Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROPLATING SYSTEM AND METHOD
CLAIM OF PRIORITY
[0001] This application claims the benefit of U.S. provisional application
60/551,087, filed
on March 8, 2004.
FIELD OF THE INVENTION
[0002] The present invention relates to a system for plating a metallic
composition onto a
substrate and more particularly relates to a system for bulk electroplating a
composition onto the
interior surface of a cylindrical or semi-cylindrical object.
BACKGROUND OF THE INVENTION
[0003] Plating of metallic compositions on to obj ects has been used to
achieve both
functional and decorative enhancements for the plated obj ect. In addition,
plating has been used
to improve the wear resistance of the object.
[0004] One particularly useful technique for plating is electroplating.
Electroplating is well
known in the art and involves the deposition of a metallic layer onto a
conductive obj ect by
placing the object into an electrolytic bath. The bath contains a solution of
the metal to be plated
i.e. an electroplating solution. A DC current is passed through the solution
to cause the metal
ions to deposit on the conductive object. The process may also be run in
reverse to cause
deplating or removal of a metallic layer. Both deposition and removal are
encompassed in
electroplating.
[0005] Electroplating has several advantages including being relatively
inexpensive and
relatively fast compared to other techniques. Two disadvantages, however,
complicate the use of
electroplating in applying wear resistance metallic compositions.
[0006] First, electroplating tends to be indiscriminate, meaning that any
conductive surface
that is exposed to the plating solution and electrical current will be coated.
Sometimes called
bleed over, this indiscriminate coating may lead to imperfections in the size
or shape of the
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coated object. . Normally such imperfections are small, but in the area of
precision parts (e.g.
gears, cogs, etc.) where tolerances are tight, even small imperfections may
lead to significant
problems.
[0007] Second, electroplating tends to deposit the metallic composition in an
uneven manner,
particularly near the edge of the obj ect being plated. So called edge effects
typically result in the
metallic composition being applied to a thickness that is 50% or more than
desired. Again
because of tight tolerances, even small edge effects may have a significant
impact on the overall
quality of the coated obj ect.
[0008] In addition to these disadvantages, commercial pressure continually
require that
production costs be minimized, production qumtities be increased, all the
while manufacturing
high quality coated objects.
[0009] The present invention overcomes one or more of these problems.
SUMMARY OF THE INVENTION
[0010] The present invention includes a method of electroplating an object,
where the objects
are stacked in at least one sleeve and the objects have an interior surface,
that upon stacking,
form a stack conduit. The sleeves are then racked to provide fluid
communication between a
plating solution reservoir and the stack conduit. Plating of the inner
surfaces of the objects
occurs by flowing an electroplating solution from the reservoir through the
stack conduit in the
presence of a current. The present invention also includes systems for
carrying out the above
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the drawings:
[0012] Fig. 1 illustrates, in perspective, an object that may be plated using
the systems and
methods of the present invention.
[0013] Fig. 2 illustrates, in horizontal cross-section, a sleeve that holds
objects during the
electroplating process as shown at section line 2--2 on Fig.4.
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[0014] Fig. 3 illustrates, in cross-section, a sleeve cut through a spacer as
shown at section
line 3--3 on Fig. 4 in the context of an electroplating solution tank..
[0015] Fig. 4 illustrates, in perspective, a rack system that holds up to four
sleeves of objects
during the electroplating process.
[0016] Fig. 5 illustrates, in top view the rack of Fig. 4.
DETAILED DESCRIPTION
[0017] The present invention includes methods and systems for bulk
electroplating objects
comprising at least one sleeve for a stack of objects and a rack to hold the
objects during the
plating process. Bulk electroplating includes the plating of at least about 20
objects
simultaneously or in a single lot. In other embodiments, the number of obj
ects simultaneously
plated is at least about 100, at least about 250, at least about 500, at least
about 750, at least about
1000, at least about 1500, at least about 2000 or more. Bulk electroplating
may be accomplished
by subdividing the objects into sub-lots of any convenient size, preferably
between about 20 and
about 50 objects per sub-lot, such that the objects in sub-lots total the
overall number of object
simultaneously plated. A sub-lot may be conveniently held within the sleeve.
