KR20040044325A - Method for Controlling Thickness of Front Portion of Hot-Rolled Steel Sheet - Google Patents

Abstract

PURPOSE: A method for controlling thickness of top end part of hot rolled strip is provided to further improve thickness accuracy of the top end part of the rolled strip by controlling thickness of the top end part of the hot rolled strip using thickness of the intermediate part of the rolled strip during hot finish rolling of strip. CONSTITUTION: In a method for hot finish rolling a hot rolled strip using a hot finishing mill(10) consisting of a plurality of rolling stands(11), the method for controlling thickness of top end part of the hot rolled strip comprises a step of measuring temperature of the hot rolled strip using a thermometer(12) at the input side of the finishing mill, obtaining temperature of the input side of the respective stands using the measured temperature values, obtaining hot deformation resistance and rolling force from the obtained input side temperature values of the stands, and obtaining roll gap set values at the respective stands for obtaining target thickness using the obtained hot deformation resistance and rolling force; a step of setting roll gaps of the finishing mill according to the obtained roll gap set values; a step of finish rolling the rolled strip after setting the roll gaps, measuring thickness of the top end part of the hot rolled strip using an intermediate thickness gauge(14) in the intermediate region of the finishing mill, and obtaining a deviation between the measured thickness values and a target thickness; a step of obtaining a roll gap correction amount for at least final stand using the obtained thickness deviation of the top end part of the rolled strip; and a step of resetting a roll gap according to the obtained roll gap correction amount.

Description

Method for Controlling Thickness of Front Portion of Hot-Rolled Steel Sheet}

The present invention relates to a method for controlling the thickness of a hot rolled steel sheet tip portion during hot rolling in a steel mill hot rolling mill, and more particularly, by using an intermediate thickness of a rolled steel sheet during hot rolling. It relates to a thickness control method of the tip of the hot rolled steel sheet to further improve the.

Hot rolling is performed by using a hot finishing mill. As shown in FIG. 1, the finishing mill arranges a plurality of stands 1 in a line along the moving direction of a rolled steel sheet, and rolls the roll gap of each stand 1 to a target value. Reduced in stages, it is a device for rolling a roughly rolled rolled steel sheet of a predetermined thickness to a target thickness.

In Fig. 1, reference numeral 2 denotes "thermometer", 3 denotes "crop sear", 4 denotes "thickness gauge", and 5 denotes "controller".

At this time, each rolling mill of a finishing mill is called a stand, and the 1st stand F1, the 2nd stand F2, and. . . This is called an nth stand (Fn).

Then, the thickness of the rolling stand passing through the final stand (Fn) is measured by the thickness measuring instrument (4), and the measured value is fed back to the controller (5), where the target thickness is obtained by comparing with the target value and thus obtained Feedback control is performed to adjust the roll gap of each rolling mill to achieve the target thickness.

In the hot finishing rolling, the thickness of the tip of the rolled steel sheet depends on the roll gap setting obtained by the mathematical model, and the thickness defect occurs due to the prediction error of the model.

Conventionally, in order to prevent the thickness defect caused by the prediction error of the tip of the rolled steel sheet, the prediction of the temperature of the water cooling section, the development of the hot deformation resistance and the rolling load prediction equation for improving the accuracy of the mathematical model have been studied.

However, these techniques had limitations in accurate prediction due to various deviation factors in the actual field, and finally, there was a limitation in improving tip thickness after passing the final stand.

For this reason, in the past, the thickness defect was cut and sent to the demand price, resulting in an increase in the workload of the correction line, which is a post-process of hot rolling, delayed delivery of demand, lower error rate, and unsatisfactory demand for uncut material. come.

The present invention is to conduct the research and experiment to solve the conventional problems as described above, and to propose the present invention on the basis of the results, the present invention by using the intermediate thickness of the rolling steel sheet during hot rolling An object of the present invention is to provide a thickness control method of a tip of a hot rolled steel sheet that can further improve the accuracy of the thickness.

1 is a schematic diagram of a finishing mill applied to a method of rolling a hot rolled steel sheet tip part according to a conventional method;

Figure 2 is a schematic diagram showing an example of a finishing mill for implementing a method for controlling the thickness of the hot rolled steel sheet tip portion according to the present invention

Figure 3 is a flow chart showing an example of a method for controlling the thickness of the tip of the hot rolled steel sheet according to the present invention

4 is a timing diagram showing a control flow according to the present invention in a finishing mill.

