CN108870152B

CN108870152B - Centering device, use thereof and vacuum bulb comprising such a device

Info

Publication number: CN108870152B
Application number: CN201810341895.3A
Authority: CN
Inventors: P.内温格
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2017-05-15
Filing date: 2018-04-17
Publication date: 2022-04-26
Anticipated expiration: 2038-04-17
Also published as: FR3066311A1; EP3404688B1; EP3404688A1; CN108870152A

Abstract

The invention discloses a centering device, application thereof and a vacuum bulb comprising the centering device. The device is intended for centering a metallic shield inside a vacuum bulb, comprising at least one metallic strip wound around the shield and fixed thereto, the strip comprising a number of cut-outs which, after plastic deformation, form tabs inclined towards the shell with respect to the surface of the shield, so that when the shield is introduced into the shell of the bulb, the tabs undergo a first elastic bending towards the shield when they come into contact with the inner wall of the shell, the tabs then performing a first centering of the shield by elastic return of the tabs towards the shell, and so that during the thermal fixing operation of the shield to the shell, these same tabs are subjected to a second bending towards the shell under the effect of the differential expansion between the shell and the shield, so as to maintain the performed first centering. The centering device is simple and economical, ensuring a low-cost centering of the shield with respect to the shell of the bulb in a reliable and durable manner.

Description

Centering device, use thereof and vacuum bulb comprising such a device

Technical Field

The present invention relates to the field of vacuum bulbs, and more precisely to the field of components of said vacuum bulbs.

The present invention relates to a device for centering a metallic shield in a vacuum bulb comprising a shell of substantially cylindrical form closed by two end caps and comprising two electrodes (one fixed and one movable), said device for centering being intended to perform centering of the shield with respect to the shell before high-temperature fixing of said shield to the shell.

Background

Vacuum bulbs are generally axisymmetric and comprise a bulb body which is essentially composed of an insulating envelope having a substantially cylindrical form which is closed by two end caps. The symmetry axis of the bulb body thus defines the symmetry axis of the vacuum bulb.

In order to limit the risk of arcing and to obtain a good electromagnetic field distribution within the bulb, the internal components that make up such a vacuum bulb assembly (such as the contacts, the shield or even the cover of the bulb) must take into account the relative concentricity with respect to the axis of symmetry of the aforementioned shell.

The concentricity is still difficult to ensure during the manufacture of the vacuum bulb. In fact, the assembly of vacuum bulbs may require cycles of elevated temperature, particularly with respect to the brazing step.

In fact, vacuum bulbs are usually sealed in a vacuum furnace at a sufficiently high temperature to melt the silver-copper brazing solder. At this temperature, the centering of the insulating housing relative to the internal copper components can be problematic due to differences in the coefficient of expansion and geometric tolerances of the components (particularly the insulating housing). During the temperature increase, thermal expansion of the bulb element may also lead to misalignment about the axis of symmetry.

It is difficult to provide good concentricity between the inner element of the bulb and the shell of the bulb without tight density tolerances on the components (mainly ceramic and shield), with the result that the cost of manufacturing the vacuum bulb increases dramatically.

In order to eliminate said drawback, it is known to equip the bulb elements with a centering system adapted to center the vacuum bulb elements with respect to the axis of the bulb shell to which they are fitted.

The centering system may take the form of resilient tabs or protrusions distributed over the outer periphery of the element such that the tabs or protrusions are located between the element and the bulb body, thereby centering the element. Such centering systems are supported on the body of the bulb so that the elements remain in place during the assembly of the bulb and in particular during the cycles of temperature increase.

The foil system is well suited for stainless steel shields because the foil is sufficiently resilient to maintain the effectiveness of the foil once the shield is placed in place. For vacuum bulbs whose electrical efficiency determines the user of the copper shield, a foil is not suitable because copper is not sufficiently flexible.

As regards the use of lamellae, they may, due to their form, and due to the openings they may leave in the case of their formation in the component by a stamping operation, lead to a reduction in the dielectric strength of the lamp bulb, which forms a triple point. When these lamellae are moved to the bulb element to be centered, costly steps, such as soldering, are usually required in order to mount the elements. Furthermore, the positioning of the lamina must be precise in order to ensure a uniform centering of the elements to be centered.

As regards the protuberances, they do not have the elastic properties of a lamina. It is therefore necessary to make precise adjustments to its shape in order to allow "thermal centering" to absorb the deformations associated with thermal expansion.

