MANUFACTURING METHOD FOR A CONTACT ELEMENT FOR VACUUM SWITCHES, CONTACT ELEMENT AND VACUUM SWITCH

Description

[0001] The present invention relates to a novel manufacturing method for a contact element for vacuum switches, a contact element produced or producible according to the method, and a vacuum switch with such a contact element.

[0002] In vacuum switches and vacuum interrupters for low, medium, and high voltage applications, radial or axial magnetic field contacts (RMF or AMF contacts) are used, particularly for interrupting currents exceeding several kiloamperes. The design, function, and operating principles of such conventional contact elements are described, for example, in K. Jenkes-Botterweck's 2003 dissertation "Modelling of Plasma in Vacuum Circuit Breakers Considering Axial Magnetic Fields," available online at http: / / publications.rwth-aachen.de / record / 58842, described comprehensively.

[0003] Widely used designs are the spiral contact and the pot contact. In the spiral contact, disclosed, for example, in DE102019216869A1 and DE102017214805A1, the required magnetic field is generated by the geometric design of the contact disc itself. In other contact forms, particularly the pot contact, also known, for example, from DE102017214805A1, the magnetic field is formed by an additional coil body onto which the contact disc is mounted.

[0004] The coil formers are preferably made from copper bar stock or preformed copper pressed parts. The magnetic field generation by the coil former, often designed as a hollow cylinder, is achieved through appropriate slotting. Especially with AMF contacts, the contact discs are often also provided with slots to reduce eddy currents. The slots of both parts must be aligned during assembly.

[0005] The contact disc and contact carrier of conventional contact elements are therefore manufactured in different production steps and from different materials to achieve the desired properties. For the contact carrier, this is particularly high conductivity; for the contact disc, a key property is resistance to the burn-off caused by arcing events during switching.

[0006] In a subsequent manufacturing step, the contact disk and contact carrier are joined together using a material-to-material bonding process, such as brazing. In practice, this manufacturing step is broken down into several individual steps and involves considerable effort and expense, as the quality of the connection between the contact disk and contact carrier significantly influences the switching performance of the vacuum interrupter. Furthermore, the necessary assessment and quality control of the connection between the contact disk and contact carrier is only possible with considerable effort.

[0007] DE 33 02 595 A1 discloses a contact carrier in which a body wound in a helical shape or provided with helical recesses is cast from a first material of lower electrical conductivity with a second material of higher conductivity and lower melting and casting temperature, with the spaces between the screw turns and the recesses being cast in particular. The body made from the first material represents part of the casting mold for the second material. A contact disk is then soldered onto the contact-making end face of the contact carrier, as already explained above.

[0008] DE 195 13 790 A1 discloses a contact element in which an arc electrode part, an arc electrode holding part, a coil electrode part, and an electrode rod (current supply part) are configured to form an integral structure. At least one of the connecting regions between the arc electrode part and the arc electrode holding part, the coil electrode part, and the current supply part is manufactured integrally using hot isostatic pressing (HIP) processing. A disadvantage of the method described in DE 195 13 790 A1 is that it requires several individual steps.

[0009] WO 2014 / 202390 A1 discloses a Field Assisted Sintering Technology (FAST) process in which an electric or electromagnetic field supports and / or induces a sintering process for the production of contact element semi-finished products for electrical switching contacts, contact elements for electrical switching contacts, and / or electrical switching contacts, particularly for vacuum tubes. The contact material is present before the sintering process in such a way that the material composition of the contact material and / or at least one property of the contact material changes in at least one body direction of the finished contact element.

[0010] DE 19612143 A1 relates to a method for producing a spiral contact piece for a vacuum switch, with a base body made of electrically conductive material, e.g. copper, and a contact coating made of electrically less conductive, erosion-resistant material, preferably a copper-chromium mixture, which are raised in a crucible to a temperature which is higher than the melting temperature of the electrically conductive material, wherein during the melting process a shaped piece with a corresponding slot geometry is introduced into the melt, which consists of a material which is not wetted by the electrically conductive material, so that after cooling the shaped piece can be removed from the solidified spiral contact piece blank.

