SURFACE TREATMENT OF FLAT PRODUCTS MADE OF ALUMINIUM ALLOYS COMPRISING COLOUR MEASUREMENTS

Abstract

A method for the surface treatment of flat products made of aluminium alloys. The method includes pickling the flat product, in particular for degreasing the flat product. The method includes carrying out a colour measurement on the surface of the flat product to determine at least one measured colour value after pickling the flat product. The method includes generating output information on the basis of the at least one measured colour value. The output information is indicative of compliance with at least one rule for the measured colour value and outputting or triggering the output of the output information. The invention further relates to a device for the surface treatment of flat products made of aluminium alloys and to a use of a colorimeter which is configured to determine at least one measured colour value in a surface treatment of flat products made of aluminium alloys.

Claims

1. Method for the surface treatment of flat products made of aluminium alloys, the method comprising: pickling the flat product; carrying out a colour measurement on the surface of the flat product to determine at least one measured colour value after pickling the flat product; generating output information on the basis of the at least one measured colour value, wherein the output information is indicative of compliance with at least one rule for the measured colour value; outputting or triggering the output of the output information, wherein the output information is characteristic of a need for error search and carrying out the error search; and wherein the output information can provide an indication that there is an error in the process flow, which is not directly attributed to the composition of at least one treatment solution for the pickling.

2. Method according to claim 1, wherein the output information is further characteristic of whether there is compliance with at least one rule parameter of the at least one treatment solution for the pickling of the flat product.

3. Method according to claim 1, wherein the output information is indicative of the degree of a self-inhibiting process.

4. Method according to claim 1, wherein at least one concentration of a component of the at least one treatment solution is monitored wherein, if there are deviations of the output information from the at least one rule, a conclusion can be drawn about the degree of the self-inhibiting process.

5. Method according to claim 1, wherein the colour measurement is carried out inline and/or at-line with the pickling of the flat product.

6. Method according to claim 1, wherein a visual output of the output information is caused or triggered.

7. Method according to claim 1, wherein, using the output information, an interaction with the treatment method takes place to avoid technical faults.

8. Method according to claim 1, wherein the flat product is pickled with at least one treatment solution and the at least one treatment solution contains at least two acids or at least two bases.

9. Method according to claim 1, wherein the generation of the output information includes a comparison of the at least one measured colour value with at least one reference value.

10. Method according to claim 9, wherein the at least one reference value is predefined at least partially as a function of the aluminium alloy of the flat product, of the dimension of the flat product, of the surface structure of the flat product and/or of the manufacture of the flat product.

11. Method according to claim 9, wherein the comparison of the at least one measured colour value with the at least one reference value includes determining a brightness difference and/or determining a colour distance.

12. Method according to claim 1, further comprising: carrying out a previous colour measurement on the surface of the flat product before the pickling and/or between pickling steps to determine at least one previous measured colour value, wherein the output information is further generated on the basis of the at least one previous measured colour value.

13. Method according to claim 1, wherein a flat product made of an aluminium alloy of the type AA 5xxx, in particular AA 5182, is treated and wherein a luminance L* of at least 58, in particular at least 60, is adjusted.

14. Method according to claim 1, wherein a flat product made of an aluminium alloy of the type AA 6xxx, in particular AA 6016, is treated and wherein a luminance L* of at least 62, in particular at least 64, is adjusted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Further configurations and advantages of the invention can be inferred in the following detailed description of some exemplary embodiments of the present invention, in particular in conjunction with the drawing. In the drawing:

[0083] FIG. 1 shows a schematic representation of an exemplary embodiment of a device according to the invention; and

[0084] FIG. 2 shows a schematic diagram regarding the dependence of the achieved luminance as a function of a treatment parameter.