In fact, during higher temperature brazing, the copper shield expands more than the ceramic shell. Thus, due to the effect of the heating, the protrusions realized on the shield move into contact with the ceramic and re-center the shield, without damaging the ceramic due to softening of the copper shield by the heating. However, tolerances with respect to the ceramic and the shield are such that the contact does not always occur.

Patent FR 3023056 is known and describes a vacuum bulb in which a copper spring is used, placed between the ceramic and the shield. The spring moves into contact with the ceramic housing during assembly and ensures cold centering of the shield relative to the ceramic. Thus, the solution enables a hot and cold centering, but is very expensive.

For all the reasons mentioned, no matter what kind of centering system remains from the elastic lamellae, the protrusions and the expander, they do not ensure that all types of vacuum bulbs assembled have the required concentric configuration. Thus, despite the use of the centering system, a sorting operation is still required to eliminate the non-compliant vacuum bulb once concentricity between two ceramic parts or between the cap and the ceramic part is measured.

The present invention solves the problem and proposes a simple and economical device for centering a metallic shield in a vacuum bulb, which ensures a low-cost centering of said shield with respect to the shell of the bulb in a reliable and lasting manner, after a heating cycle of the bulb, from the start of the assembly of the bulb until the end of the cooling operation.

Disclosure of Invention

To this end, the object of the present invention is a centering device for centering a metallic shield in a vacuum bulb of the type described above, said device being characterized in that it comprises a metallic strip wound around the shield and fixed thereto, said strip comprising several cut-outs forming tabs after plastic deformation, said tabs being inclined with respect to the shield surface towards the shell, so that when the shield is introduced into the shell of the bulb, these tabs undergo a first elastic bending towards the shell when they come into contact with the inner wall of the shell, these same tabs then performing said first centering of the shield by elastic return of the tabs towards the shell, and so that during said thermal fixing operation of the shield to the shell, these same tabs undergo a so-called second bending towards the shell under the effect of differential expansion between the shell and the ceramic, to maintain the first centering performed.

According to a particular feature, the aforesaid tab is folded along a folding axis extending in a direction substantially parallel to the axis of the bulb.

According to a particular feature, the value of the angle of inclination of the tab with respect to the surface of the shield, which corresponds to the plastic deformation performed during the manufacture of the shield to realise said tab, is at most 85 °.

According to another feature, the aforesaid strip is realized in stainless steel.

According to another feature, the aforesaid tab is realized by cutting and then at least partially stamping a portion of the aforesaid metal strip.

According to another feature, the aforementioned tabs are in the form of a semi-circle or a triangle, or have a form located between said two forms.

According to another feature, the length of the aforementioned metal strip is a few millimetres longer than the perimeter of the shield, so as to allow spot welding between the two ends of the strip.

According to another feature, the ends of the tabs are in the form of a circle, so as not to damage the casing.

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

The invention also aims at a vacuum bulb comprising at least one centering device comprising the aforementioned features taken by themselves or in combination.

According to a particular feature, the vacuum bulb comprises a housing having a substantially cylindrical form closed by two end caps and comprising two contacts, one of which is fixed and one of which is movable, the bulb further comprising a central shield positioned around the contacts and consisting of a cylindrical part comprising a collar extending from the cylindrical part of the shield in a direction perpendicular to the axis of the shield, the collar being placed between the two housing parts, the bulb being characterized in that it comprises centering means comprising the previously mentioned features taken by themselves or in combination and comprising two metal strips intended to be placed on either side of the collar, respectively.

Drawings

However, other advantages and features of the present invention will become more apparent in the following detailed description, which refers to the accompanying drawings, which are given by way of example only, and in which:

FIG. 1 is a perspective view and comprises a cut-out, showing a vacuum bulb equipped with a device for centering according to the invention,

FIG. 2 is a view of a detail from the previous figures, showing a metal strip equipped with tabs according to the invention,

FIG. 3 is a partial perspective view of the bulb showing the position of the tabs relative to the ceramic shell before the shield is placed within the shell,

figure 4 is a radial cross-section according to P in figure 3,

FIG. 4a is an element of a detail from FIG. 4, showing one tab cooperating with the housing,

figures 5 and 5a are views similar to figures 4 and 4a, but showing the position of the tabs once the shield has been assembled inside the housing, an

Fig. 6 and 6a are views similar to fig. 5 and 5a, but showing the position of the tabs relative to the shell after the operation of sealing the bulb element at elevated temperature.

