DESCALING DEVICE AND METHOD FOR CHEMICALLY DESCALING A METAL STRIP

Abstract

A descaling device (2) for chemically descaling a metal strip (4): A spraying device (12, 12a-12d) for spraying a pickling agent (14) onto a top or bottom side (16, 18) of the metal strip (4). The spraying device (12, 12a-12d) has a first outer spraying unit (50) for spraying the pickling agent (14) onto a first edge region (52) of the top/bottom side (16, 18) of the metal strip (4) and a second outer spraying unit (54) for spraying the pickling agent (14) onto a second edge region (56) of the top/bottom side (16, 18) of the metal strip (4), which second edge region lies opposite the first edge region (52). At least one of the two outer spraying units (50, 54) has one or more solid stream nozzles (20), in particular a plurality of rows of solid stream nozzles (20), and/or one or more slotted nozzles (22).

Claims

1. A descaling device for chemical descaling of a metal strip, wherein the metal strip passes through the descaling device; the metal strip having a first edge region and a second edge region extending inwardly from respective lateral edges of the metal strip passing through the descaling device; the metal strip having a middle region situated between the first and the second edge regions of the metal strip; the metal strip having a top side and a bottom side; the descaling device, comprising: at least one first spraying device and at least one second spraying device for respectively spraying a pickling agent onto a top side/bottom side of the metal strip; each of the first spraying device and the second spraying device comprises a respective first outer spraying unit for spraying the pickling agent onto the first edge region of the top side/bottom side of the metal strip and a second outer spraying unit for spraying the pickling agent onto the second edge region of the top side/bottom side of the metal strip, wherein the second edge region of the metal strip is situated opposite the first edge region of the metal strip and extending inwardly from the respective lateral edges of the metal strip; and the first spraying device further comprises a middle spraying unit for spraying the pickling agent onto a middle region of the top side/bottom side of the metal strip, the middle region is between the first and the second edge regions; at least one of the spraying units of the first/second spraying device comprises multiple rows of solid stream nozzles; each of the spraying units of the first/second spraying device comprises its own respective pickling agent distribution chamber; at least one of the two outer spraying units of the second spraying device comprises at least one slotted nozzle; and each of the two outer spraying units (50, 54) of the first and second spraying device devices comprises its own respective pickling agent distribution chamber.

2. The descaling device as claimed in claim 1, further comprising the at least one second spraying device comprises a middle spraying unit situated between the end regions for spraying the pickling agent onto a middle region of the top side/bottom side of the metal strip; wherein the middle spraying unit of the second spraying device comprises at least one of the slotted nozzles and comprises its own pickling agent distribution chamber.

3. The descaling device as claimed in claim 1, wherein each of the spraying devices comprises a spray bar.

4. The descaling device as claimed in claim 1, further comprising a control device configured for adjusting a pickling agent dispersing rate of each respective spraying unit of each of the spraying devices.

5. The descaling device as claimed in claim 4, further comprising the control device being operable for adjusting the pickling agent dispersing rate of the middle spraying unit independently of the pickling agent dispersing rate of the first outer spraying unit and independently of the pickling agent dispersing rate of the second outer spraying unit.

6. The descaling device as claimed in claim 4 further comprising the control device comprises multiple pickling agent delivery pumps configured for adjusting the pickling agent dispersing rates of the spraying units, wherein the pickling agent delivery pumps have an exit side connected to the respective ones of spraying device.

7. The descaling device as claimed in claim 4, further comprising the control device comprises multiple valves configured for adjusting the pickling agent dispersing rates of the spraying units, wherein each spraying device is connected at an entry side of the spraying device to the valves.

8. The descaling device as claimed in claim 4, further comprising the control device comprises a sensor unit having at least one sensor for detecting a surface parameter of the metal strip, and the control device is configured to adjust the pickling agent dispersing rate of the respective spraying unit in dependence on an output signal of the sensor unit.