DETAILED DESCRIPTION OF THE INVENTION

[0085] FIG. 1 shows a schematic representation of an exemplary embodiment of a device 2 according to the invention. The device 2 has a first coil 4, from which a flat product 6 designed as an aluminium alloy strip is unrolled. Means 8 for pickling the flat product 6 are provided which are designed as an immersion bath and/or as a spray apparatus, wherein the flat product 6 comes into contact with at least one treatment solution for pickling.

[0086] The pickling is carried out by means of at least one alkaline treatment solution comprising NaOH and surfactants, wherein the concentration for NaOH is 0.5 to 0.7% by weight and for surfactants is 0.3 to 0.6% by weight. Then, an acid rinse is carried out by means of at least one treatment solution comprising H.sub.2SO.sub.4 and/or HNO.sub.3 with optional addition of HF as fluorides as complexing agents. The acid concentration is in this case 2.5 to 3.5% by weight and the fluoride concentration is 300 to 600 mg/l. After the treatment is carried out, the flat product 6 is wound onto a second coil 12.

[0087] According to the invention, a colorimeter 14 is now provided which is configured to measure the colour on the surface of the flat product 6 to determine at least one measured colour value. The colorimeter 14 is arranged in the running direction of the strip after the means 8 for pickling such that a colour measurement is carried out after pickling the flat product 6. The colour measurement is carried out inline with the pickling of the flat product 6.

[0088] An evaluation apparatus 10 is provided, which is configured to generate output information on the basis of the at least one measured colour value. The generation of the output information in this case includes a comparison of the at least one measured colour value with at least one reference value. For example, the colour measurement of the surface is carried out in the CIE L*a*b* colour space and the luminance L* is determined as the measured colour value.

[0089] The output information is in this case indicative of compliance with at least one rule for the measured colour value, wherein a reference value is predefined. In the present case, it is checked whether the luminance L* complies with a minimum value to be complied with, wherein the minimum value is predefined on the basis of the aluminium alloy of the flat product.

[0090] In an optional configuration, a previous colour measurement is carried out on the surface of the flat product 6 by means of the previous colorimeter 18. The generation of the output information can also be carried out on the basis of the at least one previous measured colour value, wherein a brightness difference is formed between the luminance L* before and after the treatment. An additional rule can, for example, be that a minimum value of the brightness difference is also to be complied with.

[0091] The output information is output to a display 16. The display 16 is, for example, designed as a traffic light and displays green when there is compliance with at least one rule. A yellow signal of the traffic light moreover indicates a deviation from the at least one rule. Additionally, a red signal can be provided which signals a critical deviation, wherein the treatment is also automatically stopped when a critical deviation occurs. The effectiveness of the surface treatment can be determined here with high reliability on the basis of the colour measurement on the treated flat product 6.

[0092] The output information can therefore be characteristic of a need for error search. If it is displayed via the output information that error search is caused, a corresponding error search can be carried out. For example, the output information is also characteristic of compliance with rule parameters of the at least one treatment solution for pickling, such as for instance the pH value and/or the electrical conductivity such that, during the error search, checking the device for mechanical defects can be prioritised.

[0093] At least one treatment parameter of the pickling can be manually regulated at least partially on the basis of the at least one measured colour value. This regulation is carried out at least partially based on the output information.

[0094] For example, when there is a deviation from the at least one rule in the current treatment, an intervention can be carried out by individual treatment parameters of the at least one treatment solution being manually adapted. To this end, a yellow signal can, for example, be used. If there is a critical deviation, the device for the treatment can be checked further and the treatment can be continued after error search and correction of the error. A red signal can, for example, be used for this purpose.

[0095] For further explanation, a schematic diagram regarding the dependence of the achieved luminance, which is plotted as the ordinate, of aluminium alloys of the type AA 5xxx and AA 6xxx as a function of a treatment parameter, which is plotted as the abscissa, is shown in FIG. 2. With a greater treatment parameter, there is, generally speaking, a greater luminance L*, which results from a more complete pickling with a further removal of the oxide layer, intermetallic phases, rolled-in particles and near-surface enrichments. What is problematic with methods from the prior art in this case is that the kinetics of the pickling reaction can depend on a plurality of parameters since self-inhibiting processes also occur with the treatment, for example by the enrichment of reaction-inhibiting accompanying substances.

