JP6981435B2 - Hot-rolled steel sheet manufacturing equipment - Google Patents

Description

The present invention also relates manufacture set of hot-rolled steel sheet Bei.

Generally, when a hot-rolled steel sheet is manufactured, the surface of the steel sheet is descaled prior to rough rolling and finish rolling in order to prevent rolling defects due to scale. After removing the scale on the surface of the steel sheet in this way, the steel sheet is rolled.
However, scale is generated on the surface layer of the steel sheet from the completion of finish rolling to the winding. This scale is generally called a secondary scale. In some cases, the rolled steel sheet is processed into a final product with the secondary scale attached, but in many cases, the rolled steel sheet is pickled to remove the secondary scale and processed into a final product. do.

In the former case where the pickling treatment is not performed, scale peeling may occur when the steel sheet is processed, which may not only deteriorate the appearance of the product but also cause scale defects. Therefore, it is important to reduce the thickness of the secondary scale before processing. On the other hand, in the latter case where the pickling treatment is performed, the scale thickness can be reduced in the pickling step.

As a technique for manufacturing a thin scale steel sheet having a thin secondary scale, for example, there are methods described in Patent Document 1 and Patent Document 2. Patent Document 1 proposes a method of applying an antioxidant to the entire surface layer of a hot-rolled steel sheet between air-cooled zones from a finish rolling mill to a hot run spray. Further, in Patent Document 2, based on the winding temperature of 550 ° C., the front descaling device between the finish rolling machine and the cooling device and the rear descaling device immediately before the winding machine are used properly, and the winding temperature is used. It has been proposed to select a rear descaling device when the temperature is above 550 ° C.

Japanese Unexamined Patent Publication No. 59-42114 Japanese Patent No. 3607792

However, in the method of Patent Document 1, it is necessary to apply an antioxidant to the entire length of the coil. Furthermore, it is necessary to take environmental measures by applying an antioxidant in the rolling process. Therefore, the method of Patent Document 1 is expected to incur enormous costs. Further, in the method of Patent Document 1, it is necessary to treat the antioxidant in a process downstream of the rolling process before entering the conventional pickling process. That is, since it is necessary to add an extra process to the conventional process, this also leads to an increase in cost.

The method of Patent Document 2 is characterized in that a rear descaling device is used for a material having a take-up temperature of 550 ° C. or higher, and a front descaling device is used for a material having a take-up temperature of less than 550 ° C. In this method, two descaling devices are installed, which leads to an increase in the length of the runout table and an increase in installation cost. In addition, when the secondary scale is removed by the forward descaling device, the finish rolling temperature of the target material is high, and in the case of a material with a thick plate thickness after finish rolling, the cooling capacity due to descaling is insufficient, and the runout table. The surface layer reheats above, and the regeneration of the secondary scale begins before winding. Therefore, it is difficult to manufacture a thin scale steel sheet.

The present invention has been made focusing on the above points, and an object of the present invention is to make it possible to more effectively reduce the secondary scale of the surface of a hot-rolled steel sheet.

Here, the inventor diligently studied descaling by colliding high-pressure water with the hot-rolled steel sheet after finish rolling, and found that descaling was not always successful even if the collision pressure of the high-pressure water was simply increased. I found out that it wasn't. Further studies were conducted, and it was found that descaling can be performed more reliably by optimizing the injection conditions of high-pressure water from the collision pressure to the collision energy.

Then, in order to solve the problem, according to one aspect of the present invention, the hot-rolled steel sheet after finish rolling by a hot finish rolling machine is cooled in a cooling zone and then wound via a pinch roll for a winder. It is a descaling device that is installed in a manufacturing facility for hot-rolled steel sheets to be wound on a taker and descales the surface of the steel sheet. A jet nozzle for injecting high-pressure water toward the hot-rolled steel sheet is provided, and the high-pressure water jetted from the jet nozzle has an injection pressure of 250 kg / cm ² or more and less than 600 kg / cm ² in the injection direction. The pick-up angle is set in the range of 10 ° or more and 35 ° or less, and further, the injection is set under the condition satisfying the following equation (1).

