REPAIR OF CHROMIUM PLATED SURFACES
United States Patent 3616285
A process for repairing defective areas or spots in chromium plated surfaces in which the area is subjected to sequential steps, such as mechanical cleaning, electrocleaning, electroactivating, copper electroplating, nickel electroplating, electrocleaning and electroactivating the nickel deposit, and then chromium plating the nickel deposit. Prior to any metal deposition, the original chromium deposit is electrolytically removed from a band which borders the perimeter of the defective area. The copper electrodeposits (if used) and the nickel electrodeposit then cover the defective area and at least part of the bordering band but do not reach the contiguous originally deposited chrome-plate from which the copper and/or nickel is more likely to peel. The final chromium plating covers all of the defective area, bordering band, and contiguous originally deposited chrome-plate.
US Patent References:
Process for effecting the electrodeposition of metals
Adey - July 1936 - 2046440
/2603593.html
Blickensderfer - July 1952 - 2603593
Method of chromium plating
Schwartz - July 1968 - 3393134
Process for effecting the electrodeposition of metals
Adey - July 1936 - 2046440
/2603593.html
Blickensderfer - July 1952 - 2603593
Method of chromium plating
Schwartz - July 1968 - 3393134
Application Number:
04/889676
Publication Date:
10/26/1971
Filing Date:
12/31/1969
View Patent Images:
Export Citation:
Assignee:
Sifco Industries, Inc. (Cleveland, OH)
Primary Class:
Other Classes:
205/222, 205/206, 205/210, 205/180, 205/219
International Classes:
C25D5/00; C23B7/00; C23B1/00
Field of Search:
204/16,15,23,32,146,224
Primary Examiner:
Mack, John H.
Assistant Examiner:
Tufariello T.
Claims:
What is claimed is
1. In a process for repairing a defective area in a chromium plated surface which includes subjecting said area to the sequential steps of mechanical cleaning, electrocleaning, electroactivating, electroplating nickel thereon, and then chromium plating the nickel deposit; the improvements comprising prior to said initial electrocleaning step, electrolytically removing a band of chromium from said chromium plated surface bordering the perimeter of said defective area, then within the stated sequence nickel plating the defective area and at least part of said bordering band but short of the contiguous originally deposited chrome-plate, and finally chromium plating all of said defective area, bordering band, and contiguous originally deposited chrome-plate.
2. The process of claim 1 including, prior to the nickel plating, copper plating the defective area and at least part of the bordering band but short of the contiguous originally deposited chrome-plate.
3. The process of claim 1 wherein said electrolytic removal of the chromium band takes place with said chromium-plated surface being anodic.
4. The process of claim 1 wherein said electrolytic removal of the chromium band is carried out with the solution consisting essentially of a solution of sodium hydroxide and sodium metasilicate in water.
5. The process of claim 1 wherein said electrolytic removal of the chromium band is carried out at a voltage within a range from about 5 volts to about 20 volts.
6. The process of claim 1 wherein said chromium plated surface has a nickel undercoat, and the electrolytic removal of said chromium band terminates just short of electrically removing any portion of said nickel undercoat.
7. The process of claim 1 wherein said nickel electroplating comprises first depositing on said defective area a dull nickel plate, and then depositing thereover a bright nickel plate to provide a duplex nickel coating for said area.
8. The process of claim 1 wherein said electrocleaning of the mechanically cleaned area is by means of a brush-plating tool, the tool being an anode and the surface being a cathode.
9. The process of claim 1 wherein said electroactivating of the electrocleaned, mechanically cleaned area is by means of a brush-plating tool, the tool being an anode and the surface being a cathode.
10. The process of claim 1 wherein said nickel electroplating is by means of a brush-plating tool.
11. The process of claim 1 wherein said chromium plating is by means of a brush plating operation employing a hexavalent chromium-plating solution.
12. The process of claim 1 including polishing the electroplated nickel prior to its electrocleaning and electroactivating.
13. The process of claim 1 including polishing the electroplated chromium.
14. The process of claim 1 wherein said mechanical cleaning comprises grinding and polishing said defective area.
15. The process of claim 1 including a water rinse of said area after the initial electrocleaning.
16. The process of claim 1 including a water rinse of said area after the electrolytic removal of said chromium band.
17. In a process for brush electroplating an area on a chromium plated surface with an additional adherent deposit of chromium which includes electroactivating the previously deposited chromium surface with an acidic solution employing a brush-plating tool in which the tool is an anode and the work is a cathode, and brush-plating chromium over the activated surface using a solution containing as essential ingredients hexavalent chromium, sodium hydroxide, and sulfate ions; the improvements comprising first electrolytically removing a band of chromium from said chromium-plated surface bordering the perimeter of said area, then after said activating, nickel plating said area and at least part of said band but short of the contiguous originally deposited chrome-plate, and finally chromium plating of all said area, bordering band, and contiguous originally deposited chrome-plate.
1. In a process for repairing a defective area in a chromium plated surface which includes subjecting said area to the sequential steps of mechanical cleaning, electrocleaning, electroactivating, electroplating nickel thereon, and then chromium plating the nickel deposit; the improvements comprising prior to said initial electrocleaning step, electrolytically removing a band of chromium from said chromium plated surface bordering the perimeter of said defective area, then within the stated sequence nickel plating the defective area and at least part of said bordering band but short of the contiguous originally deposited chrome-plate, and finally chromium plating all of said defective area, bordering band, and contiguous originally deposited chrome-plate.
2. The process of claim 1 including, prior to the nickel plating, copper plating the defective area and at least part of the bordering band but short of the contiguous originally deposited chrome-plate.
3. The process of claim 1 wherein said electrolytic removal of the chromium band takes place with said chromium-plated surface being anodic.
4. The process of claim 1 wherein said electrolytic removal of the chromium band is carried out with the solution consisting essentially of a solution of sodium hydroxide and sodium metasilicate in water.
5. The process of claim 1 wherein said electrolytic removal of the chromium band is carried out at a voltage within a range from about 5 volts to about 20 volts.
6. The process of claim 1 wherein said chromium plated surface has a nickel undercoat, and the electrolytic removal of said chromium band terminates just short of electrically removing any portion of said nickel undercoat.
7. The process of claim 1 wherein said nickel electroplating comprises first depositing on said defective area a dull nickel plate, and then depositing thereover a bright nickel plate to provide a duplex nickel coating for said area.
8. The process of claim 1 wherein said electrocleaning of the mechanically cleaned area is by means of a brush-plating tool, the tool being an anode and the surface being a cathode.
9. The process of claim 1 wherein said electroactivating of the electrocleaned, mechanically cleaned area is by means of a brush-plating tool, the tool being an anode and the surface being a cathode.
