DE102020106353A1 - Method for descaling a steel strip and plant for descaling a steel strip - Google Patents

Abstract

The invention relates to a system for descaling a steel strip (1). The system has: - a treatment line, having a tub (2) filled with an acidic solution as a treatment bath (3), - a transport device (4) for inserting a steel belt (1) into the treatment line and for transporting the steel belt ( 1) through the treatment line, - an electrotechnical device (5) for continuous cathodic polarization of the steel strip (1) during transport through the treatment line. The transport device (4) is coupled to means (6) for monitoring a belt speed. There is also a control device (7) coupled to the means (6) for monitoring. The invention also relates to a method.

Description

The invention relates to a method for descaling a steel strip and an installation for descaling a steel strip.

During the production process of steel strips, so-called scale is inevitable. The term “scale” includes oxides of the iron contained in the steel as well as the other alloying elements contained in the steel. Scale is created in particular during hot rolling of steel through the reaction of oxygen, especially the oxygen contained in the air, with the elements mentioned. Scale typically has FeO, Fe ₂ O ₃ , Fe ₃ O ₄ and oxides of the alloying elements contained in steel in addition to Fe, for example MnO, SiO ₂ and others. Layers of scale are typically up to several micrometers thick.

Processes for removing layers of scale are known to the person skilled in the art.

DE 10 2005 055 768 A1 discloses a method for descaling steel strips, the respective steel strip being anodically ^{polarized with a current density of 0.3 to 20 A / dm 2} and a mixture of hydrochloric acid, sulfuric acid, pickling inhibitors and surfactants being used as the pickling solution.

EP 0 763 609 A1 discloses a method for the electrolytic pickling of steel strips comprising the treatment of the steel strips in an alkaline electrolyte with alternating anodic and cathodic strip polarization.

With the methods known from the prior art, the existing scale can essentially be completely removed. However, this can lead to excessive pickling of the grain boundaries, which can have a negative effect on subsequent process steps, in particular the application of a coating that protects against corrosion. Another disadvantage of the known methods is that the scale present on the surface is not completely removed, which can also lead to problems in subsequent process steps. Another disadvantage of the above-mentioned methods is that, although the treatment time for the steel strips is too short, the scale is not removed completely enough, but if the treatment time is only slightly too long, the steel strip itself is structurally damaged, since undesirable chemical processes are caused by the treatment liquid used Steel band is coming. The result of this is that the treatment time of the steel strip must be set in a targeted manner and must be precisely monitored in order to avoid or at least detect deviations in the treatment time - possibly also unintentional. Each of the above-mentioned disadvantages leads to a great deal of effort and, as a result, to high costs.

Against the background of the disadvantages mentioned, the problem arises of being able to provide improved possibilities for descaling steel strip.

The object is achieved with a method with the features of claim 1 and with a system for descaling with the features of claim 9.

A method is provided for the purpose of descaling a steel strip.

1. A) Einführen des Zunder aufweisenden Stahlbands in eine Behandlungslinie. Die Behandlungslinie ist ein Behandlungsbad oder eine Folge mehrerer, aus Sicht der Stahlbandtransportrichtung hintereinander angeordneter, Behandlungsbäder. Das Behandlungsbad ist beziehungsweise die Behandlungsbäder sind eine saure Lösung.
2. B) Bandtransport des Stahlbands durch die Behandlungslinie mit einer vorgegebenen Bandgeschwindigkeit. Die vorgegebene Bandgeschwindigkeit entspricht einer vorgesehenen Behandlungsdauer. Die Behandlungsdauer bezeichnet einen Zeitraum, während welcher eine Position des Stahlbands, das heißt eine Position in ihrer Längserstreckung, einem Säurekontakt ausgesetzt ist. Eine vorgesehene Behandlungsdauer ist entsprechend derjenige Zeitraum, der für eine gegebene Position des Stahlbands zum Säurekontakt planmäßig vorgesehen ist. Die vorgegebene Bandgeschwindigkeit ist bevorzugt konstant, es kann aber auch vorgesehen sein, dass die vorgegebene Bandgeschwindigkeit zeitabhängig veränderlich ist.

