A contact for a vacuum switching tube and method of manufacturing same

Abstract

The invention relates to a contact (1) for a vacuum interrupter (1) of a low-, medium- or high-voltage switchgear, and to a production method for such a contact (1). The contact (1) comprises a contact bar (2) composed of a first electrically conductive material extending along a longitudinal axis (13) of the contact (1), and a contact piece (3) composed of a second electrically conductive material fastened to an end face of the contact bar (2). The contact bar (2) and the contact piece (3) are integrally bonded to one another at a connecting face. According to the invention, at least one of either the contact bar (2) or the contact piece (3) has a wall (8) which delimits the connecting face, rises perpendicularly to the longitudinal axis (13) and is arranged such that the contact piece (3) and the contact bar (2) are also frictionally connected to one another by a force acting transversely to the longitudinal axis (13) between the contact piece (3) and the contact bar (2).

Description

Technical field

[0001] The invention relates to a contact for a vacuum switching tube of a low, medium or high voltage switchgear and a manufacturing method for such a contact. Technical background

[0002] Vacuum tubes are used in low-, medium-, and high-voltage switchgear to suppress arcing as much as possible during current switching or to extinguish arcs as quickly as possible. During switching, a moving contact is either moved away from a mating contact (opening the switch) or brought into contact with the mating contact (closing the switch). Each contact consists of a contact piece, which establishes physical and thus electrical contact with a corresponding mating piece of the other contact, and a contact bar, which acts as an electrical conductor. The contact piece usually has a larger cross-section than the contact bar to which it is attached, in order to increase the contact area exposed to the stress of an arc and to distribute the load over a larger area.Due to the still considerable stress caused by the electric arcs, mechanically and chemically resistant materials are chosen for the contact piece, but these are associated with high costs. For the contact rod, on the other hand, price and good electrical conductivity are the primary considerations. Therefore, the contact piece and contact rod are manufactured separately and joined together during the contact process.

[0003] However, the connection between the contact rod and the contact piece is subject to high mechanical stresses during the operation of the vacuum switching tube, since the switch is closed as quickly as possible and the contacts therefore collide at high speed to minimize the duration of an arc. For this reason, it is desirable to connect the contact rod and contact piece as securely and reliably as possible.

[0004] During the manufacturing process of a vacuum tube, the components are often first detachably connected or placed on top of each other without any connection. They are then placed in a vacuum soldering furnace, the furnace is evacuated, and the loose or detachable components are permanently joined by heating, thus creating a vacuum inside the tube. This can be done using either prefabricated contacts or contact rods and pieces that are also detachably or loosely connected. In the latter case, the necessary permanent connection of the contact rods and pieces is only achieved by heating in the vacuum soldering furnace. In both cases, the quality of the connection between the contact piece and the contact rod cannot be inspected after manufacturing is complete, as the contact is located inside the finished vacuum tube.

[0005] The invention aims to introduce an improved contact and a method for its production.

[0006] The invention solves this problem by means of a contact according to claim 1 and a method according to claim 9. Preferred embodiments of the invention are the subject matter of the dependent claims.

[0007] Patent documents EP 1 022 760 A2, CN 205 282 375 U, WO 2017 / 036711 A1 and US 2016 / 141119 A1 relate to the background of the present invention. Patent documents DE 199 21 475 A1 and DE 196 32 573 A1 disclose contacts in which a force-fit connection is established between the contact piece and the contact rod before the contact piece and contact rod are soldered together. Summary of the invention

[0008] A first aspect of the invention relates to a contact for a vacuum interrupter in a low-, medium-, or high-voltage switchgear. The contact comprises a contact rod extending along a longitudinal axis of the contact, comprising a first electrically conductive material, and a contact piece attached to an end face of the contact rod, comprising a second electrically conductive material and a contact surface facing away from the contact rod. The contact rod and contact piece are bonded together at a connecting surface. According to the invention, at least one of the contact rod and contact piece has a ridge defining the connecting surface, which rises perpendicular to the longitudinal axis and is arranged such that the contact piece and the contact rod are also bonded together by a force acting transversely to the longitudinal axis between the contact piece and the contact rod.

