GB2143377A - A vacuum switch tube and method of making same - Google Patents

Abstract

A movable contact bolt (3) of a vacuum switch tube is constrained in a guide bearing (10). This guide bearing (10) is normally located outside the vacuum and has a fixing ring (13) which is held in contact with the vacuum housing by means of a clamping arrangement, achieved by providing a flange on an annular component (14) around the fixing ring (13) and continuous over the entire periphery of the fixing ring (13). This is achieved during manufacture by means of a plurality of simultaneously engaging pressure rollers (21). The invention can be used with particular advantage for vacuum switch tubes which have small dimensions, for example for isolation tubes. <IMAGE>

Description

SPECIFICATION A vacuum switch tube and method of making same The invention relates to a vacuum switch tube and to a method of making such a tube.

In known vacuum switch tubes, a fixing ring of a guide bearing is fixed in position by arranging that a projecting edge zone of the cylindrical wall of a connecting flange is indented at a plurality of locations and is deformed in the radial direction.

In practice this type of fixing has proved inadequate under extreme conditions of use. Furthermore, production losses occur on account of excessive loading on the vacuum-tight connection formed between the connecting flange and the insulator.

It is an aim of the invention to provide improvements in vacuum switch tubes in relation to the fixing of the guide bearing whilst simultaneously enabling a reduction in stress on the vacuum-tight connection during manufacture.

According to one aspect of this invention there is provided a vacuum switch tube comprising a switching contact which is movable along an axis, said contact having an associated contact bolt, a housing which comprises at least one cylindrical insulator and, connected in vacuum-tight fashion thereto, a connection flange whose temperature expansion coefficient is matched to that of the insulator, the connection flange having a cylindrical wall around an end ring which is connected in vacuum-tight fashion at its outer periphery to the cylindrical wall and at its inner periphery to a bellows, the latter being connected in vacuum-tight fashion to the switching contact, the contact bolt being mounted so as to be axially displaceable in a guide bearing comprising a material having at least approximately the same temperature expansion coefficient as the material of the contact bolt, a fixing ring being integrally formed with the guide bearing and being mechanically fixed relative to the end ring by means of a clamp connection, the clamp connection being provided by means of a flange arranged to grip the entire periphery of the fixing ring.

It is advantageous for the cylindrical wall to project beyond the fixing ring and to have said flange abutting on to the fixing ring.

For more accurate centering in relation to the end ring it is advantageous to provide that a concentric annular groove is arranged in the end ring, a supporting ring being inserted into this annular groove and mechanically fixed therein, the fixing ring extending within and to this support ring which provides said flange for clamping said fixing ring.

The fixing ring and the support ring can advantageously be integrally formed with each other. For large production numbers, this integral formation is advantageously established by means of an extrusion process and in the case of small production numbers, by turning from the solid.

To prevent rotation during the clamping flange formation or during operation, the end ring and the fixing ring are designed to be resistant to mutual relative rotation by means of a recess and a spigot fitted into this recess.

In an embodiment of the invention, the vacuum switch can advantageously be assembled from materials which are difficult to join to one another, and thus for example the contact bolt and the guide bearing can basically comprise copper, the connection flange can comprise a FeNiCo-alloy and the insulator can comprise a ceramic or glass. The guide bearing advantageously comprises a bearing bush and a cylinder liner, comprising a bearing metal, and which is supported therein and permanently mechanically connected thereto. If the bearing bush is produced from copper, the temperature coefficient of the entire guide bearing largely corresponds to the temperature coefficient of the copper contact bolt.

For somewhat lower thermal stress, the guide bearing and/or the bearing bush can also comprise synthetic material which results in a particularly cost-favourable embodiment.

According to another aspect of this invention there is provided a method of making a vacuum switchtube and comprising the steps of providing a switching contact which is movable along an axis, said contact having an associated contact bolt, providing a housing which comprises at least one cylindrical insulator and, connecting in vacuum-tight fashion thereto, a connection flange whose temperature expansion coefficient is matched to that of the insulator, providing the connection flange with a cylindrical wall around an end ring which is connected in vacuum-tight fashion at its outer periphery to the cylindrical wall and at its inner periphery to a bellows, the latter being connected in vacuum-tight fashion to the switching contact, the contact bolt being mounted so as to be axially displaceable in a guide bearing comprising a material having at least approximately the same temperature expansion coefficient as the material of the contact bolt, providing a fixing ring integrally formed with the guide bearing and being mechanically fixed relative to the end ring by means of a clamp connection, the clamp connection being provided by means of a flange arranged to grip the entire periphery of the fixing ring.

In one embodiment, the vacuum switch is advantageously produced by a method in which said clamping connection flange is produced by rolling, and pressure rollers distributed at two or more points of the periphery are caused to engage simultaneously. As a result, the radial components of the forces which are exerted on the connection flange during rolling cancel each other and the connection flange is subjected to stress substantially only in the axial direction and relatively uniformly.