In order to achieve the goal, the method provides that at least the following steps are carried out:

1. A) Introducing the steel strip with scale into a treatment line. The treatment line is a treatment bath or a sequence of several treatment baths arranged one behind the other from the point of view of the steel strip transport direction. The treatment bath or the treatment baths are an acidic solution.
2. B) Belt transport of the steel belt through the treatment line at a specified belt speed. The specified belt speed corresponds to an intended treatment duration. The treatment duration denotes a period of time during which a position of the steel strip, that is to say a position in its longitudinal extension, is exposed to acid contact. An envisaged treatment duration is accordingly that period of time which is planned for a given position of the steel strip for acid contact. The predefined belt speed is preferably constant, but it can also be provided that the predefined belt speed is variable as a function of time.

This results from the fact that with a certain length of the treatment line by specifying the belt speed for a certain position or a certain section of the belt, how long the certain position of the belt is subjected to the treatment, i.e. how long it is is in the treatment bath or in one of the treatment baths. The treatment duration is therefore the total duration during which, with a given course of the procedure, a specific location along the longitudinal extension is subjected to an acid treatment, that is to say a specific point on the strip or a specific strip section in the treatment line. In the standard case of a constant belt speed of the steel belt, the treatment time is the same for every point on the steel belt. It is essential that the steel strip is treated with a treatment duration that is specified by a person performing the process.

In a special case of the method and the system described below, the treatment line is a treatment bath located in a tub, the treatment bath being divided into a sequence of treatment stages by means of separating cells. For example, it can be provided that in the different separating cells acid can be used with different periods of use that has already taken place, whereby the efficiency of use is increased overall, since the acid can be used for a longer period of time.

In the context of the present invention, “acidic solution” means that it has a pH of less than 7, preferably 0.01 to 4. An aqueous solution is preferably used, that is to say: a solution based on water. For example, an aqueous solution at least containing HCl and preferably at least one salt, an aqueous solution at least containing H ₂ SO ₄ and preferably at least one salt or an aqueous solution at least containing H ₂ SO ₄ and H ₃ PO ₄ is used as the acidic solution. It can further be provided, for example, that those salts are also used or almost completely that come from the steel strip to be treated and / or from the scale to be removed, for example iron salts, chromium salts, manganese salts, sulfate, chloride, hydroxide, etc. . present.

In a preferred embodiment of the process according to the invention, a solution containing at least one iron salt is used. Iron salts in which the iron cation has an oxidation number of +2 are preferably used. Iron salts used with particular preference are selected from the group consisting of FeSO ₄ , FeCl ₂ and mixtures thereof.

According to the invention, the steel strip is placed in a cathodically polarized state during the treatment period, that is to say during the intended treatment period and also during any additional treatment period that may be present. In a preferred variant, this means that a given position, meaning in the length extension, of the steel strip is cathodically polarized during the entire treatment period, particularly preferably that the entire steel strip is guided through the treatment line exclusively in the cathodically polarized state, i.e. after after completing the treatment line, the entire steel strip has undergone the treatment in the acid bath or baths and during which it has been cathodically polarized continuously, that is: without interruption.

According to the invention, direct current is used. This can be generated with all devices known to the person skilled in the art, for example by means of a corrosion protection rectifier which is contacted with the strip and by means of which the strip is set as a cathode. The opposite pole is preferably formed by a suitable electrode, for example a graphite or platinum electrode, which is immersed in the acidic solution. A dimensionally stable electrode is particularly preferably used.

• C) ein Überwachen der Bandgeschwindigkeit. Dies kann bedeuten, dass die Geschwindigkeit des Bands unmittelbar überwacht wird, beispielsweise mit Hilfe optischer Methoden. Alternativ oder zusätzlich kann auch vorgesehen sein, dass die Geschwindigkeit des Bands mittelbar bestimmt wird, beispielsweise über die Kontrolle der Drehzahl einer oder mehrerer zum Transport des Bands eingesetzter Transportrollen.

A further process step according to the invention takes place

• C) monitoring the belt speed. This can mean that the speed of the belt is monitored directly, for example with the help of optical methods. Alternatively or in addition, it can also be provided that the speed of the belt is determined indirectly, for example by controlling the speed of one or more transport rollers used to transport the belt.

According to the invention it is provided that if the monitoring results in a drop in the belt speed below the specified belt speed, it is determined which additional treatment duration, in particular while continuously maintaining the cathodically polarized state, of the steel belt the decrease in the belt speed leads. In the simplest case by way of example, that the decrease in the belt speed is a belt standstill for a determined belt standstill time, the belt standstill time results as an additional treatment duration.

According to the invention it is also provided that if the intended treatment duration plus the additional treatment duration does not exceed a maximum treatment duration, the steel strip is fed to a regular further processing, and otherwise the steel strip is further processed as scrap.