[0009] The force-fit connection between the contact rod and contact piece advantageously ensures that both components can be correctly positioned relative to each other before the bond is formed, and that the force-fit connection holds the two components in the desired position during the bonding process. This prevents the components from slipping relative to each other and results in a high-quality bond.

[0010] For example, a ridge can be arranged on a lateral surface of the contact rod, such that the ridge presses against an inner surface of a recess in the contact piece that is at least approximately complementary in shape to the end of the contact rod pressed into the contact disc, thus creating a force-fit connection between the contact piece and the contact rod. Likewise, the ridge can also be arranged on the inner surface of the contact piece facing the lateral surface of the contact rod, with the contact rod being inserted into the space enclosed by the ridge to establish the force-fit connection. Naturally, ridges can also be provided on both the contact rod and the contact piece to increase the stability of the force-fit connection. Multiple ridges can also be provided on the contact rod and / or the contact piece.

[0011] A wall preferably runs along a closed line, in particular along a circle. This ensures that each section of the wall is subjected to the same force.

[0012] In this process, the contact rod and the contact piece are soldered together; that is, the metallurgical bond between the contact rod and the contact piece is created by soldering, in particular brazing. For this purpose, solder is placed as a coating on the contact piece and / or contact rod, as solder foil, or in some other form, in the space enclosed between the contact rod and the contact piece before the frictional and finally the metallurgical bond are established. The ridge or ridges provide the additional advantage according to the invention of forming a barrier for the solder, which liquefies during the creation of the metallurgical bond, and thus retain it in the desired location.

[0013] The wall is preferably concentric around the longitudinal axis. This ensures that the force exerted by the wall is uniform in all directions, so that the contact rod is centered relative to the contact piece when the force-fit connection is established.

[0014] In advantageous embodiments of the contact according to the invention, a groove is provided that runs at least approximately parallel to the ridge and is arranged on a side of the ridge facing away from the contact surface of the contact piece. With multiple ridges, a corresponding groove can be provided next to each ridge. The groove has the advantage that material from the adjacent ridge can enter or be absorbed by the groove during the formation of the force-fit connection through deformation. For this reason, the groove is also arranged on the side of the ridge facing away from the contact surface of the contact piece. The presence of a groove allows for a higher-quality force-fit connection to be produced without having to apply excessively large pressing forces. The volume of a groove preferably corresponds to at least half the volume of the adjacent ridge.For example, it can be at least approximately equal to the volume of the adjacent wall, or even larger.

[0015] The contact piece can have a passage with a first opening and a second opening, the first opening facing the contact surface of the contact piece and the second opening facing a side of the contact piece facing away from the contact surface. The passage has the advantage that air trapped between the contact piece and the contact rod can escape during the formation of the frictional connection and also during the evacuation of the vacuum brazing furnace. This reduces the pressing force required to form the frictional connection and increases the quality of the bond between the contact piece and the contact rod. The contact rod can, for example, have a recess arranged in the passage of the contact piece. This recess can increase the area available for forming the frictional connection.

[0016] Alternatively or in addition to the opening for the contact piece, the wall can also have at least one opening, comprising a first opening into a space enclosed by the contact piece and the end face of the contact rod, and a second opening into the vicinity of the contact. This opening allows air trapped between the contact piece and the contact rod to escape during the evacuation of the vacuum soldering furnace, thus preventing any disruptive pressure effect from this air during heating. The at least one opening can be sealed with solder during the formation of the metallurgical bond between the contact piece and the contact rod, but remains detectable in the finished product due to the different materials of the wall and the solder. The opening can, for example, be designed as a through-hole or as a slot extending to the top of the wall.

