U.S. patent number 3,706,650 [Application Number 05/128,240] was granted by the patent office on 1972-12-19 for contour activating device.
This patent grant is currently assigned to Norton Company. Invention is credited to Steve Eisner.
United States Patent |
3,706,650 |
Eisner |
December 19, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
CONTOUR ACTIVATING DEVICE
Abstract
A rotatable activating device for contacting and activating a
contoured surface during the electrodeposition thereon of a metal
coating. The device has an outer surface composed of a
non-conductive, porous, compressible, fluid-entrapping and
circulating, fixed hard particle-supporting media contoured to
complement the contours of the surface to be activated and an
internal complete or partial core of a conductive material.
Inventors: |
Eisner; Steve (Schenectady,
NY) |
Assignee: |
Norton Company (Troy,
NY)
|
Family
ID: |
22434340 |
Appl.
No.: |
05/128,240 |
Filed: |
March 26, 1971 |
Current U.S.
Class: |
204/217;
204/224R; 204/271 |
Current CPC
Class: |
C25D
5/22 (20130101) |
Current International
Class: |
C25D
5/00 (20060101); C25D 5/22 (20060101); B23p
001/00 () |
Field of
Search: |
;204/217,DIG.10,224,271 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
18,643 |
|
1899 |
|
GB |
|
493,108 |
|
Sep 1938 |
|
GB |
|
Primary Examiner: Mack; John H.
Assistant Examiner: Fay; Regan J.
Claims
I claim:
1. A rotatable activating device having a complementary contoured
outer surface adapted to be placed in contacting relationship with
a contoured metallic work surface to be electroplated, said outer
surface comprising a layer of a porous, flexible, compressible,
non-conductive fluid-entrapping and circulating material having a
plurality of spaced hard non-conductive particles secured in fixed
relationship on at least the outer surface of such material; and an
inert anode material so disposed and arranged within said outer
surface of said rotatable activating device as to provide a
substantially uniform current density at the surface of at least
the central portion of said contoured work surface when said
rotatable device is in contact with said contoured work surface and
when said work surface is made cathodic with respect to said inert
anode.
2. A rotatable activating device as in claim 1 wherein said inert
anode material comprises an inner shell of lesser diameter at any
given point than that of said outer surface at the same point and
is spaced substantially equi-distant from said outer surface over
substantially the entire length of said rotative device.
3. A rotatable activating device as in claim 1 wherein said outer
surface is provided by a plurality of discs of such porous,
flexible, compressible, non-conductive fluid-entrapping and
circulating material mounted concentrically on a supporting shaft
with the outer peripheral portions of such discs in engagement one
with the other.
4. A rotatable activating device as in claim 3 wherein said inert
anode material is provided in the form of discs concentrically
mounted on said shaft between adjacent discs of said
fluid-entrapping and circulating material, said discs of anode
material having a lesser diameter than said discs of
fluid-entrapping and circulating material.
5. A rotatable activating device as in claim 1 wherein said inert
anode material is so disposed and arranged that when said work
surface is made cathodic with respect to said inert anode material,
the current density at the surface of the contoured workpiece has a
gradient at at least one end of said rotative device from said
uniform current density down to a current density which is less
than that which will produce a burnt electrodeposit on that surface
of such workpiece immediately adjacent and free from contact with
said end of said rotative device.
Description
RELATED APPLICATIONS:
This application represents a specific embodiment of the
porous-activating media disclosed and/or claimed in one or more of
my copending U.S. Applications Ser. No. 34,500 filed May 4, 1970,
now U.S. Pat. No. 3,619,384; Ser. No. 863,509, filed Oct. 3, 1969,
now U.S. Pat. No. 3,619,389; and Ser. No. 863,499, filed Oct. 3,
1969, now U.S. Pat. No. 3,619,401.
