NL8201978A - METHOD AND PREPARATIONS FOR ACID CLEANING OF ALUMINUM SURFACES. - Google Patents

Description

...... '* t (- 1 -

Method and preparations for cleaning with acid from aluminum surfaces.

The invention relates to cleaning aluminum surfaces.

In the manufacture of containers consisting of aluminum (which term is also meant to include aluminum alloys in this specification) a drawing and forming operation (commonly referred to as drawing and ironing) is employed.

This operation leads to the decomposition of lubricants and the formation of oils on the surfaces of the aluminum containers. In addition, fine aluminum residues, i.e. small particles of aluminum, deposit on both the inner and outer surfaces. Usually, the outer surface of the container will carry smaller amounts of fine aluminum particles than the inner surface, since during the drawing and ironing step the outer surface is not subject to such abrasion by the drawing stone as the inner surface.

Before applying any further processing such as conversion coating and hygienic coating, the surfaces of the aluminum containers must be clean and free of water breakage, ie free from impurities which impede further processing and make the containers unacceptable for use.

Compositions and methods for the low temperature cleaning of aluminum surfaces are disclosed in U.S. Pat. Nos. 4,009,115, 4,116,853, 4,124,407, and 3,969 * 135. These patents disclose cleaning compositions comprising sulfuric acid, hydrofluoric acid, or a fluoride salt, and contain a surfactant.

Preparations that fall within the scope of these patents have been technically successful and are in fact extensively used for cleaning 8201978 *% - 2 - aluminum (including aluminum alloy) containers. Such technical formulations typically use a combination of two nonionic surfactants to enhance cleaning performance and minimize foaming.

One of the problems in using the hitherto known acidic cleaning compositions is caused by the build-up of lubricants and the formation of oils used in drawing and shaping the aluminum containers when treated with the cleaning solutions. The cleaning solutions must be replaced from time to time by fresh solutions to keep the oil level low. When the oil levels become excessively high in the cleaning bath, containers being cleaned in the bath show significant water fractures after the cleaning solution has been rinsed off. Water breaks are an indication that the surface of the aluminum is not clean and that oils or other foreign deposits are present. Such containers must be discarded or cleaned again, as they are not suitable for further processing as containers for drinks and other foodstuffs.

It has now been found that an aqueous sulfuric acid / hydrofluoric acid cleaning composition containing a certain anionic surfactant, namely an alkali 2-butoxyethoxyacetate, is surprisingly advantageous.

Accordingly, the invention provides an aqueous cleaning solution for removing and dissolving small aluminum particles and cleaning aluminum surfaces of lubricating oils, which solution is 1-10 g per liter of sulfuric acid, 0.05-0.1 g per liter of hydrofluoric acid and 1-30 contains 10 g per liter of alkali 2-butoxyethoxyacetate.

The invention also provides an aqueous solution concentrate for forming the aqueous cleaning solution, which concentrate contains 200-600 g per liter of sulfuric acid and 0.01-10 parts by weight of alkali 2-butoxyethoxyacetate per part by weight of sulfuric acid.

8201978 * * \ - 3 -

The invention also provides a method for cleaning an aluminum surface, in which a) said surface is contacted with the aqueous cleaning solution, and b) the aluminum surface is rinsed to remove the cleaning solution.

It has been found that the cleaning solutions of the invention can tolerate relatively high concentrations of lubricants and molding oils without any water breakage on the containers cleaned by such solutions. Substantial savings are thus made, as large numbers of containers can be processed before the operation must be stopped to replace all or part of the cleaning solution.

Another important advantage of the present cleaning solutions is the almost complete absence of foam in the cleaning bath and in the rinsing cycle following the cleaning step. Many of the acidic cleaning compositions currently on the market exhibit foam problems to a greater or lesser extent. Such formulations are mixtures of a high-foaming non-ionic surfactant to obtain good cleaning performance with a low-foaming anionic surfactant to try to limit the amount of foam that would otherwise occur. Foaming often leads to the foam overflowing or falling on the ground of the site where the operation takes place, leading to breakneck and unsafe conditions. The appearance of foam can also cause an operator to conclude that the cleaning solution is not sufficient due to the danger of foaming. As a result, the cleaning operation of the containers is stopped while skimming or the cleaning solution is replaced, resulting in loss of time and reduced flow of the containers.

