KR100990721B1 - Method for cooling a part of hot rolled steel strip by continuous hot rolling equipment - Google Patents

Abstract

The present invention is to install a cooling device between the coil box which is a facility for winding the rough rolled hot rolled material and the jointer for joining the rear end of the preceding material and the leading end of the trailing material, so that the trailing material end is cooled from the cooling device, as much as the rough rolling time. The amount of cooling is reduced by a constant control cycle to the point where it has passed to maintain a uniform temperature over the length of the continuous hot rolled material.

Continuous hot rolling, rough rolling, coil box, chiller, splicer, finishing rolling

Description

TECHNICAL FOR COOLING A PART OF HOT ROLLED STEEL STRIP BY CONTINUOUS HOT ROLLING EQUIPMENT

1 is a graph showing the difference in bonding strength between two rolled materials using a steel strain shear bonding method.

2 is a schematic apparatus installation diagram of a hot rolling process according to an embodiment of the present invention.

3 is a graph showing that the temperature of the hot rolled material after t seconds by air cooling was calculated by Equation (3).

4A is a graph showing the temperature variation in the longitudinal direction before and after the junction when the conventional trailing material tip is not cooled.

4B is a graph showing the temperature variation in the longitudinal direction before and after the joint when cooling the trailing material tip according to the embodiment of the present invention.

5 is a flowchart illustrating a method of controlling and cooling the trailing material tip according to an embodiment of the present invention.

The present invention relates to hot rolling of steel sheets. In more detail, it is related with the manufacturing process of the continuous hot rolling which joins the wire which is rolled between a rough rolling process and a finishing rolling process, and a steel plate after mutual rolling together, and continuously rolls.

In the production of steel sheet, when several steel sheets are joined and continuously rolled, the steel sheet can be rolled at high speed, thereby improving the quality of the produced steel sheet and greatly improving the productivity.

However, since the thickness of the rolled material is thin and the rolling strength of the steel sheet can be maintained by joining, unlike the cold rolling process in which continuous rolling is common, hot rolling has a thick thickness of the rolled material, and the pre-rolled and post-rolled material must be joined at high temperature of the steel. There are many problems with continuous rolling in a hot rolling process.

Recently, many studies have been made to enable continuous rolling in a hot rolling process.

In general, in the hot rolling process, continuous rolling is performed by roughly rolling the cooled slab in the rough rolling process, winding it into coils, and then storing several coils in a newly installed coil box between the rough rolling mill and the finishing mill. After judging the progress of the process, the rear end of the preceding material and the leading end of the standby coil are joined to each other with a prepared jointer, and the finishing material connected to the preceding material is continuously rolled, and then the joint of the hot rolled hot rolled material is cut and continuously hot rolled coil. To produce.

      An important technique of continuous rolling in such hot rolling is the technique of joining the preceding material and the waiting material that are moving in proportion to the rolling speed. As a technique for joining the moving preceding material and the stationary trailing material as described above, there are a joining method in which a joining machine is also joined at the same speed as the preceding material and a joining method is instantaneously joined using a fixed joining machine.

However, due to the temperature difference between the two rolling materials themselves, whether a mobile jointer or a fixed jointer is used, there are many problems in the joint strength and the rolling rate of the joint.

In other words, the coil is rolled as the coil is released in the wound state, so that the preceding material is released from the coil state and moves to the plate state, and is exposed to air while being rapidly cooled, while the trailing material is wound in the coil box while maintaining the temperature. You are in the atmosphere. Due to the characteristics of the hot rolling process, there are many temperature differences between the rear end of the preceding material which is relatively low temperature and the trailing end of the subsequent material which is relatively high temperature.

When the joints of two rolled materials having different temperatures are joined as described above, the joint strength is decreased due to the temperature difference, so that the joint may be broken in a subsequent rolling process under a constant tension, and the joint having different temperatures may have different deformation resistance due to rolling. Therefore, the mail passability in the subsequent rolling process becomes unstable.

Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to eliminate the temperature difference between the front end of the hot rolled material and the rear end of the preceding hot rolled material in a continuous hot rolling process, so as to achieve a uniform temperature. It is to provide a method for cooling a hot rolled material by continuous rolling that can join a side rolled material.                         

It is still another object of the present invention to provide a connection between a coil box for winding a roughly rolled coil and a jointer for joining a rolled material in order to eliminate the temperature difference between the leading end of the rolling material which is followed in the continuous hot rolling process and the rear end of the preceding rolling material. It is to provide a continuous hot rolling apparatus that can increase the rolling efficiency in the continuous hot rolling process by installing a cooling device.

In order to achieve the above object, the continuous hot rolling material cooling method according to the present invention comprises the steps of: roughly rolling the slab cooled in the roughing mill; Winding the rough rolled hot rolled material into a plurality of coils in a coil box and storing the coils and waiting for a subsequent process; Cooling the front end portion of the hot rolling material which is followed during the process of continuously unwinding and moving the coil in the cooling device installed between the coil box and the jointer using the rough rolling condition of the hot rolling material; A joining step of the line and the trailing hot rolled material for joining the cooled front end of the hot rolled material and the rear end of the preceding hot rolled material to each other by a jointer; And continuously finishing rolling the joined hot rolled material in the finishing mill.

In the present invention, the cooling step is the point where the end of the hot rolled material passing through the cooling device provided between the coil box and the junction, elapsed by the rough rolling time from the front end of the hot rolled material It is desirable to cool down while gradually decreasing the cooling amount.

In addition, the cooling step in the present invention, the step of obtaining the rough rolling plate time of the hot rolled material; Obtaining a first temperature control amount and a control frequency of the trailing hot rolling material tip using the rough rolling plate time; Obtaining a one-time temperature control amount using the first temperature control amount and the control frequency; And cooling the front end of the trailing hot rolling material by using the one-time temperature control amount. It is preferable that it consists of.

In addition, the cooling step in the present invention is preferably controlled by the following equation (1) to (7).

[Equation 1]

Bar length of hot rolled material = slab weight / (thickness of hot rolled material x width of hot rolled material x density of material)

[Equation 2]

Rough rolling time = Predicted length of hot rolled material / Rolling speed

&Quot; (3) "

Temperature after t seconds by air cooling = 100 {((Initial temperature +273) / 100) ^-3 + (6xσxεxt) / (100xcpxγxh)} ^-1/3 -273

{Wherein initial temperature; Temperature of the tip of the hot-rolled hot rolled material, σ; Stephen Boltzmann constant, ε; Emissivity of the material, t; Air cooling time (rough rolling time according to equation 2), cp; Specific heat of material, γ; Density, h; thickness of hot rolled material}

&Quot; (4) "                     

1st temperature control amount = initial temperature-temperature after t seconds by air cooling

[Equation 5]

Number of control (n) = Rough rolling plate time / Control cycle (one cycle time of cooling controller)

&Quot; (6) "

1st temperature control amount = 1st temperature control amount / control frequency (n)

[Equation 7]

Q ₁ = first temperature control amount

Q _(i) = Q _(i-1) -One-time temperature control amount {i = 2, n (control count)}

In the present invention, the bonding machine used in the bonding step is preferably selected from an induction cooling method, a laser method, or a steel deformation type shear bonding method.

The present invention also provides a hot rolling apparatus for continuous rolling, including a cooling apparatus for cooling under the control of a cooling controller to cool the front end portion of the hot rolling material which follows.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Before describing the embodiment of the present invention, an example in which the difference in the bonding strength of the other joints is measured with reference to FIG. 1 in the temperature difference between the trailing end of the preceding material and the leading end of the following material in the continuous hot rolling process.

The test results shown in FIG. 1 show differences in bonding strength between two rolled materials by using the steel deformation shear bonding method shown in Korean Patent Laid-Open Publication No. 2001-0062404. The method of joining the two rolled materials includes an induction cooling method and a method using a laser. However, in the present embodiment, since there is no heating source by the jointer itself when joining the two rolled materials, the change in the bonding strength according to the temperature difference between the joints is changed. The bond strength difference was measured by the temperature difference of the joint using a steel deformation type shear joint method that can be judged relatively accurately.

