EP0571353B2 - Process of galvanizing a strip and arrangement for carrying out the process - Google Patents

Abstract

In a process for galvanising a strip (1) the strip (1) is continuously coated with zinc, is then, so as to form a Zn-Fe layer, subjected to a heat treatment in a continuous furnace (10, 11), followed by on-line monitoring of the zinc layer, the iron content of the zinc layer being measured and the galvanising operation being controlled as a function of the iron content of the zinc layer. In order to be able to manufacture a strip (1) having a defined layer structure ensuring uniform quality, a value of the iron content of the Zn-Fe layer is determined as a reference input variable, the actual value of the iron content of the Zn-Fe layer is compared with the reference input variable and any system deviation is compensated via a controller (19) by means of a change in the continuous furnace (10, 11) heating output which serves as the manipulated variable (Fig. 1). <IMAGE>

Description

The invention relates to a method for the method for galvanizing a band, in particular a steel band, the band continuously in a continuous process either electrolytically with Zinc or according to the hot-dip galvanizing process in a zinc bath is coated with zinc, then to form a Zn-Fe layer a heat treatment in a continuous furnace and further an online control of the zinc layer while measuring the iron content subjected to the zinc layer by means of X-ray fluorescence is, the galvanizing process depending on the iron content the zinc layer is controlled, and a plant for Execution of the procedure.

In modern galvanizing processes of this type (known from the EP-A 0 473 154) for the production of so-called "galvan-aged" Band, under which a thermally post-treated, metallic coated steel strip, that which is already galvanized Continuous after-glowing strip (Galvanneal). Thereby the tape is run through the galvanizing part (zinc bath + stripping system for hot-dip galvanizing plants, Galvanizing cells in electrolytic Galvanizing plants) by a continuous furnace Afterglow furnace (galvannealing furnace and holding furnace) performed. This Oven can e.g. operated inductively or with gas.

The post-annealing process causes the pure zinc layer to diffuse through converted into a Zn-Fe layer by iron. Each A product is formed according to the iron content of the Zn-Fe alloy different mechanical properties (e.g. toughness, Hardness), whereby the area of application (abrasion behavior, weldability, Paintability, corrosion resistance, deep drawing ability) is decisively determined. The Fe content can be adjusted accordingly Measuring devices (e.g. by means of X-ray fluorescence, X-ray diffraction or similar processes), i.e. on-line, be measured, e.g. described in EP-A 0 473 154 is, the measurement result is usually about one Average value of the Fe content over the thickness of the Zn-Fe layer represents.

The invention has for its object that described above Process to further develop that a galvanized Tape with a defined layer structure can, being directly and immediately in the manufacturing process for Ensuring a uniform quality of the galvanized Band can be intervened and the production of rejects is minimized. In particular, the inventive Procedure of automatic consideration of intended Enabling changes in process parameters as well as their unintentional changes, so that the manufacturing process is continuously optimized and without manual intervention.

This object is achieved by a method for Galvanizing a strip, in particular a steel strip, solved, the belt being continuously continuous either electrolytically with zinc or according to the hot-dip galvanizing process is coated with zinc in a zinc bath, then for Formation of a Zn-Fe layer of a heat treatment in one Continuous furnace and an on-line control of the zinc layer subjected to measurement of the iron content of the zinc layer by means of X-ray fluorescence is, the galvanizing process depending on the Iron content of the zinc layer is controlled, a value of Iron content of the Zn-Fe layer is determined as a reference variable, the actual value of the iron content of the Zn-Fe layer with the Reference variable compared and a control deviation over one Controller in a closed loop with the help of a Calculator, taking into account the tape dimension, the Basic material of the tape with regard to its chemical Composition and / or structure, the zinc layer thickness, the Composition of the zinc bath, e.g. its Al content, the Belt speed and possibly other parameters such as the temperature of the belt at the inlet of the continuous furnace and the Ambient temperature, the control deviation registered and by means of Control commands regulate the heating output of the continuous furnace, is balanced.

The method according to the invention is based on the knowledge that the diffusion processes of iron into the zinc layer (diffusion rate, Iron content) primarily from temperature and the duration of the heat treatment in the continuous furnace. The temperature control in the continuous furnace influences the structure of the galvannealt layer crucial and therefore also the mechanical properties of the product.

Currently, however, a temperature measurement of the belt is in the The area of the afterglow furnace is not possible because it is not an economical one conventional, non-contact temperature measuring device for Which temperature is available under these conditions could measure with sufficient accuracy. According to the invention provided the furnace temperature indirectly via the heating output adjust and thus a uniform quality of the secure coated tape.

