US2928777A - Electrolytic polishing of metals - Google Patents

Description

ELECTROLYTIC POLISHING OF METALS George H. Smith, Blasdell, N.Y., assignor'to Electro Process, Inc., Bulfalo, N.Y.

No Drawing. Application December 16, 1950 Serial No. 201,248

8 Claims. (Cl. 204140.5)

, The present invention relates to the electro-polishing: of metals and has particular application tothe polishing of iron, aluminum, magnesium, and copper and their alloys, such as high carbon steel, low carbon steel, mild alloy steel, cast iron, wrought iron, stainless steel, Monel, Inconel, and brass.

forms as, for instance, plate, rods, rigidized metal, perforated metal, cold rolled and hot rolled steel and sheets and the like, and the articles fabricated therefrom.

It is an important economic object of my invention to electro-polish metal objects in short periods of time and at low ,anode current densities on the order of. v 0.25 to 10 amperes per square inch. r

It is an object of my invention to provide animprovedmethod of polishing iron, aluminum and copper and al-" loys thereof, and a composition to be employed thereforw' It is a further object of my invention to provide a, mirror-bright finish upon the surface of the metals with simultaneous deburring of the sharp edges.

It is a further object of the invention to provide metal pr'oductssuch as-iron and its alloys whichm'ay'be directly plated with copper, nickel, chrome or other plating metals: usually employed in the art, without further preparation.

,It is a further object of this invention to prepare a surface on such metals wherein there is a greater adherence of the plating metals to the metal base than has been possible heretofore ,by electro-polishing processes available.

It is well known to the art that a great number of methods :have been proposed for the electro-p'olishing of steel and other metals. In general, the electrolyte was.- mainly composed of strong acids, such as sulfuric acid and/or ortho-phosphoric, acid, or other acids such as hy'..

drochloric, hydrofluoric, chromic and arsenic acids, nitric acid, etc., either used per se orv when necessary in admix-' ture in variable proportions with sulfuric acid. z 1 To these inorganic acids, additions of a great variety-of organic compounds were made which were supposed to provide considerable improvements over polishing soluhibitors and buffers. I

Someof these combinations have reached widespread-7 application in the electrolytic polishing of stainless steels. However, the application of electrolytic polishing to steel a'nd"ir'on has not acquired any importance since'the elec trolytes proposed by the art have failed to meet the requ remsnt .for. a m n br ht fi .debnrring of the without .further preparation,

e d t en d t oni f 1 urf ce t c ul be d.

T The prior art further discloses the use of cresol sulfonicj an effective surface brightener as illustrated in acid I The methods of electro-polishing 20 herein disclosed are applicable to all types of shapes and I 2,928,777 P atented Mar. 15, 1,969

published by Chapman & Hall, London, England, 1948, but extensive tests with the use of this additive failed to"- produce a mirror-bright finish of the steel surface. In fact, it hardly showed any improvement over the use of additives cited in the. foregoing paragraphs, and does not,

seem to have ever been adopted on an industrial scale.

I have now found, in accordance with the present invention, that a very much superior polishing eifect and a very smooth mirror-bright surface can be produced on.

. iron, aluminum, magnesium and copper, and their alloys such as stainless steel, brass, Monel, Inconel and steel, more readily and at a lower cost than was heretofore possible; the employment of an electrolytic solution for electro-polishing consisting essentially of a mixture of (a) inorganic acids or a mixture of inorganic acids and aliphatic organic acids and (b) an aromatic sulfonic acid characterized by the following general formula:

Ar(SO H) in which A-r represents an aromatic radical, single, linked or condensed of the benzene, naphthalene, anthracene etc., series, and in which X is the integer 1, 2 or more.

According to my invention, lead, stainless steel or copper is used as the cathode for the direct current (which may be produced by means of a rectifier or a motor generator), the metal to be polished being the anode, both anode and cathode being substantially immersed in the electrolytic polishing solution.

It is an important object of my invention that the current densities employed are uniquely low as compared to the current densities advocated and used by the prior art .and that I am able to polish iron and carbon steel with current densities as low as one-half to one ampere per square inch of anode surface, when the aromatic sulfonic acids of my invention are used in the electrolyte of the electro-polishing bath.

The electrolyte employed, according to my invention, is composed of a plurality of acids, one of which may; be an aliphatic carboxylic acid, such as acetic or glycolicacid; the bath may include inorganic acids or mixtures thereof, such as phosphoric or sulfuric acid, or both, andan aromatic sulfonic acid of the general type described; above. I have discovered that the addition to the electro-r polishing electrolytes of an aromatic sulfonic acid orof a mixture of the aromatic sulfonic acids of this inven tion is indispensible if a mirror-bright finish on steel, stainless steel, aluminum, Monel, Inconel, magnesium brass and copper, etc., is to be attained.