[0011] US 4,325,734 discloses compact bodies for use as contacts in vacuum circuit interrupters, plasma devices, and the like, which are manufactured from suitable powder material by vacuum hot pressing. The contacts, which may be shaped as a button or ring, are operable under high-current arc conditions. The powder material is mixed and placed between a pair of punches in a floating die cavity maintained in an inert atmosphere and placed in a vacuum chamber. A vacuum is created without pressurizing the powder material. The powder material is heated below its melting temperature for degassing. The die cavity preferably includes special degassing openings. The punches are pressurized, and the powder material reaches a sintering temperature and a vacuum of 3×10 -6 < Torr.The result is a compact body of uniform composition, essentially free of entrapped gas, and particularly suitable for use as a high-current interrupting contact in an arcing environment. Interrupting contacts made of copper with hundreds of ppm of oxygen (copper(II) or copper(I)) can be formed. Powder material made of a non-carbide-forming metal or alloy can be mechanically bonded to a porous graphite element by the process. A weak bond between the powder material and a porous graphite element can also be created by interposing an anti-bonding layer of graphite powder.

[0012] The object of the present invention is therefore to provide an improved manufacturing method for a contact element and a contact element, whereby the disadvantages described are avoided.

[0013] This object is achieved according to the invention by a manufacturing method in which a first powder-like mixture comprising particles of the first conductive material and particles of the second conductive material or a first pre-pressed, disc-shaped green body consisting of a composite of at least the first and the second conductive material is introduced into a press die. An inner press die is introduced into the die, and a second powder of the first conductive material or a second powder-like mixture comprising particles of the first conductive material or a second pre-pressed green body comprising the first conductive material is introduced into a space between the die and the inner press die. An outer press die is introduced into the space between the die and the inner press die.Pressure is exerted on the outer and inner pressing rams in such a way that a disc-shaped area forming the contact disc of the contact element is created from the first powder-like mixture or the first green body, and an area forming the contact body or contact carrier of the contact element is created from the second powder or the second powder-like mixture or the second green body.

[0014] In an advantageous development of the method according to the invention, an electrical voltage is additionally applied to the press punches and the die.

[0015] In an advantageous further development, the voltage feed points and the respective electrical power fed in are selected such that the currents flowing through the powders or green bodies are approximately evenly distributed.

[0016] In an advantageous further development, the die and / or the press punches are provided with a release agent, in particular with a graphite coating or a boron nitride coating, before being brought into contact with one of the powders or green bodies.

[0017] In an advantageous further development, the first powder is a mixture of copper particles and chromium particles, in particular in the ratio CuCr25 or CuCr30 or CuCr35.

[0018] In an advantageous further development, after pressing and sintering of the powders and / or green bodies, a plurality of obliquely arranged slots distributed over the circumference are introduced into the contact element or the area forming the contact body in such a way that, when a current flows, a magnetic field can be generated which causes a movement of a resulting arc on a predetermined path and / or a large-area spread of the arc.

[0019] The present invention further relates to a contact element for a vacuum switch produced by or producible by the aforementioned method, with a contact body consisting of a first conductive material or a composite material which comprises a first conductive material, and a contact disc consisting of a composite material, in particular a particle composite material which, in addition to the first conductive material, comprises at least a second conductive material.

[0020] The contact element is a uniform body with at least two areas with different material compositions, whereby the material composition of the two areas is based on the requirements explained above: the material of the area which corresponds to the contact carrier or the contact body of a conventional contact element is selected so that it has a high conductivity, and the material of the area which corresponds to the contact disc of a conventional contact element is selected so that it is resistant to the burn-off caused by arcing events during switching.

[0021] In advantageous developments of the present invention, the first conductive material is copper.

[0022] In advantageous developments of the present invention, the second conductive material is chromium, with CuCr25 or CuCr30 or CuCr35 being used as the (particle) composite material.

[0023] The present invention further relates to a vacuum switch having a vacuum chamber within which two contact elements are arranged, wherein at least one of the contact elements is designed according to the present invention.

[0024] An advantage of the present invention is that the manufacturing effort for a contact element according to the invention is reduced compared to the prior art. In particular, the soldering of the various parts used in the prior art for the contact body and contact disk, as well as the preparatory steps required in this connection, is eliminated. Furthermore, the present invention ensures that the connection between the contact body and contact disk is ideal at every point and does not have defects due to air inclusions, locally different solder temperatures, mechanically or thermally induced enlarged solder gaps or surface contamination, etc., which could negatively influence the magnetic field and lead to an increase in the electrical resistance of the vacuum interrupter.