According to a preferred procedure, in addition to Determination of the actual value of the iron content of the Zn-Fe layer Radiation emission (radiation intensity or radiation power) the surface of the tape after or during the Heat treatment measured using at least one pyrometer. This makes it possible, regardless of the iron content of the Zn-Fe layer determine whether the layer has reacted to the surface ("durchgalvannealt") or whether pure zinc is still on the surface, in which case the heating power of the Continuous furnace is set accordingly.

In this case, the procedure is preferably that of the belt passage by measurement using several in the direction of tape travel successively arranged pyrometer that position is determined from which the Zn-Fe layer has reacted, and by regulation the heating power of the continuous furnace this point in Belt running direction in front of a border point, from which the Zn-Fe layer must be fully reacted at the latest.

The regulation is done in a closed loop performed by a computer that registers the control deviation and the heating power of the continuous furnace by means of control commands regulates, the computer to increase reproducibility the quality of the tape produced, the tape dimension, the Basic material of the tape with regard to its chemical Composition and / or structure, the zinc layer thickness, the Composition of the zinc bath, e.g. its Al content, the Belt speed and possibly other parameters such as the temperature of the belt at the inlet of the continuous furnace and the Ambient temperature, taken into account.

A preferred embodiment is characterized in that the heating power and thus the temperature inside the continuous furnace can be set differently in individual heating zones is.

It is advantageous to take into account the Range of different measured values of the iron content of the Iron-zinc alloy the heating output in the direction of Bandwidth of adjacent heating zones varies adjustable.

According to another embodiment, the Heating output in the line running direction Heating zones can be set differently, which increases the warm-up speed of the tape or the holding time of the tape on a certain temperature in order to achieve optimal tape quality can be varied.

The measurement of the iron content and / or the Radiation emission at arranged over the bandwidth Positions carried out.

A plant for carrying out the process with a belt Continuously along a belt guiding belt guide device, one arranged on the belt run Zinc coating device, a subsequently arranged, heat treatment device formed by a continuous furnace for the belt and one also on the belt run lying, downstream of the heat treatment device Measuring device for measuring the iron content of the zinc layer characterized in that the measuring device with a a controller connected to a process computer, which is connected via a control line with the heating device of the heat treatment device is coupled.

To take into account a large number of parameters influencing the quality of the coated strip advantageously the controller is coupled to a process computer.

To determine the reaction of the Zn-Fe layer, at least one additional one is expedient: as a pyrometer trained radiation measuring device provided on the belt path after or in the heat treatment device, which is also coupled to the controller.

The invention is explained in more detail below with reference to the drawing, with FIG. 1 in a schematic representation illustrates a system for galvanizing a strip. The dependency is in the diagram shown in FIG of the iron content from the heating output. Fig. 3 shows a deviation in the iron content in the Zn-Fe layer as a function of the bandwidth, FIG. 4 the dependence of the radiation emission on the holding time.

As can be seen from Fig. 1, a steel strip 1 to be galvanized is by means of a strip guide device, the one Has a plurality of tape guide rollers 2, continuously along a tape path 3 of a not shown Unwind station to a winding station, also not shown. At the belt path 3, this arrives Steel strip first to a zinc coating device 4, which in the illustrated embodiment as a hot-dip galvanizing device is designed. This has a zinc bath 5 and a stripping device arranged downstream in the strip running direction 6 7 to ensure a constant zinc layer which is of equal thickness over the range.

Subsequently, the steel strip 1 is placed over a hot thickness measuring system 8 for measuring the thickness of the zinc layer and via a temperature measuring device 9 into a heat treatment device having two continuous furnaces 10, 11 13 initiated. In the first continuous furnace 10, the galvanized steel strip is primarily heated 1 to the required annealing temperature. In the further continuous furnace 11 arranged subsequently, the steel strip 1 primarily kept at a constant annealing temperature.

After the steel strip 1 has left the second continuous furnace 11, the radiation emission is determined by means of a pyrometer 14 of the finished annealed steel strip 1 measured. Then there are cooling devices on the belt guide 15 arranged. At a location downstream of the heat treatment device 13 of the belt path 3 there is also a measuring device 16 is provided for measuring the iron content of the Zn-Fe layer. the preferably as by the double arrow 17 indicated. Can be moved across the bandwidth so that at different points in the bandwidth a measurement can be carried out. The measuring device works according to the X-ray method.