9. A method for chemical descaling of a metal strip, comprising: spraying a pickling agent onto a top side/bottom side of the metal strip by at least one first spraying device onto the top side of the strip and by at least one second spraying device onto the bottom side of the strip; wherein the spraying of the pickling agent is by a first outer spraying unit of the first spraying device, and by a first outer spraying unit of the second spraying device onto a first edge region of the top side/bottom side of the metal strip; and the spraying of the pickling agent is also by a second outer spraying unit of the first spraying device and by a second outer spraying unit of the second spraying device onto a second edge region of the top side/bottom side of the metal strip wherein the second edge region is situated opposite the first edge region and, both of the first and the second edge region extending inwardly from respective lateral edges of the metal strip; and the spraying of the pickling agent is also by a middle spraying unit of the first spraying device onto a middle region of the top side/bottom side of the metal strip, wherein the middle region is situated between the first and second edge regions of the metal strip; the spraying of the pickling agent onto the top side/bottom side of the metal strip is by at least one of the spraying units of the first spraying device through multiple rows of solid stream nozzles; and by the spraying by at least one of the two outer spraying units of the further spraying device through one or more slotted nozzles.

10. The method as claimed in claim 9, further comprising: spraying the pickling agent onto a middle region of the top side/bottom side of the metal strip, the middle region is situated between the first and second edge regions, of the metal strip, the spraying being through at least one slotted nozzle of a middle spraying unit of the at least one second spraying device.

11. The method as claimed in claim 10, further comprising: setting a pickling agent dispersing rate of the first outer spraying unit and a pickling agent dispersing rate of the second outer spraying unit of the at least one first spraying device and/or of the at least one second spraying device, wherein the dispersing rate is set by a control device each time at a value which is different from a pickling agent dispersing rate of the respective middle spraying unit of the first spraying device and of the second spraying device.

12. The method as claimed in claim 11, further comprising: setting the pickling agent dispersing rate of the respective spraying unit of the at least one first spraying device and/or of the at least one second spraying device with the aid of the control device for acting upon the metal strip in a width direction of the strip by the first spraying device and/or by the second spraying device with a given pickling agent spray profile, wherein the pickling agent spray profile increases or decreases to a respective lateral outside of the metal strip in the first and/or in the second edge region.

13. The method as claimed in claim 12, wherein the pickling agent spray profile has no plateau.

14. The method as claimed in claim 12, wherein the pickling agent spray profile has a plateau between the two edge regions.

15. The descaling device of claim 8, wherein the surface parameter of the metal strip is dependent on the thickness of the scale layer of the metal strip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] FIG. 1 is an exemplary embodiment of a descaling device according to the invention for chemical descaling of a metal strip;

[0081] FIG. 2 is a cross section through the descaling device of FIG. 1;

[0082] FIG. 3A is a representation of a first of two spraying devices of the descaling device;

[0083] FIG. 3B is a representation of a second of the two spraying devices of the descaling device;

[0084] FIG. 4 is a pickling agent spray profile which is applied to the metal strip in the descaling device;

[0085] FIG. 5A is a representation of a first of two other spraying devices for a descaling device;

[0086] FIG. 5B is a representation of a second of two other spraying devices of the descaling device; and

[0087] FIG. 6 is a pickling agent spray profile which is applied to a metal strip when using one of the spraying devices of FIG. 5.

DESCRIPTION OF THE EMBODIMENTS

[0088] In the specification and claims / between two words or sets of words indicates one or the other is being named; and/or between two words or sets of words means either one or both.

[0089] FIG. 1 shows an exemplary embodiment of a descaling device 2 according to the invention for chemical descaling of a metal strip 4 in a schematic representation.

[0090] The descaling device 2 is outfitted with a strip conveying device 6 for transporting the metal strip 4 along a conveying direction 8. In the present exemplary embodiment, the strip conveying device 6 is designed as a roller conveyor with multiple rollers 10.

[0091] Moreover, the descaling device 2 comprises multiple first or upper spraying devices 12 for spraying a pickling agent 14 containing hydrochloric acid onto a top side 16 of the metal strip 4 and multiple second or lower spraying devices 12 for spraying the pickling agent 14 onto a bottom side 18 of the metal strip 4. In FIG. 1, as an example, four upper spraying devices 12 and four lower spraying devices 12 are shown. In theory, the descaling device 2 may also have a higher or lower number of such spraying devices 12.

