US3157585A

US3157585A - Chromium plating

Info

Publication number: US3157585A
Application number: US860436A
Authority: US
Inventors: Rollie P Durham
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1959-12-18
Filing date: 1959-12-18
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

Nov. 17, 1964 TEM/EPA TURE- "F R. P. DURHAM CHROMIUM PLATING Filed Dec. 18, 1959 TEMPEPA TURE- F .7@ Z l y/Z- Cros IN VEN TOR.

ATTORNEY United States` Patent Oiice 3,157,585 Patented Nov. 1,'7,V 19:64

3,157,585 CERMIUM PLATlNG Rotlie P. Durham, Flint, Mich., assigner to General Motors Corporation, Detroit, Mich., a corporation of Dei-aware Filed Dec. 18, 1959, Ser. No. 860,436 Ciaims. (Cl. 2114-41) This invention relates to electroplating and more particularly to chromium plated articles of exceptional durability and to a method of forming such articles.

The present disclosure is a continuation-in-part of my co-pending United States patent application Serial No. 812,081, which was filed on May 1l, 1959, and assigned to lthe assignee of the instant patent application.

Since the initial use of chromium in decorative plating, the probiem of obtaining decorative coatings of satisfactory durability has been a problem. Moreover, for unknown reasons the quality of a chromium coating will vary from time to time even though the coatings are deposited from the same solution apparently under exactly the same conditions.

Accordingly, it is a primary purpose of this invention to provide decorative chromium plated parts which exhibit vastly improved durability and to provide a method of forming such articles with an unusual degree of consistency.

in general my invention involves forming decorative chromium plated parts by applying at least two chromium.

layers of different characteristics to a suitably prepared surface of a part. Acareful selection of the individual layers used in accordance with the invention permits the consistent formation of chromium plated parts which are not only more durable than conventionalchromium coatings but also permit chromium plated steel parts to be produced which do not fail to red rust under comparatively severe corrosion testing.

rlie preparation of the part` prior to applying my chromium coating is as important to my invention as it is to conventional chromium plating. Accordingly best durability has been obtained when' protective surface coatings interjacent the chromium coating and the surface of the metal part are used. For example, I prefer to apply the dual layer iilm to a steel part which has been coated successively with copper and nickel in the known and accepted manner of preparing steel parts for chromiumV Oz./ga1. Sodium orthosilicate 8 Tetrasodium pyrophosphate 1 Sodium carbonate 1 Using a bath temperature of approximately 160 F. to 180 F. the workpiece is subjected to an anodic potential for 60 seconds to 70 seconds with a current density of approximately 50 amperes per square foot to 100 amperes per square foot.

After the anodic cleaning the part is then thoroughly rinsed in cold water and then immersed for approximately 40 seconds in a room temperature aqueous bath containing 25% muriatc acid, by volume.

Subsequently the part is removed from the muriatic aoid bath and thoroughly rinsed. The part is thenanodically cleaned a second time in the manner described above but only for approximately 30 seconds. It is then removed from the anodic cleaning bath and again rinsed and immersed for about l0 seconds in the muriatic acid bath andVv then thoroughly rinsed.

After cleaning, the workpiece is preferably immersed in a copper or nickel strike solution to insure good adherence of subsequently eletrodeposited coatings. One such solution which can beemployed to apply a thin coating of copper to the part contains the following in gradients:

Oz./ gal.. Copper cyanide 2-4 Sodium cyanide (free) 1.5-2 Caustic soda. 2-3

sion for about 10 seconds in this bath, which is at rooml temperature, aids in keeping the copper surface active to improve adhesion of the subsequently applied thicker copper coating. The part is then removed from-the sulfuric acid bath, rinsed and immersed in an acid copper plating solution. A suitable acidcopper bath has aV composition as follows:

Cupric sulfate (hydrate) ..-oz/gal.- 22-26 Sulfuric acid (concentrated) oz./ gal-- 8 Thiourea oz.'/Ual 0.000589" Sodium lauryl sulfate oz./gal 0.00566 Molasses ml /1 .25

With air and cathode rody agitation, directV electric current is passed through theY solution and copper anodes soas to impose a negative potential on the workpiece for a sucient duration to depositVv a copper coating of atV least about 0.0015 inch. The bath is preferably maintained at a temperature of approximately 70 F. to 90 F. while the cathode current density is maintained at approximately 50 amperes per squarefoot.`

Although in some instances the workpiece can be'V nickel plated directly after removal, most generally it is preferred to buff the copper coating bath prior to immersion in a nickel plating solution.A After buing,..of course, the workpieceV must be cleaned agairrto prepare. the copper surface for reception of thenickel plate.,

As the initial cleaningthis latter cleaning. can be accomplished satisfactorily in the normalV and accepted manner for such cleaning, such as by a cathodic electrolysis, an anodic electrolysis, and an acid dip. Thus, afterbufiing the part is electrolyzed for 30 seconds to 60 seconds; in an aqueous bath having about 2 ounces per` gallon to 6 ounces per gallon of a mixture containing, by weight, about 55% soda ash, 25% trisodium orthophosphate and 20% caustic soda. Using a bath temperatureof about. F., a negative potential is imposed on the workpiece sulicient to cause acathode current density of `about.50 amperes per square foot.

The part is then anodically cleaned in the manner described above for about 30 secondsrinsed and then dipped in a dilute, sulfuric acidsolution (1% HSO4, by volume, v

electroplating tank. One such solution which is suitable for depositing bright metal has the following ingredients:

Nickel sulfate (hydrated) oz./gal 30-50 Nickel chloride (hydrated) oz./ gal-- 4-10 Boric acid oz/gal-- 5-8 Wetting agent oz./gal 0.00566 Primary brightener g./ 1 .2-5 Secondary brightener mg./l 2-100 Direct electric current is passed through the solution with cathode rod agitation so as to impose a negative potential on theV part for a sucient duration to deposit a nickel coatingof at least about 0.0005 inch. The'fbath is preferably maintained at a temperature of approximately 120 F. to 150 F. and the cathode current density is maintained at approximately 40 amperes per square foot to 60 amperes per square foot.

When a sufiicient thickness of nickel has been deposited on the part, it is removed from the nickel electroplating bath, rinsed and placed in contact with a suitable chromium plating solution.

With'the preliminary copper and nickel layers applied,

,a pluralityof chromium layers is then deposited thereover.

The use of a plurality of chromium layers to improve durability of a decorative chromium plated part is known in the art. However, the plurality of layers applied by prior procedures does not present the material improvements in durability such as are obtainable with my invention. I have found that remarkable increases indurability 'of the part are obtained when the part is coated with a plurality of chromium coatings having different characteristics.

, It is well known that chromium layers deposited from different bath compositions and even from the same bath under different conditions may have distinctly different characteristics. I have found that some combinations of chromium layers having certain'characteristics will produce a Vremarkably unexpected improvement in corrosion resistance not obtainable by other combinations of chromium layers. For example, I have found that the marked increases in corrosion resistance can be obtained in a dual layer chromium coating if the rst layer (Layer A) is electrodeposited from a sulfate catalyzed chromium plating bath, and the second or outermost layer (Layer B) is electrodeposited from an aqueous bath formed in accordance with United States Patent No. 2,640,022, Stareck. The following Baths I and II Will serve as specific examples, respectively, of suitable baths for electrodepositing Layers A and B:

Bath I The initial chromium layer (Layer A) is deposited from VBath I under a cathode current density of approximately 140 amperes per square foot at a bath temperature of approximately 120 F. for approximately 5 Vminutes to 6 minutes to produce a minimum coating thickness of at least 0.000015 inch.V The part is then thoroughly rinsed and directly passed into Bath II Which is maintained at a temperature of approximately 120 F. The bath is electrolyzed at a cathode current density of approximately 125 amperes per square foot for a sufficient duration to obtain a minimum coating thickness of about 0.000015 inch.