A further advantage of the present cleaning compositions is that the alkali 2-butoxyethoxyacetate has effect 8201978

«V

K - k - tive can be used in relatively small amounts, and this factor, in combination with the cheapness of this surfactant (as the sodium salt) compared to the nonionic surfactants currently in use, leads to major economic savings over current technical preparations. Significant cost savings are also achieved even when a low foaming non-ionic surfactant or a combination of such surfactants is also present in the cleaning composition of the invention, since the non-ionic surfactant (s) may also be present in relatively small quantities *

Typically, concentrates containing the sulfuric acid and surfactant are prepared by the manufacturer and sold to container processing companies that make cleaning solutions by diluting such concentrates with water and adding hydrofluoric acid to the solutions. The concentrations currently on the market tend to be quite strongly colored due to decomposition products formed by the action of concentrated sulfuric acid on the surfactants and / or by interactions between the surfactants and impurities in the technical sulfuric acid commonly used. used for formulating the concentrates. Surprisingly, concentrates formed with an alkali 2-butoxyethoxyacetate as the sole surfactant are colorless or only slightly yellow in color. Such concentrates are stable at very low temperatures, and, for example, no precipitation occurs even at the temperature of the dry ice-acetone bath. Also, the concentrates are stable and do not discolour even when subjected to temperatures of 50 ° C for periods of three weeks or more. Most . concentrates used today discolor even at room temperature, and some form precipitates, 8201978 * "; - 5 - when concentrates of concentrates are placed in dry ice-acetone baths. The great stability of the present compositions permits their shipping and storage under unfavorable temperature conditions without problems, which offers a further substantial economic advantage.

Another advantage of the present invention is the high degree of beauty produced in the containers, especially when low foaming non-ionic surfactant is also present, thereby providing extremely uniform conversion coating and paint deposition on the containers during their further operation.

When the only anionic surfactant disclosed in U.S. Pat. Nos. U,009,115,116,853 and 1). 12U. ^ 0TS namely Tergitol Anionic 08 (sodium 15 2-ethylhexyl sulfate) is tested in the acidic cleaning compositions of these patents, interestingly water fractures occur on the aluminum containers cleaned with such compositions after the addition of only small amounts molding oils. Thus, the surprising advantages afforded by the particular anionic surfactant of the invention appear to be unique and are clearly not advantages inherent in anionic surfactants in general.

The compositions and methods of the invention provide for improvements over the compositions and methods disclosed in U.S. Pat. Nos. 009,115, U, 661, 53, and .122, 10, which are to be considered incorporated herein. The procedures and methods used therein to perform cleaning operations and forming concentrates and cleaning solutions are applicable to the present invention unless otherwise stated.

The aqueous cleaning solution according to the invention contains 1-10 g per liter, preferably 3-5 g per 35 liters of sulfuric acid, 0.05-0.1 g per liter, preferably 0.01-0.03 8201978 - 6 - g per liters of hydrofluoric acid, and 0.1-10 g per liter, preferably 0.2-0.8 g per liter of alkali 2-butoxyethoxyacetate.

The alkali 2-butoxy ethoxy acetate is preferably sodium 2-butoxyethoxyacetate 0.5 / CH3 (CH2) 30CH2CH2OCH2C-O®Na® /, which is commercially available under the trade name "Miravet B" at. Miranol Chemical Company, Inc. as an aqueous solution containing k-9.0% sodium 2-butoxyethoxyacetate. Other alkali salts can be used, for example, potassium or lithium 2-butoxyethyl acetate.

A preferred solution contains 3-5 g per liter of sulfuric acid, 0.01-0.03 g per liter of hydrofluoric acid and 0.2-0.8 g per liter of sodium 2-butoxyethoxyacetate.

The present solution preferably contains 0.1-15 g per liter, most preferably 0.2-0.8 g per liter, of low-foaming nonionic surfactant. The surfactant can be one or a combination of two or more low foaming nonionic surfactants. Preferably, a weight ratio of alkali 2-butoxyethoxy-20 acetate to nonionic surfactant of about 1: 1 is used.

The term "low foaming nonionic surfactant" means that the nonionic surfactant or combination of nonionic surfactants gives less than 20mm of foam after standing for 5 minutes in the well-known Ross-Miles foam test at 50 ° C. Examples of such low foaming nonionic surfactants which can be used alone or in combination in the practice of the invention are as follows: TRITON DF-16 (Rohm & Haas Co.), which is believed to be a modified polyethoxylated straight chain alcohol.