10. The process of claim 1 wherein said nickel electroplating is by means of a brush-plating tool.
11. The process of claim 1 wherein said chromium plating is by means of a brush plating operation employing a hexavalent chromium-plating solution.
12. The process of claim 1 including polishing the electroplated nickel prior to its electrocleaning and electroactivating.
13. The process of claim 1 including polishing the electroplated chromium.
14. The process of claim 1 wherein said mechanical cleaning comprises grinding and polishing said defective area.
15. The process of claim 1 including a water rinse of said area after the initial electrocleaning.
16. The process of claim 1 including a water rinse of said area after the electrolytic removal of said chromium band.
17. In a process for brush electroplating an area on a chromium plated surface with an additional adherent deposit of chromium which includes electroactivating the previously deposited chromium surface with an acidic solution employing a brush-plating tool in which the tool is an anode and the work is a cathode, and brush-plating chromium over the activated surface using a solution containing as essential ingredients hexavalent chromium, sodium hydroxide, and sulfate ions; the improvements comprising first electrolytically removing a band of chromium from said chromium-plated surface bordering the perimeter of said area, then after said activating, nickel plating said area and at least part of said band but short of the contiguous originally deposited chrome-plate, and finally chromium plating of all said area, bordering band, and contiguous originally deposited chrome-plate.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to improvements in a process for the spot repair of damage chromium plated surfaces and, more particularly, to a process in which the chromium is electrolytically stripped or removed from a chromium surface bordering the perimeter of the defective area at a time subsequent to the cleaning of the surface but prior to the electrolytic deposition of metal thereon.
Initial attempts to repair defective areas on chromium plated surfaces produced repaired areas which were more or less detectable to the eye. For example, the "color" of the repaired surface often failed to match exactly the undamaged chromium plated surface. The juncture between the new and old platings was often visible. The adhesion of the various successive copper, nickel, and chromium plates to the underlying metal also was not as good as desired, and the underlying or basic metal was often not properly protected against corrosion.
The process described in U.S. Pat. No. 3,393,134 to Schwartz, Jr. repairs damaged chromium plated surfaces efficiently and at reasonable cost. This process does not leave a line of demarcation between repaired and nonrepaired areas that is detectable to the eye under ordinary conditions. Also, this process employs readily available equipment and materials without requiring a high degree of skill on the part of an operator.
More particularly, the process of U.S. Pat. No. 3,393,134 embodies a series of sequential steps performed on the defective area in question, such as mechanically cleaning, electrocleaning, electroactivating, electroplating nickel, then electrocleaning and electroactivating the nickel deposit, and finally chromium plating the nickel deposit. Such electrolytic cleaning, activating, and electroplating are carried out with hand tools having porous dielectric surfaces that are saturated with electrolyte. Closely adjacent to the porous surface of the tool is an electrode maintained in contact with the solution. The porous surface is then rubbed on the surface to be repaired. Tools of this general type are well known in the art and used in "brush" plating operations.
The order of the layers of different metals deposited over a steel part, such as a bumper, is usually copper, nickel, and chromium in a direction away from the steel. Some manufacturers may be use instead: brass, nickel, and chromium. In any event, the mechanical cleaning step of the process of the cited patent usually comprises grinding and polishing the defective area. The resulting abrasion removes not only the chrome but also the nickel and often the underlying copper or brass as well. In repairing the defective area, it is necessary to replate the mechanically cleaned area with nickel, or with copper and then nickel, before depositing chromium.
In replating with nickel and/or copper, such depositions can reach and overlap sections of the originally deposited chrome-plate that are adjacent to the area being repaired. Since chromium has a particularly strong tendency to passivate, it is difficult to apply adherent deposits of other metals over it. This may be due, at least in part, to galvanic, electrochemical effects between the dissimilar metals. Chromium also is difficult to activate, that is, to receive well overapplied deposits. Generally strong corrosive activators, skill in activation, and immediate application of a desired electroplate after activation are required. Failure to activate chromium properly results in immediate apparent peeling of nickel or of nickel and copper overlays; or in nonapparent peeling which, after service, results in blistering of the coating upon exposure to corrosion effects attendant normal out-of-doors use.
It would, therefore, further improve the described process if in spot-chrome repair, the need were eliminated for treating areas of originally deposited chrome-plate adjacent to a defective area with electrodeposits of nickel or copper and nickel, and yet obtain a strongly adherent chromium plate over the entire area, including such adjacent, originally deposited chrome-plate.
SUMMARY OF THE INVENTION
In accordance with the present process, a boarder strip or band of chromium is electrolytically removed from around the defective area which is to be repaired. The electrodeposit of nickel (and of copper if used) is made over the defective area and at least part but not all of the bordering band so as to avoid the contiguous, originally deposited chrome-plate. Thereafter, the electrodeposition of chromium covers all the defined area, bordering band, and contiguous, originally deposited chrome-plate.
Even though not all of the bordering band is electroplated with nickel or with copper and nickel, this is not found to be at all serious, probably because there has been a minimum of removal of nickel from this annular bordering area during the mechanical cleaning step. Also there is no difficulty in obtaining a strong adherence of the final chrome-plate to the contiguous, originally deposited chrome-plate. This is thought to be due to the absence of galvanic action and the relatively thin layer of the chromium plate as compared to the much heavier and therefore thicker layer of copper or nickel.
The electrolytic removal of the border strip is affected by a current reverse to that employed in normal chromium plating, that is, the chromium surface is anodic. An exemplary solution for the electrolytic removal consists essentially of a solution of sodium hydroxide and sodium metasilicate in water. The removal may be effected by the same type of hand brush tool used in the normal plating operations. The electrolytic strip removal preferably takes place in the overall process after the defective area has been mechanically cleaned but before any metal has been electrodeposited.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Except for the electrolytic removal of chromium from a band bordering the defective area and except for confining the metal deposits, other than chromium, within such area and bordering band, the present process is similar to that described and claimed in U.S. Pat. No. 3,393,134. Therefore, such patent is hereby incorporated by reference.
As a general procedure, the damaged area is first straightened, welded, brazed, or otherwise preconditioned as required by the nature of the damage. The area is then mechanically cleaned as by grinding to a smooth surface and polishing with a fine abrasive to a scratch-free surface with the various layers of previously applied electroplate, such as chromium, nickel, and copper on a steel base, well feathered in.
