JP2010179322A - Slip prevention method in rough rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slip prevention method in a rough rolling capable of surely preventing slip between a rough rolling mill and a material to be rolled when rough-rolling a heated slab (the material to be rolled). <P>SOLUTION: Residual descaling water on a surface of a rough bar 7 is removed by air-spraying the surface of the rough bar 7 with air spray nozzles 6 immediately before the rough bar 7 is bitten in a rough rolling machine 1, and then the rough bar 7 is bitten in the rough rolling mill 1, so that reduction of a friction coefficient between the work rolls 3 of the rough rolling mill and the rough bar 7 is suppressed and the generation of the slip in the rough rolling is surely prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for hot rolling a steel sheet, and more particularly to a technique for preventing slip that occurs when a heated slab is roughly rolled.

  In a thin steel sheet hot rolling line, slabs are extracted one by one from a heating furnace, rolled to a predetermined thickness by a rough rolling mill (rough rolling mill train), and further, a plurality of finish rolling mills arranged continuously ( Are sequentially rolled by a finishing rolling mill train) and then wound by a winder to form a hot coil. In the rough rolling mill, in order to supply the sheet bar to the finishing mill, the thickness is reduced by rolling in 4 to 9 passes from the slab thickness (about 200 to 300 mm) to the sheet bar thickness (about 20 to 60 mm).

  Here, the steel material (rolled material) before rolling is called a slab, and the steel material (rolled material) that has passed through the roughing mill is called a sheet bar. In addition, a steel material (rolled material) in the rough rolling process is generally called a rough bar, but basically only the plate thickness is different.

  From the heated slab, the primary scale generated during heating is removed by a scale breaker before the rough rolling process. Thereafter, the secondary scale generated during the rolling (the scale generated during the hot rolling after passing through the heating-descaling) is a high-pressure (15-30 MPa) water (15-30 MPa) by a descaling device installed in front of the rolling mill. The descaling water is sprayed away. Descaling at the entry side of the roughing mill is performed to improve the surface quality. If descaling is insufficient, problems such as bite scale wrinkles and heges occur. It is a facility.

  As is well-known, the rough rolling machine row | line | column in the hot rolling line of a thin steel plate is normally equipped with the rough rolling mill of 3-6. The rough rolling mill at the first stage of the rough rolling mill row is generally called R1, and the subsequent rough rolling mills are sequentially called R2, R3. Depending on the production amount and the hardness (deformation resistance) of the material to be rolled, reverse rolling or rolling in one direction may be performed. R1 rough rolling mills are often two-stage rolling mills (2Hi rolling mills) composed of upper and lower work rolls. However, as they become downstream stands, four-stage equipped with backup rolls that reduce the deflection of the work rolls. It is often a rolling mill (4Hi rolling mill).

In the rough rolling mill, as the rolling proceeds, a black skin is generally generated on the surface of the work roll. The composition of the black skin is known to be Fe ₃ O ₄ (magnetite), and since the hardness at high temperature is high, there is an effect of reducing roll wear and protecting the roll surface.

  However, the black skin on the surface of the work roll has the effect of protecting the roll surface as described above. However, when the thickness is 10 μm or more, the roughness of the roll surface is reduced, and the friction coefficient between the work roll and the material to be rolled is reduced. Therefore, a slip phenomenon in which the material to be rolled does not progress during rolling may occur. In the case of a slight slip, the work roll speed becomes higher than the material to be rolled during rolling after biting, and the rolling proceeds while the slip mark is generated on the surface of the material to be rolled. The rolled material may not proceed and rolling may be stopped. In the case of a severe slip, the material to be rolled does not get caught in the work roll, and rolling may be stopped.

  As described above, when a slip phenomenon occurs in the rough rolling mill, rolling becomes impossible, so that the material to be rolled is scrap-processed, and the rolling efficiency is inevitably lowered.

  As an anti-slip method for solving such a problem, Patent Document 1 discloses that a speed of a material to be rolled is measured using a plate speedometer installed on the outlet side of a roughing mill, and this and a rolling mill. The advanced rate is calculated continuously from the roll peripheral speed of the roll, and the actual measured advanced rate is compared with the standard advanced rate in the stable rolling state. If this continues, a method of reducing the rolling reduction has been proposed. According to this method, it is described that even if the slip danger zone is reached, the operation can be performed without significantly reducing the rolling speed, and the productivity and the stable operation are possible.

