JPH0947808A - Hot finish rolling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defective quality due to the growth of surface scale by comparing the surface temps. of a material to be rolled which are measured on the inlet and outlet sides of a rolling mill with numerical values calculated by calculation and operating them in continuous hot rolling. SOLUTION: A scale breaker 12 is arranged in front of a continuous hot finishing mill 10, the surface scale of the material 8 to be rolled is peeled, then the surface temp. of the material is measured with a thermometer 18 on the inlet side of the finishing and rolling is executed by the rolling mill 10. After that, the surface temp. of the material is measured with the thermometer 20 on the outlet side of finishing. Next, the material is cooled with a cooling system 14 and coiled with a coiler 16. For calculating the temp. of the material after rolling based on the temp. on the inlet side of finishing and exthermic/endothermic phenomenon model, when the min. value of the temp. on the outlet side of finishing which is calculated using the heat transfer coefficient between the material and the rolls that is used for the heat transfer phenomenon model on the surface of the material when the thickness of scale between the material and the rolls is made zero is smaller than a prescribed value, an operating condition is changed and the min. value is made larger than the prescribed value and, when the min. value is larger, the value is made smaller than the prescribed value.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hot finish rolling method for rolling a material to be rolled by a plurality of continuous rolling mills,
In particular, with respect to the temperature decrease, the desired finish outlet temperature FDT
(Finisher-mill Delivery Temperature) is secured, and the temperature F on the entry side of the finishing rolling mill is set so that the surface scale between stands does not become abnormally thick even if the temperature rises.
It is possible to properly determine, on-line or off-line, the operational amount of ET (Finisher-mill Entry Temperature), rolling speed, the number of inter-stand cooling devices used, etc. in hot finish rolling of steel materials, for example. The hot finish rolling method.

[0002]

2. Description of the Related Art In hot rolling of steel or the like, it is important to control the material temperature. Furthermore, surface oxide film (called scale)
It is necessary to pay close attention to the thickness of the product because of its quality.

The conventional problem is that an error occurs in the control of the material surface temperature during rolling, and if a temperature error occurs, both low and high deviations are problems.

Another problem is that on-line scale thickness measurement is not possible with known techniques. If it is off-line, a method of cutting and measuring the material such as observing the cut surface of the material with a microscope, and an analytical method of irradiating various radiations and measuring from the reaction are known. However, you can't chop the material online. Moreover, there are many problems such as being processed, having a high temperature, moving materials, and being in a bad environment with water vapor and dust.

When the material temperature deviates to a higher temperature, scale formation is accelerated, so that flaws due to scale become remarkable. On the other hand, if the temperature deviates low, the FDT cannot be secured. That is, in hot rolling, A2, which is the transformation point of the crystal structure,
Since it is processed (rolled) at a temperature above the transformation point,
Even if processing is performed at a temperature lower than this temperature, a desired material cannot be obtained.

The reason why it is difficult to measure and calculate the material temperature is as follows. That is, the time change of the material temperature during rolling influences the crystal structure inside the material, which greatly affects the mechanical properties, that is, the quality of the material. As described above, in hot rolling, the crystal structure is the transformation point A
A temperature above two transformation points must be ensured during rolling.

For such temperature control, it is necessary to measure the temperature. However, since the environmental conditions of hot rolling are poor, it is often difficult to measure with a radiation thermometer or the like.

Therefore, the prediction by calculation is performed. That is, the temperature is estimated by calculation such as solving the heat transfer equation by the difference method, etc., and the temperature is controlled by this estimated value. A typical position is the rolling mill biting position (roll bite).

[0009] The general theory of such steel material temperature calculation is described in Chapter 4 (59) of the 2nd edition of the basic edition of "The Steel Material Online Temperature Control Subcommittee Report of the 95th Thermo-Economic Committee of the Iron and Steel Institute of Japan" (November 1994). Pp.-65).

