EP0796500B1 - Process and device for making a contact - Google Patents

Abstract

The description relates to a process for making a contact with a basic body of good electrically conductive material (first material) and a contact layer of less electrically conductive material (second material) which is resistant to arc burning, in which the contact layer has a sintered structure soaked with the material of the basic body. The basic body and the sintered structure are applied one on the other in a cup-like mould, heated therein to above the melting point of the first material but still below that of the second, so that the first material melts and penetrates the sintered structure. Here the sintered structure can be produced by scattering the second material in powder form on the first and first sintering in a degassing process below the melting point of the first material. It is also possible to produce the sintered structure beforehand and lay a green compact on the basic body.

Description

The invention relates to a method for producing a contact piece according to the Preamble of claim 1 (cf. DE 25 36 153 A1, Figure 3).

Contact pieces that must lead to an arc during a switching operation must different conditions are sufficient. Firstly, with the switch closed the contact piece has a sufficiently high electrical conductivity; to the others the contact piece must not be too fast when a switching arc occurs erode so that the service life of the switching device remains sufficiently long. While in gas-insulated high-voltage circuit breakers, the contact arrangement is divided can be in contact pieces that carry the nominal current, and contact pieces, which lead the arc and must therefore be erosion-proof, can with one Vacuum switch no contact pieces carrying the nominal current are provided be so that the only contact piece arrangement both the rated current and must lead the arc.

When switching off in a vacuum chamber, certain forms A so-called contracted electric current, which is formed by suitable shaping of the Contact pieces is set in rotation, so that the contact material burns off can be kept low. Nevertheless, the surface of the opposite Contact pieces must be provided with erosion-resistant material to prevent erosion the contact pieces, as mentioned at the beginning, remains small.

In the past, the contacts for a vacuum switch are two or More metallic components have been produced, in which a sintered metallic Structure, which often consists essentially of chrome, is impregnated with copper, so that a contact body made of a chrome-copper alloy is created. Can on an industrial scale usually such chrome-copper contacts sintered metallurgically from a powder mixture of the corresponding metals are produced, here contact pieces arise that consist entirely of this mixture.

Because the erosion-resistant material, such as chrome, has a lower electrical conductivity exhibits than copper, one strives to the chrome portion in the whole To keep the contact piece as low as possible, which is possible in many different ways. For example, a contact plate made of the composite metal can be on a base body be applied; from DE 31 07 688 it is known, for example, that Coating the surface by a plasma spraying process.

DE 35 41 584 describes a method and an apparatus for producing Metal composite materials and contact pieces made with them for electrical Switchgear has become known in which with a suitable energy beam Surface of the base body melted in areas and powder active components the melting volume and be built into the base material.

In the method according to EP 0 458 922 B1, the substrate surface, i. H. the Surface of the carrier body melted locally and the additive in the form of a loose powder layer applied to the substrate surface; this makes it in the Powder layer is wetted or the powder layer is coated with the liquid Material impregnated from the melted local area, causing the powder the powder layer is integrated into the surface of the substrate and the desired one Surface layer is formed.

EP 0 099 066 A1 describes a method for producing a composite material made of chrome and copper, in a degassed form of work Chrome powder is poured, on which powder a piece of low-oxygen Copper is placed. Then the work form is closed with a porous lid, degassed, then the furnace temperature to a temperature below the Melting temperature of the copper increased, kept constant for a while and then continue to heat until the copper melts and the chrome powder spill is completely filled with liquid copper. With this process flow A chrome-copper composite block is made that is required in contact pieces Geometry is broken down.

DE 25 36 153 A1 describes a method for producing multilayer contact pieces become known for vacuum medium voltage line switches, in which in one Crucible chrome powder or a sintered disc made of chrome and placed on it a copper disc can be placed. If the temperature is above the melting temperature of copper is increased, then the copper penetrates into the sintered layer and flows through and collects in a free space of the crucible below the sintered layer. In another embodiment, it is located below the sintered layer Chrome powder is a disc made of stainless steel or similar material; after increasing the temperature above the melting temperature of the copper penetrates the A sintered structure and soaked this, so that thereby a contact piece with chrome nickel steel and a copper-chrome layer is formed. With both methods lies the copper disc on the side of the chrome sintered or powder structure, that of the open Side of the crucible is facing.

The object of the invention is to provide a method for producing a contact piece create that is easy to carry out and in which a contact piece is made which, on the one hand, has good electrical conductivity with high arc erosion resistance as has sufficient mechanical strength.

This object is achieved by the characterizing features of claim 1.