[0025] In the following, exemplary embodiments of the present invention are explained in more detail with reference to drawings. It should be noted that all variants, configurations, and exemplary embodiments disclosed above and below can be combined with one another without restriction. Fig. 1 shows an AMF contact according to an embodiment of the present invention in a schematic representation; Fig. 2 . shows a RMF contact according to another embodiment of the present invention in a schematic representation; Fig. 3 shows a vacuum switch according to an embodiment of the present invention schematically in partial sectional view; Fig. 4A-D illustrate an embodiment of the manufacturing method according to the invention.

[0026] Fig. 1 shows an AMF contact element 10 for a vacuum switch with a contact body 11 consisting of a first conductive material or a composite material comprising a first conductive material. The first conductive material is preferably copper.

[0027] A contact disc 12 or a contact disc area is formed integrally on a surface of the contact body 11, more precisely on the surface of the contact body which is later to form the separable electrical connection of the vacuum switch.

[0028] Contact disk 12 consists of a composite material, in particular a particle composite material, which, in addition to the first conductive material, has at least one second conductive material. The second conductive material is preferably chromium or another material that increases the composite material's resistance to burn-off.

[0029] The contact element 10 has a plurality of oblique slots 13 distributed over the circumference, which are introduced into the contact element in such a way that they (together with the geometry of the corresponding mating contact) cause the formation of an axial magnetic field and thus a large-area distribution of a resulting arc on the contact disc.

[0030] Fig. 2 shows an RMF contact element 20 for a vacuum switch with a contact body 21 again consisting of a first conductive material or a composite material comprising a first conductive material. The first conductive material is preferably copper.

[0031] An annular contact disc 22 or an annular contact disc region is in turn formed integrally on a surface of the contact body 21, more precisely on the surface of the contact body which is later to form the separable electrical connection of the vacuum switch.

[0032] The annular contact disk 22 consists of a composite material, in particular a particle composite material, which, in addition to the first conductive material, comprises at least one second conductive material. Here, too, the second conductive material is preferably chromium or another material that increases the resistance of the composite material to erosion.

[0033] The contact body 21 has a plurality of oblique slots 23 distributed over the circumference, which are introduced into the contact body in such a way that they (together with the geometry of the corresponding mating contact) distribute the thermal load of the contacts by a rotation of the arc around the longitudinal axis of the arrangement on the contact disks.

[0034] Fig. 3 shows a vacuum interrupter 100 with two contacts 10, 20 according to the present invention. Two RMF contacts 20 according to Fig. 2 shown in detail, the different areas 21, 22 of which are shown clearly differently for better differentiation. In other embodiments, AMF contacts are used according to Fig. 1 or other contact forms designed in accordance with the present invention.

[0035] The vacuum switch 100 has a stationary connection disc or a stationary connection bolt 110 made of conductive material, preferably copper. This is connected to a stationary contact 10, 20 according to the present invention. A movable contact 10, 20 according to the present invention is aligned plane-parallel to the stationary contact and is supported by a movable connection bolt 170. The vacuum switch is closed by axial movement of the movable connection bolt 170 in the direction of the stationary connection bolt 110; the vacuum switch is opened by movement in the opposite direction. The movable connection bolt is guided in a guide 160.

[0036] The two contacts 10, 20 are arranged in a vacuum chamber 130, which is lined with a shield 140 and consists of a body 120 made of insulating material. A metal bellows 150 serves to seal the vacuum chamber 130 from the environment in the area where the movable connecting bolt enters the vacuum chamber.

[0037] Fig. 4 shows the example of an AMF contact according to Fig. 1 A preferred embodiment of the manufacturing method according to the invention. The preferred embodiment uses a field- and pressure-assisted sintering process, particularly preferably the so-called spark plasma sintering process (SPS process).

[0038] Generally speaking, according to the present invention, a contact element 10, 20 is produced by introducing a starting powder or a pre-pressed green body into a die and applying a uniaxial pressure via press dies. At the same time, an electric current flows through the sample to be sintered in a series circuit via the press dies and the die dies. The resulting Joule heating of the sample or die leads to very rapid heating of the sample, thus enabling efficient sintering of the material.