FIELD OF THE INVENTION
The present product, although resembling an abrasive product, is
specifically designed to provide essentially no stock removal in
use. This seemingly contradictory statement stems from a process
discovery as described and claimed in the aforementioned
application, Ser. No. 34,500 of Steve Eisner, filed May 4, 1970,
now U.S. Pat. No. 3,619,384. As related therein, the use of
products of the general type to which that of the present invention
belongs to lightly and repetitively contact a surface (an
electrodeposit surface in the cited application) results in an
activation of the surface making possible speeds of
electrodeposition far above those indicated as achievable by the
prior art. In particular, the present device relates to that
portion of the electrodeposition field wherein the surface to
receive the deposit may be other than flat and smooth and hence a
problem of obtaining uniform current density exists.
The present device is designed for use in a process in which the
current density is high compared with that of conventional
processes and in which the surface of the deposit is repetitively
contacted at extremely short time intervals by what is termed
herein as "dynamically hard" particles. By this term is meant that
the combination of the hardness of the particles, the contact
pressure of the particles on the surface of the electrodeposit and
the speed at which such particles are moving relative to the
electrodeposit surface is such as to produce an action on such
surface sufficient to mechanically "activate" the surface.
"Activating" the surface of the electrodeposit as the term is used
herein requires the generation of new surface defect sites through
mechanically distorting the crystal lattice of the metal deposited.
It is believed that the mechanism is rather complex and consists of
several actions taking place essentially simultaneously. First,
there is the new surface defect site generation resulting from
distortion of the crystal lattice structure as mentioned above.
This provides growth sites for many more asperities than would be
the case absent this mechanical distortion. Additionally, any
dominant asperities already formed are cut off or bent over and
crushed by the dynamically hard particle contact. These two actions
result in substantial elimination of the current robbing which
takes place at the asperities formed in normal plating and is
believed to be one of the major contributing factors to the ability
to maintain high current densities for substantial periods of time
while maintaining acceptable deposits with this process. Further,
the action of the activating medium is believed to result in the
removal or substantial diminution of the stagnant polarization
layer overlying the electrodeposit surface and to maintain a high
concentration of metal ions adjacent such surface due to the
pumping action of the activating medium which carries a supply of
fresh electrolyte across the electrodeposit surface at a high flow
rate.
The device utilized in this process consists of a surface
disturbing or activating medium having the characteristics of
providing a plurality of small, dynamically hard, relatively
inflexible, non-conductive particles held in substantially fixed,
spaced relationship to one another and generally vertical to the
surface receiving the deposit by a preferably porous, compressible,
fluid-entrapping and circulating matrix or supporting member.
Further, relative motion is provided during the deposition
operation between the surface receiving the deposit and the
activating medium. In addition, sufficient pressure is applied to
said activating medium in a direction normal to the electrodeposit
surface to cause mechanical distortion of the crystal lattice
structure of the metal deposited thereon. The spacing of the
particles and the speed of relative movement is such that the
deposited metal surface above any given point on the cathode
surface is contacted or influenced by a particle at extremely short
time intervals, e.g. intervals in the range of 6.1 .times.
10.sup.-.sup.2 to 3.8 .times. 10.sup.-.sup.7 seconds. Fresh
electrolyte is supplied to the zones of activated metal deposit at
a high rate through entrapment by the porous, fluid-entrapping and
circulating activating medium.
Where the surface to be plated (the cathode surface) is not flat
and smooth, i.e., has convex and concave contours, the problem
becomes complicated due to variations in current density resulting
from uneven distances from a fixed anode system. The device of the
present invention is directed primarily to this type of surface
plating. Another problem encountered is that seldom can one single
device be contoured to fit all of the contours of a complex
workpiece. This requires the use of multiple devices according to
the present invention in order to cover the entire surface of the
workpiece and imposes the additional problem of covering adjacent
areas with plate from different operations without leaving parting
lines or lines of demarcation between the plates laid down at
different times or by different devices.
DESCRIPTION OF THE PRIOR ART
Abrasive products have historically been so constructed as to
maximize the cut or abrading potential of the specific construction
concerned. In the present instance the opposite is true. Spaced
particles are essential, but they must be so positioned in the
product as to provide a minimum of abrasion in use. The closest
type of product to that described herein, we believe, has been the
brush or cloth used in so-called "brush-plating". This, however,
does not contain the spaced particles required in the present
structure.
