US3393134A - Method of chromium plating - Google Patents

Description

United States Patent Ofice 3,393,134 Patented July 16, 1968 3,393,134 METHOD OF CHROMIUM PLATING Benno A. Schwartz, Jr., 3278 W. 157th St, Cleveland, Ohio 44111 No Drawing. Filed Mar. 23, 1965, Ser. No. 442,161 16 Claims. (Cl. 20416) ABSTRACT OF THE DISCLOSURE A method of repairing defective areas or spots in chrome plate surfaces in which the area is mechanically cleaned, electrocleaned, electroactivated, electroplated with nickel and chromium plated with the use of a hexavalent chromium plating solution, the electrolytic operations being carried out by brush plating techniques.

This invention relates to the repair of damaged or defective areas of chromium plated surfaces using socalled brush plating techniques, and more particularly to methods and solutions whereby damaged or defective spots or areas of chromium plated articles can be repaired with good results and without requiring replating of the entire article.

Heretofore, the spot repair of damaged chromium plated surfaces has not been entirely successful. Prior processes and procedures have produced repaired areas which are more or less detectable to the eye. Among other shortcomings, the color of the repaired surface often failed to match the undamaged chromium plated surface, the juncture between the new and old plating was often visible, theadhesion of the plate to the underlying metal frequently was a problem and the underlying or basic metal was often not properly protected against corrosion.

A general object of the present invention, therefore, is the provision of a process whereby a damaged chromium plated surface may be spot repaired efficiently and at reasonable cost. Another object is the provision of a process whereby a damaged chromium plated surface may be spot repaired so that the color of the repaired surface matches the undamaged surface. Another object is the provision of a process whereby a damaged chromium plated surface may be spot repaired so that the repaired area is not detectable to the eye under ordinary conditions. A further object of the present invention is the provision of a process whereby a damaged chromium plated surface may be spot repaired using readily available equipment and materials and without requiring a high degree of skill on the part of the operator.

These and other objects are attained using a series of operations or steps which include electrolytic cleaning, activating and electroplating with hand tools which have porous dielectric surfaces that are saturated with electrolyte or other solution. Closely adjacent to the porous surface is an electrode which is 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 and are widely used in brush plating operations. The tools may be dipped into the solutions or may be provided with a chamber connected to a sump or storage tank from which solution is pumped. Cleanliness and freedom from particulate matter are important to the success of the present process; therefore, the solutions preferably should be filtered if they are to be recirculated.

The damaged area or part is first straightened, welded, brazed or otherwise repaired as required by the nature of the damage. The area is then ground away to a smooth surface and polished 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. The surface is then subjected to an electro-cleaning operation. A hand tool of the type described is connected to a variable voltage source of DC. that is equipped with a voltmeter and an ammeter, and is made the anode, the object having the damaged surface being the cathode. The hand tool is then rubbed on the damaged surface and beyond the periphery of the polished area and onto the adjacent original chromium surface a distance of about two to four inches. The pressure of the tool on the surface is light or sof enough pressure being applied to insure good contact between the tool and the work. The correct pressure can be determined by watching the ammeter on the power source; with too little pressure, the current will be too low and pressure in excess of that preferably employed will not cause the current to increase in proportion to the increase in pressure. The electrolyte advantageously includes 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, will give excellent results.

The rubbing action is continued 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 composition of the rinsing liquid advantageously consists essentially of a very dilute solution of commercial sulfuric acid in water. The acid neutralizes the alkaline film, and freedom from Water breaks gives a clear indication that the surface is free from grease.

After rinsing, the surface is again subjected to electrolysis, using a similar hand tool and following generally the same procedure used for the electro-cleaning, but the rubbing action is not extended quite as far onto the original chromium plated surface as before. 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 preferably is a solution of sulfuric acid in water, the solution containing much more acid than the rinsing solution.

The rubbing action is continued until a slight haze or change appears on the original chromium surface that surrounds the polished area. As this haze develops, there will be a light drag on the tool; the tool will not move as easily over the surface. The activating operation is then stopped and the rinsing solution is then used to rinse the surface thoroughly.