  Moreover, in patent document 2, in the rolling of a wire, by adjusting the pressure of descaling water after heating, a secondary scale (scale generated during hot rolling after heating-descaling) is generated. It is described to prevent slipping during rolling. This technique is a technique related to hot rolling of free-cutting steel wire containing a large amount of special S and Pb among wires.

Japanese Patent Application Laid-Open No. 07-051716 JP 60-061114

  However, the technique described in Patent Document 1 has the following problems. When the rolling processing amount per roll in rough rolling exceeds 20,000 tons, the black surface of the work roll surface is formed to about 10 μm, so the roughness of the work roll is reduced and the material between the rolled material and the work roll is reduced. The friction coefficient is reduced, and slip is likely to occur. This is because the initial roughness at the time of polishing the work roll is lowered, and a black skin is generated so as to fill the ground. Therefore, if the rolling reduction in rough rolling is reduced for the purpose of preventing slip, a new problem arises that the thickness of the sheet bar increases and slip occurs at the F1 stand of the finishing mill. Moreover, when the rolling reduction in rough rolling is reduced, deformation on the surface of the material to be rolled occurs preferentially, and warping may occur.

  In addition, when the technical idea described in Patent Document 2 is applied to slip prevention, slip in rough rolling cannot be prevented even if the secondary scale thickness after descaling can be controlled. Descaling in rough rolling is performed before rolling, and immediately after descaling, the front and back surfaces of the material to be rolled are reheated, so that a secondary scale is generated on the surface. Since this secondary scale is FeO (wustite) and has an effect of reducing the coefficient of friction in the roll bite, slip cannot be prevented.

  This invention is made | formed in view of the above situations, and when carrying out rough rolling of the heated slab (rolled material), the slip between a rough rolling mill and a rolled material is prevented appropriately. An object of the present invention is to provide a slip prevention method in rough rolling.

  In order to solve the above problems, the present inventors have intensively studied and found that descaling water is greatly involved in the occurrence of slip in rough rolling. That is, as described above, in rough rolling, there is a descaling device on the inlet side of the roughing mill in order to improve the surface quality of the rough bar. The descaling nozzle is normally installed so as to spray in the direction opposite to the line traveling direction, and descaling water is not introduced into the roll bite. However, depending on the surface condition of the coarse bar, it has been found that descaling water remains on the surface of the coarse bar and is introduced into the roll bite. This residual descaling water (residual descaling water) becomes a lubricant, It was found that the coefficient of friction between the roughing mill and the rough bar was reduced.

  By the way, the reason why descaling water remains on the surface of the coarse bar after descaling is that the scale does not peel completely during descaling, and the rough bar surface after descaling is uneven. It is thought that descaling water remains in the part. In the recess, the interface between the residual descaling water and the coarse bar is in a film boiling state, and it is estimated that the descaling water can easily remain even after descaling.

  Therefore, the present inventors removed the residual descaling water on the surface of the coarse bar by air spraying (air purge) the surface of the coarse bar immediately before the coarse bar bites into the rough rolling mill, If the rough bar is bitten into the roughing mill, the reduction of the friction coefficient between the roughing mill and the rough bar is suppressed, leading to the idea that the occurrence of slip in the rough rolling can be prevented accurately. .

  The present invention has the following features based on the above-described concept.

  [1] When a heated slab is rolled into a sheet bar by a roughing mill, after the material to be rolled is descaled before rolling, immediately before the material to be rolled bites into the roughing mill, An anti-slip method in rough rolling, wherein the surface is air-sprayed.

  [2] The air pressure in the nozzle of the air spray is 0.3 MPa or more and 1 MPa or less, and the air flow rate colliding with the material to be rolled is 100 L / nozzle / min or more and 330 L / nozzle / min or less. The slip prevention method in rough rolling according to the above [1].

  According to the present invention, slip generated in a rough rolling mill can be accurately prevented, stable rolling can be achieved, and dramatic productivity improvement can be achieved.

It is a figure which shows one Embodiment of this invention. It is a figure which shows the hot rolling line to which one Embodiment of this invention is applied. It is a figure which shows the experimental method and experimental result regarding the slip prevention mechanism in one Embodiment of this invention.

  As described above, the present invention removes residual descaling water on the surface of the coarse bar by air spraying the surface of the coarse bar immediately before the coarse bar bites into the coarse rolling mill, and then removes the coarse bar. It is based on the idea that the reduction of the friction coefficient between the rough rolling mill and the rough bar is suppressed by biting into the rough rolling mill, and the occurrence of slip in the rough rolling can be accurately prevented.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 1 (a) shows a side situation of an arbitrary rough rolling mill 1, and FIG. 1 (b) schematically shows an entrance situation of the rough rolling mill 1. Indicate.