SUMMARY
The device of the present invention is a rotatable formed wheel or
drum having an outer surface of a porous, compressible,
non-conductive hard particle-supporting media which is capable of
entrapping and circulating fluid with which it comes into contact.
The distance from the axis of the drum to the outermost portion of
such surface may be uniform throughout the drum length or it may
vary over such length. The device will be tailored for the
particular surface upon which it is to be used and will be formed
into a complementary profile of such surface.
Inwardly spaced from the outer surface is an inert, conductive
anode means. The anode means may underlie the entire outer surface
or it may underlie only a portion thereof. Further, the anode means
may be a unitary member or it may be made up of a plurality of
members, e.g. discs.
Electrical contact between the anode means and from the anode means
to ground is achieved through the shaft which extends along the
axis of rotation of the device.
DRAWINGS
FIG. 1 is a perspective view of one form of the device of the
present invention.
FIG. 2 is a sectional view of the device of FIG. 1 along the line
A--A.
FIG. 3 is a partial plan view of a modification of the device of
the present invention.
FIG. 4 is a sectional plan view of still another type of device
according to this invention.
FIG. 5 illustrates in a cross-sectional view the anode arrangement
for overlap plating.
FIG. 6 illustrates in cross section another form of the present
device.
FIG. 7 is a schematic view showing a device of the present
invention as applied to a complex contour surface.
FIG. 7-A shows another portion of the surface shown in FIG. 7 being
plated so as to overlap the portion plated in FIG. 7.
FIG. 8 illustrates the use of a device according to the present
invention using a flood of electrolyte instead of an immersed
system.
DESCRIPTION OF PREFERRED EMBODIMENTS
The device of the present invention provides for the controlled
application under pressure, both normal to and parallel with the
electrodeposit surface, of a supporting, preferably porous and
compressible, non-conductive, fluid-entrapping and circulating
matrix which supports on its surface in closely-spaced, fixed
relationship a plurality of small, relatively inflexible
non-conductive particles. These particles are so positioned in and
on the matrix as to contact the deposit forming on the cathode
(workpiece) surface. The cathode surface, itself, is normally
covered during conventional electroplating with a relatively
stagnant layer of electrolyte which may be identified as the
diffusion or polarization layer. The thickness of this layer, even
at high flow rates of electrolyte or turbulent agitation of a
plating bath, is at least 0.001 centimeters. Under application of
the supporting matrix and associated particles according to the
present invention, this polarization layer is repetitively removed
or its thickness substantially diminished repetitively throughout
the plating cycle. As described above, the electrodeposit surface
is activated by multiplying many times the number of nucleation
sites on such surface and generating a controlled growth of a
tremendous number of very short asperities which are repetitively
restricted in vertical growth throughout the deposition cycle. The
metal deposit reflects this action since photomicrographs of the
cross sections of such deposits illustrate a structure in which the
growth axis of the crystals appears substantially parallel to the
substrate rather than showing the normal columnar vertical
orientation of conventional electrodeposits.
This technique has been found to increase the limiting current
density many times beyond that possible with other methods,
resulting in much more rapid metal deposition than is possible with
such other methods and has further been found to produce a hard,
dense, smooth metal deposit. These results are achieved even
through there may be minor metal removal from the deposit on the
cathode surface, cutting down slightly the total thickness of such
deposit. This metal removal is minimized by control of the pressure
applied to the activating medium but in order to insure adequate
activation of the surface it is necessary to apply sufficient
pressure to produce a light scratch pattern in the metal deposit.
Thus the dynamic hardness of the particles may be substantially
greater than the actual hardness, e.g. a resin particle may produce
a scratch in a much harder nickel deposit. This scratch pattern may
be visible to the naked eye but, in any case, will be seen under a
magnification of 10,000 power or less. While the scratches may be
produced by metal removal, preferably the dynamic hardness is so
controlled that a displacement of metal atoms on the surface rather
than actual removal is the basis for the scratch formation.