[0018] Bulk electroplating also refers to plating a given number of objects in
a given time
period. For example, bulk electroplating may refer to plating at least about
5000 objects in a day
or in a shift. In other embodiments, the number of objects plated in a day or
a shift is at least
about 10,000, at least about 15,000, at least about 20,000, at least about
25,000, at least about
30,000, at least about 35,000, at least about 40,000, at least about 45,000,
at least about 50,000 or
more.
[0019] Any electrically conductive object may be plated with the systems and
methods
discussed herein. Preferably, the object comprises an interior surface that is
suitable for plating.
The interior surface is preferably cylindrical to create a through hole in the
obj ect, although the
object may include flat surfaces or arcuate surfaces other than cylindrical.
The area of the
interior surface is not critical but in one preferred embodiment, its axea is
about 1 in2.
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[0020] The size and shape of the object is not critical, but should be
relatively consistent,
such that when the objects are stacked one on top of another in the sleeve,
the through holes
align. Although the through holes in the obj ects are preferably centrally
located, this is not
necessarily the case. Of course, the size of sleeve may also cooperate with
the objects to help
insure alignment. The aligned through holes create a conduit through the
stacked objects.
[0021] Preferably, the objects comprise mating surfaces on their top and
bottom, such that
the junction of two objects does not substantially interrupt the conduit
through the stacked
objects. Preferably, the mating surfaces are substantially flat, although
notches, grooves or other
devices may be used to insure that the alignment of the stacked objects. Also,
the top surface of
one object and the bottom surface of another object may nest together to help
maintain a
substantially uninterrupted conduit. In addition, although not preferred,
spacers may be
interspersed between stacked objects to help maintain the continuity of the
conduit created by the
stacked objects. In this case, the spacers may be conductive or insulating.
[0022] One preferred class of suitable objects to be plated is gears 10 that
comprise a
cylindrical interior surface 12, as seen in Fig. 1. More preferably, the
interior surface is a bearing
surface. The gears also comprise a top mating surface 14 and a bottom mating
surface 16, where
the gears would touch when stacked. The mating surface surfaces help insure
that, when stacked,
the obj ects provide a relatively smooth interior surface over the entire
length of the sleeve, thus
helping to eliminate bleed through and edge effects. Alternatively, two or
more objects may be
combined to form an interior surface (e.g. halfbearings).
[0023] As suggested above, the sleeve holds the objects to be plated in
alignment when the
objects are stacked in the sleeve such that the interior surfaces of the
objects form a conduit
through the stacked obj ects. The sleeve may be made of any material;
preferably one that
exhibits stability during long term exposure to plating solution, e.g.
chemically inert. The sleeve
material should also be electrically inert.
[0024] As seen in Figs. 2-4, each sleeve 18 comprises a relative top 20 and
bottom 22. At or
near the bottom 22 is a sleeve inlet 24. At or near the top 20 is a sleeve
outlet 26. Objects 10
may be stacked within the sleeve. Electroplating solution is introduced to the
conduit of the
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stacked obj ects at the inlet 24 and exits the conduit at the outlet 26. Flow
of electroplating
solution is shown in Fig. 4 by arrows.
[0025] A cathode 28 and an anode 30 are associated with each sleeve. Both the
cathode and
the anode are located in the interior of the sleeve. Preferably the cathode is
located parallel to the
major axis of the sleeve and adjacent to the sleeve. The cathode may touch the
sleeve and may
be permanently affixed to the sleeve or may be unattached to the sleeve. The
anode is preferably
co-linear with the major axis of the sleeve. Alternatively, the anode is
centrally located in the
though holes of the stacked object; especially where the through holes of the
stacked objects are
not centrally located within the objects. Preferably the cathode and the anode
are parallel to one
another.
[0026] Preferably, the cathode touches each of the objects in the stack, while
the anode
resides within the conduit created by the stacked objects. Preferably, the
anode does not touch
the obj ects.