In the simplest case, regular further processing can be, for example, reeling immediately after descaling to provide the steel strip for distribution, but further connection steps can also be provided, such as coating, for example with a corrosion protection layer, preferably a Zn-containing corrosion protection layer .

The further processing of the steel strip as scrap is understood to mean that the steel strip for which the maximum treatment time has been exceeded is viewed as defective or potentially defective and, as a precaution, is not given for further processing or distribution, but instead is alternatively sent to recycling, for example.

According to the invention, the maximum treatment duration is 900 seconds or longer.

In other words, this means that the steel belt is monitored, and in the event of a - if, then typically unintentional - deviation of the belt transport from the specified sequence, for example due to a belt standstill despite the belt standstill, regular further processing of the Steel band is made. According to the invention, the certain condition is that in all cases an unintentional stay of the cathodically polarized steel strip, preferably the continuously cathodically polarized steel strip, more precisely: a section of the steel strip, in the treatment bath for up to 900 seconds, remains in the treatment bath without negative consequences for further processing if a specified maximum treatment time is exceeded, for example if a maximum treatment time of 900 seconds is exceeded, the steel strip is regarded as scrap.

The innovation is based on two fundamental findings, which the developers of the innovation described above noticed in the course of experiments and which they make use of for the process variants described as well as for the system explained below.

Firstly, the developers have found that treating a steel strip containing scale in an acidic solution and with continuous cathodic polarization, provided a minimum treatment time, is completely sufficient to completely remove the scale and to obtain an excellent pickling result. It is only necessary that a minimum treatment duration of, for example, about 20 seconds is achieved, which, however, is almost unavoidable in any case for reasons of practicality or is usually achieved in any case. Surprisingly, the developers have found that an exclusive, preferably during the entire stay of the steel strip in the treatment bath, continuous cathodic polarization of the steel strip is not only sufficient to remove the scale, but also does not completely pickle the grain boundaries and grain boundary oxidation is preserved.

Secondly, the developers have surprisingly found that even if the continuously cathodically polarized steel strip remains in the acid strip for a relatively long time, which is not provided for in the real production process for reasons of economy, namely with residence times of 1200 seconds and more, the steel strip, contrary to all expectations and with previously known In spite of the long possibility of an acid attack on the steel strip in the continuously cathodically polarized state, no over-pickling occurred and no standstill spots were observed. An explanation for this observation has not yet been conclusively found; the observation may be based on the establishment of an electrolytic equilibrium state on the steel strip surface. For the method according to the invention, the knowledge is specifically used that at least within certain, but against the background of the previously known knowledge, exceptionally far-reaching limits for the remaining time of the steel strip in acid, at least with cathodic polarization, further use or further processing of the steel strip is possible without any restriction . This fact is systematically exploited by the fact that if a belt standstill is detected, for example, the standstill time is measured and evaluated to the effect that, even with long standstills of more than 15 or more than 20 minutes, further processing of the steel strip still takes place and only above certain limits, for example at 1400 Seconds or 2400 seconds of downtime, to be on the safe side, the steel strip is marked as scrap.

A preferred variant of the method according to the invention comprises the step that when a belt standstill is detected, a standstill time is measured until the belt transport is resumed and, if the intended treatment duration plus the additional treatment duration caused by the standstill time does not exceed the maximum treatment duration, the steel belt of the regular further processing is fed, and otherwise the steel strip is processed further as scrap. In other words, when a tape standstill is detected, a timer is started which, for example, can be implemented in a control device for controlling a tape transport device used for tape transport, and which measures the period of time that has elapsed, beginning with the tape standstill, until the tape transport is resumed. This procedure has the advantage of being easy to implement with little investment of resources.

It is preferably provided that the intended treatment duration is between 20 seconds and 600 seconds, particularly preferably between 25 seconds and 300 seconds, even more preferably between 25 and 240 seconds. It goes without saying that the shortest possible duration of treatment is advantageous for economic reasons if the treatment result is still successful.

The current density on the steel strip can for example be set to a value between 5 and 150 A / dm ² , preferably between 20 and 120 A / dm ²

According to an advantageous further development, it is provided that upon detection of the decrease in the belt speed, the current density is automatically increased, preferably by at least 20 percent, at least during the period of the sustained decrease in the belt speed. For example, when a belt standstill is detected, the increase in the current density can be initiated automatically, for example by the control device which is coupled to a system for carrying out the method according to the invention and in particular both to a transport device for transporting the steel strip and to an electrotechnical device for cathodic polarization. This procedure is based on the idea of increasing the cathodic protection of the steel strip from adverse reactions with the acid in the event of a belt standstill.