By using small, relatively inflexible, non-conductive particles as
the activating tool, no spot on the deposit surface is covered for
any appreciable length of time by the activating particle. Further,
since the activating particles are fixed to the supporting matrix,
there is no danger of a particle being occluded as a
crack-initiating impurity in the electrodeposit. These particles
are generally randomly distributed over at least the external
surface of the matrix and are preferably spaced in fixed relation
to one another over very short spans, e.g. 1.25 .times.
10.sup.-.sup.1 inches to 5.65 .times. 20.sup.-.sup.4 inches. If
desired, accurate and non-random distribution of the particles on
the supporting matrix can be resorted to although this is generally
an unnecessary complication. By the term "particle" as is used
herein is meant not only completely separate and discrete
three-dimensional bodies, but also larger bodies with a plurality
of points, tips, projections or the like thereon as for instance a
relatively hard resinous coating on a fiber wherein the coating
contains multiple irregular spaced projections and is generally
uneven in nature. The particles, as described herein, contact or at
least influence essentially all of the surface of the
electrodeposit and are believed to knock down or cut off as they
form most of the dominant asperities on such surface. The particles
themselves may vary widely in size from 1 .times. 10.sup.-.sup.5
inches to 1.25 .times. 10.sup.-.sup.1 inches (average diameter) for
example, but should generally be in the size range of from 9
.times. 10.sup.-.sup.4 inches to 2 .times. 10.sup.-.sup.2 inches
for best results. The particles can generally be defined as hard,
i.e., having a Knoop hardness in excess of 10.0, but the degree of
hardness per se is not critical except that control should be
exercised not to use a product which is too abrasive for the
particular metal being deposited. The degree of pressure applied
must also be considered with respect to the hardness of the
particles and generally with the softer range of particles more
pressure normal to the cathode surface is required than with the
harder range of particles.
As indicated above, the controlling factor is the dynamic hardness
of the particles, i.e., the apparent hardness resulting from a
combination of the actual Knoop hardness, the pressure applied and
the speed with which the particles are moved across the
electrodeposit. A visible indication that the dynamic hardness is
sufficiently high is the presence in the deposit of the scratches
visible under 10,000X magnification.
The matrix used to support the activating particles is preferably
electrolyte-permeable, having a through porosity in the order of at
least 6.5 Sheffield units (as measured by a Sheffield porosimeter
using a 21/4 inch ring). Preferably, this matrix is also at least
somewhat compressible and deformable so that it can be conformed to
irregular surfaced cathodes and associated deposits where
necessary.
In the device of the present invention, the porous,
particle-supporting media described above is formed into a wheel or
drum. This may take several forms as is more fully described below,
but in each instance, at least the outer surface of the drum is
formed of this type of media. In some instances the outer surface
may be provided in the form of a sheath surrounding or superposed
over a central core. In other instances the outer surface may be
formed by discs of the porous media positioned around and extending
outwardly from the shaft upon which the device is rotated in
use.
Underlying the outer surface over at least a portion of the length
of the drum is an inert, conductive anode material. The distance
from the outer portion of this anode material to the outer surface
of the overlying porous, particle-supporting media is preferably
substantially the same at all points along the length of the drum
in those portions where the anode material is present.
The anode material used in the device of this invention is
preferably lead. This is easy to form, inert to most electrolytes
which are desirable for use and has the desired conductivity.
Preferably the electrolyte to be used with this device is of the
sulfate type. This causes a minimum problem with respect to
corrosion and fumes and is less toxic than most other systems. The
porous media may be of the non-woven variety, described in the
aforementioned copending applications, and may be needle-punched
for increased strength if desired. So long as the porosity and
resistance to the chemical action of the electrolyte is met, any
non-woven media may be used for the support. Woven materials may
also be used if desired and any of a variety of weaves, sateen,
leno, square, etc., can be utilized. The principle function of the
supporting media is to provide a cushioned or resilient support for
the hard particles with the secondary function of entrapping and
circulating or pumping fresh electrolyte into the plating zone. As
illustrated below, brush materials can be utilized with the hard
particles anchored on or in the bristles.
