EP4212259A1 - Reduction of surface defects during finish rolling of hot strip - Google Patents

Abstract

The invention relates to a finishing train (7) for finish-rolling hot strip (11). The object of the invention is to change an existing finishing train in such a way that the surface quality of the hot strip (11) produced is improved, but without significantly increasing the energy consumption during production. As a result, the thin hot strip (11) produced should also be able to be used for applications with high demands on the surface quality. This task is solved by a cleaning nozzle (17) cleaning the upper side of the outfeed table (15), so that scale (Z) and/or rolling dust are removed from the outfeed table (15).

Description

field of technology

The present invention relates to the technical field of hot rolling, preferably of steel. Nowadays, the majority of steel or aluminum strip-shaped starting materials are produced inexpensively by hot rolling; the products are referred to as hot strip . The hot rolling typically takes place in a so-called hot rolling mill or in a combined casting and rolling plant in which a continuous caster is coupled in-line with the hot rolling mill. The strand, which is typically continuously produced in the continuous casting machine, is either finish-rolled directly afterwards in a finishing mill to form a finished strip, or the strand is first rough-rolled in a roughing mill to form a pre-strip and the pre-strip is then immediately finish-rolled in the finishing rolling mill to form the finished strip.

State of the art

Until a few years ago it was not possible to produce thin, very thin or ultra-thin strips by hot rolling. In particular, continuous rolling on an Arvedi ESP combined casting and rolling plant makes it possible to industrially produce ultra-thin steel strips with a thickness of < 0.8 mm or even ≤ 0.6 mm by hot rolling. Further developments on the material side have also made it possible to produce directly produced hot strip (i.e. without subsequently cold-rolling the hot strip) with a high level of ductility. This means that thin, ductile hot strip can be used directly for deep drawing, for example. This means that today hot strip can be used directly for many products for which only cold strip could be used in the past.

However, the surface quality can be problematic when using hot strip. According to the prior art, it is still necessary to produce parts that must have a high or very high surface quality, such as exterior body parts, by cold rolling. As a result, the use of energy and the costs for production rise sharply. The prior art does not show how the surface quality of hot strip can be improved without increasing the use of energy.

Summary of the Invention

The object of the invention is to change a finishing train for the production of very thin hot strip in such a way that the surface quality of the hot strip produced is improved, but without significantly increasing the energy consumption during production. As a result, the thin hot strip produced should also be able to be used for applications with high demands on surface quality.

This object is achieved on the one hand by a finishing train according to claim 1. Advantageous embodiments are the subject matter of the dependent claims.

In concrete terms, the solution is provided by a finishing train for finish-rolling (thin or very thin) hot strip, preferably made of steel, the finishing train having a plurality of roll stands, the roll stands each having a lower and an upper work roll and the work rolls each forming a roll gap, so that during finish rolling, the hot strip passes through the roll gaps in the direction of transport and is thereby finish-rolled, with at least one outlet-side region of the lateral surface of the lower work roll of the last roll stand in the direction of transport being cooled by a plurality of cooling nozzles arranged below a pass line, and the cooling nozzles being exposed to a liquid cooling medium spraying on the outer surface, with the cooling medium being kept away from the hot strip by at least one scraper, which is arranged in the vertical direction between the cooling nozzles and the hot strip, with the scraper being attached to an exit table , and with at least one Cleaning nozzle is provided for cleaning the top of the outlet table with a liquid or gaseous medium, so that scale and / or rolling dust are removed at least from the top of the outlet table.

During finish rolling of thin hot strip, the outer surfaces of the work rolls are cooled by a liquid cooling medium (e.g. cooling water) in order to increase the service life of the work rolls and to prevent temperature-related deformation of the roll contours. However, in order to cool the rolling stock or the hot strip as little as possible, the cooling medium is kept away from the rolling stock/hot strip by means of scrapers.