V is expressed by the following equation (2) in consideration of the effect of bringing the injection position closer.

Here, Pe: collision energy (J / mm ² ), V: collision speed (m / s), Q: flow rate (m ³ / s), W: spray collision width (m), U: steel plate passing speed (m). / S), Po: Injection pressure (Pa), ρ: Fluid density (kg / m ³ ), λ: Pressure loss coefficient, K: Droplet deceleration constant, H: Nozzle height (m).

According to the aspect of the present invention, the secondary scale of the surface of the hot-rolled steel sheet can be reduced more effectively.

It is a figure which shows the example of the manufacturing equipment of the hot-rolled steel sheet which concerns on embodiment based on this invention. It is a figure which shows the structural example of the cooling apparatus which concerns on embodiment based on this invention.

Next, an embodiment of the present invention will be described with reference to the drawings.
(composition)
The hot-rolled steel sheet manufacturing equipment of the present embodiment includes, for example, the equipment as shown in FIG. The material from the heating device (not shown) is roughly rolled by a rough rolling mill (not shown) and then transferred to the hot finish rolling mill 1 for hot finish rolling. In FIG. 1, reference numeral 1a represents the final stand of the finishing rolling mill 1. The hot-rolled steel sheet 30 that has left the finish rolling mill is conveyed along the runout table 2 and wound up by the winder 4 via the pinch roll 3 for the winder.

A cooling zone Z is set on the exit side of the finish rolling mill 1. A second pinch roll 7 and an injection nozzle 5 of the descaling device are arranged between the cooling zone Z and the winder pinch roll 3 from the cooling zone Z side (upstream side). Reference numeral 9 indicates a finishing rolling mill output side thermometer, and reference numeral 10 indicates a prewinding machine thermometer.
In the second pinch roll 7, the distance L from the pinching position where the hot-rolled steel sheet 30 is sandwiched by the second pinch roll 7 to the pinching position where the hot-rolled steel sheet 30 is sandwiched by the winder pinch roll 3 is within 20 m. It is arranged so as to be. The distance L is preferably within 10 m. By providing the second pinch roll 7, both sides of the hot-rolled steel plate 30 traveling between the second pinch roll 7 and the winder pinch roll 3 are sandwiched in the traveling direction on the runout table 2. The fluttering of the hot-rolled steel sheet 30 traveling on the above is suppressed.

The lower limit of the distance L from the pinch roll 3 for the winder to the pinching position where the hot-rolled steel sheet 30 is sandwiched by the second pinch roll 7 is between the second pinch roll 7 and the pinch roll 3 for the winder. The injection nozzle 5 of the descaling device can be arranged, and the high-pressure water from the injection nozzle 5 is injected toward the hot-rolled steel sheet 30 located between the second pinch roll 7 and the winder pinch roll 3. If possible, there is no particular limitation.
The injection nozzle 5 of the descaling device is a device that injects high-pressure water toward the traveling hot-rolled steel sheet 30 from a position downstream of the cooling zone Z to the winder 4. The injection nozzle 5 is arranged on the upper side and the lower side of the hot-rolled steel plate 30. The injection nozzle 5 of the present embodiment is arranged so that high-pressure water can be injected toward the surface of the hot-rolled steel sheet 30 portion running between the second pinch roll 7 and the winder pinch roll 3.

Here, in the present embodiment, the basic idea is to set a descaling device in front of the winder 4 to reduce the scale of the hot-rolled steel sheet 30. Based on this, the high-pressure water ejected from the injection nozzle 5 is set to have an injection pressure of 250 kg / cm ² or more and less than 600 kg / cm ^2. Further, the angle of attack θ of the injection nozzle 5 with respect to the injection direction of the high-pressure water, that is, the traveling direction of the hot-rolled steel sheet 30, is set in the range of 10 ° or more and 35 ° or less.
Further, in the present embodiment, the high-pressure water jetted from the jet nozzle 5 is set to be jetted under the condition satisfying the following equation (1).