Preferably at this juncture, but not necessarily so, a chromium band is electrolytically removed from around the damaged or defective area. The previously described hand tool, having a porous, dielectric surface, may be used for this purpose by dipping the dielectric surface into a generally alkaline solution, for example an aqueous solution of sodium hydroxide, and rubbing the chromium surface in a continuous, closed path bordering the defective area. During this time, the chromium surface is anodic. Alternatively, the brush tool may be provided with a chamber connected to a sump or storage tank from which the electrolytic solution is pumped. The chromium removal stops short of electrically removing any of the other metal undercoats, such as a nickel undercoat.
The treated surface is then subjected to an electrocleaning operation. A handtool of the type previously described is connected to a variable voltage source of direct current that is equipped with a voltmeter and an ammeter. The tool is the anode and the object having the damage surface is the cathode. The handtool is then rubbed over the treated surface. The pressure of the tool on the surface may be "light" or "soft," enough pressure being applied to insure good contact between the tool and the work. The correct pressure can be determined by watching the ammeter. With too little pressure, the current is too low, while pressure in excess of that preferably employed does not cause the current to increase in proportion to the increase in pressure. The electrolyte used for electrocleaning may be the same as that employed for chromium stripping (but at reverse current). For instance, the electrolyte may include an alkali metal hydroxide buffered with sodium metasilicate to a pH in the range of from about 9 to about 13, and preferably in the range of from about 10 to about 12. Other alkaline cleaners, such as the proprietary cleaner marketed under the trademark "Dalic" and identified as No. 1010 provides excellent results.
The rubbing action continues until the surface can be rinsed with no water breaks being visible, that is, the surface is wetted with a continuous film of the rinsing liquid. The rinse may be simply tap water. One advantage of the present process is that it eliminates the need for strong activators and their attendant need for skill and care in application.
After rinsing, the surface is again subjected to electrolysis, using a similar hand tool and following generally the same procedure used for the electrocleaning, the rubbing action again being appreciably confined to the defective area plus its surrounding band. The electrolyte employed is an acidic solution that is capable of "activating" the area to be plated. The activating solution makes the area receptive to plating, probably by eliminating oxides from the surface. The activating solution may be a solution of sulfuric acid and water. After activation, the surface is rinsed as by tap water.
Immediately after the rinsing of the treated or activated area, nickel is electrodeposited on the surface using a like handtool. If the mechanical cleaning has also removed a significant amount of a copper plate beneath the nickel plate, copper is first electrodeposited, followed by the nickel electrodeposit. In either case, the rubbing action is similar. It starts at preferably the outer periphery of the defective area and its bordering strip but remains away from the original chrome-plate, so as to avoid depositing copper or nickel onto the chromium. The entire area to be nickel or copper plated is quickly covered to prevent the surface from becoming passive. The initial nickel plating operation forms a very thin deposit of nickel, and thereafter nickel is deposited only in the area covered by the initial deposit since the remainder of the area becomes substantially passive. The rubbing action is kept slightly within the periphery of the previously activated area.
In the preferred practice of the invention, nickel is deposited by the spot-deposition technique as two distinct layers. The first deposition is a dull nickel plating followed by a bright nickel plating. The resulting duplex nickel coat assists in obtaining a bright, shiny final surface by providing a bright nickel coating on top to which the final plating of chromium is applied. On the other hand, the dull nickel undercoat is more resistant to corrosion than the bright nickel overlay. Corrosion pit formation almost inevitably starts at scratches or openings in the chromium surface and proceeds until the underlying dull nickel plate is reached. Since the bright nickel coat is more easily corroded than the dull nickel undercoat, corrosion then proceeds laterally rather than downwardly through the dull nickel plate. Penetration to the basis steel and subsequent rapid and unattractive corrosion of the basis steel are, therefore, retarded. The double nickel coat accordingly improves brightness of the plated nickel coating (which minimizes or eliminates the need to buff the nickel coating), while at the same time improving corrosion protection.
After nickel has been deposited on the surface to a desired thickness (for example, from about 0.5 mil. to about 1 mil. in the areas of thickest deposit), it is buffed, if desired, to a high polish using procedures well known in the art. The use of a double nickel coat wherein the outer coat is bright nickel can eliminate or reduce the need for such buffing. The nickel surface is then electrocleaned and electroactivated using the same techniques previously described. The cleaning and activating operations at this stage extend over the original chrome-plate surrounding the nickel, since additional chromium is to be plated on the original chrome-plate. The treated area is then immediately flushed with a rinsing solution which can be either water or a mildly acidic aqueous solution.
The entire area is then immediately swabbed with another electrode tool that is saturated with an electrolyte that is to be used in the chromium-plating operation, but with the tool disconnected from the power source. This stops the action of the activating solution but preserves the activated area in the active state, so that an adherent deposit can be obtained. The electrolyte, as herein after described, contains hexavalent chromium, but it is modified from the usual hexavalent chromium electrolyte by the addition of materials to make it suitable for brush-plating operations.
The activated surface is then chromium plated, using the hand tool that was employed to swab the area with the chromium plating solution and following the procedure as generally outlined above. However, the chromium deposit covers the repaired area, plus its surrounding border band, and contiguous or adjacent sections of the originally deposited chrome-plate. The chromium deposited by the spot-technique is substantially undistinguishable in color and texture from the surrounding original chromium and has good corrosion resistance and adhesion. The plating operation produces a matte surface chromium coating preferably having a thickness of about 0.05 mil. to about 0.15 mil. The surface is then washed and the satin or matte deposit is buffed by conventional means to a high polish.
In order that those skilled in the art may better understand how the present invention may be carried to effect, the following examples are given by way of illustration and not by way of limitations. All parts and percentages are by weight unless otherwise specified.
A typical automobile bumper having a damaged chromium surface is repaired as follows:
The bumper is straightened and the damaged surface ground away exposing a nickel or, in some cases, nickel and copper electrodeposits beneath the electrodeposited chromium, and the steel base metal beneath the electrodeposits. The grinding leaves a level semipolished surface about 4 inches in diameter, for example. The damaged area is, if necessary, precleaned using conventional solvents and cleaners, and the surface is then polished with a series of progressively finer abrasives, up to 400 grit aluminum oxide paper, and a conventional disc-type polisher until the surface to be repaired is substantially scratch-free with layers of previously applied electroplate well feathered in.
The surface is then electrolytically cleaned using a hand tool comprising a graphite electrode supporting a porous cotton tip about three-eights inch thick held in place by cotton gauze. The bumper is made the cathode in a DC circuit, and the tool the anode. The voltage of the power source is adjusted to about 18 to 20 volts. The tool is saturated with solution A set forth below and rubbed over the polished surface with a circular motion, starting at the center and working to the periphery of the prepared surface area. The rubbing is continued until the surface being cleaned is covered entirely with a uniform film of solution and no gas bubbles persist or remain on the surface. This indicates that the surface is clean. The operation ordinarily requires about 1 minute for the area in question. The average current is about 15 amperes, and the tool area in contact with the surface is about 5 square inches making the cathode current density 3 amperes per square inch. The amount of current used is about 0.002 ampere hour per square inch.