Although optimum results are obtained by applying Layer `A in the manner indicated above, improvements Y can be obtained using any of the bath formulations and conditions which are generally satisfactory forapplying single coatings ofV chromium from a sulfate catalyzed bath. Generally Layer A can be formed in theV normal and accepted manner of electrodepositing chromium from a sulfate catalyzed bath. In most instances highly satisfactory results are obtained with my invention if Layer A is deposited from the sulfate catalyzed bath in the mannery which would provide best durability if Layer A were used as a single layer. The chromium coating of this example of my invention generally provides optimum results if Layer A is deposited Ywith as sparse a crack pattern as possible.

. Similarly, the composition of Bath Il, as well as the conditions of using it, ca n be varied. The composition of Bath 1I and its conditions of use can vary generally as described in United States Patent No. 2,640,022, Stareck.

These variations are as material to the subject invention as they are to conventional chromium plating to obtain maximum durability. In most instances optimum results are obtainedwhen Layer B is deposited so as to have a relatively dense crack pattern when compared to Layer A.

'It has also been found that the advantages of my invention can also be obtained using a bath compositionV made up in accordance with the aforementioned United States Patent No. 2,640,022, Stareck, hereinafter listed as Bath IV, in conjunction with a bath composition and method of chromium plating such as described in United States Patent No. 2,916,424, Stareck et al., hereinafter listed as Bath III. The immediately following disclosure of Baths III and IV and the method of using same is presented to serve as a specific example of this embodiment of the invention.

The initial chromium layer (Layer A) is deposited from Bath III under a cathode'currentdensity of approximately 220 amperes per square foot at a bath temperature of approximately F. for a'suiiicient duration to produce a minimum coating thickness of about 0.000015 inch. The bath was then Vthoroughly rinsed and directly passed into Bath IV which was maintained at a temperature of approximately 120 F. Bath IVv was then electrolyzed at a cathode current density of approximately 200 amperes per square foot for a suthcient duration to abtain a minimum coating thickness'of approximately 0.000015 inch.

The sulfate ion concentration in Bath III was attained by adding suitable amounts of sulfuric acid to the bath solution which was previously saturated with strontium sulfate. The silicouoride ion centration was attained using K2SiF6.

The aforementioned United States Patent No, 2,916,- 4124, Stareck et al., is specifically directed toV providing a process for plating crack-free chromium surfaces of mir- Y modified by depositing a lesser thickness of chromium.`

As indicatedV above, significantly improved results have been obtainedwhen the deposit of the Layer A chromium is only about 0.000015 inchV in thickness.

The aforementioned United States Patent No. 2,916,- 424, Stareck et al., discloses a relationship pertinent to Bath Il] between temperature, concentration and ratio, such as illustrated by FIGURES 1 and 2. The sulfate and silicofluoride ions in Bath III are referred to as catalyst ions. The term ratio as used in the discussion of FIGURES 1 and 2 refers to the ratio of the weight of Cr03 to the weight of the catalyst ions in th bath.

Stareck et al. disclose that bright, crack-free chromium can be electroplated at temperatures between 112 F. and 119 F. as shown in FIGURE 1 by using a high ratio. FIGURE 1 also indicates that at 115 F. a ratio of about 115:1 is the limiting ratio whereas at 112 F. it is 150:1. It is further stated that in many combinations of the three variables; temperature, concentration and ratio, electrodeposition of bright, crack-free chromium between the temperatures of 117 F. and 135 F. is preferred. It is preferred to utilize Cr03 concentrations between about 250 grams per liter and about 425 grams per liter within this latter temperature range; the relationship between the three variables being dened by the areas enclosed by the curve in FIGURE 2. Within the enclosed area ABC in FIGURE 2, ratios of 80:1 and 150:1 may be used. Within the area deiined as ABD, the preferred range of ratios is narrower with the limiting preferred range at the line ADB being 115:1 to 150:1.