[0096] Optimal treatment parameters can be adjusted here with the colour measurement on the surface of the treated flat product, and the regulation can also be used for a plurality of different flat products. The different flat products can, for example, have different alloys, manufacturing methods and geometries.

[0097] For example, a comparison of the at least one measured colour value with at least one reference value is carried out. The at least one reference value is determined as a function of the aluminium alloy of the flat product 6, wherein a value L.sub.min is predefined for alloys of the types AA 6xxx and a value L′.sub.min is predefined for alloys of the types AA 5xxx. The value L′.sub.min for the alloys of the types AA 5xxx is, in this example, lower than the value L′.sub.min for the alloys of the types AA 6xxx. For example, a concentration, such as a lye concentration or acid concentration, can be adjusted in the at least one treatment solution, not only on the basis of an absolute value, but rather it is selected such that the minimum values of the luminance L.sub.min or L′.sub.min are achieved with a concentration that is simultaneously as low as possible.

[0098] Additionally, the luminance L* has been measured on flat products from different aluminium alloys under different treatment parameters. The colour measurement of the surface is carried out in the CIE L*a*b* colour space excluding the direct reflection in 45°/0° geometry using a standard illuminant D65 and a viewing angle of 10°.

[0099] Results for the luminance L* for flat products made of the alloy AA 5182 are compiled in Table 1.

TABLE-US-00001 TABLE 1 Alkaline degreasing/pickling Acid rinse/etching NaOH Surfactant Fluoride AA 5182 [% by [% by Etching acid concentration Example L* weight] weight] [% by weight] [mg/l] Result 1 60 0.8 0.5 3.2 329 + 2 60 0.8 0.5 3.2 329 + 3 60 0.8 0.5 3.2 329 + 4 60 0.8 0.5 3.2 329 + 5 59 0.8 0.5 3.2 329 + 6 60 0.7 0.7 3.0 344 + 7 60 0.7 0.7 3.0 344 + 8 58 0.7 0.7 3.0 344 + 9 56 0.8 0.3 2.9 359 − 10 54 0.7 0.3 2.9 212 − 11 55 0.7 0.3 2.9 212 −

[0100] The surfaces of the examples 1-8, which have a satisfactory treatment and therefore a complete removal of the rolling residues, the oxide layer as well as particles and enrichments, are marked here with a result “+”. The examples 9-11, in contrast, exhibit an inadequate treatment of the surface with a result “−”, which in particular can be attributed to an excessively low surfactant concentration in the alkaline treatment zone and a somewhat lower acid concentration during rinsing or etching.

[0101] However, the quality of the treated surface can be determined on the basis of the values for the luminance L*, wherein the positive results of the treatment for the alloy of the type AA 5182 achieve values for the luminance of 58 and in particular 60. For example, a corresponding deviation can be indicated with the present method. For example, the acid concentration can be manually or partially automatically regulated during etching on the basis of the measured luminance L* such that the mentioned values of the luminance are achieved.

[0102] Further results for the luminance L* for flat products made of the alloy AA 6016 are compiled in Table 2.

TABLE-US-00002 TABLE 2 Alkaline Acid rinse/etching degreasing/pickling Fluoride AA 6016 NaOH Surfactant Etching acid concentration Example L* [m/m %] [m/m %] [m/m %] [mg/l] Result 12 64 0.8 0.3 2.9 378 + 13 62 0.7 0.4 3.1 300 + 14 62 0.7 0.7 3.0 344 + 15 63 0.7 0.7 3.0 344 + 16 62 0.7 0.7 3.0 344 + 17 62 0.7 0.7 3.0 344 + 18 62 0.6 0.3 3.5 284 + 19 62 0.6 0.3 3.5 284 + 20 57 0.8 0.7 2.7 277 − 21 59 0.8 0.2 3.3 495 − 22 60 0.7 0.4 2.8 358 −

[0103] A positive treatment result has shown here for the examples 12-19, while the treatment for the examples 20-22 is only inadequate. For the examples 20 and 22, it can be assumed that the negative result is associated with an excessively low acid concentration during etching. Example 20 has also been etched with an excessively low fluoride concentration. Example 21 is, in contrast, treated with comparatively high concentrations during etching, wherein a low surfactant concentration is present, however, during pickling/degreasing.