[0027] The anode and cathode may be made of any suitable material but
preferably are non-
eroding. Non-eroding (e.g. steel) anodes have several advantages over eroding
anodes. In
particular, with a non-eroding anode, anode eroding compositions may be
eliminated, which in
turn eliminates deposits of carbonate salts and the associated uneven plated
surface. Also, a non-
eroding anode provides a more consistent plated surface because the thickness
of plating can be
controlled more precisely. In particular, as the anode erodes, the amount of
metal ions in
solution fluctuates because of uneven erosion. Also, anode replacement is an
expense that can be
eliminated.
[0028] The orientation and spacing of the cathode and anode may be insured
through the use
of an inlet spacer 32 and/or an outlet spacer 34. The inlet spacer may be
permanently affixed to
the sleeve or merely held within the sleeve, with the later being preferred.
The outlet spacer is
typically not permanently attached to the sleeve. The spacers rnay include one
or more locating
holes adapted to receive the cathode and/or anode therein. A cathode locating
hole may be
positioned near or on the periphery of the spacer so that the cathode is near
or adjacent to the
sleeve. The cathode locating hole may or may not be a through hole, but
preferably is. An anode
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locating hole is preferably positioned at the center of the spacer so that its
axis is co-linear with
the major axis of the sleeve. Alternatively, the anode locating hole is
positioned to locate the
anode in any preferred location within the stacked conduit. Preferably, the
anode locating hole is
a through hole in the inlet spacer that aligns with the sleeve inlet. The
spacers help to maintain a
set distance between the cathode and the anode and help prevent arcing and
preferably made of
an insulating material.
[0029] The anode may also comprise one or more centering devices. In one
embodiment, the
anode comprises an arrow head 36 or other device that is adapted to center the
received anode in
the anode locating hole of the inlet or outlet spacer. In another embodiment,
the anode comprises
a cross 3~ or other device that positions the anode along the major axis of
the sleeve. Such a
cross is typically located at or near the sleeve outlet and cooperates with
the sleeve or spacer to
align the anode, while only partially or minimally interfering with the
plating solution as it exits
the sleeve. The arrow heads and crosses may be used in combination.
[0030] The anode may also comprise an insulating sheath located near the top
(and/or
bottom) of the sleeve. The insulating sheath helps to prevent bleed through by
preventing the top
of the last object in the stack from being exposed to plating solution and
current.
[0031] The sleeve may also contain one or more guide rods 40 attached to the
interior of the
sleeve. The guide rods may be positioned within the sleeve such that the
objects are temporarily
held in place when stacked in sleeve. For example, when the object is a gear,
the guide rod may
be sized to substantially fill the space between two teeth on the gear. By
using two or more guide
rods, the object may be accurately held in position in the sleeve during the
plating process. In
one preferred embodiment, the cathode acts as a guide rod. The inlet and
outlet spacers may also
include holes for the guide rods. The guide rods are preferably electrically
inert, either because
of their composition or because they are not connected to an electrical
source.
[0032] With regard to Fig. 3, the rack 42 holds at least one sleeve 18 of
objects. Preferably,
the rack is adapted to hold at least 2, at least 4, at least g, at least 12,
at least 16 or more sleeves
of obj ects.
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[0033] As seen in Fig. 4, the rack includes at least ona manifold 50 having an
inlet 44 to
receive electroplating solution provided by a pump 46 from a reservoir. For
each sleeve, the
manifold also comprises an outlet 48. The outlet is designed to be fluidly
connected to the sleeve
at the sleeve inlet. In one embodiment, the reservoir is an open topped tank;
in another
embodiment, the reservoir is a closed top vessel. In a preferred embodiment,
the rack with
sleeves is place in the open topped taut during the electroplating process.
[0034] In addition, the rack comprises an anode bar 52 and a cathode bar 54.
