Adjusting a targeted temperature profile at the strip head and strip base prior to cross-cutting a metal strip

Abstract

A rolling mill with a cooling zone for cooling and scissors for cross-cutting metal strips, which are preferably made of steel. A method and a device enables metal strips with thicknesses >4 mm and/or metal strips made of high-strength materials to be cross-cut by the scissors arranged after a production line and a cooling zone. In the method, the metal strip (6) is cooled in the cooling zone (10) to a specified temperature profile in the longitudinal direction of the metal strip (6) such that the metal strip (6) has a higher temperature in the region of the strip head of the trailing metal strip portion (31) and the strip base of the leading metal strip portion (32) than in the upstream and downstream regions.

Claims

1. A method for cross-cutting a metal strip, the metal strip having a preceding section with a strip tail and a following section with a strip head, the method comprising: feeding the metal strip in a direction of transport through a finishing line and thereafter a controllable cooling zone so that, in the direction of transport, the strip head of the following section of the metal strip follows on immediately after the strip tail of the preceding section of metal strip, the metal strip being more than 4 mm thick; cooling the metal strip preceding section and following section to a cooling temperature according to a temperature profile while the metal strip is transported through the controllable cooling zone to define a cross-cut region having a higher temperature and lower yield strength located between the cooled preceding section and the cooled following section of the metal strip; and cross-cutting the metal strip along the higher temperature cross-cut region with shears that are not capable of cutting the strip at the cooling temperature of the following section and the preceding section to define the strip tail of the preceding section and the strip head of the following section.

2. The method as claimed in claim 1, further comprising tracking the strip head of the following section and the strip tail of the preceding section, at least from the start of the controllable cooling zone up to the shears.

3. The method as claimed in claim 1, wherein the temperature profile is selected to have a ramp profile.

4. The method as claimed in claim 1, wherein the higher temperature cross-cut region is at least 100 C. above the cooling temperature of the preceding and following sections.

5. The method as claimed in claim 4, further comprising not applying the cooling to the strip head of the following section and the strip tail of the preceding section to obtain the higher temperature cross-cut region.

6. The method as claimed in claim 1, wherein the metal strip has a yield stress of 500 MPa or more.

7. The method as claimed in claim 6, wherein the metal strip is comprised of pipe steel, hot strip multi-phase steel or fully martensitic steel.

8. The method as claimed in claim 1, further comprising setting the temperature profile by applying a determined quantity of coolant fed onto the metal strip.

9. The method as claimed in claim 8, further comprising adjusting discretely the quantity of coolant fed.

10. The method as claimed in claim 1, further comprising, before cooling the metal strip in the controllable cooling zone, rolling the metal strip on a rolling line of a combined casting/rolling facility.

11. The method as claimed in claim 1, further comprising, after cross-cutting the metal strip, winding the metal strip on a coiler to obtain a coil.

12. The method as claimed in claim 11, wherein the metal strip is wound to have a coil section and a partial piece with a length that is the same as the circumference of the coil section, and a temperature higher than the coil section.

13. The method as claimed in claim 1, further comprising setting a blade gap of the shears as a function of the thickness of the metal strip.

14. A facility for cross-cutting a metal strip that is thicker than 4 mm, comprising: a roller track configured for feeding the metal strip that is thicker than 4 mm in a direction of transport; a finishing line; shears located after the finishing line and configured and operable for cross-cutting the metal strip at intervals as the metal strip passes the shears, so that the metal strip is cross-cut into a preceding section of metal strip having a strip tail and a following section of metal strip having a strip head, the strip head of the following section being immediately behind the strip tail of the preceding section in the direction of transport, the shears being unable to cross-cut a strip that is more than 4 mm thick when the metal strip is below a threshold temperature and has a yield strength at the threshold temperature that would not permit cross-cutting by the shears, and the shears being operable to cross-cut the metal strip along a cross-cut region located between the strip head of the following section and the strip tail of the preceding section; at least one controllable cooling facility located after the finishing line and arranged in the direction of transport before the shears; a tracking facility configured and operable for tracking the position of the strip head of the following section and the strip tail of the preceding section, at least from the start of the cooling facility up to the shears; and a control facility configured and operable to control the controllable cooling facility and the shears as a function of the position of the strip head of the following section and the strip tail of the preceding section to cool the metal strip such that the cross-cut region is hotter than the threshold temperature to have a lower yield strength than the rest of the metal strip when passing by the shears while the rest of the metal strip is at a temperature below the threshold temperature, and for operating the shears for cross-cutting the strip along the cross-cut region.

15. The facility as claimed in claim 14, wherein the cooling facility has at least three cooling sections which are separate from each other at spaced intervals along the metal strip, and wherein the at least three cooling sections are controlled or regulated separately from each other by the control facility.

16. The facility as claimed in claim 14, wherein the tracking facility has a computing facility configured and operable for determining when the cooling facility is to be operated and has a position sensor or a speed sensor for the metal strip for enabling the computing facility to operate the cooling facility.

