GB2066298A

GB2066298A - A method for the production of materials for contact members

Info

Publication number: GB2066298A
Application number: GB8036502A
Authority: GB
Original assignee: INST PRUEFFELD ELEKT
Current assignee: INST PRUEFFELD ELEKT
Priority date: 1979-12-08
Filing date: 1980-11-13
Publication date: 1981-07-08
Also published as: JPS5767141A; DD155861A3; DE3040384A1; GB2066298B

Abstract

It is the object of the invention to combine in one method the advantages of the powder-metallurgical production and the melting-metallurgical production of materials for contact members of vacuum switches from CuCo, CuFe or CuCr alloys. This is brought about in that CuCo, CuFe or CuCr melt, which latter is in two phases, is degassed, deoxidised and atomised. Depending on the composition of the powders, sintering in the solid state, with a liquid phase or the impregnation of skeleton bodies is possible. By alloying Cr with Cu, there comes about the possibility of the melting-metallurgical degassing in a vacuum induction furnace, since it is not necessary to reach the melting point of the Cr of approximately 1900 DEG C but only the liquidus temperature of the Cu-Cr system of 1470 DEG C has to be reached. Although two melts of different composition arise above this temperature, homogeneous alloys are brought about by the simultaneous atomisation of the two melts.

Description

SPECIFICATION A method for the production of materials for contact members The invention relates to a method for the production of contact members for vacuum arc extinguishing chambers and enclosed switchgear from Cu-Cr, Cu-Fe or Cu-Co based alloys or from combinations of these alloying elements.

There have been several descriptions in the patent literature of the production and use of CuCr, CuFe and CuCo alloys for contact members of vacuum arc extinguishing chambers.

The production is generally effected by impregnating with Cu or Cu alloys porous basic bodies which have been pressed from Cr, Fe or Co and which may have been sintered (DD PS 74881, AT PS 297833, FR PS 1524604, CH PS 495618, DEARS 1640039, US PS 3818163, SU PS 475676, SU PS 355826, DE OS 2324317, GB PS 1388283, DE OS 2522832, DE 0S2357333). However, there is also known the sintering of compacts from mixtures of powders of the respective metals as well as the production by melting engineering of alloys of metals of the iron group (Fe, Co, Cr) and copper. For example, there are known protective rights concerning the production by melting engineering of alloys consisting of Cu in concentrations in excess of 40% and the metals Fe, Co, Ni, Cr in concentrations between the solubility limit in the Cu and 60% as well as Pb of 0.035 to 7%. (GB PS 1255685).

The advantage of the powder-metallurgical production consists, above all, in the fact that, due to the powder -particle size chosen, a defined structure can be given to the penetrating composite metal. However the insufficient degassing of the material connected therewith is disadvantageous. During the sintering process, specific temperatures must not be exceeded, since at least the melting temperature of the constituent having a higher melting point must not be exceeded, but the solubility thereof in the possibly existing liquid phase has also to be kept low. The degassing process is thus diffusion controlled and consequently requires long degassing times. Under the conditions which are technically realisable, high residue contents are left in the sintered material.

During the melting process, there exist extremely favourable degassing conditions on account of the rapid material transportation to the phase interface. Furthermore, the preconditions for the use of deoxidising elements are considerably more favourable.

However, the separation tendency of the mentioned alloys during solidification is disadvantageous, which tendency progressively increases over the Cu-Co, Cu-Fe, Cu-Cr systems and, in the Cu-Cr system, even exists in the molten state. It has therefore hitherto been impossible to produce homogeneous CuCr alloys with Cr contents above 20% by weight or Cr-Cu alloys in a manner that is homogeneous from the point of view of melting engineering along with a fine distribution of both phases.

The aim of the invention consists in combining in one method the advantages of the powder-metallurgical production and the melting-metallurgical production of materials for contact members of vacuum switches from CuCo, CuFe or CuCr alloys, in that the fine distribution or an even finer distribution of the structural constituents and the alloying elements is aimed at, such as is ensured by powder metallurgy, and in that lower gas contents are guaranteed, such as are realisable only by melting metallurgy.

The task underlying the invention is to provide a method for the production of contact members for vacuum switches or enclosed switchgear. The essence of the invention consists in that CuCo, CuFe or CuCr melts, which have been degassed and deoxidised, are atomised so that there are formed powders wherein the powder particles contain the alloying elements in an extremely fine distribution. In the case of CuCr, the two melts L1 and L2, which exist above 1470"C and which are not soluble one within the other, are atomised so that a mixture consisting of two powders of different Cr and Cu concentrations is formed, the powder particles of the melt that is rich in Cu containing the Cu constituents in very finely distributed manner.

The distribution of the alloying elements can consequently be still considerably finer than it is in the powder-metallurgical methods, in which the powders of the pure alloying elements are intermixed, pressed and sintered or in which skeleton bodies of the constituent having a higher melting point are impregnated with Cu or Cu alloys. The very fine distribution of the alloying elements has an advantageous effect on the switching behaviour. For example, it results in a noticeable reduction of the contact member wear.

The atomisation can be effected by way of an inert-gas counter-current, in vacuo or, in the case of CuCo and CuFe alloys, in a water bath. In the latter case, the powders were ground, dried and possibly already reduced as pressed parts under hydrogen prior to further processing.

Depending on the composition of the powders, the sintering thereof in a solid state, with a liquid phase or the impregnation of skeleton bodies is possible.

Above all, in the case of the CuCr alloys, there is -brought about a decisive jump in the improvement of the production technology and quality. For the degassing of pure Cr by melting engineering there would be necessary a temperature of at least round about 1900"C. Vacuum induction melting is therefore out of the question because of the arising crucible reaction, and melting in the electron bombardment furnace is unsuitable because of the high vapour pressure of the Cr, which is round about 1 torr at 1900"C. However, a Cu addition of approximately 7% by weight already lowers the liquidus temperature to 1470"C. This means that it is possible to melt CrCu alloys having Cu contents exceeding 7% by weight in a temperature range which can be reached without difficulties by induction melting. The coarse separations arising in the cast material consisting of such alloys, which are mainly caused by the presence of two melts L, and L2 are avoided according to the invention, in that the mixture of the melts is atomised and there is thus produced an extremely fine mixture of powders.

This means that above 1470"C all operations relating to melting metallurgy, such as degassing, deoxidising or alloying with further elements, can be carried out without any additional technological expenditure.

Claims

1. A method for the Cu-Cr, Cu-Fe or Cu-Co based production of materials for contact members of vacuum switches or other switchgear, characterised in that the alloying melts of these systems are degassed, deoxidised and possibly alloyed with further elements and are atomised, and in that subsequently the powders of these alloys are pressed and sintered and possibly impregnated so as to form contact member blanks.

2. A method for the Cr-Cu based production of materials for contact members of vacuum switches or other switchgear, characterised in that the melts L, and L2, which exist in the region of 38 to 93% Cr by weight above 1470"C and which are not soluble one within the other, are atomised following deoxidation and degassing and possibly the addition of further alloying elements, and in that there is thus produced a mixture of alloy powders of high and low Cr concentrations with an extremely fine distribution of the alloying elements in-the powder particles, which mixture can be processed into homogeneous sintered bodies.

3. A method for the Cu-Cr, Cu-Fe or Cu-Co based production of materials for contact members of vacuum switches or other switchgear, substantially as described herein.