DE2143844C3 - Process for the production of two-layer contact pieces as a molded part - Google Patents

Description

The invention relates to a method for producing two-layer contact pieces with a low-erosion contact layer and a solderable and / or weldable carrier layer, wherein on one a second layer consisting of a low-melting metal or alloy powder Layer of a powder mixture of at least one refractory metal or a refractory metal Alloy or a high-melting point metal compound and at least one low-melting point Metal of high electrical conductivity or a low-melting alloy of high electrical conductivity Conductivity is applied, both layers are compacted to form a molded body and this Shaped body above the melting temperature of the material of the first layer under protective gas, Inert gas or vacuum is heat-treated so that as a result of the measured amount of powder of the first layer the pores of the second layer are completely soaked and the carrier layer is formed.

One difficulty in the manufacture of contact pieces is to manufacture a contact material, which, in addition to the smallest possible burn-off in the arc, also has a small welding force during the Has switching of short-circuit currents, so that the contact pieces do not under these switching conditions weld. Furthermore, the switching chamber should be high-voltage-proof after rated current and short-circuit switching be. The closed contact pieces should also have a low contact resistance, so the heating with continuous rated current is not too high ■ -, increases In addition, the contact piece with the Carrier metal can be securely connected. In addition, the contact pieces should be large Quantities can be produced as economically as possible. In such composite materials it is used

κι difficult, with economical production costs produce the above-mentioned two-layer contacts as finished molded parts. To a little burn too achieve, the contact material should have the highest possible degree of space filling or the lowest possible

ι i have porosity. A small amount of burn-off is achieved using a metal framework made of a high-melting metal such as tungsten, molybdenum or rhenium. To improve the conductivity of the metal structure made of high-melting metal, it becomes a metal

m high electrical conductivity, such as silver or copper, added. With these metal composite materials, it is difficult to produce a

To achieve a degree of space filling close to 1.0. From US-PS 33 59 623 is the manufacture of

j, two-layer contact pieces with a low-erosion Contact layer and a solderable and weldable carrier layer known. ' The composite Contact piece by simultaneously compressing the difficult-to-melt powder for the contact layer

μ ι and the powder for the carrier layer produced for the Contact layer is a powder mixture of at least one refractory metal (W, Mo) or a refractory alloy or a refractory metal compound (WC) and from at least

i "> ens a low-melting metal of high conductivity (Ag, Cu) or a low-melting alloy of high electrical conductivity (Ag-Cu) is used. For the carrier layer is a powder mixture of a low-melting metal, such as silver and / or

i'i copper as well as iron, nickel or a nickel-copper alloy, used. The compacted molded body produced from these layers is at a temperature sintered above the melting temperature of the metal of the carrier layer.

ι> It is known from two different powder layers by filling and pressing a two-layer compact to produce a two-layer sintered body below the melting temperature of both layers is sintered (»powder metallurgy

Mi gie electrical contacts «, Springer-Verlag Berlin, 1964, page 148/149 and pages 211 to 213; “Sintered multilayer finished form contacts ", Siemens-Zeitschrift 36, 1962, pages 804 to 808). Because the gearing of the two powder layers in the size of the powder

■> ') chen, can be done by leveling the first layer or By pre-pressing this layer a more even contact surface between the two layers can be achieved.

From the French patent 10 79 067 electrical contacts are known that consist of penetration

i.o composite metal exist, for the production of a Powder mix from a high-melting metal, a highly conductive metal with a low melting point and nickel into one by means of a press die provided with regular indentations

tv> molded body is compressed, in its surface depressions portions of the Metal with a low melting point after sintering with liquid phase result in a good conductive layer.

The sintering impregnation technique is also known. Here, the higher-melting component is used a frame pressed and sintered and a second pressed body made of a lower melting component in a second heat treatment, in the so-called impregnation process, placed on or under the framework, after the second pressed body has melted, the framework is impregnated This technique creates an interpenetrating composite metal (e.g. WCu) as a single-layer contact piece.