As shown in FIG. 1, it can be seen that the greater the temperature variation, the lower the bonding strength and the lower the bonding strength of both sides than the center of the rolled material.

Figure 2 is a schematic device installation diagram of a hot rolling process with a cooling device for cooling the junction in the embodiment of the present invention.

In the embodiment of the present invention, the joint cooling device 30 is installed between the coil box 10 and the jointer 20 of the continuous hot rolling process.

The coil box 10 is installed after the roughing mill 1 for rolling the slab, and wound and stored in the coil state of the hot rolling material 5 hot-rolled in the roughing mill 1 in a coil state. The coil stored in the first coil box 10 is released from the tip portion, passes through the cooling device 30 and the splicer 20, and is then rolled in the finishing mill 50 to produce a hot rolled coil having a desired thickness.

When the trailing hot rolled material 9 begins to pass through the cooling device 30, the front end of the trailing hot rolled material 9 begins to cool. The cooling of the hot rolled material 7 is performed while decreasing the amount of cooling at regular intervals from the front end portion where the trailing hot rolled material 9 begins to cool to the section where the trailing hot rolled material 9 proceeds by the rough rolling time.

Considering the amount of the hot rolled material (9) is air-cooled while passing through the hot rolling process, the subsequent hot rolled material (9) is gradually cooled from the beginning to a predetermined point to be followed by the preceding hot rolled material (7). The uniform temperature is maintained over the entire length of the hot rolled material 9 in the longitudinal direction.

As described above, in the state where the hot rolled material 9 maintains a uniform temperature in the longitudinal direction and when the end of the preceding material 7 reaches the jointer 20, the end of the preceding material 7 is the coil box 10. Unbonded by the front end of the trailing material (9) that is continuously moved to the preceding material (7) is joined by the jointer (20). At this time, the rear end of the preceding material 7 passing through the splicer 20 does not cool separately even though passing through the cooling device 30, but if the temperature of the rear end of the preceding material is higher than the front end of the cooled trailing material, the rear end of the preceding material, if necessary. It can also be cooled to the same temperature as the tip of the trailing material.

In the embodiment of the present invention, the cooling device 30 may use any of air, water, steam, or mist as the cooling source. The cooling source is sprayed by the nozzle to cool the leading end of the trailing material. Since the cooling device 30 may use a technique generally known in the art, a detailed description thereof will be omitted.

In the embodiment of the present invention, the splicer 20 may use an induction cooling method and a laser method, but it is preferable to use a rigid deformation type splicing method, and the splicer 20 may be movable or fixed. .

Hereinafter, the cooling method of the tip of the trailing material 9 will be described in detail.                     

According to an embodiment of the present invention, a method of cooling a trailing edge of a trailing material 9 is obtained by calculating rough rolling time of the roughly rolled hot rolling material 5 and using the rough rolling time of the first material of the trailing material. Obtaining the temperature control amount and the control frequency, and obtaining the one-time temperature control amount using the first temperature control amount and the control frequency, and gradually cooling from the beginning of the trailing material (9) to the predetermined point.

First, the step of obtaining the rough rolling plate time of the rough-rolled hot rolling material (5) is as follows.

Rough rolling time is calculated using the predicted length of the hot rolled material after the cooled slab is hot rolled by the rough mill. The predicted length of such hot rolled material is calculated by Equation 1 below.

[Equation 1]

Bar Length of Hot Rolled Material = Weight / (Thickness of Hot Rolled Material x Width of Hot Rolled Material x Material Density)

Thus, rough rolling plate time is calculated by Equation 2 below using the predicted length of the hot rolled material calculated by Equation 1.

[Equation 2]

Rough rolling time = Predicted length of hot rolled material / Rolling speed

In Equation 1, the weight is preferably applied to a value excluding the scale lose amount from the actual weight of the slab, and the hot rolled material thickness and the hot rolled material width are previously known in general rough rolling models. Since the calculated value is applied and the density of the material varies depending on the steel grade and temperature, it is preferable to apply a range value of 7.0 to 8.5 in this embodiment.