SOLUTION A
Sodium hydroxide 15 grams per liter of final solution.
Sodium metasilicate (Na 2 Si0 3 ) 10 grams per liter of final solution.
Water Remainder.
pH 11.6
Specific gravity 1.021
Either distilled water or tap water can be used.
As an example of an alternate solution A, "Dalic" 1010 Cleaner may be employed. This is a proprietary solution marketed by The Steel Improvement and Forge Company of Cleveland, Ohio.
After a water rinse of the electrocleaned surface, it is ready for the chromium-stripping step. A border or band from about 2 to 4 inches in width is wiped around the previously prepared area, stripping chromium therefrom with no appreciable attack on the other materials present or exposed on the bumper. The same type of brush tool may be used as for the plating operations. The electrolytes are generally alkaline solutions with ionizable basic compounds. For example, the electrolyte solution may be the same as solution A. The tool and solution used for stripping, however, are preferably not used for cleaning in order to avoid cross-contamination. During chromium stripping, the DC current is reversed from that normally used, that is, the bumper is anodic. The voltage is preferably about 12.5 volts, although it may range from about 5 volts to about 20 volts.
The chromium stripping is continued until all chromium within the desired area is removed and the underlying nickel and its characteristic color show. Contact with any copper plate should be avoided since some stripping of the copper could result. After the chromium-stripping step, the area is rinsed with tap water.
The surface is next activated preparatory to electroplating nickel, or copper and then nickel. The activation is accomplished with still another handtool having a graphite electrode and porous cotton tip about three-eighth inch thick. During this step the tool is the anode and the bumper is the cathode of a DC circuit. The voltage is about 7.5 volts. The tool is saturated with the following solution B and then rubbed over the surface as before, but the rubbing does not extend beyond the prepared surface onto the original chromium plate which it is desired to retain in its passive state. This operation ordinarily requires about 30 seconds. At this time, about 0.1 ampere hour of current has been passed, making the amount of current about 0.0013 ampere hour per square inch. The actual current is about 12 amperes and the area of electrode tool in contact with the work is about 6 square inches, resulting in a current density of about 2 amperes per square inch of tool.
SOLUTION B
Sulfuric acid (1.84 sp. g.) 20 ml.
Water 980 ml. As before, commercial sulfuric acid and tap water can be employed.
Whether or not a copper plate is deposited depends primarily on how much, if any, copper was removed by the mechanical cleaning step. If copper is to be plated, various well-known copper-plating solutions may be used of which the following is an example:
SOLUTION C
Copper cyanide 8 ounces.
Potassium cyanide 0.75 to 1.5 ounces.
Caustic potash 4 to 7 ounces.
Water To make one gallon.
To use solution C at the conclusion of the activating treatment with solution B, the surface is immediately rinsed with tap water. Then, with another tool having a graphite electrode, the previously activated area is plated with copper using the indicated solution.
Similarly, when nickel is to be plated, either directly after the activating treatment if no copper is to be plated, or after the copper deposition, the surface is rinsed with tap water and with another like tool, the treated area is plated with nickel using the following solution D as the electrolyte:
SOLUTION D
Nickel sulfate (NiSO 4 6H 2 0) 538 grams.
Citric acid 30 grams.
Water (distilled) To make 1.010 liter.
Excellent results results also can be obtained using as an alternate solution D is proprietary product sold under the trade name "Dalic" Nickel S.
The tool saturated with solution D is made the anode in a DC circuit in which the bumper is the cathode. The power source is set to about 15 volts, and the tool is rubbed rapidly over the entire surface to be plated. A soft, circular rubbing action is then applied starting at the periphery of the polished area and working toward the center. After the tool has warmed, the voltage may be increased to about 20 volts. The rubbing and electrodeposition are continued about 20 minutes, the tool being frequently dipped into the composition of solution D to keep it saturated. Alternatively, the solution may be pumped to the tool. A gray or matte satin nickel finish appears. At the completion of the electrolysis, 7 ampere hours have been passed in about 20 minutes, making the current about 0.25 ampere hour per square inch of plated surface. During most of the electrolysis, the actual current is preferably about 25 amperes, and the area of the electrode tool in contact with the surface is about 6 square inches so that the current density is about 4 amperes per square inch of tool.
As previously indicated, it is preferred to carry out the nickel plating as two steps. The nickel-plating step just described using solution D may be taken as one of the steps corresponding to deposition of dull nickel. A bright nickel deposition of composition known in the art can then be immediately applied, such as the following solution E.
SOLUTION E
Nickel sulfate 538 grams
Citric acid 30 grams
Saccharin (brightener) 1 gram
Water To make 1 liter.
A water rinse between the dull and bright nickel plating steps is optional. It is preferred, although not necessary, to preswab the bright nickel solution onto the area to be plated while using no plating current. Then bright nickel is electroplated over the dull nickel to a thickness of about 0.5 mil. The bright nickel deposit can have a narrowing, tapered thickness at its edges.
A voltage of 10 to 15 volts can initially be used. However, the voltage can be raised ultimately to 18 to 20 volts as the solution and bumper warm under the action of electroplating. The plating current initially should be about 7 amperes on flat surfaces and somewhat less on curved surfaces. Ultimately, approximately 20 amperes are drawn with a conventional brush type of tool applicator. The tool movement should be at a moderate speed and circular, dwelling mostly on the sanded and steel exposed area. The tool may be dipped into solution about every 10 seconds or solution may be dripped or pumped through the tool. The plating time for about 0.5 mil. may be controlled as follows:
After the bright nickel-plating step is concluded, the area should be rinsed with water to remove any electrolyte and then dried, followed possibly by light buffing prior to the chromium plating, as by a conventional buffing wheel.
The chromium plating is carried out with a handtool similar to those previously described but embodying a lead electrode and a polyester fabric or fiber pad composed, for example, of "Dacron," the pad being about one-half inch thick and covered with gauze also made of a polyester material such as "Dacron." Polyester fabrics are employed since these materials have good resistance to attack by chromic acid. Cotton, such as used with the other electrolytes, is attached by chromic acid reducing the hexavalent chromium ions to trivalent chromium which seriously interferes with the operation of the electrolyte. The tool is saturated with the following solution F electrolyte and, before the tool is connected to the power source, it is rubbed quickly over the entire surface that is to be plated. Then the circuit is completed with the tool the anode and the bumper the cathode, and the power source adjusted for an output of about 10 volts. The following electrolyte gives good results:
SOLUTION F
Chromic acid 300 grams
Sulfuric acid 1.25 grams
Trichloroacetic acid 15 grams
Trivalent chromium 5 grams
Sodium hydroxide 40 grams
Distilled water To make 1 liter. This electrolyte is of the type disclosed in Belgian Pat. No. 632,459 of May 16, 1963, with the addition of sodium hydroxide, which is essential for a good brush plating. An alternate solution F is:
Chromic acid per liter grams 400
Sodium hydroxide, per liter grams 58
Sulfuric acid (1.84 sp. gr.), per liter ml. 6
Distilled water To make 1 liter.