[0092] The upper spraying devices 12 are arranged in succession in the conveying direction 8 of the strip conveying device 6. Likewise, the lower spraying devices 12 are arranged in succession in the conveying direction 8 of the strip conveying device 6. Moreover, the spraying devices 12 are each configured as a spray bar.

[0093] In the present exemplary embodiment, all the upper spraying devices 12 of the descaling device 2 are arranged at the same height. All the upper spraying devices 12 of the descaling device 2 have the same distance to the top side 16 of the metal strip 4. Moreover, all the lower spraying devices 12 of the descaling device 2 are arranged at the same height. All the lower spraying devices 12 of the descaling device 2 have the same distance to the bottom side 18 of the metal strip 4.

[0094] The distance of the upper spraying devices 12 from the top side 16 of the metal strip 4 may be less than or greater than the distance of the lower spraying devices 12 from the bottom side 18 of the metal strip 4. Alternatively, these two distances may be equal. It is especially preferable when the distance of the lower spraying devices 12 from the bottom side 18 of the metal strip 4 is smaller than the distance of the upper spraying devices 12 from the top side 16 of the metal strip 4.

[0095] Some of the upper and lower spraying devices 12 may be spraying devices 12a of a first type. Some others of the upper and lower spraying devices 12 may be spraying devices 12b of a second type. The spraying devices 12a of the first type comprise a multitude of solid stream nozzles 20, whereas the spraying devices 12b of the second type comprise a multitude of slotted nozzles 22 (see FIGS. 3A and 3B).

[0096] In the present exemplary embodiment, the spraying devices 12a of the first type and the spraying devices 12b of the second type are arranged alternating in the conveying direction 8 of the strip conveying device 6. That is, a spraying device 12a of the first type is followed in the conveying direction 6 by a spraying device 12b of the second type, which in turn is followed in the conveying direction 8 by a spraying device 12a of the first type, and so forth. But, such alternation of two spraying devices next to each other is not required.

[0097] The spraying devices 12b of the second type, i.e., the spraying devices 12b with slotted nozzles 22, are utilized in this embodiment in particular to homogenize the descaling result.

[0098] However, the arrangement of the spraying devices 12 need not be such an alternating one. Moreover, the same number of spraying devices 12a of the first type and spraying devices 12b of the second type need not be present. Furthermore, it is basically possible to use only spraying devices 12 of the same type in the descaling device 2.

[0099] Moreover, the descaling device 2 comprises a pickling chamber 24, in which said spraying devices 12 are arranged. The pickling chamber 24 comprises a lower chamber portion 26 to receive the pickling agent 14 draining from the metal strip 4 and an upper chamber portion 28 arranged above the lower chamber portion 26.

[0100] Furthermore, the descaling device 2 comprises a first squeezing roller pair 30 and a second squeezing roller pair 32 each having an upper squeezing roller 34 and a lower squeezing roller 36. The first squeezing roller pair 30 is arranged in front of the pickling chamber 24 in terms of the conveying direction 8, while the second squeezing roller pair 32 is arranged in the pickling chamber 24. The squeezing rollers 34, 36 support and guide the metal strip 4. In moving through a squeezing roller pair 30, 32, a liquid present on the metal strip surface is expelled by the squeezing rollers 34, 36.

[0101] Furthermore, the descaling device 2 comprises a control device 38, of which FIG. 1 shows its control unit 40, its first sensor unit 42a and its second sensor unit 42b.

[0102] Said sensor units 42a, 42b are connected to the control unit 40 and each comprise an upper sensor row 44 and a lower sensor row 46. The sensor rows 44, 46 of the first sensor unit 42a are arranged in front of or preceding the spraying devices 12 in regard to the conveying direction 8 of the strip conveying device 6. The sensor rows 44, 46 of the second sensor unit 42b are arranged behind or following the spraying devices 12 in regard to the conveying direction 8 of the strip conveying device 6. Preferably, the sensor rows 44, 46 of the respective sensor unit 42a, 42bas shown in FIG. 1are arranged outside the pickling chamber 24.

