Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED DIRECT CURRENT CHROME
PLATING PROCESS AND VARIANT LAYERED
CHROME PRODUCT
CROSS-REFERENCE TO RELATED U.S. APPLICATION
[1] This application claims the benefit under 35 U.S.C.
119(e) of the earlier filing date of U.S. Provisional
Application Serial Number 60/817,662 filed on June 27,
2006, which is hereby incorporated by reference.
FIELD OF THE INVENTION
[2] The present invention relates generally to chrome plated
products and more particularly to chrome plated piston
assemblies of hydraulic cylinders.
BACKGROUND OF THE INVENTION
[3] Chrome plated products are widely used in fluid power
applications, such as hydraulic cylinders, because of
their durable characteristics. A chrome-plated product has
superior corrosion resistance, increased wear resistance,
and a low coefficient of friction. For example, the piston
assembly of a hydraulic cylinder typically includes a
chrome plated steel bar. The steel bar provides the
strength and support necessary for hydraulically moving
heavy loads.
[4] Frequently, these cylinders are used in bulldozers, dump
trucks and backhoes at construction sites, or on forklifts
in factories. In these environments, the cylinders are
subjected to severe environments or conditions that would
normally cause the steel bar to corrode and prematurely
wear over a short period of time. However, by plating the
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steel bar with chrome, the bar is protected against the
environment, and its service life is extended until a
point when the chrome plating is worn or damaged. Further,
the chrome plating reduces the friction of the steel
surface, and this surface reduces wear on the hydraulic
seals in the cylinder, thus extending their service life
as well.
[5] Known arrangements for producing chrome-plated products,
as typically used in the fluid power industry, involve
electrochemical plating. The plating process is powered
with direct current electricity because it provides
constant power, unlike alternating current electricity.
The plating process is performed through a series of
polishing, cleaning, plating, and post-plating operations.
The result is a chrome-plated product having a single
chrome layer, as shown in Figure 1.
[6] A single-layered chrome product produced using the direct
current chrome plating process is normally characterized
by micro cracks on the order of 1,400 micro cracks per
linear inch. Hardness of the chrome plating is on the
order of 65 - 72 Rc (as measured using the Rockwell `C'
hardness test). The appearance of direct current single
layered chrome surface is bright and shiny with a mirror-
like reflective appearance. A typical chrome thickness
layer is 0.001".
[7] Failure modes for chrome-plated products used in the fluid
power industry include wear and premature corrosion of the
steel substrate. The service life and, in conjunction
therewith, the operating costs of the chrome plated
product is a function of how well the product is capable
of resisting corrosion. A standardized, accelerated test
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involving a highly corrosive environment of salt spray,
humidity and increased temperatures is used to measure the
corrosion resistance of the chrome-plated product. One
standardized test is the ASTM B117 Salt Spray Test which
is typically specified for chrome-plated bars. The test
involves a 5 percent salt spray solution with testing
parameters set at 100 percent relative humidity and 35
degrees Celsius to incidence the occurrence of corrosion
of the chrome-plated sample. The testing criteria
determine the number of hours it takes for corrosion to
occur, with longer time, measured in hours, indicating
that the sample is more resistant to corrosion.
[8] It has been found that during a test of the type just
outlined, a single layered chrome-plated product can
typically maintain 200 - 300 hours before it fails by
break down of the chrome layer and the steel substrate
objectionably corrodes. It is noted that greater
corrosion resistance would not only be desirable in many
industries, but even essential in view of customer
expectations and demands.
[9] To elaborate on this further, products manufactured using
the direct current plating process have been the industry
standard in the fluid power industry for many years.
Through improvements in quality and process controls, the
products have proven reliable and durable in most
applications. However, despite these improvements, the 4
chrome plating on the product has still been found to wear
appreciably during use and is also subject to corrosive
environments involving rain, wet operating conditions,
harsh chemicals, heat, and salt spray, particularly in sea
or roadway locations. In this environment, the product
begins to corrode and eventually the corrosion is severe
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enough, or the product fails completely, and it must be
replaced.
