Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROU~3D OF THE INVENTION
Field of the invention
The present invention relates to internally
oxidized Ag-SnO system alloy electrical contacts and to a
method of manufacturing the same.
Ag alloys which contain 0.5 to 12 weight ~ of Sn
and which have been internal oxidized, are widely used as
electrical contact materials in various electrical devices
such as switches, contactors, relays and circuit breakers.
These Ag alloys which are molten, cast, and rolled
or drawn, and are generally in the form of thin plates with
or without backing thin pure Ag plates joined to a side of
the Ag alloy thin plates, are internally oxidized by
subjecting them to an oxygen atmosphere under a pressure.
They are different from those sintered Ag-metal oxides
alloys which are made by mixing matric Ag powders with
powders of the metal oxides and sintering them. One of
their noticeable differences is that the former, viz.
internal oxidized Ag-Sn system alloys are far superior to
the latter in respect to structural density, while the
latter has the more uniform dispersion of metal oxides than
the former. The latter may be very readily consumed in too
rapid and frequent switching operations. oxygen which has
penetrated into the Ag alloys as time passes, oxidizes
metallic solute elements in the alloys and precipitates them
as minute metallic oxides distributed in their Ag matrices.
Said metallic oxidized precipitates afford refractoriness
and
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consequently anti-welding properties to the Ag alloys. The
backing thin pure Ag plates when they are employed, work as
mediums for brazing the oxidized Ag alloy contact materials
to support or base metals of electrical contacts.
It has been observed, however, that when Ag alloys of
the above-mentioned kind are internal oxidized, metallic
solute elements in the Ag alloys do not precipitate and
distribute evenly in their Ag matrices, but they tend to
precipitate at a high concentration about outer areas which
are suhjected directly to oxygen. Such precipitation of 10
metallic oxides at outer areas produces their segregations
about the outer areas, particularly at top surfaces, and
bring in turn depletion layers of an unnegligible thickness
which lie between the top and bottom surfaces of the Ag
alloys, when they are internally oxidized from both sides
thereof. The segregations of metallic oxides at a high
concentration about outer sur~aces of electrical contact
materials make the outer surfaces physically too hard, and
produces electrically a high contact resistance of the mate-
rials especially at an initial stage of operations and 20
consequently an excessive temperature raise. In practice,
such segregations about the outer areas are often shaved off
by files and so on. This is not only laborious, but also it
makes difficult to reuse filings of the outer areas, since
they are contaminated by ~ilings of the files.
Compared to internal oxidized Ag-Sn system alloys,
internal oxidized Ag-Cd system alloys which had competed
with the Ag-Sn system alloys, have a more uniform dispersion
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of metal oxides. This is chiefly because that the diffusion
velocity of Cd in a silver matrix is inherently well balan-
ced with the diffusion velocity of oxygen in the internal
oxidation, while they are not so in the case of internal
oxidation of Ag-Sn system alloys. In other words, electri-
cal contact materials made of internal oxidized Ag-Cd system
alloy and methods for preparing them can hardly be referen-
ces which are utilizable for the preparation of Ag-Sn system
alloys and the internal oxidation thereof.
At all events, the segregation of tin oxides about 10
contact surfaces makes them too hard, and often brings about
cracks of the surfaces. High electrical contact resistances
especially of an initial stage of operations of electrical
contacts made from internal oxidized Ag-Sn alloys result
from the segregation or excessive concentration of tin
oxides about top surfaces. Unduly high raise of temperature
of contacts results also from the segregation.
In order to avoid the production of such segregations,
there were invented by the present inventor certain methods
such as disclosed in V.S. Patent No. 4,457,787 in which 20
vac~ant lattice voids are produced in Ag alloys by having
them absorbed with hydrogen and the like, and in the course
of internal oxidation, solute melts fill in the voids and
precipitate as oxides at the innumerable oxide nuclei on an
atomic s¢ale, without diffusing about much but only to such
extent that they reach most adjacent voids, and consequently
without any segregation and depletion thereof, and U.S.
L%9t6~
Patent No. 4,472,211 in which a high contact resistance
which is caused by high concentration or supersaturation o~
metal oxides including tin oxides about a contact surface,
is avoided by having solute metals sublimated, reduced or
extracted about the contact surface before the internal
oxidation thereof.