Immediately after the rinsing of the treated or activated area, a layer of nickel is deposited on the surface using a similar hand tool. The rubbing action is similar but is started at preferably the outer periphery and the entire area to be nickel plated is quickly covered to prevent the surface from becoming passive. This initial 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 passive. The rubbing action is kept slightly within the periphery of the previously activated area. The character of the nickel deposit is of importance to the success of the process. The deposit should be adherent and substantially free from stress, should initially present a matte appearance and should be soft enough so that it can be buffed to a high lustre. Examples of appropriate solutions for this purpose are given later in this specification.

After nickel has been deposited on the surface to the desired thickness (e.g., from 0.0005 to 0.0010" in the areas of thickest deposit) it is buffed to a high polish using procedures well-known to those skilled in the art. The direction of the polishing operation should be from the nickel and onto the surrounding chrome to feather out slightly the periphery of the nickel. In order to minimize the difiiculty of subsequently cleaning the buffed surface, heavily greased bufling compounds should not be employed.

The nickel surface and the immediately adjacent chromium surfaces are then electrocleaned and electroactivated as before. The cleaning and activating operations are extended an inch or two onto the chromium surface surrounding the nickel and the activation is stopped as soon as the characteristic haze appears on the chromium and the characteristic drag on the tool is felt. The area is then immediately rinsed with the rinsing solution and then the entire area is immediately swabbed with another electrode tool that is saturated with the 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 explained below, contains hexavalent chromium, but 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. The chromium deposit is extended beyond the periphery of the nickel deposit and onto the original chrome, but is stopped a little short of the periphery of the activated area. The plating operation is carried out to produce a matte surface chromium coating preferably having a thickness of the order of 0.000050" to 0.000150". The surface is then washed and the satin or matte deposit is buffed by conventional means to a high polish. If the work is done correctly, the repaired area will be undetectable, or nearly so, to the naked eye, being substantially undistinguishable in color and texture from the surrounding original chromium and having good corrosion resistance and adhesion.

In order that those skilled in the art may better understand how the present invention maybe carried into effect, the following examples are given by way of illustration and not by way of limitation. 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 the usual nickel or, in some cases, nickel and copper electrodeposits beneath the electrodeposited chromium and the steel base metal beneath the K electrodeposits. The grinding leaves a level semi-polished surface about four inches in diameter, for example. The damaged area and the adjacent area of the surrounding chromium are, 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 aluminium oxide paper, and a conventional disc type polisher until the surface to he 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 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 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 beyond the periphery of the semipoiished surface about four inches. 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. This operation ordinarily requires about one 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 .002 ampere hour per square inch.

As an example of an alternate Solution A, Dalic 1010 Cleaner, a proprietary solution marketed by The Steel Improvement and Forge Company of Cleveland, Ohio, may be employed. After the electrocleaning operation has been continued long enough so that the surface being treated is apparently clean, which ordinarily takes about one minute, the surface is rinsed with Solution B given below:

SOLUTION B Sulfuric acid (H 1.84 sp. g.) 6 ml. per liter of final solution. Water (H O) To make 1 liter. pH 1.25. Specific gravity 1.0056.

Commercial sulfuric acid and ordinary tap water can be employed.

If the cleaning operation has been carried out satisfactorily, the rinsing liquid leaves a thin continuous film with no visible water breaks.

After rinsing with Solution B, the surface is activated preparatory to electroplating with nickel. The activation is accomplished with another hand tool having a graphite electrode and porous cotton tip about thick. As before, the tool is the anode and the bumper is the cathode in a DC. circuit. The voltage is about 7.5 volts. The tool is saturated with Solution C below, and rubbed over the surface as before but the rubbing is extended about only 3 inches beyond the periphery of the previously polished area. The rubbing is continued until a light haze appears on the chromium surface adjacent the surface to be replated and adjacent the area being repaired and until the characteristic drag on the tool develops. This ordinarily requires about 30 seconds. At this time, about .1 ampere hour of current has been passed making the amount of current about .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 C ml. Sulfuric acid (H SO 1.84 sp. g.) 200 Water (H O) 800 As before, commercial sulfuric acid and tap water can be employed.

At the conclusion of the activating treatment with Solution C, the surface is immediately rinsed with more of Solution B. Then, with another tool having a graphite electrode, the previously activated area is plated with a nickel using the following Solution D as the electrolyte:

SOLUTION D Nickel sulfate (NiSO -6H O) 538 grams per liter. Citric acid (C H O 30 grams per liter. Water (distilled) To make 1.010 liter.