And in the formula 2, the rolling speed is preferably to use the speed multiplied by the advance rate of the main speed of the roll.

The following describes the steps for obtaining the first temperature control amount and the control frequency of the trailing material tip using the rough rolling plate time of Equation 2.

The first temperature control amount of the trailing material tip is calculated by applying the temperature drop equation of the hot rolled air cooling section. That is, the temperature of the hot rolled material (Bar) after t seconds by air cooling can be obtained by the following Equation 3, which is expressed as a graph as shown in FIG.

&Quot; (3) "

temperature after t seconds = 100 {((initial temperature +273) / 100) ^-3 + (6xσxεxt) / (100xcpxγxh)} ^-1/3 -273

{Where σ: Stefanboltzmann constant (= 4.88), ε: material emissivity (= 0.6), t: air cooling time, cp: specific heat of material, γ: material density, h: thickness of hot rolled material (= 30mm) is}

In Equation 3, the initial temperature is preferably applied to the temperature value of the tip end portion of the rough-rolled hot rolled material, which is a trailing material, and the air-cooling time is preferably applied to the rough rolling plate time calculated by Equation 2.

Thus, the first temperature control amount is obtained from the tip of the trailing material by the temperature of the hot rolled material by air cooling, and this first temperature control amount is calculated by Equation 4 below.

&Quot; (4) "

1st temperature control amount = initial temperature-temperature after t seconds

When the first temperature control amount is calculated as described above, the control frequency (n) is calculated by Equation 5 using the rough rolling plate time.

[Equation 5]

Number of control (n) = Rough rolling time / control cycle

In Equation 5, the control period is a value representing one cycle time of the cooling controller 40, that is, the speed of the control system. In the embodiment of the present invention, 0.01 to 0.10 seconds is applied.

The steps for obtaining the one-time temperature control amount using the first temperature control amount and the number of times of control are as follows.

&Quot; (6) "

1st temperature control amount = 1st temperature control amount / control frequency (n)

When the one-time temperature control amount calculated by Equation 5 is applied to the actual hot rolling process, it is preferable to apply a slight error in consideration.

Finally, the steps of gradually cooling from the beginning of the trailing edge portion 9 to a predetermined point using the calculated values obtained in the above manner will be described.

The cooling device 30 of the present invention is controlled by the cooling controller 40 and the starting point of cooling of the preceding material is the rough rolling time from the portion where the preceding material passing through the cooling device 30 first passes through the cooling device 30. Cool down to the point where it moved by, and cooling amount is cooled by one time temperature control amount according to Equation 6, and to the point where hot rolling material moves by rough rolling time while reducing cooling amount by a certain control cycle according to Equation 7 below. Cool.

[Equation 7]

Q ₁ = first temperature control amount

Q _(i) = Q _(i-1) -One-time temperature control amount {i = 2, n (control count)}

Reduction of the temperature control amount according to Equation 7 is a constant control from the point where the trailing end of the trailing material begins to pass through the cooling device 30 to the first temperature control amount and then the second temperature control amount from the second temperature control amount to the point passed by rough rolling time. In the period, that is, the cooling amount is gradually reduced by the control number n at the temperature control amount Q (i) according to the above formula 7 at intervals of 0.01 to 0.10 seconds.

When the trailing material tip is cooled according to the cooling method of the trailing material 9 according to the embodiment of the present invention described above, and the finishing rolling is performed by joining the leading material trailing edge and the trailing material tip in the splicer 20, hot rolling is performed. The measurement result of the longitudinal temperature difference before and behind the joint joint part is shown in FIG.

As shown in FIG. 4, when cooling the trailing edge of the trailing material 9 according to the embodiment of the present invention, a uniform temperature is maintained over the entire length of the joint in the longitudinal direction with little temperature variation in the longitudinal direction before and after the joint.

5 sequentially shows a method of cooling the trailing edge of the trailing material 9 according to the embodiment of the present invention described above.