Investigations by the applicant have shown that, in particular, very thin hot strip with a thickness of <1.2 mm sometimes has surface scratches on the underside and this is due to contact with scale, rolling dust, etc. in the exit area of the last rolling stand of the finishing train (see figure 7 ). Although thin hot strip is clamped between the roll gap of the last roll stand and the driver rolls in front of the "flying shears" after the cooling section, even in continuous operation, it can Waves occur in the central area of the hot strip, so that the bottom of the hot strip (particularly antinodes on the bottom of the hot strip) is scratched by scale, rolling dust, etc. Cleaning the top of the outfeed table with a liquid or gaseous medium during operation reliably prevents scale, rolling dust, dirt, etc. from accumulating there and these residues from caking due to high temperatures and high humidity. This reliably prevents the build-up of scale, rolling dust, dirt... in the outlet area of the last roll stand, so that the finishing train according to the invention can ensure a high surface quality of the hot strip. In the following, cleaning by means of a liquid medium is also referred to as hosing down, cleaning by means of a gaseous medium as rinsing.

The run-out table is cleaned either constantly during hot rolling or depending on the time during which the hot strip is being rolled. Preferably, the run-out table is cleaned by short pulses of relatively high pressure during hot rolling. This achieves a better cleaning effect than continuous cleaning or hosing down/rinsing with low or medium pressure. The pulses can be generated, for example, by a valve that is arranged in the supply line for the medium.

Of course, it is possible that the cleaning nozzle or the cleaning nozzles are provided not only in the last roll stand of the finishing train, but also in other or all roll stands. In addition, it is possible to clean not only the outfeed table, but also the so-called infeed table (i.e. the table on the infeed side).

The cleaning nozzle or the cleaning nozzles are arranged essentially horizontally (and thus in the width direction of the hot strip), so that residues in the width direction of the hot strip are sprayed off or rinsed off the outfeed table.

The cleaning nozzles are typically pressurized with a liquid cooling medium, preferably the same cooling medium used to cool the work rolls. This creates a jet on the front of the spray nozzle that sprays the top of the outfeed table. Alternatively, it is possible to operate the cleaning nozzles with a gaseous medium (e.g. air) under pressure.

The spraying effect is improved if at least one first cleaning nozzle is arranged on the drive side of the roll stand and at least one second cleaning nozzle is arranged on the operator side of the roll stand. As a result, the outfeed table from two sides cleaned or hosed down so that larger/heavier particles can also be removed.

It is advantageous if the cleaning nozzles are designed as flat jet nozzles and in particular if the cleaning nozzle on the drive side is offset in the transport direction in relation to the cleaning nozzle on the operator side. In the second case, spray jets are prevented from meeting in the middle of the hot strip, so that particles are always removed from the strip.

In addition, it is advantageous if the width b of the outlet opening of the cleaning nozzle is larger, preferably at least 3 times larger, than the height h of the outlet opening. In other words b >h or preferably b ≧3. h.

Finally, it is advantageous if the cleaning nozzle is not arranged exactly horizontally, but rather is inclined at an angle α to the horizontal, so that the upper side of the run-out table is cleaned or sprayed without affecting the underside of the hot strip.

It is also very advantageous if at least one lifting roller, which is arranged in the width direction of the hot strip, is arranged in the transport direction between the last roll stand and a cooling section for cooling the finish-rolled hot strip, and the lifting roller transports the hot strip during finish-rolling in the vertical direction above the lifts the passline so that the bottom of the hot strip does not touch the exit table.

Simple tubing or tubing of the cleaning nozzle(s) is achieved if a pipe or hose line fluidly connects a cooling nozzle to at least one cleaning nozzle.

The technical problem is also solved by a finishing train according to claim 6. Advantageous embodiments are the subject matter of the dependent claims.

