U.S. patent number 3,610,859 [Application Number 04/748,460] was granted by the patent office on 1971-10-05 for composite contact structure for vacuum-type circuit interrupters.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Helmut Ohmann, Horst Schreiner.
United States Patent |
3,610,859 |
Schreiner , et al. |
October 5, 1971 |
COMPOSITE CONTACT STRUCTURE FOR VACUUM-TYPE CIRCUIT
INTERRUPTERS
Abstract
A composite contact for a vacuum-type circuit interrupter is
formed from a porous sintered refractory structure, such as
tungsten or molybdenum, infiltrated with an impregnating metal
having a liquid phase below 400.degree. C. To assure a wetting
action between the porous refractory sintered structure and the
infiltrant stock, preferably an auxiliary agent, or an additive, of
small quantity is utilized, such as silver, cobalt, copper, iron,
nickel, titanium and zirconium in small quantities, for example, a
few tenths of one percent. In use in a vacuum-type circuit
interrupter such a composite contact results in a vaporization of
the low-melting-point infiltrant. For certain constructions, a
reservoir may be provided interiorly of the composite contact to
provide an additional quantity of the low-melting-point
infiltrant.
Inventors: |
Schreiner; Horst (Nuremberg,
DT), Ohmann; Helmut (Erlangen, DT) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin and Munich, DT)
|
Family
ID: |
7530813 |
Appl.
No.: |
04/748,460 |
Filed: |
July 29, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Aug 5, 1967 [DT] |
|
|
P 15 58 647.7 |
|
Current U.S.
Class: |
200/264; 200/267;
200/266; 200/270 |
Current CPC
Class: |
H01H
33/664 (20130101); B22F 3/11 (20130101); B22F
3/26 (20130101); C22C 1/0475 (20130101); H01H
1/0203 (20130101); H01H 2001/0208 (20130101) |
Current International
Class: |
H01H
33/66 (20060101); H01H 1/02 (20060101); H01H
33/664 (20060101); C22C 1/04 (20060101); H01h
001/02 () |
Field of
Search: |
;200/166C,144.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Jones; H. O.
Claims
We claim:
1. A composite contact material having a low volume of gas content
for use as an electrical contact material in vacuum-type switching
devices consisting of a porous sintered refractory structure of an
arc-resisting metal, the pores of which are infiltrated with a
lower melting point metal, characterized in that the pores of the
skeleton refractory structure are filled with the low-melting-point
constituent which forms a liquid phase under 400.degree. C. and
which also has in comparison with the first-mentioned refractory
structure a lower arc voltage, a reservoir being provided in the
metallic skeleton structure to accommodate a greater supply of the
low-melting-point impregnating metal.
2. A composite contact material having a low volume of gas content
for use as an electrical contact material in vacuum-type switching
devices consisting of a porous sintered refractory structure of an
arc-resisting metal, the pores of which are infiltrated with a
lower melting point metal, characterized in that the pores of the
skeleton refractory structure are filled with the low-melting-point
constituent which forms a liquid phase under 400.degree. C. and
which also has in comparison with the first-mentioned refractory
structure a lower arc voltage, the skeleton structure being a metal
selected from the group consisting of tungsten, molybdenum, and
rhenium and their alloys, whereas the low-melting-point
impregnating metal being selected from the group consisting of
bismuth, cadmium, gallium, indium, lead, tin, and thallium and
their alloys, and a reservoir being provided within the contact
body for accommodating an extra supply of the impregnating
metal.
3. A composite contact material having a low volume of gas content
for use as an electrical contact material in vacuum-type switching
devices consisting of a porous sintered refractory structure of an
arc-resisting metal, the pores of which are infiltrated with a
lower melting point metal, characterized in that the pores of the
skeleton refractory structure are filled with the low-melting-point
constituent which forms a liquid phase under 400.degree. C. and
which also has in comparison with the first-mentioned refractory
structure a lower arc voltage, an additive in a few tenths of 1
percent being added to increase the wettability between the
metallic skeleton structure and the impregnating metal, and the
additive being a metal selected from the group consisting of
silver, cobalt, copper, iron, nickel, titanium and zirconium.