[0039] The starting point is Fig. 4A , a mixture 32 of particles of a first and a second material, preferably copper and chromium, more preferably one of the previously mentioned mixtures of copper and chromium with a chromium content of 25%, 30%, or 35%. This mixture is placed into the pressing die consisting of a sleeve 210 and a lower punch 240. Instead of the powder, a disc-shaped, pre-pressed green body can also be inserted into the die. This flatly distributed material 32 or the disc-shaped green body later forms the contact disc region 12, 22 of the contact element 10, 20.

[0040] Subsequently, an inner press punch 220 in the form of a cylinder is inserted, which has a smaller outer diameter compared to the inner diameter of the sleeve 210 of the press die.

[0041] Powder 31 of the first material, preferably copper powder, is then poured into the resulting gap or free space between the inner press punch 220 and the sleeve 210 of the die. Alternatively, a hollow cylindrical pre-pressed green body or a pre-machined cylindrical blank can also be inserted here. This powder 31 or the hollow cylindrical green body will later form the contact body region 11, 21 of the contact element 10, 20.

[0042] Afterwards, Fig. 4B , an outer pressing die 230 in the form of a pipe section or hollow cylinder is inserted, which fits exactly into the gap or free space between the inner pressing die 220 and the sleeve 210, and a pressing pressure A is exerted. Preferably, a voltage is applied to the pressing tools at the same time in order to effect the targeted heating described above.

[0043] The shape of the outer press ram 230 is preferably selected so that when a pressing pressure A is applied, the higher layered powder 31 is pressed first, before the pressing pressure A is increased if necessary and also acts as pressing pressure B on the inner press ram, Fig. 4D so that the pressing pressure and the electrical current are distributed as evenly as possible over the entire surface of both pressing rams 220, 230.

[0044] In embodiments of the invention, the pressing or sintering can be carried out in two steps, by following a first, in Fig. 4B In the pressing step shown, the outer pressing punch 230 is removed, further powder 31A is filled into the gap or free space between the inner pressing punch 220 and the sleeve 210, and the outer pressing punch 230 is again inserted into the gap or free space between the inner pressing punch 220 and the sleeve 210, and the second, final pressing is carried out, Fig. 4C und Fig. 4D .

[0045] Fig. 4D shows a special embodiment with a lower punch 240 movable relative to the sleeve 210 and pressing action A on the outer punch 230, pressing action B on the inner punch 220 and pressing action C on the lower punch 240. The pressing action A and B and C is effected by a press, wherein the Fig. 4B The shape of the inner and outer press rams described above means that initially only the outer press ram 230 is subjected to a pressing pressure A and only after a certain compaction of the powder 31 is a pressing pressure B also exerted on the inner press ram 220 and the powder 32 is pressed, which is optionally supported by a movement C of the lower ram 240 relative to the sleeve 210. By exerting the pressing pressure or pressures and optionally applying an electrical voltage, sintering takes place with at least diffusion processes and, as a rule, also chemical reactions or alloy formation in the interface area between the two materials.

[0046] By the method described above, a dense, monolithic contact comprising a contact disk region 12, 22 and a coil body region 11, 21 is produced in-situ.

[0047] Preferably, metal surfaces in contact with one another and / or those surfaces of the individual parts 210, 220, 230, 240 of the press die that are in contact with the powder or green body to be sintered are provided with a release agent, for example, a graphite coating or a boron nitride coating. Such a release agent facilitates disassembly of the press die and removal of the produced composite body after the pressing process.

[0048] With the method described above, it is possible to produce full-surface contact discs 10 as shown in Fig. 1 shown and annular contact discs 20 as in Fig. 2 shown to produce.

[0049] At the end of the SPS process, a contact element is available, the surfaces of which still need to be processed depending on the desired quality, for example, by polishing, to achieve a contact surface that is as flat and groove-free as possible. Likewise, it is usually necessary to slit either the coil body or the entire contact, as in connection with Fig. 1 und Fig. 2 discussed.

[0050] The advantage here is that the slots in the contact disc areas 12, 22 and the contact body areas 11, 21 can be introduced in one work step and the laborious alignment of pre-slit individual elements, as is required in the prior art, can be omitted.

[0051] Another advantage is that the sintered contact element is very close to the final shape, i.e. only a small amount of waste material is produced during final processing.

[0052] In advantageous developments of the present invention, it is also possible to manufacture the contact body from a composite material by adding, instead of pure copper powder 31, 31A, a suitable powder mixture of copper and another material that exceeds the strength of copper in the sintered state. This can also be done locally, i.e., for example, in areas of the contact body 11, 21 that are subject to particular mechanical and / or electrical stresses, such as the joints between contact 10, 20 and connecting bolts 110, 170.