POLYTERGENT S-505 LF (Olin Corp.), 35 of which is believed to be a modified polyethoxylated 8201978 5 -5-7 straight chain alcohol.

SURFONIC LF-17 (Jefferson Chemical Co.), which is believed to be an alkyl polyethoxylated ether.

ANTAROX BL 330 (GAF Corp.), which is believed to be an alkyl poly (ethyleneoxy) ethanol.

TRITON CF-10 (Rohm & Haas Co.), which is believed to be an alkylaryl polyester with a carbon chain of about 1 carbon atoms and about 16 moles of ethoxylation.

PLURONIC L061 (BASF Wyandotte, Inc.) believed to be a condensate containing only ethylene oxide and propylene oxide chains.

ANTAROX LF-330 (GAF Corp.) believed to be an alkyl poly (ethyleneoxy) ethanol, and 15 MINIFOAM IX (Union Carbide Corp.) believed to be an alkyloxy (polyethyleneoxypropyleneoxyisopropanol) having a molecular weight of about 706.

The pH of the cleaning solution according to the invention is usually 0.6-2.0, preferably 1.0-1.8 and most preferably 1.2-1.5.

The concentrates according to the invention contain 200-600 g per liter sulfuric acid and 0.01-10, preferably 0.02-0.27 parts by weight of alkali 2-butoxyethoxyacetate per part by weight of sulfuric acid. An appropriate amount of alkali 2-butoxyethoxy-25 acetate in a given concentrate can be determined by using these ratios and the amount of sulfuric acid desired in the cleaning solution so that the desired amount of alkali 2-butoxyethoxyacetate is present in the cleaning solution when the concentrate is diluted with an appropriate amount of water. For example, if 1 g per liter of sulfuric acid is desired in the cleaning solution, 0.1-10 g of alkali 2-butoxyethoxyacetate is present in the concentrate per g of sulfuric acid, and if TO g per liter of sulfuric acid is desired in the cleaning solution, 0.1-1 g of alkali 35 2-butoxyethoxyacetate present in the concentrate per g of sulfuric acid.

Possibly also. 0.01-10 ", preferably 0.08 ± 0.27 parts of low-foaming nonionic surfactant present in the concentrate.

The present concentrate can be added to water in controlled amounts sufficient to obtain a cleaning solution with the desired concentrations of sulfuric acid and alkali 2-butoxyethoxyacetate. Hydrofluoric acid is usually added individually in amounts sufficient to give its desired concentration. Although the hydrofluoric acid can be added to the concentrate in amounts sufficient to give the required amounts in the cleaning solution, when the concentrate is added to water, it is much more preferable to add the hydrofluoric acid separately to the cleaning solution in accurately measured amounts. on a constantly arranged tasis. Separately controlled addition of hydrofluoric acid is preferred because the cleaning solution continuously loses hydrofluoric acid as etching of the aluminum surfaces occurs during the cleaning step.

The aluminum (including aluminum alloy) surface to be cleaned with the aqueous cleaning composition of the invention can be contacted with the solution by any of the art-known contact methods, such as conventional spraying or dipping methods. The temperature of the cleaning composition is usually 32 ° C. Preferably, the temperature is kept at b6-63 ° C for maximum cleaning effect. Treatment times with the cleaning solutions usually fall in the range of 15 seconds to 2 minutes. Desirably, the hydrofluoric acid content of the cleaning solution and the contact time with the aluminum surface are adjusted to dissolve 90-280 mg, preferably 100-220 mg, of aluminum per 35 square meters of treated aluminum surface. The amount of 8201978-9-hydrofluoric acid in the cleaning solution is thus preferably such that 90-280 mg of aluminum per square meter of treated aluminum surface dissolves at a temperature of 5 ° C and a contact time of 1 minute. Aluminum cans are preferably treated according to the present method.

The invention will now be illustrated by the following examples, in which 3004 alloy refers to a conventional aluminum alloy known by this name and containing about 1.2 wt.% Manganese and 1.0 wt.% Magnesium with the remainder aluminum and normal contaminants.