  As shown in FIG. 1, the roughing mill 1 includes a backup roll 2 (upper backup roll 2a, lower backup roll 2b), a work roll 3 (upper work roll 3a, lower work roll 3b), and a work roll cooling nozzle 4. (Upper work roll cooling nozzle 4a, lower work roll cooling nozzle 4b), work roll exit side / entrance side warper 5 (upper work roll exit side / ingress side warper 5a, lower work roll exit side / ingress side warper 5b), It has. The roll group of the roughing mill 1 is not shown, but is fixed by a chock and inserted into a housing post, and a spindle, a speed reducer, a motor, and the like are connected. Furthermore, a descaling nozzle 8 (upper descaling nozzle 8a, lower side) that removes secondary scale on the surface of the coarse bar 7 by spraying high-pressure (15 MPa to 30 MPa) descaling water on the entry side of the roughing mill 1 A descaling nozzle 8b) is arranged.

  In addition, in this embodiment, on the entry side of the rough rolling mill 1, the surface of the rough bar 7 is air sprayed to remove residual descaling water on the surface of the rough bar 7 (upper surface). An air spray nozzle 6a and a lower air spray nozzle 6b) are installed.

  Here, it is important for the air spray nozzle 6 installed on the entry side of the rough rolling mill 1 to spray at least the surface of the rough bar 7 on the opposite side to the rolling direction starting from the upper and lower points of the roll bite entry point. is there. When moving away from the roll bite entry point, roll transfer water, leakage water and residual descaling water may be introduced into the roll bite.

    The nozzle type of the air spray nozzle 6 is preferably a flat spray nozzle. If it is a flat spray nozzle, the number of nozzles can be reduced by the spread of air, and the residual descaling water on the surface of the coarse bar 7 can be efficiently removed.

  Moreover, it is suitable that the air pressure in the nozzle of the air spray nozzle 6 is 0.3 MPa or more. If it is less than 0.3 MPa, the residual descaling water between the scales on the surface of the coarse bar 7 cannot be sufficiently removed. Moreover, when the air pressure in the nozzle of the air spray nozzle 6 exceeds 1 MPa, residual descaling water or the like may fly on the surface of the coarse bar 7 due to the air pressure and be introduced into the roll bite. Therefore, it is necessary to appropriately control the air pressure in the nozzle of the air spray nozzle 6.

    If the nozzle type is determined, the air flow rate is also determined, but the air flow rate is preferably a relatively large capacity. In order to sufficiently remove residual descaling water remaining on the surface of the coarse bar 7, the air flow rate is preferably 100 L / nozzle / min or more. Air interference and scattering of residual descaling water become significant, and residual descaling water on the surface of the coarse bar 7 cannot be removed sufficiently.

  Next, an example of the hot rolling line to which this embodiment is applied is shown in FIG.

  As shown in FIG. 2, the hot rolling line 100 includes a rough rolling mill group 101 (R1 to R3) and a finishing rolling mill group 102 (F1 to F7), which are not shown, A heating furnace that heats the slab to a predetermined temperature, a width press device that performs width sizing, a descaling device that removes the scale of the slab surface extracted from the heating furnace, and a cutting that cuts the trailing edge crop of the sheet bar A run-out table, a winder, and the like installed on the finishing roll group side are installed, and thereby a hot coil (hot rolled steel strip) is manufactured from the slab.

  And when applying this embodiment to the hot rolling line 100, the rough rolling mill 1 shown in FIG. 1 is used for the rough rolling mill in which the generation of slip is concerned in the rough rolling mill group 101 (R1 to R3). Is used.

  Next, in this embodiment, a mechanism (slip prevention mechanism) that prevents slip in rough rolling will be described.

  As shown in FIG. 1, the descaling nozzle 8 is installed so as to spray in the direction opposite to the line traveling direction, and descaling water is not introduced into the roll bite of the rough rolling mill 1. . However, depending on the surface state of the rough bar 7, it has been found that descaling water remains on the surface of the rough bar 7 and is introduced into the roll bite. The friction coefficient between the work roll 3 and the rough bar 7 is reduced.

  Therefore, immediately before the coarse bar 7 bites into the rough rolling mill 1, the surface of the coarse bar 7 is air sprayed by the air spray nozzle 6 to remove residual descaling water and the like on the surface of the coarse bar 7, If the rough bar 7 is engaged with the rough rolling mill 1, the reduction of the friction coefficient between the rough rolling mill and the rough bar is suppressed, and the occurrence of slip in the rough rolling can be prevented accurately.