[0017] For example, the wall can have multiple such openings, which are arranged at least approximately equidistantly. This ensures that the same mechanical properties, such as bendability and deformability, are achieved along the entire length of the wall.

[0018] It is particularly preferred that the first coefficient of thermal expansion of the first material is greater than the second coefficient of thermal expansion of the second material. This ensures that the force required to create the frictional connection increases during heating, so that the frictional connection can be established with less force and becomes more reliable and strong during the formation of the material-bonded connection.

[0019] The first material can be copper, stainless steel, or a copper or stainless steel alloy. The second material can be a copper-chromium composite, a tungsten-copper compound, or a tungsten carbide-metal compound such as tungsten carbide-silver or tungsten carbide-copper.

[0020] A second aspect of the invention relates to a method for producing a contact according to the invention. It comprises at least the following steps: -- Providing the contact rod; -- Providing the contact piece; -- Placing solder in a space enclosed between contact rod (2) and contact piece (3); -- Force-fit connection of contact rod and contact piece by applying a pressing force along the longitudinal axis; and -- Material-fit connection of contact rod and contact piece, namely by soldering contact rod and contact piece, by heating contact rod and contact piece.

[0021] The special embodiments of the contact described above can readily be transferred into corresponding embodiments of the manufacturing process according to the invention. Brief description of the images

[0022] The invention is explained in more detail below with reference to illustrations of exemplary embodiments. These show: Figure 1 shows an example of a vacuum switching tube in which a contact according to the invention can be used, in a sectional drawing; Figure 2 shows a first embodiment of a contact according to the invention in a sectional drawing; Figure 3 shows a second embodiment of a contact according to the invention in a sectional drawing; Figure 4 shows a third embodiment of a contact according to the invention in a sectional drawing; Figure 5 shows a fourth embodiment of a contact according to the invention in a sectional drawing; Figure 6 shows a fifth embodiment of a contact according to the invention in a sectional drawing; Figure 7 shows a sixth embodiment of a contact according to the invention in a sectional drawing; and Figure 8 shows an embodiment of the method according to the invention for producing a contact according to the invention. Detailed image description

[0023] Figure 1Figure 1 shows a sectional drawing of an example of a vacuum switching tube 100 in which a contact 1 according to the invention can be used. The vacuum switching tube 100 comprises two contacts 1 arranged opposite each other in a ceramic housing 7, one of which is typically designed as a moving contact and the other as a fixed contact. The moving contact is displaceable along a direction of movement 4 within the vacuum switching tube 100, so that the respective contact surfaces 14 of the two contacts 1 can be brought into contact with each other or separated from each other. A flexible bellows 5 ensures that the vacuum prevailing in the vacuum switching tube 100 is maintained despite the movement of the moving contact.

[0024] Each contact 1 comprises a contact rod 2 extending along a longitudinal axis 13 and a contact piece 3 attached to one end of the contact rod 2 with opposing contact surfaces 14. A shield 6 serves to protect the ceramic behind it from deposition with contact material from switching arcs and, if necessary, to assume a potential between the potentials of the contacts 1, thereby advantageously influencing the electric field prevailing in the vacuum switching tube 100.

[0025] Figure 2Figure 1 shows a first embodiment of a contact 1 according to the invention in a sectional drawing. The contact rod 2 of the contact 1 has a projection 10 which is inserted into a correspondingly shaped passage 11 of the contact piece 3. The projection 10 can, in particular, be cylindrical. The passage 11 has the additional advantage that gas located between the contact rod 2 and the contact piece 3 can escape when the vacuum soldering furnace is evacuated. If gas remains in the vacuum soldering furnace, undesirable chemical reactions can occur on the surfaces of the contact 1 and inside the vacuum switching tube 100. Furthermore, trapped gas can prevent the formation of a sufficiently strong metallurgical bond.