Example I

One liter of concentrate containing the following amounts of ingredients is prepared: per liter of H 2 SO 4 (66 ° Baume) - 467.2 g (256 ml) of H 2 O - 709.6 g (711 ml) of MIRAWET B - 88, 6 g (80 ml)

The concentrate is clear and almost colorless. 60.0 ml of the concentrate is added to 5.9 ^ 0 l of water to form 6 l of solution, which is 4.67 g per liter of H ^ SO ^ (66 ° 25 Baume) and 0.4-34 g per liters of sodium 2-butoxyethoxyacetate (0.886 g per liter of MIRAWET B). 20 parts per million hydrofluoric acid is added to form a cleaning solution, and it is stirred to make it uniform in composition.

30 Aluminum cans of 3004 alloy drawn into one-piece containers are used in this procedure. The cans were covered with fine aluminum particles and pulling oil.

Test samples are treated as follows: a) spraying with the above cleaning solution, which is kept at 5 ° C, for 1 minute, h) rinsing with water by immersion in cold water for 30 seconds, c) leave for 30 seconds, then examine for water breaks on both the inside and outside, and d) wipe the inside with a clean white cloth and examine the cloth for fine aluminum particles.

10 A look is tested as described above and the data is recorded. Then 5 ml of a cooling oil emulsion as used by the Reynolds Aluminum Company in drawing and forming aluminum cans, is added to the cleaning solution and another can is tested and the results are recorded. Then 5 ml of cooling oil is added to the bath and another can is tested and the results are recorded. Additional 5 ml portions of cooling oil are added and a can is tested after each addition until water breaks appear. After each addition of cooling oil, the amount of foam in the bath is recorded.

The results of these tests are shown in the following Table A:

Table A

25 add degree of fine aluminum foam in cooling oil emulsion water fracture nium on cloth bath_ 0 none none 5 ml none none minute 10 ml none none minute 30 15 ml none none minute 20 ml none none minute 25 ml none none minute 30 ml slightly none minimal * "Mimin" means no more than 0.6 cm of foam.

8201918 -11-

Example II

6 liters of cleaning solution are prepared by adding to water 28.02 g of SO 2 SO (66 ° Baum), 1.30 g of sodium 2-butoxyethoxyacetate and 20 parts per million of fluoro-5 hydrochloric acid. This cleaning solution contains g per liter of H2SOU and g per liter of sodium 2-butoxyetboxyacetate (i.e. half of the amount present in the cleaning solution of Example I).

Aluminum cans from the same batch as used in Example I are tested under the conditions and procedures set forth in Example I with the following results:

Table B

15 adding degree of fine aluminum foam cooling oil emulsion water break on cloth in bath 0 none none none 5 ml none none minute 10 ml none none minute 20 15 ml none none minute 20 ml none none minute 25 ml none none minute 30 ml slightly none minute 5 "Minor" means no more than 0.6 cm of foam.

Comparative Example III

6 liters of an aqueous cleaning solution containing the following amounts of ingredients per liter are prepared:

HgSO4 (66 ° Baume) - b, 67 g

Sodium 2-ethylhexyl sulfate - 0.5½g (0.98ml TERGIT0L MIONIC 08) 35 HF 20ppm 8201978 -12-

Aluminum cans from the same batch as those used in Example I are tested under the conditions and procedures shown in Example I with the following results:

Table C

addition of degree of fine aluminum foam cooling oil emulsion water breakage on cloth in bath 0 slightly none none. * 10 5 ml extended none none 10 ml extended none none * "Extended" means unacceptable to the trade.

^ Comparative example ry

6 liters of an aqueous cleaning solution containing the amounts of ingredients shown in Example 3 are prepared, but now 0.928 g per liter of sodium 2-ethylhexyl sulfate are used. Test procedures are carried out as in Example III with the following results:

Table D

addition of degree of fine aluminum foam cooling oil emulsion water breakage on cloth in bath ^ 0 slightly none none 5 ml extended none none 10 ml extended none none ^ * "Extended" means unacceptable to the trade.

Comparative example V

6 liters of an aqueous cleaning composition containing the following amounts of ingredients per liter are prepared: 8201978 -13-H 2 SO 4 (66 ° Baumê) - 4.70 g

Ethoxylated Abetic Acid (Hercules.

Surfactant AR 150) - 1,053 g

Alkylpoly (ethyl-5-leenoxy) ethanol (ANTAROX LF-330) - 0.673 g HF 20 ppm

Both non-ionic surfactants.

10

Aluminum cans from the same batch as those used in Example I are treated according to the procedures and conditions shown in Example I with the following results:

Table E

adding degree of fine aluminum foam cooling oil emulsion water breakage on cloth in bath. . a.