According to my invention I may use the aromatic sulfonic acid with phosphoric acid alone, if a bright polishv is desired on brass, copper, aluminum, carbon and stain-Q less steel, for instance; or, I may use the aromatic sulfonic acid with sulfuric acid to polish stainless steel, aluminum and carbon steel; or, I may usethe aromatic sulfonic acid with both phosphoric and sulfuric acid to cause a bright mirror polish on aluminum, stainless steel, Monel, Inconel, magnesium, carbon steel and its alloys.

Small amounts of air-aliphatic carboxylic acid of from 1% to 20% by weight of the electrolyte may also be used in the electro-p'olishing composition, according to the present invention, which additions broaden the scope of operating efficiency of such solutions over a wider range of temperatures. But, these additions are; not essential to the achievement of'a mirror-bright polish on any of the previously mentioned metals and alloys ifthe aromatic sul fonic acids are being usedas illustrated by the examples given below."

' Thus metals may be polished by immersingmetalf to be treated as an anode in an electrolytic bath compris i ing 1 to 50% of an aromatic sulfonic acid of the tvpe h contemplated herein, 50 to 90% "byweight of B6. sulfuric acid. Where an aliphatic carboxylic acid is employed in the bath the aliphatic carboxylic acid may be present from 1 to 70% by weight, the aromatic sulfonic acid from 1 to 50% by weight, with from 40 to 85% by weight of 66 B. sulfuric acid. It is possible to polish metals anodically in a bath of from S to 90% by weight of 66 B. sulfuric acid containing from 1 to 50% of benzene sulfonic acid.

The time of treatment may be varied over a wide range, depending upon the acid mixture used with the aromatic sulfonic acid and the quality of metal being polished. Under optimal conditions, stainless steel may be polished in one to two minutes; brass and. copper in one to two minutes; aluminum, carbon steel, Monel, Inconel, magnesium, in two to four minutes.

The amounts of metal removed from the anode to be brightened are very minute; the amounts removed in two minutes with an electrode potential of 12 volts, and a typical electrolyte of the present invention is, for ex- Z-naphthol 3-6-8 tri-sulfonic acid have been found especially suitable for imparting a bright mirror finish to carbon steel, stainless steel, aluminum, Monel, lnconel and magnesium.

Concentrations of the aromatic hydrocarbon sulfonic acid, or mixtures thereof, of l to by weight of the total weight of the electrolyte are effective in improving the lustre of these metals and alloys.

Especially suitable are mixtures of naphthylaminesulfonic acids which are by-produets and wastes from organic intermediates production, and contain sulfuric acid in high concentration and in particular, the mono, di and tri sulfonic acid derivatives of beta-naphthylamine when used as a mixture, as they occur in the waste liquor of beta-naphthylamine sulfonation.

The following examples are given as further illustrations of the several methods which I have found to give the desired results, but these examples should not be taken as a limitation of my invention but merely as illusample, as follows: 20 trative thereof.

(Inches E 1 Carbon steel 0.0015 xample Aluminum 0.001 24.8% by weight of benzene sulfonic acid of-a techni- Stainless steel (l88) 0.002 cal grade containing 71% free benzene mono-sulfonie Copper or brass 0.0025 acid, 37.4% by weight sulfuric acid 96%,, 34.0% by Monel and Inconel 0.002 weight ortho-phosphoric acid 85% and 3.8% by weight Magnesium 0.001 water.

Time, iliemp. 1 Amps Metal Min. Bath Cathode Volts spa; Nature of Finish Aluminum 25 pan a so. Copper 15 I 0.5 Very brightsmcoth polish. Stainless 188 17-chr0me 3 80 0--.- 10 23 Very bright polish. Low carbon steei 5 70 Lead 10 2.0 Mirror-bright finish. High carbon steeL- 4 70 do 8 1% Do. Magnesium 1% 7O Stninless-steel 8 154 Do.

The aromatic sulfonic acids which may be used, according to this invention, are derived from aromatic hydrocarbons such as benzene, naphthalene, anthracene, acenaphthene, phenanthrene, retene (7-isopropyl-l-methyl-phenanthrene), fluorene, etc., and may containone or more sulfonic acid radicals, usually not more than three, to induce solubility in the electrolyte. Aliphatic side chains may be present, such as methyl, isopropyl, butyl, ctc'., radicals. I have also found that, in many instances, the aromatic sulfonic acid may be substituted by an aminogroup or a nitro group, but that the presence of a hydroxyl group, in general, impairs the results to a considerable degree unless a plurality of sulfonic acid radicals is present.

Other substitutes, such as halogens, do not, in general, yield the desired results because of the too great insolubility generally inherent in the halogenated aromatic sulfoacids.