On the other hand, as a patent application for calculating the temperature on the delivery side of the hot rolling finish rolling mill, for example, Japanese Patent Application Laid-Open No. 5-501.
There is 43. This is to correct the rolling temperature prediction value based on the difference between the surface temperature of the steel sheet measured after the rough rolling and the estimated surface temperature based on the rolling temperature prediction. It is a kind.

In such temperature calculation, calculation formulas that model various physical phenomena are used. Two models are important in this calculation: a model of the surface heat transfer phenomenon on the surface of the steel sheet, and a model of the heat generation / endotherm phenomenon inside the steel sheet. As the model of the surface heat transfer phenomenon, the heat transfer coefficient between air and the steel plate surface, the heat transfer coefficient between cooling water and the steel plate surface, and the contact heat transfer coefficient between the rolling roll and the steel plate surface are typical physical constants (parameters). The surface heat transfer model equation, the friction coefficient between the rolling roll and the steel plate surface, the conversion efficiency at which the friction energy is converted into heat energy, and the friction heat generation with the rate at which the friction heat energy is distributed to the steel plate surface as parameters. There is a model formula. Further, the latter model of heat generation / heat absorption phenomenon includes deformation heat resistance, conversion efficiency by which work deformation is converted into heat energy in the steel plate, and work heat generation using a function indicating the distribution of heat energy in the steel plate or a simplified constant as parameters. There are model formulas and material change model formulas that use a function or a simplified constant as a parameter to describe the change in the thermal energy inside the steel product that changes the crystal state inside the steel product due to the temperature such as transformation heat generation.

In order to perform highly accurate temperature prediction calculation, the model formula should be a formula that accurately expresses an actual physical phenomenon, and
You must substitute the parameter constant of the model formula that matches the value in the online state. Many parameters included in these models are determined from theory or an experiment in which the rolling state is reproduced offline, and correction learning of parameter values is performed online to correct the parameters to more appropriate values.

However, regarding the thickness of the surface scale, it is difficult to grasp the actual condition even after making corrections by theory, experiment, and learning. Especially when modeling the phenomenon of the roll bite in the state where the material is caught in the rolling mill, which is a problem in the calculation of temperature and scale thickness,
Since the scale thickness of the surface is unknown, a calculation error occurs in the amount of contact heat transfer.

That is, in hot rolling of steel, the material temperature is 1
Since it is at a level of 000 ° C., the oxidation reaction proceeds on the surface of the material in the atmosphere, and an oxide film called scale is generated, which hinders hot rolling. The scale thickness is a factor that changes the contact heat transfer coefficient between the roll and the material surface at the roll biting portion. That is, since the scale acts as a thermal resistance (heat insulating layer) existing on the surface in the heat transfer phenomenon, the surface temperature greatly changes with the scale thickness. That is, since the amount of heat transfer in contact with the roll changes depending on the scale thickness, the material surface temperature on the roll exit side changes greatly. For example, in the 7-stage continuous rolling in which the thickness of the material to be rolled is reduced from 30 mm to 2 mm, when the material speed on the delivery side of the 7th stand is 100 mpm, the scale thickness of the roll bite of all stands is 1 μm.
When the calculation is performed by changing the thickness from 100 μm to 100 μm, the surface temperature has a difference of 80 ° C. at the minimum and maximum scale thicknesses. As described above, the function of the scale as the surface heat insulating layer changes the surface temperature greatly, and therefore, it is necessary to accurately estimate the scale thickness in the temperature calculation.

The generation of scale itself is a problem in terms of surface quality. That is, if the scale is nonuniformly attached and rolled, various problems relating to the material surface quality occur. For example, an uneven scale creates an irregular pattern on the surface,
This is a quality problem. Further, the partially peeled scale collides with the rolling roll or is rolled up, thereby damaging the roll surface. Further, the peeled scale piece is rolled up, causing a flaw on the surface of the material.

