JP2007307620A - Rolling method with cold tandem mill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling method in a cold tandem mill, with which occurrence of heat scratch can be prevented without hindering productivity. <P>SOLUTION: By beforehand specifying a stand which is apt to cause the heat scratch, performing rolling while performing air-cooling between the outlet side of the roll bite of a rolling mill and a sheet temperature detector in the specified stand, detecting the thickness on the inlet and outlet sides of the rolling mill, rolling load and others, the coefficient of friction and deformation resistance are determined on the basis of these detected values. By determining the temperature rising of the sheet inside the roll bite, draft is controlled so that these values do not exceed the target temperature for controlling the heat scratch. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rolling method for preventing the occurrence of heat scratch without impairing productivity in a cold tandem rolling mill having a plurality of cold rolling mills.

  In a cold tandem rolling mill, heat scratches may occur due to an increase in work roll speed or rolling reduction. A heat scratch is a seizure flaw generated by metal contact between a work roll and a rolled material as a result of an increase in the interface temperature between the roll and the rolled material in the roll bite and an oil film breaking in the roll bite. .

  When the heat scratch occurs, the surface defect of the product occurs, so that not only the product yield is lowered, but also the work roll of the stand where the heat scratch is generated needs to be changed, so that the productivity is remarkably lowered.

  The presence or absence of the occurrence of heat scratch can be predicted by the interface rising temperature in the roll bite during rolling. In actual operation, although the rolling schedule differs depending on the steel type, the same steel type is rolled under substantially the same rolling conditions (hereinafter also including cooling conditions), so the interface rising temperature can be substituted by the plate temperature on the stand exit side. Therefore, control is performed so that the plate temperature on the delivery side of the rolling mill is detected and the plate temperature is equal to or lower than the appropriate value based on the detected value.

  The above-described method of controlling the plate temperature on the stand exit side as the roll bite temperature is effective under almost the same rolling conditions (constant speed, coolant, etc.). For example, in the case where cooling is not performed between the rolling mill roll bite exit side and the plate temperature detector (air cooling), there is no significant problem. In the case of the i stand of FIG. 2, the upper and lower work rolls are cooled by the roll cooling device 30, but the cooling water is prevented from hitting the plate S by the draining device 32. Therefore, since the measurement value of the temperature detector 34 is not affected by roll cooling, it is possible to prevent i-stand heat scratching by the conventional technique.

However, when cooling is performed between the sheet temperature detector from the rolling mill roll bite exit side (water cooling), it becomes a big problem. For example, in the case of (i-1) stand of FIG. 2, the plate S is cooled by the plate cooling device 20 on the exit side of the rolling mill, and the cooling water remains on the surface. The remaining cooling water is drained by the draining and tension detecting device 22, and then the temperature is measured by the temperature detector 24. Therefore, the influence of the plate cooling device 20 on the temperature detector 24 is large. Even if the amount of cooling water is the same, the temperature of the cooling water is affected. The water temperature is about 20 ° C. in the summer and about 5 ° C. in the winter, and in the summer and winter, the heat scratch control target temperature _TL of the control according to the prior art must be provided on the table according to the water temperature. Moreover, since it is necessary to confirm this heat scratch control target temperature _TL by experiment, the setting was a problem. Further, when the amount of water in the plate cooling device 20 is significantly changed, there is a problem that the influence of the amount of water cannot be ignored. Depending on the lubricant used, the accuracy may be improved by controlling the interface rise temperature (the temperature difference between the plates on the entrance and exit of the rolling mill) rather than controlling the plate surface temperature (maximum temperature).

  Regarding heat scratch prevention, for example, as disclosed in Japanese Patent Laid-Open No. 5-98283, a method using a rolling lubricant having excellent seizure resistance, or as disclosed in Japanese Patent Laid-Open No. 56-111505. In addition, there are a method for reducing the temperature of the plate and the work roll by controlling the amount of coolant, and a method for reducing the work roll speed as disclosed in Japanese Patent Laid-Open No. 6-63624. Both methods relate to a method of preventing an increase in the interface temperature between the work roll and the rolled material in the roll bite or preventing the oil film from breaking even if the interface temperature in the roll bite increases. However, the use of rolling lubricants with excellent seizure resistance may increase costs, and although the plate and roll temperature control by controlling the coolant amount is effective, there are some problems with its responsiveness. The decrease in the roll speed has a problem that the productivity decreases.