0 no trace slightly 20 5 nil slightly trace slightly 10 ml extended * trace slightly £ "Extended" means unacceptable to trade. "Somewhat" means between 0.6-2.5 cm.

Comparative example VI

6 liters of an aqueous cleaning solution containing the following amounts of ingredients per liter are prepared: 30 o H ^ SO ^ (66 Baumê) - 4.67 g

Modified polyethoxylated straight chain alcohol (TRITON DF-16) - 0.464 g (non-ionic surfactant) 8201978 -111 · HF - 20 ppm

Aluminum cans from the same batch as those used in Example X are treated according to procedures 5 and conditions shown in Example I with the following results:

Table F

addition of fine aluminum foam 10 cooling oil emulsion water break on cloth in bath * 0 no trace slightly 5 ml no trace slightly 10 ml no trace slightly 15 ml no trace slightly 15 20 ml no trace slightly • 25 ml slightly trace slightly "Somewhat" means between 0.6-2.5 cm.

^ Example VIIA and Comparative Examples VIIE, VIIC and VIIC.

The following concentrates are prepared: A per liter H2SO ^ (66 ° Baumê) - 1 + 67.2 g HO - 709.6 g 25 ^

Sodium 2-butoxyethoxy acetate - 1 + 3.1 + g

B

HgSO4 (66 ° Baume) - 709.6 g

Sodium 2-ethyl-hexyl sulfate - 1 + 6.1 + g

C

HgSO 3 (66 ° Baumê) - 1 + 69.6 g H 2 O - 627.0 g

Ethoxylated Abietinic Acid (Hercules Surfacant AR 150) - 105.3 g 8201978 Λ -15-

Alkylpoly (.ethyleneoxy) ethanol (ANTAROX LF-330) - 6? , 3 g

D

H 2 SO 4 (66 ° Baume) - U67.2 g, 5 H 2 O - 709.6 g

Modified polyethoxylated straight are called alcohol (TRITON DF-16) - k6, k g

Samples of the above concentrates 10 were treated according to the conditions shown in and with the results shown in Table G below:

Table G

Concen- Dry ice / ace- 0 ° C during- 55 ° C for 15 trate ton bath the 2h hour 2k hour A slightly fish-clear, after-clear, almost choice, clear enough color-colorless solution virtually colorless solution solution sing B * - 20 C considerable considerable very dark brown precipitate precipitation discolouration, some separation in layers D slightly fish-light brown medium brown choice light-colored colored brown-colored solution solution 25 solution * Homogeneous solution could not be obtained. TERGITOL 08 formed a layer on top of the sulfuric acid solution. 1 2 3 4 5 6 8201 978 2

Concentrate A is then introduced into an oven which is kept at 50 ° C for three weeks. When the solution 3 is taken out again, it is clear and almost 4 colorless, i.e. no color change has taken place in this period.

6 * -16-

Example VIII

6 liters of an aqueous cleaning solution containing the following amounts of ingredients per liter are prepared: 5 H ^ SO ^ ^ 6 ° Baum®) - * 1.7 g MIRAWET B 0.9 g HF 20 ppm

Aluminum cans of 300 * 1 alloy 10 drawn in one piece are used in this procedure. The cans were covered with fine aluminum particles and pulling oil.

Test samples are treated as follows: a) spraying with the above cleaning solution, which is kept at 53 ° C, b) rinsing with water by immersion in cold water for 30 seconds and c) standing for 30 seconds, after which it is examined for water breaks on both the inside and outside.

20 Look as above with a spray time at step a) of 30 seconds and record the results. A second look as above is tested with a spray time at step a) of seconds and the results are recorded.

Then 200 parts per million MLC0 DL 17 * 1 (a 25 mineral oil based on coolant and lubricant for drawing and ironing aluminum cans) is added to the cleaning solution, and tested a third can as above with a spraying time at step a) of 30 seconds, and a fourth can with a spraying time in step a) of * 15 seconds.

The results of these tests are shown in the following Table H:

Table K.

addition of spraying time in the amount of 35 NALCO XL 17 * 1 ·. ppm seconds water breakage 8201978 -17- 0 30 none 0 1 + 5 none 200 30 none 200 1 + 5 none 5

Comparative example IX

6 liters of cleaning solution are prepared by adding to water, jg per liter H ^ SO ^ (66 ° Baumé), 1.053g per liter Hercules Surfactant AR-150, 0.673g per 10 liters SUEF0HIC LF 17 and 20 parts per million hydrogen fluoride - sour.