Excellent results also can be obtained using as an alternate Solution D under the trade name Dalic Nickel S. The tool is saturated with Solution D and made the anode in a DC. circuit in which the bumper is the cathode.

The power source is set to about 15 volts and as previously pointed out, the first operation is to rub the tool as rapidly as reasonably possible over the entire surface to be plated. A soft, circular rubbing action is then applied starting about one inch beyond the periphery of the polished area and working toward the center. After the tool has war-med, the voltage may be increased to about 20 volts. The rubbing and electrodeposition are continued about 20 minutes, the tool is frequently dipped into the solution to keep it saturated with Solution D. If the voltage and operation are carried out correctly, 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 .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.

After the nickel plating has been completed, the surface is then rinsed with tap water until the electrolyte is removed and then is wiped dry. It is good practice then to test the adhesion of the nickel plate. This may be accomplished by firmly sticking a piece of plastic electrical tape across the area that has been replated. After the tape has been pressed firmly on the surface, it is pulled off sharply at a 90 angle. The tape is then inspected. If any particles of nickel appear in the center of the tape over the repaired spot, it indicates that the procedure has not been carried out properly and the nickel must be removed by grinding and polishing and the whole process repeated. If small pieces of nickel appear near the outer edges of the tape where the deposit is on previously deposited chromium or nickel, these difiiculties are probably inconsequential and the non-adhering portions of the nickel will be removed in the following buffing procedure. However, if the foregoing procedures have been carried out correctly, there Will be little, if any, nickel adhering to the tape when it is removed.

Assuming that a good deposit of nickel has been obtained, the next step is to buif the satin-finish nickel to a bright polish. This is accomplished with a conventional buffing wheel such as a 3" to 5" diameter wheel having a thickness of 1" to 1% that is driven at 2,000 rpm. or more by an electric motor. A conventional polishing compound is spread initially on the bumper, the bufling operation is carried out from the center of the spot outwardly over the surrounding chromium. A soft circular motion is employed until the desired highly polished surface appears. The outer surface of the wheel must be kept soft and the Wheel should be periodically cleaned to prevent it becoming loaded with compound. When the color of the plating is true and all marks have been polished out, the bufiing should be completed with a clean wheel that is passed over the surface in One direction, the movement being in the same direction as the wheel is turning. Any buffing compound is removed before the final bufiing, using a clean damp rag.

Next, the area that has been nickel plated and surrounding area of the original chrome are electrocleaned as before using Solution A and rinsed with Solution B. Then the surface is activated as before with Solution C, the activating covering over the entire nickel plated surface and the adjacent chromium surface about two inches beyond the periphery of the previously ap lied nickel. The activated surface is then rinsed with Solution B and the chromium plating operation started immediately, before the surface has a chance to dry or become passive.

The chromium plating operation is carried out with a 'hand tool 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 a gauze 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 attacked 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 electrolyte which is Solution E given below, and before the tool is connected to the power source and while the surface of the work is still wet with solution B, the tool is rubbed quickly once over the entire surface that is to be plated, wetting it with solution E. 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 E Grams per liter Distilled Water, balance.

This electrolyte is of the type disclosed in Belgian Patent No. 632,459 of May 16, 1963, with the addition of sodium hydroxide, which is essential for a good brush plating. An alternate solution E is as follows:

Chromic acid, per liter grams 400 Sodium hydroxide, per liter do 58 Sulfuric acid (H SO 1.84 sp. gr.), per liter ml 6 Distilled water, balance.

A satisfactory and in some respects preferred solution E can be prepared utilizing proprietary materials as follows:

Grams per liter Duramir 200 330 Sulfuric acid (H SO l.84 sp. gr.) 0.65 Sodium hydroxide 40 Trivalent chromium 5 Distilled water, balance. 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 .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 chromium deposit. This is the area where a ring that is visible before butting develops and the final low-voltage pass decreases the darkness of the ring and reduces the amount of buffing 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 chromium plate. The color of the repaired area matches that of the remainder of the chromium surface and if the operations are properly carried out, the repaired area is not readily detectable by visual inspection.