[10] This replacement process may involve the equipment, such
as the bulldozer or dump truck, being out of operation for
hours or even days, as a replacement part is assembled and
installed into the equipment. At the same time, the
assembly seals may also be replaced because of wear
accelerated by the corroded surface of the chrome-plated
part. To the end user of this equipment, then, the
downtime and expense of repairing and replacing the
corroded parts, can be significant and can occur many
times during the expected operating life of the equipment.
As a result, the fluid power industry, as well as other
industries, have a demonstrable interest in chrome-plated
products that have increased corrosion resistance. Such
products would reduce the costs of operation by increasing
the duration of use before being replaced or repaired due
to corrosion.
[11] Accordingly, a compelling need has been recognized in
connection with providing chrome-plated products, and
methods and arrangements for forming same, that ensure
greater durability and corrosion resistance than has
hitherto been the norm.
S'[JNIlKARY OF THE INVENTION
[12] In accordance with at least one embodiment of the present
invention, an improved direct current chrome plating
process will result in increased corrosion resistance as
compared to a conventional processes such as those just
described.
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[13] A process in accordance with at least one embodiment of
the present invention can use the same type of processing
equipment as conventional direct current chrome plating
processes. However, an improved process as broadly
contemplated herein can preferably include an additional
processing step involving the application of a distinct
chemical solution. This additional step, consequently,
will lead to a chrome plated product having variant layers
of chrome plating rather than the single layer as produced
conventionally.
[14] In summary, there is broadly contemplated herein, in
accordance with at least one presently preferred
embodiment of the present invention, a method of chrome-
plating a substrate, the method comprising the steps of:
providing a substrate; applying a first chrome layer onto
the substrate, the first chrome layer being crack-free;
applying a second chrome layer onto the first chrome
layer, the second chrome layer comprising micro cracks;
the step of applying a first chrome layer comprising
applying a first chrome plating solution which comprises
catalyst in a concentration of between about 0 percent and
about 20 percent vs. active ingredients.
[15] The novel features which are considered characteristic of
the present invention are set forth herebelow. The
invention itself, however, both as to its construction and
its method of operation, together with additional objects
and advantages thereof, will be best understood from the
following description of the specific embodiments when
read and understood in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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[16] For the present invention to be clearly understood and
readily practiced, the present invention will be described
in conjunction with the following figures, wherein like
reference characters designate the same or similar
elements, which figures are incorporated into and
constitute a part of the specification
[17] Fig. 1 provides a photographic cross-sectional view of a
conventional chrome plated product having a single layer.
[18] Fig. 2 provides a photographic cross-sectional view of a
chrome plated product, in accordance with an embodiment of
the present invention, having two chrome layers.
[19] Fig. 3 is a schematic illustration of a conventional
direct current single layered chrome plating process.
[20] Fig. 4 is a schematic illustration of a process, in
accordance with an embodiment of the present invention,
that can be used to manufacture variant layered chrome
plated bar products.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[21] It is to be understood that the figures and descriptions
of the present invention have been simplified to
illustrate elements that are relevant for a clear
understanding of the invention, while eliminating, for
purposes of clarity, other elements that may be well
known. The detailed description will be provided
herebelow with reference to the attached drawings.
[22] Building on the previous background discussion, Fig. 3
provides a schematic illustration of a conventional direct
current single layered chrome plating process. For the
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purposes of illustration, this process will be described
in connection with applications for plating steel bars;
however, it should be understood that an analogous process
which makes use of essentially the same method steps can
be employed in other contexts.
[23] As is known, a bar is first ground (P1) to a specified
surface roughness, typically a Ra value of 2.0 - 10.0
micro-inches and a Rz value of 12 - 30 micro-inches. The
next series of operations, P2, P3 and P4 are completed in
tanks containing liquid solutions.