[0053] In embodiments of the invention, it is possible to first create an annular contact disk region in a first sintering process and to transform this annular contact disk region into a full-surface contact disk in a second sintering process (not shown). A different material composition can be selected for the annular contact disk region than for the inner contact disk region; for example, the proportion of chromium in the inner contact disk region can be increased compared to the surrounding annular contact disk region, or other materials can be added. In this way, a full-surface contact disk 12 can be produced whose conductivity and magnetic properties vary across the radius of the contact disk in order to advantageously influence the current distribution and / or heat dissipation in the contacted state and / or the arc conduction during the opening process.

[0054] In yet other embodiments, varying material compositions can be achieved across the radius of the contact disk by filling the compression die with radially different powder compositions instead of a uniformly mixed powder 32. This configuration has the advantage of creating smooth transitions between the individual regions, thus resulting in less abrupt changes in the electrical and / or magnetic properties than in the previously described embodiment.

[0055] It should be noted that only selected exemplary embodiments that utilize the present invention have been described here. In particular, it is possible, for example, to design and manufacture other forms of contacts using the principles described here. Likewise, the materials designated as preferred are preferred, but the invention is not limited to these materials. Furthermore, as already mentioned, it is possible, for example, to choose an additive manufacturing process (3D printing) instead of the sintering process, for which most of the considerations and advantages disclosed in connection with the sintering process apply equally.

Claims

1. Method for producing a contact element (10, 20) for a vacuum switch (100), comprising the following steps: - introducing a first powder-like mixture (32), comprising particles of a first conductive material and particles of a second conductive material, or a first pre-pressed, disk-shaped green body consisting of a composite of at least a first and a second conductive material, into a pressing die (210, 240); - introducing an inner pressing stamp (220) into the die (210) ; - pouring a second powder (31, 31A) of the first conductive material or a second powder-like mixture, comprising particles of the first conductive material, or a second pre-pressed green body, comprising the first conductive material, into an intermediate space between the die (210) and inner pressing stamp (220); characterized by the following steps: - introducing an outer pressing stamp (230) into the intermediate space between the die (210) and inner pressing stamp (220); and - exerting pressing pressure (A, B) on the outer pressing stamp and on the inner pressing stamp in such a way that a disk-shaped region forming a contact disk (12, 22) of the contact element (10) is created from the first powder-like mixture (32) or the first green body, and a region forming a contact body (11, 21) of the contact element is created from the second powder (31, 31A) or the second powder-like mixture or the second green body.

2. Method according to Claim 1, in which an electrical voltage is additionally applied to the pressing stamps (220, 230) and the die (210, 240).

3. Method according to Claim 2, in which voltage feed-in points and the respectively fed-in electrical power are selected in such a way that the electrical currents flowing through the powder (31, 32) or green body are distributed approximately uniformly.

4. Method according to one of the preceding claims, in which the die and / or the pressing stamps are provided with a release agent before being brought into contact with one of the powders or green bodies.

5. Method according to one of the preceding claims, in which the first powder (32) is a mixture of copper particles and chromium particles.

6. Method according to one of the preceding claims, in which, after pressing and sintering of the powders (31, 32) and / or green bodies, a plurality of circumferentially distributed, oblique slots (13, 23) are introduced into the contact element (10, 20) or the region forming the contact body (11, 21) thereof in such a way that, during a flow of current, a magnetic field can be generated which brings about a movement of a resulting arc on a predetermined path and / or an extensive spreading of the arc.

7. Contact element (10, 20) for a vacuum switch (100) produced or producible by the method according to one of the preceding claims, having a contact body (11, 21) consisting of a first conductive material or a composite material which comprises a first conductive material, and a contact disk (12, 22) consisting of a composite material which, in addition to the first conductive material, comprises at least one second conductive material.

8. Contact element according to Claim 7, in which the first conductive material is copper.

9. Contact element according to either of Claims 7 and 8, in which the second conductive material is chromium.

10. Contact element according to Claim 9, in which the composite material is CuCr25 or CuCr30 or CuCr35.

11. Vacuum switch (100) having a vacuum chamber (130) within which two contact elements (10, 20) are arranged, wherein at least one of the contact elements (10, 20) is a contact element according to one of Claims 7 to 10.