A satisfactory and in some respects preferred solution F can be prepared utilizing proprietary materials as follows:
Duramir 200 330 grams
Sulfuric acid (1.84 sp. gr.) 0.65 gram
Sodium hydroxide 40 grams
Trivalent chromium 5 grams
Distilled water To make 1 liter.
Duramir 200 catalyst, 19.4 units. The resulting solution contains hexavalent chromium. The sodium hydroxide is required to enable the electrolyte to be used in brush plating, to give more uniform color, and to prevent spotting.
The rubbing and electroplating operation are continued for about 10 minutes, the tool being redipped in the solution to keep the porous polyester padding saturated. After about 10 minutes, a characteristic gray satin or matte finish appears. At this point, 5.0 ampere hours have been passed making the amount of current about 0.10 ampere hour per square inch. The actual current during the electrolysis is preferably about 40 amperes. In the chromium plating, the area of the electrode tool in contact with the surface is about 8 square inches and the current density about 5 amperes per square inch. It is desirable to reduce the voltage at the end of the chromium-plating operation to about 5 volts and make a final pass with the tool around the periphery of the spot chromium deposit. In this area a ring that is visible before buffing may develop. The final low voltage pass decreases the darkness of the ring and reduces the amount of buffing that may be required to eliminate it.
The chromium plate is rinsed thoroughly with tap water, wiped dry with a clean rag, and buffed to a highly polished bright surface. The buffing is from the center outward, blending the new chromium plate with the undamaged, originally deposited chromium plate. The color of the repaired area matches that of the remainder of the chromium surface, and the repaired area is not readily detectable by visual inspection.
For a further discussion of the electroplating steps, handtools, current densities, voltages, electrocleaning, electroactivating, and related aspects, reference is made to the cited U.S. Pat. No. 3,393,134. While the practice of this patent is to overlap the areas of repair and the surrounding original chromium plated surface, the present process confines the depositions of metals, other than chromium, to within the defective area and a surrounding chromium-free strip or border. The improved practice prevents contact between copper or nickel with originally deposited chromium. Normally, it is difficult to activate such original chrome-deposit and difficult as well to secure good adherence with an additional nickel or copper deposition.
The bounds of such confinement are marked in the present invention by using a reverse current to strip chromium from around the defective area to provide effectively a barrier beyond which the electrodepostion of nickel or chromium does not extend. In particular, the chromium stripping technique eliminates the need to use stronger activators which tend to attack unintentionally adjacent areas of original chromium; reduces the amount, speed, and skill necessary to carry out the activating steps; and improves adhesion and the ability of the spot-chrome deposits to withstand corrosion in out-of-doors environment. Yet, the defective area is repaired in such a manner that the outlines of the repaired area are not readily discernible to the naked eye.
Even though chromium is deposited on the originally deposited chromium, there is no difficulty in securing good adherence as there is in the case of deposits of nickel or copper. This is thought to be due to the absence of galvanic action normally met when dissimilar metals contact each other; and also due to a much thinner layer of chromium. While deposits of copper or nickel over steel parts, such as a bumper, may each be about 1.5 mil. in thickness, the top chrome deposit may be only 0.020 mil. in thickness. Accordingly, there is a much less demand or strain on the adhesion of a chrome layer atop the original chrome-plate.
While the foregoing describes a presently preferred embodiment and several modifications thereof, it is understood that the invention may be practiced in still other forms within the scope of the following claims.
The present invention relates to improvements in a process for the spot repair of damage chromium plated surfaces and, more particularly, to a process in which the chromium is electrolytically stripped or removed from a chromium surface bordering the perimeter of the defective area at a time subsequent to the cleaning of the surface but prior to the electrolytic deposition of metal thereon.
Initial attempts to repair defective areas on chromium plated surfaces produced repaired areas which were more or less detectable to the eye. For example, the "color" of the repaired surface often failed to match exactly the undamaged chromium plated surface. The juncture between the new and old platings was often visible. The adhesion of the various successive copper, nickel, and chromium plates to the underlying metal also was not as good as desired, and the underlying or basic metal was often not properly protected against corrosion.
The process described in U.S. Pat. No. 3,393,134 to Schwartz, Jr. repairs damaged chromium plated surfaces efficiently and at reasonable cost. This process does not leave a line of demarcation between repaired and nonrepaired areas that is detectable to the eye under ordinary conditions. Also, this process employs readily available equipment and materials without requiring a high degree of skill on the part of an operator.
More particularly, the process of U.S. Pat. No. 3,393,134 embodies a series of sequential steps performed on the defective area in question, such as mechanically cleaning, electrocleaning, electroactivating, electroplating nickel, then electrocleaning and electroactivating the nickel deposit, and finally chromium plating the nickel deposit. Such electrolytic cleaning, activating, and electroplating are carried out with hand tools having porous dielectric surfaces that are saturated with electrolyte. Closely adjacent to the porous surface of the tool is an electrode maintained in contact with the solution. The porous surface is then rubbed on the surface to be repaired. Tools of this general type are well known in the art and used in "brush" plating operations.
The order of the layers of different metals deposited over a steel part, such as a bumper, is usually copper, nickel, and chromium in a direction away from the steel. Some manufacturers may be use instead: brass, nickel, and chromium. In any event, the mechanical cleaning step of the process of the cited patent usually comprises grinding and polishing the defective area. The resulting abrasion removes not only the chrome but also the nickel and often the underlying copper or brass as well. In repairing the defective area, it is necessary to replate the mechanically cleaned area with nickel, or with copper and then nickel, before depositing chromium.
In replating with nickel and/or copper, such depositions can reach and overlap sections of the originally deposited chrome-plate that are adjacent to the area being repaired. Since chromium has a particularly strong tendency to passivate, it is difficult to apply adherent deposits of other metals over it. This may be due, at least in part, to galvanic, electrochemical effects between the dissimilar metals. Chromium also is difficult to activate, that is, to receive well overapplied deposits. Generally strong corrosive activators, skill in activation, and immediate application of a desired electroplate after activation are required. Failure to activate chromium properly results in immediate apparent peeling of nickel or of nickel and copper overlays; or in nonapparent peeling which, after service, results in blistering of the coating upon exposure to corrosion effects attendant normal out-of-doors use.