The maximum duration of treatment is preferably at least 1200 seconds. Since no adverse effects on the surface, structure and / or microstructure of the steel strip could be detected even if the steel strip remained in the acid for such a long time, it is advisable to set the maximum treatment time to a value of or above 1200 seconds in order to avoid possible process windows to enlarge further. In order to enable the implementation and, in particular, the implementation in terms of equipment, for example, an upper value for the specified maximum treatment duration of 1400 or 2400 seconds can be provided.

The steel strip is preferably a hot strip.

The treatment can take place at a temperature higher than room temperature, for example at a treatment bath temperature between 30 degrees Celsius and 70 degrees Celsius.

Sulfuric acid or hydrochloric acid, for example, can be provided as the acidic solution.

In a preferred embodiment, an aqueous solution at least containing HCl and preferably at least one salt, an aqueous solution at least containing H ₂ SO4 and preferably at least one salt or an aqueous solution at least containing H ₂ SO4 and H3PO4 is used as the acidic solution.

According to the invention, all salts which originate from the flat steel product to be treated or from the scale to be removed can be present as salts, for example iron salts, chromium salts, manganese salts etc. Sulphate, chloride, hydroxide etc. can be present as counterions. According to the invention, the salts preferably present in the solution are not additionally added to the solution from outside, but rather the salts get into the solution in the process from the flat steel product or the scale. The concentrations of the salts mentioned as preferred are reached after a very short time.

In a preferred embodiment of the process according to the invention, a solution containing at least one iron salt is used. Iron salts in which the iron cation has an oxidation number of +2 are preferably used. Iron salts used with particular preference are selected from the group consisting of FeSO ₄ , FeCl ₂ and mixtures thereof.

The solutions preferably contain an iron salt selected from the group consisting of FeSO ₄ , FeCl ₂ and mixtures thereof.

If an aqueous solution containing at least H ₂ SO _{4 is} used, it preferably contains 100 to 400 g / L, particularly preferably 180 to 300 g / L, H ₂ SO ₄ .

If an aqueous solution containing at least HCl is used, it preferably contains 10 to 30% by weight, particularly preferably 15 to 25% by weight, of HCl.

If an aqueous solution containing at least one iron salt is used, it preferably contains 10 to 50 g / L, particularly preferably 20 to 45 g / L, of the at least one iron salt.

If an aqueous solution containing HCl and at least one iron salt is used, it preferably contains 10 to 30% by weight, particularly preferably 15 to 25% by weight, HCl and 10 to 50 g / L, particularly preferably 20 to 40 g / L , the at least one iron salt, in particular FeCl ₂ .

If an aqueous solution containing H ₂ SO ₄ and at least one iron salt is used, it preferably contains 100 to 400 g / L, particularly preferably 180 to 300 g / L, H ₂ SO ₄ and 10 to 50 g / L, particularly preferably 20 up to 45 g / L, of the at least one iron salt, in particular FeSO4.

If an aqueous solution containing at least H ₂ SO ₄ and H ₃ PO _{4 is} used, it preferably contains 20 to 60% by volume, particularly preferably 30 to 50% by volume, very particularly preferably 40 to 50% by volume, H ₃ PO ₄ and 20 to 60% by volume, particularly preferably 30 to 50% by volume, very particularly preferably 30 to 40% by volume, H ₂ SO ₄ .

Further components, for example surfactants, may optionally be present in the solutions mentioned.

• - aus einem Stahl besteht, der kein Edelstahl ist, oder
• - aus einem Stahl besteht, der ein IF-Stahl ist.

The method with steel belt is particularly preferably used, which

• - consists of a steel that is not stainless steel, or
• - consists of a steel that is an IF steel.

For such steels, the method unfolds its particular advantages, since steels made from them have shown a high susceptibility to standstill spots in known pickling processes.