The aforementioned depletion layers in which
metallic oxides lack completely or they are extremely thin,
can hardly stand up to severe switching operations, since
they have poor refractoriness. Therefore, when a contact
material having a depletion layer between its upper contact
surface and lower surface is used till its wear reaches the
depletion layer, its life ends. This means that while the
lower half of the contact material which lies below the
depletion layer can join with the upper half above the
depletion layer to disperse heat generated with switching
operations and to give a desired height of the material, it
can not be active as a contact surface. Often, the
existence of such lower half of the contact material is
meaningless.
The object of the present invention is, therefore,
to provide internal oxidized An-SnO system alloy electrical
contacts having contact surfaces of a moderate initial
contact resistance and having no depletion layer, and a
method of manufacturing such excellent contacts, not using
such methods as disclosed in the above-mentioned U.S.
Patents which methods are difficult to ade~uately control.
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Brief Summary of the Invention
It has been found by the present inventor that though
internally oxidized structures of an An-Sn system alloy
about its surface or surfaces with which oxygen comes to
contact first and from which it penetrates into the alloy,
are rough, the deeper they lie in the alloy, the finer they
become. In other words, the internal oxidized structures
which have been produced in the alloy at the forwardmost
area along a progressive direction of internal oxidation,
are fine and free from the segregation of tin oxides. They 10
are, therefore, most suited as contact surfaces.
It has been observed by the inventor that along with
the progressive direction of internal oxidation, grain sizes
of tin oxides precipitated in Ag matrices become gradually
larger~ Hence, the contrast between the Ag matrices and the
tin oxides becomes clearer or more remarkable in the progre-
ssive direction of internal oxidation, which contrast can be
expressed by the above words that the internal oxidized
structure at the forwardmost area along the progressive
direction of internal oxidation is most fine. The larger 20
the size of precipitates of tin oxides has, the larger area
the Ag matrices can occupy so that lower electrical contact
resistances are assured and unduly high raise of temperature
of contacts can accordingly be avoided. Granting that a
concentration of Sn throughout an alloy or from the rearmost
area to the forwardmost area of internal oxidation of the
alloy is constant, the forwardmost area which is consisted
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of Ag matrices and one grain ~for exampl~ only) o~ tin
oxides of a certain weight % of the Ag matrices can afford
to the Ag matrices larger contact surfaces, compared to the
rearmost area which is consisted of the ten grains ~for
example) of the same weight % in total and Ag matrices.
It shall be noted also that the larger precipitates of tin
oxides are, the lesser the strain to be produced in the tin
oxides with the internal oxidation becomes, so that and
whereby precipitates come to have a moderate hardness which
can scarcely bring about cracks of contact surfaces. 10
In view of the above, "the forwardmost area along a
progressive direction of internal oxidation" used in the
specification and claims can readily be comprehended micros-
copically by those skilled in this art and can define this
invention.
Such fine internal oxidized Ag-Sn alloy structures at
the front or forwardmost area of internal oxidation appear,
when the alloy is oxidized from both sides, centrally in the
alloy with a depletion zone therebetween, and when the alloy
is oxidized from a single side, at a bottom opposite to a 20
surface from which oxygen penetrates into the alloy. Since
the depletion zone or a zone where tin oxides are poor lies
usually next to the forwardmost area of internal oxidation,
said area which is employed in this invention as a contact
surface, should be free from the above zones. -
Typical constituents of Ag-Sn alloys employable in this
invention are those comprising of Ag matrices, 0.5 - 12
weight % of Sn, and 0.5 - 15 weight % of In, and those
comprising of Ag ~atrices, 3 - 12 weight % of Sn, and 0.~1
- less than 1.5 weight ~ of Bi. Said constituents may contain
one or more metallic elements selected from 0.1 - 5 weight
~ of Cd, 0.1 - 2 weight % of Zn, 0.1 - 2 weight ~ of Sb,
and 0.01 - 2 weight ~ of Pb. In the case of the above-men-
tioned latter constituents, 0.1 - less than 2 weight % of
In may be contained. Further, they may contain less than
0.5 weight % of one or more elements of iron family.