It would, therefore, further improve the described process if in spot-chrome repair, the need were eliminated for treating areas of originally deposited chrome-plate adjacent to a defective area with electrodeposits of nickel or copper and nickel, and yet obtain a strongly adherent chromium plate over the entire area, including such adjacent, originally deposited chrome-plate.
SUMMARY OF THE INVENTION
In accordance with the present process, a boarder strip or band of chromium is electrolytically removed from around the defective area which is to be repaired. The electrodeposit of nickel (and of copper if used) is made over the defective area and at least part but not all of the bordering band so as to avoid the contiguous, originally deposited chrome-plate. Thereafter, the electrodeposition of chromium covers all the defined area, bordering band, and contiguous, originally deposited chrome-plate.
Even though not all of the bordering band is electroplated with nickel or with copper and nickel, this is not found to be at all serious, probably because there has been a minimum of removal of nickel from this annular bordering area during the mechanical cleaning step. Also there is no difficulty in obtaining a strong adherence of the final chrome-plate to the contiguous, originally deposited chrome-plate. This is thought to be due to the absence of galvanic action and the relatively thin layer of the chromium plate as compared to the much heavier and therefore thicker layer of copper or nickel.
The electrolytic removal of the border strip is affected by a current reverse to that employed in normal chromium plating, that is, the chromium surface is anodic. An exemplary solution for the electrolytic removal consists essentially of a solution of sodium hydroxide and sodium metasilicate in water. The removal may be effected by the same type of hand brush tool used in the normal plating operations. The electrolytic strip removal preferably takes place in the overall process after the defective area has been mechanically cleaned but before any metal has been electrodeposited.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Except for the electrolytic removal of chromium from a band bordering the defective area and except for confining the metal deposits, other than chromium, within such area and bordering band, the present process is similar to that described and claimed in U.S. Pat. No. 3,393,134. Therefore, such patent is hereby incorporated by reference.
As a general procedure, the damaged area is first straightened, welded, brazed, or otherwise preconditioned as required by the nature of the damage. The area is then mechanically cleaned as by grinding to a smooth surface and polishing with a fine abrasive to a scratch-free surface with the various layers of previously applied electroplate, such as chromium, nickel, and copper on a steel base, well feathered in.
Preferably at this juncture, but not necessarily so, a chromium band is electrolytically removed from around the damaged or defective area. The previously described hand tool, having a porous, dielectric surface, may be used for this purpose by dipping the dielectric surface into a generally alkaline solution, for example an aqueous solution of sodium hydroxide, and rubbing the chromium surface in a continuous, closed path bordering the defective area. During this time, the chromium surface is anodic. Alternatively, the brush tool may be provided with a chamber connected to a sump or storage tank from which the electrolytic solution is pumped. The chromium removal stops short of electrically removing any of the other metal undercoats, such as a nickel undercoat.
The treated surface is then subjected to an electrocleaning operation. A handtool of the type previously described is connected to a variable voltage source of direct current that is equipped with a voltmeter and an ammeter. The tool is the anode and the object having the damage surface is the cathode. The handtool is then rubbed over the treated surface. The pressure of the tool on the surface may be "light" or "soft," enough pressure being applied to insure good contact between the tool and the work. The correct pressure can be determined by watching the ammeter. With too little pressure, the current is too low, while pressure in excess of that preferably employed does not cause the current to increase in proportion to the increase in pressure. The electrolyte used for electrocleaning may be the same as that employed for chromium stripping (but at reverse current). For instance, the electrolyte may include an alkali metal hydroxide buffered with sodium metasilicate to a pH in the range of from about 9 to about 13, and preferably in the range of from about 10 to about 12. Other alkaline cleaners, such as the proprietary cleaner marketed under the trademark "Dalic" and identified as No. 1010 provides excellent results.
The rubbing action continues until the surface can be rinsed with no water breaks being visible, that is, the surface is wetted with a continuous film of the rinsing liquid. The rinse may be simply tap water. One advantage of the present process is that it eliminates the need for strong activators and their attendant need for skill and care in application.
After rinsing, the surface is again subjected to electrolysis, using a similar hand tool and following generally the same procedure used for the electrocleaning, the rubbing action again being appreciably confined to the defective area plus its surrounding band. The electrolyte employed is an acidic solution that is capable of "activating" the area to be plated. The activating solution makes the area receptive to plating, probably by eliminating oxides from the surface. The activating solution may be a solution of sulfuric acid and water. After activation, the surface is rinsed as by tap water.
Immediately after the rinsing of the treated or activated area, nickel is electrodeposited on the surface using a like handtool. If the mechanical cleaning has also removed a significant amount of a copper plate beneath the nickel plate, copper is first electrodeposited, followed by the nickel electrodeposit. In either case, the rubbing action is similar. It starts at preferably the outer periphery of the defective area and its bordering strip but remains away from the original chrome-plate, so as to avoid depositing copper or nickel onto the chromium. The entire area to be nickel or copper plated is quickly covered to prevent the surface from becoming passive. The initial nickel plating operation forms a very thin deposit of nickel, and thereafter nickel is deposited only in the area covered by the initial deposit since the remainder of the area becomes substantially passive. The rubbing action is kept slightly within the periphery of the previously activated area.
In the preferred practice of the invention, nickel is deposited by the spot-deposition technique as two distinct layers. The first deposition is a dull nickel plating followed by a bright nickel plating. The resulting duplex nickel coat assists in obtaining a bright, shiny final surface by providing a bright nickel coating on top to which the final plating of chromium is applied. On the other hand, the dull nickel undercoat is more resistant to corrosion than the bright nickel overlay. Corrosion pit formation almost inevitably starts at scratches or openings in the chromium surface and proceeds until the underlying dull nickel plate is reached. Since the bright nickel coat is more easily corroded than the dull nickel undercoat, corrosion then proceeds laterally rather than downwardly through the dull nickel plate. Penetration to the basis steel and subsequent rapid and unattractive corrosion of the basis steel are, therefore, retarded. The double nickel coat accordingly improves brightness of the plated nickel coating (which minimizes or eliminates the need to buff the nickel coating), while at the same time improving corrosion protection.
After nickel has been deposited on the surface to a desired thickness (for example, from about 0.5 mil. to about 1 mil. in the areas of thickest deposit), it is buffed, if desired, to a high polish using procedures well known in the art. The use of a double nickel coat wherein the outer coat is bright nickel can eliminate or reduce the need for such buffing. The nickel surface is then electrocleaned and electroactivated using the same techniques previously described. The cleaning and activating operations at this stage extend over the original chrome-plate surrounding the nickel, since additional chromium is to be plated on the original chrome-plate. The treated area is then immediately flushed with a rinsing solution which can be either water or a mildly acidic aqueous solution.