  As a method for preventing heat scratching without causing a decrease in productivity and an increase in manufacturing cost, Japanese Patent Laid-Open No. 60-49802 discloses changing the rolling schedule and tension, It is not clear how to predict the occurrence in advance and how to determine the amount of control.

  As a method of preventing heat scratch without causing a decrease in productivity and an increase in manufacturing cost as described above, when changing the tension, naturally, if the value is high, the rolling load is reduced, and the effect of preventing heat scratch However, if the tension is increased, the plate may break.If the tension is increased gradually while observing the rolling condition, the responsiveness deteriorates, heat scratches occur, and the plate thickness accuracy deteriorates. There is. Further, when the plate temperature on the stand exit side is detected and the tension is controlled based on the temperature, the control is performed when the temperature becomes higher than the temperature at which the heat scratch occurs, so that the heat scratch is temporarily generated. There is a risk.

  This invention makes it a subject to provide the rolling method in a cold tandem rolling mill which prevents generation | occurrence | production of a heat scratch, without inhibiting productivity.

The rolling method in the cold tandem rolling mill according to the present invention designates a stand where heat scratches are likely to occur in advance, and in the designated stand, air cooling is performed between the sheet temperature detector from the rolling mill roll bite outlet side, and the next step Roll with
(A) First step of detecting stand entry / exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit plate thickness, stand entry / exit side tension (b) Stand entry / exit plate temperature, stand delivery side thickness, and the detected value of the stand delivery side speed, the estimated increase in temperature [Delta] T _f in the second step (c) said roll bite for determining temperature rise [Delta] T _f in the roll bite in the rolling state is preset If more than a heat scratch control target temperature [Delta] T _L, the friction of the strip from the rolling load, the work roll speed, stand delivery side speed, thickness at delivery side of the stand incident and, and the detection value of the stand entry-exit side tension of the first step Step 3 for obtaining coefficient and deformation resistance (d) The rolling state is determined by the detected value of the third step, the friction coefficient, and the deformation resistance. That 'and the plate temperature increases the _{T m} of if you change the reduction ratio' leaf temperature increase _{T E} in the roll bite sought, fourth obtaining the reduction ratio which _{ΔT L -ΔT f ≧ T m '} -T E' Step (e) Fifth step of controlling the reduction ratio using the reduction ratio obtained in the fourth step as a target value

  In the present invention, the friction coefficient and the deformation resistance are obtained based on the stand entry / exit side plate thickness, rolling load, and other detected values. And the temperature rise in a roll bite is calculated | required by these values, and a rolling reduction is controlled so that these may not exceed heat scratch control target temperature. Therefore, the temperature inside the roll bite can be maintained below the temperature at which heat scratches do not occur.

  The temperature inside the roll bite can be suppressed with high accuracy below a temperature at which heat scratches do not occur, and generation of heat scratches can be prevented without impairing productivity.

FIG. 1 shows an example of a cold tandem rolling mill in which the rolling method of the present invention is implemented. In this cold tandem rolling mill, the plate cooling device 20 provided on the stand designated as being prone to heat scratching, and the draining function of the draining and tension detecting device 22 are not used in this invention, but for convenience, It is shown and described. However, when the plate cooling device 20 is not used, the draining and tension detecting device 22 functions only as a tension detecting device.
Although the number of stands of the cold tandem rolling mill is usually 2 to 8, and 5 stands are shown in FIG. 1, the number of stands is not limited to this. The stands 1 to 5 are each composed of a work roll 11, an intermediate roll 13, and a backup roll 15. The stands where heat scratches are likely to occur vary depending on the reduction ratio, plate thickness, rolling load, tension, rolling material, lubrication conditions, etc. of each stand. Usually, heat scratches tend to occur at a later stage stand where the rolling load and work roll speed increase. In the cold tandem rolling mill of FIG. 1, the fourth stand 4 is in a state where heat scratches frequently occur because the final stand 5 is under light rolling dull rolling. In the case where there is a possibility that heat scratches may occur in a stand other than the subsequent stand, the present invention can be applied to those stands. A lubricating oil supply device 26 is disposed on the entry side of each stand. The final stand 5 includes a work roll cooling device 30 and a roll cooling drainer 32.