  In order to confirm the above-described anti-slip mechanism (inhibiting the reduction of the friction coefficient by air spraying the surface of the coarse bar 7), the following laboratory experiment was conducted.

  FIG. 3 (a) schematically shows a laboratory experiment method. The descaling nozzles 8a and 8b and the air spray nozzles 6a and 6b are installed on the roll bite entrance side of the laboratory rolling mill, and the surface of the heated material 7 to be rolled is descaled by the descaling nozzles 8a and 8b. The surface of No. 7 was air sprayed by air spray nozzles 6a and 6b and then rolled. At that time, the rolling load was measured, and the coefficient of friction was calculated backward from Orowan's rolling load formula (for example, rolling theory and practice edited by the Iron and Steel Institute).

  The experimental conditions are as follows.

Rolled material: low carbon steel plate, plate thickness 20mm, plate width 300mm
Heating temperature: 1000 ° C
Laboratory rolling mill: roll diameter 300 mm, roll barrel length 400 mm, roll speed 50 m / min reduction ratio: 30%
Descaling nozzle: Water pressure 15 MPa, Water volume 300 L / min Air spray nozzle: Flat nozzle, spray width 300 mm
Air pressure 0.05MPa ~ 1.6MPa

  The laboratory experiment results are shown in FIG. When the pressure of the air spray nozzle 8 (air nozzle pressure) is 0.3 MPa or more and 1 MPa or less, the friction coefficient is 0.25 or more. The air flow rate was 100 L / min when the air nozzle pressure was 0.3 MPa, and 330 L / min when the air nozzle pressure was 1 MPa. Under the condition that the air nozzle pressure is less than 0.3 MPa, the residual descaling water on the surface of the material 7 to be rolled cannot be sufficiently removed, and the friction coefficient during rolling is lowered. On the other hand, when the air nozzle pressure exceeds 1.0 MPa, the residual descaling water is splattered in the air spray, and the residual descaling water is entrained in the roll bite, and the friction coefficient decreases.

  In this way, the residual descaling water on the surface of the material 7 to be rolled is sufficiently removed under a suitable condition of air spray, resulting in a dry friction state, and the friction coefficient is increased. For comparison, the coefficient of friction when rolling was performed with descaling turned off was 0.31.

  From the above results, it was possible to confirm the slip prevention mechanism in this embodiment (which suppresses the reduction of the friction coefficient by air spraying the surface of the material to be rolled).

  The effect of the present invention was confirmed by applying the present invention to a hot-rolled steel sheet production line.

  The hot rolling line to which the present invention is applied is the hot rolling line 100 shown in FIG. 2, and rolling was performed under the following conditions.

(Rough rolling conditions)
Rough rolling mill row: R1 to R3 (R1 is a 2Hi rolling mill, R2 and R3 are 4Hi rolling mills)
R3 rough rolling mill: roll diameter 1000mm, barrel length 2100mm
Slab: Low carbon steel (C: 0.02-0.05wt%)
260mm thick, 1040-1300mm wide, 5-11m long,
Weight 13-30 tons Heating temperature: 1100-1200 ° C (heating time 2-4 hours)
R1 pass condition: 3 pass reverse rolling R2 pass condition: 3 pass reverse rolling R3 pass condition: 1 pass unidirectional rolling Total number of rough rolling passes: 7 passes R3 entry rough bar thickness: 40-80 mm
R3 outlet coarse bar thickness: 30-40mm
R3 rolling reduction: 20 to 50% / 1 pass Descaling device: R1 to R3 entry side water pressure 15 to 30 MPa
(Finish rolling conditions)
Finishing mill line: F1-F7 stand (4Hi rolling mill)
F1-F4 stand: Work roll diameter 800mm
F5-F7 stand: Work roll diameter 680mm
Finish thickness: 1.2-5mm

  Since the slip phenomenon occurs almost in the R3 rough rolling mill, the following examples of the present invention, comparative examples, and conventional examples were compared for the R3 rough rolling mill.

  At that time, slip is likely to occur at a rolling processing amount of about 20,000 tons or more where roll black skin is generated and roll wear has progressed, so the processing amount of the R3 rough rolling mill is 20,000 tons (about 600 slabs). ) And the occurrence of slip was evaluated up to 30,000 tons. Further, as described above, if the rolling reduction in rough rolling is reduced in order to reduce the slip, warping and slipping at the F1 stand may occur. Therefore, the occurrence of warpage and slip generation at the F1 stand is also evaluated. did.