It is further stated that bright, crack-free chromium can be deposited at a maximum thickness when plating with the rectangular area'ABCD of FIGURE 1 at ratios between about 105:1 to 135:1, wherein baths having a CrO3 concentration between about i275 grams per liter and 400' grams per liter and plating temperatures of about 125 F. and 138 F. are used.

When the temperatures and the Cr03 concentrations are maintained within the area defined by the closed curve ADFG in FIGURE 1, it is stated as possible to deposit bright, crack-free chromium in all ratios between 80:1 and 150:1.

The advantages of the invention have also been btained by applying a chromium coating having a plurality of alternately different chromium layers using two sulfate catalyzed chromium plating baths having compositions as follows:

The initial chromium layer (Layer A) was deposited from Bath V, which was at a temperature of approximately 102 F. to 106 F., under a cathode current density of approximately 108 amperes per square foot. The bath was electrolyzed for approximately 71/2 minutes to apply a minimum coating thickness of about 0.000015 inch. The part was then removed from Bath V, thoroughly rinsed and placed in Bath VI, which Was at a temperature of approximately 122 F. to 126 F. The second layer (Layer B) was deposited from Bath VI under a cathode current density of 144 amperes per square foot for approximately 5 minutes to obtain the minimum Layer B thickness of about 0.000015 inch.

Layer A should be deposited with a relatively sparse crack pattern while Layer B should be deposited with a comparatively dense crack pattern. Baths V and VI can be varied to some extent without losing the benelits of the invention. For example Layer A and Layer B can,

6. respectively, be satisfactorily formed'using bath compositions and conditions such as follows:

Bath I/(A) Chromic acid 20-35 oz./gal. Sulfuric acid .20-.35 02./gal. Temperature F.-1 115 F. Average cathode current density 90 a.s.f.-140 a.s.f.

Bath Vl (A) Chromic acid 40-70 oz./ gal. Sulfuric acid .4S-.70 oz./gal. Temperature F.-l50 F. Average cathode current density asf-300 a.s.f.

As previously indicated, the material advantages of the invention are obtained with a coating composed' of alternate layers of two diiferent types of chromium deposits. These advantages can be obtained with two or more layers of chromium provided that the necessary relationships between contacting chromium layers are present. In analogous arrangement, in certain instances, more than two distinctly different types of deposits may be used to obtain the unexpected benefits. The different types of deposits may be formed with diierent or similar bath solutions. It is known that a plurality of chromium coatings having significantly different characteristics may be deposited from the same bath by adjusting the conditions of deposition. Should these latter coatings be of the' required character, they may be used to practice the invention.

The peculiar durability ofthe product of my invention appears to be associated with relative crack pattern and nobility characteristics of the chromium layers. Moreover, the relative nobility of the chromium layers to a subjacent nickel layer is believed to be important to 0btain optimumdurability of steel parts without corrosion failure to red rust. By the use of the term noble or nobility I refer to relative differences between the electromotive potentials of two metals. A metal of lesser nobility than another would be one which would exhibit an anodic potential with the other metal when the two metals comprise a voltaic cell.

Especially high corrosion resistance was obtained when one of the chromium layers, particularly Layer A, was of a lesser nobility than the activated nickel layer. Satisfactory results may be obtained when both Layers A and B are of a lesser nobility than the activated nickel layer. However, optimum results were obtained when Layer B was more noble than the nickel layer and Layer A was less noble than the nickel layer.