[24] Accordingly, after grinding, the bar, or typically a batch
of bars, are placed onto a fixture so that they can be
submerged and suspended into a tank containing an etching
solution (P2). The etching operation applies a reverse
direct current to the bar through the electrically
conductive fixture, at the parameters shown in Tables 3,
4, and 5. (These and other tables are provided in the
Appendix found at the close of the present disclosure).
After etch (P2), the fixtured bars are transferred and
submerged into the tank containing the chrome plating
solution (P3).
[25] An illustrative make-up of a chrome plating solution, as
may be used in a conventional process as outlined in Fig.
3, is set forth in Table 1. A continuous direct current
is applied to the bar based on the parameters that are
listed in Tables 3, 4 and 5. The thickness of the single
layered chrome will vary depending on customer
specifications. Based on Table 6, regarding plating
thickness application rates, a typical thickness of .001"
is achieved in 33 minutes. When the desired single layer
plating thickness is achieved, the bar moves through the
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rinsing process (P4), and then is post-polished (P5) to
improve the surface smoothness and finish of the bar.
[26] An improved direct current chrome plating process, in
accordance with at least one embodiment of the present
invention, will provide increased corrosion resistance as
compared to a conventional process such as that shown in
Fig. 3. A process in accordance with at least one
embodiment of the present invention can use the same type
of processing equipment as conventional direct current
chrome plating processes. However, an improved process as
broadly contemplated herein can preferably include an
additional processing step involving the application of a
distinct chemical solution. This additional step,
consequently, will lead to a chrome plated product having
variant layers of chrome plating rather than the single
layer as produced conventionally. (Hereafter, the variant
layered chrome plated product will be referred to as the
"variant layered chrome plated product".)
[27] As illustrated in the photographic cross-section of Fig.
2, a variant layered chrome plated product in accordance
with a preferred embodiment of the present invention has
two chrome layers as follows: (1) a boundary layer on the
steel substrate consisting of a crack-free chrome layer;
and (2) an outer micro-cracked chrome layer. The micro-
cracked layer has similar micro-cracks as compared to the
single layered chrome product produced using the known
process described above, yet it has significantly longer
corrosion resistance life. This reduces effort and costs
to the end user as it relates to failure and replacement
of the chrome-plated product during its operating
lifetime.
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[281 Continuing the discussion, Fig. 4 schematically
illustrates a process, in accordance with an embodiment of
the present invention, that it can be used to manufacture
variant layered chrome plated bar products. As shown, the
bar is first preferably ground to specification (PI1); the
specification may typically involve a Ra value of 2.0 -
10.0 micro-inches and an Rz value of 12 - 30 micro-inches.
After grinding, the bar is preferably placed on an
electrically conductive fixture and submerged into an
etching solution (P12). During the etching process, a
reversed direct current is applied to the part at the
parameters that are noted in Tables 3, 4, and 5.
[29] The bars are then preferably transferred to the next
operation, (PI3A), involving a modified chrome plating
solution and constituting the "additional step" mentioned
above. The make-up of the modified chrome plating
solution, in accordance with an illustrative and non-
restrictive embodiment, is shown in Table 2. As shown,
the solution includes catalyst in a concentration of
between about 0 percent and about 20 percent vs. active
ingredients (the active ingredients in this case being
chrome trioxide and sulfuric acid); in other words, the
volume of catalyst is preferably between about 0 percent
and about 20 percent of the total volume of the active
ingredients.
[30] The fixtured bars are submerged into the modified chrome,
plating solution and a continuous direct current is
applied at the parameters noted in Tables 3, 4, and 5.
Based on the application rate noted in Table 6, a desired
0.0002"-0.0004" layer of direct current crack-free layered
chrome will result after 10-20 minutes in this solution.
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[31] The fixtured bars are then preferably transferred and
submerged into a second chrome plating solution (PI3B).
