U.S. patent number 3,576,415 [Application Number 04/678,174] was granted by the patent office on 1971-04-27 for electrical contact surface plate having a mercury amalgam.
This patent grant is currently assigned to Textron Inc.. Invention is credited to Childress B. Gwyn, Jr..
United States Patent |
3,576,415 |
Gwyn, Jr. |
April 27, 1971 |
ELECTRICAL CONTACT SURFACE PLATE HAVING A MERCURY AMALGAM
Abstract
An electrical contact surface is prepared by forming a thin
nickel or cobalt plate over a conductive substrate, coating the
nickel plate with a thin silver plate, and thereafter coating the
silver surface with mercury and causing the mercury to amalgamate
into the lower nickel and silver plates. The silver layer may be
further coated with a layer of gold or a layer of one or more of
the platinum group family metals before the application of the
mercury surface. Cadmium may be applied over the mercury layer
before amalgamating the mercury into the silver layer.
Inventors: |
Gwyn, Jr.; Childress B.
(Wethersfield, CT) |
Assignee: |
Textron Inc. (Providence,
RI)
|
Family
ID: |
24721699 |
Appl.
No.: |
04/678,174 |
Filed: |
October 26, 1967 |
Current U.S.
Class: |
200/269; 257/766;
200/266 |
Current CPC
Class: |
H01H
1/08 (20130101) |
Current International
Class: |
H01H
1/08 (20060101); H01H 1/06 (20060101); H01h
001/02 () |
Field of
Search: |
;204/37,40,38.3,35
;29/199 ;117/131 ;200/166 (C)/ |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jones; H. O.
Claims
I claim:
1. An electrical contact structure comprising a conductive
substrate, a thin first layer of material selected from the group
consisting of nickel and cobalt extending across at least a portion
of a surface of said substrate, a thin silver layer extending
across the upper surface of said thin first layer, and mercury
amalgamated into said silver layer and, to a lesser extent, into
said first layer.
2. The contact structure as set forth in claim 1 which includes a
further layer of cadmium plated atop said silver layer.
3. The contact structure of claim 1 which further includes a third
layer of material selected from the group consisting of gold and
the platinum group family metals plated across said silver layer;
and mercury amalgamated into said third layer.
4. The contact structure of claim 1 wherein said first layer has a
thickness of at least 0.0001 inches and said silver layer has a
thickness of at least 0.00005 inches.
Description
This invention relates to electrical contact structures and methods
of making such structures, and more particularly relates to a novel
plated contact.
Electrical contacts are commonly formed by plating a silver or
silver alloy layer over a conductive substrate such as a brass
rivet, brass or copper plate, or the like, which is to cooperate
with another contact. Similarly, surfaces which are to receive
sliding contact engagement are commonly silver plated to reduce
contact resistance and mechanical friction.
Platings or cladding used in the past have exhibited relatively
high rises in contact resistance or unexpected changes in contact
resistance, due in part from localized electrolytic action between
the plating and the substrate. Moreover, relatively soft platings
such as silver are subject to flow under pressure, leading to
inadvertent open or closed circuits between the plated contact
surface and its cooperating contact (which may also be a plated
contact).
A principle object of the present invention is to provide a contact
surface layer for a conductive substrate which has a relatively
consistent resistance drop.
Another object of this invention is to provide an electrical
contact surface having a low resistance drop which is smooth and
hard.
A further object of this invention is to provide a novel contact
surface layer structure which is relatively inexpensive.
These and other objects of this invention will become more apparent
from the following description and examples of carrying out the
invention, reference being made to FIGS. 1 and 2 of the drawings
showing alternative embodiments thereof, though not necessarily to
scale.
EXAMPLE 1
A copper plate 10 (FIG. 1) which is the conductive substrate to be
clad is first cleaned in the manner well known for preparing a
surface for a nickel plate. Thereafter, a nickel plating 12 is
applied to the surface to be clad to a thickness of at least 0.0001
inches. This nickel layer can be applied by any desired process
such as mistplating, vacuum plating, electroplating or electroless
plating. Thereafter a layer of silver 14 is plated over the nickel
plate to a thickness of at least 0.00005 inches.
The upper surface 14 of the silver surface is then wet with mercury
16 and the substrate and mercury are tumbled or agitated until the
silver surface is coated uniformly with a mercury coating having a
thickness of at least 0.00001 inches.
The mercury coated plate is then placed in a suitable oven and
heated to a temperature greater than 100.degree. C., but less than
300.degree. C., until the mercury coating 16 amalgamates into the
lower silver layer 14, and, to a lesser extent, the nickel layer
12.
The completed contact surface formed in the above manner has been
found to exhibit a very stable resistance rise and has a hard,
smooth finish which will not cold flow or deform easily.
EXAMPLE 2
Thin nickel 12 and silver 14 layers were first applied to a
conductive substrate 10, as described in Example 1. Thereafter, and
prior to application of the mercury layer 16, a thin layer of gold
18 (FIG. 2) having a thickness of about 0.0001 inches was plated
atop the silver 14. Mercury 16 was then coated atop the gold layer
18 and amalgamated into the three lower layers by heating as
described above.
EXAMPLE 3
The process of Example 2 was repeated where the gold layer 18 was
replaced by a layer of one or more of the platinum group family
metals including palladium, osmium, rhodium, platinum, and
ruthenium.
EXAMPLE 4
The process of Example 1 was repeated to the point of spreading
mercury 16 over the lower silver layer 14. Before amalgamating the
mercury, a thin cadmium layer 20 (FIG. 1, in phantom) was plated
over the mercury 16 to a thickness of about 0.0001 inches. The
platings were then heated to force the amalgamation or diffusion of
the mercury into the silver layer and partly into the bottom nickel
layer.
EXAMPLE 5
The process of Example 1 was repeated with the nickel layer 12
replaced by cobalt. It was found that the cobalt performed in a
manner similar to nickel in its cooperation with the mercury after
amalgamation of the mercury.
It has been shown through electrical and/or electrochemical life
tests that the addition of and incorporation of mercury in the
cladding prevents or sufficiently ameliorates the electrolytic or
so-called battery actions often existing between the individual
members of a contact assembly under humid or liquid operational
conditions, so that the resultant two or multilayer cladding is not
subject thereto. This is particularly important for the contact
requirements of dry circuitry, of television tuner circuits etc.,
and for low impressed voltage contact requirements. It is well
known in the art that such electrolytic actions can markedly affect
the direction and degree of current flow under low voltage and low
current flow conditions.
These tests have further shown that the millivolt drop (surface
resistance rise) across single or mating contacts prepared
according to this invention remains consistently lower than for
parts similarly plated, but not containing mercury. Furthermore,
these tests have also shown that to obtain optimum results both the
nickel clad surface and the diffused or amalgamated mercury are
necessary components or constituents. Although not as yet fully
determined as to its nature, there is a resultant definite
advantageous synergistic action obtained through the mutual
inclusion and use of the nickel or cobalt and the mercury.
Furthermore sliding frictional value tests have shown that the
incorporation of mercury appreciably lowers the overall drag or
frictional resistance over the same materials not containing
mercury. This is somewhat surprising, since the overall (surface)
hardness is also greater for the contacts incorporating mercury
than for those not containing mercury.
Although this invention has been described with respect to its
preferred embodiments, it should be understood that many variations
and modifications will now be obvious to those skilled in the art,
and it is preferred, therefore, that the scope of the invention be
limited not by the specific disclosure herein, but only by the
appended claims.
The embodiments of the invention in which an exclusive privilege or
property is claimed are defined as follows:
* * * * *