It is generally preferred that there be differences in the nobility of the respective chromium layers as they exist in the multilayer coating. ln most instances best results were obtained when these differences were approximately 0.025 volt to 0.150 volt and in certain instances diierences as great as 0.175 volt may be used. Moreover, it is preferred that Layer A, when active, be less noble than the nickel layer, when active. Differences in electro-motive potential between these latter two layers, when activated, from about 0.025 vol-t to 0.10 volt and even as high as 0.13 volt are useful in obtaining the advantages of the invention. l

Moreover, it is generally preferred that the two chromium layers of a dual chromium coating have dilerent crack patterns. Preferably one of the layers should have a dense microscopic crack pattern while the other of the chromium layers has a comparatively sparse crack pattern. Improved results can be obtained if Layer A has afine crack pattern and Layer B is virtually crack-free. However, optimum results are obtained when the outermost chromium layer (Layer B) has the ne crack pattern and Layer A has a-comparatively sparse crack pattern. Although it is preferred that Layer B have a crack pattern which is approximately 30 to 100 times denser than that of Layer A, in some instances it may be preferred to employ rfoi-.Layer B 4a crack patternwhich is only 5 times denser than that of Layer A or as much as 125 times denser than that of Layer A. Improved results may be obtained when Layer B has from about 50 to 1200 cracks per lineal inch. Y

Most generallyV l prefetto employ the more favorable relative crack' pattern relationship and nobility relationship hereinafter described in combination to obtain opti- Vper square foot from a bath at a temperature of approximately 95 F. to 115 F. containing approximately 20 ounces per gallon to 3S ounces per gallon (lr03 and about .2() ounce per gallon (avdp.) to .35 ounce per gallon (avdp.) YH2804, and then, without intervening abrasive treatment of said chromium plated surface and under an average cathode current density of approximately 130 amperes per square foot to 300 amperes per square foot, electrodepositing onto said rst layer a second decorative chromium layer which has-a denser crack pattern than said first layer using a bath at a temperature of approximately 120 F. to 150 F. containing about 40 ounces per gallon to 70 ounces per gallon CrO3 and .45 ounce per gallon (avdp.) to .70 ounce per gallon (avdp.) H2804.

2. The method of forming a highly durable multi-layer decorative chromium plated article which comprises successively electrodepositing a nickel coating and two different decorative chromium layers without intervening abrasive treatment of the iirst chromium plated layer before application of the second chromium layer, wherein the first of said layers is electrodeposited from an aqueous bath solution which is at a temperature between 112 F. and 140 F., said bath containing less than 0.05 gram per liter of chloride ion and comprising essentially between 180 grams per liter and 540 grams per liter of Cros, a total catalyst ion concentration of between 1.2 grams per liter and 6.3 grams per liter of sulfate and silicouoride ions, the ratio of (lr03 concentration to total catalyst ion concentration being between and 85% ofthe total catalyst concentration, the (lr03 concentration, ratio and temperature havinga relationship deiined by the areas enclosed by the curves in FIGURE 1 and the Second of said layers is electrodeposited from an aqueous chromium plating bath containing about 100 grams to 500 grams per liter of CrO3, two catalyst-supplying compounds, and a soluble, non-catalytic compound, one of said catalyst-supplying compounds being strontium sulfate in an amount suicient to saturate said bath and to provide an undissolved residue of strontium sulfate in the bath, the other of said catalyst-supplying compounds being an alkali metal silicofluoride in an amount sufficient to saturate said bath and to provide an undissolved residue of alkali metal silicoiuoride in the bath, said alkali metal being selected from the class consisting of potassium and sodium, said non-catalytic compound being a strontium compound in an amount sufficient to suppress the concentration of said strontium sulfate in solution in said bath from the unsuppressed saturation concentrationof the latter compound to a lower but' greater than zero concentration. Y Y Y 3. The method of forming a highly durable multi-layer decorative chromium plated article which comprises successively electrodepositing a nickel coatingand'at least two different decorative chromiumlayers without intervening abrasive treatment of the first chromium plated layer before application of the second chromium layer, wherein the iirst applied Vof said layers is electrodeposited from an aqueous bath solution which is at a temperature between 117 F. and 135 F., said bath containing less than 0.02 gram per liter'o'i chloride ion and comprising essentially between 250V grams lper liter and 425 grams per liter of C1O3, a total catalyst ion concentration of sulfate and silicoiluoride'ions to achieve a ratio of CrO3 concentration to total catalyst ion concentration between :1Y and 150:1, the sulfate ion content being between 35% and 75% of the total catalyst concentration, the CrO3 concentration, ratio and temperature having a relationship defined by the areas enclosed by the-curves inl l FIGURE 2 and the second applied of said layers is electrodeposited from a bath solution containing about grams to 500 grams per liter of CrO3, two catalystsupplying compounds, and a soluble, non-catalyticV compound, one of said catalyst-supplying compounds being strontium sulfate in an amount sufficient to saturate said bath and to provide an undissolved residue of strontium sulfate in the bath, the other of said catalyst-'supplying .compounds being an alkali metal silicouoride in an amount suilcient to saturate said bath and to provide an undissolved Vresidue of alkali metal sicofluoride in the bath, said alkali metal being selected from the class consistingV of potassium and sodium, said non-catalytic compound being a strontium compound in an amount sutcient to suppress the concentration of said strontium sulfate in solution in said bath from the unsuppressed saturation concentration of the latter compound to a lower but greater than zero concentration.