According to the invention, the second material for forming the sintered structure should be in powder form or applied in the form of a presintered plate (green compact) to the first material become. After that, the materials are first brought to a sintering temperature or degassing temperature below the melting temperature of the first material to be produced the sintered structure and then both above the melting temperature of the first Heated material.

According to the invention, the two materials are thus preferably cup-like Form introduced that the first material on the bottom side and the second material are arranged on the open side of the cup-like shape; that forms the first Material the base body and the second material the sintered structure for the contact surface. To form the sintered structure, the second material is powdered onto the first Material applied or sprinkled. Alternatively, the second material is in the form of a prescreen, So a green body is placed on the first material, after which both materials are first to a sintering temperature below the melting temperature of the first material to create the sintered structure and then the melting temperature of the first Heated material.

Studies have shown that, in particular, if the mold is made of steel, the copper wets the inner wall of the steel mold, so that if the amount of powder is at the same level or below the edge of the Shape, the applied chrome copper layer sinks inwards from the edge, so that the entire contact body layer during post-processing in the edge area is turned off.

For this reason, the mold is overfilled with powder, so that the powder reaches the edge of the Form dominates. So that the powder does not trickle down on the side, a form ring is placed on the Base body placed, which ensures that the powder is tapered in the edge area is; the cone angle is an embankment angle that depends on the grain size of the powder. In any case, such an angle must be chosen so that the powder do not trickle down to the outside in this area.

The base body can also have a cup-shaped depression on its contact side have, into which the second material is introduced; the edge of the depression should then protrude the edge of the shape.

There is also the option of creating a cup-shaped recess Place the ring of the first material on the base body, the inner wall touches the form and inside the second material in powder form z. B. located. This ring should also protrude from the edge of the shape.

Even in the event that the second material is already presintered in Shape of a plate, d. H. in the form of a green compact, on which the first material is placed, this presintered plate should protrude beyond the edge of the mold.

The cup-like shape can be made of metal, preferably steel or stainless steel; This shape then remains on the finished contact piece as a so-called lost shape. This lost shape has the advantage of being opposite to that of the contact surface lying side the contact piece mechanically reinforced and stiffened. Used If you use ferritic steel, you will expediently become the wall of the bowl shape only partially remove it, to the extent that when switching off the Arc does not reach the end edge of the form from the ferritic steel. Hereby you get another advantage: there are different types of contact pieces, for example Spiral contact pieces, between which a radial magnetic field when switched off is produced. The arc contracts and is shaped by the spiral shape in Rotation offset. It is expedient to generate an axial magnetic field because the axial Magnetic field creates a diffuse arc. If the wall shape cooling is only partially turned off, i.e. on the outer edge of the contact piece is still present, then this wall reinforced together with the wall of the opposite contact piece in the circumferential area, the axial magnetic field.

It is also possible to make the mold out of ceramic; instead of being made entirely of ceramic, it can have a bottom made of carbon (graphite) and a wall made of ceramic pressed against the bottom. The inner surface of the wall made of ceramic is not wetted by the first material, so that after solidification the surface is convex. Al ₂ O ₃ can advantageously be used as the ceramic.

Studies have shown that when cooling without further measures Blowholes can arise in the central area, so that such a contact piece is not usable. Therefore, the cooling process must be controlled so that cooling in the area of the central axis of the contact piece takes place earlier than in Peripheral area, and for this purpose the peripheral area of the contact piece surrounded by shielding plates in the furnace, which follow from the edge of the contact piece reflect heat radiated from the outside, so that the cooling from the inside, ie from the central axis of the contact piece can be made. This will be in the middle Avoid blowholes and any small blowholes in the outside area can be turned off easily and be removed.

If a contact piece is to be made that is built into a vacuum interrupter then oxygen-free highly conductive copper is used as copper and the heating is carried out in a high vacuum furnace. The chrome powder degasses in a high vacuum furnace at temperatures below the copper melting point. In the course of this extrusion degassing, the powder sinters into a rigid, porous framework together, the thickness of the layer changing insignificantly. Of course there is also the possibility of the chrome powder during this degassing process subject to a pressure force, which is done with a corresponding pressure stamp can. After completing this process, the system is briefly over heated the copper melting point, so that the porous chrome layer is non-porous with high-purity Copper is soaked.

It is also possible to carry out the process in a protective gas atmosphere instead of in vacuum perform. which can consist of argon or helium.

Any type of metal can of course be used instead of chrome powder alone, provided that its melting temperature is above that of the melting temperature of the carrier body. Instead of chrome alone, any other metal can be used and mixtures of these metals can be used.