Hereinafter, an example of applying the cooling method of the tip end portion of the trailing material 9 according to the embodiment of the present invention will be described.

The weight of 18 tons, hot rolled material is 30mm, hot rolled material is 1200mm, and material density is 7.8.

The length of the hot rolled material according to Equation 1 according to the rough rolling conditions is as follows.

18ton / (0.03m x 1.2m x 7.8) = 64.1m

When the rolling speed is 4.0m / sec, the rough rolling plate time according to Equation 2 is calculated as follows.

64.1 / 4.0 = 16.0 sec

When the initial temperature of the end portion of the trailing material after the rough rolling is 1050 ° C., the air cooling temperature after t seconds is calculated by Equation 3 as follows.

[100 {((1050 + 273 ) / 100) -3 + (6xσxεx16.0) / (100xcpxγx30)} -1/3 -273] = 1029 ℃

According to the above calculation result, the first temperature control amount is calculated by Equation 4 as follows.

1050 ℃-1029 ℃ = 21 ℃

When the control period is controlled to 0.05 sec using the first temperature control amount, the control frequency (n) is calculated by Equation 5 as follows.                     

16.0 / 0.05 = 320

Using this to calculate the one-time temperature control amount according to Equation 6 as follows.

21/320 = 0.0656 ° C

On the basis of the calculated value as described above, the cooling sequence for gradually cooling the temperature of the trailing material tip portion by the equation 7 using the cooling controller 40 according to the embodiment of the present invention is calculated as follows.

First temperature control amount = 21 ℃

2nd temperature control amount (21-0.0656) = 20.9344 ℃

3rd temperature control amount (20.9344-0.0656) = 20.8688 ℃

nth temperature control amount Q _(n) = Q _(n-1) -0.0656

Final temperature control amount = 0.0656 ℃

When the temperature of the trailing material is controlled in the direction of decreasing the amount of cooling gradually from the cooling device 30 to the point passed by the rough rolling time in the cooling sequence as described above, the longitudinal length of the trailing material from the rear end of the preceding material after the joining. It maintains a uniform temperature with little temperature variation over.

According to an embodiment of the present invention, a cooling device is installed between a coil box, which is a facility for winding a roughly rolled hot rolled material, and a jointer for joining the rear end portion of the preceding material and the front end portion of the trailing material so that the trailing material tip is roughly rolled from the cooling device. When cooling by reducing the cooling amount by a certain control cycle to the point passed by the mailing time, it maintains a uniform temperature over the longitudinal length of the continuous hot rolled material,

It prevents the falling of joint strength due to the temperature difference when joining the rear end of the preceding material and the leading end of the following material, and reduces the breakage of the joint caused by exaggeration force at the moment when the joint with large temperature difference passes each stand of the finishing mill. It is possible to solve the problem that the rolling is stopped due to the breakage accident, and to minimize the instability of the sheet due to the difference in the average strain resistance when the part having the temperature difference is rolled in the finishing mill.

Claims (8)