[0104] A conclusion regarding the result of the treatment on the basis of the luminance L* can also be made here, wherein the values for the luminance L* of the positive examples 12-19 are at least 62 and in particular at least 64.

[0105] The method therefore enables the treatment of a plurality of flat products made of different aluminium alloys, wherein reference values such as minimum luminance L* to be achieved, for example, are determined on the basis of the properties of the flat products.

[0106] Table 3 shows, in relation to the possible variation of the values for the luminance L*, colour measurements on alloys of the types AA 5754 and AA 6451. Comparatively high values for the luminance L* of at least 68 are achieved with a positive treatment result on alloys of the types AA 5754. Comparatively low minimum values for the luminance L* of at least 55 are achieved with a positive treatment result on alloys of the types AA 6451. The luminance values for alloys of the types AA 6451 are here also lower than luminance values, which are usually obtained for other alloys of the type AA 6xxx.

TABLE-US-00003 TABLE 3 Alkaline Acid etching degreasing/pickling Fluoride NaOH Surfactant Etching acid Concentration Alloy L* [m/m %] [m/m %] [m/m %] [mg/l] Result AA 5754 74 0.8 0.3 2.9 378 + AA 5754 71 0.8 0.3 2.9 378 + AA 5754 68 0.8 0.3 2.9 359 + AA 5754 68 0.8 0.3 2.9 359 + AA 6451 57 0.8 0.3 2.9 378 + AA 6451 56 0.8 0.3 2.9 378 + AA 6451 56 0.8 0.4 3.6 326 + AA 6451 55 0.8 0.4 3.6 326 +

[0107] In addition to the luminance L*, other measured colour values can also be used for assessing the effect of the treatment. To this end, Table 4 shows an overview of measured colour values together with an assessment of the treatment result.

[0108] The colour measurement was carried out in this case after the treatment. The flat products consist of an alloy of the type AA 6016.

[0109] For example, b* can also be used here as the measured colour value in order to obtain output information indicative of compliance with at least one rule. In the measurement series of Table 4, for example, lower values for b* and in particular values of b* below 10.0 or 8.0 are indicative of a good treatment result.y

[0110] Similarly, ΔE* can alternatively or cumulatively be used for the assessment, wherein a maximum distance to a reference pattern and/or a minimum distance to a colour measurement before the surface treatment displays a good treatment result. The maximum distance to a reference pattern is a lower value of ΔE*. The minimum distance to a colour measurement before the surface treatment corresponds to higher values of ΔE*.

[0111] In Table 5a, another example of a treatment comprising the pickling of a flat product made of an alloy of the type AA 5182 is shown, which takes place under a chemical reaction, wherein a self-inhibiting process occurs in the chemical reaction. In this case, the treatment parameters detectable online have been automatically regulated during the treatments and kept in a predefined interval. The treatment parameters detectable online are, for example, the conductivity of the at least one alkaline treatment solution for degreasing/pickling and the conductivity of the at least one acid treatment solution for rinsing. The treatment parameters detectable online are recorded for different times on the same day in Table 5a.

[0112] Treatment parameters have also been collected discontinuously in an offline measurement, which parameters are reproduced in Table 5b. The concentrations measured here were also in the respectively predefined intervals.

