Method for operating a steckel mill

Abstract

A Steckel mill has a reversing unit for rolling a rolled product and winding furnaces arranged on the entrance side and exit side of the reversing unit. When rolling the rolled product in a region of a head of the rolled product, a target thickness of the rolled product is ignored, while measuring a current thickness and/or a hardness of the rolled product and comparing this with a setpoint value. One the measured variable reaches or is below the setpoint value, the reversing unit is operated with a view to achieving the target thickness of the rolled product. The Steckel mill is operated to allow for rolling of a cold, non-rollable piece of the rolled product, so that malfunctions are avoided and the usable part of the rolled product is as large as possible.

Claims

1. A method for operating a Steckel mill having a reversing unit for rolling a rolled product, the Steckel mill having winding furnaces for the rolled product, the winding furnaces including an entry-side winding furnace arranged at an entry side of the reversing unit, and an exit-side winding furnace arranged at an exit side of the reversing unit, the method comprising: during rolling of the rolled product in the reversing unit, in a region of a head end of the rolled product, ignoring a target thickness of the rolled product; while rolling the rolled product and ignoring the target thickness, determining a measured variable which correlates to at least one of a current thickness and a current hardness of the rolled product, the measured variable being determined as the rolled product progresses through the reversing unit; comparing the measured variable with a reference value; and if the measured variable is equal to or less than the reference value, operating the reversing unit with an aim of achieving the target thickness of the rolled product.

2. The method as claimed in claim 1, wherein when the head end of the rolled product is rolled in the reversing unit, a force applied by the reversing unit is regulated to correspond with a pre-determined force pattern.

3. The method as claimed in claim 2, wherein the pre-determined force pattern comprises a constant force of between 5 MN and 100 MN.

4. The method as claimed in claim 2, wherein the pre-determined force pattern comprises a constant force of between 5 MN and 60 MN.

5. The method as claimed in claim 1, wherein when the head end of the rolled product is rolled, a force applied by the reversing unit is regulated based on a reference force, and the reference force is determined for the reversing unit from the measured variable.

6. The method as claimed in claim 1, wherein the rolled product has a cold section comprising the head end of the rolled product, the cold section of the rolled product has a predetermined expected minimum length, and during rolling of the cold section of the rolled product in a region of the minimum length, the target thickness is ignored and the measured variable is not determined.

7. The method as claimed in claim 1, wherein the rolled product has a cold section comprising the head end of the rolled product, the cold section of the rolled product has a predetermined expected maximum length, a predetermined expected minimum length and a transition region between the minimum length and the maximum length, and wherein the measured variable is determined and compared with a reference value only while rolling the rolled product in the transition region.

8. The method as claimed in claim 7, wherein after the maximum length has passed through the reversing unit, the reversing unit is automatically switched over to closed-loop control with the aim of achieving the target thickness.

9. The method as claimed in claim 1, wherein a rolled section of the rolled product is a section currently being rolled by the reversing unit, and the current thickness of the rolled section of the rolled product is calculated based on a measured rolling force and a measured setting of a roll gap of the reversing unit.

10. The method as claimed in claim 1, wherein the rolled product has first cold section at the head end of the rolled product, the rolled product has second cold section at a foot end of the rolled product, between the cold sections, the reversing unit is operated with a closed-loop control with the aim of achieving the target thickness, and at the second cold section in foot end of the rolled product, the reversing unit is switched to a closed-loop control in which the target thickness is ignored.

11. The method as claimed in claim 6, wherein the minimum length is between 0 m and 5 m.

12. The method as claimed in claim 7, wherein the maximum length is approximately 10 m.

13. The method as claimed in claim 7, wherein the maximum length corresponds to a separation distance between the reversing unit and one of the winding furnaces.

14. The method as claimed in claim 1, wherein if there is a fault in the rolling process while operating the reversing unit with the aim of achieving the target thickness, then: rolling conditions are switched such that the target thickness of the rolled product is ignored; the measured variable is determined and compared with the reference value; and if the measured variable again becomes equal to or less than the reference value, the reversing unit again is operated with an aim of achieving the target thickness of the rolled product.