The entire area is then immediately swabbed with another electrode tool that is saturated with an electrolyte that is to be used in the chromium-plating operation, but with the tool disconnected from the power source. This stops the action of the activating solution but preserves the activated area in the active state, so that an adherent deposit can be obtained. The electrolyte, as herein after described, contains hexavalent chromium, but it is modified from the usual hexavalent chromium electrolyte by the addition of materials to make it suitable for brush-plating operations.
The activated surface is then chromium plated, using the hand tool that was employed to swab the area with the chromium plating solution and following the procedure as generally outlined above. However, the chromium deposit covers the repaired area, plus its surrounding border band, and contiguous or adjacent sections of the originally deposited chrome-plate. The chromium deposited by the spot-technique is substantially undistinguishable in color and texture from the surrounding original chromium and has good corrosion resistance and adhesion. The plating operation produces a matte surface chromium coating preferably having a thickness of about 0.05 mil. to about 0.15 mil. The surface is then washed and the satin or matte deposit is buffed by conventional means to a high polish.
In order that those skilled in the art may better understand how the present invention may be carried to effect, the following examples are given by way of illustration and not by way of limitations. All parts and percentages are by weight unless otherwise specified.
A typical automobile bumper having a damaged chromium surface is repaired as follows:
The bumper is straightened and the damaged surface ground away exposing a nickel or, in some cases, nickel and copper electrodeposits beneath the electrodeposited chromium, and the steel base metal beneath the electrodeposits. The grinding leaves a level semipolished surface about 4 inches in diameter, for example. The damaged area is, if necessary, precleaned using conventional solvents and cleaners, and the surface is then polished with a series of progressively finer abrasives, up to 400 grit aluminum oxide paper, and a conventional disc-type polisher until the surface to be repaired is substantially scratch-free with layers of previously applied electroplate well feathered in.
The surface is then electrolytically cleaned using a hand tool comprising a graphite electrode supporting a porous cotton tip about three-eights inch thick held in place by cotton gauze. The bumper is made the cathode in a DC circuit, and the tool the anode. The voltage of the power source is adjusted to about 18 to 20 volts. The tool is saturated with solution A set forth below and rubbed over the polished surface with a circular motion, starting at the center and working to the periphery of the prepared surface area. The rubbing is continued until the surface being cleaned is covered entirely with a uniform film of solution and no gas bubbles persist or remain on the surface. This indicates that the surface is clean. The operation ordinarily requires about 1 minute for the area in question. The average current is about 15 amperes, and the tool area in contact with the surface is about 5 square inches making the cathode current density 3 amperes per square inch. The amount of current used is about 0.002 ampere hour per square inch.
SOLUTION A
Sodium hydroxide 15 grams per liter of final solution.
Sodium metasilicate (Na 2 Si0 3 ) 10 grams per liter of final solution.
Water Remainder.
pH 11.6
Specific gravity 1.021
Either distilled water or tap water can be used.
As an example of an alternate solution A, "Dalic" 1010 Cleaner may be employed. This is a proprietary solution marketed by The Steel Improvement and Forge Company of Cleveland, Ohio.
After a water rinse of the electrocleaned surface, it is ready for the chromium-stripping step. A border or band from about 2 to 4 inches in width is wiped around the previously prepared area, stripping chromium therefrom with no appreciable attack on the other materials present or exposed on the bumper. The same type of brush tool may be used as for the plating operations. The electrolytes are generally alkaline solutions with ionizable basic compounds. For example, the electrolyte solution may be the same as solution A. The tool and solution used for stripping, however, are preferably not used for cleaning in order to avoid cross-contamination. During chromium stripping, the DC current is reversed from that normally used, that is, the bumper is anodic. The voltage is preferably about 12.5 volts, although it may range from about 5 volts to about 20 volts.
The chromium stripping is continued until all chromium within the desired area is removed and the underlying nickel and its characteristic color show. Contact with any copper plate should be avoided since some stripping of the copper could result. After the chromium-stripping step, the area is rinsed with tap water.
The surface is next activated preparatory to electroplating nickel, or copper and then nickel. The activation is accomplished with still another handtool having a graphite electrode and porous cotton tip about three-eighth inch thick. During this step the tool is the anode and the bumper is the cathode of a DC circuit. The voltage is about 7.5 volts. The tool is saturated with the following solution B and then rubbed over the surface as before, but the rubbing does not extend beyond the prepared surface onto the original chromium plate which it is desired to retain in its passive state. This operation ordinarily requires about 30 seconds. At this time, about 0.1 ampere hour of current has been passed, making the amount of current about 0.0013 ampere hour per square inch. The actual current is about 12 amperes and the area of electrode tool in contact with the work is about 6 square inches, resulting in a current density of about 2 amperes per square inch of tool.
SOLUTION B
Sulfuric acid (1.84 sp. g.) 20 ml.
Water 980 ml. As before, commercial sulfuric acid and tap water can be employed.
Whether or not a copper plate is deposited depends primarily on how much, if any, copper was removed by the mechanical cleaning step. If copper is to be plated, various well-known copper-plating solutions may be used of which the following is an example:
SOLUTION C
Copper cyanide 8 ounces.
Potassium cyanide 0.75 to 1.5 ounces.
Caustic potash 4 to 7 ounces.
Water To make one gallon.
To use solution C at the conclusion of the activating treatment with solution B, the surface is immediately rinsed with tap water. Then, with another tool having a graphite electrode, the previously activated area is plated with copper using the indicated solution.
Similarly, when nickel is to be plated, either directly after the activating treatment if no copper is to be plated, or after the copper deposition, the surface is rinsed with tap water and with another like tool, the treated area is plated with nickel using the following solution D as the electrolyte:
SOLUTION D
Nickel sulfate (NiSO 4 6H 2 0) 538 grams.
Citric acid 30 grams.
Water (distilled) To make 1.010 liter.
Excellent results results also can be obtained using as an alternate solution D is proprietary product sold under the trade name "Dalic" Nickel S.