As mentioned above, so far as I am aware, it has not been possible heretofore to make satisfactory spot repairs or secure proper adhesion on the chromium and the repaired area was always readily visible to the naked eye. Various factors contribute to the success of the present process. Attention is directed particularly to the followmg:

The preliminary preparation of the surface is important. The electrolytic cleaning operation is preferably carried out using a solution with alkali metal ions and the cleaning' is extended substantially beyond the area of the repair. While alkali metal hydroxides are preferably employed, other cleaning solutions known to those skilled in the art may be used. The activating solution is of particular importance. While steel, nickel and copper surfaces are not difiicult to plate, the activation of the surrounding chromium surface so that it will receive adherent plated coatings and so that the final chromium plate will blend into the original chromium plate is of great importance. This is carried out, as explained above, with a solution containing sulfuric acid preparatory to both the nickel and chromium plating steps. In both cases, the activating is kept to a minimum consistent with the desired result so that the original chromium plating surrounding the area that is repaired will not be damaged but will be made receptive to subsequent chromium plating. It is also to be noted that the plating takes place immediately, while the surfaces to be plated are still wet with the slightly acidic rinse.

The character of the nickel deposit is also of importance. A nickel solution is required that can be used as a brush plating solution and that will give dense, adherent deposits that are soft and relatively free from stress. It is important that the deposits be adherent and free from stress, otherwise cracks or peeling will develop and the underlying metal will corrode in service. Soft deposits are in general freer from stress than hard deposits and furthermore, the soft deposits are easier to buff to the desired polish and to feather into the surrounding and underlying original chromium.

A factor of controlling importance is the use of hexavalent chromium solutions in the process. Heretofore, so far as I am aware, hexavalent chromium solutions have not been used successfuly for brush plating, although hexavalent solutions are customarily used in tank plating. According to the present invention, known hexavalent chromium solutions are modified so that they can be used in brush plating; the resultant deposits are adherent and dense and have a good color match with the surrounding previously plated chromium that in all probability was produced by immersion plating, using a hexavalent chromium solution. The addition of sodium hydroxide to the hexavalent chromium solutions makes them suitable for brush plating. It is also important to DC. source having a low A.C. ripple factor in carrying out the chromium plating operation. Furthermore, the brush plating tool should be made with an absorbent material that will not contaminate the chromium solutions. It is for this reason that polyester materials are preferably used, since these materials are inert to the plating solution. If cotton, which is entirely satisfactory for the other solutions, were employed, the reaction between the electrolyte and the cotton would result in the introduction of an excess of trivalent chromium into the solution and reduce the effectiveness of the chromium plating operation. The voltages and currents employed give a matte surface chromium deposit which is easily buffed to a bright condition that matches the originally plated chrome and which is more adherent and freer from cracks than bright deposits of chromium.

In carrying out the entire operation, it is desirable to keep the solutions free from particulate matter and other contaminants, and while the work is often done under adverse conditions in the ordinary automobile shop, efforts should be made to keep the solutions and tools clean and to avoid mixing and contamination.

Another characteristic feature of the present invention is the extent of the areas which are mechanically ground and polished, electrocleaned, electroactivated and electroplated. The area which is mechanically ground and polished of course encompasses the damaged area that is to be repaired and goes far enough beyond the damaged area so that the various existing layers may be feathered into each other. Thus, the center may be bare steel surrounded by copper (if the original part embodied an electroplated copper substratum), then nickel and finally the original chromium plate. This mechanically polished area is plated with nickel and the nickel is extended slightly over the original chromium plate. The final chromium plating covers all of the nickel and extends slightly over the original chromium plate so that it can be blended into the original chromium.

In carrying out the electrolytic operations, the area which is electrocleaned is the greatest, extending substantially beyond the periphery of the mechanically polished area onto the undamaged chromium surface for a distance of, for example, 3" to 6". The area which is activated to receive the plating is extended beyond the periphery of the original mechanically polished surface but preferably stops 1 to 1 /2 inches short of the periphery of the cleaned area. The electrodeposit of nickel extends beyond the periphery of the semi-polished surface onto the undamaged surrounding chromium surface that has been activated but preferably not more than about 1 to 1 /2 inches onto the chromium. The chromium deposit covers significantly beyond the nickel, preferably 1 to 1% inches. The chromium deposit should not extend beyond the activated area and preferably is kept about 1 inch short of the boundary of the activated area.