A scale breaker is installed to evenly peel off the scale, which is the source of the problem. This scale breaker, which rarely uses a mechanical peeling machine such as a brush, usually uses high-pressure jet water of 100 to 300 Kg / mm ² .

FIG. 1 shows an example of a six-stand continuous hot finishing mill 10 and the equipment layout around it. As shown in the figure, the scale breaker (S
It is usual that B) 12 is provided, the surface scale of the material 8 to be rolled is peeled off, and then the material is rolled by the rolling mill 10.

In FIG. 1, 14 is a cooling device, 16 is a take-up device, and 18 and 20 are finish-inside material surface thermometer (Sin) and finish-outside material surface thermometer (Sout), respectively.
It is.

In recent years, a scale breaker is often arranged in the middle of the rolling stand. However, this scale breaker cannot be used extensively. The reason is that the surface of the material is supercooled by a large amount of water in the high-pressure water stream, and there is a risk that the material temperature deviates from the material temperature to be maintained for hot rolling. Therefore, grasp the scale generation state of the material surface,
If necessary, a scale breaker or strip cooling system between stands should be used.

[0020]

However, in the past, since the generation state of scale was unknown, it was used with empirical know-how. The generation and growth of scale strongly depends on the material surface temperature. However, the surface temperature of this material is not constant in the long material being rolled. The temperature decreases from the front end to the tail end of the material by air cooling, and the degree of the decrease changes depending on the acceleration / deceleration of the rolling speed and is not monotonous.

Further, the material has a maximum / minimum portion of temperature as shown in FIG. 2 due to uneven heating in the heating furnace in the preceding stage. FIG. 2 shows a change state of the material surface temperature (temperature measured by the thermometer 18 or 20 in FIG. 1) measured at a fixed point in the longitudinal direction of the material. From FIG. 2, it can be easily inferred that the scale thickness varies depending on the position of the long material. Since the scale thickness differs due to such a difference in temperature and its history (temperature change), the scale thickness cannot be directly estimated even if the temperature is measured at several points.

Considering the effect of the scale on the material temperature with the roll bite, it is estimated that there is a positive feedback non-linear effect due to the thickness of the scale. That is, when the scale of the roll bite is thin, heat is removed, the temperature drops, and the scale does not grow. Therefore, the scale of the roll bite remains thin, the heat is removed further, the temperature further decreases, and the scale does not grow at all. On the other hand, if the scale of the roll bite is thick, heat removal due to heat insulation (heat retention) by the scale decreases, the effect of heat generation during processing increases, the temperature rises, and the scale grows. Then, the scale of the roll bite becomes thicker, the heat insulation (heat retention) effect is further enhanced, the temperature is further raised, and the scale is further grown.

Therefore, the temperature drops or rises in a snowball manner with a certain scale thickness as a boundary, so that the temperature suddenly changes with a slight change in conditions. Such a phenomenon also makes it difficult to grasp the situation. It is presumed that such a phenomenon occurs at the maximum value or the minimum value of the temperature in a long steel plate, but conventionally, since a thermometer is not installed before and after each rolling roll, the scale thickness is quantified. I can't understand it.

As described above, the scale thickness is a value that varies in the longitudinal direction of the material, and also changes depending on the history of temperature changes. Therefore, by grasping the temperature change history as shown in FIG.
From this, it is necessary to calculate the thickness increase due to the oxidation reaction. In FIG. 3, Sin is the material temperature thermometer 1 on the finishing entry side.
8 is a disposition position, SB is a disposition position of the scale breaker 12, F1 to F6 are disposition positions of the finishing first to sixth stands, and Sout is a disposition position of the finishing delivery side material surface thermometer 20. .

The temperature history can be obtained by calculation such as solving the heat transfer equation by the difference method. Also, due to the progress of oxidation,
As shown in the following equation, the scale thickness s is an exponential function with respect to the temperature T and becomes thicker with a square root with respect to the elapsed time t.
This is known from the theory and experiments in which the oxidation reaction is regarded as a thermal diffusion phenomenon.