In FIG. 1, a temperature detector 24 is provided after the draining and tension detecting device 22 on the entrance side and the exit side of the rolling stand of the fourth stand 4, and the plate temperature T of the plate S being rolled is detected at a constant cycle. Has been. The temperature detector 24 is preferably a non-contact type, for example, a radiation thermometer. The rolling load P of the fourth stand 4 is detected by a load cell (not shown). The tension (force per unit area) σ _b and σ _f on the entry side and exit side of the rolling mill can be obtained by dividing the total tension by the plate cross-sectional area (plate thickness / plate width). The total tension is detected by a load cell (not shown) of the draining / tension detecting device 22 provided on the inlet side and the outlet side of the rolling mill. A plate thickness measuring device 17 such as an X-ray plate thickness meter is provided on the entry side and the exit side of the fourth stand 4, and a plate speedometer (not shown) is provided on the exit side of the fourth stand 4 and the third stand 3. ), For example, a laser plate speedometer is provided. By these measuring instruments, the inlet side and outlet side plate thicknesses H and h of the fourth stand 4 and the inlet side and outlet side plate speeds V _I and V _O are detected, respectively. Work roll velocity V _R of the fourth stand 4 is detected by the rotation speed detector (not shown) the rotational speed of the motor that drives the work rolls 11, the detected rotational speed of the motor and the work roll diameter D and the gear It is obtained by calculating using the ratio. Further, the plate S is cooled by the plate cooling device 20 on the entrance side and the exit side of the fourth stand.

In the cold tandem rolling mill, the work roll diameter D, the roll drive system gear ratio, the plate width W, the material plate thickness (H _S : the entrance side plate thickness of the first stand 1), and the yield stress σ during simple tension of the material. _y is known and can be input in advance to a calculator (not shown). The rolling load of the present invention is a load required for plastic deformation of the material, and when the stand has a shape control device such as a bender, those forces were detected and obtained by the load cell described above. This means the load excluding the force of the bender etc. from the load.

Next, a plate temperature estimation method will be described. The sheet temperature detector 24 provided on the rolling mill exit side detects the sheet temperature on the rolling mill exit side at a constant period τ (for example, 5 _s ).

  In the case of air cooling according to the present invention, the temperature change due to air cooling can be ignored when the air cooling time is within about 0.5 seconds (rolling speed of about 500 m / min or more). Therefore, the exit side plate temperature of the front stand can be regarded as the plate temperature at the plate temperature detection position as it is.

Based on this temperature data, the roll bite outlet plate temperature in a steady state is estimated. For example, if the control cycle of reduction (control cycle of reduction to prevent heat scratching) is set to 1 minute, the plate temperature data for the past 1 minute (12 pieces in this case, but the reduction conditions are constant data) ) Is substituted into a function that represents an asymptotic curve that asymptotically approaches a constant value, and a constant of the function is determined by performing multiple regression, and the asymptotic value is determined as a plate temperature at the roll bite outlet in a steady state. Is an estimated value _Tf . Examples of such a function representing an asymptotic curve that finally approaches a constant value include a · tan h (cX) and a + b (1−e ^−cx ). In this function, a, b, and c are constants, and finally asymptotically approach a and a + b, respectively. Therefore, the measured temperature data is substituted into such a function to obtain the asymptotic value a or a + b, which is used as the estimated value T _f of the steady state plate temperature.

In addition to such a method, for example, the control period of reduction (control period of reduction to prevent heat scratch) is set to 30 seconds, for example, and the six obtained in 30 seconds, which is the control period, are set. The temperature data may be linearly regressed, and the plate temperature 30 seconds after the next reduction control timing (next reduction control timing) may be estimated to be used as the estimated value _Tf of the plate temperature.

