U.S. patent number 3,562,467 [Application Number 04/830,433] was granted by the patent office on 1971-02-09 for electrical contact.
This patent grant is currently assigned to Engelhard Minerals & Chemicals Corporation. Invention is credited to Victor G. Mooradian.
United States Patent |
3,562,467 |
Mooradian |
February 9, 1971 |
ELECTRICAL CONTACT
Abstract
An electrical contact of the rivet type comprising a metal head
and a metal shank, the head being a bimetallic head composed of a
layer of contact metal, e.g. silver, and a backing layer of another
metal from which extends the rivet shank and which is preferably of
the same metal composition as the metal backing layer, both the
shank and the backing layer, including the under surface and the
peripheral sides of the backing layer being coated with a layer of
metal solder having a lower melting point than the contact metal,
the backing layer and the shank.
Inventors: |
Mooradian; Victor G. (Summit,
NJ) |
Assignee: |
Engelhard Minerals & Chemicals
Corporation (Newark, NJ)
|
Family
ID: |
25257001 |
Appl.
No.: |
04/830,433 |
Filed: |
June 4, 1969 |
Current U.S.
Class: |
200/268;
200/275 |
Current CPC
Class: |
H01H
11/045 (20130101) |
Current International
Class: |
H01H
11/04 (20060101); H01h 001/02 () |
Field of
Search: |
;29/630,622
;200/166C |
Primary Examiner: Jones; H. O.
Claims
I claim:
1. An electrical contact of the rivet type comprising a metal head
and a metal shank extending from one side of the head, the shank,
and the side of the head adjacent the shank having coated thereon
layer of metal solder having a lower melting point than the metal
of the head and the metal of the shank, the metal solder layer
having a thickness between about 0.005 to about 0.0002 inch.
2. An electrical contact according to claim 1, wherein the head is
a bimetallic head composed of a surface layer of contact metal
bonded to a backing layer of a metal different from the contact
metal, and said metal solder layer extending over the peripheral
surface of the said backing layer.
3. An electrical contact assembly comprising an electrical contact
of the rivet type having a metal head and a metal shank joined to
the head, the shank, and the side of the head adjacent the shank
having coated thereon a layer of metal solder having a lower
melting point than the metal of the head and the metal of the
shank, the metal solder layer having a thickness between about
0.003 and 0.0005 inch, a metal arm having an aperture therethrough
defined by the aperture wall, the shank of the rivet passing
through the aperture with the solder-coated side of the head
adjacent the shank abutting one side of the arm adjacent the
aperture, the free end of the shank being staked in abutment with
the opposite side of the arm adjacent the aperture, the solder
being in heat alloyed condition as a soldered bond between the head
of the rivet and the metal of the arm adjacent the aperture and
between the rivet shank and the wall defining the arm aperture.
Description
BACKGROUND OF THE INVENTION
Electrical contacts of the rivet type with the rivet head composed
in part of a contact metal selected for its electrical performance,
e.g. a bimetallic rivet head having a surface contact layer of
silver and the remaining portion, or backing layer, and the shank,
composed of a metal different from the contact metal, e.g. copper,
are well known as evidenced by U.S. Pat. No. 3,026,603. Such
contacts are generally mounted on a contact arm and mechanically
secured on the contact arm through an aperture therein by cold
staking or hot staking the end portion of the shank passing through
the aperture into abutment with the surface of the arm surrounding
the aperture. It has been experienced during the operation of such
contacts for substantial periods that the mechanical securing of
the contact to the contact arm is sometimes subject to loosening
with the result that the contact does not operate efficiently and
otherwise electrical conductivity is adversely influenced by
oxidation of the shank portion which undesirably increases the
electrical resistance of the assembly. In addition to such
disadvantage, after substantially prolonged usage, the bimetallic
head undergoes a distortion such that the peripheral marginal
portions of the head adjacent the contact arm separate from the
surface of the contact arm at least partly about the circumference
of the head effecting a bent distortion, e.g. "curling" of the
contact metal layer, which seriously affects the performance of the
contact. The present invention contemplates the provision of an
electrical contact and contact assembly which obviates such
disadvantages.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided an electrical
contact of the rivet type comprising a metal head and a metal
shank, the head being a bimetallic head composed of a layer of
contact metal, e.g. silver, and a backing layer of a different
metal, e.g. copper from which extends the rivet shank and which
shank is preferably of the same metal composition as the backing
layer, both the peripheral surfaces of the shank and the backing
layer including the undersurface of an the peripheral sides of the
backing layer being coated with a layer of solder having a melting
point lower than that of the contact metal, the backing layer and
the shank. Specifically, the thickness of the solder coat layer is
between the range of 0.005 and 0.0002 inches, preferably between
0.003 and 0.0005 inches. The criticality of the invention lies in
the particular thickness of solder coat as well as the combination
including such solder thickness and the above-mentioned surfaces
coated with the solder layer.