In concrete terms, the solution is provided by a finishing train for finish-rolling (thin or very thin) hot strip, preferably made of steel, the finishing train having a plurality of roll stands, the roll stands each having a lower and an upper work roll and the work rolls each forming a roll gap, so that the hot strip passes through the roll gaps in the direction of transport and is thereby finish-rolled, with at least one region of the outer surface on the outlet side being finish-rolled the lower work roll of the last roll stand in the transport direction is cooled by several cooling nozzles arranged below a pass line and the cooling nozzles spray a liquid cooling medium onto the lateral surface, the cooling medium being arranged in the vertical direction between the finish-rolled hot strip and the cooling nozzles by at least one scraper is kept away from the hot strip, with the scraper being attached to a run-out table, with at least one lifting roller, which is arranged in the width direction of the hot strip, being arranged in the transport direction between the last rolling stand and a cooling section for cooling the finish-rolled hot strip, and the lift roller can lift the hot strip vertically above the pass line during finish rolling so that the bottom of the hot strip does not touch the run-out table.

Contact between the underside of the hot strip and the upper side of the run-out table is also reliably prevented in this alternative solution for solving the technical problem according to claim 1 . The lifting roll is a "normal" roll and not a roll that can be used to inspect the flatness of the hot strip. Flatness inspection rolls are expensive and delicate and should be excluded from the scope of protection. The flatness inspection is preferably carried out optically.

A first, preferably optical, surface inspection unit for inspecting the upper side of the hot strip is preferably arranged between the lifting roller and a first cooling unit of the cooling section.

According to a further advantageous embodiment, a pyrometer and a first blow-off device for blowing off the upper side of the hot strip are arranged between the last roll stand and the first surface inspection unit. The pyrometer is preferably located in front of the blow-off device in the transport direction.

According to a further advantageous embodiment, a second, preferably optical, surface inspection unit for inspecting the underside of the hot strip is arranged between a last cooling unit of the cooling section and a pair of shears.

It is advantageous if a pyrometer and a second blow-off device for blowing off the upper side of the hot strip are arranged between the second surface inspection unit and the shears. The blow-off device is preferably located in front of the pyrometer in the transport direction.

In a typical embodiment, a drive roller unit with at least one drivable drive roller that can be placed against the hot strip is arranged between the second blow-off device and the shears.

Preferably, the finishing train comprises a controller which is connected to a drive for raising the lifting roller and the second surface inspection unit for inspecting the underside of the hot strip, the controller further raising the lifting roller as soon as the second surface inspection unit detects surface defects on the underside of the hot strip. The information about surface defects on the underside of the hot strip is automatically used to further raise the lifting roller and thus increase the distance between the hot strip and the passline.

Alternatively, the lifting roller can also be extended further manually.

A combined casting and rolling plant preferably comprises a continuous casting plant for continuously casting a strand, optionally a roughing train for rough-rolling the strand to form an intermediate strip, and the finishing train according to the invention. An induction heater for heating the intermediate strip to rolling temperature is preferably arranged between the typically multi-stand roughing train and the finishing train.

In a further embodiment, a tunnel furnace for heating through and/or maintaining the temperature of the strand is arranged in front of the roughing train.

It is advantageous that the roughing train has three roll stands and the finishing train has five roll stands. This configuration has proven itself in Arvedi ESP plants and is also of great advantage for other cast-rolling compound plants.

Brief description of the drawings

• Fig 1 eine schematische Darstellung einer erfindungsgemäß ausgeführten Gieß-Walz-Verbundanlage,
• Fig 2 eine Detaildarstellung des letzten Walzgerüsts der Fertigwalzstraße mit einer Hubrolle sowie mehreren Reinigungsdüsen zum Abspritzen der Oberseite des Auslauftisches,
• Fig 3 eine Detaildarstellung des letzten Walzgerüsts der Fertigwalzstraße mit mehreren Reinigungsdüsen zum Abspritzen der Oberseite des Auslauftisches,
• Fig 4 eine Draufsicht auf das Walzgerüst und den Auslauftisch des letzten Walzgerüsts der Fertigwalzstraße mit den Reinigungsdüsen aus Fig 3,
• Fig 5a eine Vorderansicht mit einer Reinigungsdüse zum Abspritzen der Oberseite des Auslauftisches,
• Fig 5b eine Seitenansicht der Reinigungsdüsen aus Fig 5a,
• Fig 6 eine Detaildarstellung des letzten Walzgerüsts der Fertigwalzstraße mit einer Hubrolle zum Anheben des Warmbands, sodass die Unterseite des Warmbands den Auslauftisch nicht berührt, und
• Fig 7 ein Foto eines Oberflächenfehlers an der Unterseite eines Warmbands, das nach dem Fertigwalzen durch Zunder zerkratzt worden ist.