A controller 19 coupled to a process computer 18 is provided with heating devices of the two continuous furnaces 10, 11 coupled to adjust the heating power. as illustrated by the double arrows 20.

The function of the system is as follows:

The aluminum dissolved in zinc bath 5 initially forms an iron-aluminum layer (Fe ₂ Al ₅ ) on the steel strip due to its higher affinity for iron. which prevents a reaction of the iron substrate of the steel strip 1 and the zinc layer. This system (steel strip 1 + Fe-Al layer + liquid Zn layer) enters the first continuous furnace 10 and is brought to a temperature of 450 ° C to 700 ° C. In the second continuous furnace 11, the steel strip 1 is kept at a certain temperature or heated even further. The process of diffusion of iron into the zinc layer that occurs converts the pure zinc layer into a zinc-iron layer.

First, the Fe-Al barrier layer formed in the zinc bath is formed by the Zn-Fe growth at the grain boundaries of the base material is broken up, and a mushroom-shaped growth of the Zn-Fe complexes begins. Depending on the iron content different metallurgical phases are formed. that have different properties.

The main phases are listed in the table below: phase % Fe Crystal structure Hardness (MPa) Eta .. <0.03 Hexagonal 300-500 Zeta .. 5 - 6 Monoclinic 1800-2700 Delta .. 7-12 Hexagonal 2500 - 4500 Gamma .. 21-28 Cubic 4500 - 5500

As can be seen from the table above, the phases with increasing iron content increasingly harder or more brittle. This can with subsequent deformation (e.g. deep drawing) to increased Cause abrasion, which causes the adhesion of the Zn-Fe layer very much gets bad.

The process is in the case of electrolytic galvanizing plants analogously, but the Al content, however, plays a subordinate role plays.

To set the optimal iron content, i.e. one Iron content, which is a deformation of the galvanized steel strip 1 with no problems, with an online X-ray fluorescence measurement with the help of the measuring device 16 Iron content of the Fe-Zn layer is determined, preferably via the entire bandwidth and also over the entire band length. This The actual value of the iron content of the Zn-Fe layer is determined using the Controller 19 with a value of the predetermined as a reference variable Iron content of the Zn-Fe layer compared. A possible one Control deviation is over the controller 19 by changing the the heating output of the first or the second continuous furnace 10, 11 balanced. Is that about measured iron content less than the desired, the Heating capacity of the continuous furnace increased until the Control deviation becomes zero or below a specified value has dropped (dead band), as is shown in FIG. 2 below is explained:

The course I gives the relationship between the Fe content of the Zn-Fe layer and heating output. This is determined empirically and e.g. as a formula or in tabular form Control computer (controller 19) provided.

If the steel strip 1 behaves exactly according to the course I, the desired setting of the Fe content Fe ₁ (point A) is achieved with the power setting P ₁ . If the strip behaves somewhat differently, e.g. according to curve II, due to unintentional changes in process parameters, such as drift of the ambient temperature, drift in the transformer output when the continuous furnaces are electrically heated or if other faults occur, the strip will have an Fe content of Fe ₂ which deviates from the nominal value Fe ₁ (point B).

The heating power is now changed, for example depending on the slope dP / dFe in point A'des course I, for example by the value k. dP dFe . ΔFe

For the gain factor k = 1, the changed power is shown in the picture with P ₂ . The result is an improved value of the Fe content (point C). Regulation takes place as long as a system deviation is determined (Fe content ≠ Fe ₁ ).

1) ungleichmäßige Beschichtungsdicke

2) Querwölbung des Bandes

3) Bandprofil

4) ungleichmäßige Heizleistung über die Bandbreite

5) ungleichmäßige Temperaturverteilung über die Bandbreite beim Eintritt des Bandes in den Galvannealingofen usw. Primär ist die Beschichtungsdicke innerhalb enger Toleranzen gleichmäßig über die Bandbreite einzustellen (bekannte Verfahren zur Schichtdickenregelung). Trotz gleichmäßiger Schichtdicke über die Bandbreite entsteht durch die Ursachen 2) bis 5) usw. ein ungleichmäßiger Fe-Gehalt über die Bandbreite. Der Einfluß ungleichmäßiger Wärmeeinbringung in das Stahlband 1 kann z.B. zu dem in Fig. 3 dargestellten Fe-Gehalt führen, obwohl die Beschichtungsdicke gleichmäßig über die Bandbreite ist.Gewünscht werden aber eine möglichst gleichmäßige Beschichtungsdicke und ein gleichmäßiger Fe-Gehalt über die Bandbreite (und -länge).Durch Reduktion der Heizleistung der Durchlauföfen 10, 11 in Heizzonen 12, die hauptsächlich auf die Bandmitte wirken, oder durch Erhöhung der Heizleistung in Heizzonen 12', die hauptsächlich auf die Bandränder wirken, kann die Gleichmäßigkeit des Fe-Gehaltes über die Bandbreite verbessert werden.Mit Hilfe des erfindungsgemäßen Verfahrens lassen sich weiters noch folgende Beeinflussungen berücksichtigen:

6) Die Dicke der Zinkschicht: Mit der Schichtdicke verändern sich die Diffusionswege und daher auch der Gefügeaufbau der Beschichtung. Unter gleichen Ofenleistungsverhältnissen führt eine kleinere Schichtdicke (geringere Schichtauflage) zu einem höheren Eisengehalt. Man kann dies bei den Bandkanten beobachten, die eine andere Schichtdicke als im Bandmittenbereich aufweisen können.

7) Der Aluminiumgehalt im Zinkbad: Das im Zinkbad 5 gelöste Aluminium lagert sich vor allem in folgenden zwei Schichten ab:

a) Grenzschicht zwischen Eisensubstrat und Zinkschicht: Durch seine hohe Affinität zum Eisen bildet das Aluminium im Zinkbad zuerst eine Fe₂Al₅-Sperrschicht aus, die ein vorzeitiges Wachstum der spröden Zn-Fe-Phase verhindert. Diese muß beim Galvannealingprozeß durchbrochen werden, um das Zink-Eisen-Wachstum zu starten.

b) Oberflächenoxidschicht: Ein Großteil des Aluminiums liegt als Al₂O₃ an der Oberfläche der Zinkbeschichtung vor.

8) Die Geschwindigkeit, mit der das Stahlband 1 durch die Anlage bewegt wird: Sie beeinflußt die Aufenthaltsdauer (Haltezeit) des Stahlbandes 1 in den Durchlauföfen 11, 12 und somit die Temperaturführung für das Stahlband 1. Dadurch wird die Reaktionszeit verändert, und dies beeinflußt den Eisengehalt.

9) Die chemische Zusammensetzung des Stahlbandes 1 und dessen Gefüge: Da das Wachstum der Zn-Fe-Komplexe hauptsächlich an den Korngrenzen beginnt, hängt die Reaktionsfähigkeit auch von der Grundmaterialzusammensetzung und dem Gefüge ab.

10) Des weiteren beeinflussen die Bandabmessungen die Wärmeeinbringung und damit die Diffusionsbedingungen.

Uneven Fe content profiles across the range can result from various effects:

1) uneven coating thickness

2) Cross curvature of the band

3) Belt profile

4) uneven heating power across the range

5) Uneven temperature distribution over the bandwidth when the strip enters the galvannealing furnace etc. Primarily, the coating thickness has to be adjusted uniformly over the bandwidth within narrow tolerances (known methods for regulating the layer thickness). Despite the uniform layer thickness over the bandwidth, causes 2) to 5) etc. cause an uneven Fe content over the bandwidth. The influence of uneven heat input into the steel strip 1 can, for example, lead to the Fe content shown in FIG. 3, although the coating thickness is uniform over the bandwidth. However, a coating thickness that is as uniform as possible and a uniform Fe content over the bandwidth are desired (and - By reducing the heating capacity of the continuous furnaces 10, 11 in heating zones 12, which mainly affect the strip center, or by increasing the heating capacity in heating zones 12 ', which mainly affect the strip edges, the uniformity of the Fe content over the strip width can be reduced The following influences can also be taken into account with the aid of the method according to the invention:

6) The thickness of the zinc layer: With the layer thickness the diffusion paths change and therefore also the structure of the coating. Under the same furnace performance ratios, a smaller layer thickness (less layer support) leads to a higher iron content. This can be observed with the strip edges, which can have a different layer thickness than in the strip center area.

7) The aluminum content in the zinc bath: The aluminum dissolved in the zinc bath 5 is mainly deposited in the following two layers:

a) Boundary layer between the iron substrate and the zinc layer: Due to its high affinity for iron, the aluminum in the zinc bath first forms an Fe ₂ Al ₅ barrier layer, which prevents the brittle Zn-Fe phase from growing prematurely. This must be broken during the galvannealing process in order to start zinc-iron growth.

b) Surface oxide layer: A large part of the aluminum is present as Al ₂ O ₃ on the surface of the zinc coating.