15. The method as claimed in claim 1, wherein the rolled product has a cold section comprising the head end of the rolled product, and the cold section has passed the reversing unit when the measured variable becomes equal to or less than the reference value.

16. An open-loop and/or closed-loop control device for a Steckel mill with a machine-readable program code which has control instructions which, on execution of the program code, cause the open-loop and/or closed-loop control device to carry out a method as claimed in claim 1.

17. A Steckel mill comprising: a reversing unit for rolling a rolled product; winding furnaces for the rolled product arranged respectively at an entry side and an exit side with respect to the reversing unit; and an open-loop and/or closed-loop control device to: ignore a target thickness of the rolled product, during rolling of the rolled product in the reversing unit, in a region of a head end of the rolled product; determine a measured variable which correlates to at least one of a current thickness and a current hardness of the rolled product, the measured variable being determined while rolling the rolled product and ignoring the target thickness, the measured variable being determined as the rolled product progresses through the reversing unit; compare the measured variable with a reference value; and operate the reversing unit with an aim of achieving the target thickness of the rolled product if the measured variable is equal to or less than the reference value.

18. A non-transitory computer readable storage medium storing a computer program, which when executed by a processor, causes the processor to perform a method for operating a Steckel mill having a reversing unit for rolling a rolled product, the Steckel mill having winding furnaces for the rolled product, the winding furnaces including an entry-side winding furnace arranged at an entry side of the reversing unit, and an exit-side winding furnace arranged at an exit side of the reversing unit, the method comprising: during rolling of the rolled product in the reversing unit, in a region of a head end of the rolled product, ignoring a target thickness of the rolled product; while rolling the rolled product and ignoring the target thickness, determining a measured variable which correlates to at least one of a current thickness and a current hardness of the rolled product, the measured variable being determined as the rolled product progresses through the reversing unit; comparing the measured variable with a reference value; and if the measured variable is equal to or less than the reference value, operating the reversing unit with an aim of achieving the target thickness of the rolled product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 is a schematic representation of a Steckel mill for rolling a metal strip, and

(3) FIG. 2 is a block flow diagram showing the sequence of the operating method for a Steckel mill of this type.

(4) The same reference signs have the same meaning in the different figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

(6) The Steckel mill 2 shown in FIG. 1 comprises a reversing unit 4 with two working rolls 6 between which a roll gap 7 is formed, and two backup rolls 8, as well as winding furnaces arranged on the entry side and the exit side with respect to the reversing unit 4, of which, however in FIG. 1, only the entry-side winding furnace 10 is shown. The Steckel mill 2, in particular the reversing unit 4, is controlled by an open-loop and/or closed-loop control device 9 which is shown symbolically in FIG. 1.

(7) Arranged in the winding furnace 10 is a rolled product 14 to be rolled, a metal strip in the exemplary embodiment shown, wound on a Steckel drum 12. In the winding furnace 10, the rolled strip 14 is kept hot so that it can be rolled by the reversing unit 4 to a target thickness d.sub.target.

(8) A general problem with a Steckel mill 2 of this type is that even after short delays, the material outside the winding furnaces 10 is so cold that it can no longer be rolled to a target thickness of d.sub.target. In order to solve this problem, the operating method shown schematically in FIG. 2 is provided for the Steckel mill 2.

(9) According to the operating method shown schematically in FIG. 2, in S1, in the region of a cold head end 16 of the strip 14, the reversing unit 4 is initially regulated such that contact between the working roll 6 and the metal strip 4 takes place, but no substantial reduction in thickness takes place. In particular, for this purpose, a constant rolling force is pre-set which is selected such that detection of the rolled strip 14 in the roll gap 7 between the working rolls 6 is possible, but the force F must not be too great such that the reversing unit 2 is damaged by the cold and therefore harder section in the region of the head end 16 of the rolled strip 14.