[0103] The metal strip 4 is transported by the strip conveying device 6 parallel to its length direction 48 through the descaling device 2. In the pickling chamber 24, the metal strip 4 has the pickling agent 14 applied to it by the spraying devices 12 in order to chemically descale the metal strip 4, in other words, to remove a scale layer located on the metal strip 4.

[0104] The upper sensor row 44 of the first sensor unit 42a detects, in front of or preceding the spraying devices 12 and resolved in location across the width of the metal strip 4, a surface parameter of the metal strip 4 which is dependent on the thickness of the scale layer on the top side 16 of the metal strip 4. Accordingly, the lower sensor row 46 of the first sensor unit 42a detects, preceding or in front of the spraying devices 12 and resolved in location across the width of the metal strip 4, a surface parameter of the metal strip 4 which is dependent on the thickness of the scale layer on the bottom side 18 of the metal strip 4.

[0105] The upper sensor row 44 of the second sensor unit 42b likewise detects, after or following behind the spraying devices 12 and resolved in location across the width of the metal strip 4, a surface parameter of the metal strip 4 which is dependent on the thickness of the scale layer on the top side 16 of the metal strip 4. Accordingly, the lower sensor row 46 of the second sensor unit 42b detects, after or following behind the spraying devices 12 and resolved in location across the width of the metal strip 4, a surface parameter of the metal strip 4 which is dependent on the thickness of the scale layer on the bottom side 18 of the metal strip 4. The sensor rows 44, 46 of the second sensor unit 42b may in particular detect each time the same surface parameter as the sensor rows 44, 46 of the first sensor unit 42a.

[0106] The sensor signals generated by the sensor rows 44, 46 of the sensor units 42a, 42b are relayed to the control unit 40.

[0107] With the help of the control unit 40, the pickling agent application on the metal strip 4 is controlled in dependence on the aforementioned sensor signals so that the most homogeneous possible descaling result is achieved, preferably with complete removal of the scale layer.

[0108] Basically, it is possible for the descaling device 2 to have only one of the two sensor units 42a, 42b, instead of both sensor units 42a, 42b, and to control accordingly the pickling agent application on the metal strip 4 in dependence on the sensor signals of only one of the sensor units 42a, 42b.

[0109] The descaling device 2 can moreover have one or more dip tanks (not shown) for a dip pickling treatment of the metal strip 4. For example, the descaling device 2 may have one dip tank before the pickling chamber 24 and a further dip tank after the pickling chamber 24. In the respective dip tank, the same pickling agent may be used as is sprayed by the spraying devices 12 onto the metal strip 4, or a different pickling agent may be used.

[0110] FIG. 2 shows a cross section through the descaling device 2 along the sectioning plane II-II of FIG. 1.

[0111] Referring to FIG. 2, the configuration of the spraying devices 12 shall now be described more closely.

[0112] As already mentioned, the spraying devices 12 are each configured as a spray bar.

[0113] The upper spraying devices 12 each comprise a first outer spraying unit 50 for spraying the pickling agent 14 onto a first edge region 52 of the top side 16 of the metal strip 4, a second outer spraying unit 54 for spraying the pickling agent 14 onto a second edge region 56 of the top side 16 of the metal strip 4, situated opposite the first edge region 52, and a middle spraying unit 58, arranged between the two outer spraying units 50, 54, for spraying the pickling agent 14 onto a middle region 60 of the top side 16 of the metal strip 4 situated between the edge regions 52, 56.

[0114] Accordingly, the lower spraying devices 12 each comprise a first outer spraying unit 50 for spraying the pickling agent 14 onto a first edge region 52 of the bottom side 18 of the metal strip 4, a second outer spraying unit 54 for spraying the pickling agent 14 onto a second edge region 56 of the bottom side 18 of the metal strip 4, situated opposite the first edge region 52, and a middle spraying unit 58, arranged between the two outer spraying units 50, 54, for spraying the pickling agent 14 onto a middle region 60 of the bottom side 18 of the metal strip 4 situated between the edge regions 52, 56.

[0115] Said spraying units 50, 54, 58 of the respective spraying device 12 are arranged in succession in the width direction 62 of the metal strip 4. Moreover, each of the spraying units 50, 54, 58 comprises multiple nozzles 20, 22 (see FIG. 3).

