EP3404688A1 - Device for centring a metal screen in a vacuum interrupter, and vacuum interrupter comprising such a device - Google Patents

Abstract

The present invention relates to a device for centering a metal screen inside a vacuum interrupter, this centering device being intended to carry out the centering of the screen relative to the envelope prior to fixing said screen. to the envelope at high temperature. This device is characterized in that it comprises at least one metal strip (12,13) wound around the screen (6,6a) and fixed thereto, said strip (12,13) comprising several cutouts forming, after plastic deformation, tabs (15) inclined with respect to the surface of the screen in the direction of the envelope, so that when the screen is introduced into the envelope of the bulb, these tongues are subject to a first elastic deflection towards the screen (6, 6a) when they come into contact with the inner wall (1b) of the envelope (1), then these same tongues (15) make a first centering of said screen (6, 6a) by elastic return of the tongues in the direction of the envelope, and that during the hot fixing operation of said screen to the envelope (1,1a), these same tongues (15) are subjected to a second deflection in direction of the envelope, under the effect of the differential expansion between the envelope and the screen , so as to maintain the first centering achieved.

Description

TECHNICAL AREA

The invention relates to the field of vacuum bulbs and more specifically to the field of assembly of these vacuum bulbs.
The present invention relates to a device for centering a metal screen inside a vacuum bottle, said bulb comprising a substantially cylindrical envelope closed by two end covers and enclosing two electrodes respectively fixed and mobile, said centering device being intended to perform the centering of the screen relative to the envelope prior to fixing said screen to the envelope at high temperature.

STATE OF THE PRIOR ART

A vacuum bulb is generally of axial symmetry and comprises a bulb body consisting mainly of an insulating envelope of substantially cylindrical shape closed by two end covers. The axis of symmetry of this bulb body thus defines the axis of symmetry of the vacuum bulb.
In order to limit the risk of arcing and to obtain a good distribution of the electromagnetic field in the bulb, the internal components of such vacuum bulbs, such as contacts, the screen or even the lids of the bulb must respect a relative concentricity vis-à-vis the axis of symmetry of the aforementioned envelope.
This concentricity remains difficult to guarantee during the manufacture of a vacuum bulb. Indeed, the assembly of a vacuum bulb may require temperature rise cycles, particularly with regard to the brazing steps.

Indeed, the sealing of the vacuum bulbs is usually done in a vacuum oven at a temperature high enough to melt copper silver solders. At this temperature, the centering of the insulating casing with respect to the internal copper parts poses a problem due to the difference in coefficient of expansion and to the geometric tolerances of the parts and in particular of the insulating envelope. And the thermal expansion of these bulb elements during these rise in temperature can cause misalignment vis-à-vis the axis of symmetry.
It is difficult to provide a good concentricity between these internal elements of the bulb and the envelope of the bulb without imposing extremely tight tolerances on the parts (essentially ceramics and screens), which has the effect of increasing drastically the cost of manufacturing a vacuum bulb.
To remedy this drawback, it is known to equip the bulb elements with centering systems which are adapted to center said vacuum bulb elements with respect to the axis of the envelope of the bulb they equip.
These centering systems can take the form of either elastic lamellae or bosses which are distributed around the outer periphery of the element so that these lamellae or bosses are interposed between the element and the bulb body thus allowing to center the element. Thus such centering systems bearing on the bulb body can hold the elements in place during assembly of the bulb and in particular during the temperature rise cycles.
These slat systems are suitable for stainless steel screens, because the slats are elastic enough to keep their effectiveness once the screen is in place. For vacuum bulbs where the electric performance requires copper screens, the lamellae are not suitable because the copper is not sufficiently elastic.
Regarding the use of lamellae, these can cause a decrease in the dielectric strength of the bulb because of their shape, the latter forming a triple point, and the opening they can leave in the case where they are formed in the element by a punching process. Of Such strips, when attached to the centering bulb element, generally require an expensive step, such as brazing, to be installed on said element. In addition, the positioning of these slats must be precise to ensure the conformity of the centering of the elements to be centered.
As regards the embossings, they do not have the elastic properties of the slats. It is therefore necessary that their shape is precisely adjusted to allow a centering "hot" to absorb deformations related to thermal expansion.
Indeed, during soldering in temperature, the copper screen expands more than the ceramic envelope. The bosses made on the screen then come into contact with the ceramic and refocus the screen by the effect of heating without damaging the ceramic because the copper screen is softened by heating. However, the tolerances on the ceramic and the screen are such that this contact does not always take place.
The patent is known FR 3 023 056 describing a vacuum bulb in which is used a copper spring, placed between the ceramic and the screen. This spring during assembly, comes into contact with the ceramic casing and ensures a cold centering of the screen relative to the ceramic. Thus, this solution provides a cold and hot centering, but is however very expensive.