More particularly, the invention first proposes
a method of making an internally oxidized Ag-SnO system alloy
electrical contact which comprises:
preparing an Ag alloy comprising a silver matrix
and either 0~5 - 12 weight % of Sn and 0.5 - weight % of
In or 3 to 12 weight % of Sn and 0.01 - less than 1.5 weight
% of Bi:
completely internally oxidizing the alloy;
the alloy resulting from such an internal oxida-
tion comprising a plurality of areas extending parallel to
a surface of the alloy from which oxygen was diffused to
achieve said internal oxidation, said areas extending adjacent
to each other in the progressive direction of said internal oxidation
and including in said progressive direction an external oxide seyregation
area, an internally oxidized intermediate area, a forwardmost area
of internal oxidation and an internal oxide depletion area;
and
forming contact surfaces by cutting or shaving
the alloy remotely from the surface from which oxygen was
diffused into the alloy to achieve internal oxydation thereof
so that the oxide depletion area is removed from the alloy
and the forwardmost area is exposed to form a contact surfaceO
the invention also proposes a method of making an internally
oxidized Ag-SnO system alloy electrical contact, which com-
prises:
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preparing an Ag alloy layer having a thickness
at least twice as thick as a preselected thickness a~d compri-
sing a silver matrix and either 0.5 - 12 weight % of Sn and
0.5 - 15 weight % of In or 3 to 12 weight % Sn and 0.01 -
less than 1.5 weight % of Bi;
fixedly sandwiching the alloy layer between thin
pure silver layers;
completely internally oxidizing said alloy layer
to form an oxide depletion layer intermediate its cpposed
surfaces;
slitting said alloy to a desired configuration
after internal oxidation thereof;
cutting the alloy into two parts along said deple-
tion layer; and
removing the depletion layer left on one of said
parts,
wherein said one part after such a removal forming
said contact.
Of course, the invention further proposes contacts
obtained by any of the above mentioned methods.
As aforesaid, the Ag alloy may be prepared to
a flat plate or disk having a height which is at least twice
a desired final height and to while may be added the height
of a depletion layer which is expected to be produced when
the Ag-alloy is completely internal-oxidized. This Ag-alloy
is backed at its both surfaces by thin pure Ag layers.
Then, the so prepared Ag-alloy is completely
internal oxidized in an oxygen atmosphere under a pressure
and at an elevated temperature.
During the internal oxidation of the Ag-alloy,
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the backing thin pure Ag layers work as follows.
Since the partial pressure of oxygen, which has
been dissolved into silver at the elevated temperature, is
comparatively low, and since an amount of oxygen which diffu-
ses through the silver is constant at a predetermined specific
temperature, and under an oxygen atmosphere of a predeter-
mined specific pressure, an amount of oxygen which shall
be diffused into a metal alloy via the silver for oxidizing
the former, can readily and freely be controlled. In additi~
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to this advantage, since the oxygen in this instance is
diffused into the metal alloy through the silver, and conse-
quently at a selected direction of paths of oxygen, crystal-
line metallic grains oxidized and precipitated in the metal
alloy are not arranged at random but can be prismatically
aligned in the paths of oxygen. Since these prismatically
aligned metallic oxides are also in parallel with electric
current paths passing through the internal oxidized Ag alloy
contact mat~rial, electric resistance by the material is
lowered. 10
The completely internal oxidlzed Ag alloy plate or disk
havlng a depletion layer which lies centrally and transver-
sely to the axis or height of plate or disk, is cut along
said depletion layer by a super hard and high speed cutting
device such as a mill with a width more than the width of
the depletion layer. Unlikely to the conventional sanding
off of segregation of metal oxides from outer surfaces of
oxidized Ag alloys, said cutting operation does not give any
contamination to cut surfaces and a cut-off portion of the
Ag alloy which includes the depletion layer. 20
Two parts thus cut off from the plate or disk have
respectively a completely internal oxidized Ag alloy body
having a fresh contact surface of a moderate hardness and
inltial resistance and a pure silver backing at its bottom
surface, and having no depletion layer.
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Preferred Embodiments
Example 1.
(1) Ag-Sn 8~-In ~%
(2) Ag-Sn 8~-In 4~-Cd 0.5%
(3) Ag-Sn 7%-Bi 0.5~
(4) Ag-Sn 7%-Bi 0.5%-Zn 0.3%
Alloys of the above (1) to (4) were melted in a high
frequency melting furnace at about 1f100 to 1,200C and
poured into molds for obtaining ingots of about 5 Kg each.