8) The speed at which the steel strip 1 is moved through the system: it influences the length of stay (holding time) of the steel strip 1 in the continuous furnaces 11, 12 and thus the temperature control for the steel strip 1. This changes the reaction time, and this affects the iron content.

9) The chemical composition of the steel strip 1 and its structure: Since the growth of the Zn-Fe complexes mainly begins at the grain boundaries, the reactivity also depends on the base material composition and the structure.

10) Furthermore, the strip dimensions influence the heat input and thus the diffusion conditions.

All of those listed above that affect iron content According to the invention, factors can be taken into account by that these factors defining data in the process computer 18th can be entered and due to the coupling of the process computer 18th with the controller 19 of the latter when determining the Heating power of the heat treatment device 13 is taken into account become.

Desired changes in process parameters, e.g. on Changing the dimension of the steel strip 1, changing the chemical composition of the steel strip 1, a change of Zinc layer thickness or a change in the conveying speed of the Steel strip 1, to take into account the heat output of the Heat treatment device entered the process computer 18.

Since the conversion of the zinc layer into a Zn-Fe layer the emissivity of the coating changes abruptly as soon as the surface of the Zn-Fe layer has iron (see FIG. 4), can make a radiation emission measurement using a pyrometer 14 used to assess the galvanized layer become. The pyrometer 14 can after or in the Heat treatment device 13 (e.g. between galvannealing furnace 10 and holding furnace 11) can be arranged. In this measurement it is information about the purely of the Surface of the steel strip 1, i.e. its Zn-Fe layer, emitted radiant energy, which is a function of temperature and the emission number of the surface condition. That's the way it is Emission number of a pure zinc surface below 0.2 and the a fully reacted Fe-Zn surface at about 0.6. Is the Zn-Fe layer not at the point of the pyrometer yet fully reacted, the heating power of the continuous furnaces 10, 11th with the help of the controller connected to a process computer 18 19, to which the measured value of the pyrometer is entered, increases until a reaction through the pyrometer can be determined. The heating power is the control variable of the control process.

Due to the strong change in emissivity in the case of Occurrence of the so-called through reaction, i.e. if the iron It penetrates as far as the surface of the Zn layer possible to recognize that point in the tape running direction 6 from which the through reaction is complete. This can e.g. thereby take place that two or more pyrometers in the tape running direction 6 be arranged one behind the other. By knowing about the Emissivity jump when reacting through the Zn-Fe layer and from the measured radiation intensities the pyrometer 14 can be concluded on that point of the belt path 3 from which the Zn-Fe layer has already reacted.

The heating power of the continuous furnaces 10, 11 is now using the Regulator 19 controlled so that the reaction from one certain desired position is completed. Another Possibility of recognizing the point in the tape running direction at the the through reaction is complete, the pyrometer measurement to compare with a thermal model calculation.

For this purpose, the pyrometer measurement is the empirically determined one Emissivity for the pure zinc layer and a second time empirically determined emissivity of the fully reacted layer based on. In terms of calculations, this initially results in two different according to the different emission numbers Pyrometer temperature values for the running belt.

By comparing these two values with one in parallel for the Model calculation of the relevant band section Temperature resulting from the entry temperature of the steel strip into the heat treatment device and the one supplied to it Performance calculated, it is determined which of the two Pyrometer temperature values with the calculated temperature matches. This temperature value is then considered correct Temperature of the running steel strip 1 viewed. The associated one Emissivity indicates whether the steel strip is still a pure zinc coating or whether the coating has already reacted is. The heat output of the heat treatment device is so regulated that the reaction at the point of the pyrometer 14th is completed.

For the quality of the product it is very important that the Zn-Fe layer has an Fe content within narrow limits and that at the same time the coating is complete is fully reacted. Because from the information about the Fe content of the Zn-Fe layer alone cannot be closed immediately, that the coating has also reacted, it is advantageous the heat output distribution over the length of the heat treatment device due to a combination of the two information, namely the Fe content of the Zn-Fe layer and the Emissivity determination.

Each of the control methods described above is in one closed loop operated.

The manipulated variables for the heat treatment device 13 are from a computer of the controller 19 from the measured values and the target-actual deviation for the iron content and, if applicable calculated for emissivity. The measured values can be used the hot measurement (layer thickness measurement) and / or one before Afterglow furnace arranged temperature measurement, the Belt speed, the heating power supplied in the individual zones of the heat treatment device 13 are used to increase the accuracy of the control process, as indicated by the arrows 20, 21.