Next, the setting of the heat scratch control temperature will be described. The minimum roll bite outlet plate temperature at which heat scratches are generated is obtained through experiments in which the work roll speed, rolling reduction, rolling lubrication conditions, etc. are changed in advance, and this is _defined as the limit temperature T _Lim . The limit temperature may be set as the heat scratch control target temperature _TL , but the heat scratch control target temperature _TL is set to a temperature slightly lower than the limit temperature T _Lim described above, for example, about 3 to 6 ° C. Is preferred.

The estimated value _Tf of the plate temperature at the roll bite outlet and the above-described heat scratch control target temperature _TL are compared in the stand where heat scratches are likely to occur, in the fourth stand in the embodiment. If ΔT = T _L −T _f is positive, there is no possibility of heat scratching, so rolling continues. When ΔT = T _L −T _f is a negative value, heat scratch may occur. Therefore, rolling is performed by changing the rolling reduction so that ΔT becomes positive.

ここで、σ_ｙは圧延材の単純引張時の降伏応力であり、εはひずみである。 A method for calculating the rolling reduction to be changed will be described below.
First, the deformation resistance K _m and the friction coefficient during rolling mu. For the deformation resistance of the rolled material, the values of constants a, ε ₀ , and n shown in Equation (1) are obtained in advance by a tensile test.

Here, σ _y is the yield stress during simple tension of the rolled material, and ε is the strain.

Incidentally, the deformation resistance is affected by the strain rate of the impacts and the plate temperature, deformation resistance K _m obtained from the equation (1) is not necessarily exact value during rolling. Therefore, in the present invention, the rolling load formula and the advanced rate formula are combined to determine the deformation resistance and the friction coefficient during rolling. For example, the deformation resistance is obtained by developing Hill's load equation as shown in equation (2). In addition, the Bland & Ford advanced rate equation is developed for the friction coefficient as shown in Equation (3), and the deformation resistance obtained in Equation (2) is substituted into Equation (3) to obtain the friction coefficient. In the expressions (2) and (3), the subscript E is a detected value at the time of rolling the stand and a calculated value based on the detected value, and will be referred to as an actually measured value in the following description. As described above, the calculated value is a value obtained by dividing the pretension detected by the load cell by the plate cross-sectional area or excluding the bending force from the rolling load detected by the load cell.

In the above equation, there are two unknowns: a coefficient of friction μ _E and a constant (a in equation (1)) in the deformation resistance equation K _mE , the others are known and the number of equations is two. Therefore, this equation can be solved. The calculation when is about 0.05 as an initial value of the coefficient of friction mu _E is a value obtained by tensile testing as an initial value of the constant a in the deformation resistance formulas are preferably used.

On the other hand, the rising temperature T ′ at the interface between the roll at the exit of the roll bite and the rolled material at this time is expressed by, for example, Expression (4) using the expression of Ono et al.

T _dmax is the temperature rise at the exit of the roll bite at the interface between the roll and the rolled material, which is increased by the heat of deformation, and is expressed by equation (6). T _fmax is the temperature rise at the exit of the roll bite at the interface that increases due to frictional heat, and is expressed by equation (5).

Substituting the physical property values and actual measured values of the respective stands into the equations (5) and (6), and the friction coefficient μ _E and deformation resistance K _mE obtained by the method using the equations (2) and (3) described above. Then, an actual measurement value T _E ′ of the temperature rise T ′ at the interface between the roll at the exit of the roll bit of the stand and the rolled material is obtained.

Then, instead to estimate the temperature change in case of changing the reduction ratio, firstly the friction coefficient obtained mu _E and deformation resistance K _mE, and using the measured values of the stands except reduction ratio, only the reduction ratio The rolling load P and the advanced rate f _s are calculated. Strictly speaking, changing the rolling reduction also changes the friction coefficient. However, since the fluid lubrication is almost dominant at a rolling speed of 1000 m / min or more, the influence of the rolling reduction on the friction coefficient may be ignored under the condition that heat scratch occurs.