For all these reasons, regardless of the type of centering system chosen among the elastic lamellae, the bosses, and the stents, these do not make it possible to guarantee that all the types of assembled vacuum bulbs have the required concentric configuration. . It is therefore necessary, in spite of the use of these centering systems, to sort out the non-compliant vacuum bulbs after measuring the concentricity between the two ceramic parts or between a cover and a ceramic part.
The present invention solves these problems and proposes a simple and economical centering device of a metal screen in a vacuum bulb to ensure a reliable and durable centering at a lower cost of said screen relative to the envelope of the bulb, from the beginning of the assembly of the bulb until the end of the cooling after the heating cycles of the bulb.

SUMMARY OF THE INVENTION

For this purpose, the present invention relates to a device for centering a metal screen inside a vacuum bottle of the kind mentioned above, this device being characterized in that it comprises a metal strip wound around the screen and fixed thereto, said strip comprising a plurality of cuts forming, after plastic deformation, tabs inclined relative to the surface of the screen in the direction of the envelope, so that when the screen is introduced in the envelope of the bulb, these tongues are subjected to a first elastic deflection towards the screen when they come into contact with the inner wall of the envelope, these same tongues making a first centering of said screen by elastic return of the tongues in the direction of the envelope, and that during the hot fixing operation of said screen to the envelope, these same tongues are subjected to a said second deflection to ection of the envelope, under the effect of the differential expansion between the screen and the ceramic, so as to maintain the first centering achieved.

According to a particular characteristic, the aforementioned tabs are folded along a fold axis extending in a direction substantially parallel to the axis of the bulb.

According to a particular characteristic, the value of the angle of inclination of the tongues with respect to the surface of the screen corresponding to the plastic deformation produced during the manufacture of the screen in order to produce these tongues, is at most 85 °.

According to another characteristic, the aforementioned strip is made of stainless steel.

According to another characteristic, the aforementioned tongues are made by cutting and then at least partially stamping a portion of the aforementioned metal strip.

According to another characteristic, the aforementioned tongues have a semi-round or triangular shape or a shape located between these two forms.

According to another feature, the length of the aforementioned metal strip is greater than a few millimeters to the perimeter of the screen to allow the realization of a spot weld between the two ends of the strip.

According to another characteristic, the end of the tongues has a rounded shape so as not to damage the envelope.

According to another characteristic, this device is used to perform the centering of a so-called central screen mounted around said contacts, and / or a so-called end shield located at one end of the bulb.

The present invention also relates to a vacuum interrupter comprising at least one centering device comprising the previously mentioned features taken alone or in combination.

According to a particular characteristic, this vacuum interrupter comprises a casing of substantially cylindrical shape closed by two end caps and enclosing two respectively fixed and movable contacts, said bulb also comprising a central screen located around the contacts and being constituted by a part cylindrical having a flange extending from the cylindrical portion of the screen in a direction perpendicular to the axis of the screen, said collar being placed between two envelope parts, this bulb being characterized in that it comprises a device centering device comprising the aforementioned features taken alone or in combination, and comprising two metal strips intended to be placed respectively on either side of said collar.

• La figure 1 est une vue en perspective et comportant un arraché, illustrant une ampoule à vide équipée d'un dispositif de centrage selon l'invention,
• La figure 2 est une vue de détail de la figure précédente, montrant une bande métallique équipée des languettes selon l'invention,
• La figure 3 est une vue partielle en perspective de l'ampoule, illustrant la position des languettes par rapport à l'enveloppe, avant la mise en place de l'écran à l'intérieur de l'enveloppe en céramique,
• La figure 4 est une vue en coupe radiale selon P de la figure 3, -La figure 4a est un élément de détail de la figure 4, illustrant l'une des languettes coopérant avec l'enveloppe,
• Les figures 5 et 5a sont des vues similaires aux figures 4 et 4a, mais illustrant la position des languettes après le montage de l'écran à l'intérieur de l'enveloppe, et
• Les figures 6 et 6a sont des vues similaires aux figures 5 et 5a, mais illustrant la position des languettes par rapport à l'enveloppe, après l'opération de scellement des éléments de l'ampoule à température élevée.