To reduce manual labor, it is also known to use a two-layer pressed body to heat a lower melting layer above the melting temperature of this layer and with it to soak the first layer. Here, too, a single-layer penetrating composite metal is created. at With this technique, the irregularly adhering excess had to be used up to now the impregnation metal can be reworked by cutting (German Auslegeschrift 20 18 642).

The invention is based on the object of a method for producing two-layer contact pieces which largely overcomes the above-mentioned difficulties.

According to the invention the object is achieved in that the shaped body before the heat treatment with the first layer is arranged on a profiled ceramic plate with regular depressions.

In the method according to the invention, it is not necessary that in each case first the powder for the carrier layer is filled into the filling space of the die. It can also be the powder for the first Contact layer are filled into the filling space of the die and then the powder for the carrier layer are given.

To form the carrier layer, for. B. silver powder, copper powder or a silver or Copper alloy powder. To form the contact layer, for. B. powder mixtures of at least one of the Me'alle tungsten, molybdenum or rhenium or their alloy or from carbides of these metals and from powder of silver, copper or a mixture or alloy of these metals with nickel, iron or Cobalt can be used.

The invention is explained with reference to the drawing and exemplary embodiments.

On the basis of FIG. 1 to F i g. 9 shows the production of the two-layer molded body.

In Fig. 1 is a schematic representation in section of a die for pressing ctes two-layer molded body In the cylindrical filling space of the die 1, a Powder layer 2 made of a metal or a lower melting point compared to the contact layer Alloy, e.g. B. made of copper, silver or a silver or copper alloy, filled to form the contact layer a second powder coating is applied to layer 2 3 from at least one refractory metal or a refractory alloy or a refractory metal compound and from at least a low-melting metal! high electrical conductivity or a low-melting alloy high electrical conductivity, e.g. B. powder mixtures of at least one of the metals tungsten, Molybdenum or rhenium or their alloy or from carbides of these metals and from powder of silver, Copper or a mixture or alloy of these metals with nickel, iron or cobalt. Both Powder layers 2 and 3 become a two-layer molded body in and of itself between the punches 4 and 5 compressed in a known manner, which by relieving the upper punch 5 and raising the lower punch 4 is ejected from the die 1.

F i g. 2 shows a schematic representation in cross section the pressed two-layer molded body 6. It consists of the compression-molded carrier layer 2 'and the compression-molded contact layer 3 '. The two-layer molded body 6 is now with its carrier layer 2 'arranged on a profiled ceramic plate 9 with the regular depressions 10 and one Heat treatment above the melting temperature of the low-melting metal of the carrier layer 2 ' subjected to a protective gas atmosphere, inert gas or vacuum. Melts during the heat treatment the low-melting metal and fills the open pores of the contact layer. The amount of metal the Carrier layer 2 'is dimensioned so that it is sufficient to fill the pores of the contact layer 3' and in the In the molten state, an excess remains on the underside of the contact layer as a carrier layer

3 shows a schematic representation Section through the finished two-layer contact piece. The contact piece 11 consists of the contact layer 12 and the carrier layer 2 ″. The section 14 shows schematically the structure within the contact piece 11 after heat treatment. The pore space of the contact layer is made of the metal of the carrier layer filled out

2 In order to produce contact pieces with a spherical contact layer, it is advantageous, as is shown schematically in FIG. The metal powder 3 for the contact layer is first filled into the cavity and precompacted with the upper punch 5. After extension of the upper punch 5, the metal powder 2 is filled for the carrier layer and layers are both Pulve ^r compressed with the upper punch. 5 The pressing pressure for pressing the contact layer can be less than, equal to or greater than the pressing pressure for compressing the second layer. When pressing the two layers, the pebble areas are more compact than the middle area. During the heat treatment above the melting temperature of the metal or alloy of the carrier layer, the pore space of the contact layer is first filled and the excess of the molten metal of the carrier layer remains in the concave surface of the contact layer and fills it. This results in a thicker layer in the middle made of the lower metal of the carrier layer. B. made possible by soldering and welding.