If the hot-rolled steel sheet 30 is thin, it has a large effect on the plate-passability and the winding temperature. From this point of view, the upper limit of the collision energy Pe is, for example, less than 3.0.
V is expressed by the following equation (2) in consideration of the effect of bringing the injection position closer.

Here, Pe: collision energy (J / mm ² ), V: collision speed (m / s), Q: flow rate (m ³ / s), W: spray collision width (m), U: hot-rolled steel plate passing speed. (M / s), Po: Injection pressure (Pa), ρ: Fluid density (kg / m ³ ), λ: Pressure loss coefficient, K: Droplet deceleration constant, H: Nozzle height (m). The outer peripheral contour of the area where the high-pressure water jetted from the nozzle collides with the surface of the hot-rolled steel sheet has an elliptical shape. The spray collision width W is represented by the long axis of the elliptical contour.

An example of the above parameters has the following values.
Q = 200m ³ / s, W = 0.07m, U ^{= 13m / s, Po = 3 × 10 6} Pa, ρ = ^{995kg / m 3} , λ = 0.75, K = 0.44, H = 0. 15m
Here, the reason why the injection pressure is set to 250 kg / cm ² or more and less than 600 kg / cm ² is that when the injection pressure is ^{less than 250 kg / cm 2} , the speed of the hot-rolled steel sheet 30 in front of the winder 4 is high, and the formula (1) is used. This is because the condition of can not be satisfied and the descaling ability is almost lost. Further, if the injection pressure is 600 kg / cm ² or more, the hot-rolled steel sheet 30 may flutter due to the injection pressure, and the running of the steel sheet may become unstable.

In the cooling zone Z, a cooling laminar 8 of a cooling device for cooling the hot-rolled steel sheet 30 rolled by the finish rolling mill 1 is arranged. The cooling device includes a cooling laminar 8 and a cooling control unit 20.
The cooling laminar 8 is a device that injects cooling water onto a portion of a hot-rolled steel sheet 30 running in a cooling zone Z in a runout table 2.
The cooling control unit 20 controls the amount of cooling water from the cooling laminar 8 described above. The cooling control unit 20 controls the amount of cooling water from the cooling laminar 8 to perform cooling control for cooling the hot-rolled steel sheet 30 hot-rolled by the finish rolling mill 1 to a target winding temperature. It is a device.

The cooling control calculates, for example, the temperature transition of the sampling point on the runout table 2 whose temperature is measured by the finish rolling mill output side thermometer 9, and tracks the position of the above sampling point, and this position and the temperature state. Based on the quantity, the take-up temperature of the sampling point is predicted for each sampling cycle, and based on this predicted value and the measured value by the thermometer 10 before the take-up machine (actual temperature before the take-up machine), the cooling laminar 8 is used. Controls the opening and closing (cooling water amount) of the valve of each nozzle.
However, in the present embodiment, after the cooling control by the cooling device, high pressure water is injected from the injection nozzle 5 of the descaling device onto the hot-rolled steel sheet 30, so that the hot-rolled steel sheet 30 may be overcooled. Therefore, in the present embodiment, the amount of heat removed (temperature drop) from the hot-rolled steel sheet 30 due to the injection of high-pressure water from the injection nozzle 5 of the descaling device is predicted and calculated, and the cooling device is calculated by the predicted temperature drop. Correct the winding temperature, which is the target of. As a result, the winding temperature of the hot-rolled steel sheet 30 after passing through the descaling device is brought close to the target winding temperature.

For example, as shown in FIG. 2, the cooling control unit 20 includes a descaling temperature drop calculation unit 20A, a temperature drop calculation unit 20B, a temperature drop recalculation unit 20C, and a cooling water amount control unit 20D.
The descaling temperature drop calculation unit 20A predicts and calculates the temperature drop of the steel sheet due to descaling based on the amount of high-pressure water jetted from the injection nozzle 5, the water temperature, and the like. A third thermometer is installed between the cooling zone Z and the second pinch roll 7, and based on the temperature difference between the measured value by the third thermometer and the measured value by the prewinder thermometer 10. The temperature drop due to descaling may be predicted and calculated.