The manipulated variables are calculated using a Rule model, which corresponds to the on the specific system for Available measuring devices and control devices can be different. For a concrete one Plant configuration becomes the rule model through model parameters described. These model parameters can be used for different Base material, tape dimension, Al content in the zinc bath different his. Base material, tape dimension, Al content in the zinc bath can from a higher-level computer (e.g. Production planning computer) or an external input unit are transmitted to the process computer 18. You can use the target value for the product to be manufactured to the computer of the controller 19 are transmitted, cf. Arrow 22.

The computer of the controller 19 then calculates taking into account this model parameter of the control model the corresponding Control commands.

Depending on the design of the continuous furnace 10, 11, the total output or the performance of parts of the continuous furnaces 10, 11 (zones in Belt length direction) is set within certain limits become. It is particularly advantageous if the distribution of the Heat input on the belt, i.e. the heating power of the Continuous furnaces 10, 11, also within the width certain limits can be set, since this makes it possible to achieve the deviation shown in FIG. 3 of the Fe content of the Zn-Fe layer, which can occur despite the uniform thickness of the Zn-Fe layer.

Claims (10)

1. A process of galvanizing a strip (1), in particular a steel strip (1), wherein the strip (1) is continuously coated with zinc in a continuous process either electrolytically or in a zinc bath according to the hot dip galvanizing method, subsequently is subjected to a heat treatment in an open-ended furnace (10, 11) for the formation of a Zn-Fe layer and, furthermore, to an on-line control of the zinc layer by measuring the iron content of the zinc layer by means of X-ray fluorescence, wherein the galvanizing procedure is controlled as a function of the iron content of the zinc layer, characterized in that a value of the iron content of the Zn-Fe layer is determined as a reference input value, the actual value of the iron content of the Zn-Fe layer is compared to the reference input value, and a control deviation is compensated for via an automatic control (19) in a closed control circuit by aid of a computer which registers the control deviation by taking into account the dimension of the strip, the base material of the strip (1) in terms of its chemical composition and/or structure, the thickness of the zinc layer, the composition of the zinc bath, such as, e.g., its Al-content, the strip speed as well as, optionally, additional parameters, such as the temperature of the strip (1) at the entry of the open-ended furnace (10, 11) and the ambient temperature, and controls the calorific output of the open-ended furnace (10, 11) via actuating commands.
2. A process according to claim 1, characterized in that for determining the complete reaction of the Zn-Fe layer, the radiation emission of the surface of the strip (1) is measured after or during the heat treatment by means of at least one pyrometer (14).
3. A process according to claim 2, characterized in that along the strip conveying path (3) that site is determined by measurement by means of several pyrometers (14) consecutively arranged in the strip conveying direction (6), from which the Zn-Fe layer has completely reacted, and that this site, by controlling the calorific output of the open-ended furnace (10, 11), is brought in front of a boundary site, seen in the strip conveying direction (6), from which the Zn-Fe layer must have completely reacted at the latest.
4. A process according to one or several of claims 1 to 3, characterized in that the calorific output and thus the temperature within the open-ended furnace (10, 11) are adjustable to be different in individual heating zones (12, 12').
5. A process according to claim 4, characterized in that the calorific output is adjustable to be different in heating zones (12, 12') adjacently arranged in the sense of the strip width.
6. A process according to claim 4 or 5, characterized in that the calorific output is adjustable to be different in heating zones consecutively arranged in the strip conveying direction.
7. A process according to one or several of claims 4 to 6, characterized in that measurement of the iron content and/or of the radiation emission is effected at positions distributed over the strip width.
8. An arrangement for carrying out the process according to one or several of claims 1 to 7, comprising a strip guiding means (2) guiding a strip (1) continuously along a strip conveying path (3), a zinc coating means (4) arranged on the strip conveying path (3), a consecutively arranged heat treating means (13) for the strip (1), formed by an open-ended furnace (10, 11), and a measuring means (16) for measuring the iron content of the zinc layer also located on the strip conveying path (3) downstream of the heat treating means (13), characterized in that the measuring means (16) is coupled with an automatic control (19), which, in turn, is coupled with the heating means of the heat treating means (13) via a control line.
9. An arrangement according to claim 8, characterized in that the automatic control (19) is coupled with a process computer (18).
10. An arrangement according to claim 8 or 9, characterized in that at least one additional radiation measuring means designed as a pyrometer (14) is provided on the strip conveying path (3) downstream of, or within, the heat treating means (13), and also is coupled with the automatic control (19).

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