[0116] Furthermore, the spraying units 50, 54, 58 are designed to spray the pickling agent 14 perpendicularly onto the top side 16 or bottom side 18 of the metal strip 4. The nozzles 20, 22 of the spraying units 50, 54, 58 are oriented such that the spraying units 50, 54, 58 each have a spraying direction 64 which is directed perpendicular to the top side 16 or bottom side 18 of the metal strip 4, i.e., vertically upward or vertically downward.

[0117] The distance of the spraying devices 12 from the strip surface, or more properly the distance of their nozzles 20, 22 from the strip surface, may be as much as 500 mm in the present example.

[0118] Furthermore, each of the spraying units 50, 54, 58 has its own pickling agent distribution chamber 66, to which the nozzles 20, 22 of the respective spraying units 50, 54, 58 are each connected by their inlet-side nozzle end.

[0119] Moreover, the descaling device 2 comprises a pickling agent supply line 68 for each of the spraying units 50, 54, 58. The respective pickling agent supply line 68 empties into the respective spraying unit 50, 54, 58 perpendicular to its spraying direction 64, so that a uniform pressure distribution is achieved in the individual spraying units 50, 54, 58.

[0120] Furthermore, the aforementioned control device 38 comprises multiple pickling agent delivery pumps 70, in the present exemplary embodiment there being provided a separate pickling agent delivery pump 70 for each of the spraying units 50, 54, 58 (see FIG. 3). Each of the spraying units 50, 54, 58 is connected at the inlet side to the corresponding pickling agent delivery pump 70 across the pickling agent supply line 68 connected to it. Basically, it is possible to supply spraying units 50, 54, 58 of different spraying devices 12 with pickling agent 14 across a common pickling agent delivery pump 70. In this case, the descaling device may comprise for example a total of three pickling agent delivery pumps 70 for all spraying devices 12 taken together.

[0121] Said pickling agent delivery pumps 70 are moreover each connected to the aforementioned control unit 40 of the control device 38, which is designed to use a given control algorithm to control the pickling agent volume flow of the pickling agent delivery pumps 70.

[0122] The control device 38 is designed to set the pickling agent dispersing rate of the respective spraying units 50, 54, 58, and this independently of the pickling agent dispersing rates of the other spraying units 50, 54, 58. By a change in the pickling agent volume flow of one of the pickling agent delivery pumps 70, the control unit 40 can change the pickling agent dispersing rate of the corresponding spraying unit 50, 54, 58.

[0123] Preferably, the sum of the pickling agent dispersing rates of the three spraying units 50, 54, 58 of the respective spraying device 12 lies in the range of 100 to 150 m.sup.3/h.

[0124] As mentioned above, the pickling agent application on the metal strip 4 is controlled in dependence on the previously mentioned sensor signals of the sensor units 42a, 42b such that the most homogeneous possible descaling result is achieved.

[0125] If the thickness of the scale layer in the middle region 60 of the metal strip 4 is less than that on the edge regions 52, 56 of the metal strip 4, the pickling agent dispersing rate of its first outer spraying unit 50 and the pickling agent dispersing rate of its second outer spraying unit 54 in the respective spraying device 12 will be set by the control device 38 respectively at a value which is greater than the pickling agent dispersing rate of its middle spraying unit 58. On the other hand, if the thickness of the scale layer in the middle region 60 of the metal strip 4 is greater than that on the edge regions 52, 56 of the metal strip 4, the pickling agent dispersing rate of its first outer spraying unit 50 and the pickling agent dispersing rate of its second outer spraying unit 54 in the respective spraying device 12 will be set by the control device 38 respectively at a value which is smaller than the pickling agent dispersing rate of its middle spraying unit 58.

[0126] If the thickness of the scale layer is symmetrical with respect to a vertical strip center plane, the pickling agent dispersing rate of its first outer spraying unit 50 and the pickling agent dispersing rate of its second outer spraying unit 54 in the respective spraying device 12 will be set by the control device 38 at the same value.