This solution is similar in make-up to the plating
solution used by the known direct current chrome plating
process (Table 1); this also corresponds essentially to
step (P3) of Fig. 1. In this operation (PI3B), the
solution includes catalyst in a concentration of between
about 80 percent and about 120 percent vs. active
ingredients); in other words, the volume of catalyst is
preferably between about 80 percent and about 120 percent
of the total volume of the active ingredients.
[32] A continuous direct current is applied to the bars based
on the parameters laid out in Tables 3, 4, and 5. The
thickness of the direct current micro-cracked layered
chrome will vary to meet end-user specifications. Based on
application rates such as those set forth in Table 6, a
typical thickness of 0.001" can be achieved in 33 minutes.
When this or any other desired thickness is achieved, the
bar is transferred through a rinsing operation (P14), and
is then post polished (P15) to achieve final smoothness
and surface reflectivity.
[33] Again, it should be appreciated that, in accordance with a
preferred embodiment of the present invention, the
additional step (PI3A) described hereabove and illustrated
in Fig. 4, will lead to a product having two distinct
layers of chrome. A review of Fig. 2 will reveal that the
variant chrome layers include a boundary crack-free chrome
layer (or direct current crack-free chrome layer) and an
outer micro-cracked chrome layer. The direct current
crack-free chrome layer will have zero micro cracks per
linear inch in its structure, while the micro-cracked
layer will have approximately the same number of micro-
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cracks per linear inch as the single chrome layer of a
chrome plated bar produced in accordance with known direct
current single layer chrome plating processes.
[34] By way of advantages, a crack-free chrome boundary layer
as broadly contemplated herein provides an additional
barrier which protects the substrate from corrosive
elements. Meanwhile, the outer micro-cracked chrome layer
provides wear resistance and a low coefficient of friction
that is characteristic of a typical micro-cracked layer.
During standardized, accelerated corrosion testing per
ASTM B-117 Salt Spray, it was found that a product
produced in accordance with a process of the present
invention achieved corrosion resistance in excess of 500
hours, which is clearly a considerable improvement over
the 200-300 hours previously mentioned.
[35] Additionally, a crack free boundary layer as employed in
accordance with at least one embodiment of the present
invention has a generally lower hardness, thus increasing
its ductility. An illustrative hardness of this layer can
be about 47 Rc (Rockwell 'C' scale), while the Compressive
Residual Stress of the layer can be about 1,445 MPa. The
increased ductility enables the layer to resist cracking
due to stresses applied to the product during use. This
crack resistance is an additional feature that lengthens
service life in relation to wear and corrosion.
[36] By way of brief recapitulation, an improved direct current
chrome plating process in accordance with at least one
embodiment of the present invention:
[37] plates the substrate part through an additional
processing step using a novel chemical solution;
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[38] produces a variant layered chrome plated product
having two layers of chrome, with the first, boundary
layer being free of micro cracks (the direct current
crack-free chrome layer), and a second outer layer
having micro cracks;
[39] produces a variant layered chrome plated product
having increased corrosion resistance due to the
nature of the two chrome layers; and
[40] produces a variant layered chrome plated product
having a direct current crack-free chrome layer with a
compressive residual stress value of 1,445 MPa that
improves the ductility of the layer, further reducing
damaging effects of stresses and increasing corrosion
resistance.
[41] Generally, it should be understood that a chrome plated
product having variant layers of chrome, as broadly
contemplated herein in accordance with at least one
preferred embodiment of the present invention, can be used
on a cylinder rod in an assembly of a hydraulic and/or
pneumatic cylinder. As such, there are a multitude of
potential applications for such rods and cylinders.
Though certainly not an exhaustive list, the following
industries can provide contexts of hydraulic and pneumatic
cylinder rod uses for embodiments of the present
invention: fluid power, aerospace, marine and automotiv' e.
