DIRECT CURRENT CHROME PLATING PROCESS AND VARIANT LAYERED CHROME PRODUCT

Abstract

An improved direct current chrome plating process which results in increased corrosion resistance as compared to conventional processes. Particularly, in comparison with conventional processes, 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.

Description

CROSS-REFERENCE TO RELATED U.S. APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of the earlier filing date of U.S. Provisional Application Ser. No. 60/817,662 filed on Jun. 27, 2006, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to chrome plated products and more particularly to chrome plated piston assemblies of hydraulic cylinders.

BACKGROUND OF THE INVENTION

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.

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 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.

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 FIG. 1.

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″.

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 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.

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.

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 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 enough, or the product fails completely, and it must be replaced.

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.

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.

SUMMARY OF THE INVENTION

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.

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.

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.

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

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

FIG. 1 provides a photographic cross-sectional view of a conventional chrome plated product having a single layer.

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.

FIG. 3 is a schematic illustration of a conventional direct current single layered chrome plating process.

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

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.

Building on the previous background discussion, FIG. 3 provides a schematic illustration of a conventional direct current single layered chrome plating process. For the 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.

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.

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).

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 0.001″ is achieved in 33 minutes. When the desired single layer plating thickness is achieved, the bar moves through the rinsing process (P4), and then is post-polished (P5) to improve the surface smoothness and finish of the bar.

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”.)

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.

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 (PI2). 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.

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.

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.

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.

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 (PI4), and is then post polished (PI5) to achieve final smoothness and surface reflectivity.

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-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.

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.

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.

By way of brief recapitulation, an improved direct current chrome plating process in accordance with at least one embodiment of the present invention:

• • plates the substrate part through an additional processing step using a novel chemical solution;
  • 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;
  • produces a variant layered chrome plated product having increased corrosion resistance due to the nature of the two chrome layers; and
  • 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.

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 automotive. 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 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.

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.

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.

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.

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 come within the meaning and range of equivalency of the claims are to be embraced within their scope.

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        80-120%

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

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

Claims

1. A method of chrome-plating a substrate, said 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;

said 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.

2. The method according to claim 1, wherein the first chrome plating solution further comprises chrome trioxide.

3. The method according to claim 1, wherein the first chrome plating solution further comprises chrome trioxide in a concentration of between about 20 oz. and about 48 oz. per gallon.

4. The method according to claim 1, wherein the first chrome plating solution further comprises sulfuric acid.

5. The method according to claim 1, wherein the first chrome plating solution further comprises sulfuric acid in a concentration of between about 0.20 oz. and about 0.60 oz. per gallon.

6. The method according to claim 1, wherein said step of applying a first chrome layer comprises immersing the substrate in the first chrome plating solution and applying a continuous direct current.

7. The method according to claim 1, wherein said step of applying a second chrome layer comprises immersing the substrate with applied first chrome layer in a first chrome plating solution and applying a continuous direct current.

8. The method according to claim 1, wherein said providing step comprises providing a substrate ground to specification with an Ra value of between about 2.0 and about 10.0 micro-inches.

9. The method according to claim 1, wherein said providing step comprises providing a substrate ground to specification with an Rz value of between about 12 and about 30 micro-inches.

10. The method according to claim 1, further comprising the step of immersing the substrate in etching solution prior to said step of applying a first chrome layer.

11. The method according to claim 10, wherein said step of immersing the substrate in etching solution further comprises applying a reversed direct current.

12. The method according to claim 1, wherein:

the second chrome plating solution further comprises chrome trioxide.

13. The method according to claim 1, wherein the second chrome plating solution further comprises chrome trioxide in a concentration of between about 20 oz. and about 48 oz. per gallon.

14. The method according to claim 1, wherein the second chrome plating solution further comprises sulfuric acid.

15. The method according to claim 1, wherein the second chrome plating solution further comprises sulfuric acid in a concentration of between about 0.20 oz. and about 0.60 oz. per gallon.

16. The method according to claim 1, wherein said step of applying a second chrome layer comprises applying a chrome plating solution which comprises catalyst in a concentration of between about 80 percent and about 120 percent vs. active ingredients.

17. The method according to claim 16, wherein said step of applying a first chrome layer comprises immersing the substrate in the first chrome plating solution and applying a first continuous direct current.

18. The method according to claim 17, wherein said step of applying a second chrome layer comprises immersing the substrate with applied first chrome layer in a first chrome plating solution and applying a second continuous direct current.

19. The method according to claim 18, wherein:

the first chrome plating solution further comprises chrome trioxide.

20. The method according to claim 19, wherein the first chrome plating solution further comprises chrome trioxide in a concentration of between about 20 oz. and about 48 oz. per gallon.

21. The method according to claim 18, wherein the first chrome plating solution further comprises sulfuric acid.

22. The method according to claim 21, wherein the first chrome plating solution further comprises sulfuric acid in a concentration of between about 0.20 oz. and about 0.60 oz. per gallon.

23. The method according to claim 18, wherein said providing step comprises providing a substrate ground to specification with an Ra value of between about 2.0 and about 10.0 micro-inches.

24. The method according to claim 23, wherein said providing step comprises providing a substrate ground to specification with an Rz value of between about 12 and about 30 micro-inches.

25. The method according to claim 18, further comprising the step of immersing the substrate in etching solution prior to said step of applying a first chrome layer.

26. The method according to claim 25, wherein said step of immersing the substrate in etching solution further comprises applying a reversed direct current.

27. The method according to claim 26, wherein said step of applying a reversed direct current comprises applying a current with voltage in a range of between about 12 and about 18 volts.

28. The method according to claim 26, wherein said step of applying a reversed direct current comprises applying a current in a range of between about 0.5 and about 3.0 amps per square inch.

29. The method according to claim 26, wherein said step of applying a reversed direct current comprises applying a current for a duration of between about 8 and about 25 seconds.

30. The method according to claim 18, wherein said step of applying a first continuous direct current comprises applying a current with voltage in a range of between about 3 and about 16 volts.

31. The method according to claim 18, wherein said step of applying a first continuous direct current comprises applying a current in a range of between about 1.0 and about 5.0 amps per square inch.

32. The method according to claim 18, wherein said step of applying a first continuous direct current comprises applying a current for a duration of between about 10 and about 20 minutes.

33. The method according to claim 18, wherein said step of applying a first continuous direct current comprises applying a current with voltage in a range of between about 3 and about 16 volts.

34. The method according to claim 18, wherein said step of applying a second continuous direct current comprises applying a current in a range of between about 1.0 and about 5.0 amps per square inch.

35. The method according to claim 18, wherein said step of applying a second continuous direct current comprises applying a current for a duration of between about 20 and about 50 minutes.

36. The method according to claim 18, wherein the first chrome layer has a thickness of between about 2 and about 4 times the thickness of the second chrome layer.

37. The method according to claim 18, wherein the first chrome layer has a thickness of between about 0.0002 inch and about 0.0004 inch.

38. The method according to claim 18, wherein the substrate comprises a rod.

39. The method according to claim 38, wherein the rod comprises a piston rod for a hydraulic or pneumatic cylinder.