17. The facility as claimed in claim 14, wherein the cooling facility comprises a water cooling line configured for supplying water to the metal strip.

18. The facility as claimed in claim 17, further comprising water jets for flowing of water from the cooling line; wherein the control facility controls the amount of flow through the water jets in the direction of transport of the metal strip individually or in sections.

19. The facility as claimed in claim 14, further comprising a setting facility which is linked to the control facility, wherein the tracking facility is a temperature measurement facility.

20. The facility as claimed in claim 14, wherein the shears have shearing blades with a blade gap, and further comprising a facility for adjusting the blade gap between the blades of the shears, wherein a current thickness of the metal strip is fed to the facility to adjust the blade gap.

21. The method as claimed in claim 2, wherein the strip head of the following section and the strip tail of the preceding section are tracked constantly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of a combined casting-rolling plant in accordance with the prior art.

(2) FIG. 2 is a schematic representation of a combined casting-rolling plant for cross-cutting metal strips in accordance with the invention.

(3) FIG. 3A and FIG. 3B show the hot packing of a coil.

(4) FIGS. 4A and 4B together show a temperature profile in accordance with the invention for a metal strip.

(5) FIG. 5A and FIG. 5B show variant embodiments of a position sensor and a speed sensor.

(6) FIG. 6 shows a diagram of yield stress against temperature, from M. Spittel and T. Spittel Landolt-Bornstein Group VIII: Advanced Materials and Technologies, Volume 2, Springer Verlag, 2007, p. 11.

(7) FIG. 7A and FIG. 7B show the inventive temperature profile of a metal strip shortly before and shortly after cross-cutting.

(8) FIG. 7C shows the temperature profile of the strip head of the following section of metal strip and strip tail of the preceding section of the metal strip.

DESCRIPTION OF AN EMBODIMENT

(9) FIG. 1 shows a combined casting-rolling plant 1. In normal operation, a continuous-casting plant 2 produces a continually cast starting material 3 with a slab cross-section, which is transported by means of a roller track 4 to a pre-rolling line 5. After pre-rolling on the pre-rolling line 5, the metal strip 6 reaches the cutting facility 7. In accordance with the prior art, cross-cutting of the metal strip 6 would take place here using a cutting facility 7 which in this case is pendulum shears. After this, gaps are introduced between the metal strips 6a-6d by powered rollers of the roller track 4. The leading strip heads 31a-31d and the trailing strip tails 32a-32d are formed by the cross-cutting. After passage through the induction furnace 8, the finishing line 9 and the cooling zone 10, the metal strip is wound up on the coiler 13.

(10) FIG. 2 shows a form of embodiment in accordance with the invention of the facility for cross-cutting metal strips. The first steps as far as the pre-rolling line 5 are carried out analogously with the prior art as in FIG. 1. This is not followed by cross-cutting, but the metal strip 6 passes uncut through the induction furnace 8, the finishing line 9 and after this reaches the cooling zone 10. Before the metal strip 6 enters into the cooling zone 10, the actual temperature of the metal strip 6 is detected by a first temperature sensor 15, and is transmitted to the control facility 14. In the cooling zone 10, the desired temperature profile is produced on the metal strip 6 by appropriate actuation by the control facility 14 of the water spray bar sections 20 or even only individual spray bars 21of the cooling facility 19. The strip head 31 of the following section of metal strip and the strip tail 32 of the preceding section of metal strip of the metal strip 6 (see bottom of FIGS. 4A and 4B) are determined by the control facility 14 with the aid of the position sensor 16 and the computing facility 22, and their position is continuously determined. The position sensor 16 can be implemented either in a contact format (e.g. by pressing onto a roller, or from the rotational speed at the coiler) or in a non-contact format (optically, e.g. using a laser). The position sensor 16 and the computing facility 22 form the tracking facility 23. The spray bars 21 can be adjusted over the entire passage of the strip head 31 of the following section of metal strip and the strip tail 32 of the preceding section of metal strip according to the prescribed temperature profile. After its passage through the cooling facility 19, the metal strip 6 hasin the region of the strip head 31 of the following section of metal strip and the strip tail 32 of the preceding section of metal stripa higher temperature than in the regions before and after them. After the strip head 31 of the following section of metal strip and the strip tail 32 of the preceding section of metal strip have passed completely through the cooling zone 10, the temperature profile is once again detected by a second temperature sensor 17 and is communicated to the control facility 14 in order to compare the actual profile with the intended profile. When the strip head 31 of the following section of metal strip and the strip tail 32 of the preceding section of metal strip have reached the shears 12, the latter receives a signal from the control facility 14, and the metal strip 6 is cross-cut. The preceding metal strip 28 is finish-wound on the coiler 13, following which the strip head 31 of the following section of metal strip is threaded onto the coiler 13 and the coiling procedure is started.