4. A composite contact material having a low volume of gas content
for use as an electrical contact material in vacuum-type switching
devices consisting of a porous sintered refractory structure of an
arc-resisting metal, the pores of which are infiltrated with a
lower melting point metal, characterized in that the pores of the
skeleton refractory structure are filled with the low-melting-point
constituent which forms a liquid phase under 400.degree. C. and
which also has in comparison with the first-mentioned refractory
structure a lower arc voltage, an additive in a few tenths of 1
percent being added to increase the wettability between the
metallic skeleton structure and the impregnating metal, and the
additive being a metal selected from the group consisting of
aluminum, cobalt, iron, nickel, titanium, zirconium, as well as the
alkaline and alkaline earth metals.
5. A composite contact for a vacuum-type circuit interrupter
consisting of a metallic refractory matrix filled with a
low-melting-point metallic infiltrant stock, said metallic
refractory matrix formed of a refractory metal selected from the
group consisting of tungsten, molybdenum, and rhenium and their
alloys, and said low melting point metallic infiltrant stock having
a liquid phase below 400.degree. C., and the low-melting-point
metallic infiltrant stock being a metal selected from the group
consisting of bismuth, cadmium, gallium, indium, lead, tin, and
thallium and their alloys with an additive metal selected from the
group consisting of silver, copper, mercury, antimony and zinc in a
few tenths of 1 percent for increasing wettability.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
U.S. Pats. Nos. 3,360,348 and 3,340,022 are concerned with the
provision of composite contact structures for switching
devices.
BACKGROUND OF THE INVENTION
Contact materials, which are used in vacuum-type circuit
interrupters, ought to have, besides extremely low content of gases
and of impurities, which give off gases, particularly the
characteristics of small welding forces and low erosion due to
vaporization in the arc during operating conditions. Generally, the
known contact materials consist of copper alloys, which
demonstrate, particularly in applications to vacuum-type circuit
interrupters, high welding forces and considerable erosion. There
has been proposed heretofore contact materials of arc-resisting
characteristics, for example, high-melting-point metals, such as
tungsten and molybdenum, which contain within the porous structure
relatively low-melting-point metals with relatively high-vapor
pressure and low-arc voltage. The distribution of such constituents
leads to a larger vaporization of the low-melting-point
constituent, and to a reduction of the surface portion of the
arc-erosion-resisting material.
The object of the present invention is the provision of a composite
contact material, which is particularly suitable for contacts
utilized in vacuum-type circuit interrupters. Such a composite
contact material will preferably have considerable life.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention,
a composite contact is provided particularly suitable for
vacuum-type circuit interrupters, in which a high-melting-point
refractory metal, such as tungsten or molybdenum, has a porous
structure, when in the sintered condition, which is infiltrated
with an infiltration stock, or an impregnating metal, having a
liquid phase below 400.degree. C. In addition, to assure an
adequate wetting condition between the refractory porous sintered
structure and the infiltrant filler material, there is provided an
auxiliary agent, or an additive, which provides the desired wetting
action.
Accordingly, a general object of the present invention is the
provision of an improved composite contact for a vacuum-type
circuit interrupter, which will render improved performance and
long life.
Still a further object of the present invention is the provision of
an improved composite contact for a vacuum-type circuit interrupter
comprising a porous refractory high-melting-point skeleton
structure, which is impregnated, or penetrated, with an
infiltration stock, comprising a relatively low-melting-point
nonrefractory material, which has a liquid phase below 400.degree.
C.
Further objects and advantages will readily become apparent upon
reading the following specification taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a somewhat diagrammatic vertical sectional view taken
through a vacuum-type circuit interrupter, the contact structure
being illustrated in the open-circuit position;
FIG. 2 is an enlarged view, partially in section, of one of the
contacts utilized in the vacuum-type circuit interrupter of FIG.
1;
FIG. 3 is a modification of the contact structure of FIG. 2
illustrating the use of a reservoir; and,
FIG. 4 is a variant structure showing a different location of the
reservoir .