Referring now to the drawings, FIGS. 1 and 2 illustrate one type of
device embodying the present invention. A drum 10 having a concave
portion 11 is provided with an outer sheath of a non-conductive,
porous particle-supporting media 12 having a plurality of spaced
particles 13 affixed thereto. Internal of the outer sheath 12 is a
corresponding layer of inert anode material 14. The anode material
14 is supported from a centrally-disposed hollow hub member 15 by a
plurality of support members 16. Hub member 15 is adapted to slip
over and fasten rotatably to a drive shaft 17 which is connected to
the positive pole of a D.C. source as shown at 18. Keys 19 are used
to connect shaft 17 to hub 15 and electrical conductivity is
maintained from the shaft 17 through hub 15 and support members 16
to the anode layer 14.
FIG. 3 illustrates another type of device embodying the present
invention. Here a plurality of discs 20 of the porous
non-conductive particle-supporting media are provided affixed to a
rotatable shaft 21. Again, a plurality of spaced particles 22 are
affixed to at least the surfaces of the discs 20. Interleaved
between discs 20 on shaft 21 are a plurality of inert anode discs
23, likewise mounted for rotation on shaft 21. For purposes of
illustration, the discs 23 are shown as providing definite
demarcation areas between the outer ends of discs 20. In actual
construction, the discs 20 are usually sufficiently uneven and
compressibly resilient that the outer ends of discs 20 will form a
substantially unbroken surface and anode discs 23 will be
completely hidden. Again, shaft 21 is designed to be electrically
grounded and to in turn ground the anode discs 23.
FIG. 4 illustrates the use of bristles 40 having spaced hard
particles 41 affixed to the outer ends thereof. Here, as in FIG. 3,
a plurality of inert anode discs 42 are provided, mounted for
rotation on shaft 43 which acts also to electrically connect the
anode discs 42 to the positive pole of a D.C. source. Bristles 40
are shown as mounted at their inner ends in resin blocks 44 affixed
to shaft 43. As illustrated, the anode discs 42 and bristles 40
vary in length to provide a contour surface for the device. It will
be noted here, as in FIGS. 1-3, that the distance between the outer
surface of the particle-supporting media 40 and outer ends of the
anode discs 42 remains substantially the same over the entire
length of the device regardless of the variation in distance
between such outer surface and the shaft 43. As mentioned in
connection with FIG. 3, the particle-supporting media tends to hide
the presence of the anode discs and the characteristic is
illustrated in this drawing.
FIG. 5 illustrates an anode to outer surface configuration which is
used to minimize problems where overlapping plate is to be
deposited. As will be more clearly shown in FIGS. 7 and 7-A, it is
frequently necessary, in order to cover all the contours of a
multi-contoured article, to utilize two or more formed devices
according to the present invention. The best way to accomplish this
is to ensure that the edges of the deposit laid down beyond or
immediately adjacent the end of an activating device, such as those
illustrated herein, are not burnt. By keeping the current density
at the ends of the activator low enough to prevent any burnt
electrodeposit growth at such ends, a tapered plate is deposited
under the activator. When the next device overlaps to apply plate
to the next section of the workpiece, the plate goes down without
leaving any noticeable line of demarcation. This current density
gradient is obtained by spacing the anode from the ends of the
device as is illustrated in FIG. 5. Here, in contrast to the
alternate anode disc-porous media disc construction of FIG. 3, a
unit is shown with a single anode disc 50 mounted on shaft 51 which
again is connected to the positive pole of a D.C. source. Multiple
porous media discs 52 carrying spaced particles 53 are mounted on
each side of anode disc 50 as shown. The current density at the
outer ends 54 of the last discs 52 will be low enough to prevent
burning and to prevent overlap of the plate deposited.