[0026] According to the invention, a wall 8 is provided, which in the embodiment shown here is arranged on the contact rod 2 and more precisely on the projection 10 of the contact rod 2. The wall 8 surrounds the projection 10 and can thus form a ring around it. The ring can, in particular, be arranged concentrically around the longitudinal axis 13 of the contact 1. The wall 8 serves to establish a frictional connection between the contact rod 2 and the contact piece 3 before a material-bonded connection is subsequently established. The frictional connection holds the contact piece 3 and the contact rod 2 relative to each other in the desired position for establishing the material-bonded connection. For the latter, solder 9, for example, a solder foil, can be placed between the contact rod 2 and the contact piece 3 at the point where the material-bonded connection is to be effected at a connecting surface of the two parts.Wall 8 serves as a boundary for the bonding surface, as the solder 9, which is heated and liquefied during the creation of the metallurgical bond, cannot pass through Wall 8. This prevents the liquefied solder 9 from leaving the bonding surface, which could impair the quality of the metallurgical bond and contaminate the contact surface 14 of the contact piece 3 with solder.

[0027] Figure 3Figure 1 shows a second embodiment of a contact 1 according to the invention in a sectional drawing. In the second embodiment, the end of the contact rod connected to the contact piece 3 is stepped. In the second embodiment, the wall 8 limits the contact surface on its other side. The first and second embodiments can advantageously be combined in a vacuum switching tube 100 if the upper contact is implemented according to the first embodiment and the lower contact according to the second embodiment, since, with a vertical placement of the vacuum switching tube 100 in the vacuum soldering furnace, the solder 9 can be held at the intended location at both contacts against the force of gravity.

[0028] Figure 4Figure 1 shows a third embodiment of a contact 1 according to the invention in a sectional drawing, in which two ridges 8 are provided, thereby increasing the strength of the force-fit connection. The arrangement of the ridges 8 in the embodiment shown here also has the effect of limiting the contact surface on both sides, so that the solder 9 cannot leave the space bounded by the ridges 8, thus sharply defining the contact surface where the material bond is formed.

[0029] Figure 5 A fourth embodiment of a contact 1 according to the invention is shown in a sectional drawing, which largely corresponds to the second embodiment of Figure 3The difference between the two embodiments is that here the wall 8 is not arranged on the contact rod 2 but on the contact piece 3. In principle, in all embodiments of the invention, a wall 8 can be arranged on either the contact rod 2 or the contact piece 3. It is also possible to provide one or more walls on both the contact rod 2 and the contact piece 3. Generally, however, the material of the contact rod 2 will be softer and more flexible than that of the contact piece 3, so that a wall 8 on the contact rod 2 allows the force-fit connection to be established with a lower pressing force.

[0030] Figure 6Figure 1 shows a fifth embodiment of a contact 1 according to the invention in a sectional drawing, in which the contact piece 3 is embedded in the contact rod 2. Such an embodiment can be chosen if the coefficient of thermal expansion of the material of the contact piece 3 is greater than that of the material of the contact rod 2. As a result, the contact piece 3 expands more than the contact rod 2 when heated, so that the strength of the frictional connection is temporarily increased during the formation of the bond. This makes it possible to establish the frictional connection with a relatively low force, while a greater force acts during the soldering process and holds the contact piece 3 and contact rod 2 in the desired position relative to each other.

[0031] Figure 7A sixth embodiment of a contact 1 according to the invention is shown in a sectional drawing, in which several walls 8 are provided, which, however, in contrast to the embodiment of the Figure 4All the walls 8 define the contact surface at the same end. Such arrangements of walls 8 are, of course, also possible in the other embodiments shown. In the sixth embodiment, trenches 12 are also provided, each running alongside one of the walls 8. Each trench 12 is arranged on the side of the associated wall 8 facing away from the contact side 14. This has the advantage that the wall 8 becomes flexible and, when the frictional connection is established, a portion of the wall 8 material can be displaced into the associated trench 12. This increases the contact area of ​​the frictional connection and simultaneously reduces the maximum contact force, advantageously distributing it over the surface. As a result, a better frictional connection can be achieved with a reduced pressing force.Naturally, such a trench 12 or several trenches 12 can also be provided in the other embodiments shown.