[0113] Due to the occurrence of self-inhibiting processes, the pickling attack of the at least one treatment solutions can be reduced or slowed down, which can lead to an insufficient treatment result. The self-inhibiting processes can lead to a latent effect such as a “dropping off” of the at least one treatment solution, for example. The effect of the self-inhibiting processes may prevent a definite statement regarding the pickling result on the basis of global parameters that are detectable online such as the electrical conductivity and the pH value, and non-continuously determinable treatment parameters such as Al concentration or the concentration of the individual components of the at least one treatment solution. It can be discerned from Table 5a that, in spite of the substantially constant treatment parameters for the at least one treatment solution, the pickling attack on the flat product varied and notably decreased within a few hours.

[0114] For the brightness L* however, there was a good correlation with the treatment result, such that based on the measured colour values, output information can be made available which is characteristic of the need for error search. The output information can also be characteristic of compliance with the rule parameters of the at least one treatment solution for the treatment of the flat product such as from Tables 5a and 5b, for example.

[0115] Another example of a treatment comprising the pickling of flat products made of alloys of the type AA 5754 and of the type AA 5182 is shown in Table 6a. The times noted in Table 6a relate to a different day to the measurements shown in Table 5a. The treatment parameters that are detectable discontinuously and offline are reproduced in Table 6b.

[0116] The difference in the brightness values L* between 19:42 and 20:33 is at least partially due to the change of the alloys, wherein both brightness values still indicate a good treatment result. The brightness value L* of the third measurement at 21:03, however, both in comparison to the previously manufactured alloy of the same type and in comparison to a reference value for L* of at least 58, in particular 60, does not comply with a rule for the brightness value.

[0117] The brightness measurement L* therefore allows to conclude that in the time period between 20:33 and 21:03 a problem must have occurred, since the lower brightness is indicative of an excessively low pickling attack. Accordingly, output information could be generated that is characteristic of the fact that error search is necessary. The output information could also be characteristic of the fact that the measured treatment parameters of the at least one treatment solutions maintained are compliant with the rule parameters.

[0118] In error search triggered at this point, a defective spray ring was able to be identified, whose failure would not have been readily noticed if relying solely on the chemical analyses of the baths.

TABLE-US-00004 TABLE 4 Alkaline degreasing/pickling Acid etching Measured Al Fluoride Al- colour values NaOH Surfactant concentration Etching acid concentration concentration Alloy L* a* b* ΔE* [m/m %] [m/m %] [g/l] [m/m %] [mg/l] [g/l] Result AA6016 64 −9.3 7.8 32 0.6 0.5 1.4 3.3 378 1.8 + AA6016 64 −9.2 8.0 32 0.6 0.3 1.2 3.0 460 1.0 + AA6016 57 −20.8 16.0 43 0.5 0.4 0.2 2.8 326 0.9 −

TABLE-US-00005 TABLE 5a Conductivity Conductivity (alkaline) (acid) Time Alloy L* [mS/cm] [mS/cm] 18:48 AA5182 56 34.2 104.6 19:29 AA5182 54 34.6 103.7 20:57 AA5182 50 34.5 103.6

TABLE-US-00006 TABLE 5b Al Lye Surfactant Al Fluoride Acid concentration concentration concentration concentration concentration concentration (alkaline) [g/l] [mime %] [mime %] (acid) [g/l] [mg/l] [mime %] 1.4 0.8 0.6 0.6 512 3.1

TABLE-US-00007 TABLE 6a Conductivity Conductivity (acid) Time Alloy L* (alkaline) [mS/cm] Result 19:42 AA5754 68 33.1 97.8 + 20:33 AA5182 63 33.8 98.5 + 21:03 AA5182 56 34.6 97.9 −

TABLE-US-00008 TABLE 6b Al Lye Surfactant Al Fluoride Acid concentration concentration concentration concentration concentration concentration (alkaline) [g/l] [mime %] [mime %] (acid) [g/l] [mg/l] [mime %] 1.8 0.8 0.3 0.4 367 2.9

[0119] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0120] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0121] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.