U.S. patent number 3,685,134 [Application Number 05/048,650] was granted by the patent office on 1972-08-22 for method of making electrical contact materials.
This patent grant is currently assigned to P. R. Mallory & Co. Inc.. Invention is credited to Philip L. Blue.
United States Patent |
3,685,134 |
Blue |
* August 22, 1972 |
METHOD OF MAKING ELECTRICAL CONTACT MATERIALS
Abstract
An electrical contact material consisting of a thin cold rolled
material constructed of a high electrically and thermally
conductive material and a refractory wherein particles of the
refractory are dispersed within a matrix of the high electrically
and thermally conductive material and also are layered in a
predetermined direction.
Inventors: |
Blue; Philip L. (Centerville,
OH) |
Assignee: |
P. R. Mallory & Co. Inc.
(Indianapolis, IN)
|
[*] Notice: |
The portion of the term of this patent
subsequent to April 28, 1987 has been disclaimed. |
Family
ID: |
21955689 |
Appl.
No.: |
05/048,650 |
Filed: |
May 15, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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741606 |
Jul 1, 1968 |
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627962 |
Apr 3, 1967 |
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Current U.S.
Class: |
419/23;
29/DIG.31; 75/247; 419/26; 419/28; 428/929; 29/875; 75/248; 419/27;
419/58 |
Current CPC
Class: |
C22C
1/045 (20130101); H01B 1/00 (20130101); B22F
3/16 (20130101); H01H 1/025 (20130101); C22C
1/0425 (20130101); C22C 32/0052 (20130101); Y10S
428/929 (20130101); Y10T 29/49206 (20150115); Y10S
29/031 (20130101) |
Current International
Class: |
C22C
32/00 (20060101); H01B 1/00 (20060101); H01H
1/025 (20060101); H01H 1/02 (20060101); B22F
3/12 (20060101); B22F 3/16 (20060101); C22C
1/04 (20060101); B22f 003/24 () |
Field of
Search: |
;29/182,182.1,182.2,420.5,63C,DIG.31 ;75/204,28R,214,221 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Campbell; John F.
Assistant Examiner: Reiley, III; Donald C.
Parent Case Text
This is a division of application Ser. No. 741,606, filed July 1,
1968, now abandoned, which in turn is a continuation-in-part of
application Ser. No. 627,962, filed April 3, 1967, now abandoned.
Claims
What is claimed is:
1. A process for forming thin electrical contact material which
comprises: blending a mixture of powder of a refractory material
taken from the class consisting of tungsten, titanium, molybdenum,
and carbides thereof; and a powdered conductive material selected
from the group consisting of copper and copper alloys, said
conductive material being present in an amount of 20 to 90 percent
by weight of said mixture; said refractory powders having a
particle size of from about 4 to 20 microns as measured by FAPS
analysis; pressing said mixture into bars; sintering said bars in a
non-oxidizing atmosphere; cold-rolling said bars in a single path
to yield at least about one-third reduction in the bar's thickness;
resintering said bars; and thereafter alternately rolling and
annealing said bars in cycles to yield reduction of thickness of
about 10 to 30 percent in each cycle.
2. A process according to claim 1, wherein said refractory material
is tungsten.
3. A process according to claim 1, wherein said high electrically
and thermally conductive material is in an amount of from about
50-80 percent by weight of said body, the balance being tungsten
carbide.
4. A process according to claim 1, wherein said high electrically
and thermally conductive material is in an amount of from about
50-80 percent of said body, the balance being molybdenum.
5. A process according to claim 1, wherein said material of high
electrically and thermally conductive material is copper in an
amount of from about 20-50 percent by weight of said body, the
balance being said refractory material.
6. A process according to claim 5, wherein said refractory material
is taken from the group consisting of tungsten and molybdenum.
7. A process according to claim 1, wherein said high electrically
and thermally conductive material is copper in an amount of from
about 25-50 percent by weight of said body, the balance being
tungsten carbide.
8. A process according to claim 1, wherein said non-oxidizing
atmosphere is dissociated ammonia.
9. A process according to claim 1, wherein said refractory material
has a particle size of from 4-20 microns and said high electrically
and thermally conductive material has a particle size of from 4-10
microns.
10. A process according to claim 1, wherein said sintering is
carried out at a temperature which is inversely proportional to the
refractory particle size such that there will be no bleed-out of
the high electrically and thermally conductive material.