S = C1√ (t) × {exp (C2 / T)} (1) Here, C1 and C2 are reaction constants.

When the surface temperature changes, it suffices to add the changes in the scale thickness s for each minute time interval obtained from the relationship of equation (1). This is also a known calculation method.
FIG. 4 shows an example of calculating the change in the material surface scale thickness s corresponding to the temperature calculation history of FIG. 3 by this method.

A problem in the calculation of the temperature and the scale thickness is the calculation when the material is caught in the rolling mill (roll bite). In the roll bite, several physical phenomena occur under the condition of high temperature and high speed, and calculation of temperature and scale thickness requires a formula to model them.
The finite element method and the like, which mechanically predict and calculate the deformation of the scale layer, are also under study, but they are not in the practical stage. Regarding the model of temperature calculation, there is a known model based on the physical law as described above, but regarding the model of how the scale thickness in the roll bite for scale thickness calculation changes, the entire material thickness is rolled. Only a simple model is known in which the thinning rate is the same as the thinning rate.

However, in the roll bite, the material bulk (inside) having a different composition and the surface scale should not be thinned at the same ratio, and the above simple model is not established. Also, the surface temperature is required when calculating the scale thickness, but since the surface temperature itself is affected by the scale thickness, either the temperature or the scale thickness (usually the scale thickness) In many cases, extremely large error wrinkles occur.

The present invention has been made to solve the above-mentioned conventional problems, and there are problems due to the temperature deviation of the material, that is, the FDT falls below the target temperature to cause defective material properties, and the temperature between the stands. Is beyond the limit, and the growth of the surface scale becomes remarkable, and it is possible to prevent the deterioration of the material surface quality.

A second object of the present invention is to make it possible to accurately measure the scale thickness in a roll bite immediately after being rolled by a single stand.

[0032]

SUMMARY OF THE INVENTION The present invention is a hot finish rolling method for rolling a material to be rolled by a plurality of continuous rolling mills. In calculating the temperature of the rolled material after rolling based on the model of heat transfer phenomenon on the surface and the exothermic / endothermic phenomenon model of the rolled material, the thickness of the scale between the rolled material and the work roll is zero, Or using the heat transfer coefficient between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the surface of the material to be rolled when the minimum value is set, while calculating the minimum value of the exit side temperature of the finishing rolling mill. , The heat transfer coefficient between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the surface of the material to be rolled when the thickness of the scale between the material to be rolled and the work roll is set to infinity or the maximum value. Calculate the temperature between the stands using If the minimum value of the calculated finish rolling mill outlet side temperature is less than or equal to a predetermined value, the operating conditions are changed to increase the finish rolling mill outlet side temperature above a predetermined value, and the calculated temperature between the stands is When the temperature is equal to or more than the predetermined value, the operating condition is changed so that the temperature between the stands is smaller than the predetermined value, thereby achieving the first object.

Further, the scale thickness between the stands is obtained based on the calculated temperature between the stands, and when the calculated minimum value of the exit side temperature of the finish rolling mill is not more than a predetermined value, the operating condition is changed. If the temperature of the finishing rolling mill is higher than a predetermined value and the calculated scale thickness between the stands is greater than or equal to a predetermined value, the operating conditions are changed to make the scale thickness between the stands smaller than the predetermined value. In this way, the above first object is also achieved.

Further, in the hot finish rolling method of rolling the material to be rolled by a plurality of continuous rolling mills, the measured value of the temperature of the material to be rolled at the entrance side of any rolling mill and the heat transfer phenomenon on the surface of the material to be rolled. In calculating the post-rolling temperature of the material to be rolled based on the model and the model of heat generation and heat absorption of the material to be rolled, between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the surface of the material to be rolled Changing the heat transfer coefficient of, the calculated temperature, the heat transfer coefficient when the measured value of the material to be rolled on the rolling mill outlet side is substantially equal to,
The second object is achieved by calculating the scale thickness of the material to be rolled based on the value of the heat transfer coefficient.