The rolling load P is calculated, for example, using the Hill load equation shown in Equation (7). The advanced rate f _s is calculated using the Bland & Ford equation shown in equation (8). The roll flatness R _E ′ is calculated using the Hitchcook equation shown in equation (9).

The rolling load is obtained by performing convergence calculation using equation (7) and roll flat equation (9), and the advanced rate is obtained from equation (8). By substituting these values into the equations (4) to (6), the temperature increase T _m ′ at the roll bite outlet interface when the rolling reduction condition is changed can be obtained. That is, the measured value T _E ′ of the temperature rise at the interface of the roll bite outlet in the stand and the estimated value T _m ′ of the temperature rise at the roll bite outlet when the rolling reduction is changed are obtained. Although the temperature at the interface between the roll and the rolled material at the roll bite exit and the plate temperature at the stand exit side are not strictly the same, the temperature change when the rolling reduction condition is changed may be regarded as the same. Therefore, the difference between T _m ′ and T _E ′ (ΔT ′ = T _m ′ −T _E ′) and the difference between _TL and T _f described above (ΔT = _TL− T _f ) are obtained. In comparison, a rolling reduction condition such that ΔT ′ is equal to or smaller than ΔT (ΔT ′ ≦ ΔT) can be obtained by repeated calculation using, for example, the Newton method. The rolling reduction set value of the rolling mill is changed to the rolling reduction value obtained as described above. Several rolling reduction values that do not generate heat scratches that satisfy the above relationship can be obtained. An appropriate rolling reduction value may be selected from these rolling reduction values according to the rolling condition, but it is desirable to select the lowest rolling reduction value raim and change the rolling reduction setting value of the stand accordingly.

  In addition, since the amount of change in the rolling load can be predicted in advance during these controls, the thickness and shape can be controlled so that the plate thickness accuracy and plate shape defects do not occur.

The above shows the common part between the method of controlling the heat scratch by the plate temperature at the exit side of the rolling mill roll bite and the method of controlling by the rising temperature in the roll bite. In some cases, it may be better to control the temperature within the roll tool. A method in that case will be described. In this case, it detected by the temperature detector the temperature T _i of the plate in the rolling mill inlet side. In the case where water cooling is not performed from the temperature detector to the entrance side of the rolling mill, even if the lubricating oil is applied to the plate surface at a rolling speed of 500 m / min or more, the influence on the plate temperature at the roll bite inlet can be ignored. Accordingly, we do it in the same manner by using a _T O _{'= T} O -T _i instead of the aforementioned _{T O.}

[Reference example]
The reference example is an embodiment of the first invention of the original patent application (1999 patent application No. 6029). This invention is different from the invention of the reference example (the first invention described above) in that the rolled sheet is not cooled, but both are a rolling mill, a measuring device, rolling conditions, a friction coefficient / deformation resistance estimating method, and a roll bite temperature. There are many common parts such as the estimation of the rise and the control by the rolling reduction of the temperature rise in the roll tool. Therefore, a reference example will be described below as a reference of the present invention. In the case of the present invention, the temperature of the plate is detected by the temperature detector even on the entrance side of the rolling mill. Since there is no water cooling between the temperature detector and the rolling mill entrance side, even if the lubricating oil is applied to the plate surface at a rolling speed of 500 m / min or more, the influence on the plate temperature at the roll bite inlet is ignored. it can.
The cold tandem rolling mill used is a tandem rolling mill consisting of the same five stands as shown in FIG. 1. Table 1 shows the rolling conditions of the fourth stand as a stand where heat scratches occur.

  Under the operating conditions, when a large number of coils of the same size are rolled under the same rolling conditions, the average temperature of the work roll rises and the plate temperature on the fourth stand outlet side rises. From operation data so far, it is empirically known that heat scratches frequently occur when the plate temperature on the outlet side of the fourth stand is about 160 ° C. or higher. Therefore, the invention of this reference example was applied and its effect was experimentally investigated.