• Das Stahlband besteht bevorzugt aus einem Stahl gemäß einer der der fünf nachfolgend genannten Legierungsvorschriften:
  • I:
    • 0,16 bis 0,18 C; 0,35 bis 0,45 Si; 1,45 bis 1,60 Mn; 0,00 bis 0,02 P; 0,00 bis 0,008 S; 0,02 bis 0,045 Al; 0,00 bis 0,08 Cr; 0,00 bis 0,12 Cu; 0,00 bis 0,03 Mo; 0,0035 bis 0,0085 N; 0,00 bis 0,10 Ni; 0,02 bis 0,03 Nb; 0,01 bis 0,02 Ti; 0,00 bis 0,02 V; 0,00 bis 0,0005 B; Rest Fe und unvermeidbare Verunreinigungen.
  • II:
    • 0,13 bis 0,15 C; 0,15 bis 0,25 Si; 1,55 bis 1,70 Mn; 0,00 bis 0,015 P; 0,00 bis 0,003 S; 0,02 bis 0,05 Al; 0,70 bis 0,85 Cr; 0,00 bis 0,10 Cu; 0,00 bis 0,10 Mo; 0,00 bis 0,008 N; 0,00 bis 0,10 Ni; 0,00 bis 0,005 Nb; 0,03 bis 0,04 Ti; 0,00 bis 0,01 V; 0,0008 bis 0,0012 B; Rest Fe und unvermeidbare Verunreinigungen.
  • III:
    • 0,100 bis 0,500 C; 0,01 bis 1,50 Si; 0,50 bis 2,00 Mn; 0,000 bis 0,020 P; 0,000 bis 0,005 S; 0,00 bis 1,50 Al; 0,01 bis 1,00 Cr; 0,00 bis 0,10 Cu; 0,01 bis 0,2 Mo; 0,000 bis 0,001 N; 0,00 bis 0,01 Ni; 0,0010 bis 0,0100 B; Rest Fe und unvermeidbare Verunreinigungen.
  • IV:
    • 0 bis 0,2 C; 0 bis 2 Si; 0 bis 1 Mn; 0,000 bis 0,100 P; 0,000 bis 0,030 S; 3 bis 7 Al; 3 bis 11 Cr; 0 bis 3 Cu; 0 bis 2 Mo; 0 bis 0,1 N; 0 bis 2 Ni; 0 bis 1 Nb; 0,25 bis 0,3 Ti; 0 bis 1 V; 0,0000 bis 0,1000 B; Rest Fe und unvermeidbare Verunreinigungen.
  • V:
    • 0,1 bis 1 C; 0,6 bis 1,8 Si; 15 bis 26 Mn; 0 bis 0,08 P; <0,001 bis 0,03 S; 0,3 bis 2 Al; 0 bis 8 Cr; 0 bis 5 Cu; 0 bis 2 Mo; 0,003 bis 0,1 N; 0,1 bis 8 Ni; 0,1 bis 0,3 Nb; 0 bis 0,5 Ti; 0 bis 0,5 V; 0 bis 0,01 B; Rest Fe und unvermeidbare Verunreinigungen.

For example, a steel can be used, in addition to iron and unavoidable impurities, consisting of (each in percent by weight, in short:% by weight):

• The steel strip is preferably made of a steel in accordance with one of the five alloy specifications listed below:
  • I:
    • 0.16 to 0.18 C; 0.35 to 0.45 Si; 1.45 to 1.60 Mn; 0.00 to 0.02 P; 0.00 to 0.008 S; 0.02 to 0.045 Al; 0.00 to 0.08 Cr; 0.00 to 0.12 Cu; 0.00 to 0.03 Mo; 0.0035 to 0.0085 N; 0.00 to 0.10 Ni; 0.02 to 0.03 Nb; 0.01 to 0.02 Ti; 0.00 to 0.02 V; 0.00 to 0.0005 B; Remainder Fe and unavoidable impurities.
  • II:
    • 0.13 to 0.15 C; 0.15 to 0.25 Si; 1.55 to 1.70 Mn; 0.00 to 0.015 P; 0.00 to 0.003 S; 0.02 to 0.05 Al; 0.70 to 0.85 Cr; 0.00 to 0.10 Cu; 0.00 to 0.10 Mo; 0.00 to 0.008 N; 0.00 to 0.10 Ni; 0.00 to 0.005 Nb; 0.03 to 0.04 Ti; 0.00 to 0.01 V; 0.0008 to 0.0012 B; Remainder Fe and unavoidable impurities.
  • III:
    • 0.100 to 0.500 C; 0.01 to 1.50 Si; 0.50 to 2.00 Mn; 0.000 to 0.020 P; 0.000 to 0.005 S; 0.00 to 1.50 Al; 0.01 to 1.00 Cr; 0.00 to 0.10 Cu; 0.01 to 0.2 Mo; 0.000 to 0.001 N; 0.00 to 0.01 Ni; 0.0010 to 0.0100 B; Remainder Fe and unavoidable impurities.
  • IV:
    • 0 to 0.2 C; 0 to 2 Si; 0 to 1 Mn; 0.000 to 0.100 P; 0.000 to 0.030 S; 3 to 7 Al; 3 to 11 Cr; 0 to 3 Cu; 0 to 2 Mo; 0 to 0.1 N; 0 to 2 Ni; 0 to 1 Nb; 0.25 to 0.3 Ti; 0 to 1 V; 0.0000 to 0.1000 B; Remainder Fe and unavoidable impurities.
  • V:
    • 0.1 to 1 C; 0.6 to 1.8 Si; 15 to 26 Mn; 0 to 0.08 P; <0.001 to 0.03 S; 0.3 to 2 Al; 0 to 8 Cr; 0 to 5 Cu; 0 to 2 Mo; 0.003 to 0.1 N; 0.1 to 8 Ni; 0.1 to 0.3 Nb; 0 to 0.5 Ti; 0 to 0.5 V; 0 to 0.01 B; Remainder Fe and unavoidable impurities.