11. A process according to claim 1, wherein said rolling is cold
rolling.
Description
Silver, copper, gold, bronze and brass are ideal electrical contact
materials because of their high electrical conductivity and
excellent heat dissipating or high thermal conductivity properties.
However, when subjected to large short-circuit currents, on the
order of 5,000 amps, for example, the materials are subject to
severe arc erosion. Consequently, it has been the practice to
fabricate such heavy duty contacts from mixtures of a high
electrically and thermally conductive material and a high melting
point refractory material such as tungsten. With this combination
the tungsten, while it carries a substantial amount of current,
acts as a skeleton for holding the high electrically and thermally
conductive material. The tungsten phase also provides greater
resistance to arc erosion.
Prior to this invention, silver-tungsten contacts, for example,
were for the most part deficient in many respects, the deficiencies
arising mainly from the methods by which the contacts were
produced. Such deficiencies include but are not limited to
relatively poor electrical conductivity due to the oxide barrier
between the tungsten particles and the silver matrix, discontinuity
of the silver matrix, inability to make thin strips or sheets of
the material, and non-uniformity in physical properties such as
hardness and density.
Among the objects of the present invention is the provision of an
electrical contact material composed of a high electrically and
thermally conductive material and a refractory material, such as
for example, tungsten, titanium, molybdenum, carbide mixtures
thereof and the like wherein the refractory particles are in
substantial intimate contact with a matrix of the high electrically
and thermally conductive material.
Another object of the invention is the provision of an electrical
contact material wherein the refractory particles that are
dispersed within a substantially continuous matrix of a high
electrically and thermally conductive material are layered in a
predetermined direction.
Another object of the invention is to provide such a contact
material which is fabricated as a thin body with sufficient
ductility so that it can be readily formed into desired shapes.
Still another object of the invention is to provide such a contact
material which has more uniform physical properties such as those
of hardness, density and lack of porosity.
Another object of the such contact is to provide a bar rolling
technique for forming contact material.
Still another object of the invention is to provide a bar rolling
technique wherein powders of the refractory material are blended
with powders of the high electrically and thermally conductive
material, pressed into bars, sintered, cold rolled, resintered and
cold rolled with or without intermittent annealing treatments.
With the above and other objects in view, which will appear as he
description proceeds, this invention resides in a novel article of
manufacture and a process for making the same such as substantially
described herein and more particularly defined by the appended
claims, it being understood that such changes in the precise
embodiment of the invention here disclosed may be made as come with
the scope of the claims.
In the drawings:
FIG. 1 is a flow sheet showing the various steps in forming the
novel electrical contact material;
FIG. 2 is an enlarged cross section of a silver-tungsten electrical
contact material showing the structure resulting from a commonly
used sintering method;
FIG. 3 is an enlarged transverse cross section of a high
electrically and thermally conductive refractory contact material
showing the structure formed by using the method of invention;
and
FIG. 4 is an enlarged longitudinal section of a high electrically
and thermally conductive refractory contact material showing the
structure formed by using the method of the invention.
The invention in its broadest aspect contemplates providing as an
article of manufacture a body of an electrical contact material
having an active contact face fabricated of a high electrically and
thermally conductive material and a refractory material taken from
the group consisting of tungsten, titanium, molybdenum, carbides
thereof and the like, the powder particle size of the refractory
material being from 4--20 microns with the refractory particles
being in intimate contact with a continuous matrix of the high
electrically and thermally conductive material to yield a contact
having a high electrical conductivity. The electrical contact
material is further characterized by the refractory particles being
layered in a predetermined direction. Also the invention
contemplates providing a process for forming such contact which
comprises blending a mixture of powders of a refractory material
taken from the group consisting of tungsten, titanium, molybdenum,
carbides thereof and the like, and powders of a high electrically
and thermally conductive material, said refractory powders having a
particle size of from 4-20 microns as measured by F.A.P.S.
analysis, pressing said mixtures into bars, sintering said bars in
a non-oxidizing atmosphere, cold rolling said bars in a single pass
to yield about a one-third reduction in the bar's thickness,
resintering and cold rolling said bars, annealing said bars to
remove all rolled grain structure, and thereafter alternately cold
rolling and annealing said bars in cycles to yield reductions in
thickness of from 10-30 percent in each cycle until the desired
physical properties are obtained.