Thus, the aromatic sulfonic acids which I usually prefer to use in the free acidic state, according to my' invention, comprise the following examples:

Benzene mono sulfonic acid Benzene 1.3-di sulfonic acid Ortho-toluene mono sulfonic acid Para-toluene mono sulfonic aicd Meta-toluene mono sulfonic acid Orthoxylene-4 sulfonic acid 2.6 naphthalene di sulfo acid 2.7 naphthalene di sulfo acid Retene di sulfonic acid The aromatic sulfonic acids of the benzene series, such as bcnzene-mono-sulfonic acid, I have found to be especially effective for polishing. steel, stainless steel, aluminum and magnesium. The aromatic sulzlinnicv acids of the naphthalene series. especially theZ-naphthylamine 5-! disulfonic acid, Z-naphthylamine 1-5-7 tri-sulfonic acid and After the electro-polishing, the metals were rinsed in soft water or a solution of hard water containing 1% of a softening agent, such as ethylene diamine tetra acetic acid or a sequestrating agent for the calcium and magnesium salts present in the hard water, and dried. This procedure was generally followed in the accomplishment of allthe examples given below:

Example II Naphthalene 2,6 and 2,7 di-sulfonic acids in adequate quantities show excellent results on carbon steels, aluminum and stainless steel. in the following electrolyte: 12.4% by weight 2,6 naphthalene di-sulfonic acid, 12.4% byweight 2,7 naphthalene di-sulfonic acid, 37.5% by .weiglit sulfuric. acid 96%, 34% by weight orthophosphoric acid and 3.7% by weight water.

18% by weight technical benzene sultonic acid. containing free benzene mono-sulfonic acid, 4.5% sulfuricacid (H 80 1.8%. hi-phenyl sulfone (CQHblgSQg plus unaccounted for material consisting. of water, benzol and unidentified organic byproducts, 38% by weight saga-e sulfuric acid 9 6%, 40% by weight orthophosphoric acid 85% and 4% by weight water.

5% by weight retene di-sulfonic acid and 16% by weight of water. i

Time, Tem Amps. Nature of I Time Temp. Amps. Nature's! Metal Min. of Cathode Volts per Finish 5 Metal Min. of Cathode Volts per Finish" Bath Sq. In. Bath Sq. In.

Aluminum, 3 80 Stainless 15 0.5 Very bright, Copper 2 50 Copper.... 10 0.5 Mirror- 2S 36E. steel. smooth bright v finish. mb. iv 4 Stainless 18-8. 3 80 ..do 10 2.3 Very bright Brass 2 50 -do 10 I 0.6 o. i 0 V1pxorlish. 10 Low carbon 70 .--do l 2.0 L orsteel. brie t Aromatic sulfomc acids in the field of electrolytic High 4 70 8 1 polishing aremost efiectively used in the percentages steeld 8 1 D indicated in above examples, i.e., from 1 to 20% by Magnesium 2 A 15 weight of the bath. 1

' However, smaller percentages may be used according- Example IV 9.3% by weight of toluene sulfonic acid 80% para 20% ortho (94%) 45.8% by weight of 96% H 80 38.5% by weight of 85% ortho-phosphoric acid, and 6.4% by weight of water.

Time, Temp. Amps. Nature oi Metal Min. of Cathode Volts per Finish Bath Sq. In.

Aluminum 3 35 Copper 0. 5 Smooth alloy. bright polish. Stainless 18-8. 2 35 Lead l0 2. 3 veryrblrllght po Low carbon 5 70 do 10 1.0 Very bright steel. smooth polish.

1 32 s 3411, Le, 12.5% $1, 1.0 Mg, 0.9% Ni, 0.9% Cu, one-half hard.

Example V The following electrolyte gives a mirror-bright polish on carbon steel and magnesium and consists of 4.8% by weight water, 7.8% by Weight of technical glycolic acid, 40.2% by weight of sulfuric acid 96%, 38.4% by weight ortho-phosphoric acid 85%, and 8.8% by weight 71% benzene sulfonic acid. Very good results were obtained by using para-toluene sulfonic acid as a substitute for benzene sulfonic acid in this formula.

50% by weight para-toluene sulfonic acid (94%), 18.5% by weight benzene sulfonic acid (71%), 31.5% by weight orthophosphoric acid (85%).

Time, Temp. Amps. Nature of Metal Min. of Cathode Volts per Finish Bath Sq. In.

Low carbon 5 60 Lead 10 0.8 Very bright steel. polish.