In addition, the invention can also be used to produce contact pieces for Switching devices are used that are not vacuum interrupters. If instead a plate-shaped base body shape, the base body has a rounded dome shape having. then this can also be used in a form made of steel, for example are: it is then completely filled with the second material, so that the dome-shaped body is completely covered; here too is an overcrowding of Form with the second material makes sense in the same way as with the disc-shaped Contact pieces.

The thickness of the contact layer is also determined with the thickness of the powder layer; ever Depending on the grain size of the powder and sintering process, the proportion of chromium in the Contact layer can be varied.

Using the drawing, in which some embodiments of the invention are shown are, the invention and other advantageous refinements and improvements the invention and further advantages are explained and described in more detail.

Show it:

1 to 5

different configurations of the form with inserted Components,

Fig. 6

2 shows a sectional view through a mold with shielding plates,

7 and 8

two further embodiments of a mold according to the invention,

9 and 10

two finished contact pieces,

11 and 12

two further embodiments of the invention,

Fig. 13

12 after the heat treatment, and

Fig. 14

a temperature-time diagram for the heat treatment of the contact pieces.

To carry out the method according to the invention and to produce a contact piece with a base body made of electrically highly conductive material, preferably made of copper, and a contact layer, preferably made of chrome-copper is like manufactured as follows:

In a cup-shaped mold 10 with a bottom 11 and a side wall 12, a base body 13 made of copper is inserted, which has a cup-shaped depression 14 with an axially projecting edge 15 on its contact-side surface; Chrome powder 16 is filled into the bowl shape 14, 15. The annular gap 17 between the inner surface of the mold 10 and the outer surface of the base body 13 should be as narrow as possible. Then the mold 10 with the base body 13 and the chrome powder 16 (hereinafter also referred to as contact layer 16) is introduced into a high vacuum furnace and subjected to a heat treatment according to FIG. 14. First, the arrangement is heated to a temperature T ₁ , which is below the melting point of the material from which the base body 13 is made. For copper this is a temperature of 1,083 ° C; the temperature T ₁ must be less than 1,083 ° C. During the period Δt _E , the arrangement is degassed and the powder 16 sinters together through the fusion and forms a porous structure, a sintered structure. By increasing the temperature inside the furnace to the value T ₂ , which is above the melting point of copper but below the melting point of the chrome powder, the sintered structure is impregnated with copper, so that the contact layer is formed. The cooling then takes place inside the furnace, with a shield 18 being arranged around the arrangement according to FIG. 6, each having an opening 19 and 20 in the wall 21 and 22 running parallel to the bottom 11 of the mold 10 in the region of the central axis MM of the arrangement the shield 18 has. Thereby, heat energy E can radiate through the openings 19 and 20, whereas the heat energy W, which is radiated from the edge of the arrangement, is reflected again by the shield 18 towards the edge. As a result, the cooling is controlled from the inside, ie from the center MM to the outside. thus preventing blowholes in the area of the center MM: should small blowholes possibly appear in the area of the edge, these can easily be removed by machining. 6 shows the finished contact piece 23 and it can be seen that the collar 15 has disappeared in the contact layer 16a of FIG. 6; the material of this collar has flowed into the sintered structure. The thickness of the contact layer 16a depends on the depth or height of the powder layer 16 of FIG. 1.

1, the shape is made of a material made of the copper of the base body 13 is not wetted.

2, the shape 24 is made of metal, stainless steel or steel manufactured; this form is wetted by copper and is then a so-called lost Shape; it is part of the contact piece.

In the embodiment according to FIG. 3, a cover or a plate 25 is on the collar 15 applied, which has holes 26, through the powder during the sintering and degassing process the gas can escape. Possibly. can the outside diameter of the Plate 25 may be smaller than the inner diameter of the collar 15; then the plate can 25 are pressed against the powder with a certain pressure force, whereby the Size of the cavities formed during the sintering and degassing process is affected can be.

4, the bottom 27 of the mold 24 and the side wall 28 coated with ceramic 29 and 30, so that the sintered contact piece from the Form 24 can be removed. There is also the option of Omit coating 29 so that the copper of the base body 13 the bottom 27 wetted.

5, a plate 31 made of copper is inserted into the mold 24. On the plate 31 made of copper, a ring 32 is placed, which has a radial collar 33 and has a cylindrical projection 34. The cylindrical projection 34 has an outer diameter that fits snugly into the wall 28 of the mold 24. The inner surface 35 of the cylindrical projection 32 is conical, namely to Bottom 24 designed to expand. The angle α that a surface line with the neighboring one Surface of the copper plate 31 forms. is to be measured in this way. that that on the Plate 31 placed powder 36 does not trickle down when the ring 32 is removed. The angle α is practically a slope angle; it depends on the grain size of the Powder 36.

