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 means of 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 comprising: feeding the metal strip in a direction of transport through a cooling zone; cooling the metal strip while the metal strip is transported through the cooling zone; then cross-cutting the metal strip on 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; wherein in the direction of transport, the strip head of the following section of metal strip follows on immediately after the strip tail of the preceding section of metal strip; and cooling the metal strip in the cooling zone to a prescribed temperature profile in the transport direction of the metal strip so that, in a respective region of both of the strip head of the following section of metal strip and the strip tail of the preceding section of metal strip, the metal strip has a higher temperature than in the preceding and following regions of the sections of metal strip.

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

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

4. The method as claimed in claim 1, wherein the temperature in the region of the strip head of the following section of metal strip and of the strip tail of the preceding section of metal strip lies at least 100 C. above the temperature of the rest of the metal strip.

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

6. The method as claimed in claim 1, wherein the metal strip is comprised of high and ultra-high strength materials.

7. The method as claimed in claim 1, wherein the metal strip has a thickness >4 mm.

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 in the cooling zone to achieve the temperature to be set.

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, before cooling the metal strip in the 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.

12. The method as claimed in claim 11, further comprising a length of a partial piece of the metal strip which has a raised temperature is the circumference of a coil, so that the coil is hot-packed by the strip tail of the following section of metal strip.

13. The method as claimed in claim 1, 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, for carrying out the method in accordance with claim 1, comprising: a roller track configured for feeding the metal strip in a direction of transport; shears located along the roller track 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; at least one cooling facility arranged in the direction of transfer before the shears and before the cross-cutting of the metal strip; the shears being operable so that the metal strip is cross-cut into a preceding leading section of metal strip with a strip tail of the preceding section of metal strip and a trailing following section of metal strip with a strip head of the following section of metal strip, so that the strip head of the following section of metal strip follows in the direction of transport immediately behind the strip tail of the preceding section of metal strip; a tracking facility configured and operable for tracking the position of the strip head of the following section of metal strip and the strip tail of the preceding section of metal strip, at least from the start of the cooling facility up to the shears; and a control facility configured and operable for controlling the cooling facility and the shears as a function of the position of the strip head of the following section of metal strip and the strip tail of the preceding section of metal strip for operating the cooling facility to cool the metal strip such that the strip head and the strip tail are hotter than the rest of the metal strip when passing by the shears and for operating the shears for cross-cutting the strip between the strip tail of the preceding section and the strip head of the following section of the metal strip.

15. The facility as claimed in claim 14, further comprising the cooling facility has at least three of the cooling sections which are separate from each other at spaced intervals along the metal strip, 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, further comprising 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, further comprising the cooling facility is 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; the control facility controlling the amount of flow through the water jets of the cooling facility 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, the tracking facility is a temperature measurement facility.

20. The facility as claimed in claim 14, further comprising the shears having shearing blades with a blade gap, and having 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 for adjusting for the purpose of adjusting the blade gap.

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

22. The method as claimed in claim 1, further comprising not cooling the region of the strip head of the following section of metal strip and the strip tail of the preceding section of metal strip to obtain the temperature of the following and the preceding section of the metal strip.

23. The method as claimed in claim 6, wherein the materials are pipe, hot strip multi-phase steels or fully martensitic steels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is a schematic representation of a combined casting-rolling plant in accordance with the prior art.

[0045] FIG. 2 is a schematic representation of a combined casting-rolling plant for cross-cutting metal strips in accordance with the invention.

[0046] FIG. 3A and FIG. 3B show the hot packing of a coil.

[0047] FIG. 4A shows a temperature profile in accordance with the invention for a metal strip.

[0048] FIG. 4B shows

[0049] FIG. 5A and FIG. 5B show variant embodiments of a position sensor and a speed sensor.

[0050] 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.

[0051] FIG. 7A and FIG. 7B show the inventive temperature profile of a metal strip shortly before and shortly after cross-cutting.

[0052] 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

[0053] 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.

[0054] 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. Instead, 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 the cooling zone 10, the actual temperature of the metal strip 6 then at a first temperature sensor 15 is detected by the first temperature sensor 15. That sensed temperature is transmitted to a control facility 14. In the subsequent cooling zone 10, the desired temperature profile is produced on the metal strip 6 then passing by appropriate actuation by the control facility 14 of the water spray bar sections 20, or even only of individual spray bars 21, of 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 FIG. 4) are determined by the control facility 14 with the aid of a position sensor 16 for the strip head and tail then passing the 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 a 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 has in 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 strip a higher temperature than in the regions before and after them. This result is governed by the control facility 14. 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 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.

[0055] 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 been transported to the shears 12, the shears receive a signal from the control facility 14, and the metal strip 6 is cross-cut by the shears. The preceding metal strip 28 is finish-wound on the coiler 13. Following that the strip head 31 of the following section of metal strip is threaded onto the coiler 13 and the coiling procedure is started.

[0056] 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.

[0057] FIG. 3B shows that the hot partial piece of metal strip 33 encloses the coil 30.

[0058] FIG. 4 shows a typical temperature profile in accordance with the invention along the temperature-profiled length xp of a metal strip 6. The temperature T.sub.1 in the region of the strip tail 32 of the preceding metal strip along the strip tail length xf is higher than after length xf, where a temperature T.sub.0 is set, until finally the region of the strip head 31 of the following section of metal strip follows, where a temperature T.sub.1 is again set along 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 T.sub.1. 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-cutting, at least as soon as the two sections reach the cooling facility, it is defined as a preceding section of metal strip 28 and a following section of metal strip 29.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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

[0063] 1 Combined casting/rolling plant [0064] 2 Continuous casting plant [0065] 3 Preliminary material [0066] 4 Roller track [0067] 5 Pre-rolling line [0068] 6, 6a-6d Metal strip [0069] 7 Cutting facility [0070] 8 Induction furnace [0071] 9 Finishing line [0072] 10 Cooling zone [0073] 12 Shears [0074] 13 Coiler [0075] 14 Control facility [0076] 15 First temperature sensor [0077] 16 Position sensor [0078] 18 Speed sensor [0079] 17 Second temperature sensor [0080] 19 Cooling facility [0081] 20 Spray bar sections [0082] 21 Spray bars [0083] 22 Computing facility [0084] 23 Tracking facility [0085] 28 Preceding section of metal strip [0086] 29 Following section of metal strip [0087] 30 Coil [0088] 31 Strip head of the following section of metal strip [0089] 31a-31d Strip head [0090] 32 Strip tail of the preceding section of metal strip [0091] 32a-32d Strip tail [0092] 33 Partial piece of metal strip [0093] 34 Direction of transport [0094] 41 Roller [0095] 42 Optical sensor [0096] 43 Angular rotation encoder [0097] L Length of the partial piece of metal strip [0098] T Temperature [0099] xp Length of temperature profile [0100] xf Length of strip tail [0101] xk Length of strip head [0102] x Length of metal strip [0103] .sub.f Yield stress