FIG. 6 illustrates a cross section of another device somewhat
similar to that of FIG. 1 in that a sheath or covering 60 of porous
particle-supporting media is provided having a plurality of spaced
particles 61 thereon. In this instance, the anode 62 forms a shell
inside the cover 60 and is adapted to fasten at one end to a drive
shaft 63 by means of bushing 64. Shaft 63 is electrically connected
to the positive pole of a D.C. source.
FIGS. 7 and 7-A illustrate the application of a device of the
present invention to a complex shape and further illustrate the
overlap plating mentioned above. Here a plating bath 70 is provided
in a suitable tank 71. Mounted within the plating bath 70 is a
contoured workpiece 72 which is to be plated. As shown, this is
supported by members 73 and 74 in a fixed relationship to tank 71.
Workpiece 72 is electrically connected, as schematically shown at
75, to act as a cathode in the bath 70 and, in order to prevent
immersion plating, has previously been given a "strike" or thin,
conventionally-electrodeposited metal film. This use of a strike is
required when the contoured part is to be plated immersed as shown
in FIGS. 7 and 7-A. In FIG. 7, a formed wheel 76 mounted on drive
shaft 77 which is connected to the positive pole of a D.C. source
is shown. As in the previous illustrations, the outer surface of
wheel 76 is composed of a porous media supporting spaced particles
thereon. Wheel 76 contacts a portion of one end only of workpiece
72 as shown. The anodic center of wheel 76 is illustrated in dashed
lines at 78. As the wheel 76 rotates under the drive of shaft 77
from a suitable driving source such as an electric motor (not
shown) the surface of workpiece 72 in contact with wheel 76
receives an electrodeposit at a high rate of speed. Due to the
configuration of the anode 78, that portion of the workpiece 72
designated as "X" in the drawing will receive a plate which thins
out as the outer edge of the wheel is reached. In FIG. 7-A, the
same workpiece 72 is now being plated over an adjacent section by
wheel 80. Here the anode center 81 tapers slightly, as illustrated,
to keep a current density gradient going from a minimum at the
wheel end 82 to a maximum just beyond the portion "X" of workpiece
72. Wheel 80 is rotated by shaft 83 which is also mounted for
lateral oscillation as shown by the arrows. The plate which is now
deposited on portion "X" complements the plate deposited thereon in
the illustration of FIG. 7 and gives a uniform structure of equal
thickness to that elsewhere deposited under the activating wheels
76 and 80.
FIG. 8 illustrates another manner of using the devices of the
present invention in a plating operation. Here a formed wheel 90,
again consisting of the type of construction previously described,
is rotated by ground shaft 91 against a portion of the surface of a
cathodic workpiece 92. Here, however, workpiece 92 is not immersed
in a plating bath but the electrolyte 93 is supplied by high
pressure jets 94 and 95 directly into the interface between wheel
90 and workpiece 92. Excess electrolyte 93 is collected in the
bottom 96 of a suitable container 97 and recirculated as at 98 for
re-use. In this type of system, a preliminary "strike" on the
workpiece 92 is not required although it may be used if
desired.