From Fig. 5 it can be seen that the free surface of the powder 36 is the edge of the Overhanging side wall 24. This is due to the following:

2, 3 there is the problem that the copper of the Base body 13 wetted the side wall 28 of the mold 24. This pulls through Copper of the base body 13 on the inner wall to the edge of the side wall 28 high, so that the thickness of the finished contact piece in the middle, ie in the center M-M is lower than on the outer peripheral edge; the contact layer 16a is concave. so that in the manufacture of the actual contact piece on the peripheral edge There is a risk that the entire contact layer is twisted off. Such a structure is not to be used. For this reason, the height of the powder layer 36 is chosen so that it projects beyond the edge of the side wall 28. The form 24 is overcrowded and it forms a contact piece shape, in which the parting plane 16b Contact layer 16 and the base body 13a is very flat, provided that the adjacent one The surface of the base body 13a was flat. If the neighboring area of the base body 13a has a different shape, then this parting plane becomes this correspond to another shape since the sintered structure through this surface of the contact body or base body 13 is affected.

If the mold is made from a non-wetting material, then it will form a convexly curved surface of the contact layer 16a, see also FIG. 13.

In order to avoid a concave configuration of the contact layer 16a, according to FIG Fig. 7 of the base body 70 with a projecting collar 71 to form a recess 72 dimensioned such that it has the free edge 73 of the side wall 74 of the mold 75. which corresponds to form 24, towers above.

Instead of an integrally formed edge or collar 71, the base body can be 80 a ring 81 are placed, the outer diameter of the inner diameter the side wall 74 corresponds to the shape 75. The ring 81 dominates the Margin 73.

9, the side wall 74 of the lost mold 75 is turned off, the free edge 76 being chamfered and below the parting plane 77 lies between the base body 78 and the contact layer 79, so that an arc does not contact the side wall 74 of the mold.

10, the bevelled edge surface or end surface to be replaced by a concave arch shape 82.

9 and 10, the mold 75 is made of ferritic material manufactured. This creates in the area of the side walls 74 between the 9 and FIG. 10 contact piece and a similarly formed, opposite Contact piece an axial magnetic field 83, which has other advantages has, especially if there are suitable measures between the opening ones Contact pieces an axial magnetic field is generated.

In the embodiments according to FIGS. 1 to 10, the base body is a disk, possibly with protruding edge drawn. There is also the possibility, see Fig. 11, in a shape 84, which corresponds to the shapes 24, 75, a dome-shaped base body 85 insert and the space 86 between the shape 84 and the base body 85 with Fill in powder 87, with the free surface 88 of the powder covering the edge 89 of the mold 84 protrudes and there again an embankment similar to the embankment 35 of FIG. 5 is formed becomes. You can now the arrangement according to FIG. 11 in the same way Submit heat treatment processes such. B. the arrangements according to FIG. 1 to 6. Then the dome-shaped base body 85 into the sintered structure through the powder 87 is formed, penetrate and by a suitable cutting Post-processing can thereby form a dome-shaped contact piece, which is used as an arcing break contact in a high-voltage circuit breaker can be used in which an insulating gas is used as the extinguishing medium.

The shape according to FIG. 1 is a ceramic shape, which can be made of Al ₂ O ₃ , for example.

In the embodiment according to FIGS. 12 and 13, a mold is used which has a carbon plate (graphite plate) 90 on which a cylindrical ring 91 made of Al ₂ O _{3 is} placed. In the ring 91, a base body is inserted on the plate, which, since it is the same as the base bodies according to FIGS. 1 to 4, is given the reference number 13. The ring 91 must be pressed against the plate 90 with mechanical force F in order to prevent liquid copper from escaping through the gap between the ring 91 and the plate 90. After the heat treatment, which proceeds in the same way as the process sequences described above, the contact layer 92 is convexly curved, in particular in the peripheral edge, since the copper of the base body 13 does not wet the ceramic ring. In all arrangements, oxygen-free, highly conductive copper is preferably used for the base body; Chrome powder is used to form the contact layer. It goes without saying that any type of material can be used for both the base body and the contact layer, provided that the material of the base body is electrically conductive and the material for the contact layer is erosion-resistant and has a low tendency to weld. Copper and chrome are just common materials that are commonly used in vacuum interrupters. As is known, the copper-chromium mixture ratio can be set in a wide range by sintered metallurgy, so that the electrical resistance value, the arc resistance and the tendency to weld can be optimized. The chrome powder can have different grain sizes or only a grain size in a narrow size range. Grains of different shapes can also be used, it being additionally possible to use a mixture of chrome-copper powder to form the sintered structure for the contact layer.