In Figure 5 is a schematic representation in Section shows a convex contact piece. With 2 ″, the carrier layer and with U is the cheap contact layer designated.

The production technique according to the two-layer press-sinter-impregnation technique according to the invention leads to a dense contact layer and a melted compact carrier layer in a heat treatment process. As a result of the impervious impregnation of the contact layer It is not necessary to re-press after the heat treatment to increase the density. The surface of the carrier layer on the connection

side with the carrier metal can, for. B. be leveled or profiled by embossing with low pressure. So offers the embossing of a grid for contact pieces that are to be connected to the carrier metal by brazing, advantages for a secure soldered connection. Contact pieces that are to be welded on can create bottlenecks on the carrier layer by embossing obtained in the form of one or more humps. The contact properties of the Contact layer which consists of at least three metals, the metal of the carrier layer being the powdery metals penetrate the contact layer as a network. The metal of the carrier layer already be present in the powder base of the contact layer.

example 1

For the production of a two-layer contact piece with a contact layer made of WAg and a carrier layer made of Ag as a finished molded part, the procedure according to the invention is as follows:

A layer of electrolytic silver powder of particle size is placed in a steel press die <37 μΐη and above a layer of a powder mixture Tungsten powder obtained by reduction from WO3 (particle size <45 μπι) and electrolysis silver powder of the particle size <37 μπι filled. The composition of the WAg powder mixture is depending chosen according to the desired final composition of the WAg contact layer. In this example it consists of 65% tungsten powder and 35% electrolytic silver powder. The fill levels of the two layers are adapted to the contact layer height of the finished molded part. The two layers of powder filled on top of each other are compacted together to form a solid-edged pressed body with a given composition The WAg powder mixture can affect the final composition of the contact layer over the used Compression pin certain limits can be chosen. The density ρ of a compact from the WAg35 powder mixture as well as the associated degree of space fulfillment for

'WAgJS "" »J i" i ixviii- TT viii am ι y / yt CUIIlC \ Jt uinaic auucil or right ordinate inside) as a function of the pressing pressure are given in Fig. 6. For example, the density ρ of the pressed body from WAg 35, which was compacted with a pressure of 2 Mp / cm ² , at 10.0 g / cm ^3. This corresponds to a degree of space filling AvAg35 of 0.673. Based on the tungsten content, the degree of space filling is rw = 0.337. The heat treatment takes place at 1100 ° C for 1 hr. in hydrogen atmosphere. Above 960 ⁰ C, the silver present in the liquid phase. during sintering of the contact layer impregnation is carried out by the liquid silver, so that a substantially void-free contact layer is obtained.

The increase in density of the WAg35 layer under these sintering conditions is given in FIG. The increase in density and thus the increase in the degree of space filling can be seen from curve 5. In the example described, the pore volume in the sintered state is filled by the silver of the second layer. After the impregnation, the contact layer consists of 63.4 percent by volume silver and 36.6 percent by volume tungsten. This corresponds to 333% silver and 66.7% tungsten. The height of the silver layer of the pressed body is such that the pore volume of the contact layer is filled and a remainder for a silver layer thickness of 0.15 mm remains. The flow properties of the metal powder are determined by the flow time in a 60 ° funnel and a nozzle with a diameter of 4 mm; it is the length of time that elapses for 100 g of the metal powder to flow through the funnel. If the starting powder does not meet these flow properties and the flow time t _F < > 40sec / 100g, they are

in powder by conventional granulation processes into a transferring flowable form.

After the heat treatment, a WAg two-layer contact piece with a silver layer is applied Carrier side obtained directly by soldering or

1 '' welding to be connected to the base metal can. A cross-section through the contact piece shows a practically pore-free structure made of WAg and a second one Layer of practically pore-free pure silver.