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As well known by those skilled in the art, the contact materials
which are used in vacuum-type circuit interrupters ought to have,
besides an extremely low content of gases and impurities giving off
gases, particularly low welding forces and low arc erosion, due to
vaporization in the arc during operating conditions. Generally, in
the past, the known contact materials have consisted of copper
alloys, which show particularly in the applications to vacuum-type
circuit interrupters, high-welding forces and considerable arc
erosion. It has, therefore, been proposed to utilize contact
materials which are particularly resistant to arc erosion for
example high-melting-point materials, such as tungsten and
molybdenum, which contain in the pore structure relatively
low-melting-point metals having relatively high vapor pressure and
a low-arc voltage. The thus-obtained distribution of the
constituents leads to a larger vaporization of the
low-melting-point constituent, and to a reduction of the surface
portion of the high-melting-point arc-errosion-resisting
material.
Accordingly it would be desirable to provide a composite contact
material, which is particularly suitable for use in vacuum-type
circuit interrupters, which consists of a porous sintered structure
of an erosion-resisting metal, or a metallic alloy, the pores of
which are filled with a low-melting-point metal, or a
low-melting-point alloy.
According to the present invention, the pores of the sintered
structure are filled with a low-melting-point constituent, which
forms a liquid phase below 400.degree. C, and which has, in
comparison with the high-melting-point, arc-erosion-resisting
constituent, a lower arc voltage. Further, in accordance with the
principles of the present invention, the refractory porous
structure and/or the filler component, or infiltrant metal, contain
auxiliary agents, or additives, which assure of a desired wetting
action between the porous sintered structure and the filler
material.
An important difference which exists from known composite contact
material consists in that in the case of the composite materials
according to the present invention, there is obtained a finer and
in narrower limits controllable distribution of both constituents
with mutual respect. In the composite material according to the
present invention, namely the arc-erosion-resisting constituent,
which consists preferably of tungsten, molybdenum or rhenium, there
exists in the form of the sintered body a definite porosity, the
pores of which are filled with the low-melting-point constituent,
or infiltrant. The pore part of the sintered body, and therefore
the volume part of the low-melting-point constituent can be suited
to the switching conditions. At the relatively low switching
currents, the pore part is assumed at being 20 percent; at the
higher currents, and at the highest switching currents, the pore
part is assumed as being up to 60 percent. The porosity of the
porous refractory sintered structure is thus fitted to the
switching conditions. The part of the low-melting-point effective
constituent obtained at the 20 percent volume porosity is
sufficient to eliminate the chopping effect at the low
currents.
TABLE A
---------------------------------------------------------------------------
Refractory Skeleton Structure
Melting Pt. .degree.C. Mo Molybdenum 2,625.degree. C. W Tungsten
3,410.degree. C. Re Rhenium 3,170.degree. C.
__________________________________________________________________________
TABLE B
---------------------------------------------------------------------------
Nonrefractory Infiltrant Stock
Melting Pt. C. Bi Bismuth 271.3.degree. C. Cd Cadmium 320.9.degree.
C. Ga Gallium 29.8.degree. C. In Indium 156.4.degree. C. Pb Lead
327.4.degree. C. Sn Tin 231.9.degree. C. Tl Thallium 300.degree. C.
__________________________________________________________________________
according to the present invention, the low-melting-point
constituent consists of metals, or metal alloys, which exist in
liquid form below 400.degree. C. Due to this, there is assured a
sufficiently fast subsequent delivery of the constituent removed,
or lost from the pores at the contact surface by vaporization.
Suitable low-melting-point metals, utilized for the infiltrant
stock are, for example, bismuth, cadmium, gallium, indium, lead,
tin, and thallium, as shown in table B below. Their melting points
are listed below to show that all of them have a liquid phase below
400.degree. C.
In addition to the above low-melting-point infiltrants, in
addition, their alloys with the metals silver, copper, mercury,
antimony, and zinc may be utilized.
