DE1100833B - High density composite metal for heavy-duty electrical contacts - Google Patents

Description

GERMAN

Silver is suitable for use thanks to its physical, chemical and technological properties well suited as contact material. In the case of high electrical loads, however, the erosion resistance is sufficient and the welding security of pure silver is no longer sufficient. The erosion resistance is known and the sweat security through additives, z. B. of tungsten, molybdenum or nickel to increase. There these metals do not have to have solubility in silver either in the liquid or in the solid state the "composite metals" in question are manufactured using the powder metallurgical process. The erosion resistance of a contact material largely depends on its relative density (degree of space filling) dependent: the aim is therefore to achieve as complete a dense sintering as possible. This is however difficult when the components of the composite metal have significantly different melting points have, as z. B. with tungsten, molybdenum and nickel with a melting point of 3380 resp. 2620 or 1452 ° C compared to silver with a melting point of 960 ° C is the case. One sintered namely above the melting point of silver, some of it escapes, and despite this it becomes more fluid Phase practically no increase in density reached.

Composite metals with a relatively high density are known as heavy metal alloys known. They consist of 85 to 95% tungsten, 3 to 10% nickel and 2 to 5% copper. the Starting powder mixtures of these substances can be sintered for one hour between 1400 and 1500 ° C sinter to almost theoretical density. The cause of the large increase in density achieved during sintering lies in the appearance of a liquid phase in which the tungsten is soluble. In the case of the aforementioned On the other hand, there is no increase in density in the tungsten-silver system because tungsten, as I said, is generally not soluble in liquid silver either.

The invention relates to a composite metal for heavy-duty electrical contacts. This composite metal made according to the invention of at least 90 ⁰ Zo) tungsten and silver, and of two further components, each with 0.1 to 5% of the metals copper, nickel, cobalt or iron. The percentages here and - unless stated otherwise - also in the following refer to percentages by weight. The composite metal according to the invention has a density which is at least 95% of the theoretical density; this is what makes it particularly resilient as an electrical contact. The high density is achieved by the liquid nickel-copper phase that forms during sintering, in which tungsten is soluble up to a proportion of more than 20%. As it cools, the solubility of tungsten decreases sharply, a high-density composite metal
for heavy-duty electrical contacts

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Dr. techn. habil. Horst Schreiner, Nuremberg,
has been named as the inventor

and it is eliminated again. In the silver, which still contains some copper, nickel and tungsten dissolved, is the tungsten embedded in the form of round particles. The resulting contact material is practical non-porous. The electrical conductivity is essentially made up of the volumetric proportions of the tungsten and the binder metal alloy together. Its very low contact resistance is particularly advantageous. The tungsten content is adapted to the respective requirements; is particularly advantageous a proportion of tungsten between 30 and 60 percent by volume.

The composite metal according to the invention is produced by the known powder metallurgical process. The sintering is generally carried out in a manner known per se in an inert or protective gas atmosphere. For contacts of vacuum switches, sintering takes place in a high vacuum, preferably at a pressure of less than 10 ^-3 Torr. Care must be taken that the sintering temperature is increased so slowly before the appearance of the liquid phase that the pores of the compact remain open for degassing. A residual gas outbreak occurs in the liquid phase.

Examples are given below with data on the composition and the manufacturing process:

example 1

A tungsten-silver-copper-nickel mixture with the proportions 50: 40: 5: 5 is assumed. After intimate mixing, the metal powder mixture is ^{pressed at 1 t / cm 2} and at 1050 ° C for a

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1 1 OO 833

Sintered in a hydrogen atmosphere for an hour. This creates a liquid phase in which the tungsten is partially soluble. The sintering increases the compressed density from 7.55 g / cm ³ to 12.95 g / cm ³ . With a theoretical density of 13.28 g / cm ³ , this corresponds to a degree of space filling of 0.975. The composite metal is still plastically deformable in the cold and can be re-pressed cold up to the practically theoretical density.

Example 2

A mixture of the components of Example 1 in proportions 54:44: 1: 1 is processed under the same pressing and sintering conditions as in this example. The compressed density increases from 8.02 g / cm ³ to 13.4 g / cm ³ ; this corresponds to a degree of space utilization of 0.968. The conductivity is 32 m / Ω · mm ² . With a corresponding vacuum sintering with a pressure of less than 10 ~ ^s Torr, the theoretical density is practically achieved. The composite metal produced in this way is characterized by a favorable contact resistance; With a contact load of 1.5 kg it is 0.21 mÖ and is therefore only about twice as high as the contact resistance measured under the same conditions for pure silver. This means that the contact material is also suitable for air shooters thanks to its good erosion resistance and welding reliability.

The structure of this contact material is shown in an approximately 500-fold enlargement in the drawing. The dark tungsten particles are embedded in the light silver-copper-nickel base metal. the mean tungsten grain size is about 6 μ. The size 10 μ is given as a scale comparison.

Example 3

A mixture of the components of Example 1 in the proportions 54.8: 44.8: 0.2: 0.2 is processed under the same pressing and sintering conditions as in this example. The pressed density of 8.0 g / cm ³ is increased to 12.35 g / cm ^{3 by sintering;} this corresponds to a degree of space utilization of 0.89. A correspondingly composed and sintered compact without the copper-nickel addition, on the other hand, only has a sintered density of 8.70 g / cm ³ , so there is practically no increase in density during sintering. This example shows that even relatively very small copper-nickel additions produce the effect according to the invention.

Example 4

An intimate tungsten-silver-copper-cobalt mixture with the proportions 54: 44: 1: 1 is ^{pressed at 1 t / cm 2} and a pressed density of 7.85 g / cm ^{3 is} achieved. Sintering for 1 hour at 1150 ° C. in a hydrogen atmosphere increases the density to 13.04 g / cm ³ ; this corresponds to a degree of space filling of about 0.84. The theoretical value is obtained practically by cold re-pressing.

Example 5

An intimate tungsten-silver-iron-nickel mixture with the proportions 63: 34: 1: 1 is ^{pressed at 1 t / cm 2} and sintered for one hour at 1100 ° C. in a hydrogen atmosphere. The compressed density increases from 8.0 g / cm ³ to 13.5 g / cm ³ ; this corresponds to a degree of space utilization of 0.92. This composite metal, too, can practically be compressed to the theoretical value by cold re-pressing.

Claims (4)

Patent claims: 1. High-density composite metal for heavy-duty electrical contacts, characterized in that that it consists of at least 90% tungsten and silver and two other components of 0.1 to each 5 ° / o of the metals copper, nickel, cobalt, or Iron is made. 2. Composite metal according to claim 1, characterized in that the proportion of tungsten to 30 to 60 percent by volume. 3. A method for producing a composite metal according to one of claims 1 and 2 according to the powder metallurgical process, characterized in that the sintering is known per se Way is carried out in an inert or protective gas atmosphere. 4. A method for producing a composite metal according to one of claims 1 or 2 according to the powder metallurgical process, characterized in that the sintering in a high vacuum, preferably at a pressure less than 10 ^-3 Torr, carried out and the sintering temperature before the occurrence of the liquid phase is increased so slowly that the pores of the compact remain open for degassing. Considered publications:
German patent specification No. 756 337. 1 sheet of drawings © 109 528/600 2.61