From FIG. 6 the values for the applicable

jii denden pressing pressure to produce WAg contact layers with a higher tungsten content compared to the example given. At a pressure of 8 Mp / cm ² and the WAg35 powder mixture used, a contact layer with a

- "> Tungsten fill ratio rif of 0.44 obtained.

Example 2

In F1 g. 7 is analogous to example 1, the density and the Degree of space filling over the pressing pressure for the

ii Powder mixture WAg20 specified. It can be so that WAg contact layers with a tungsten degree of space filling Λν between 0.4 and 0.58 can be achieved. From a powder mixture of reducing tungsten powder of particle size <45 μπι and electrolysis silver

i · '' powder of particle size <37 μm in a mixing ratio of 80% tungsten and 20% silver, a two-layer pressed body with a silver layer and a second contact layer was produced with a pressure P of 4 Mp / cm ² Density of 12.05 g / cm ³ , corresponding to a degree of space filling of / \ vAg »-0.73 and one

TT Ulli ail | -I \ auillCI l

i au / VV Tun v ^ ri-

. t / iv TT al -

treatment takes place at 1100 ° C for 1 hour in ^ Atmosphere. During the heat treatment

'·> The density of the contact layer is practically retained, so that the S curve coincides with the P curve. During the heat treatment, the pores of the Contact layer is practically completely filled by the liquid silver of the second layer

>'| Contact layer made of 51 percent by volume tungsten and 49 percent by volume silver. The density ρ of the contact layer is 14.98 g / cm ³ . The composition of the contact layer corresponds to 34.4% silver and 65.6% tungsten. The height of the silver layer was such that the

«The pore volume of the contact layer was filled and a residual amount for a silver layer thickness of 0.13 mm remained.

Example 3

fco Should the contact layer still contain tungsten are higher, a powder mixture of 90% tungsten powder and 10% silver powder is assumed. As in the preceding examples is a two-layer compact, consisting of a silver layer and a Contact layer made from the WAglO powder mixture F i g. 8 shows the density and the degree of space filling as a function of the pressing pressure for the contact layer from WAgIO. Depending on the choice of press pressure

a tungsten degree of space filling between 0.5 and 0.65 can be set. The two-layer pressed body is subjected to a heat treatment at HOO ⁰ C for 1 hour in a! ^ - atmosphere. The density of a WAg 10 contact layer practically does not increase during the heat treatment, so that the sintered density curve S coincides with the pressed density curve P. The WAglO layer pressed at 6 Mp / cm ^{2 had} a density of 133 g / cm ³ . After filling the pore volume of the contact layer with silver, the contact layer consists of 62.5 percent by volume tungsten and 37.5 percent by volume silver, corresponding to 75.4% tungsten and 24.6% silver.

The density of the contact layer is 15.95 g / cm ³ . This finished form contact piece also has a 0.15 mm thick silver layer on the solder side.

The method according to the invention offers the possibility of dimensioning the second layer of pure silver so that that it is not sufficient to fill the entire pore volume of the contact layer. In In this case, an associated amount of silver remains in the contact layer in accordance with the selected amount of silver Residual porosity, while the remaining silver layer on the solder side is only due to the surface tension of the Silver results in a very thin layer <50 μπι.

It is the generally accepted opinion of the technical world that sintered impregnation contact pieces in the contact layer as possible should be used pore-free. Measurements of the burn-up value in the arc at a maximum current of 350 A (L) have shown that with a residual porosity of j% in the contact layer, the erosion value compared to the pore-free contact material increases only 10%. Only when the residual porosity increases further the burnup value doubles to 10%.

Example 4

Contact layer made of WAgNi,
second layer of pure silver

A powder mixture was used for the contact layer SUS D ^ HiiI / tirtncti / rdfromniilvpr Tpilrhpncrr Größe <45 lim.