The properties, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of an exemplary embodiment, which will be explained in more detail in connection with the drawings. show:

• figure 1 a schematic representation of a casting-rolling compound plant designed according to the invention,
• figure 2 a detailed view of the last rolling stand of the finishing train with a lifting roller and several cleaning nozzles for spraying down the top of the run-out table,
• figure 3 a detailed representation of the last roll stand of the finishing train with several cleaning nozzles for spraying down the upper side of the run-out table,
• figure 4 shows a top view of the roll stand and the run-out table of the last roll stand of the finishing train with the cleaning nozzles figure 3 ,
• Figure 5a a front view with a cleaning nozzle for hosing down the top of the outfeed table,
• Figure 5b a side view of the cleaning nozzles Figure 5a ,
• figure 6 a detailed view of the last stand of the finishing train with a lifting roller for lifting the hot strip so that the bottom of the hot strip does not touch the run-out table, and
• figure 7 a photo of a surface defect on the underside of a hot strip scratched by scale after finish rolling.

Description of the embodiments

The figure 1 shows a schematic of a combined casting and rolling plant for the production of thin hot-rolled steel strip. Liquid steel is cast in the mold 2 of the continuous casting machine 1 to form a strand with a slab or thin slab cross section and is continuously drawn out of the mold 2 . The strand is supported in the curved strand guide 3, guided and further cooled and then bent back into the horizontal. The solidified strand is then pre-rolled in the roughing train 4 to form a pre-strip. Thereafter, the pre-strip is heated to rolling temperature by the furnace 5, preferably an induction furnace with several induction modules, and is descaled by a descaler 6 before it enters the finishing train 7. In the finishing train 7, the pre-strip is finish-rolled into the hot strip (also known as the finished strip). Typically, the finished strip has a thickness between 0.6 and 3.6 mm. After finish rolling, the hot strip 11 is cooled down to the coiling temperature in the cooling section 8 by a number of cooling units. Shortly before coiling, the cooled hot strip 11 is divided transversely by shears 9 to coil lengths and coiled by several coilers or coilers 10 or alternatively by a rotating carousel coiler. In particular in the production of thin or very thin hot strip, it is advantageous to operate the combined casting and rolling plant in continuous operation.

According to the invention, after the last roll stand 7e of the finishing train 7, there is a lifting roller 18 for lifting the finished strip above the pass line P and/or at least one cleaning nozzle 17 for cleaning the upper side of the run-out table 15 with a liquid medium (e.g. cooling water) or rinsing with a gaseous medium (e.g. air) present so that scale and/or rolling dust are removed from the run-out table 15.

In the former case, the finish-rolled hot strip 11 is lifted above the pass line P by the lifting roller 18, which is arranged in the width direction of the hot strip 11, so that contact between the underside of the hot strip 11 and the run-out table 15 is avoided in any case.

In the second-mentioned case, at least the outfeed table 15, and according to a variant for very thin strip also the infeed table 24, of at least the last roll stand 7e of the finishing train 7 is freed from scale and/or rolling dust by at least one cleaning nozzle 17, so that no contamination accumulates on the upper side of the Outlet table 15 can accumulate, which could scratch the underside of the hot strip 11.

According to a preferred embodiment, both cases mentioned are combined, ie a lifting roller 18 and at least one cleaning nozzle 17 are present after the last roll stand 7e. This case is in figure 2 shown.

