DD249992A1 - MAIN CONTACT FROM MOLYBDAEN COPPER FOR HEAVY VACUUM SHOOTING - Google Patents

Abstract

Main contacts for heavy vacuum protection generally consist of a molybdenum-copper alloy provided with additives. The goal is to create a material-economical and moderately favorable main contact. The problem to be solved is to be seen in the warranty of a gas-poor, erosion-resistant, sufficiently electrically conductive contact, whose anti-whitening behavior is improved with good loability compared to the known main contacts. The problem is solved by the fact that the Molybdaenanteil at least 64, but at the most 70 Ma .-% be tre.

Description

Joachim Cmok. P 1232

Kurt Lauterbach's IPK: H 01 H, 1/02

Edeltraud Mörinig. 05/21/1986

Gerhard Mönnig

Title of the invention

Main contact made of molybdenum-copper for heavy yakuum contactors

Field of application of the invention

The invention relates to a main contact of molybdenum-copper for heavy vacuum contactors, which are applied in the low voltage range between 100A and 1000 A in the field of electrical engineering.

Such contacts must except very good erosion resistance, which causes a long life, also have sufficiently good anti-perspirant properties, because the forces necessary for contact separation when switching off should be as small as possible. Furthermore, high electrical conductivity and low contact resistance are desirable in order to reduce the current heat dissipation. Lusten in the on state to minimize. Not least, the solderability is sought by means of conventional vacuum brazing, so that the further processing of the contacts by joining operations can be done without additional effort, such as the application of solderable layers or the use of gold-containing brazing alloys.

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Characteristic of the known technical solutions

There are already known contacts for vacuum switches, in which the porous skeleton of tungsten or molybdenum was infiltrated in vacuo with molten copper or copper alloys. The use of the high-melting metals tungsten or molybdenum as builder ensures a very good erosion resistance and infiltration in vacuum low gas contents of the contacts, while alloying additives to copper, such as Ti or Zr, increase the wetting behavior of the copper melt and the gettering of the contacts.

Although the pure molybdenum-copper contacts having compositions of about 55 parts by weight of molybdenum and 45 parts by weight of copper produced in a known manner under hydrogen protective gas are distinguished by high electrical conductivity and erosion resistance in connection with comparatively low production costs, they tend to weld under extreme switch-on conditions the switching pieces.

It is also known to effectively add to the copper alloying additives, such as Pb, Sb, Bi or Te, to effectively improve the antiperspirant properties of such impregnation contacts, which at the same time, in addition to improved antiperspirant properties, can reduce the unwanted break-off current.

In contrast, another known solution for improving the antiperspirancy behavior provides embrittling additives, such as Al or Sn, to the framework body substance.

It is also known to provide a contact body of molybdenum or tungsten or of infiltrated scaffold bodies of these two metals with holes on the contact surface, are embedded in the intermetallic Sb compounds.

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In these known technical solutions, the mentioned alloying additions to tungsten copper or molybdenum copper, although the desired improvement in the anti-whitening behavior of contacts so produced, but have the defect that their electrical conductivity at the same time significantly reduced and also the solderability is impaired such that before the soldering, the application of solderable intermediate layers is essential.

Object of the invention

The invention is intended to eliminate the disadvantages of the known technical solutions and to provide a main contact which has a favorable material composition and whose technology is simplified.

Explanation of the essence of the invention

The invention is therefore an object of the invention to provide a Hauptkontäkt for heavy vacuum contactors, which is sufficiently low in gas, has a high erosion resistance and sufficient electrical conductivity and an improved anti-whitening behavior with sufficiently good solderability with conventional Vakuumhartloten shows.

According to the invention, this object is achieved in that the molybdenum content is at least 64 and at most 70% by mass with a correspondingly reduced copper content. For this purpose, molybdenum powder is pressed into a porous base body, sintered under protective hydrogen gas and impregnated with molten copper.