• - Eine Behandlungslinie, aufweisend eine Wanne, gefüllt mit einer sauren Lösung als Behandlungsbad. Es kann beispielsweise eine der sauren Lösungen genutzt werden, wie sie in Zusammenhang mit dem Verfahren oben genannt werden.
• - Eine Transportvorrichtung zum Einführen eines Stahlbands in das Behandlungsbad der Behandlungslinie hinein und zum Transportieren des Stahlbands durch das Behandlungsbad hindurch. Insbesondere kann die Transportvorrichtung eine oder mehrere Transportrollen aufweisen.
• - Eine elektrotechnische Einrichtung zur kontinuierlichen kathodischen Polarisierung des Stahlbands während des Transports, bevorzugt während des gesamten Transports, durch die Behandlungslinie. Die elektrotechnische Vorrichtung kann insbesondere einen Gleichrichter und eine elektrische Kontaktierung des Minuspols des Gleichrichters mit dem Stahlband aufweisen.

Another idea of the invention relates to a system for descaling a steel strip, preferably by means of a method in accordance with the method management explained at the beginning or one of its developments. A plant for descaling the steel strip comprises at least:

• - A treatment line comprising a tub filled with an acidic solution as a treatment bath. For example, one of the acidic solutions mentioned above in connection with the method can be used.
• A transport device for introducing a steel strip into the treatment bath of the treatment line and for transporting the steel strip through the treatment bath. In particular, the transport device can have one or more transport rollers.
• - An electrotechnical device for the continuous cathodic polarization of the steel strip during transport, preferably during the entire transport, through the treatment line. The electrotechnical device can in particular have a rectifier and electrical contacting of the negative pole of the rectifier with the steel strip.

• - Die Anlage weist außerdem eine Steuervorrichtung auf, die mit den Mitteln zur Überwachung gekoppelt ist und eingerichtet ist, in Abhängigkeit von der Überwachung der Bandgeschwindigkeit das Überschreiten einer Maximalbehandlungsdauer des Stahlbands zu erkennen und bei Überschreiten der Maximalbehandlungsdauer das Stahlband als Ausschuss zu markieren. Das „Markieren“ als Ausschuss ist dahingehend zu verstehen, dass in nachvollziehbarer Weise dokumentiert wird, dass ein betroffenes Stahlband als Ausschuss zu behandeln ist, wobei neben unmittelbar auf dem Band angebrachte Markierungen auch Einträge in einem Durchführungsprotokoll und dergleichen als „Markierung“ zu verstehen sein sollen.

The transport device is coupled to means for monitoring a belt speed. The means for monitoring the belt speed can, for example, determine the belt speed directly, for example by means of optical detection of the guided steel belt. As an alternative or in addition, it can be provided that the means for monitoring the belt speed determine the belt speed indirectly; For example, the means for monitoring can have a speed sensor, which is arranged on a transport roller to detect the speed of rotation.

• The system also has a control device which is coupled to the monitoring means and is set up to recognize the exceeding of a maximum treatment duration of the steel strip as a function of the monitoring of the belt speed and to mark the steel belt as scrap if the maximum treatment duration is exceeded. "Marking" as scrap is to be understood to mean that it is documented in a comprehensible manner that an affected steel strip is to be treated as scrap, whereby, in addition to markings attached directly to the strip, entries in an execution protocol and the like are to be understood as "marking" should.