The conditions employed in carrying out the electrolytic operations may be varied within reasonable limits and permit the use of readily available equipment. However, as previously noted, the power supply should have a low A.C. ripple content, preferably less than 15% and advantageously about 4%. Advantageously, the entire process is carried out without the application of heat other than that developed during the operation. The solutions may be kept at normal room temperatures, preferably at temperatures in the range of from about 50 F. to about F. During the electrolysis, there is a noticeable elevation in temperature by the flow of electric current, particularly during the nickel deposition. The temperature of the electrolyte may rise to as high as 200 F. increasing the conductivity of the electrolyte and the permissible maximum current densities, thus permitting acceleration of the deposition of the nickel.

The voltage of the source should be adjustable from about 5 volts to about 30 volts. In the case of the nickel plating, the nickel begins burning at progressively lower current densities with progressively lower temperatures. This effect is predominant over the effect of temperature on current density. In practice, therefore, the nickel should be started at lower voltages when the temperature is lower. When the conductivity of the solution is low because of low temperatures, it may be desirable for the cleaning and activating and chromium plating operations to use higher voltages initially than those specified heretofore in order to force sufficient current through the electrolyte to start the electrolysis. This is well known to those skilled in the art.

The optimum operating current densities for carrying out the electrolysis for each of the steps of the process are of the order of the current densities heretofore set forth. Preferably, the current density for effectively electrocleaning the surface is in the range of a minimum of about 2 amperes per square inch of tool surface. The maximum is limited only by the heating effect on the electrolyte. The amount of current ordinarily necessary for cleaning depends on the degree of cleanliness of the original surface but it is at least .003 ampere hour per square inch for an apparently clean surface.

The current densities preferably used for activating are preferably in the range of from about 1 ampere per square inch to about 3 amperes per square inch of tool surface. The amount of current usually necessary for activating is about .001 ampere hour per square inch. Too much or too prolonged activating removes chromium from the surface without any advantage and in fact with some disadvantages. Therefore, the activation should be stopped as soon as the characteristic haze appears on the chromium surface.

In the electrodeposition of nickel, electrolyte temperatures of 130 to 190 F. and higher current densities short of the point of burning are advantageously used. Heat develops quickly during the nickel plating and the heat developed from the current is generally adequate. When the solution and part are cold, current density preferably should not be higher than about 2 amperes per square inch of tool. When a temperature of about 130 F. or higher is reached, the current density can range from 3 to 8 amperes per square inch of tool area. Preferably the current density should be in the range of from about 4 amperes per square inch to about 6 amperes per square inch of tool area during the major portion of the plating operation. The thickness of the nickel layer should be kept bet-Ween 0.0005 inch and about 0.0015 inch for best results. The amount of current required for such thicknesses of nickel is in the range of from about .125 ampere hour per square inch to about .375 ampere hour per square inch.

In depositing chromium, the preferred current densities are in the range of from about 2 amperes per square inch to about 10 amperes per square inch of tool area. Preferably, the chromium is deposited with current densities in the range of from about 3 amperes per square inch to about 6 amperes per square inch. The thickness of the chromium layer is preferably in the range of from about 0.000050 inch to about 0.000150 inch. The amount of current necessary for obtaining thicknesses in this range is from about 0.05 ampere hour per square inch to about 0.15 ampere hour per square inch. Greater thickness of chromium does not improve the final result and costs more in plating and buffing time.

The hand tools used for carrying out the present process are well known to those skilled in the art. Generally, the tools include anodes which are for all practical purposes inert and insoluble in the electrolyte solution with which they are to be used. For the electrocleaning, activating and the electrodeposition of nickel, the anode preferably is composed of graphite. Other materials, however, such as, for example, platinum, platinum on titanium or atntalum, rhodium on titanium or tantalum, or lead may be used. For the electrodeposition of chromium, the anode is preferably made from lead. Graphite, carbon, platinum, platinum on titanium and the like, however, may be substituted. The working area of the electrode preferably is about 4 to 10 square inches. For the electrocleaning, activating and nickel plating operations, the porous absorbant material is preferably cotton batting held in place by cotton gauze. For electroplating of chromium, a polyester fiber batting such as Dacron held in place by a polyester gauze is employed. Undoubtedly, other materials that are inert to the various electrolytes could be used with success.

The tools preferably are moved at speeds of about 4 to 10 inches per second during the various operations, and are kept well saturated with the several electrolytes by frequent dipping into the supplies. Current densities can be increased with more rapid movements of the tools.