4. The method of forming a highly durable decorative.

plating bath solutionV at a temperature between 112 F.

and F. said bath containing less than 0.05 gram per liter of chloride ion and comprising essentially between grams per liter and 540 grams per liter of CrO3, a total catalyst ion concentration of between 1.2 grams per literV and 6.3 grams per liter of sulfate and silicouoride ions, the ratio of CrO3 concentration to total catalyst ion concentration being between 80:1 and 150:1, the sulfate ion content being between 20% and 85% of the total catalyst concentration, the Cr03 concentratiom ratio and temperature having a relationship defined by the areas enclosed by the curves in FGURE 1, the sulfate in said bath being added in the Vform of strontium sulfate and silicoiiuoride added in the form of potassium silicofluoride, each in an amount sufficient to saturate said bath and to provide therein an undissolved residue of strontium sulfate and potassium silicouoride respectively, and a soluble non-catalytic potassium compound to suppress'the concentration of silicofluoride ions, the second applied of said layers being deposited from a chromium platingV bath solution containing about 100 grams to 500 grams per liter of' (lr03, two catalyst supplying compounds, and a soluble, non-catalytic compound, Vone of said catalystsupplying compounds being strontium sulfate in an amountV A sumcient to saturate said bath and to provide anV undissolved residue of strontium sulfate in the bath, the other of said catalyst-supplying compounds being an alkali metal Vsilicotiuoride in an amount sulicientto saturate saidbath and to provide an undissolved residue of alkaii metal `silicoiuoride in the bath, said alkali metal being selected from the class consisting of potassiumand sodium, saidk non-catalytic compound being a strontium compound in an amount suicient to suppress the'concentration of said strontium sulfate in solution in said bath from the unsuppressed saturation concentration of the latter compound to a lower but greater than zero concentration 5. The method of forming a highly durable decorative chromium coating which comprises successively applying to the surface of a metal part a copper coating, a nickel coating and a multi-layer decorative chromium coating having successive layers, at least about 0.000015 inch in thickness, applied Without intervening abrasive treatment in which the rst applied of said layers is electrodeposited from an aqueous chromium plating bath solution at a temperature between 117 F. and 135 F., said bath containing less than 0.02 gram per liter of chloride ion and comprising essentially between 250 grams per liter and 425 grams per liter of Cr03, a total catalyst ion concentration of sulfate and silicotloride ions to achieve a ratio of CrO3 concentration to total catalyst ion concentration between 80:1 and 150:1, the sulfate ion content being between 35% and 75% of the total catalyst concentration, the CIOs concentration, ratio and temperature having a relationship defined by the areas enclosed by the curves in FIGURE 2, and the second applied of said layers being deposited from an .aqueous bath solution containing about 100 grams to 500 grams per liter of CIOS, two catalyst supplying compounds, and a soluble, non-catalytic compound, one of said catalyst-supplying compounds being strontium sulfate in an amount suicient to saturate said bath and to provide an undissolved residue of strontium sulfate in the bath, the other of said catalyst-supplying compounds being an alkali metal silicoliuoride in an amount suicient to saturate said bath and to provide an undissolved residue of alkali metal silicofluoride in the bath, said alkali metal being selected from the class consisting of potassium and sodium, said noncatalytic compound being a strontium compound in an amount suicient to suppress the concentration of said strontium sulfate in solution in said hath from the unsuppressed saturation concentration of the latter compound to a lower but greater than zero concentration.