Referring now to FIG. 1, the first step in making the novel
electrical contact material is that of blending the powders
together. To this end, powders of the high electrically and
thermally conductive material which preferably have a particle size
of from 4-10 microns by F.A.P.S. analysis are blended with the
refractory powder having a particle size of from 4-20 microns by
F.A.P.S. analysis. The high electrically and thermally conductive
materials includes silver, copper, gold, brass and bronze. The
particle size of the refractory is particularly critical. In
general, if the particle size becomes excessively large, a good
intimate electrical contact is difficult to achieve between the
refractory and the high electrically and thermally conductive
material and the electrical load carrying capability of the contact
is reduced; while on the other hand, if the refractory particle
size becomes too small, the material becomes brittle and cracks
develop during the rolling operation. Preferably the particle size
of the tungsten should be from about 6-20 microns, while for the
tungsten carbide and molybdenum, it should be about 4-12
microns.
In general, the composition, that is, the weight percent of the
refractory and the electrically and thermally conductive material
is dependent upon the electrical properties desired and, in the
case of the present invention, the rolling ability of the mixture.
With too little electrically and thermally conductive material, the
rolling operation becomes very difficult due to the high refractory
material content. On the other hand, with too much electrically and
thermally conductive material, the fine particles of the material
reduce the material's current carrying capacity. In general, a high
electrically and thermally conductive material in an amount of from
about 20 to 90 percent by weight with the balance being the
refractory material has been found to be suitable. Table I shows
the ranges and the preferred percentages of silver and the ranges
of copper for some of the named refractory materials of the
invention.
TABLE I
%-Ag-by weight % cu - by weight Refractory Material Range Preferred
Range Tungsten 20-90 27,35,50,90 20-50 Tungsten Carbide 50-80 50
25-50 Molybdenum 65-80 65 20-50
The mixture is then, as shown in FIG. 1, pressed into bars of a
suitable shape by placing the mixture into a mold and applying
pressure to it.
The bars are then, in step three, sintered in a a non-oxidizing
atmosphere in a furnace of either the muffle or open element type.
The atmosphere may be a neutral atmosphere such as pure nitrogen,
but a reducing atmosphere such as dissociated ammonia or pure
hydrogen is preferred from the standpoint of reducing the tendency
for the formation of oxide layers on the refractory.
Sintering temperatures depend upon the particle size of the
refractory material and composition of mix, the temperature, in
general, being inversely proportional to both. The larger particle
sizes, within the aforementioned range, tend to cause bleed-out of
the high electrically and thermally conductive material or to cause
the bars to deform. In such case, solid phase sintering at a
temperature near the melting point of the high electrically and
thermally conductive material (about 980.degree. C for silver) is
adequate. Bars which may be sintered above the melting point
(liquid-phase) of the electrically and thermally conductive
material may be sintered in the range of from about
1,000.degree.-1,130.degree. C. Optimum temperature conditions are
dependent upon the electrically and thermally conductive refractory
composition of the mixture. And, in addition, enough refractory
structure must be present to hold the matrix of electrically and
thermally conductive material. For example, with a mixture of 50
percent silver, 50 percent tungsten liquid phase sintering at
temperatures up to 1,130.degree. C may be used. With a 90% Ag/ 10%
W mixture solid phase sintering with temperatures of from
900.degree. to 950.degree. C would be used regardless of particle
size. With a 35%/65% mixture, liquid phase sintering with
temperatures up to 1,130.degree. C may be used. In any event the
maximum temperature is thought to be about 1,130.degree. C to
prevent excessive vaporization of the electrically and thermally
conductive material.
A sintering temperature for 50 percent silver, balance molybdenum
would be 1,100.degree. C, as would the sintering temperature for a
65 percent silver, balance tungsten carbide composite. Greater
silver contents within the ranges shown in Table I should be
sintered at about 940.degree. C. Sintering temperatures for a
mixture of from about 20-50 percent copper by weight, the balance
being tungsten would be from about 1,140.degree.-1,150.degree.
C.
Again referring to the drawing, after the bars have been sintered,
they are cold rolled through a suitable rolling mill, the roll gap
being set to about two-thirds of the bar's thickness to yield a
one-third reduction in thickness in a single pass. With a one-third
reduction, optimum economic rolling conditions are achieved without
having a tendency for the bars to crack, especially along the
edges.