The Figures 3 and 4 show the case in which three cleaning nozzles 17 are arranged on the outfeed table 15, one on the drive side A and two on the operator side B of the roll stand 7e. The cleaning nozzles 17 each have an offset x in the transport direction T. In addition to the cleaning nozzles 17 on the outfeed table 15, three further cleaning nozzles 17 are arranged on the infeed table 24. These cleaning nozzles 17 also serve to clean the upper side of the run-in table from scale, rolling dust, etc. by spraying or rinsing.

The Figures 5a and 5b show a front view and a side view of a cleaning nozzle 17 which is arranged on the upper side of the outlet table 15. The cleaning nozzle 17 is a flat jet nozzle, with the spray jet being wider than it is high. Specifically, the outlet opening of the cleaning nozzle 17 has a width b that is at least 3 times as wide as the height h of the outlet opening. This forms a flat full jet. In addition, the cleaning nozzle 17 is inclined to the horizontal at the angle α, so that the top of the run-out table 15 is sprayed without cooling the underside of the hot strip, not shown.

The figure 6 shows the last rolling stand 7e of the finishing train 7 with a lifting roller 18 for lifting the finished hot strip 11 above the pass line P. Specifically, the rotatable, horizontally arranged lifting roller 18 is raised by a linear drive 23, so that the hot strip 11 is above the pass line P of the rolling stand 7e lies. This ensures that there is no contact between the underside of the hot strip 11 and the run-out table 15 . The hot strip 11 can be lifted in a position-controlled and/or force-controlled manner. An actual distance x in the vertical direction between the upper side of the run-out table 15 and the lower side of the hot strip 11 is set by the position control. The force control prevents the typically thin or very thin hot strip 11 from being overstretched. Both regulations are preferably superimposed on one another, so that both the position of the lifting roller 18 and the elongation of the hot strip 11 are adjusted in a controlled manner.

The photo in figure 7 shows a surface defect on the underside of a thin hot strip 11 which has been scratched by scale Z after finish rolling. These surface defects are avoided by the invention, which increases the quality and the yield of the hot strip.

Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Reference List

1

continuous casting machine

2

mold

3

strand guide

4

roughing mill

5

Oven

6

descaler

7

finishing train

7a... 7e

mill stand

8th

cooling line

9

Scissors

10

reel or winding device

11

hot strip

12

stripper

13

backup roll

14

cooling nozzle

15

outlet table

16

scraper

17

cleaning nozzle

18

lifting roller

19

Cooling unit of the cooling line

20

powertrain

22

thickness measurement

23

lifting device

24

infeed table

A

drive side

a

Angle of inclination of the cleaning nozzle to the horizontal

B

operating side

b

width of the outlet opening

H

height of the outlet opening

P

pass line

T

transport direction

x

offset

Z

Tinder

Claims (15)