Further, when the calculated scale thickness is equal to or larger than a predetermined value, an alarm is issued.

The operation of the present invention will be described below.

It is difficult to measure the scale thickness s online. However, it suffices if the maximum and minimum influences of the scale thickness on the material temperature can be properly suppressed and the operating condition can be set to the safe side, and the strict thickness value is not always necessary during the operation. The scale thickness affects the contact heat transfer between the scale surface and the roll in the roll bite. Therefore, if the upper and lower limits of the contact heat transfer coefficient corresponding to the maximum thickness and the minimum thickness of the scale are suppressed, two worst cases of the temperature maximum line and the temperature minimum line can be simulated, and the upper and lower limit ranges of operating conditions can be determined.

Now, regarding the contact heat transfer coefficient k between the rolling roll and the steel plate surface, the contact time (roll bite time) t _B
And the thermal characteristics of the contact material (thermal conductivity λ, specific heat c, density ρ)
Can be represented by

Now, consider a temperature change of two objects which have started contact with each other through a heat insulating layer having a thickness s at time t = 0. It is assumed that the sandwiched heat insulating layer (oxide film) has a linear temperature distribution in which the interfacial temperatures of the objects in contact are connected by a straight line. This is an assumption that can be tolerated by the phenomenon of a roll bite in which the interface is forcibly contacted by an external force for a short time. Under this assumption, the known analytical solution of the heat transfer equation (including the Gaussian distribution error function Φ) is transformed.

From this and the definition of heat transfer, the contact heat transfer coefficient k is calculated as follows: contact time (roll bite time) t _B , heat insulating layer (scale) thickness s, thermal characteristics of materials involved in contact (thermal conductivity λ , Specific heat c, specific gravity ρ) can be expressed as the following equation.

K = [b ₃ / {2√ (t _B )}] · [(e ⁿ² / n) (1-Φ (n))-(1 / n) + {2 / √ (π)}] (2) n = (2λ ₂ / b ₃ ) · {√ (t _B ) / s} (3) Here, the subscript 1 is the physical property value of the hot rolling roll, and the subscript 2 is the oxide of iron (scale). And the subscript 3 indicates the physical property value of the steel material.

From the limit of scale thickness s = 0,
The upper limit value k _u of the contact heat transfer coefficient is analytically expressed by the following equation (4), and the contact heat transfer is performed from the limit (contact between the lump of the scale and the roll) when the scale thickness s = ∞ (infinity). The lower limit value k _{l of the} coefficient is analytically expressed by the following equation (5).

K _u = b ₃ / √ (πt _B ) ... (4) k _l = √ [{1 / (πt _B )} · {2b ₁ b ₂ / (b ₁ + b ₂ )}] (5) Here, b = √ (cρλ) (6).

The approximate expression of the contact heat transfer coefficient at these scale thicknesses s and the expression for giving the upper and lower limits of the contact heat transfer coefficient are, for example, "Archiv fuer das Eisenhuettenwe".
n, 40. Jahrgaug, Heft 10-Oktober 19
69 ", pages 821-827, Von O
"Berechnung der Waermedurch" by skar Pawelski
gangszahl fuer das Warmwalzen und Schmieden ”
Paper (hereinafter simply referred to as Pawelski's paper)
The above equation (2) is the equation (35) in Pawelski's paper, the above equation (3) is the same equation (34), the above equation (4) is the same equation (38), and the above equation (5). Similarly, the equation corresponds to the equation (50), and the above equation (6) also corresponds to the equation (33).