Each ingot was stripped at its one surface. Then, each 10
~ingot was butted opposite at its stripped surface to a nickel plate
by means of a hydraulic press, and rolled to a plate of
about 2.2 mm with the nickel back of about O.l mm.
Each plate was subjected to an oxygen atmosphere for
200 hours and at 650C so that the plate was completely
internal-oxidized. Since the nickel back is unoxidizable,
internal oxidation progressed from the stripped surface
only. Segregation of tin oxides was observed around the
stripped surface. The internal oxidized structures which
had been produced in the plate at the forwardmost area along 20
the progressive direction of internal oxidation, viz., in
this instance about 2 mm deep from the stripped surface,
were;extremely fine and completely free from the segregation
of metal oxides. A depletlon zone or a zone where tin
oxides are poor next to said forwardmost area with a depth
of about O.l mm.
Each of the internal oxidized plates were placed in a
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H2 gas atmosphere and heated at 750C for ten minutes, so
that metal oxides about the stripped surface were reduced or
decomposed whereby the stripped surface could be brazeable
to a movable or stationary contact base.
~ he nickel plate can be replaced by other metals ~,7hich
are not oxidizable, and the reduction or decomposition of
metal oxides about the stripped surface may be made by
heating in a flux or im~ersing it into an acid solution.
Then, the plates were horizontally cut at a plane of
0.2 mm from the bottom surface. And, plates were slitted to obtain 10
square electrical contacts of 5 mm sides and of a thickness
of 1.9 mm, having the forwardmost areas of internal oxida-
tion along its progressive direction as contact surfaces,
and the reduced or decomposed stripped surfaces as backs.
Instead of slitting the plates after the internal oxi-
dation, they may be cut or pressed out to desired configura-
tion before the internal oxidation.
In order to compare the above electrical contacts made
in accordance with this invention, the following contacts
were made. 20
(5) Ag-Sn 8%-In 4%
(6) Ag-Sn 8%-ln 4%-Cd 0.5%
(7) Ag-Sn 7%-Bi 0.5%
~) Ag-Sn 7%-Bi 0.5%-Zn 0.3%
Similarly to the above example, the above alloys (5) to
(8) were prepared to ingots. Then, each ingot was butted at
its stripped surface to a pure silver plate by means of a
hydraulic press, platen of which was heated at about 440C,
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and rolled to a plate of about 2 mm thickness, while it was
annealed at about 600C, at every stages of rolling rates of
30 ~ in reduction~
Each plate was internally oxidized in an oxygen atmos-
phere for 200 hours and at 650C. Then, internally oxidized
plates were pressed by a punch of 6 mm in diameter to obtain
electrical contacts of 2 mm in thickness which were backed
with a thin silver layer.
The above contact samples of alloys 11) to (4) of this
invention and of alloys ~5) to (8) of prior known samples 10
were checked of their contact surface hardness, and of their
initial contact resistance with the ~ollowing conditions.
Initial contact resistance:
Contact pressure - 400g
Current - DC 6V, 1A
TABLE 1
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Samples Hardness (HR "F")
________________________________________________
(1) 69 - 82
~2) 67 - 74 20
(3) 64 - 76
(4) "of this invention" 67 - 76
(5) 95 - 105
(6~ 93 - 9~
(7) 90 - 100
(8) "of prior known samples" 90 - 100
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TABLE 2
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Samples Initial contact resistance (~ Q)
______________________ _________________________
(1) ~.6 - 2.1
(2) 0~6 - 2.1
~3) 1.5 - 1.4
(4) "of this invention" 0.5 - 1.6
(5~ 1.2 - 2.2
(6) 1.2 - 2.2
(7) 0.7 - 2.1
(8) "of prior known samples" 1.7 - 2.2
____________________ ___________________________
Thus, it is known from the above tables that the con-
tact materials made in accordance with this invention have 10
moderate hardness and lower initial contact resistance,
compared to corresponding prior-known contact materials.
Example 2
An alloy ingot of Ag-Sn 8%-In 4% was drawn to a wire of
5 mm in diameter, from which there were prepared a number of
pieces each having a body portion of 5 mm in diameter and
3.3 mm length, which was integrally provided at its both
sides with projections of 2.5 mm in diameter and 1 mm in
height. Those pieces were completely internally oxidized,
and then transversely to thelr axes cut right in two by a 20
mill with kerf of 0.3 mm so that~such rivet-shaped contact
materials each having a contact head of 5 mm diameter and
1.5 mm height with a shank of 2.5 mm diameter and 1 mm
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height, which were characterized by making the forwardmost
areas of internal oxidation as contact surfaces, were pro-
duced. The pieces may be subjected to H2 gas before or
after they were cut to two so that the shank can be brazeab-
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le to a contact support metal as described in Example 1.