The temperature drop calculation unit 20B acquires the target take-up temperature from the upper computer 21, acquires the pre-cooling temperature measured by the finish rolling machine output side thermometer 9, and descaling the temperature drop calculation unit 20A. To get. The temperature drop calculation unit 20B calculates the required temperature drop in laminar cooling from the target winding temperature, the pre-cooling temperature, and the descaling temperature drop from the descaling temperature drop calculation unit 20A. For example, the required temperature drop is obtained from the target take-up temperature and the pre-cooling temperature, and the obtained required temperature drop is corrected to be smaller by the amount corresponding to the descaling temperature drop.
The temperature drop recalculation unit 20C corrects the required temperature drop amount obtained by the temperature drop calculation unit 20B by feedback control based on the actual temperature before the winder based on the measured value of the take-out side thermometer of the winder.

In the cooling water amount calculation unit, the temperature drop recalculation unit 20C feedforwards and controls the opening / closing (cooling water amount) of the valve of each nozzle of the cooling laminar 8 based on the corrected required temperature drop amount.
Here, in the above embodiment, an example in which the second pinch roll 7 is provided is described, but the second pinch roll 7 may not be provided. In this case, the injection nozzle 5 of the descaling device may be arranged at an arbitrary position downstream of the cooling zone Z and up to the winder 4, such as a position immediately after the cooling zone Z ends.
Further, in the present embodiment, the injection nozzle 5 of the descaling device is arranged immediately before the pinch roll 3 for the winder, but the injection nozzle 5 of the descaling device is immediately after the pinch roll 3 for the winder. It may be arranged.

(Operation and others)
In the present embodiment, the slab heated by the heating device (not shown) is roughly rolled by the rough rolling mill (not shown) and then hot-finished by the finish rolling mill 1. The hot-rolled hot-rolled steel sheet 30 is cooled by the cooling water from the cooling laminar 8 while traveling in the cooling zone Z on the runout table 2, and then the surface of the hot-rolled steel sheet 30 is descaled by a descaling device. Scaling is performed to reduce the scale of the surface of the hot-rolled steel sheet 30. After that, the hot-rolled steel sheet 30 is wound by the winder 4 to form a coil.

At this time, in this embodiment, the following configuration is adopted.
(1) The descaling device includes an injection nozzle 5 that injects high-pressure water toward the hot-rolled steel sheet 30 from a position downstream of the cooling zone Z to the winder 4. The high-pressure water ejected from the injection nozzle 5 has an injection pressure of 250 kg / cm ² or more and less than 600 kg / cm ² , and the angle of attack θ in the injection direction is set in the range of 10 ° or more and 35 ° or less. ) Adopt a configuration that injects under conditions that satisfy the energy formula.
According to this configuration, descaling can be reliably performed by descaling at a position close to the winder 4. Further, by setting the conditions of the high-pressure water injected from the injection nozzle 5 as described above, descaling can be performed more reliably and stably. For example, a thin-scale hot-rolled steel sheet 30 having a thickness of 2 μm or less can be obtained. It can be manufactured (see the examples below).

Here, it is known that the growth of the scale generally follows the parabolic law in the case of steel, and when the scale thickness is δ and the time is t, the following equation (3) is obtained.
δ ² = K × t ・ ・ ・ (3)
K is a reaction rate constant and is expressed by the following equation (4).
K = A ・ exp (−Q / (R × T)) ・ ・ ・ (4)
here,
A: constant, Q: activation energy, R: gas constant, T: absolute temperature.
That is, the scale continues to grow from after the finishing rolling mill 1 to the winding machine 4, but in the present embodiment, by descaling immediately before the winding machine 4, a thin-scale hot-rolled steel sheet of 2 μm or less is used. 30 can be manufactured more reliably.