A particularly precise production is possible by arranging that a pressure device comprising a plurality of pressure rollers is guided axially over the movable contact bolt and the axis of the contact bolt is thus adjusted laterally to be aligned with the axis of rotation of the fixed contact, and thus as a result of the flange formation by means of the pressure rollers an accurate mutual fixing of the relative positions of the two switching contacts is automatically achieved.

Embodiments of this invention will now be de scribed, by way of example, with reference to the accompanying drawings in which: Figure 1 is a part sectional view of a vacuum switching tube embodying the invention; and Figures 2 and 3 are sectional views of respective different forms for a portion of the tube shown in Figure 1.

Referring to the drawings, a vacuum switch tube comprises a housing 1 and a movable switching contact 2 with an associated contact bolt 3. The housing 1 comprises an insulator4which is preferably made of a glass or ceramic material, for example, Al203-ceramic. This insulator 4 is adjoined, by means of a vacuum-tight connection, by a connection flange 5 having a cylindrical wall 6 an end ring 7, an intermediate ring 8 and a bellows 9.

Outside the vacuum there is arranged a guide bearing 10 which laterally guides the contact bolt 3 which is movable in the longitudinal axial direction.

The guide bearing 10 is composed of a bearing bush 11 and a cylinder liner 12, composed of bearing metal, which is materially bonded to the bearing bush.

The bearing bush 11 is integrally formed with a fixing ring 13 which is inserted into a support ring 14 whose edge zone is flanged and thus clamps the fixing ring 13 in its position and presses the ring 13 continuously over its entire periphery against the end ring 7.

The support ring 14 is connected to the end ring 7 in a mechanically stable manner. Prior to the vacuum-tight assembly of the tube, the ring 14 can have been welded on to the end ring 7 or soldered by means of a hard solder having a high melting point.

However, the support ring 14 and end ring 7 can also be produced integrally from a single component (turning or extrusion).

A particularly precise position fixing is achieved by arranging that the support ring 14 is inserted into an annular groove 15 in the end ring 7 and coaxial therewith (Figure 3). Depending upon the temperature stress which is likely to occur during operation, the supporting ring 14 can be secured by means of adhesive or soldered in to the annular groove 15 or can be additionally welded to the end ring. This additional fixing does not need to be provided over the entire periphery of the ring.

Depending upon the likely mechanical and thermal stresses, the bearing bush 11 and fixing ring 13 can consist of a synthetic material or metal. The temperature expansion coefficient of the bearing bush 11 is advantageously matched to that of the contact bolt 3. The contact bolt 3 is normally produced from copper so that a copper alloy provides a particularly suitable material for the bearing bush 11.

As shown in Figure 3, a recess 18 is formed in the fixing ring 13 and a spigot 16 ofthe end ring 7 engages this recess. This serves to avoid rotation between the bearing bush and the end ring both during operation and during production and thus avoids any change in the lateral position of the contact bolt.

In the alternative embodiment shown in Figure 2, the fixing ring 13 extends substantially to the cylindrical wall 6, the edge zone 19 of the cylindrical wall 6 comprising an angled flange and holding the fixing ring 13 in its position. The fixing ring 13 has a spigot 200 which engages a recess 210 in an end ring 17 and prevents the two components 13 and 17 from rotating relative to one another. This embodiment is extremely suitable for bearing bushes consisting of metal, whereas the embodiment shown in Figure 3 is particularly suitable for bearing bushes consisting of synthetic material since in the case of the latter the spigot consists of metal and the recess consists of the normally softer synthetic material.

As shown in Figure 1, the support ring 14 and the edge zone 19 of the cylindrical wall 6 can be shaped by a process in which pressure rollers 21, whose axes form a constant, acute angle with the central longitudinal axis of the contact bolt 3, are pressed against the support ring and the edge zone 19 as indicated by the arrow B and are simultaneously rotated about the central longitudinal axis of the contact bolt as indicated by the arrow A. The mechanical stress to which the vacuum-tight housing 1 is thus subjected does not lead to any damage of the housing if the pressure rollers 21 are brought into engagement simultaneously and uniformly distributed over the periphery of the support ring 14 and the cylindrical wall 6.This is effected by means of a pressure device 22 whose axis of rotation coincides with the central longitudinal axis of the fixed contact 23 of the vacuum switch tube, where this pressure device 22 is provided with a bore 24 which serves to accommodate and to centre the contact bolt 3. A precise centering of the contact bolt 3 can be achieved if the pressure device 22 contains a cylinder liner 25 consisting of bearing metal which coaxially surrounds the contact bolt 3 and is adapted to the diameter thereof with the tolerances of a sliding bearing. The introduction of the contact bolt 3 into the bore 24 is facilitated by means of a conical edge zone 26 in the cylinder 25.

The pressure device 22 has at least two of the pressure rollers 21 which are arranged opposite one another relative to the axis of rotation and whose peripheral surfaces form the same acute angle with the axis of rotation. An advantageous embodiment has three such pressure rollers 21 which are uniformly distributed round the periphery of the support ring and the cylindrical wall. Ball bearings or roller bearings are particularly suitable as pressure rollers 21.