It is not herein regarded as a novel expedient to merely flash coat
by electroplating a contact rivet with a metal such as silver
within the thickness range of, for example, 0.0001 to less than
0.0002 inches to preserve it against oxidation and corrosion during
its shelf life. The silver flash coat could very well be a silver
alloy of a solder composition, but unless its thickness is within
the range herein contemplated, it cannot operate to provide an
effective solder joint. The same applies if the solder is applied
to the contact in a thickness exceeding about 0.005 inches. For
example, if the solder was applied to a thickness less than about
0.0002 inches, during subsequent heating it diffuses rapidly into
the shank and backing metal and also into the surrounding adjacent
metal, i.e. the walls of the aperture in the contact arm into which
the shank is inserted, so that no solder metal is left to provide a
bond layer at the interface between the adjacent metals. If the
solder was applied to a thickness exceeding about 0.005 inches,
during subsequent heating there would be some solder in the solder
layer at the interface in unalloyed condition with the adjacent
metals thereby providing an unsatisfactorily weak bond. Otherwise,
a lot of the solder would, during melting, exude from between
adjacent surfaces and contaminate the contact surface.
DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a partly cross-sectional and partly elevational
side view of an electrical contact according to the invention;
FIG. 2 illustrates a fragmentary elevational side view of a contact
assembly; and
FIG. 3 illustrates a cross-sectional view of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, the electrical contact of the invention is in
the form of a rivet having a rivet head 1 and a rivet shank 2. The
rivet head is preferably in the form of a bimetallic head having a
surface layer 3 composed of contact metal, e.g. silver, silver
alloy, a platinum group metal especially platinum or palladium,
gold or a gold alloy, or a tungsten-molybdenum alloy. The contact
metal surface layer is mounted on a backing layer 4 composed of a
metal different from the contact metal, e.g. a base metal such as
copper, bronze, brass, nickel or steel, and the shank 2 extends
from the backing layer thereby forming a rivet shape.
The sides 5 of shank 2, the bottom surface 6 of backing layer 4 and
the peripheral surface 7 of the backing layer are coated with a
layer 8 of solder having a melting point lower than that of the
contact metal 3 the backing layer 4 and the core metal of shank 2.
Specifically, the thickness of the solder coat layer is preferably
between the range of about 0.003 and 0.0005 inch. As stated above,
the criticality of the invention lies in the combination of the
solder coated surfaces as well as the thickness of the solder
coat.
The solder layer 8 is composed of solder alloys such as 15 percent
Ag-80 percent Cu-5 percent P; 35 percent Ag-26 percent Cu-21
percent Zn-18 percent Cd; 45 percent Ag-15 percent Cu-16 percent
Zn-24 percent Cd; 5 percent Ag-16.6 percent Zn-78.4 percent Cd; 5
percent Ag-95 percent Cd; 56 percent Ag-22 percent Cu-17 percent
Zn-5 percent Sn. The selection of a suitable solder composition for
the solder layer 8 will depend upon the permissible temperatures to
which the contact assembly such as illustrated by FIGS. 2 and 3
will be subjected to during fabrication or use of the contact
assembly.
The rivet type contact may be formed in known manner, for example,
as disclosed in U.S. Pat. No. 3,208,129, and while the solder layer
8 may be applied as an alloy sheath on a base metal wire core prior
to forming the bimetallic head 1, it can also be provided by
alternately electroplating layers of different metals such as
silver, copper, zinc, tin, etc. on the base metal wire core prior
to forming the rivet head and then allowing the solder to be formed
from these layers during hot staking onto the contact arm 9 or by
passing the cold staked rivet through a controlled temperature as
in an oven.
Regarding FIGS. 2 and 3, a metal contact strip or arm 9, e.g. an
arm of copper, bronze, brass or steel, is provided with an aperture
formed therethrough and defined by aperture wall 10. The rivet of
FIG. 1 is inserted into the aperture with the solder layer 8
coating the bottom surface 6 of the backing layer 4 abutting one
side of the strip or arm adjacent the aperture and the free end of
the shank 2 extending out of the aperture. Thereafter, the free end
portion 11 (FIG. 1) of the rivet is deformed into a second
retaining head 12 having an inner solder coated face 13 in abutment
with the opposite side of the arm adjacent the aperture to form a
contact assembly. Preferably, the rivet is mounted in the arm 9
aperture and the end portion 11 is hot staked to form the retaining
head 12 by the use of well-known electrically heating electrodes
(not shown) having die cavities contoured to contain the head 1
while shaping the head 12 into its headlike convex head.
When the rivet contact is hot staked into arm 9, the solder layer
8, being present in the above-stated critical range of thickness,
the solder melts and alloys with the metal of side 5 of shank 2 and
the metal of the aperture walls 10, as well as between the metal of
the undersurface 6 of back 4 and the portion of the contact arm 9
underlying the head 1 and also forming a small annular fillet 14
between the periphery of the backing layer 4 and the contact arm
due to the flow of solder 8b from the peripheral sides of the
backing layer.
While the melts and the solder joint is thereby formed by hot
staking as described above, the rivets may also be applied by cold
staking after which the solder can be melted to form the joint by
passing the assembly through an oven under controlled temperature
conditions.
With the contact rivet so staked and soldered, it avoids the
tendency of the contact head to separate from the contact arm, as
by curling, and also insures the rivet shank against loosening in
the aperture of the contact arm.
* * * * *