In an advantageous development, the transport device has at least one transport roller, the means for monitoring being designed as means for monitoring the roller speed of the transport roller, for example as a speed sensor which is arranged on the transport roller. The control device is set up to determine a standstill time up to the resumption of the belt transport when a roller standstill is detected and to mark the steel belt as scrap if the maximum treatment time is exceeded by the standstill time plus an intended treatment time.

The maximum duration of treatment is preferably at least 900 seconds, particularly preferably at least 1200 seconds. The maximum treatment time is advantageously less than 2400 seconds.

The acidic solution is preferably a sulfuric acid or a hydrochloric acid.

According to a further development, the control device is also coupled to the electrotechnical device and configured to cause the electrotechnical device to automatically increase a current density generated for cathodic polarization upon detection of a reduction in the transport speed or a standstill of the transport roller.

Further details, features and advantages of the subject matter of the invention emerge from the following description in connection with the figure.

It goes without saying that the features mentioned above and also explained below can be used not only in the respectively specified combination, but also in other combinations or on their own.

• 1: eine schematische Darstellung einer erfindungsgemäßen Anlage;

Show it:

• 1 : a schematic representation of a system according to the invention;

Examples

The invention is explained in more detail below on the basis of exemplary embodiments.

Samples of the steel grades listed in Table 1 with the dimensions 20 × 30 × 4.3 mm ³ (hot strip) are treated with the solutions listed in Table 1 under the corresponding test conditions with regard to electrolyte, current density, treatment duration, bath temperature and turbulence. The types of steel 1 , 2 , 3 , 4th and 5 have the compositions according to Table 1 (all data in% by weight):

The samples are immersed in the electrolyte (temperature between 55 degrees Celsius and 70 degrees Celsius) and cathodically polarized. A rectifier is used as the power source and a platinum mesh is used as the counter electrode. A new sample is used for each individual experiment. The following tests were carried out for each type of steel: cathodic polarization at 40 A / dm ² for 180 seconds, at 60 A / dm ² for 210 seconds, at 100 A / dm ² for 180 seconds, at 60 A / dm ² for 600 seconds, at 60 A / dm ² for 1,200 seconds.

• Elektrolyt 1H₂SO₄ (250 g/L) , FeSO₄ × 7 H₂O (40 g/L) in Wasser
• Elektrolyt 2HCl (20 % gew.-ig), FeCl₂ × 4 H₂O (30 g/L) in Wasser.
• Anschließend erfolgt eine metallographische Bewertung jeder der gebeizten Proben am metallographischen Schliffbild. Es zeigte sich, dass bei jeder Probe der Zunder entfernt war, aber bei keiner Probe das Grundmaterial angegriffen war, insbesondere war kein Angriff der Korngrenzenoxidation und kein Überbeizen feststellbar, wider Erwarten selbst bei den längsten Beizdauern nicht.

The following electrolytes are used:

• Electrolyte 1H ₂ SO ₄ (250 g / L), FeSO ₄ × 7 H ₂ O (40 g / L) in water
• Electrolyte 2HCl (20% by weight), FeCl ₂ × 4 H ₂ O (30 g / L) in water.
• A metallographic evaluation of each of the pickled samples is then carried out on the metallographic micrograph. It was found that the scale had been removed from every sample, but the base material was not attacked in any of the samples; in particular, no attack by grain boundary oxidation and no overpickling could be detected, contrary to expectations, not even with the longest pickling times.

• - eine Wanne 2, gefüllt mit einer sauren Lösung 3 als Behandlungsbad 3,
• - eine Transportvorrichtung 4 zum Einführen des Stahlbands 1 in das Behandlungsbad 3 hinein und zum Transportieren des Stahlbands 1 durch das Behandlungsbad hindurch,
• - eine elektrotechnische Einrichtung 5 zur kontinuierlichen kathodischen Polarisierung des Stahlbands während des Transports, wobei die Transportvorrichtung mit Mitteln 6 zur Überwachung einer Bandgeschwindigkeit gekoppelt ist,
• - eine mit den Mitteln 6 zur Überwachung gekoppelte Steuervorrichtung 7, die eingerichtet ist, in Abhängigkeit von der Überwachung der Bandgeschwindigkeit das Überschreiten einer