In any such industries, the embodiments of the present
invention may readily be employed in the context of
hydraulic and pneumatic components and control systems, as
well as mechanical components and control systems. By
way of some illustrative and non-restrictive examples, in
the mobile equipment markets, cylinders of the type just
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described are used in construction equipment, such as
bulldozers, dump trucks, and backhoes, and in factory
equipment, such as forklift trucks. Suitable commercial
cylinders for making use of the embodiments of the present
invention are also found on aircraft, in their landing
gear assemblies. It is to be appreciated that a great
variety of other conceivable applications are at hand.
[42] Without further analysis, the foregoing will so fully
reveal the gist of the embodiments of the present
invention that others can, by applying current knowledge,
readily adapt it for various applications without omitting
features that, from the standpoint of prior art, fairly
constitute characteristics of the generic or specific
aspects of the embodiments of the present invention.
[43] If not otherwise stated herein, it may be assumed that all
components and/or processes described heretofore may, if
appropriate, be considered to be interchangeable with
similar components and/or processes disclosed elsewhere in
the specification, unless an express indication is made to
the contrary.
[44] If not otherwise stated herein, any and all patents,
patent publications, articles and other printed
publications discussed or mentioned herein are hereby
incorporated by reference as if set forth in their
entirety herein.
[45] It should be appreciated that the apparatus and method of
the present invention may be configured and conducted as
appropriate for any context at hand. The embodiments
described above are to be considered in all respects only
as illustrative and not restrictive. All changes which
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come within the meaning and range of equivalency of the
claims are to be embraced within their scope.
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APPENDIX
Table 1- Make-up of the chrome plating solution, used in both the
known direct current chrome plating process, P3 (Fig. 3), and in
an improved direct current chrome plating process, PI3B (Fig. 4).
Component Parameter Range
Chrome Trioxide 20 - 48 oz./gal.
Sulfuric Acid 0.20 - 0.60 oz./gal.
Catalyst 80 - 12001
Table 2- Make-up of a modified chrome plating solution used in an
improved direct current chrome plating process, PI3A (Fig. 4).
Component Parameter Range
Chrome Trioxide 20 - 48 oz./gal
Sulfuric Acid 0.20 - 0.60 oz./gal.
Catalyst 0 - 20 %
Table 3- Parameter for applied electricity in Amps per Square Inch
Operation Parameter Range
Etch 0.5 - 3.0 ASI
DCCFLC 1.0 - 5.0 ASI
DCSLC/ DCMCLC 1.0 - 5.0 ASI
* DCSLC = Direct Current Single Layered Chrome operation
* DCCFLC = Direct Current Crack Free Layered Chrome operation
* DCMCLC = Direct Current Micro Cracked Layered Chrome operation
Table 4- Parameter for applied electricity in Volts
Operation Parameter Range
Etch 12 - 18 Volts
DCCFLC 3 - 16 Volts
DCSLC/ DCMCLC 3 16 Volts
* DCSLC = Direct Current Single Layered Chrome
* DCCFLC = Direct Current Crack Free Layered Chrome
* DCMCLC = Direct Current Micro Cracked Layered Chrome
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Table 5- Processing time in each operation
Operation Process Time Range
Etch 8 - 25 Seconds
DCCFLC 10 - 20 Minutes
DCSLC/ DCMCLC 20 - 50 Minutes
* DCSLC = Direct Current Single Layered Chrome
* DCCFLC = Direct Current Crack Free Layered Chrome
* DCMCLC = Direct Current Micro Cracked Layered Chrome
Table 6- Plating thickness application rates
Operation Plating Thickness Rates
DCCFLC 0.00001" - 0.00003" /minute
DCSLC/ DCMCLC 0.00002" - 0.00004" /minute
* DCSLC = Direct Current Single Layered Chrome
* DCCFLC = Direct Current Crack Free Layered Chrome
* DCMCLC = Direct Current Micro Cracked Layered Chrome
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