But other advantages and features of the invention will become more apparent in the detailed description which follows and refers to the accompanying drawings given solely by way of example and in which:

• The figure 1 is a perspective view and comprising a snatch, illustrating a vacuum interrupter equipped with a centering device according to the invention,
• The figure 2 is a detail view of the previous figure, showing a metal strip equipped with tongues according to the invention,
• The figure 3 is a partial perspective view of the bulb, illustrating the position of the tabs relative to the envelope, before the introduction of the screen inside the ceramic envelope,
• The figure 4 is a radial sectional view along P of the figure 3 , -The figure 4a is an element of detail of the figure 4 , illustrating one of the tabs cooperating with the envelope,
• The Figures 5 and 5a are similar views to Figures 4 and 4a but illustrating the position of the tabs after mounting the screen inside the envelope, and
• The Figures 6 and 6a are similar views to Figures 5 and 5a but illustrating the position of the tabs relative to the envelope, after the sealing operation of the elements of the bulb at high temperature.

On the figure 1 , a vacuum interrupter A according to the invention is shown, which is intended to be used in a switch to perform the cut in an electrical circuit. In a manner known per se, this bulb A comprises a cylindrical envelope 1, 1a closed by two end covers 2, 3 in which are housed two arc contacts 4, one of which, fixed 4, is integral with the one of the aforementioned hoods 2 while the other, mobile 5, is mounted to slide axially inside the cartridge through the so-called bottom end cover 3. Each contact has a contact pad fixed on an electrode, the electrode of the fixed contact being fixed to the said upper cover 2, while the electrode of the moving contact is slidably mounted through the so-called lower end cap 3, a sealing bellows 10 being interposed between the moving electrode and the lower end cap. This bulb A also comprises dielectric screens comprising a so-called central screen 6,6a (in two parts) placed around the contacts, a so-called end screen 7 placed around the so-called lower end cap 3, another screen known as end 8 located around the cover said upper 2 and a screen 9 located around the sealing bellows 10, these screens being constituted by a metal material, preferably steel.
According to the embodiment shown on the figure 1 , the envelope of the bulb consists of two parts 1,1a. The central screen situated around the contacts is constituted by two cylindrical parts 6, 6a intended to be fixed to each other and one of which comprises a collar 11 extending from the corresponding cylindrical portion of the screen in a direction perpendicular to the axis X of the screen, said flange being intended to be placed between the two parts of envelope 1.1a. Fixing said screen on the envelope is achieved by placing the flange 11 between the two parts of envelopes 1.1a and making a solder between the screen 6, 6a and the envelope 1,1a on both sides of the collar 11.
This bulb is equipped with a centering device D according to the invention, making it possible to center the central screen 6, 6 with respect to the casing 1, 1a, before the final hot fixing of said screen.

This centering device D comprises two thin metal strips 12, 13 mounted on either side of the above collar 11, being wound around the screen 6, 6 and then fixed to the screen by a weld made between the two. ends facing each of the metal strips.
These metal strips are preferably made of stainless steel, for example type 304L, but could be made of another material, inexpensive, elastic, and having a coefficient of expansion close to that of copper.

According to a particular embodiment illustrated in the figures, these metal strips 12, 13 have portions formed by cutting and then partially stamping part of the metal strip so as to form elastic tongues 15 able to bend along a Y axis of folding. extending in a direction substantially parallel to the axis X of the bulb.
Advantageously, these tabs 15 have a half-round shape but could have another shape such as a triangular shape or a shape located between these two forms, or any other form to obtain simply by cutting an elastic tongue.
This strip is cut to a length a few millimeters longer than the perimeter of the screen 6, 6 and then wrapped around the screen 6, 6a. Advantageously, each of the aforementioned strips 12, 13 is placed in an annular recess 16 made for this purpose around the screen. Each of the strips 12, 13 is held in position against the screen 6, 6a by performing a spot weld between the two ends of the strip, which ends overlapping slightly so as to allow this weld.
In the state of rest, prior to the mounting of the screen 6, 6a in the casing 1, 1a the elastic tabs 15 are folded in a direction opposite to the screen 6, 6a at an angle of inclination α whose value is preferably less than or equal to 85 °.
It should be noted that the angle of inclination is not too important and that one must be careful not to exceed the elastic limit of the material used, knowing a maximum value of 85 ° for the first angle of inclination is preferable in order to facilitate the placement of the screen.
Advantageously, the end of the tongues 15 is rounded so as not to damage the ceramic during the introduction of the screen 6, 6a inside the casing 1, 1a.
The elasticity of the tongues 15 makes it possible to limit the contact pressure and thus not to damage the ceramic material of the envelope 1.
When the inside of the ceramic casing is inserted cold, the assembly formed by the screen 6, 6a and the two metal strips 12, 13 having the elastic tabs apart, these tabs 15 are subjected to first deflection towards the screen 6, 6a when they come into contact with the inner wall 1b of the casing 1, and the elastic return of the tongues 15 in the rest position against this inner wall 1b makes it possible to perform a first centering said cold.