Electrolysis silver powder, particle size <37 μm, and carbonyl nickel powder, particle size <10 μm, used. The composition of the powder mixture is 63.8% tungsten powder, 35% silver powder and 1.2% nickel powder. 9 shows the density ρ and the degree of space filling r for WAg35Nil, 2 pressed bodies as a function of the pressing pressure. A layer of electrolysis silver powder and then a second layer of the powder mixture WAg35Nil, 2 was first placed in a press die. The pressure used for compaction was 2 Mp / cm ² , a compact with a density of 10.1 g / cm ^{3 being} obtained. The heat treatment of the two-layered compact was at 1100 ⁰ C for 1 hour in hydrogen atmosphere. The density of the contact layer increases to 13.1 g / cm ³ (S curve in FIG. 9). The influence of the addition of nickel on the contact layer is shown when comparing FIG. 9 with FIG. 6 clearly. Without the addition of nickel, the density of the ^{body pressed at 2 Mp / cm 2} only increases to 10.9 g / cm ³ (compared to 13.1 g / cm ³ for the nickel-containing sample). The second layer of the pressed body made of pure silver is dimensioned in such a way that the liquid silver phase completely soaks the pore volume of the first layer during the heat treatment and an excess of about 0.15 mm of silver layer remains on the solder side a contact layer of 583% tungsten, 40.1% silver and 1.1% nickel, corresponding to the volume proportions 43.6% W, 54.6% Ag and 1.8% Ni.

Example 5

Contact layer made of WAgCuNi and a second layer on the solder side made of AgCu

A powder mixture of reducing tungsten powder of the particle size was used for the contact layer

ίο <45 μπι, electrolysis silver powder of particle size <37 μπι and carbonyl nickel powder of particle size <10 μπι used. The composition of the powder strip is 63.8% tungsten powder, 35% silver powder and 1.2% nickel powder. First a layer of electrolytic copper powder and then a second layer of the powder mixture WAg35Ni 1.2 was filled into a press die. The pressure used for compaction was 5 Mp / ciii ² . The density of the compression-molded contact layer made of WAg35Nil.2 was 11.8 g / cm ³ . During the heat treatment of the two-layer compact at 1100 ° C. for 1 hour in a hydrogen atmosphere, a liquid silver phase is formed in the contact layer and a liquid copper phase is formed in the second layer. While

2 ^r> the heat treatment of 1 hour is practically place a concentration equalization, so as to obtain a contact layer with a tungsten skeleton whose pores are impregnated with a AgCuNi alloy and a second layer which also consists of AgCuNi.

Example 6

According to the examples given above, a pressed body made of a powder mixture of WAg for the contact layer and made from a powder mixture of AgCu or AgCu alloy powder. In the subsequent heat treatment above the melting temperature of the silver and the silver-copper alloy One contact layer is formed from WAgCu and a second layer is formed on the solder side from AgCu.

. .

Example 7

The two-layer compact consists of a layer of a powder mixture of tungsten carbide with silver powder and a second layer of 5 silver powder. In the case of heat treatment above the At the silver melting temperature, a contact piece with a contact layer made of WCAg and on the solder side is created from a layer of silver.

- ₀ example

The two-layer pressed body consists of a powder mixture made of WRelO alloy powder and Consists of electrolytic copper powder and a second layer of electrolytic silver powder. In the subsequent Heat treatment above the copper melting temperature creates a two-layer contact piece with a contact layer made of WReCuAg and a second layer on the solder side made of AgCu.

_M example 9

The two-layer compact consists of a first layer made up of a powder mixture Consists of tungsten powder, tungsten carbide powder and silver powder and a second layer of copper powder After the heat treatment above the copper melting temperature, a two-layer contact piece is obtained, consisting of a contact layer of W, WC, AgCu and a second layer of CuAg.

The advantages of the method according to the invention are summarized below.

So far, the opinion has been that with the known sintering impregnation technology, no finished form contact pieces within the tolerance IT 12 according to DIN 7151 can be obtained. It was therefore surprising that there were the combination of the two-layer pressing technology with the sintering impregnation technology is quite possible, molded parts produce, in which even on the usual Nachpreßtechnik to achieve tight end tolerances is applied, can be dispensed with.