The tool saturated with solution D is made the anode in a DC circuit in which the bumper is the cathode. The power source is set to about 15 volts, and the tool is rubbed rapidly over the entire surface to be plated. A soft, circular rubbing action is then applied starting at the periphery of the polished area and working toward the center. After the tool has warmed, the voltage may be increased to about 20 volts. The rubbing and electrodeposition are continued about 20 minutes, the tool being frequently dipped into the composition of solution D to keep it saturated. Alternatively, the solution may be pumped to the tool. A gray or matte satin nickel finish appears. At the completion of the electrolysis, 7 ampere hours have been passed in about 20 minutes, making the current about 0.25 ampere hour per square inch of plated surface. During most of the electrolysis, the actual current is preferably about 25 amperes, and the area of the electrode tool in contact with the surface is about 6 square inches so that the current density is about 4 amperes per square inch of tool.
As previously indicated, it is preferred to carry out the nickel plating as two steps. The nickel-plating step just described using solution D may be taken as one of the steps corresponding to deposition of dull nickel. A bright nickel deposition of composition known in the art can then be immediately applied, such as the following solution E.
SOLUTION E
Nickel sulfate 538 grams
Citric acid 30 grams
Saccharin (brightener) 1 gram
Water To make 1 liter.
A water rinse between the dull and bright nickel plating steps is optional. It is preferred, although not necessary, to preswab the bright nickel solution onto the area to be plated while using no plating current. Then bright nickel is electroplated over the dull nickel to a thickness of about 0.5 mil. The bright nickel deposit can have a narrowing, tapered thickness at its edges.
A voltage of 10 to 15 volts can initially be used. However, the voltage can be raised ultimately to 18 to 20 volts as the solution and bumper warm under the action of electroplating. The plating current initially should be about 7 amperes on flat surfaces and somewhat less on curved surfaces. Ultimately, approximately 20 amperes are drawn with a conventional brush type of tool applicator. The tool movement should be at a moderate speed and circular, dwelling mostly on the sanded and steel exposed area. The tool may be dipped into solution about every 10 seconds or solution may be dripped or pumped through the tool. The plating time for about 0.5 mil. may be controlled as follows:
After the bright nickel-plating step is concluded, the area should be rinsed with water to remove any electrolyte and then dried, followed possibly by light buffing prior to the chromium plating, as by a conventional buffing wheel.
The chromium plating is carried out with a handtool similar to those previously described but embodying a lead electrode and a polyester fabric or fiber pad composed, for example, of "Dacron," the pad being about one-half inch thick and covered with gauze also made of a polyester material such as "Dacron." Polyester fabrics are employed since these materials have good resistance to attack by chromic acid. Cotton, such as used with the other electrolytes, is attached by chromic acid reducing the hexavalent chromium ions to trivalent chromium which seriously interferes with the operation of the electrolyte. The tool is saturated with the following solution F electrolyte and, before the tool is connected to the power source, it is rubbed quickly over the entire surface that is to be plated. Then the circuit is completed with the tool the anode and the bumper the cathode, and the power source adjusted for an output of about 10 volts. The following electrolyte gives good results:
SOLUTION F
Chromic acid 300 grams
Sulfuric acid 1.25 grams
Trichloroacetic acid 15 grams
Trivalent chromium 5 grams
Sodium hydroxide 40 grams
Distilled water To make 1 liter. This electrolyte is of the type disclosed in Belgian Pat. No. 632,459 of May 16, 1963, with the addition of sodium hydroxide, which is essential for a good brush plating. An alternate solution F is:
Chromic acid per liter grams 400
Sodium hydroxide, per liter grams 58
Sulfuric acid (1.84 sp. gr.), per liter ml. 6
Distilled water To make 1 liter.
A satisfactory and in some respects preferred solution F can be prepared utilizing proprietary materials as follows:
Duramir 200 330 grams
Sulfuric acid (1.84 sp. gr.) 0.65 gram
Sodium hydroxide 40 grams
Trivalent chromium 5 grams
Distilled water To make 1 liter.
Duramir 200 catalyst, 19.4 units. The resulting solution contains hexavalent chromium. The sodium hydroxide is required to enable the electrolyte to be used in brush plating, to give more uniform color, and to prevent spotting.
The rubbing and electroplating operation are continued for about 10 minutes, the tool being redipped in the solution to keep the porous polyester padding saturated. After about 10 minutes, a characteristic gray satin or matte finish appears. At this point, 5.0 ampere hours have been passed making the amount of current about 0.10 ampere hour per square inch. The actual current during the electrolysis is preferably about 40 amperes. In the chromium plating, the area of the electrode tool in contact with the surface is about 8 square inches and the current density about 5 amperes per square inch. It is desirable to reduce the voltage at the end of the chromium-plating operation to about 5 volts and make a final pass with the tool around the periphery of the spot chromium deposit. In this area a ring that is visible before buffing may develop. The final low voltage pass decreases the darkness of the ring and reduces the amount of buffing that may be required to eliminate it.
The chromium plate is rinsed thoroughly with tap water, wiped dry with a clean rag, and buffed to a highly polished bright surface. The buffing is from the center outward, blending the new chromium plate with the undamaged, originally deposited chromium plate. The color of the repaired area matches that of the remainder of the chromium surface, and the repaired area is not readily detectable by visual inspection.
For a further discussion of the electroplating steps, handtools, current densities, voltages, electrocleaning, electroactivating, and related aspects, reference is made to the cited U.S. Pat. No. 3,393,134. While the practice of this patent is to overlap the areas of repair and the surrounding original chromium plated surface, the present process confines the depositions of metals, other than chromium, to within the defective area and a surrounding chromium-free strip or border. The improved practice prevents contact between copper or nickel with originally deposited chromium. Normally, it is difficult to activate such original chrome-deposit and difficult as well to secure good adherence with an additional nickel or copper deposition.
The bounds of such confinement are marked in the present invention by using a reverse current to strip chromium from around the defective area to provide effectively a barrier beyond which the electrodepostion of nickel or chromium does not extend. In particular, the chromium stripping technique eliminates the need to use stronger activators which tend to attack unintentionally adjacent areas of original chromium; reduces the amount, speed, and skill necessary to carry out the activating steps; and improves adhesion and the ability of the spot-chrome deposits to withstand corrosion in out-of-doors environment. Yet, the defective area is repaired in such a manner that the outlines of the repaired area are not readily discernible to the naked eye.
Even though chromium is deposited on the originally deposited chromium, there is no difficulty in securing good adherence as there is in the case of deposits of nickel or copper. This is thought to be due to the absence of galvanic action normally met when dissimilar metals contact each other; and also due to a much thinner layer of chromium. While deposits of copper or nickel over steel parts, such as a bumper, may each be about 1.5 mil. in thickness, the top chrome deposit may be only 0.020 mil. in thickness. Accordingly, there is a much less demand or strain on the adhesion of a chrome layer atop the original chrome-plate.
While the foregoing describes a presently preferred embodiment and several modifications thereof, it is understood that the invention may be practiced in still other forms within the scope of the following claims.