Each of the
anode and cathode bar comprises a connection point 56 foDr an anode and a
cathode associated
with each sleeve. Preferably, the connection points are adapted for the quick
connection of the
anode or cathode to the respective bar. For example, clips or clamps may be
used. As seen in
Fig. 2a, wing-nut clamps are preferred to connect the anodes and cathodes to
their respective
bars. Each of the anode and cathode bars comprises a master connection point
58, where the bars
may be connected to an electrical source (e.g. one or more rectifiers).
[0035] In one embodiment, the combination of the rack outlet and the
anode/cathode
connection points help hold the sleeves to the rack. This combination is
particularly useful
where the cathode is affixed to the sleeve. Alternately, an additional
attachment device may be
used to secure each sleeve or a group of sleeves to the racy. In one suitable
embodiment, the
rack outlets and anode/cathode connection points are located such that during
electroplating, the
sleeves are held in an upright position and the anode/cathode bars are in a
horizontal position,
although this is not necessarily the case.
[0036] Any metallic composition (e.g. metal, alloy or metal containing
composition) may be
plated on to an object according to the present invention. for example, bronze
and nickel are the
preferred metallic compositions that may be plated with the present invention.
[0037] The plated objects that result from the use of the present system and
method may
advantageously have a highly consistent thickness of plated material. For
example, the thickness
preferably varies by less than about X20% over the plated surface. More
preferably, the thickness
varies by less than about X10% over the plated surface, while most preferably
the thickness
varies by less than about ~5% over the plated surface. In one embodiment, the
thickness of the
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plated material is less than about 0.0100 inches, less than about 0.0050
inches, less than about
0.0025 inches, less than about 0.0015 inches, less than about 0.001 inches,
and less than about
0.0005 inches. In a preferred embodiment, the thickness is about 0.0008
inches, where the
thickness may range by X0.00005 inches.
[0038] The high consistency in the thickness of the plated material results in
the elimination
of post-processing finishing steps. Known plating methods require a post-
processing step such
as a grinding, honing or reaming step to achieve thick~less uniformity. Such a
post-processing
step also requires that the surface be inspected after processing to insure
that the processing did
not otherwise spoil the surface. Thus, both the post-processing and inspection
steps can be
eliminated by using the method and system of the present invention, although
these steps may be
used if desired.
[0039] Because of the alignment of the stacked objects in the sleeve to create
a substantially
uninterrupted conduit, the interior surface of the object is the only portion
of the object that is
plated. That is, the object is substantially free of plating except on its
interior surface.
[0040] The plating process according the present invention is described below.
Although
specifically described with respect to the preferred embodiment of plating of
bearing surfaces of
gears, it should be understood that the method is more generally applicable.
[0041] The method has several steps including stacking the gears in the
sleeves, racking the
sleeves and plating the bearing surfaces of the gears. Stacking the gears
involves placing the
gears in the sleeve in such a manner as provide the best possible alignment
with the least amount
of effort. An inlet spacer is placed in the sleeve and aligned because of the
cathode and
preferably at least one guide rod. Next, the gears are placed in the sleeve.
Again the cathode and
the guide rod help insure that the proper alignment is achieved, such that the
interior surfaces
(e.g. the bearing surfaces) of the stacked gears form a substantially
uninterrupted conduit. An
outlet spacer is used to top off the stack of gears. Attachment of the cathode
and guide rod to the
sleeve eases the placement of spacers and gears, but is not required. After
the sleeve is filled
with spacers and gears, the anode is inserted into the conduit formed by the
stack of gears. The
arrowhead on the anode is lodged in the inlet spacer, insuring that that end
of the anode in
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centrally located in the conduit. The cross helps insure that the other end of
the anode is
centrally located within the conduit. Together, the centering devices help to
properly align the
anode with respect to the gear stack and cathode. Although described in a
particular sequence,
these steps may be performed in other sequences without departing from the
invention.
[0042] Next, racking of the stacked gears involves fluidly connecting the
inlet of each sleeve
to the manifold outlet. The sleeve is set in place on the rack outlet and may
be held in place by
gravity or otherwise clamped to the manifold or the rack. Next, the cathode
and anode are
connected to their respective bars at the connection points, fuxther securing
the sleeve to the rack.