It is shown above that all sintered structures are made by powder applied to the base body in free-flowing form and then the free-flowing Powder is sintered. There is also the option of a previously sintered one Place the plate on the base body; which in the embodiments according to FIGS. 1 to 13 applicable considerations regarding convex or concave surface shape must also be observed when a sintered plate (green compact) is placed on top.

The problem with using a mold made of steel or stainless steel is that a certain amount of steel alloyed into the copper melt. If necessary, the inner surface of the mold 24 could be covered with a sheet of material that is in the Copper melt is insoluble, e.g. B. tungsten or molybdenum, so that the Form of the copper melt, similar to the version with the coating 29, 30 with ceramic, is separated.

A high vacuum furnace is used to manufacture contact pieces for a vacuum switch be used so that the chrome powder can be degassed sufficiently can. At least in the embodiment according to FIG. 11, a protective gas atmosphere could also be used prevail in the oven.

Claims (19)

1. Method of producing a contact element having a base body made of a first material having good electrical conductivity and a contact layer made of a second material which has a less good electrical conductivity and is resistant to arc erosion, the contact layer having a sinter structure which is impregnated with the material of the base body, the base body and the sinter structure being placed one above the other in a cup-like mould and being heated therein to above the melting temperature of the first material but still below the melting temperature of the second material, so that the first material fuses and penetrates into the sinter structure, characterized in that, in order to form the sinter structure, the second material is applied in powder form or in the form of a presintered plate onto the first material, in that the materials are firstly heated to a sintering temperature or degassing temperature which is below the melting temperature of the first material, in order to produce the sinter structure, and then both materials are heated to above the melting temperature of the first material.
2. Method according to Claim 1, characterized in that the amount of powder scattered onto the contact body is such that the powder protrudes above the rim of the mould.
3. Method according to Claim 2, characterized in that the powder in the peripheral region is scattered onto the base body in a conically bevelled manner, the cone or slope angle being selected such that the powder is prevented from trickling downwards.
4. Method according to Claim 3, characterized in that the slope angle is produced by means of a moulding ring which is placed onto the base body.
5. Method according to one of the preceding claims, characterized in that the base body has a cup-like depression, into which the second material is introduced, on its contact side.
6. Method according to one of the preceding claims, characterized in that a ring made of the first material is placed onto the base body, which ring touches the inner wall of the mould and into the interior of which ring the second material is introduced.
7. Method according to Claim 6, characterized in that the ring protrudes above the rim of the mould.
8. Method according to Claim 1, characterized in that the plate is sintered such that it has a thickness which is such that it protrudes above the free rim of the mould after being placed onto the base body.
9. Method according to one of the preceding claims, characterized in that the sinter structure is preferably produced from chromium, molybdenum, tungsten, hafnium, niobium and tantalum and mixtures thereof.
10. Method according to Claim 9, characterized in that a sintering aid is admixed to the metal powder, which sintering aid is either a metal powder or a readily decomposable metal salt.
11. Method according to one of the preceding claims, characterized in that the cup-like mould used is one which consists of metal, preferably of steel or stainless steel.
12. Method according to Claim 11, characterized in that after cooling the wall of the mould is at least partially removed by turning.
13. Method according to one of Claims 11 to 13, characterized in that at least the inner surface of the wall of the mould is covered with a ceramic layer before the Cu plate and sinter structure are inserted.
14. Method according to one of Claims 11 and 12, characterized in that before the Cu plate and sinter structure are inserted the inner surface of the mould made of metal is lined with a foil made of a metal which is not soluble with the first material, so that during fusion of the first material the metal of the mould is prevented from dissolving.
15. Method according to one of Claims 1 to 10, characterized in that the mould is formed at least partially from ceramic.
16. Method according to Claim 15, characterized in that the mould is produced in such a manner that it has a bottom made of carbon and a wall made of ceramic, preferably Al₂O₃, which is pressed against the bottom.
17. Method according to one of Claims 11 to 16, characterized in that the powder layer is covered with a metal plate which is joined to the contact layer in a fixed and pore-free manner during the impregnation operation and which has bores or grooves for degassing.
18. Method according to one of Claims 11 to 17, characterized in that the cooling operation is controlled in a furnace such that the contact element cools down more rapidly in the region of the centre axis than in the region of the periphery.
19. Method according to Claim 18, characterized in that the peripheral region of the contact element is surrounded in the furnace by screening plates which reflect the heat radiated from the edge of the contact element during cooling, so that the cooling takes place from the inside, that is to say from the centre axis of the contact element.

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