A clamp connection which grips the entire periphery of the fixing ring surprisingly not only represents an improved support for the guide bearing but also can be established more gently than a punctiform indentation of the cylindrical wall.

As a result of this flange-forming operation the vacuum-tight housing 1 of the vacuum switch tube is subject to a relatively low stress. In particular, the forces active in the radial direction cancei each other out. The remaining forces in the axial direction can be harmlessly absorbed by the vacuum-tight connection between the connection component and insulator. The stress on the vacuum switch tube which is to be overcome in this way is considerably less than that resulting from the provision of inde ntations in the edge zone of the support ring 14 or the cylindrical wall 6, although such identations represent only a local deformation of very small extent. At the same time, the holding force provided by fixing the components as described above is several times better than that attainable by means of individual indentations.

In order to safeguard the movable contact bolt from rotating during the assembly of the switch tube the bearing bush and the contact bolt can be designed as complemental profiles as described above or can be provided with groove and spring. In this way even the slightest variations in the mechanical tolerances can be graduated.

Claims (13)

1. A vacuum switch tube comprising a switching contact which is movable along an axis, said contact having an associated contact bolt, a housing which comprises at least one cylindrical insulator and, connected in vacuum-tight fashion thereto, a connection flange whose temperature expansion coefficient is matched to that of the insulator, the connection flange having a cylindrical wall around an end ring which is connected in vacuum-tight fashion at its outer periphery to the cylindrical wall and at its inner periphery to a bellows, the latter being connected in vacuum-tight fashion to the switching contact, the contact bolt being mounted so as to be axially displaceable in a guide bearing comprising a material having at least approximately the same temperature expansion coefficient as the material of the contact as the material of the contact bolt, a fixing ring being integrally formed with the guide bearing and being mechanically fixed relative to the end ring by means of a clamp connection, the clamp connection being provided by means of a flange arranged to grip the entire periphery of the fixing ring.

2. A vacuum switch tube as claimed in claim 1 wherein the cylindrical wall projects beyond the fixing ring and has said flange abutting on to the fixing ring so as to clamp the latter.

3. A vacuum switch tube as claimed in claim 1, wherein a concentric annular groove is arranged in the end ring, a supporting ring being inserted into this annular groove and mechanically fixed therein, the fixing ring extending within and to this support ring which provides said flange for clamping said fixing ring.

4. A vacuum switch tube as claimed in claim 1, wherein the end ring is integrally formed with a concentric support ring and is produced by turning or extrusion, the fixing ring extending within and to this support ring and that this support ring is provided with said flange for clamping the fixing ring.

5. Avacuum switch tube as claimed in any one of the preceding claims wherein the end ring and the fixing ring are designed to be resistant to mutual relative rotation by means of a recess and a spigot fitted into this recess.

6. A vacuum switch tube as claimed in any one of the preceding claims wherein the guide bearing comprises a bearing bush and a cylinder liner composed of bearing metal which is supported in said bearing bush and is connected thereto in a mechanically stable manner.

7. A vacuum switch tube as claimed in any one of the preceding claims wherein the contact bolt and the guide bearing basically comprise copper, the connection flange basically comprises a FeNiCoalloy and the insulator comprises a ceramic or glass.

8. A vacuum switch tube as claimed in any one of the preceding claims wherein the guide bearing and/orthe bearing bush comprise a synthetic material.

9. A vacuum switch tube substantially as described herein with reference to Figures 1 to 3 or as modified by Figure 2 of the accompanying drawings.

10. A method of making a vacuum switch tube and comprising the steps of providing a switching contact which is movable along an axis, said contact having an associated contact bolt, providing a housing which comprises at least one cylindrical insulator and, connecting in vacuum-tight fashion thereto, a connection flange whose temperature expansion coefficient is matched to that of the insulator, providing the connection flange with a cylindrical wall around an end ring which is connected in vacuum-tight fashion at its outer periphery to the cylindrical wall and at its inner periphery to a bellows, the latter being connected in vacuum-tight fashion to the switching contact, the contact bolt being mounted so as to be axially displaceable in a guide bearing comprising a material having at least approximately the same temperature expansion coefficient as the material of the contact bolt, providing a fixing ring integrally formed with the guide bearing and being mechanically fixed relative to the end ring by means of a clamp connection, the clamp connection being provided by means of a flange arranged to grip the entire periphery of the fixing ring.

11. A method as claimed in claim 10 wherein said clamping connection flange is produced by rolling, and pressure rollers distributed at two or more points of the periphery are caused to engage simultaneously.

12. A method as claimed in claim 11, wherein a pressure device comprising a plurality of pressure rollers is guided axially over the movable contact bolt, and the axis of the contact bolt is thus adjusted laterally to be aligned with the axis of rotation of the fixed contact, and thus as a result of the flange formation by means of the pressure rollers an accurate mutual fixing of the relative positions of the two switching contacts is automatically achieved.

13. A method of making a vacuum switch tube and substantially as described herein with reference to Figures 1 and 3 or as modified by Figure 2 of the accompanying drawings.