(2) In the present embodiment, a second pinch roll 7 for sandwiching the traveling hot-rolled steel sheet 30 from the plate thickness direction is provided downstream of the cooling zone Z and upstream of the winder pinch roll 3. The injection nozzle 5 is arranged so that high-pressure water can be injected toward the hot-rolled steel sheet 30 located between the second pinch roll 7 and the winder pinch roll 3.
According to this configuration, high-pressure water can be made to collide with the surface of the hot-rolled steel sheet 30 in a state where the fluttering of the hot-rolled steel sheet 30 is suppressed, and descaling can be performed more stably and more reliably.
Further, even if the descaling is performed in the immediate vicinity of the winder 4, the fluttering of the hot-rolled steel sheet 30 due to the collision of high-pressure water is suppressed, and the coil failure due to the descaling in the immediate vicinity of the winder 4 can be prevented. It will be possible.

(3) In the present embodiment, the distance from the pinching position where the hot-rolled steel sheet 30 is sandwiched by the second pinch roll 7 to the pinching position where the hot-rolled steel sheet 30 is sandwiched by the winder pinch roll 3 is within 20 m. be.
According to this configuration, the fluttering of the hot-rolled steel sheet 30 can be reliably suppressed.

(4) In the present embodiment, the manufacturing facility for the hot-rolled steel sheet 30 is provided with a cooling device for cooling the hot-rolled hot-rolled steel sheet 30 to a target temperature while traveling in the cooling zone Z, and is a descaling device. The temperature drop due to scaling is estimated, and the temperature drop in the cooling device is increased by the estimated temperature drop.
According to this configuration, even if the cooling device is descaled on the downstream side, the winding temperature of the hot-rolled steel sheet 30 can be brought close to the target winding temperature.

Next, an example based on this embodiment will be described.
A thin-scale hot-rolled steel sheet 30 was manufactured using the equipment having the configuration shown in FIG. 1, which is the embodiment of the present invention described above.
Table 1 shows the results of the winding temperature, descaling conditions, and descaling effect of the hot-rolled steel sheet 30 in this embodiment. In Table 1, the unit of the injection pressure is [MPa].
The descaling effect was “◯” when the scale thickness was 2 μm or less, “×” when the scale thickness was 9 μm or more, and “Δ” when the scale thickness was thicker than 2 μm and less than 9 μm.

In Table 1, No. Reference numerals 1 to 3 represent conventional examples in which descaling before the winder 4 is not performed. No. 4 to 10 are examples based on the present invention. In addition, No. 11 to 15 perform descaling immediately before the winder 4, but this is a comparative example when the descaling condition is outside the present invention.
As can be seen from Table 1, the conventional example No. In Nos. 1 to 3, the scale thickness was 15 to 21 μm, whereas in Example No. 1 of the present invention. In Nos. 4 to 10, a uniform thin-scale hot-rolled steel sheet 30 having a scale thickness of 2 μm or less over the entire length was obtained.

Comparative Example No. In No. 11, the descaling capacity became insufficient due to the lack of collision energy due to the injection pressure being lowered to 15 MPa, the scale thickness became 10 μm, and the thin-scale hot-rolled steel sheet 30 could not be obtained.
In addition, Comparative Example No. In the cases 12 and 13, the angle of attack θ was set to 0 °, but the scale thickness could not be 2 μm or less even though the collision energy was sufficiently satisfied. It is considered that the reason for this is that the angle of attack θ was not set within the range of the present invention, so that the accumulated water after the injection hindered the collision of the droplets and could not provide sufficient collision energy to the scale. Moreover, Comparative Example No. In Nos. 12 and 13, the scale thickness of the entire length of the plate was not uniform, and the scale peeled off in a mottled pattern, which was an unfavorable appearance.

Comparative Example No. 14 and 15 show the case where the angle of attack θ is as large as 40 ° and 45 °. Although a certain effect was observed in thinning the scale, the scale thickness could not be reduced to 2 μm or less. In addition, by increasing the angle of attack θ, it is necessary to make the injection port closer to the steel sheet in order to obtain collision energy equivalent to θ = 0 °.
From the above, it can be seen that it is desirable that the angle of attack θ is 10 ° or more and 35 ° or less in order to easily satisfy the equation (1).