5 is a graph showing the thickness of the rolled steel sheet passed through the finishing mill when the hot rolled steel sheet tip ends are rolled according to the conventional method.

Figure 6 is a graph showing the thickness of the rolled steel sheet passed through the finishing mill in case of controlling the thickness of the hot rolled steel sheet tip portion according to the present invention by length

Explanation of symbols on the main parts of the drawings

1, 11. . . Stand 2, 12. . . Thermometer 4, 13. . . Final thickness meter

14. . . Intermediate Thickness Gauge 5, 15. . . Controller

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is a method for hot-thin rolling a hot rolled steel sheet using a hot finishing mill consisting of a plurality of rolling stands,

The temperature of the rolled steel sheet is measured at the entrance of the finishing mill, and each stand entrance temperature is obtained using the measured temperature values, and the hot deformation resistance and the rolling load are obtained from the entrance temperature values thus obtained, and then these values are used. Obtaining a roll gap set value at each stand to obtain a target thickness;

Setting a roll gap of the rolling mill according to the roll gap set value obtained as described above;

Setting the roll gap as described above, followed by finishing rolling the rolled steel sheet, measuring the thickness of the tip of the rolled steel sheet in the intermediate region of the finishing mill, and obtaining a deviation between the measured values and the target thickness;

Obtaining a roll gap correction amount for at least the final stand (Fn) by using the thickness variation of the tip of the rolled steel sheet obtained as described above; And

It relates to a method for controlling the thickness of the hot rolled steel sheet tip portion comprising the step of resetting the roll gap in accordance with the roll gap correction amount obtained as described above.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention more accurately predicts the thickness variation (error) of the leading edge of the strip after passing through the final stand by using the deviation between the thickness of the rolled steel sheet and the target thickness measured in the middle of the finishing mill stand in hot rolling. Determine the roll gap correction amount of at least the final stand Fn, preferably the final stand Fn and the front stand Fn-1, and correct the roll gap of the stand according to the roll gap correction amount to The present invention relates to a thickness control method of a hot rolled steel sheet tip portion which can further improve the thickness accuracy of the rolled steel sheet tip portion by rolling.

An example of a preferred hot finishing mill for implementing the present invention is shown in FIG. 2.

As shown in FIG. 2, a preferred hot finishing mill 10 for implementing the present invention includes a plurality of rolling stands 11, a thermometer 12 is provided at the entrance side thereof, and at the exit of the finishing mill. The final thickness meter 13 for measuring the thickness of the finishing rolled steel sheet is provided.

In addition, the intermediate region of the finishing mill is provided with an intermediate thickness measuring instrument 14 for measuring the thickness of the rolled steel sheet. Further, the roll gap correction amount is obtained using the thickness measurement measured from the intermediate thickness measuring instrument 13 and the rolled steel sheet is obtained. A controller 15 is provided that is configured to effect roll gap correction before entering the stand.

The intermediate region of the finishing mill may be changed according to the number of stands constituting the finishing mill. Preferably, the finishing mill is set between F3 stands and F5 stands.

That is, when the finishing mill consists of six stands, the intermediate thickness measuring instrument 14 is preferably provided to measure the thickness of the tip of the rolled steel sheet rolled by the F3 stand, or the tip of the rolled steel sheet rolled by the F4 stand.

In Fig. 2, reference numeral 16 denotes a "crop sear".

Figure 3 shows a flow chart of a preferred example of a method for controlling the thickness of the end of the rolled steel sheet during hot finishing rolling in accordance with the present invention, the present invention will be described in more detail with reference to Figs.

According to the present invention, in order to roll the tip of the rolled steel sheet in hot finishing rolling, the temperature of the rolling steel sheet to be subjected to finishing rolling is measured by a thermometer 12 installed at the inlet side of the finishing mill 10, and the measured temperature value is used. After calculating the stand temperature of each stand 11, the hot deformation resistance and the rolling load were obtained from the obtained stand temperature values, and then the roll gap set values at each stand 11 were obtained by using these values to obtain the target thickness. According to the roll gap setting value, the rolling gap of the rolling mill is actually set to perform hot finishing rolling.