The molybdenum content of the invention causes less copper from the near-surface areas of the contact volume during bouncing when the vacuum contactor is switched on

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on the button exits, whereby there the formation of larger copper enrichments is omitted and thus the welding of the contacts is avoided to the extent necessary. Although the electrical conductivity of contacts thus produced decreases slightly due to the reduced copper content with slightly increased hardness, the decrease in conductivity is considerably lower than by the addition of embrittling alloying elements as long as the molybdenum content is less than 70 mass%. Abbrandfestigkeit and solderability also remain unchanged, as well as the degassing behavior of the contacts and their good resistance to loss of substance by evaporation.

embodiment

The invention will be described below with reference to an embodiment, wherein it is assumed that the copper is subsequently directed to solidification. In the application of the invention, however, the directed solidification of the copper can also be dispensed with if it succeeds in another way to produce solderable intermediate layers.

For 320 A rated heavy-duty vacuum contactors, disc-shaped main contacts of 36 mm diameter and 7 mm height are required, including a one-sided, 0.5 mm thick copper layer for soldering. These contacts are made of the interpenetration composite molybdenum-copper, wherein a target value of the molybdenum content in the molybdenum-copper of. 65 mass? is sought. From the 65 mass% molybdenum, using the density values for molybdenum and copper, the required density of sintered molybdenum billets is calculated to be 6.33 g.cm prior to impregnation

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During the impregnation process itself, only slight changes in density of the molybdenum billets take place. From pressing and sintering experiments with the employed molybdenum powder as a function of the sintering density values is determined by the values of the pressing density in the range interssierenden and thereby also determines the linear shrinkage of the compacts during sintering for the selected sintering temperature of 1300 ⁰ C.

In the present example, for a molybdenum powder having a mean particle size of 3.4 μm, the desired molding density is 5.35 g · cm at a linear shrinkage of 5 %. As a machining allowance about 1 mm are provided for the outer diameter and for the height of the discs, so that, taking into account the sintering shrinkage and the copper layer Preßteilabmessungen of 39 mm diameter and 8 mm height. From the Preßdichtewert of 5.35 g.cm

and the Preßteilvolumen of 9.56 cm ^{3 is} calculated

Mass to 51.1 g. Accordingly, each 51.1 g of molybdenum. powder weighted by means of a hydraulic press pressed into disks of -39 mm diameter and 9 mm in height and then sintered under a protective gas at 1300 ⁰ C in a push-through furnace for about 1 hour. Thereafter, in a furnace of the same type also at 1300 ⁰ C under hydrogen protective the impregnation of the sintered porous molybdenum discs by Auflegedränkung in matching graphite crucibles with electrolytic copper, which was previously remelted under water protective gas zv / ecks cleaning. The calculated to complete filling the pores copper amount with a surcharge of 10% determines the Auflegemasse, which is increased by the amount of copper to form a copper layer about 2.5 mm thick on the top of the impregnated disks and thus consists of a total of 56 g of copper. The initial temperature for a directional solidification of the copper melt after impregnation is at most 115O ⁰ C.

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If the trough used does not have two separate heating zones and corresponding total length, the directional solidification is carried out in a separate push-through at 11.30 ⁰ C under hydrogen inert gas. The largest permissible feed rate of this furnace must generally be determined depending on the type of construction as a compromise between throughput on the one hand and deprivation of Gasblasenlunkern on the other hand by experiments, the

-1

average speed of 45 cm.h of the example considered serves as a reference value. Subsequently, the molded body made of molybdenum-copper is machined to be machined. After washing and drying, the contacts pass through even a Reinigungsglühung at 850 ⁰ C -having hydrogen protective gas before further processing by ν ^ μηΐηίοΐβη done with the contact carriers. The measured values for the electrical conductivity of contacts produced according to the invention with improved anti-whitening behavior fluctuate between

nn η j on c ~ 2 / Siemens .Meter \ ·,. ·, -, · -l-ii. ·· ±. 27.9 and 30.6 Smmm C 2) at Bnnell hardnesses

from 123 to 140 HB. In comparison, the known molybdenum-copper contacts with the mentioned unfavorable anti-whitening behavior have only slightly better conductivities between 31.1 and 33.5 S.m.mm at Brinell hardness between 114 and 130 HB.

Claims (1)

• _ 7 - P 1232 Claim for invention . Main contact of molybdenum-copper for heavy vacuum contactors, characterized in that the molybdenum content is at least 64 and at most 70% by mass.