In the process according to the invention, the surprising effect occurred that when using z. B. a contact layer made of the powder mixture WAg35Ni and a carrier layer made of copper powder in the Sintering of the two-layer compact above the melting temperature of the copper within about 15 The concentration was practically equalized in minutes. In this way, contact pieces with a contact layer made of a high-tech machine Manufacture metal components, such as B. tungsten and a low-melting metal component such. B. an AgCu alloy, and a second layer on the carrier side made of AgCu, their concentration is practically the same as the low-melting component of the contact layer

Another technical advantage is that with poorly wetting alloys on the way according to the invention by incorporating an alloy component in the framework a flawless and Uniform impregnation both with complete pore filling and with partial pore filling of the framework of the high melting point component.

So far, two pressing processes were required for impregnating materials. In the first pressing process a Frame of the higher melting component pressed and after sintering this frame in a second Heat treatment impregnated with a predetermined amount of impregnation in the form of a second compact. at the method according to the invention is only a pressing process and in special cases an additional intermediate pressing process necessary.

Fiat nwip Vprfahrpn I> iptpt Hip Possibility of producing a penetrating composite material in a single heat treatment (T above the melting temperature of the metal of the carrier layer).

Another advantage is the saving of costly post-processing. Because the previous ones Penetrating composite metals work according to the usual impregnation technique with an excess of impregnation had to, irregularities of the surface occurred on the impregnation side due to this impregnation excess. the The final shape could only be achieved by machining these surfaces. In which

ίο method according to the invention is the amount of impregnation as second layer of the molded body dosed so that after the heat treatment, the liquid phase of the Carrier layer is absorbed as the predominant part by the porous framework and only part of the

ii excess of the carrier layer a practically flat, Solderable surface remains as a second layer on the contact piece.

A significant advance was made by the very economical production method (only one pre-press

ΛΙ gang - cvcniücii a ZwiSCiiCnprcßvorgarig Ufid "Μι a heat treatment during the contact piece production). This allows such contact pieces to be manufactured at low manufacturing costs. A further cost saving is achieved because the two-layer contact pieces no longer have to be machined as molded parts.

The method according to the invention also avoids a reject rate that is common with the usual Sinter-soaking technology occurs. With this technique, the sintered frameworks are pressed onto compacts from the Impregnation metal powder placed. The parts placed one on top of the other are put through a continuous furnace or a push-through furnace directed. Due to the vibrations that occur, some of them slip against each other, which means a reject arises as a result of incorrect impregnations. This error can also be caused by using Ceramic molded parts cannot be safely avoided. If the ceramic fit is too tight, the impregnation metal increases between the ceramic rings and contact parts so that

■ no more molded parts are obtained. When the invention Procedures, however, these errors are avoided. This is especially true for larger, high contact pieces and small contact pieces new methods superior to previous technology.

For this purpose 3 sheets of drawings

Claims (2)

Patent claims: 1. Method for producing two-layer contact pieces with a low-erosion contact layer and a solderable and / or weldable carrier layer, wherein on a first of a a second layer consisting of each low-melting metal or alloy powder Layer of a powder mixture of at least one refractory metal or a refractory alloy or a refractory Metal compound and of at least one low-melting metal high electrical Conductivity or a low-melting alloy of high electrical conductivity applied is, both layers are compacted to form a shaped body and this shaped body above the melting temperature of the material of the first layer under protective gas, inert gas or vacuum so is heat treated, as a result of the dimensioned Amount of powder of the first layer and the pores of the second layer are completely soaked Carrier layer is formed, characterized in that that the shaped body prior to the heat treatment with the first layer on a profiled ceramic plate is arranged with regular recesses. 2. Application of the method according to claim 1 to silver powder, copper powder or a silver or Kupier alloy powder for the carrier layer and on a powder mixture of at least one of the metals tungsten, molybdenum, rhenium or one Alloy of these metals, made from carbides of these Metals and from powder of silver, lupfer or a mixture or alloy of these metals with nickel, Iron or cobalt for the contact layer.