While preferred embodiments of the invention have been disclosed, other modifications and variations thereof are undoubtedly possible. The scope of the invention is defined by the appended claims.

I claim:

1. A method for repairing a defective area in a chromium plated suface which includes, in order, the steps of mechanically grinding and polishing the surface to remove the defective plating in the area to be repaired, electrocleaning the defective area and the surrounding original chromium plated area by means of a brush plating tool, the tool the anode and the surface the cathode, electroactivating the electrocleaned surface by means of a brush plating tool with the tool the anode and the surface the cathode, electroplating nickel on the activated area by means of a brush plating tool, the nickel plating extending over the previously damaged surface and onto the surrounding original chromium area, polishing the electrodeposited nickel, electrocleaning and electroactivating the nickel deposit and the surrounding chromium area as before, and chromium plating the nickel deposit and the immediately surrounding activated area of the original chromium by a brush plating operation employing a hexavalent chromium plating solution, and finally polishing the chromium deposit.

2. A method according to claim 1 wherein the activating solution consists essentially of a solution of sulfuric acid in water.

3. A method according to claim 2 wherein the activating solution consists essentially of a solution of 200 ml. per liter of sulfuric acid of 1.84 specific gravity in water.

4. A method according to claim 1 wherein the cleaning is carried out with a solution consisting essentially of a solution of sodium hydroxide and sodium metasilicate in water.

5. A method according to claim 1 wherein the nickel plating is carried out with a solution consisting essentially of nickel sulfate, citric acid and water.

6. A method according to claim 1 wherein after the electroactivating operations and prior to the nickel plating and chromium plating operations, the surface is rinsed with :a dilute acidic solution.

7. A method according to claim 6 wherein the dilute acidic solution consists essentially of 6 ml. per liter of sulfuric acid of 1.84 specific gravity in water.

8. A method according to claim 1 wherein the hexavalent chromium solution contains sodium hydroxide.

9. The method of brush electroplating a chromium surface with an additional adherent deposit of chromium which includes the steps of electroactivating the previously deposited chromium surface with a solution of sulfuric acid employing a brush plating tool in which the brush plating tool is the anode and the work the cathode, rinsing the surface with a dilute solution of sulfuric acid and brush plating a coating of chromium over the activated surface using a solution containing as essential ingredients hexavalent chromium, sodium hydroxide and sulfate ions.

10. The method according to claim 9 wherein the electroactivating operation is stopped substantially as soon as a haze appears on the surface of the previously deposited chromium.

11. The method according to claim 10 wherein the surface to be chromium plated is swabbed with the chromium plating electrolyte immediately after activating and rinsing and the brush electroplating operation is started immediately thereafter.

12. The method according to claim 11 wherein the tool is connected to a DC. source having less than 15% AC. ripple.

13. The method according to claim 12 wherein the voltage is about 10 volts and the current density about 5 amperes per square inch of tool area.

14. The method according to claim 13 wherein the brush plating tool embodies an absorbent pad composed of polyester fibers.

15. A process for repairing a defective area in a chromium plated surface of an object which comprises in sequence:

(1) grinding said defective area to expose a semipolished underlying surface;

(2) electrocleaning said semi-polished surface and the surrounding area by making said surface the cathode in an electric circuit, providing an anode, spacing said anode from said surface, maintaining a porous dielectric material between and touching said surface and said anode, saturating said material with an alkaline aqueous solution, and rubbing said surfce with said porous material whereby said solution is subjected to electrolysis at said surface;

(3) rinsing said surface with a weakly acidic solution;

(4) activating said surface and the surrounding area by making said surface the cathade in an electric crcuit, providing an anode, spacing said anode from said surface, maintaining a porous dielectric material between and touching said anode and said surface, saturating said porous dielectric material with an activating solution consisting essentially of an aqueous solution of sulfuric acid, and rubbing said surface with said porous material;

(5) rinsing said surface with said weakly acidic solution;

(6) electrodepositing nickel on said surface and the immediately adjacent chromium area by making said surface the cathode in an electric circuit, providing an anode, spacing said anode from said surface, maintaining a porous dielectric material between and touching said anode and said surface, saturating said porous dielectric material with an aqueous solution containing nickel ions and rubbing said surface with said porous material whereby a layer of nickel is deposited on said surface;