Example VII The addition of aromatic sulfonic acids to orthophosphoric acids greatly improves the lustre and brightness of polish attained on copper and brass. Small quantities of para-nitrotoluene ortho-sulfonic acid or retene di-sulfonic acid are especially efiective in improving the polish on brass and copper. An example of this electrolyte is: 79% by weight of 85 ortho-phosphoric acid,

to the case. Their effect on the final polish, the current consumption and time necessary. to achieve a mirror brightfinish, is substantial. It is alsopossible, .by vary-: ing the percentages of the aromatic sulfonic acids-used to obtain different shades on the polished surface which may vary from a brown tone on stainless steel, to the bluish brilliance of chrome plated steel.

Low carbon steel polished according to Example I gives a mirror-bright finish which can be plated with nickel or chrome without further preparation.

What is claimed is:

1. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1 /2 to 5 minutes as an anode in an aqueous electrolytic bath consisting of 1.0 to 50% by weight of an aromatic hydrocarbon sulfonic acid and 50 to 70% by weight of orthophosphoric acid, the current being of willcient density to overcome any etching and result in a polishing of the metal being used as an anode.

2. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1 /2 to 5 minuta as an anode in an electrolytic bath. consisting of 1 to 50% by weight of an aromatic hydro carbon sulfonic acid and a combination of inorganic acids of 40 to by weight said inorganic acids being selected from the group consisting of sulfuric acid and orthophosphoric acid.

3. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1 /2 to 5 minutes as an anode in an electrolytic bath consisting of 1 to 50% by weight of an aromatic hydrocarbon sulfonic acid, 1 to 7% by weight of an aliphatic carboxylic acid and 40 to 90% by weight of a combination of phosphoric and sulfuric acid.

4. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1% to 5 minutes as an anode in an electrolytic bath con sisting of 1.0 to 50% by weight of benzene sulfonic acid and 50 to 79% by weight 85% ortho-phosphoric acid, the current being of suflicient density to overcome any etching and result in a polishing of the metal being used as an anode.

5. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1 /2 to 5 minutes as an anode in an electrolytic bath con sisting of 1 to 7% of an aliphatic carboxylic acid, 1 to 50% by weight of sulfonic acid of the formula where Ar is an aromatic hydrocarbon radical and n is an integer of less than 4 the remainder being substantially inorganic acid selected from the group of inorganic acids consisting of sulfuric acid and orthophosphoric acid.

6. A method of anodically polishing metals which comprises immersing the metal to be treated for from 1 /2 to 5 minutes as an anode in an electrolytic bath consisting of l to 50% by weight of a sulfonic acid of the formula Ar(SO OH),, where Ar is an aromatic hydrocarbon radical and n is an integer less than 4, and 40 to 7 90%by weight of a combination of phosphoric and sulfuric acids.

7. A method of anodically polishing metals which comprises immersing the metal to be treated for from IV: to 5 minutes as an anode in an electrolytic bath consisting of 1 to 50% by weight of a sulfonic acid of the formula Ar(SO OH),, where Ar is an aromatic hydrocarbon radical and n is an integer less than 4,. and- 1 to 7% by weight of an aliphatic carboxylic acid and 40 to 90% by weight of a combination of phosphoric and sul- 10 furic acids.

8; A method of anodically polishing metals which comprises immersing the metal to be treated for from 1% to 5 minutes as an anode in an electrolytic bath consisting of 1 to 59% benzene sulfonic acid in combination with 50. to'70% of inorganic acid selected from the group of: inorganic acids consisting of sulfuric acid and orthophosphoric acid, the time, temperature and current densities of the bath being adjusted so as to achieve a bright polish.

8 References Cited in the file of this patent UNITED STATES PATENTS 1,956,571 Grillet May 1, 1934 2,335,354 Ostrofsky Nov. 30, 1943 2,386,078 Weisberg et al Oct. 2, 1945 FOREIGN PATENTS 504,026 Great Britain Apr. 17, 1939 594,932 Great Britain Nov. 21, 1947 OTHER REFERENCES Richters Organic Chemistry, vol. 2 (published in 1922), page 172.

Chemical and Electroplated Finisher, by H. Silman, published in 1948' by Chapman and Hall, Ltd., pages 100, 101.

Claims (1)

1. A METHOD OF ANODICALLY POLISHING METALS WHICH COMPRISES IMMERSING THE METAL TO BE TREATED FOR FROM 1 1/2 TO 5 MINUTES AS AN ANODE IN AN AQUEOUS ELECTROLYTIC BATH CONSISTING OF 1.0 TO 50% BY WEIGHT OF AN AROMATIC HYDROCARBON SULDONIC ACID AND 50 TO 70% BY WEIGHT OF 85% ORTHOPHOSPHORIC ACID, THE CURRENT BEING OF SUFFICIENT DENSITY TO OVERCOME ANY ETCHING AND RESULT IN A POLISHING OF THE METAL BEING USED AS AN ANODE.