The above relationship is based on the hot rolling roll, iron oxide,
Typical thermophysical properties of steel materials (b value of hot rolling roll: b ₁ =
210 [Kcal / m ² · h ^1/2 · ° C], b value of iron oxide (scale): b ₂ = 35 [Kcal / m ² · h ^1/2 ·
℃], also λ value: λ ₂ = 1.4 [Kcal / m ² · h
^1/2・ ° C], b value of steel material: b ₃ = 210 [Kcal /
m ² · h ^1/2 · ° C]) is shown in FIG. From FIG. 5, it is understood that the roll contact heat transfer coefficient k is given if the roll bite time t _B and the scale thickness s are given.

The first invention utilizes the above relationships,
Using the heat transfer coefficient between the work material and the work roll used in the model of the heat transfer phenomenon on the work material surface when the thickness of the scale between the work material and the work roll is set to zero or the minimum value , It is used as a model of heat transfer phenomenon on the surface of the material to be rolled when the minimum value of the exit side temperature of the finishing rolling mill is calculated and the thickness of the scale between the material to be rolled and the work roll is set to infinity or maximum value. The temperature between the stands is calculated using the heat transfer coefficient between the rolling material and the work rolls,
If the calculated minimum value of the exit side temperature of the finish rolling mill is a predetermined time, the operating conditions are changed to make the exit side temperature of the finish rolling mill larger than a predetermined value, and the calculated temperature between the stands is predetermined. When the value is equal to or more than the value, the operating condition is changed so that the temperature between the stands is smaller than the predetermined value. Therefore, the minimum value of the exit side temperature of the finishing rolling mill is lower than the target temperature, and a material property defective portion occurs,
Since the inter-stand temperature exceeds the limit and the growth of the surface scale becomes remarkable, it is possible to prevent the material surface quality from being reduced.

When changing the operating conditions, the FET
It is conceivable that the number of finishing scale breakers used may be increased or decreased, the number of finishing scale breakers used may be increased or decreased, or the number of strip cooling water injection devices between stands may be increased or decreased. When the FET or rolling speed is increased, the temperature rises, and when the number of finishing scale breakers or strip cooling water injection devices between stands is increased, the temperature drops.

Further, the scale thickness between the stands is obtained based on the calculated temperature between the stands, and when the calculated scale thickness between the stands is equal to or more than a predetermined value, the operating condition is changed to change the space between the stands. If the scale thickness is set smaller than a predetermined value, the scale thickness between the stands can be directly controlled.

Further, when the temperature on the outlet side of the roll is calculated on the basis of the measured temperature on the inlet side of the rolling roll, while the temperature on the outlet side is measured, the difference between the measured value and the calculated value is the scale thickness s. Should be zero when calculated with an appropriate assumption. Second
The invention uses this idea, and since the difference in scale thickness changes the temperature immediately after rolling, the scale thickness is determined in reverse from the temperature.

For example, it is installed on the entrance side of a hot rolling stand.
The measured value Tin of the thermometer is set as the initial temperature
Calculation model for surface heat transfer, friction heat generation, and processing heat generation
Out. In addition, air and the heat transfer coefficient of the steel plate surface and cooling water
The heat transfer coefficient of the steel plate surface is dependent on the temperature change in the roll bite.
Is negligible and can be ignored.)
Ask for. To obtain the contact heat transfer coefficient k of the roll,
Roll bite time t _BAnd scale thickness s are required
You. Roll bite time t_BIs calculated
On the other hand, the scale thickness s is unknown. Therefore, s is appropriate
Calculate based on the assumption. A typical example thereof is shown in FIG. this
Is plain steel with a thickness of 10 mm to 5 mm, 100 mpm
When rolling at the exit speed of the
The scale thickness s is assumed to be 0, 50 and ∞ μm, respectively.
Then, from the equations (4), (2) and (5),
The results obtained by calculating the numbers are shown. scale
In the calculation of thickness s = 0 μm, formula (4), scale thickness s =
In the calculation of 50 μm, the formula (2) is used to calculate the scale thickness s = ∞.
Equation (5) is used in the calculation.