Detailed Description

Fig. 1 shows a vacuum bulb a according to the invention, which is intended for use in a switch for breaking an electric circuit. In a manner known per se, said bulb a comprises a

cylindrical shell

1, 1a closed by two

end caps

2, 3, in which two

arcing contacts

4, 5 are housed, one of which (fixed arcing contact 4) is fixed to one of the caps 2 and the other (movable arcing contact 5) is mounted so as to slide axially inside the column up to the so-called bottom end cap 3. Each contact comprises a contact pad fixed to an electrode fixed to a so-called top cap 2, while the electrode of the movable contact is mounted to slide up to a so-called bottom end cap 3, between which a bellows seal 10 is interposed. The lamp bulb a further comprises a dielectric shield comprising a so-called

central shield

6, 6a (in two parts) placed around the contacts, a so-called end shield 7 placed around the so-called bottom end cap 3, another so-called end shield 8 around the so-called top cap 2 and a shield 9 around a bellows seal 10, which shield is made of a metallic material, preferably steel.

According to the illustration shown in fig. 1, the housing of the lamp bulb is formed from two

parts

1, 1 a. The central shield around the contact is made up of 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 part of the shield in a direction perpendicular to the axis X of the shield, said collar being intended to be placed between the two

housing parts

1, 1 a. The fixing of the shields on the housing is performed by placing the collar 11 between the two

housing parts

1, 1a and by performing a soldering between the

shields

6, 6a on both sides of the collar 11 and the

housing

1, 1 a.

The bulb is equipped with means for centering D according to the invention, which allow centering of the

central shield

6, 6a with respect to the

shell

1, 1a to be performed before final thermal fixing of the shield.

Said means D for centring comprise two

thin metal strips

12, 13, said two

thin metal strips

12, 13 being mounted on both sides of the aforementioned collar 11 by being wound around the

shields

6, 6a and then fixed to the shields by performing welding between the two ends of each strip facing the other.

The metal strips are preferably realized in stainless steel, for example in 304L-shape, but may be realized in a different, less expensive, elastic material with a coefficient of expansion close to that of copper.

According to the particular implementation shown in the figures, the metal strips 12, 13 have portions formed by cutting and then partially stamping a portion of the metal strip (to form the elastic tabs 15), the elastic tabs 15 being adapted to be folded along a folding axis Y extending in a direction substantially parallel to the axis X of the bulb.

In an advantageous manner, said tab 15 is of semicircular form, but can have a different form, such as a triangular form or a form located between said two forms, or any other form allowing the elastic tab to be obtained simply by cutting it out.

The strip is cut to a length that is several millimeters longer than the circumference of the

shield

6, 6a and then wound around the

shield

6, 6 a. In an advantageous manner, each of the

aforementioned strips

12, 13 is placed in a groove having a ring-shaped form 16, which ring-shaped form 16 is realized around the shield for the purpose. Each of the

strips

12, 13 is held in place against the

shield

6, 6a by effecting spot welding between the two ends of the strip, which overlap slightly to allow said welding.

In the rest state, before assembling the

shield

6, 6a in the

housing

1, 1a, the elastic tab 15 is folded according to an inclination angle α, preferably of a value less than or equal to 85 °, in the opposite direction to the

shield

6, 6 a.

It should be noted that the angle of inclination is not so critical and it is necessary to ensure that the elastic limit of the material used is not exceeded, it being known that a value of maximum 85 ° is preferred for the first angle of inclination to facilitate the implementation of the shield.

In an advantageous manner, the ends of the tabs 15 are rounded so as not to break the ceramic when the

shield

6, 6a is mounted in the

housing

1, 1 a.

The elasticity of the tabs 15 allows to limit the contact pressure and therefore the ceramic material of the housing 1 is not damaged.

When the assembly consisting of the

shield

6, 6a and the two

metal strips

12, 13 comprising the unfolded elastic tab is inserted in the ceramic housing in the cold condition, said tab 15 undergoes a first bending in the direction of the

shield

6, 6a when it comes into contact with the inner wall 1b of the housing 1, and the elastic return of the tab 15 against said inner wall 1b in the rest position allows to perform a first so-called cold centering.