1 is a system for descaling a steel strip 1 refer to. The system has:

• - a tub 2 , filled with an acidic solution 3 as a treatment bath 3 ,
• - a transport device 4th for inserting the steel band 1 in the treatment bath 3 in and for transporting the steel belt 1 through the treatment bath,
• - an electrotechnical device 5 for continuous cathodic polarization of the steel strip during transport, the transport device having means 6th is coupled to monitor a belt speed,
• - one with the means 6th control device coupled for monitoring 7th which is set up, depending on the monitoring of the belt speed, the exceeding of a

Recognize the maximum treatment time of the steel strip and, if the maximum treatment time is exceeded, mark the steel strip as scrap.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102005055768 A1 [0004]
• EP 0763609 A1 [0005]

Claims (13)

A method for descaling a steel strip, wherein at least the following steps are carried out: A) Introducing the steel strip with scale into a treatment line, the treatment line having an acidic solution, B) Belt transport of the steel belt through the treatment line at a predetermined belt speed, which corresponds to an intended treatment duration, the steel belt being put into a cathodically polarized state, C) monitoring the belt speed, whereby if the monitoring reveals a drop in the belt speed below the specified belt speed, the additional treatment time caused by the decrease in the belt speed is determined, where, if the envisaged treatment duration plus the additional treatment duration do not exceed a maximum treatment duration, the steel strip is fed to a regular further processing, and otherwise the steel strip is further processed as scrap, the maximum duration of treatment being at least 900 seconds. Procedure according to Claim 1 , whereby when a belt standstill is detected, a standstill time is measured until the belt transport is resumed and, if the intended treatment duration plus the additional treatment duration caused by the standstill time does not exceed the maximum treatment duration, the steel belt is fed to the regular further processing, and otherwise the steel belt is rejected is processed further. Method according to one of the preceding claims, wherein the intended treatment duration is between 20 seconds and 600 seconds, preferably between 25 seconds and 300 seconds, particularly preferably between 25 and 240 seconds. Method according to one of the preceding claims, wherein the steel strip is put into the cathodic state ^{with a current density between 5 and 150 A / dm 2} , preferably between 20 and 120 A / dm ^2. Procedure according to Claim 4 , the current density being increased automatically, preferably by at least 20 percent, upon detection of the decrease in the belt speed, at least during the period of the decrease in the belt speed. Method according to one of the preceding claims, wherein the maximum treatment duration is at least 1200 seconds, preferably between 1200 seconds and 1400 seconds, particularly preferably between 1200 and 2400 seconds. A method according to any one of the preceding claims, wherein the acidic solution is a sulfuric acid or a hydrochloric acid. Method according to one of the preceding claims, wherein the steel strip consists of a steel that is not stainless steel or consists of a steel that is an IF steel. Plant for descaling a steel strip (1), preferably by means of a method according to one of the Claims 1 until 8th , comprising: - a treatment line, having a tub (2), filled with an acidic solution as a treatment bath (3), - a transport device (4) for inserting a steel belt (1) into the treatment line and for transporting the steel belt (1) through the treatment line, - an electrotechnical device (5) for continuous cathodic polarization of the steel strip (1) during transport, preferably during the entire duration of the transport, through the treatment line, the transport device (4) having means (6) for monitoring a belt speed, - a control device (7) coupled to the monitoring means (6) which is set up to recognize the exceeding of a maximum treatment time of the steel belt (1) as a function of the monitoring of the belt speed and, if the maximum treatment time is exceeded, the steel belt (1) Mark as committee. Plant after Claim 9 , wherein the transport device (4) has at least one transport roller, wherein the means (6) for monitoring are designed as means for monitoring the roller speed of the transport roller, the control device (7) being set up, when a roller standstill is detected, a downtime until the resumption of the To determine belt transport and, if the maximum treatment time is exceeded due to the downtime plus an intended treatment time, the steel belt (1) is to be marked as scrap. Plant after Claim 9 or after Claim 10 , wherein the maximum treatment duration is at least 900 seconds, preferably at least 1200 seconds. Plant according to one of the Claims 9 until 11 , wherein the acidic solution is a sulfuric acid or a hydrochloric acid. Plant according to one of the Claims 9 until 12th , wherein the control device (7) is also coupled to the electrotechnical device (5) and is set up to automatically increase a current density generated for the cathodic polarization by means of the electrotechnical device (5) when a reduction in the transport speed or a roller standstill of the transport roller is detected cause.

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