References Cited in the tile of this patent UNITED STATES PATENTS 1,746,751 Van Derhoef Feb. 11, 1930 1,813,842 Fink July 7, 1931 1,836,598 Humphries Dec. 15, 1931 2,018,814 Smith Oct. 29, 1935 2,093,428 Ford Sept. 21, 1937 2,412,977 Eskin Dec. 24, 1946 2,640,022 Stareck May 26, 1953 2,678,908 Tucker May 8, 1954 2,800,437 Stareck July 23, 1957 2,800,438 Stareck July 23, 1957 2,822,326 Safranek Feb. 4, 1958 2,856,334 Topelain Oct. 14, 1958 2,898,234 Nack Aug. 4, 1959 2,916,424 Stareck Dec. 8, 1959 2,952,590 Stareck Sept. 13, 1960 FOREIGN PATENTS 568,161 Great Britain Mar. 21, 1945 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Parent No.D 3,151585 November im 1%4 Rollie Pe Durham It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 2 for "aoi'd'" read acid g line 35V for "(hydrate)" read (hydrated) column lY line 56, for "abtain" read obtain line 62, for "Centration" read concentration line 7l for "may" read my Signed and sealed this 6th day of April 1965.,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting Officer Commissioner of Patents

Claims

1. A METHOD OF FORMING A MULTI-LAYER DECORATIVE CHROMIUM COATING WHICH COMPRISES ELECTRODEPOSITING A NICKEL COATING ONTO THE SURFACE OF A METAL PART, ELECTRODEPOSITING A FIRST BRIGHT DECORATIVE CHROMIUM LAYER ONTO THE SURFACE OF SAID PART UNDER AN AVERAGE CATHODE CURRENT DENSITY OF APPROXIMATELY 90 AMPERES PER SQUARE FOOT TO 140 AMPERES PER SQUARE FOOT FROM A BATH AT A TEMPERATURE OF APPROXIMATELY 95*F. TO 115*F. CONTAINING APPROXIMATELY 20 OUNCES PER GALLON TO 35 OUNCES PER GALLON CRO3 AND ABOUT .20 OUNCE PER GALLON (AVDP.) TO .35 OUNCE PER GALLON (AVDP.) H2SO4, AND THEN, WITHOUT INTERVENING ABRASIVE TREATMENT OF SAID CHROMIUM PLATED SURFACE AND UNDER AN AVERAGE CATHODE CURRENT DENSITY OF APPROXIMATELY 130 AMPERES PER SQUARE FOOT TO 300 AMPERES PER SQUARE FOOT, ELECTRODEPOSITING ONTO SAID FIRST LAYER A SECOND DECORATIVE CHROMIUM LAYER WHICH HAS A DENSER CRACK PATTERN THAN SAID FIRST LAYER USING A BATH AT A TEMPERATURE OF APPROXIMATELY 120*F. TO 150*F. CONTAINING ABOUT 40 OUNCES PER GALLON TO 70 OUNCES PER GALLON CRO3 AND .45 OUNCE PER GALLON (AVDP.) TO .70 OUNCE PER GALLON (AVDP.) H2SO4.