (12), the end (21) having a thickness (h) slightly greater than the thickness of the first blade (12);

   - the contact finger (10) is positioned flat on the second blade (14) side on the fixed electrode (32) of a welding press (31), the notch (24) of the first blade (12) limiting a housing (25) with the juxtaposed flat face of the second blade (14);

   - the end (21) is then resistance heated and incrusted by hot compression in the housing (25) by means of the mobile electrode (30), the opposite edges of the contact finger (10) having being previously blocked at the level of the connection zone, the mechanical blocking effect being exerted perpendicularly to the direction of compression and welding current flow to prevent local deformation of the blades (12, 14).
2. The connection process according to claim 1, characterized in that electrodes (30, 32) with flat bearing faces are used to obtain complementary lateral surfaces at the connection zone level without overspill of material after the welding operation performed without addition of solder, and that the excess copper due to the overthickness of the compacted end (21) of the braided strip (20) is compensated automatically in the connection when the hot incrustation operation is performed.
3. The connection process according to claim 2, characterized in that the excess copper is reduced by maximum crushing of the turns of the compacted end (21).
4. The connection process according to claim 2, characterized in that the excess copper is compensated by being removed to an aperture (26) of the second juxtaposed blade (14), generating an additional gripping effect to improve the tensile strength of the welded connection.
5. An electrical contact finger, notably for a high current circuit breaker, comprising side by side stacking of two elementary blades (12, 14) having identical external profiles and made of a good electrical conducting material, assembled at the rear by a contact pad (18), and at the rear end by a connecting strip (20), characterized in that the first blade (12) is provided with a semi-open notch (24) cooperating with the juxtaposed flat surface of the second blade (14) to define a housing (25) receiving a compacted end (21) of the braided strip (20), said end being hot incrusted in the housing (25) by welding under pressure, without local deformation of the blades (12, 14).
6. The electrical contact finger according to claim 5, characterized in that the second blade (14) comprises an overspill aperture (26) located facing the notch (24) to enable the molten copper to be transferred during the welding operation, the surface of the aperture (26) being smaller than that of the notch (24).
7. The electrical contact finger according to claim 6, characterized in that the aperture (26) is located in proximity to the bottom of the notch (24) to form an additional securing of the welded connection.

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