(10) In S2, during the force-regulated rolling process, a current actual thickness d.sub.current of the rolled section of the rolled strip 14 is determined. For this purpose, in the exemplary embodiment shown, a minimum length L.sub.min and a maximum length L.sub.max of the cold section of the rolled strip 14 are pre-determined. The minimum length L.sub.min varies, in particular, between 0 and 5 m, and in the exemplary embodiment shown, it is 1 m. The maximum length L.sub.max corresponds, for example, to the separation between the reversing unit 2 and the entry-side winding furnace 10, while allowing a safety margin. The maximum length L.sub.max is, for example, 10 m.

(11) During rolling of the section of the strip 14 in the region of the minimum length L.sub.min, in the exemplary embodiment shown, the reversing unit 4 is regulated solely for force.

(12) Only after the passage of the region of minimum length L.sub.min is it to be expected that the rolled strip 14 is hot enough to be rolled to the target thickness d.sub.target. However, it is not known where the cold section at the head end 16 of the rolled strip 14 finishes. For this reason, in a transition region 18 after the minimum length L.sub.min but within the maximum length L.sub.max, during rolling of the metal strip 14, the current thickness d.sub.current is determined, particularly continuously, and is compared with a pre-determined reference thickness d.sub.ref. Determination of the current thickness d.sub.current takes place, in particular, by the rolling force F and the size of the roll gap 7 between the working rolls 6. The current thickness d.sub.current is therefore determined indirectly. Alternatively, it can also be measured directly. In place of the current thickness d.sub.current, the hardness of the strip 14 can also be determined directly or indirectly. Suitable measured variables for determination of the current thickness d.sub.current or the hardness are, for example, the rolling force F and a setting of the roll gap 7.

(13) If the determined thickness d.sub.current is smaller than or equal to a reference thickness d.sub.ref, in accordance with S3, the operating method is initiated wherein switching over takes place from the force regulation to a thickness regulation of the reversing unit 4. The roll gap 7 is adjusted such that the rolled strip 14 is rolled to the pre-determined target thickness d.sub.target.

(14) A force regulation in accordance with S1 can already be set during the first pass. Alternatively, the method shown in FIG. 2 is only initiated once, following a plurality of rolling passes, the ends of the rolled strip 14 have already cooled down or when a fault has occurred during reversing.

(15) When the foot end of the strip 14 has reached the reversing unit 4, a similar procedure is followed as in the region of the head end 16. In this process, an actual rolling force is compared with a reference force and, if the actual rolling force exceeds the reference force, i.e. if the foot end is too cold to be rolled to the desired target thickness d.sub.target, switching over to force regulation in accordance with S1 again takes place. Similarly as for the head end 16, in the region of the foot end, a minimum length L.sub.min, a maximum length L.sub.max and a transition region 18 for the cold section can be provided.

(16) As an alternative to the comparison of the determined current thickness d.sub.current with the reference value d.sub.ref, a thickness deviation or thickness difference which is determined when the hot section of the rolled product 14 reaches the roll gap 7 can be compared with a pre-determined reference value and, on exceeding this reference value, i.e. if the thickness deviation is too great, switching over from force regulation to the normal roll gap monitoring takes place.

(17) The method described above for operation of the Steckel mill 2 is based on automated recognition of the transition from the non-rollable to the rollable material section. If, during force regulation wherein the target thickness d.sub.target is ignored, the current thickness d.sub.current of the rolled product 14 falls below the pre-determined reference thickness d.sub.ref, switching over to the normal, thickness-regulated rolling operation (e.g. AGC) takes place. The method is also suitable for automatic tapering in order to achieve thin dimensions. For this purpose, the head end and the foot end become so cold that, on certain occasions, they can no longer be rolled to the target thickness, whilst the head and foot lengths and thicknesses are set such that the largest possible portion of the rolled product 14 is optimally utilized in a fault-free operation of the Steckel mill 2.

(18) The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase at least one of A, B and C as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).