During the final brazing of the bulb a, which allows fixing the different internal elements of the bulb to the ceramic shell, and in particular the

central shield

6, 6a, the tabs 15 are again slightly bent further in the direction of the shell, due to the greater expansion of the shield with respect to the ceramic.

Thus, the centering already performed in the cold condition maintains the heat and remains effective. On cooling, the shield is well fixed to the ceramic housing, since brazing of the copper shield to the housing has been achieved.

It should be noted that the metal strip according to the invention can be easily pre-cut to the correct length using a prefabricated steel roll.

Said solution is simple and less costly than the solution using a helical spring, and it ensures true centering compared to the solution using a projection. There is no further value in using external tools to achieve centering.

According to the implementation shown in the figures, the device for centering according to the invention is used to perform centering of the central shield of the bulb, but can be used in the same way to perform centering of one of the other shields.

This will allow automatic centering to be performed and thus external centering tools can be omitted and the ceramic cost of the same bulb reduced even by allowing less tight density tolerances.

Of course, the invention is not limited to the described and illustrated embodiments, which are given by way of example only.

Thus, according to another implementation, the tabs may be implemented such that their fold axes extend along an axis substantially perpendicular to the axis of the shield. However, this would dictate the particular mounting orientation used and would require a wider metal strip.

On the contrary, the invention includes all technical equivalents of the means described and their combinations if these are implemented according to the spirit of the invention.

Claims

1. A centering device for centering a metallic shield inside a vacuum bulb, said bulb comprising a shell having a substantially cylindrical form closed by two end caps and comprising two electrodes, one of which is fixed and one of which is movable, said centering device being intended for performing centering of the shield with respect to the shell before high-temperature fixing of the shield to the shell, characterized in that the device comprises at least one metal strip (12, 13) wound around and fixed to the shield (6, 6a), said strip (12, 13) comprising several notches which, after plastic deformation, form tabs (15) which are inclined with respect to the surface of the shield towards the shell, so that when the shield is introduced into the shell of the bulb, said tabs, at their mutual contact with the shell (1, 1a) then these same tabs (15) perform a first centering of said shield (6, 6a) by elastic return of the tabs towards the housing (1, 1a) and so that, during the operation of thermal fixing of said shield (6, 6a) to the housing (1, 1a), these same tabs (15) undergo a second bending towards the housing (1, 1a) under the effect of the differential expansion between the latter, to maintain the first centering performed,

the tab (15) is folded along a folding axis Y extending in a direction substantially parallel to the axis X of the bulb.

2. Centring device according to claim 1, characterized in that the value α of the angle of inclination of the tab (15) with respect to the surface of the shield corresponds to a maximum of 85 ° performed during the manufacture of the shield to achieve plastic deformation of the tab.

3. Centring device according to any one of claims 1 to 2, characterized in that said strips (12, 13) are realized in stainless steel.

4. Centring device according to one of claims 1 to 3, characterized in that the tab (15) is realized by cutting and then at least partially punching a portion of the metal strip (12, 13).

5. Centring device according to one of the preceding claims, characterized in that the tab (15) is of semicircular or triangular form or has a form lying between the two forms.

6. Centring device according to any one of the preceding claims, characterised in that the length of the metal strip (12, 13) is a few millimetres longer than the circumference of the shield (6, 6a) to allow spot welding between the two ends of the strip (12, 13).

7. Centring device according to one of the preceding claims, characterized in that the end of the tab (15) is of rounded form in order to avoid damaging the housing.

8. Use of a centering device according to any of claims 1 to 7, in order to perform centering of a so-called central shield (6, 6a) mounted around the contacts (4, 5) and/or a so-called end shield (7, 8) located at one of the bulb ends in a vacuum bulb A.

9. Vacuum bulb, characterized in that it comprises at least one centering device according to any one of claims 1 to 7.

10. A vacuum bulb comprises a housing (1) having a substantially cylindrical form closed by two end caps (2, 3), and comprising two contacts (4, 5), one of which is fixed and one of which is movable, the bulb A further comprising a central shield (6, 6a) located around the contacts (4, 5) and consisting of a cylindrical part comprising a collar (11), extending from the cylindrical part of the shield (6, 6a) in a direction perpendicular to the axis X of the shield (6, 6a), said collar (11) being placed between the two housing parts, characterized in that the vacuum bulb comprises a centering device according to any one of claims 1 to 7, the centering means comprise two metal strips intended to be placed on either side of the collar (11), respectively.