As shown in step 5, following the cold rolling, the material is
resintered. This step completely relieves the stresses of rolling
and promotes rapid grain growth in the matrix of electrically and
thermally conductive material to exclude voids. This void exclusion
is a result of grain growth in the solid sinter and refractory
particle wetting in liquid phase sintering. More important, the
resinter step at this point provides for a continuous matrix of
electrically and thermally conductive material, uninterrupted by a
refractory skeleton as exists in prior art infiltrated materials.
This continuous matrix provides better electrical properties with
no expense of hardness. Electrical conductivity tests consistently
indicate superior conductivity for these rolled materials over
materials of the same composition produced by so-called standard
techniques.
It is believed that the cold rolling substantially eliminates the
oxide barrier normally formed on the refractory particles, thus
leaving, as shown in FIG. 3, a direct or intimate contact between
the refractory particles 10' and the matrix 12' so as to achieve a
good intimate electrical contact between the refractory and the
electrically and thermally conductive material. While not desiring
to be so limited, it is thought that the cold rolling step sets up
an abrasive action between the refractory particles so as to cause
the substantial elimination of the oxide barrier. Although there
may be an abrasive action with hot rolling, there may still be the
tendency to create an oxide layer due to the heat involved. The
substantial elimination of the oxide barrier yields a better
electrical contact between the refractory particles and the matrix
of electrically and thermally conductive material thus yielding
increased electrical conductivity. As previously noted, the
resintering step promotes grain growth so as to eliminate voids in
the material.
Thus these two steps have eliminated two of the major defects of
prior art electrical contact materials which, as shown in FIG. 2,
includes voids 14, and substantially no intimate contact between
the refractory particles 10 and matrix 12 thus making it difficult
to achieve a good intimate electrical contact between the
refractory particles and the matrix of electrically and thermally
conductive material.
As shown in FIG. 1, in the next two steps the body is rolled and
annealed and then as shown in the last step the rolling and
annealing is continued in cycles with a 10-30 percent reduction in
thickness in each cycle until the desired properties of hardness,
density, thickness, etc., are obtained. The optimum amount of
reduction in thickness is a balance of reducing the thickness as
quickly as possible without causing cracks in the rolled body and
is dependent upon the composition of the original mixture.
For a 90 percent by weight of silver, 10 percent tungsten mixture a
30 percent reduction is thought to be optimum; for a 30%/50%
mixture, 15 percent would be optimum; for a 35%/65% mixture, 10
percent is thought to be optimum; and for a 27%/73% mixture, a 10
percent reduction per cycle is thought to be optimum. For a 50
percent by weight silver-50 percent molybdenum composite a 15
percent reduction is thought to be optimum. For a 65 percent by
weight silver-35 percent tungsten carbide composite, a 10 percent
reduction is thought to be optimum. For a mixture of from about
20-50% by weight copper, the balance being tungsten, a 15-20%
reduction per cycle would be used.
Annealing for all compositions consists of heating the rolled body
in a reducing atmosphere such as dissociated ammonia at a
temperature of about 900.degree. C for about one half hour. This
procedure completely removes the rolled grain structure, permitting
further reductions in thickness without cracking or splitting the
bar.
With reference to FIG. 4 there is shown a longitudinal cross
section of a finished strip of contact material similar to that of
FIG. 3 showing its structure. That is, the section is taken along
the length of a strip, which is the direction of rolling. It is
seen that the refractory particles 10' are dispersed or suspended
within the matrix 12' of electrically and thermally conductive
material and are layered, shown generally at 16, in a predetermined
direction, that is, the rolling direction. The layering effect 16,
which is shown between the dotted lines, extends along the length
of the material and across its width. This layering of the
refractory particles in a predetermined direction gives a better
ductility of the contact material such that is can be more readily
formed.
Using the method herein described, electrical contacts of a high
electrically and thermally conductive refractory composition have
been formed in very thin continuous strips. These strips, which can
be "blanked out" to form electrical contacts of various sizes and
shapes, not only have better electrical conductivity due to the
intimate contact of the refractory particles with the matrix of
high electrically and thermally conductive material, but also have
a more uniform density and hardness than those of the prior art.
This can be more clearly shown by the following examples and
accompanying test data.
EXAMPLE 1
A powder mixture of 50 percent silver-50 percent tungsten by weight
is pressed and sintered to a bar size of 0.125 inches in thickness.