(7) rinsing said surface with water;

(8) drying said surface of said nickel layer;

(9) bufiing said surface of said nickel layer to a bright finish;

(10) electrocleaning the surface of said nickel layer using the procedure of step 2;

(l1) rinsing said surface of said nickel layer with said weakly acidic solution;

(12) activating said surface of said nickel layer and a portion of the surrounding chromium using the procedure of step 4;

(l3) rinsing said activated surface with said weakly acidic solution;

(14) electrodepositing chromium on said surface of said nickel layer and the immediately surrounding chromium by making said surface the cathode in an electric circuit, providing an anode, spacing said anode from said surface, maintaining a porous dielectric material between and touching said anode and said surface of said nickel layer, saturating said porous material with a hexavalent chromium plating solution, and rubbing said activated surface of said nickel layer and the surrounding chromium with said porous material whereby a layer of chromium is deposited;

(15) rinsing the surface of said chromium layer;

(16) drying said chromium layer; and

(17) buffing said surface of said chromium layer to a bright finish.

16. A process for repairing a defective area in a chromium plated surface which comprises:

(1) mechanically grinding and polishing the surface to remove the defective plating in the area to be repaired;

(2) electrocleaning the defective area by means of a brush plating tool comprising a graphite electrode and an absorbent porous dielectric material, making the tool the anode in a DC. circuit, making the surface the cathode in the circuit, substantially saturat- 2 amperes per square inch of tool surface in contact with the work, the rate of rubbing being in the range of from about 4 inches per second to about 10 inches per second;

(3) rinsing said surface with an aqueous solution consisting essentially of about 6 ml. per liter of commercial sulfuric acid and the balance water;

(4) electroactivating the electrocleaned surface using the procedure of step 2 but employing a solution consisting essentially of about 200 ml. commercial sulfuric acid having a specific gravity of 1.84 and 800 ml. of water, and stopping the activation when a haze appears on the chromium area surrounding the defective area;

(5) rinsing as in step 3;

(6) immediately electroplating nickel on the major portion of the activated area using the procedure outlined in step 2 but with a solution consisting essentially of about 538 grams per liter of nickel sulfate (NiSO -6H O), and 30 grams per liter of citric acid, the current density being in the range of from about 3 to about 4 amperes per square inch of electrode surface, rubbing the tool over the defective area and a portion of the activated area of chromium surrounding the defective area but stopping the tool short of the periphery of the activated area and providing a nickel deposit having a thickness of from about 0.0005" to about 0.0010" having a matte appearance;

(7) rinsing the resultant nickel deposit with water;

(8) drying the nickel deposit;

(9) bufling the nickel deposit until it has a polished surface;

(10) electrocleaning the nickel surface as in step 2;

(11) rinsing as in step 3;

(12) electroactivating the nickel surface and the surrounding chromium surface for a distance of about 2 to 3 inches beyond the periphery of the nickel deposit as in step 4;

(l3) rinsing as in step 5;

(l4) electroplating chromium using the procedure outlined in step 1 but with a solution containing as essential ingredients hexavalent chromium, sodium hydroxide and a small amount of sulfate ions, the rubbing action of the tool being extended beyond the periphery of the nickel plated area a distance of from about 1 inch to about 1 /2 inches but stopping short of the periphery of the activated area;

(15) rinsing the resultant chromium deposit as in step 7; and

(16) bufiin-g said chromium deposit.

References Cited UNITED STATES PATENTS 2,046,440 7/1936 Adey 204--l5 2,118,956 5/ 1938 Wagner 204-32 2,145,518 l/1939 Lindh 20436 2,965,551 12/1960 Richaud 204-32 2,992,171 7/ 1961 MacLean 20432 3,313,715 4/1967 Schwartz 204-15 FOREIGN PATENTS 848,585 9/ 1960 Great Britain.

OTHER REFERENCES Polishing and Bufiing for Chromium Plating, Eldridge, C. H., Metal Industry, vol. 26, No. 6, June 1928, pp.

The Effects of Various Surface Treatments in Cleaning and Preparing, Copper, Nickel and Steel for Chromium Plating, Metal Finishing, August 1946, pp. 340-345.

JOHN H. MACK, Primary Examiner.

HOWARD S. NVILLIAMS, Examiner.

T. TUFARIELLO, Assistant Examiner.