(11) FIG. 3A and FIG. 3B show how the coil 30 is hot-packed. FIG. 3A shows the wound-up coil 30, on the inside the strip head 31a, a partial piece of metal strip with a temperature T.sub.0, a partial piece of metal strip 33 with a length of L with a temperature T.sub.1 together with the strip tail 32a. The length L of the partial piece of metal strip is here the length of the circumference of the coil 30. The temperature of the partial piece of metal strip 33 is here a higher temperature T.sub.1 than the temperature T.sub.0 of the preceding part of the metal strip. The diagram shows the temperature T along the length x of the metal strip which is here the extended length.

(12) FIG. 3B shows that the hot partial piece of metal strip 33 encloses the coil 30.

(13) FIGS. 4A and 4B show a typical temperature profile in accordance with the invention along the temperature-profiled length xp of a metal strip 6. The temperature T1 in the region of the strip tail 32 of the preceding metal stripalong the strip tail length xfis higher than after it, where a temperature T0 is set, until finally the region of the strip head 31 of the following section of metal strip follows, where a temperature T1 is again setalong the strip head length xk. The strip head length xk and the strip tail length xf need not be, as shown here, the same. They can also have different lengths. The strip head 31a of the preceding metal strip 28 also has a temperature profile with the temperature T1. After cross-cutting on the shears, the metal strip 6 is divided into a preceding section of metal strip 28 and a following section of metal strip 29. However, even before the cross-cuttingat least as soon as the two sections reach the cooling facilityit is defined as a preceding section of metal strip 28 and a following section of metal strip 29.

(14) FIG. 5A shows in more detail an embodiment of a position sensor 16, which includes a roller 41, which is pressed down onto the metal strip 6. The movement of the metal strip 6 rotates the roller 41 which is pressed down on the strip, and this is detected by an optical sensor 42. The signal thereby generated is processed further in the control facility 14. From this signal and various further information, such as, for example, the desired length of the metal strip, the control facility 14 calculates the position of what will later be the strip head and strip tail, at least in the region from the start of the cooling zone 10 up to the shears 12. The spray bar sections 20 or, if applicable, the individual spray bars 21 in the cooling zone are actuated to establish a desired temperature profile on the metal strip 6.

(15) FIG. 5B shows a variant embodiment of a speed sensor 18. It detects the position of the metal strip 6 from the rotational speed of the coiler 13 by an angular rotation encoder 43. Based on knowledge of the thickness of the metal strip 6, the diameter of the coiler 13 and further information which is critical for its manufacture, for example the desired length of the metal strip, the positions of the strip head 31 and strip tail 32 in the cooling zone 10 are determined.

(16) FIG. 6 shows the relationship of the yield stress .sub.F against the temperature T for an H360LA steel. The yield stress of 300 MPa at about 600 C. falls to 150 MPa at about 800 C. Thus, by raising the temperature of the metal strip by about 200 C., it is possible to greatly reduce the cutting forces at a set of shears.

(17) FIG. 7A shows the metal strip 6 immediately before cross-cutting. The strip tail 32 of the preceding section of metal strip and the strip head 31 of the following section of metal strip are still identical prior to the cross-cutting, and are only there as an imaginary plane. The preceding section of metal strip already has a strip head 31a, caused by the previous cross-cutting FIG. 7B, shows the stripe after the cross-cutting. In the transport direction 34 there is a preceding section of metal strip 28 with the strip tail 32 of the preceding section of metal strip and a following section of metal strip 29 with a strip head 31 of the following section of metal strip. After cross-cutting, the preceding section of metal strip has a strip head 31a and the strip tail 32 of the preceding section of metal strip. The region of the strip head 31 of the following section of metal strip and the region of the strip tail 32 of the preceding section of metal strip have the temperature profile shown in FIG. 7C.

LIST OF REFERENCE MARKS

(18) 1 Combined casting/rolling plant 2 Continuous casting plant 3 Preliminary material 4 Roller track 5 Pre-rolling line 6, 6a-6d Metal strip 7 Cutting facility 8 Induction furnace 9 Finishing line 10 Cooling zone 12 Shears 13 Coiler 14 Control facility 15 First temperature sensor 16 Position sensor 18 Speed sensor 17 Second temperature sensor 19 Cooling facility 20 Spray bar sections 21 Spray bars 22 Computing facility 23 Tracking facility 28 Preceding section of metal strip 29 Following section of metal strip 30 Coil 31 Strip head of the following section of metal strip 31a-31d Strip head 32 Strip tail of the preceding section of metal strip 32a-32d Strip tail 33 Partial piece of metal strip 34 Direction of transport 41 Roller 42 Optical sensor 43 Angular rotation encoder L Length of the partial piece of metal strip T Temperature xp Length of temperature profile xf Length of strip tail xk Length of strip head x Length of metal strip .sub.f Yield stress