The mark ● in FIG. 6 indicates the measured temperature Tme at that time.
It can be seen that the scale thickness s is larger than 50 μm. Next, the scale thickness s is set to 50, 10.
FIG. 7 shows the result of calculation assuming 0 and ∞ μm. Figure 7
From the above, it can be seen that the scale thickness s is thicker than 100 μm. By repeating such an operation, that is, an operation of narrowing the range of the scale thickness s by half, for example, it is possible to search for the scale thickness s with a desired accuracy. In this way, the scale thickness s can be obtained with the required accuracy.

In the second invention, based on such knowledge,
When the heat transfer coefficient between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the surface of the material to be rolled is changed, and the calculated temperature substantially matches the measured value of the material to be rolled on the outlet side of the rolling mill. Since the heat transfer coefficient is calculated and the thickness of the scale of the material to be rolled is calculated based on the value of the heat transfer coefficient, the scale thickness of the material to be rolled can be accurately calculated.

In operation, the absolute value of the scale thickness s is not always necessary, and it is desirable to give a warning when the surface of the material becomes hot and the oxidation reaction progresses significantly. If the operator performs an operation to add spray between stands or use of a scale breaker by the warning, it is possible to prevent the occurrence of surface flaw. Therefore, the upper limit value of the scale thickness between the stands is experimentally or theoretically given, and when the scale thickness s exceeding the upper limit value is obtained as a result of the search calculation, the material peroxidation alarm may be issued.

[0054]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 8 shows the procedure for determining the operation according to the method of the first invention. The left side of FIG. 8 is the prevention of the case where the temperature is too low to cause FDT cracking, and the right side is the prevention of the case where the temperature is too high between the stands and a thick scale which causes a problem in surface quality is formed.

First, the left side of the figure will be described. If all roll bites of all finishing stands are assumed to have scale thickness s = 0, the worst case simulation will be when the contact heat transfer between the roll and the material is maximum and the material temperature is the lowest. . FD obtained in this case
If T is greater than or equal to the desired FDTobj, then the actual FDT
Is guaranteed to be more than that. Therefore, the simulation is performed in step 110 under the initial operating conditions given in step 100. If the result of determination in step 120 is less than the desired value FDTobj, in step 130, for example, the FET is turned up. The operating conditions are changed by any one of or a combination of increasing the rolling speed, reducing the number of finishing scale breakers FSB used, and reducing the number of inter-stand strip cooling water injection device SC used.

In this way, the conditions under which the FDT becomes the desired value FDTobj are obtained by trial and error. At the time of actual rolling, a scale having a non-zero thickness is generated, so that the desired value FDTobj can be secured. Here, the assumption that the scale thickness is 0 specifically means that the contact heat transfer coefficient upper limit value k _u given by the above-mentioned equation (4) is used in the calculation. Experimentally the minimum scale thickness s for roll bite
_{When min} is known, as shown by the broken line in FIG.
If the equation (2) is used instead of the equation (4) and the minimum value s _min is substituted for the scale thickness for calculation, the accuracy of the simulation is improved.

On the other hand, on the contrary, the temperature may be too high, which may cause a problem in surface quality. This is the second worst case, in which the material surface is covered with a thick scale and the surface heat insulation effect is maximum and the temperature rises. The right side of FIG. 8 shows the work in this case. In this work, it is assumed that the scale thickness is ∞ (contact between the roll and the scale lump). Specifically, step 140
Then, the lower limit value k of the contact heat transfer coefficient given by the above equation (5)
It is to use _l for calculation. Experimentally, when the maximum scale thickness s _max on the roll bite is known,
As shown by the broken line in FIG. 8, if the equation (2) is used instead of the equation (5) and the maximum value s _max is substituted for the scale thickness for calculation, the accuracy of the simulation is improved.

The temperature check portion (position) obtained from the calculation result is the material surface temperature FMT between the stands of the finish rolling mill, and its maximum value FMTmax is particularly noted.