finishing train (7) for finish rolling hot strip (11), preferably made of steel, wherein the finishing train (7) has a plurality of roll stands (7a...7e), wherein the roll stands (7a...7e) each have a lower and an upper work roll (12) and the work rolls (12) each form a roll gap, so that the hot strip (11) during finish rolling passes through the roll gaps in the transport direction (T) and is finish-rolled becomes, wherein during the finish rolling at least one outlet-side area of the lateral surface of the lower work roll (12) of the last rolling stand (7e) in the transport direction (T) is cooled by a plurality of cooling nozzles (14) arranged below a pass line (P), and the cooling nozzles (14) spray a liquid cooling medium onto the lateral surface, wherein the cooling medium is kept away from the hot strip (11) by at least one scraper (16) which is arranged in the vertical direction between the cooling nozzles (14) and the hot strip (11), wherein the scraper (16) is attached to an outfeed table (15), at least one cleaning nozzle (17) being provided for cleaning the upper side of the run-out table (15), so that scale (Z) and/or rolling dust are removed. Finishing rolling train according to Claim 1, characterized in that at least one first cleaning nozzle (17) is arranged on the drive side (A) of the rolling stand (7e) and at least one second cleaning nozzle (17) is arranged on the operating side (B) of the rolling stand (7e). Finishing train according to Claim 2, characterized in that the cleaning nozzle (17) on the drive side (A) is offset (x) in the transport direction from the cleaning nozzle (17) on the operator side (B). Finishing rolling train according to one of Claims 1 to 3, characterized in that in the transport direction (T) between the work rolls (12) of the last roll stand (7e) and a cooling section (8) for cooling the finish-rolled hot strip (11) at least one lifting roller (18) , which is arranged in the width direction of the hot strip (11), and the lift roller (18) lifts the hot strip (11) in the vertical direction above the pass line (P) during finish rolling so that the bottom of the hot strip (11) faces the outfeed table (15) is not touched. Finishing rolling train according to one of the preceding claims, characterized in that a pipe or hose line fluidically connects a cooling nozzle (14) to a cleaning nozzle (17). finishing train (7) for finish rolling hot strip (11), preferably made of steel, wherein the finishing train (7) has a plurality of roll stands (7a...7e), wherein the roll stands (7a...7e) each have a lower and an upper work roll (12) and the work rolls (12) each form a roll gap, so that the hot strip (11) during finish rolling passes through the roll gaps in the transport direction (T) and is finish-rolled becomes, wherein during the finish rolling at least one outlet-side area of the lateral surface of the lower work roll (12) of the last rolling stand (7e) in the transport direction (T) is cooled by a plurality of cooling nozzles (14) arranged below a pass line (P), and the cooling nozzles (14) spray a liquid cooling medium onto the lateral surface, wherein the cooling medium is kept away from the hot strip (11) by at least one scraper (16) which is arranged in the vertical direction between the cooling nozzles (14) and the hot strip (11), wherein the scraper (16) is attached to an outfeed table (15), at least one lifting roller (18), which is arranged in the width direction of the hot strip (11), being arranged in the transport direction (T) between the last rolling stand (7e) and a cooling section (8) for cooling the finish-rolled hot strip (11), and the lifting roller (18) can lift the hot strip (11) in the vertical direction above the pass line (P) during finish rolling so that the underside of the hot strip (11) does not touch the run-out table (15). Finishing rolling train according to one of the preceding claims, characterized in that a first, preferably optical, surface inspection unit for inspecting an upper side of the hot strip (11) is arranged between the lifting roller (18) and a first cooling unit (19) of the cooling section (8). Finishing train according to Claim 7, characterized in that a pyrometer and a first blow-off device for blowing off the upper side of the hot strip (11) are arranged between the last roll stand (7e) and the first surface inspection unit. Finishing rolling train according to one of the preceding claims, characterized in that between a last cooling unit (19) of the cooling section (8) and a pair of shears (9) a second, preferably optical, surface inspection unit is arranged for inspecting the underside of the hot strip (11). Finishing rolling train according to Claim 9, characterized in that a pyrometer and a second blow-off device for blowing off the upper side of the hot strip (11) are arranged between the second surface inspection unit and the shears (9). Finishing rolling train according to Claim 10, characterized in that between the second blow-off device and the shears (9) there is a driver roller unit with at least one drivable driving roller which can be placed against the hot strip. Finishing rolling train according to one of Claims 9 to 11, characterized in that a controller is connected to a drive for raising the lifting roller (18) and the second surface inspection unit for inspecting the underside of the hot strip (11), the controller further moving the lifting roller (18). increases as soon as the second surface inspection unit detects surface defects on the underside of the hot strip. Casting-rolling compound plant, comprehensive a continuous casting installation (1) for continuously casting a strand, optionally a pre-rolling train (4) for pre-rolling the strand to form an intermediate strip, optionally a furnace (5), preferably an induction furnace, for heating the intermediate strip to rolling temperature, and the finishing train (7) according to any one of the preceding claims. Casting-rolling compound installation according to Claim 13, characterized in that a tunnel furnace for heating through and/or maintaining the temperature of the strand is arranged in front of the roughing train (4). Casting-rolling compound installation according to Claim 13 or 14, characterized in that the roughing train (4) has three roll stands and the finishing train (7) has five roll stands.

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