Although, as indicated above, a variety of structures embodying the
present invention are available, the method of formation of the
devices of this invention is common to all up to a point. In all
instances it is desirable to first prepare a line drawing of the
contour surface to be plated. This can conveniently be done either
from a drawing of the part to be plated if one is available, or
directly from the part using a contour or profile gage. This is an
assemblage of flat plates, usually aluminum, and quite commonly of
about one-sixteenth inch thickness per plate. The plurality of
plates is slideably mounted on one or more rods so that the
vertical distance of any one plate can be altered with respect to
that of any other plate. Suitable clamping means are provided in
these conventional devices to hold the plates in any desired
relationship. The assembly of plates is applied to the contour to
be plated and the gage is adjusted so that the contour is defined
by the edges of the plates. The plates are then clamped in this
position and a line is drawn on a sheet of paper connecting each
edge of the plates thus giving a reproduction of the contour on the
paper. A second line parallel to this contour line is then drawn at
a short distance from the first line. This distance, which will be
the distance between the outside edge of the anode and the outside
surface of the porous particle-supporting media in the finished
drum, can be varied within quite wide limits, i.e., from about
one-sixteenth inch or less to as much 4 inch or more. Generally it
is desired to maintain this distance as short as possible in order
to minimize the IR drop between the anode and the contoured
workpiece cathode. The minimum distance is set by the distance at
which short circuiting becomes a problem and this will be
controlled somewhat by the type of porous surface media used in
terms of its compressibility and wearability. Also, the amount of
movement permitted by the work-mounting fixture and the drive
spindle of the device must be considered. The preferred distance
between the anode and the outer surface of the porous media ranges
from one-sixteenth to 1 inch although, as indicated above, greater
and lesser spacings are operable. Once these two lines are
established, they can be used to lay out the design for the drum or
wheel. A base line is drawn to represent the axis of rotation and
lines are drawn normal to such base line at each end of the portion
of the contour it is desired to reproduce in wheel form. This then
represents a plan view of one half of the wheel to be formed. If
spaced discs are to be used, the width of the discs and the anode
spacers is determined and then lines are drawn to represent these.
The distance from the base line to the nearest contour line is the
radius of the anodes while the distance to the farther of the
contour line from the base line is the radius of the porous media
discs. If a sheath-type wheel is to be made, the anode can be
formed using the contour drawing for measurement of proper
dimensions. For the disc-type structure, a center hole is provided
in each disc dependent upon the size of shaft upon which they are
to be mounted.
As a simple example of this type of device, a formed wheel was made
up of alternate lead anode discs and porous non-woven material
discs. The anode discs were one-sixteenth inch thick while the
porous non-woven was approximately one-fourth inch thick. A profile
was made of a contour consisting of the arc of a 11/2 inch circle.
The chord of the arc was 13/4 inch. Using a profile gage, this
contour was transferred to a sheet of paper and the measurements
from an arbitrarily drawn base line gave the following dimensions
for the porous discs (reading from left to right as the discs were
to be assembled:
Disc
1. 11/8 to 11/4 inch (11/4 inch)
2. 13/8 to 1-7/16 inch (1-7/16 inch)
3. 1 1/2 to 1-1/2 inch (1 1/2 inch)
4. 1 1/2 to 1-7/16 inch (1-7/16 inch)
5. 13/8 to 11/4 inch (1 1/4 inch)
Rather than to exactly match the contour, the longer radius was
used in each instance as indicated in the parenthesis. The anode
discs which go between each of the porous discs were then measured
from the diagram with "A" being the anode disc between discs 1 and
2 above, etc.:
Anode Disc
A -- 1-1/16-11/8 inch (11/8 inch)
B -- 1 -3/16-11/4 inch (11/41 inch)
C -- 11/4 - 11/4 inch (11/4 inch)
D -- 1-3/16 inch- 11/8 inch (11/8 inch)
Again, the longer radius for each disc was used as indicated in the
parenthesis. Two additional lead discs, treated with stop-off
lacquer (conventional plating technique) of 1 inch radius were used
outside discs 1 and 5. The discs were then assembled on a 1/4 inch
diameter steel shaft having threaded ends and a nut was threaded up
against each outside lead disc to hold the assembly in position.
The make-up of the wheel, using the numerical designations above
was:
1 inch lead disc-1-A-2-B-3-C-4-D-5-1 inch lead disc
The formed wheel was then mounted in a drill chuck affixed to an
electric motor and rotated at a speed of 250-300 RPM. The contour
part was immersed in a room temperature, brightener-free zinc
pyrophosphate plating bath and connected to a source of negative
potential. The wheel was then rotated against the contour surface
for one minute and plate was deposited at a current density of
1,200 amps/ft..sup.2. A uniform bright zinc plate plate was
deposited in the area under the wheel. In the adjacent areas of the
contour outside that covered by the wheel, the deposit was dull and
burnt.