The temperature measurement of the rolled steel sheet at the inlet side of the finishing mill by the thermometer 12 is performed at a predetermined interval, preferably at 0.1 second intervals.

The said roll gap setting value can be performed by a conventional method, Preferably it is as follows.

The temperature at which the rolled steel sheet reaches each stand by the water cooling section temperature drop formula shown in Equation (1) from the rolled steel tip end temperature data measured by the thermometer 12 as described above.

(Equation 1)

Water cooling section temperature drop = 80 + (Temperature of rolled steel sheet -80) × Exp (heat transfer coefficient × water cooling section distance × 82.67 / thickness / speed)

Using the temperature at the time of reaching each stand calculated | required as mentioned above, the hot deformation resistance Km is calculated | required by following formula (2), and using this hot deformation resistance Km is shown by following formula (3) The rolling load RF at each stand is obtained.

(Equation 2)

Hot Average Strain Resistance (Km) = 1.15 × δf × fm × (ε / 10) ^m

[Equation (2), δ f represents a function of the component and the rolling temperature, fm represents a function of the strain, ε represents a function of the strain rate, m represents the strain coefficient]

(Equation 3)

Rolling Load (RF) = Km × B × Ld × Qp

In Equation 3, Km denotes a hot average strain resistance (kg / mm ² ), B denotes a sheet width (mm), Ld denotes a projection contact length (mm) of a roll and a strip, and Qp denotes a reduction force function. ]

Next, using the rolling load, steel type, thickness, width, reduction ratio, speed, etc. determined as described above, a roll gap set value for finally obtaining a target thickness is obtained by the following equation (4).

(Equation 4)

Roll gap (Sn) = Hn-(RFn / Mn) + OFn + GMn

In Equation 4, S denotes a roll gap, n denotes the number of the corresponding stand, Hn denotes the exit target thickness at the nth stand Fn, and Mn denotes the rolling mill elastic deformation coefficient at the nth stand Fn. (Ton / mm), RFn is the rolling load (Ton) at the nth stand (Fn), OFn is the oil film change amount at the nth stand (Fn), and GMn is the gauge error value at the nth stand (Fn). Indicates]

Next, the roll gap is set as described above, and then the finishing rolling is started, and in the case where the finishing mill consists of six stands, preferably the rolling mill consists of six stands, the rolled steel sheet is provided by an intermediate thickness measuring instrument provided between the F3 stands and the F5 stands. Measure the tip thickness and calculate the deviation between the measured thickness values and the target thickness.

The thickness measurement of the front end of the strip by the intermediate thickness meter 14 and the determination of the thickness deviation (error) using the same can be performed by a conventional method, and preferred examples are as follows.

That is, when the thickness of the tip of the rolled steel sheet is measured for the first time by the intermediate thickness meter, the measured value is initially unstable due to the supercooled part of the rolled steel pole tip and the measuring principle of the measuring instrument. For the stability of the data, five times are measured at 0.1 second intervals and averaged over three data except the largest value and the smallest value.

(Equation 5)

Tip thickness deviation value (ΔHm) = (ΔHm1 + ΔHm2 + ΔHm3) / 3

The amount of roll gap correction for at least the final stand Fn, preferably the final stand Fn and the front stand Fn-1 is obtained using the tip thickness deviation value obtained as described above.

A preferred method for obtaining the roll gap correction amount is as follows.

First, using the tip thickness deviation value obtained as described above, the estimated thickness deviation for at least the final stand (Fn), preferably the final stand (Fn) and the front stand (Fn-1) according to Equation (6) ΔHn) is obtained.

(Equation 6)

Expected Thickness Deviation from the Stand of Fn Stand (ΔHn) = ΔHm × (Rn / Rs-n)

[Equation (6), n represents the number of the stand, ΔHm represents the thickness deviation value in the intermediate thickness meter, Rn represents the rolling amount in the n-th stand (Fn), Rs-n is The rolling amount from the intermediate thickness gauge to the final stand (Fn)]

In order to eliminate the estimated thickness deviation obtained as described above, the amount of roll gap correction for at least the final stand Fn, preferably the final stand Fn and the front stand Fn-1 is obtained by the following equation (7).