Aluminum cans from the same batch as used in Example VIII are tested under the conditions and procedures set forth in Example VIII with the following results:

Table J

addition of spraying time in terms of MLCO XI 17l + «ppm second water break 20 0 30 none 0 1 + 5 none 200 30 extended 200 1 + 5 slightly

Example X

6 liters of an aqueous cleaning solution, which is heavily contaminated with NALC0 XL 17I +, is prepared and contains the following amounts of ingredients per liter: H ^ SO ^ Baum®) “l +, 7 g 30 MIRAWET B 0.9 g HF 20 ppm IALC0 XL 17 ^ - 500 ppm

Aluminum cans of 3001+ alloy, 35 drawn in one piece, were used in this procedure. The cans were covered with fine aluminum particles and pulling oil.

Test samples are treated as follows: a) washing with tap water at 53 ° C for 30 seconds, b) spraying with the above cleaning solution, which is kept at 53 ° C, for 0 seconds, c) rinsing by spraying with tap water for 20 seconds, 10 d) rinsing by spraying with deionized water and e) standing for 30 seconds, after which water fractures on the inside and outside are examined.

15 A look is tested as described above and the results are recorded. Then 0.9 g per liter of the low foaming non-ionic surfactant Plurafac BA 30 is added to a portion of the cleaning solution which is contaminated as mentioned above and a different can as described above is tested. This procedure is repeated adding 0.9 g per liter of the various low foaming nonionic surfactants specified in the table below to fresh portions of the cleaning solution contaminated as above. The results obtained are shown in the following table K:

Table K.

addition of 0.9 g / 1 degree of water fracture 30 non-ionic surfactant _ no extended PLURAFAC RA 30 slightly TRITOR DF 16 no 35 SURF0RIC LF 7 no 8201978

"W

-19- SUEPONIC IF 17 no ANTAROX LF 330 moderate

As can be seen from this example, even when a very heavy contamination of a technically used coolant is present in the composition of the invention, the presence of a small amount of a low foaming nonionic surfactant in addition to the alkali 2-butoxyethoxyacetate does The cleaning power of the composition can increase significantly.

8201978

Claims (9)

1. Aqueous cleaning solution before removing and dissolving fine aluminum particles and cleaning aluminum surfaces of lubricating oils, which solution contains sulfuric acid, hydrofluoric acid and a surfactant, characterized in that the solution contains 1-10 g per liter of sulfuric acid 0.005-0.1 g per liter of hydrofluoric acid and 0.1-10 g per liter of alkali 2-butoxy ethoxy acetate ". Solution according to claim 1, characterized in that the alkali 2-butoxyethoxyacetate is sodium 2-butoxyethoxyacetate and is present in an amount of 0.2-0.8 g per liter. Solution according to claim 1 or 2, characterized in that its pH is 1.0-1.8. k. Solution according to any one of claims 1 to 3, characterized in that the sulfuric acid is present in an amount of 3-5 g per liter and the hydrofluoric acid in an amount of 0.01-0.03 g per liter. Solution according to any one of the preceding claims, characterized in that the hydrofluoric acid is present in an amount such that the solution has an aluminum dissolution rate of 90-280 mg per m aluminum surface treated at a temperature of 5 °. C and a contact time of 1 minute. 6. An aqueous solution concentrate for forming the aqueous cleaning solution according to any one of the preceding claims, characterized in that the concentrate contains 200-600 g per liter of sulfuric acid and 0.01-10 parts by weight of alkali 2-butoxyethoxyacetate per part by weight of sulfuric acid. Concentrate according to claim 6, characterized in that the alkali is 2-butoxyethoxyacetate sodium 2-butoxyethoxyacetate and it is present in an amount of 0.0 ^ -0.27 parts by weight per sulfuric acid part. 8. A method of cleaning an aluminum surface 8201978-21 by a) contacting the surface with an aqueous cleaning solution containing sulfuric acid, hydrofluoric acid and a surfactant, and b) applying the aluminum surface. rinses to remove the cleaning solution, characterized in that the solution according to any one of the preceding claims 1 to 5 is used as the cleaning solution. 9. Process according to claim 8, characterized in that the solution is kept at 46-63 ° C. Method according to claim 8 or 9, 2, characterized in that 90-280 mg of aluminum dissolve per m area. 15 8201978