The particle size of the tungsten is about 6 microns, and the
silver about 10 microns. The powders are pressed with a pressure of
from about 20-25 ton/in..sup.2. They are sintered in an atmosphere
of dissociated ammonia for about 20 minutes at a temperature of
about 1,130.degree.C. The pressed bars are then cold rolled in air
at a 30 percent thickness reduction for one pass. The bars are then
resintered in an atmosphere of dissociated ammonia for about 5-10
minutes at a temperature of about 1,000.degree. C. After
resintering the bars are then alternately cold rolled and annealed
until a strip having a thickness of about 0.031 inches is produced.
The annealing is done at a temperature of about 900.degree. C for
about one half hour in an atmosphere of dissociated ammonia. The
cold rolling is done in passes with a 10-15 percent reduction in
each pass.
EXAMPLE 2
A powder mixture of 65 percent silver-35 percent tungsten carbide
by weight is pressed and sintered to a bar size of 0.100 inch in
thickness. The particle size of the tungsten carbide is about 4
microns, and the silver about 10 microns. The powders are pressed
with a pressure of from about 20-25 ton/in..sup.2. They are
sintered in an atmosphere of dissociated ammonia for about 15
minutes at a temperature of about 1,300.degree. C. The pressed bars
are then cold rolled in air at a 30 percent thickness reduction for
one pass. The bars are then resintered in an atmosphere of
dissociated ammonia for about 5-10 minutes at a temperature of
about 1,200.degree. C. After resintering the bars are then
alternately cold rolled and annealed until a strip having a
thickness of about 0.031 inch is produced. The annealing is done at
a temperature of 900.degree. C for about one half hour in an
atmosphere of dissociated ammonia. The cold rolling is done in
passes having a 10 percent reduction in each pass.
EXAMPLE 3
A powder mixture of 60 percent silver-40 percent molybdenum by
weight is pressed and sintered to a bar size of 0.125 inch in
thickness. The particle size of the molybdenum is about 4 microns,
and the silver about 10-12 microns. The powders are pressed with a
pressure of from about 20-25 ton/in..sup.2. They are sintered in an
atmosphere of dissociated ammonia for about 20 minutes at a
temperature of about 1,200.degree. C. The pressed bars are then
cold rolled in air at about a 30 percent thickness reduction for
one pass. The bars are then resintered in an atmosphere of
dissociated ammonia for about 5 minutes at a temperature of about
1,100.degree. C. After resintering the bars are then alternately
cold rolled and annealed until a strip having a thickness of about
0.031 inch is produced. The annealing is done at a temperature of
about 900.degree. C for about one half hour in an atmosphere of
dissociated ammonia. The cold rolling is done in passes having a
reduction of about 10 percent in each pass.
EXAMPLE 4
A powder mixture of 50 percent copper-50 percent tungsten by weight
is pressed to a bar size of 0.125 inch in thickness. The particle
size of the tungsten is about 5-6 microns and the copper about
12-13 microns. The powders are pressed with a pressure of from
about 15-20 ton/in..sup.2. They are sintered in an atmosphere of
dissociated ammonia for about 15 minutes at a temperature of about
1,140.degree. C. The pressed bars are then resintered in an
atmosphere of dissociated ammonia for about 10 minutes at a
temperature of about 1,140.degree. C. After resintering the bars
are alternately cold rolled and annealed until a strip having a
thickness of about 0.020 inch is produced. The annealing is done at
a temperature of about 900.degree. C for about 10 minutes in an
atmosphere of dissociated ammonia. The cold rolling is done in
passes with a 10-15 percent reduction per pass.
EXAMPLE 5
A powder mixture of 25 percent copper-75 percent tungsten by weight
is pressed and sintered to a bar size of 0.125 inch in thickness.
The particle size of the tungsten is about 5-6 microns, and the
copper about 12-13 microns. The powders are pressed with a pressure
of from about 20-25 ton/in..sup.2. They are sintered in an
atmosphere of dissociated ammonia for about 15 minutes at a
temperature of about 1,150.degree. C. The pressed bars are then
cold rolled in air at a 30 percent thickness reduction for two
passes. The bars are then resintered in an atmosphere of
dissociated ammonia for about 15 minutes at a temperature of about
1,150.degree. C. After resintering the bars are alternately cold
rolled and annealed until a strip having a thickness of about 0.020
inch is produced. The annealing is done at a temperature of about
1,000.degree. C for about one half hour in dissociated ammonia. The
cold-rolling is done in passes with a 10-15 percent reduction per
pass.