As described above, according to the present invention, the effect of descaling can be sufficiently exerted regardless of the winding temperature, and descaling is performed immediately before the winding machine suitable for manufacturing the thinnest scale hot-rolled steel sheet 30. Therefore, it has become possible to manufacture a thin-scale hot-rolled steel sheet 30 having a secondary scale of 2 μm or less regardless of the temperature on the finished side and the plate thickness.

1 Finishing Roller 2 Runout Table 3 Pinch Roll for Winding Machine 4 Winding Machine 5 Injection Nozzle 7 Second Pinch Roll 8 Cooling Laminator 9 Finishing Roller Outside Thermometer 10 Winding Machine Front Thermometer 20 Cooling Control Unit 20A Descaling temperature drop calculation section 20B Temperature drop calculation section 20C Temperature drop recalculation section 20D Cooling water amount control section 30 Hot-rolled steel plate

Claims (3)

A hot-rolled steel sheet manufacturing facility that cools hot-rolled steel sheets after finish rolling with a hot-finishing rolling mill in a cooling zone and then winds them up to a winder via a pinch roll for a winder.
A descaling device for descaling the surface of the steel sheet and a cooling device for lowering the temperature of the hot-rolled hot-rolled steel sheet to a target temperature while traveling in the cooling zone are provided.
The descaling device includes an injection nozzle located downstream of the cooling zone and injecting high-pressure water toward the hot-rolled steel sheet up to the winder.
A third thermometer is installed between the cooling zone and the descaling device.
The high-pressure water ejected from the injection nozzle has an injection pressure of 250 kg / cm ² or more and less than 600 kg / cm ² , and the angle of attack in the injection direction is set in the range of 15 ° or more and 35 ° or less. Set to inject under conditions that satisfy the equation,
The cooling device includes a cooling laminar that injects cooling water onto a hot-rolled steel plate portion traveling in the cooling zone, and a cooling control unit that controls the amount of cooling water from the cooling laminar.
The cooling control unit is
The temperature drop due to descaling of the descaling device is the temperature between the measured value by the third thermometer and the measured value by the thermometer provided between the pinch roll for the winder and the winder. Descaling temperature drop calculation unit that performs prediction calculation based on the difference,
From the preset target take-up temperature, the required temperature drop due to cooling by the cooling laminar is obtained, and the required temperature drop is predicted and calculated by the descaling temperature drop calculation unit. A temperature drop calculation unit that corrects the amount according to the amount
The temperature drop recalculation that corrects the required temperature drop amount obtained by the temperature drop calculation unit by feedback control based on the measured value by the thermometer provided between the pinch roll for the winder and the winder. Department and
A cooling water amount calculation unit for feedforward control of the cooling water amount of the cooling laminar based on the corrected required temperature drop amount is provided.
A hot-rolled steel sheet manufacturing facility characterized by this.

However,
V is expressed by the following equation (2) in consideration of the effect of bringing the injection position closer.

Further, Pe: collision energy (J / mm ² ), V: collision speed (m / s), Q: flow rate (m ³ / s), W: spray collision width (m), U: steel plate passing speed (m / s). s), Po: Injection pressure (Pa), ρ: Fluid density (kg / m ³ ), λ: Pressure loss coefficient, K: Droplet deceleration constant, H: Nozzle height (m). A second pinch roll that sandwiches the traveling hot-rolled steel sheet from the plate thickness direction is provided downstream of the cooling zone and upstream of the winder pinch roll.
The first aspect of the present invention is characterized in that the injection nozzle is arranged so as to be able to inject high-pressure water from the second pinch roll toward the hot-rolled steel sheet located between the pinch rolls for a winder. Hot-rolled steel sheet manufacturing equipment. 2. The listed hot-rolled steel sheet manufacturing equipment.

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