Rough rolling the slab cooled in the rough rolling mill; Winding the rough rolled hot rolled material into a plurality of coils in a coil box and storing the coils and waiting for a subsequent process; Cooling the front end portion of the hot rolling material which is followed during the process of continuously unwinding and moving the coil in the cooling device installed between the coil box and the jointer using the rough rolling condition of the hot rolling material; A joining step of the line and the trailing hot rolled material for joining the cooled front end of the hot rolled material and the rear end of the preceding hot rolled material to each other by a jointer; And Continuously finishing rolling the joined hot rolled material in a finishing mill; Cooling method of the hot rolled material by continuous rolling comprising a. In claim 1, The cooling step When the leading end of the trailing hot rolled material passes through the cooling device provided between the coil box and the junction, The cooling method of the hot rolled material by continuous rolling, characterized by cooling while gradually reducing the cooling amount from the leading end of the hot rolled material to the point passed by rough rolling plate time. In claim 2, The cooling step Obtaining a rough rolling time of the hot rolled material; Obtaining a first temperature control amount and a control frequency of the trailing hot rolling material tip using the rough rolling plate time; Obtaining a one-time temperature control amount using the first temperature control amount and the control frequency; And Cooling the leading end of the trailing hot rolled material using the one temperature control amount; Cooling method of hot rolled material by continuous rolling, characterized in that consisting of. 4. The method of claim 3, The cooling step Cooling method of the hot rolled material by continuous rolling, characterized in that controlled by the following formula (1) to (7). [Equation 1] Bar length of hot rolled material = slab weight / (thickness of hot rolled material x width of hot rolled material x density of material) [Equation 2] Rough rolling time = Predicted length of hot rolled material / Rolling speed &Quot; (3) " Temperature after t seconds by air cooling = 100 {((Initial temperature +273) / 100) ^-3 + (6xσxεxt) / (100xcpxγxh)} ^-1/3 -273 {Wherein initial temperature; Temperature of the tip of the hot-rolled hot rolled material, σ; Stephen Boltzmann constant, ε; Emissivity of the material, t; Air cooling time (rough rolling time according to equation 2), cp; Specific heat of material, γ; Density, h; thickness of hot rolled material} &Quot; (4) " 1st temperature control amount = initial temperature-temperature after t seconds by air cooling [Equation 5] Number of control (n) = Rough rolling plate time / Control cycle (one cycle time of cooling controller) &Quot; (6) " 1st temperature control amount = 1st temperature control amount / control frequency (n) [Equation 7] Q ₁ = first temperature control amount Q _(i) = Q _(i-1) -One-time temperature control amount {i = 2, n (control count)} In claim 4, The slab weight in Equation 1, except the scale loss in the actual weight of the slab, the density of the material is in the range of 7.0 ~ 8.5, the control period in the equation 5 is characterized in that the hot rolling by continuous rolling, characterized in that 0.01 ~ 0.10 seconds Cooling method of rolled material. In any one of claims 1 to 5 The bonding machine used in the bonding step is a method of cooling the hot rolled material by continuous rolling, characterized in that selected from the induction cooling method, the laser method or the steel deformation shear bonding method. A rough rolling mill for roughly rolling the cooled slab; A coil box for winding and storing the hot rolled material roughly rolled in the roughing mill with a plurality of coils and supplying the hot rolled material in a subsequent process; A cooling device installed between the coil box and the jointer and cooled by a cooling controller controlled by applying the following Equations 1 to 7 to the front end portion of the hot rolled material which is followed during the process of continuously unwinding and moving the coils; A jointer for mutually joining the front end of the cooled hot rolling material and the rear end of the preceding hot rolling material; And A finishing mill for continuously finishing rolling the joined hot rolled material; Hot rolling device for continuous rolling comprising a. [Equation 1] Bar length of hot rolled material = slab weight / (thickness of hot rolled material x width of hot rolled material x density of material) [Equation 2] Rough rolling time = Predicted length of hot rolled material / Rolling speed &Quot; (3) " Temperature after t seconds by air cooling = 100 {((Initial temperature +273) / 100) ^-3 + (6xσxεxt) / (100xcpxγxh)} ^-1/3 -273 {Wherein initial temperature; Temperature of the tip of the hot-rolled hot rolled material, σ; Stephen Boltzmann constant, ε; Emissivity of the material, t; Air cooling time (rough rolling time according to equation 2), cp; Specific heat of material, γ; Density, h; thickness of hot rolled material} &Quot; (4) " 1st temperature control amount = initial temperature-temperature after t seconds by air cooling [Equation 5] Number of control (n) = Rough rolling plate time / Control cycle (one cycle time of cooling controller) &Quot; (6) " 1st temperature control amount = 1st temperature control amount / control frequency (n) [Equation 7] Q ₁ = first temperature control amount Q _(i) = Q _(i-1) -One-time temperature control amount {i = 2, n (control count)} In claim 7, The bonding machine is a hot rolling apparatus for continuous rolling, characterized in that selected from the induction cooling method or the laser-based method or a steel deformation shear bonding method.

Images