The limit temperature T _Lim, which is the lowest roll bite outlet plate temperature at which heat scratches are obtained in advance, was 162 ° C., and the heat scratch control target temperature was T _L = 162−4 = 158 ° C. Also, the control cycle of the reduction ratio for heat scratch control is 30 seconds, the sampling time is 5 seconds, the plate temperature at the roll bite outlet is calculated from the data of 30 seconds (six) during that period, and linear regression is performed, 30 seconds The subsequent roll bite outlet plate temperature was determined and used as the estimated plate temperature _Tf .

FIG. 3 is a diagram showing the effect of the invention of the reference example, and shows the relationship between the number of rolling coils and the plate temperature on the fourth stand roll tool outlet side. In FIG. 3, ○ indicates the case of the conventional rolling method, and ● indicates the case of applying the invention of the reference example. In the conventional rolling method, the estimated value of the roll bite outlet plate temperature is 160 ° C. or more when the number of coils is eleven, and there is a risk of heat scratching. Therefore, the work roll speed is reduced to 900 m · min ⁻¹ to operate. It was. However, by applying this invention, the reduction rate is changed from 28.6% to 23-25%, so that the plate temperature does not exceed 158 ° C. even with 30 coils and the work roll speed is reduced. It was rolled without any heat treatment and, of course, no heat scratch was generated. Of course, when the rolling reduction rate of the fourth stand is changed, the plate thickness (product plate thickness) changes, so it goes without saying that the insufficient rolling reduction amount needs to be adjusted by another stand. Preferably, the adjustment is performed with the first stand that generates the least heat scratches.

Since the accuracy deteriorated when the plate cooling conditions of the third stand were significantly changed, the present invention was applied. That is, the limit temperature ΔT _Lim, which is the roll bite rise temperature at which heat scratches are obtained in advance by experiments, is 108 ° C., and the heat scratch control target temperature is ΔT _L = 108−4 = 104 ° C. Also, the rolling cycle control cycle is 30 seconds, the sampling time is 5 seconds, the roll bite rise temperature is calculated from the data of 30 seconds (six) during that period, and linear regression is performed to obtain the roll bite rise temperature after 30 seconds. This was used as the estimated value ΔT _f of the plate temperature. As a result, no heat scratch was generated even when the plate cooling conditions of the third stand were significantly changed.

It is a block diagram which shows an example of the cold tandem rolling mill which implements this invention. It is an enlarged view of 2 stands in a cold tandem rolling mill. It is a graph which shows the relationship between the roll bite exit temperature of a rolling material, and the number of rolling coils.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Work roll 13 Intermediate roll 15 Backup roll 17 Plate thickness detector 20 Plate cooling device 22 Draining and tension detection device 24 Temperature detector 26 Lubricating oil supply device S Rolling material (plate)

Claims (1)

A rolling method in a cold tandem rolling mill, in which a stand where heat scratches are likely to occur is designated in advance, and rolling is performed in the next step while air cooling is performed between the sheet temperature detector from the rolling mill roll bite exit side.
(B) First step of detecting stand entry / exit side plate temperature, rolling load, work roll speed, stand exit side plate speed, stand entry / exit side plate thickness, stand entry / exit side tension, respectively (b) Stand entry / exit delivery side temperature, stand delivery side thickness, and the detected value of the stand delivery side speed, setting the estimated temperature rise [Delta] T _f in the second step (c) said roll bite for determining temperature rise [Delta] T _f in the roll bite in the rolling state in advance if you exceed the heat scratch control target temperature [Delta] T _L has, rolling load of the first step, the work roll speed, stand delivery side speed, thickness at delivery side of the stand incident and, and from the detected value of the stand entry-exit side tension of the rolling material 3rd step to obtain friction coefficient and deformation resistance (d) Rolled shape by detection value of 3rd step, friction coefficient and deformation resistance 'And the plate temperature increases the _{T m} of if you change the reduction ratio' leaf temperature increase _{T E} in the roll bite in seeking, fourth obtaining the reduction ratio which _{ΔT L -ΔT f ≧ T m '} -T E' Step (e) Fifth step of controlling the reduction ratio using the reduction ratio obtained in the fourth step as a target value

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