That is,
(1) Slip occurrence rate in the rough rolling mill R3 (R3 slip occurrence rate)
(2) Warpage occurrence rate on the exit side of the rough rolling mill R3 (R3 warpage occurrence rate)
(3) Slip occurrence rate in finish rolling mill F1 (F1 slip occurrence rate)
Evaluation was carried out.

  Here, the R3 slip occurrence rate of (1) includes a slight slip, and the case where the progress of the coarse bar is delayed during rolling is also counted. Further, the R3 warpage occurrence rate in (2) is the case where finish rolling is disabled due to the occurrence of warpage in the roughing mill R3.

  Before rolling with the R3 rough rolling mill, the secondary scale of the coarse bar was removed by descaling with a water pressure of 15 MPa.

(Example of the present invention)
In the present invention example, one embodiment of the present invention shown in FIG. 1 was applied to an R3 rough rolling mill. The width of the air spray nozzle (flat nozzle) was 300 mm, and the distance between the coarse bar and the air spray nozzle was fixed at 300 mm. Eight air spray nozzles and eight lower nozzles were installed. With the start of descaling, air spray was applied to the surface of the coarse bar at a predetermined air pressure (0.08 MPa to 0.9 MPa). In addition, the air spray was stopped in synchronization with the descaling stop state.

(Comparative example)
In the comparative example, normal rough rolling was performed without air spraying.

(Conventional example 1)
In Conventional Example 1, based on the technical idea of Patent Document 2, the descaling water pressure on the R3 roughing mill entry side was increased from 15 MPa to 30 MPa to increase the removal amount of the secondary scale.

(Conventional example 2)
In Conventional Example 2, the method described in Patent Document 1 was applied to an R3 rough rolling mill. That is, a plate speedometer was installed on the exit side of the R3 roughing mill, the advanced rate fs was obtained, and the roll speed and the reduction rate were controlled so that slip did not occur.

  Table 1 shows the results of comparing the air pressure, the R3 slip occurrence rate, the R3 warpage occurrence rate, and the F1 slip occurrence rate for the above-described inventive examples, comparative examples, and conventional examples.

  First, in the inventive examples (Inventive Examples 1 to 5), the R3 slip occurrence rate was reduced, and the warpage in the rough rolling mill R3 and the slip in the F1 finishing rolling mill could be prevented. In particular, the slip in the R3 roughing mill was completely prevented under the conditions of the preferred range of Invention Examples 3-5.

  On the other hand, in Conventional Example 1, the R3 slip occurrence rate was almost the same as that of the comparative example, and was not effective in preventing slip.

  Further, in the conventional example 2, since the reduction ratio in the R3 rough rolling mill is reduced, no uniform strain is added in the plate thickness direction of the rough bar, warping occurs, and the sheet bar cannot be provided to the finishing mill. A case has occurred. Furthermore, since the reduction ratio in the R3 rough rolling mill was reduced, the sheet bar thickness was increased, slip was generated in the F1 finish rolling mill, and the rolling efficiency was greatly reduced.

  From the above results, the effectiveness of the present invention was confirmed.

DESCRIPTION OF SYMBOLS 1 Rough rolling mill 2 Backup roll 2a Upper backup roll 2b Lower backup roll 3 Work roll 3a Upper work roll 3b Lower work roll 4 Roll cooling nozzle 4a Upper roll cooling nozzle 4b Lower roll cooling nozzle 5 Roll wiper 5a Upper roll wiper 5b Lower roll Wiper 6 Air spray nozzle 6a Upper air spray nozzle 6b Lower air spray nozzle 7 Coarse bar 8 Descaling nozzle 8a Upper descaling nozzle 8b Lower descaling nozzle 100 Hot rolling line 101 Coarse rolling mill row 102 Finish rolling mill row

Claims (2)

  When a heated slab is rolled into a sheet bar by a roughing mill, after the descaling of the material to be rolled is performed before rolling, the surface of the material to be rolled is aired immediately before the material to be rolled bites into the roughing mill. A slip prevention method in rough rolling, characterized by spraying.   The air pressure in the nozzle of the air spray is 0.3 MPa or more and 1 MPa or less, and the air flow rate colliding with the material to be rolled is 100 L / nozzle / min or more and 330 L / nozzle / min or less. The slip prevention method in rough rolling as described in 2.

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