Further, the composite contact material, according to the present
invention, contains in its structure, or the infiltrant stock, or
filler material, an additive, or an auxiliary agent, which provides
a desired wetting condition. It has appeared that a sintered body
with a metallically clean surface, and the necessarily low gas
content, which can be obtained by sintering in hydrogen, subsequent
heat treatment in high vacuum, and impregnation with the filler
metal in high vacuum is not sufficient; but that a satisfactory
wetting, and thus adequate impregnation, can be obtained only
through suitable additives to the sintered body and/or to the
filler material.
As effective additives to the sintered body there have proven
themselves effectives the following metals; silver cobalt, copper,
iron, nickel, titanium, and zirconium. As additives for the filler
infiltrant stock, there have proved effective aluminum, cobalt,
iron, nickel, titanium, zirconium, as well as alkaline or
alkaline-earth metals. These additives, or auxiliary agents, are
effective in small quantities of, for example, a few tenths of 1
percent.
FIG. 1 illustrates schematically a vertical sectional view taken
through a vacuum-type circuit interrupter embodying the composite
contact materials of the present invention. It will be noted that
the vacuum-type circuit interrupter 1 comprises an evacuated
envelope, or housing 2 with end plates or covers 3 and 4 made of
metal. The stationary contact 5 is brought into the evacuated
envelope 2 through the upper cover 3, and the movable contact 6 is
brought, in a vacuum-type manner, through the lower cover 4 by
means of a flexible metallic bellows 7.
FIG. 2 shows, in a specially simple and advantageous design, a form
of a composite vacuum circuit breaker contact. The reference
numeral 8 is a rodlike current lead made of pure copper, or of
low-alloyed copper. The reference numeral 9 designates a plate made
of the sintered body provided with the filler material. It may be
threaded, cemented, soldered (brazed), or welded into position.
An especially desirable form of contact construction for the
sintered plate of the vacuum interrupter contacts is shown in FIGS.
3 and 4. The refractory sintered body 12 is provided with an
impregnating metal reservoir 13, similar to that provided in an oil
reservoir of a self-lubricating sintered bearing. If the supply of
the low-melting-point constituent contained in the pores of the
refractory sintered body 12 does not suffice, the vaporization loss
over the operational life of the composite contact can be replaced
from this reservoir 13. The reservoir 13 is located, as it is shown
in FIG. 3, preferably inside of the sintered body and beneath the
requisite thickness of the contact layer 12. It is filled during
the infiltration, or impregnation process. However, the reservoir
13 of the infiltrant stock may be located also on the underside of
the contact piece 12, as it is shown in FIG. 4.
EXAMPLE
Tungsten powder graded to pass 100 mesh and be retained on a
200-mesh screen is placed in a compaction die of suitable strength
and compacted at approximately 50,000 p.s.i. The compact is then
sintered 1 hour in dry hyrodgen at 1,250.degree. C. The hydrogen is
pumped off and sintering continued one-half hour in vacuum. The
sintered compact is then lowered into a pool of molten In or Pb
located in a cooler portion of the furnace. Wetting elements such
as Ti may be added to the In or Pb to improve impregnation of the
tungsten by indium or lead.
The impregnated sintered structure may assume various geometrical
shapes or forms. For example, it may constitute the center portion
of a generally platelike contact piece. Moreover it may assume a
ring part, or the outer portion of a contact piece. In addition, it
may assume a spiral path formed, or it may be a ring part with
spirally shaped outwardly running strips, not shown.
From the foregoing it will be apparent that there has been provided
an improved composite contact for a vacuum-type circuit interrupter
generally comprising a refractory porous sintered body, which is
impregnated or infiltrated with a relatively low-melting-point
metal having a liquid phase below 400.degree. C., and having a
relatively low arc voltage compared with that of the aforesaid
refractory sintered body. To promote a desired wetting action
therebetween, preferably an auxiliary agent, or an additive is
provided to provide a tight bonding of the materials.
Although there has been illustrated and described specific
structures and formulations, it is to be clearly understood that
the same were merely for the purpose of illustration, and that
changes and modifications may readily be made therein by those
skilled in the art without departing from the spirit and scope of
the invention.
* * * * *