EXAMPLE 6
A powder mixture of 20 percent copper-80 percent tungsten by weight
is pressed and sintered to a bar size of 0.125 inch in thickness.
The particle size of the tungsten is about 5-6 microns, and the
copper about 12-13 microns. The powders are pressed with a pressure
of from about 20-25 ton/in..sup.2. They are sintered in an
atmosphere of dissociated ammonia for about 15 minutes at a
temperature of about 1,150.degree. C. The pressed bars are then
cold rolled in air at a 30 percent thickness reduction for two
passes. The bars are then resintered in an atmosphere of
dissociated ammonia for about 15 minutes at a temperature of about
1,150.degree. C. After resintering the bars are alternately cold
rolled and annealed until a strip having a thickness of about 0.020
inch is produced. The annealing is done at a temperature of about
1,000.degree. C for about one half hour in dissociated ammonia. The
cold rolling is done in passes with a 10-15 percent reduction per
pass.
Electrical contact materials of the type noted in the examples are
then formed into suitable electrical contacts for testing, the
contacts being "blanked out" of the strips. The contacts are tested
along with contacts formed by standard prior art infiltrating
techniques to give a basis of comparison. The contacts, having
silver as the matrix, are compared for weight loss and voltage drop
while contacts using silver and copper are tested for electrical
conductivity.
For the weight loss measurements of a silver matrix, sample weld
buttons are mounted and tested in an RBM appliance relay. Four
pairs of contacts from each lot are tested. The test parameters
are:
Contact Closed Force 30 grams Contact Opening Force 75 grams
Contact Gap 020" minimum Relay Overtravel .030" minimum Operations
150,000 at 45/minute Circuit Voltage 120 volts AC Load Current
Ag-Mo, 5 amps Ag-WC, 5 amps Ag-W, 9 amps
The contacts are weighed before and after testing. Contact
resistance measurements are made at intervals during the test.
Table II shows the results of the tests performed on the materials
produced as indicated by the examples as compared to similar
materials produced by standard infiltrating techniques. The
compositions of the materials made by the infiltration techniques
are the same as those indicated in the example.
TABLE II
Avg. Wt. loss per Composition cycle - X10 .sup.-.sup.7 Avg. voltage
drop Ag-W (Std.) 3.69 421 Ag-W (Exp, 1) 3.35 405 Ag-WC(Std.) 3.13
323 Ag-WC (Exp. 2) 3.97 260 Ag-Mo (Std.) 2.05 523 Ag-Mo (Exp. 3)
1.36 417
Electrical conductivity comparisons were made of materials of the
present invention and materials made by standard infiltrating
techniques using eddy current methods. The materials were compared
as a percentage of the International Annealed Copper Standard
(I.A.C.S.) The results are shown in Tables III and IV.
TABLE III
Conductivity - % I.A.C.S. Composition Materials of Invention
Infiltrated 50% Ag - 50% W 71-73 64-65 35% Ag - 65% W 60-62 54-56
27% Ag - 73% W 50-52 46-48 65% AG - 35% WC 71-72 61-65 50% Ag - 50%
Mo 64-661/2 53-55 40% Ag - 60% Mo 581/2 - 60 47-19
TABLE IV
Conductivity - % I.A.C.S. Composition Materials of Invention
Infiltrated 50% Cu - 50% W 55-65 51-65 25% Cu - 75% W 45-53 42-49
20% Cu - 80- W 40-50 38-45
it is readily seen from Table II that the materials of the present
invention show appreciably less voltage drop compared to that of
the standard infiltrated material. Such decrease in voltage drop
indicates a lower resistance at the contact interface. Such lower
resistance means that less heat is being generated, thus prolonging
contact life. Except for the tungsten carbide-silver combination,
the materials of the invention showed less weight loss than that of
the standard materials.
It is clearly shown by Tables III and IV that the materials of the
invention have a much higher conductive value than that of commonly
used electrical contact materials.
In addition to the advantages shown by the above noted tests, it
should be understood that the material of the present invention is
much easier to fabricate into useful electrical contacts because of
the ease in "blanking out" the contacts from the strip or sheets
into which the present material is formed.
The electrical contact material of the present invention, as
hereinbefore described, is merely illustrative and not exhaustive
in scope. It is intended that all matter contained in the above
description and shown in the accompanying drawings shall be
interposed as illustrative and not in a limiting sense.
* * * * *