[0032] Figure 8Figure 1 shows an embodiment of the inventive method for producing a contact according to the invention, which begins in a starting step S0 and continues with a step S1 in which a contact rod is provided. In step S2, a suitable contact piece is provided. In step S3, solder is placed between the contact rod and the contact piece. Steps S1, S2, and S3 can generally be carried out in any order or simultaneously. Subsequently, in step S4, the contact rod and contact piece are force-fitted by applying a pressing force along the longitudinal axis. In step S5, the contact rod and contact piece are material-fitted, which may include partial steps of evacuating and heating a vacuum soldering furnace. The method ends in a final step S6 after the vacuum soldering furnace has cooled and the contact has been completed.

[0033] The invention has been explained in more detail with reference to illustrations of exemplary embodiments. These exemplary embodiments serve only to improve understanding and are not intended to limit the invention, which is defined exclusively by the following patent claims. Reference symbol list

[0034] 1 Contact 2 Contact rod 3 Contact piece 4 Direction of movement 5 Bellows 6 Shield 7 Ceramic housing 8 Wall 9 Plumb bob 10 Shape 11 Passage 12 Trench 13 Longitudinal axis 14 Contact surface 100 vacuum switching tubes

Claims

1. Contact (1) for a vacuum interrupter (100) of a low-, medium- or high-voltage switchgear, the contact (1) comprising a contact rod (2), which extends along a longitudinal axis (13) of the contact (1) and comprises a first electrically conductive material, and a contact piece (3), which is fastened to an end face of the contact rod, comprises a second electrically conductive material, and has a contact face (14) remote from the contact rod, wherein the contact piece (3) and the contact rod (2) are materially bonded to one another, namely soldered to one another, on a connecting face, characterized in that at least one of the contact rod (2) and contact piece (3) has a wall (8) that delimits the connecting face, acts as a barrier to liquefied solder on the connecting face, rises perpendicularly to the longitudinal axis (13), and is arranged such that the contact piece (3) and the contact rod (2) are also connected to one another in a force fit as a result of a force acting transversely to the longitudinal axis (13) between the contact piece (3) and the contact rod (2).

2. Contact (1) of the preceding claim, in which the wall (8) runs concentrically around the longitudinal axis (13).

3. Contact (1) of either of the preceding claims, having a trench (12) which runs at least approximately parallel to the wall (8) and is arranged on a side of the wall (8) that is remote from the contact face (14) of the contact piece (3).

4. Contact (1) of one of the preceding claims, in which the contact piece (3) has a passage (11) which has a first opening and a second opening, wherein the first opening is open towards the contact face (14) of the contact piece (3) and wherein the second opening is open towards a side of the contact piece (3) that is remote from the contact face (14) of the contact piece (3).

5. Contact (1) of the preceding claim, in which the contact rod (2) has a formation (10) arranged in the passage (11) in the contact piece (3).

6. Contact (1) of one of the preceding claims, in which a first coefficient of thermal expansion of the first material is greater than a second coefficient of thermal expansion of the second material.

7. Contact (1) of one of the preceding claims, in which the first material is copper, stainless steel, or a copper or stainless steel alloy.

8. Contact (1) of one of the preceding claims, in which the second material is a copper-chromium composite material, a tungsten-copper compound, or a tungsten carbide-metal compound.

9. Method for producing a contact (1) according to one of the preceding claims, having the following steps: -- providing the contact rod (2); -- providing the contact piece (3); -- placing solder in a space enclosed between the contact rod (2) and the contact piece (3); -- connecting the contact rod (2) and the contact piece (3) in a force fit by applying a pressing force along the longitudinal axis (13); and -- materially bonding the contact rod (2) and the contact piece (3), namely by soldering the contact rod (2) and the contact piece (3), by heating the contact rod (2) and the contact piece (3).

Images