[0127] In the event of a production-related decrease in the delivery speed of the metal strip 4, one or more spraying units 50, 54, 58 of the spraying devices 12 can be switched off to avoid an overpickling of the metal strip 4.

[0128] FIG. 3A shows a spraying device 12a of the first type and FIG. 3B shows a spraying device 12b of the second type of the descaling device 2, each from their side facing toward the metal strip 4.

[0129] In FIG. 3A the aforementioned solid stream nozzles 20 of the spraying device 12a of the first type and in FIG. 3B, the aforementioned slotted nozzles 22 of the spraying device 12b of the second type can be seen.

[0130] Moreover, the already mentioned pickling agent delivery pumps 70 and the pickling agent supply lines 68 connected to the spraying units 50, 54, 58 are represented in FIGS. 3A and 3B.

[0131] In the spraying device 12a of the first type in FIG. 3A, the solid stream nozzles 20 are arranged in multiple nozzle rows oriented perpendicular to the conveying direction 8, these nozzle rows being arranged equidistant from each other. In the respective nozzle row, the solid stream nozzles 20 are likewise arranged equidistant from each other.

[0132] The distance between adjacent solid stream nozzles 20 from the same nozzle row may correspond in particular to the distance between adjacent nozzle rows. This distance may amount to 25 mm, for example. At their exit opening, the solid stream nozzles 20 preferably have an inner diameter of 4 mm.

[0133] Moreover, the solid stream nozzles 20 of one nozzle row are arranged with an offset with respect to the row length direction from the solid stream nozzles 20 of the adjacent nozzle row, in order to avoid the formation of a striped spray pattern on the metal strip 4.

[0134] In the spraying device 12b of the second type in FIG. 3B, each of its spraying units 50, 54, 58 has slotted nozzles 22 of different width, which are arranged equidistant in succession in the conveying direction 8 of the strip conveying device 6, the slotted nozzles 22 each being oriented perpendicular to the conveying direction 8.

[0135] In both the spraying device 12a of the first type in FIG. 3A and in the spraying device 12b of the second type in FIG. 3B, the pickling agent distribution chambers 66 of the two outer spraying units 50, 54 have a triangular cross section form, while the middle spraying unit 58 has a cross section form which corresponds to an equilateral trapezium. The arrangement of the solid stream nozzles 20 and the width of the slotted nozzles 22 is adapted to the cross section form in the respective spraying unit 50, 54, 58.

[0136] In both the spraying device 12a of the first type and in the spraying device 12b of the second type, the pickling agent distribution chambers 66 are separated from each other by partition walls, which are indicated in FIG. 3 by dashed lines.

[0137] Alternatively or additionally, for one or more of the spraying devices 12a, 12b of the first or second type the descaling device 2 may have a spraying device not divided into three spraying units whose pickling agent dispersing rates are adjustable independently of each other, but instead has only a single spraying unit. Such a spraying device may have slotted nozzles, for example, which extend substantially across the entire width of the spraying device.

[0138] FIG. 4 shows a pickling agent spray profile which is applied to the metal strip 4 by one of the spraying devices 12a of the first type or one of the spraying devices 12b of the second type, in the form of a diagram.

[0139] In the diagram, the quantity of pickling agent V sprayed by the spraying device 12a, 12b onto the metal strip 4 is represented as a solid line as a function of a length coordinate x in the width direction 62 of the metal strip 4. The value b of the abscissa length coordinate x corresponds to the width of the metal strip 4.

[0140] The contribution of the two outer spraying units 50, 54 to the pickling agent spray profile is represented in the diagram respectively by means of a dashed line, whereas the contribution of the middle spraying unit 58 is represented by a dotted line.

[0141] The pickling agent spray profile shown has a mirror symmetry. In the middle region 60 of the metal strip 4, the pickling agent spray profile has a plateau 72. In the middle region 60 the pickling agent spray profile does not change with the length coordinate x. In the first and in the second edge region 52, 56 of the metal strip 4, however, the pickling agent spray profile increases toward the outside (starting from the plateau 72).

[0142] FIG. 5A shows a spraying device 12c of a third type and FIG. 5B shows a spraying device 12d of a fourth type.