For many types of decorative plate, the exacting procedure outlined
above is not required. It will usually be used in forming a wheel
or drum using a cover sheath over a shaped anode but may often be
dispensed with in the case of the ganged disc construction. For
example, using the same contoured workpiece described above, a
porous wheel was made up using the same non-woven,
particle-supporting media as was used in the above example. Here
the discs were all 4 inches in diameter and were roughly trimmed on
the outside surface of the desired curvature. Five non-woven discs,
each about one-fourth inch thick were assembled on a 1/4 inch
diameter steel shaft alternating with 1/16 inch thick lead washers.
In this instance, no attempt was made to match the contour of the
washers with the outer surface contour and all six of the lead
discs were 23/4 inch in diameter. The outer lead discs were again
treated with stop-off lacquer. Used in the same manner as the
previously-formed assembly, an acceptable plate from the standpoint
of appearance was produced on the curved work surface.
A further example showing the overlap capability of this type of
device was run utilizing a flat, highly polished sheet of copper as
the substrate to be plated. This type of surface was used since an
overlap line could more readily be seen on such surface than on a
contoured surface.
Here the wheel was made up of two sections of porous non-woven,
each 11/4 inch thick and 4 inch in diameter. The anode was a single
one-sixteenth inch thick disc, 23/4 inch in diameter, positioned on
a 1/4 inch shaft between the two porous disc sections. Mounted as
above and rotated at 250-300 RPM on the substrate immersed in the
pyrophosphate zinc bath, plate was deposited at 80 amps/ft..sup.2
for 1 minute. The area under the wheel was a bright zinc plate
which visibly tapered in thickness towards the ends of the wheel.
The wheel was then moved so that it overlapped by one-half inch the
first plated section and the run repeated. The resulting deposit
showed no overlap lines. The same experiment was repeated with a
Watts nickel bath and under the same conditions as above, no
overlap line was detectable. In all instances described above, the
porous non-woven was of the type illustrated in U.S. Pat. No.
3,020,139 to J. C. Mueller and the spaced non-conductive particles
bonded thereon were flint grains of about 220 grit size.
As illustrated immediately above, it is necessary where the
rotative device of the present invention covers only a portion of
the contoured surface to be plated to provide a variation in
current density over the surface under the device. Where the single
device covers the entire surface to be plated, this necessity does
not exist and the current density is preferably maintained
substantially uniform over the entire surface, i.e., the anode will
conform to the contour in the outer surface of the rotative device
and will be maintained at substantially equal distances from such
outer surface over the entire length of the rotative device. Where
a second device is to be used to apply additional plate adjacent to
an area covered by a first device, it is then necessary to so
dispose the interior anode within each device as to provide a
current density gradient at the ends of the rotative device, or at
least at the end of each where the overlap is to occur. This is
generally done by increasing the distance from the anode to the
workpiece at such ends. Preferably the distance is such that the
porous particle-carrying media covers all of the plate deposited
with such plate tapering down from the relatively uniform thickness
common to the central portion of the area covered by the device to
zero thickness at the ends of the device. This is not always
practical and the controlling factor is that any plate which does
extend beyond the edge of the rotative device must be unburnt. If
this criteria is met, the plate will inherently taper and will
provide a smooth juncture with such plate laid down by the adjacent
rotative device as to minimize any apparent parting or demarcation
line between the adjacent plating zones. Determination of the
arrangement of the internal anode to accomplish this is essentially
empirical since a wide variety of variables enter into the plate
deposition. As a guide to accomplish this arrangement, a
conventional Hull cell may be used. This is filled with the porous
particle-supporting media to be used and with the plating solution
to be used. The cell is run at the current density to be used in
the actual plating and the run is continued for the time period
which will be employed for the obtaining of the desired thickness
of deposit. The distance along the line perpendicular to the anode
from the anode to the edge of the burnt area of deposit on the cell
plate gives an approximation of the correct distance of the edge of
the anode in the rotative device from the end of the rotative
device. This is a guide only, and the correct distance will be
found empirically as stated above for each particular device.
Oscillation of the rotative device may be employed in some
instances to help brake up any sharp line of demarcation between
adjacent plate areas.
* * * * *