(Equation 7)

Roll gap correction amount (ΔSn) =-{(Mn + Qn) / Mn} × ΔHm × (Rn / Rs-n) × Gn

[Equation 7] ΔS represents the roll gap correction amount, n represents the number of the stand, Mn represents the rolling mill elastic deformation coefficient (Ton / mm) in the n-th stand (Fn), Qn is the nth The plastic deformation coefficient (Ton / mm) at the stand (Fn), ΔHm is the thickness deviation value at the intermediate thickness meter, Rn is the rolling amount at the nth stand (Fn), Rs-n is the intermediate thickness meter The rolling amount from then on to the final stand, and Gn represents the applied gate at the nth stand (Fn).]

Next, the roll gap is reset to at least the final stand Fn, preferably the final stand Fn and the front stand Fn-1 according to the roll gap correction amount determined as described above.

That is, by controlling the roll gap with the roll gap reset values for the final stand Fn and the front stand Fn-1 obtained by the following equation (8), it is possible to control the thickness of the tip portion of the hot rolled steel sheet.

(Equation 8)

Reset roll gap of the Fn stand (Sn) = Hn-(RFn / Mn) + OFn + GMn + ΔS n

[In Equation (8), S represents a roll gap reset value, n represents the number of the stand, Hn represents the exiting target thickness in the nth stand Fn, and Mn represents a rolling mill in the nth stand Fn. The modulus of elasticity (Ton / mm), RFn is the rolling load (Ton) at the nth stand (Fn), OFn is the oil film change at the nth stand (Fn), and GMn is at the nth stand (Fn). ΔS n represents the roll gap correction amount at the nth stand (Fn).

According to the present invention described above, the thickness of the rolled steel sheet tip can be improved by controlling the roll gap to control the thickness of the rolled steel sheet tip.

In the case of controlling the roll gap with the reset roll gap Sn as described above, other conditions should be considered as in the conventional method.

As described above, after the roll gap is adjusted, the roll gap is input to receive the feedback measurement value measured from the final thickness meter 13 provided on the exit side of the finishing mill 10 according to the conventional rolling thickness control method. Feedback control.

The above-described initial roll gap setting values, thickness deviations, roll gap correction amounts, reset roll gap values, and the like, and control of roll gaps and the like are performed by a controller.

Figure 4 is a timing diagram showing the operation timing of each device of the finishing mill shown in Figure 2 when the control method according to the present invention is applied, according to the present invention, the steel grade of the material to be rolled provided before the starting of the finishing rolling, The roll gap setting value of each rolling stand F1-Fn is calculated | required from thickness, width, temperature, etc., and the roll gap of all the stands F1-Fn is initialized to a setting value.

In the above state, when the rolled steel sheet enters the intermediate thickness meter installed in the middle of the stand, the thickness of the tip is measured to obtain a deviation from the target thickness, and at least the final stand F6 and preferably the final stand F6 using the deviation value. After obtaining the roll gap reset amount of the front stand (F5), and after determining whether the conditions to control the roll gap reset amount is established, the roll gap is actually modified and passed through the rolled steel sheet.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

A hot rolled steel sheet tip was rolled according to the present invention on a general carbon steel material having a thickness of 2.3 mm, a width of 1032 mm, and a temperature of 1083 ° C. at the inlet side of the finishing mill according to the present invention.

The default roll gap setting for each stand is 15.34mm for Stand 1 (F1) and Stand 2 for F2 (F2).

8.28 mm, stand No. 3 (F3) was 5.11 mm, stand No. 4 (F4) was 3.78 mm, stand No. 5 (F5) was 2.06 mm, and stand No. 6 (F6) was 1.96 mm.

The thickness of the rolled steel sheet at the exit of stand No. 3 (F3) where the intermediate thickness measuring device is located was measured to be 5.841 mm 131 μm thick compared to the target thickness 5.71 mm, and the estimated thickness deviation at stand No. 5 was expressed by Equation (6) (△ H5) was 41.08 μm, and the thickness deviation estimate (ΔH6) at stand No. 6 was calculated to be 20.93 μm, and according to Equation (5), the number 5 stand roll gap correction amount (ΔS5) was −110 μm, at No. 6 The stand roll gap correction amount (ΔS6) was determined to be −50 μm. According to Equation (8), the reset roll gap was calculated to be 1.95 mm for the 5th stand and 1.91 mm for the 6th stand. It can be seen that less.