During the final soldering of the bulb A for fixing the various internal elements of the bulb to the ceramic envelope, and in particular the central screen 6, 6a, the tongues 15 flex a little further towards the envelope due to a higher expansion of the screen relative to the ceramic.
Thus, the centering which has been made cold is kept hot, and remains effective. At the time of cooling, the brazing of the copper screen to the envelope having been made, the screen is firmly attached to the ceramic envelope.
Note that the metal strip according to the invention can be easily cut to the right length in advance from prefabricated steel rolls.
This solution is simple and less expensive than the solution using a coil spring and, unlike the solution using bosses, it guarantees a true centering. It is no longer useful to use external tools to achieve centering.
According to the embodiment illustrated in the figures, the centering device according to the invention is used to carry out the centering of the central screen of the bulb, but could similarly be used to center one of the other screens.
This would make self-centering and thus remove external centering tools and even reduce the cost of ceramics of these same bulbs by allowing less tight tolerances.

Of course, the invention is not limited to the embodiment described and illustrated which has been given by way of example.
Thus, according to another embodiment, the tongues could be made so that their fold axis extends along an axis substantially perpendicular to the axis of the screen. This, however, would impose a particular fitting direction and require a wider metal band.

On the contrary, the invention comprises all the technical equivalents of the means described and their combinations if they have been carried out according to its spirit.

Claims (11)

Device for centering a metal screen inside a vacuum bulb, said bulb comprising an envelope of substantially cylindrical shape closed by two end covers and enclosing two electrodes respectively fixed and movable, said centering device being intended centering the screen relative to the envelope prior to attachment of said screen to the high temperature envelope, characterized in that it comprises at least one metal strip (12, 13) wound around the envelope; screen (6,6a) and fixed thereto, said strip (12,13) having a plurality of cuts forming, after plastic deformation, tabs (15) inclined relative to the surface of the screen in the direction of the envelope , such that when the screen is introduced into the envelope of the bulb, these tongues are subjected to a first elastic deflection towards the screen (6, 6a) when they come into contact with the wall int. erne (1b) of the casing (1,1a), these same tongues (15) thus achieving a first centering of said screen (6,6a) by elastic return of the tongues towards the casing (1,1a), and that during the operation of hot fixing of said screen (6, 6a) to the envelope (1, 1a), these same tongues (15) are subjected to a second deflection in the direction of the envelope (1, 1a) under the effect of the differential expansion between the envelope and the screen, so as to maintain the first centering achieved. Centering device according to claim 1, characterized in that the aforementioned tongues (15) are folded along a fold axis Y extending in a direction substantially parallel to the axis X of the bulb. Centering device according to claim 1 or 2, characterized in that the value α of the angle of inclination of the tongues (15) relative to the surface of the screen corresponding to the plastic deformation achieved during the production of the screen in order to produce the aforementioned tongues is at most 85 °. Centering device according to any one of claims 1 to 3, characterized in that the aforementioned strip (12,13) is made of stainless steel. Centering device according to any one of claims 1 to 4, characterized in that the aforementioned tongues (15) are made by cutting and then stamping at least part of the aforementioned metal strip (11,12). Centering device according to any one of the preceding claims, characterized in that the aforementioned tongues (15) have a semi-round or triangular shape or a shape located between these two forms. Centering device according to any one of the preceding claims, characterized in that the length of the aforesaid metal strip (12, 13) is a few millimeters larger than the perimeter of the screen (6, 6a) in order to allow the production of a spot weld between the two ends of the strip (11, 12). Centering device according to any one of the preceding claims, characterized in that the end of the tongues (15) has a rounded shape so as not to damage the envelope. Use of a centering device according to any one of claims 1 to 8 for centering a so-called central screen (6,6a) mounted around the contacts (4,5) in a vacuum bulb A, and / or an end screen (7,8) located at one end of the bulb. Vacuum bulb characterized in that it comprises at least one centering device according to any one of claims 1 to 8. Vacuum bulb comprising a casing (1) of substantially cylindrical shape closed by two end covers (2, 3) and enclosing two fixed and movable contacts (4, 5) respectively, said bulb A also comprising a central screen (6 , 6a) located around the contacts (4,5) and being constituted by a cylindrical portion having a flange (11) extending from the cylindrical portion of the screen (6,6a) in a direction perpendicular to the X-axis of the screen (6, 6a), said flange (11) being placed between two shell parts, characterized in that it comprises a centering device according to any one of claims 1 to 8 comprising two strips metal intended to be placed respectively on either side of said flange (11).

Images