The rivet-shaped contact materials thus obtained, had
sxcellent physical and electrical characteristics, compared
to their correspondent conventional contact materials. It
has been observed that their hardness was about 30 % less
than that of conventional ones, and their initial contact
resistance was as much as 50 % less.
Example 3
~ 9) Ag-Sn 8%-In 4%
l10~ Ag-Sn 8%-In 4%-Cd 0.5% 10
t11) Ag-Sn 7%-Bi 0.5%
(12) Ag-Sn 7%-Bi 0.5%-Zn 0.3%
Alloys of the above (9) to (12) were melted in a high
frequency melting furnace at about 1,100 to 1,200C and
poured into molds for obtaining ingots of about 5 Kg. Each
ingot was stripped at its both surfaces. Then, each ingot
was butted at its stripped both surfaces to pure silver
plates by means of a hydraulic press, platens of which were
heated at about 400C, and rolled to a plate of 3.1 mm
thickness. while it was annealed at about 500C at every 20
stages of rolling rates of 30 % in reduction.
Each plate had one of the above alloys t9), (10), (11)
and (12) of 2.5 mm thickness joined at its both surfaces by
the pure silver layer of 0.3 mm thickness.
Each plate was completely internally oxidized in an
oxygen atmosphere for 200 hours and at 650C. The plate had
centrally a depletion layer of about 0.1 - 0~2 mm thickness.
Then, the plates were horizontally cut right in two by a
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mill with a Xerf of 0.5 mm. And, the plates were slitted to
obtain square electrical contacts of 5 mm sides and of a
thickness of 1 mm, which were backed at one of the surfaces
with a thin silver layer of 0.3 mm.
Instead of slitting the plates after the internal oxi-
dation, they may be cut or pressed out to desired configura-
tions before the internal oxidation.
The above contact samples of alloys (9) to (12~ of this
invention and of alloys (5) to (8~ of prior known samples
(Example 1) were checked of their contact surface hardness, 10
and of their initial contact resistance with the following
conditions.
Initial contact resistance:
Contact pressure - 400g
Cu~rent - DC 6V, 1A
TABLE 1
Samples Hardness (HR "F")
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(9) 69 - 80
(10) 67 - 72 20
(11) 64 - 75
(12) "of this invention" 67 - 75
t5) 95 105
(5) 93 - 94
(7) 90 - 100
(8) "of prior known samples" 90 - 100
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TABLE 2
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Samples Initial contact resistance (m a )
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Ig) 0.6 - 2.0
(10) 0.6 - 2.0
(11) 1.5 - 1.3
(12) "of this invention" 0.5 - 1.4
l5) 1.2 - 2.2
(6) 1.2 - 2.2
0.7 - 2~1
~8) "of prior known samples" 1.7 - 2.2
Thus, it is known from the above tables that the con- 10
tact materials made in accordance with this invention have
moderate hardness and lower initial contact resistance,
compared to corresponding prior-known contact materials.
Though in the above examples, Ag-Sn syste~ alloys were
prepared by a melting method and then subjected to internal
oxidation, they can be prepared powdermetallurgically prefe-
rably with subsequent forging and then be subjected to
internal oxidation. It is a matter of course that since
internal oxidation mechanisms in the case of the latter
aLloys work exactly same to the case of the former alloys, 2D
this invention as defined in the claims undoubtedly cover
the latter alloys too. It shall be noted also that though
the electrical contact materials (9) to (12) obtained in
Example 3 in accordance with this invention in which they
were contacted to oxygen not directly but indirectly through
pure silver screens, had less rough oxidation structures at
their surfaces which were immediately next to said silver
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screens and hence came to contact first with the oxygen,
compared to the internal oxidized structures around the
stripped surfaces of the alloys (1) to (4) of Example 1;
their forwardmost areas along the progressive direction of
internal oxidation had finer structures which were clearly
distinctive by microscopic observations as aforementioned.
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