[0043] Plating the bearing surfaces involves placing the rack into a tank of
plating solution.
The level of plating solution in the tank should not be so high as to flow
into the sleeve outlets.
The rack inlet is fluidly connected to a pump that will circulate plating
solution from the tank
through the rack passages to the sleeve inlet. The plating solution travels
through the stack
conduit and out of the sleeve outlet and back into the tank, where the
circulation begins again.
The cathode and anode are electrically connected to a rectifier that provides
the electricity needed
to plate the gears. An anode insulating sheath is used to minimize plating of
the top or bottom
gear.
[0044] Several aspects of the plating step may be manipulated to influence the
resultant plate
on the bearing surface of the gears. Initially, the use of flowing plating
solution helps create a
consistent plate thickness because the relative concentration of electrolytes
in solution is stable
because the solution is continually being refreshed.
[0045] In addition, the flow rate of the solution through the stacked conduit
may help
determine the consistency of the thickness of the plate by preventing defects.
The pumping of
electroplating solution also prevents/removes bubbles from the bearing surface
of the gears.
Bubbles, if allowed to remain, cause defects in the plated layer.
[0046] While any flow rate may be used, preferred flow rates from the pump to
the sleeve
intake range up to about 200 gal/min at the sleeve intake, and more preferably
the flow rate is up
to about 1~5 gal/min. Preferred flow rates from the pump to the sleeve outlet
range up to about
150 gal/min, an more preferably up to about 140 gal/min.
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[0047] Higher flow rates also decrease the plating time because higher current
densities may
be use without attendant deposition of soot. Higher rates of metal deposition
are associated with
higher current densities.
[0048] With the present process, a wide range of current densities may be
used. The current
density, i.e. the amount of electricity supplied through the anode and
cathode, also influences the
consistency of the plate thickness. Although any current density may be
suitable, densities
between about 0.20 amps/in2 and about 0.70 amps/in2 are preferred. More
preferably, the current
density ranges between about 0.30 amps/in2 and about 0.55 amps/in2. Another
method of
quantifying the current density is in the amount of current applied to each
rack. Preferably
between about 100 amps and about 300 amps are applied to the rack having 16
sleeves with
between 25 and 35 objects per sleeve. More preferably between about 150 amps
and about 250
amps are applied to a rack having 16 sleeves with about 29 objects per sleeve.
[0049] Because the thickness of the plating layer and the speed of plating
rnay be minutely
controlled through selection of flow rate and current densities, grain
refiners may be eliminated,
thus producing a cost savings.
[0050] It will be further appreciated that functions or structures of a
plurality of components
or steps may be combined into a single component or step, or the functions or
structures of one-
step or component may be split among plural steps or components. The present
invention
contemplates all of these combinations. Unless stated otherwise, dimensions
and geometries of
the various structures depicted herein are not intended to be restrictive of
the invention, and other
dimensions or geometries are possible. Plural structural components or steps
can be provided by
a single integrated structure or step. Alternatively, a single integrated
structure or step might be
divided into separate plural components or steps. In addition, while a feature
of the present
invention may have been described in the context of only one of the
illustrated embodiments,
such feature may be combined with one or more other features of other
embodiments, for any
given application. It will also be appreciated from the above that the
fabrication of the unique
structures herein and the operation thereof also constitute methods in
accordance with the present
invention.
to
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[0051] The explanations and illustrations presented herein are intended to
acquaint others
skilled in the art with the invention, its principles, and its practical
application. Those skilled in
the art may adapt and apply the invention in its numerous forms, as may be
best suited to the
requirements of a particular use. Accordingly, the specific embodiments of the
present invention
as set forth are not intended as being exhaustive or limiting of the
invention. The scope of the
invention should, therefore, be determined not with reference to the above
description, but should
instead be determined with reference to the appended claims, along with the
full scope of
equivalents to which such claims are entitled. The disclosures of all articles
and references,
including patent applications and publications, are incorporated by reference
for all purposes.
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