The rolling deformation modulus of the mill used here was 430 (Ton / mm) for the 5th stand (M5) and 415 (Ton / mm) for the 6th stand (M6). In addition, the firing coefficient of the 5th stand (Q5) was 505 (Ton / mm), the 6th stand (Q6) was 574 (Ton / mm), and the rolling reduction amount (R5) of the 5th stand was 1.06 mm, the 6th stand ( R6) was 0.54mm, and the rolling reduction Rs-n from the intermediate thickness meter to the final stand was 3.38 mm, the gain 5 of the stand 5 was 1.23, and the gain 6 of the stand 6 was 1.0.

As described above, the thickness of the rolled steel sheet by controlling the tip is measured, and the result is shown in FIG. 6, and the thickness measurement result of the filamentary rolled steel sheet when the roll gap modification of the tip is not applied according to the present invention is illustrated in FIG. 5. Shown in

As shown in FIG. 5, when the roll gap correction of the tip portion according to the present invention is not applied, it can be seen that an error of about +100 μm occurs at the tip portion.

On the contrary, when the roll gap correction of the tip portion according to the present invention is applied, as shown in FIG. 6, it can be seen that the error of the tip portion thickness decreases to about +20 μm.

As described above, the present invention does not only depend on the roll gap setting by the predictive model during hot rolling, but also uses the deviation (error) of the intermediate thickness in the hot finishing rolling process to reset the roll gap of the rear stand to the tip of the hot rolled steel sheet. By controlling the thickness of the hot rolled steel sheet, the thickness of the end of the hot rolled steel sheet can be prevented, so that the cutting process of the defective part can be omitted, thereby reducing the volume of hot rolling correction work, and consequently shortening the delivery time of the demand and improving the error rate. Not only that, but the demand for uncut material for defective parts can be resolved by the demand from India.

Claims (3)

In the method for hot-thin rolling of a hot rolled steel sheet using a hot finishing mill consisting of a plurality of rolling stands, The temperature of the rolled steel sheet is measured at the entrance of the finishing mill, and each stand entrance temperature is obtained using the measured temperature values, and the hot deformation resistance and the rolling load are obtained from the entrance temperature values thus obtained, and then these values are used. Obtaining a roll gap set value at each stand to obtain a target thickness; Setting a roll gap of the rolling mill according to the roll gap set value obtained as described above; Setting the roll gap as described above, followed by finishing rolling the rolled steel sheet, measuring the thickness of the tip of the rolled steel sheet in the intermediate region of the finishing mill, and obtaining a deviation between the measured values and the target thickness; Obtaining a roll gap correction amount for at least the final stand (Fn) by using the thickness variation of the tip of the rolled steel sheet obtained as described above; And Thickness control method of the tip portion of the hot rolled steel sheet comprising the step of resetting the roll gap according to the roll gap correction amount obtained as described above The thickness control method according to claim 1, wherein the roll gap correction amount is obtained by the following equation (7). (Equation 7) Roll gap correction amount (ΔSn) =-{(Mn + Qn) / Mn} × ΔHm × (Rn / Rs-n) × Gn [Equation 7] ΔS represents the roll gap correction amount, n represents the number of the stand, Mn represents the rolling mill elastic deformation coefficient (Ton / mm) in the n-th stand (Fn), Qn is the nth The plastic deformation coefficient (Ton / mm) at the stand Fn, ΔHm is the thickness deviation value at the intermediate thickness meter, Rn is the rolling amount at the nth stand (Fn), and Rs-n is the intermediate thickness meter. Rolling amount from the last stand to the last stand, and Gn represents the applied gate at the nth stand (Fn)]. The method according to claim 1 or 2, wherein the roll gap correction amount is determined for each of the final stand Fn and the front stand Fn-1, and the final stand Fn and the front stand Fn according to the roll gap correction amount thus obtained. -1) thickness control method of the tip of the hot rolled steel sheet, characterized in that to reset the roll gap