[0143] These two spraying devices 12c, 12d may be used in the descaling device 2 of FIG. 1 alternatively or additionally to one or more of the previously described spraying devices 12a, 12b.

[0144] The spraying device 12c of the third type, like the spraying device 12a of the first type, comprises a multitude of solid stream nozzles 20, whereas the spraying device 12d of the fourth type, like the spraying device 12b of the second type, comprises a multitude of slotted nozzles 22.

[0145] The spraying devices 12c, 12d of the third and fourth type in FIGS. 3A and 3B differ from the two spraying devices 12a, 12b of the first and second type in FIGS. 5A and 5B in that the pickling agent distribution chambers 66 of the two outer spraying units 50, 54 and the pickling agent distribution chamber 66 of the middle spraying unit 58 in the spraying device 12c of the third type in FIG. 5A and the spraying device 12d of the fourth type in FIG. 5B respectively have a triangular cross section form.

[0146] Moreover, in the embodiments of FIGS. 5A and 5B valves 74 are provided to control the pickling agent dispersing rate of the respective spraying unit 50, 54, 58 instead of pickling agent delivery pumps. In the present example, the valves 74 are each arranged in one of the pickling agent supply lines 68. The valves 74 may be controlled by a control unit such as the control unit 40 of the descaling device 2 of FIG. 1. Basically, it is possible to use valves and pickling agent delivery pumps in combination to control the pickling agent dispersing rate of the respective spraying unit 50, 54, 58.

[0147] FIG. 6 shows a pickling agent spray profile which is applied to a metal strip 4 when one of the two spraying devices 12c, 12d of FIGS. 5A and 5B is used for the pickling agent application on the metal strip 4.

[0148] This pickling agent spray profile differs from the pickling agent spray profile of FIG. 4 in that it has no plateau in the middle region 60 of the metal strip 4. Instead, the pickling agent spray profile of FIG. 6 increases outwardly from the strip middle.

[0149] The pickling agent spray profiles represented in the diagrams of FIG. 4 and FIG. 6 are exemplary pickling agent spray profiles. In each of these two diagrams, the area enclosed by the two dashed lines and the dotted line respectively with the abscissa represents for example a regulating range of the corresponding spraying unit 50, 54, 58. Depending on the adjusted pickling agent dispersing rate of the respective spraying unit 50, 54, 58, the quantity of pickling agent V sprayed onto the metal strip 4 may take on other values in the first edge region 52, in the middle region 60 and/or in the second edge region 56.

[0150] Although the invention has been illustrated and described more closely in detail by the preferred exemplary embodiments, the invention is not limited by the examples disclosed and other variations may be derived from it, without leaving the scope of protection of the invention.

LIST OF REFERENCE NUMBERS

[0151] 2 Descaling device [0152] 4 Metal strip [0153] 6 Strip conveying device [0154] 8 Conveying direction [0155] 10 Roller [0156] 12 Spraying device [0157] 12a Spraying device of first type [0158] 12b Spraying device of second type [0159] 12c Spraying device of third type [0160] 12d Spraying device of fourth type [0161] 14 Pickling agent [0162] 16 Top side [0163] 18 Bottom side [0164] 20 Solid-stream nozzle [0165] 22 Slotted nozzle [0166] 24 Pickling chamber [0167] 26 Chamber portion [0168] 28 Chamber portion [0169] 30 Squeezing roller pair [0170] 32 Squeezing roller pair [0171] 34 Squeezing roller [0172] 36 Squeezing roller [0173] 38 Control device [0174] 40 Control unit [0175] 42a Sensor unit [0176] 42b Sensor unit [0177] 44 Sensor row [0178] 46 Sensor row [0179] 48 Length direction [0180] 50 Spraying unit [0181] 52 Edge region [0182] 54 Spraying unit [0183] 56 Edge region [0184] 58 Spraying unit [0185] 60 Middle region [0186] 62 Width direction [0187] 64 Spraying direction [0188] 66 Pickling agent distribution chamber [0189] 68 Pickling agent supply line [0190] 70 Pickling agent delivery pump [0191] 72 Plateau [0192] 74 Valve