Specifically, the limit temperature of the FMT is investigated in advance by experiments, theory, etc., that is, the material surface temperature between the stands exceeds 1200 ° C., which is not good. If it is determined in step 150, this limit temperature FMT
If it exceeds bount, in step 160, for example, lowering the FET, lowering the rolling speed, the finishing scale breaker FSB of the previous stage (upstream) at the position where FMTmax is reached.
The operation is changed by either increasing the number of used strip cooling water injection devices SC between stands or increasing the number of used strip cooling water injection devices SC between stands.

In step 140, the scale thickness is calculated from the temperature by using the temperature change obtained above.
You can simulate changes in scale between stands. As the maximum value s _{max at} that time, a value that has been previously investigated by experiments, theory or the like can be used. Also in this case, the scale thickness limit value between the stands, which is obtained from an experiment such as sudden stop of the material during rolling, that is, the limit value s _bound which causes a problem on the surface quality of the scale flaw when the limit is exceeded, is set in advance. Keep it down. When it is determined in step 150 that the maximum scale thickness s _max between the stands obtained from the scale thickness calculation exceeds the limit value s _bound ,
At step 160, the above operation change is performed.

In this way, the case where the material surface temperature becomes the minimum is calculated by the former worst case simulation,
The lower limit of the finish outlet temperature FDT is estimated, and the outlet temperature is secured by raising this limit. In the latter worst case simulation, the surface material temperature is used to estimate the maximum temperature rise between the stands of the finishing mill. Since this is the case where the scale becomes thickest between the stands, the temperature FMT in this case, or directly, the scale thickness s, is set to be equal to or less than the previously known limit.

It should be noted that, since the two operation changes are reverse operations, one change gives a good result in improving the worst case of the former, but the other worst case does not. That is the opposite effect. Therefore, in steps 170 to 190, it is necessary to find the operation change condition that satisfies both conditions by trial and error. Here, in the worst case of the former, it is sufficient if the book edge is matched at the last FDT, and in the worst case of the latter, anything is acceptable at the end as long as the intermediate temperature is lowered (high temperature is also possible), so the condition to satisfy both is found. It is possible. For example, in the latter worst case, it is sufficient to lower the temperature at the pre-finishing stage (F1, F2 stand) position where the temperature is high. It can be said that it is not used for securing.

In the simulation of the present invention, it is possible to carry out the simulation under the conditions that consider the non-uniformity of the temperature of the material described in the problem, that is, the maximum and minimum parts of the temperature for non-uniform heating in the heating furnace. Give more effective results. That is, since FDT cracks and poor surface quality almost always occur at the extreme values of the temperature shown in FIG. 2, it is desirable to carry out the present invention under the conditions of these extreme values.

FIG. 9 shows a solid line in which the strip coolant between the stands is changed to OFF according to the present invention for an operation example in which the FDTobj is lower than the stands F3 to F7 as shown by a broken line before the present invention is carried out. As shown, an example in which the FDT is secured will be shown. FIG. 10 is an example of confirming that the upper temperature limit is equal to or less than FMTbound under the new condition of the present invention of FIG.

In FIG. 11, before the present invention, as shown by the broken line, for the operation example in which the FMTbound was exceeded on the exit side of the stand F3, the strip coolant on the F2 exit side was changed to ON according to the present invention. Then, as shown by the solid line, FMTbo
This is an example of avoiding excess of und. FIG. 12 shows an example of confirming that the temperature lower limit is equal to or higher than FDT under the new condition according to the present invention of FIG.

FIG. 13 shows that, under both conditions of the upper limit calculated by the equation (4) and the lower limit calculated by the equation (5),
It is a diagram showing a simulation example that satisfies the temperature conditions.

FIG. 14 is a diagram showing an example in which the scale thickness is calculated under the same conditions as in FIG.

FIG. 15 shows a layout for carrying out the second invention. Compared with FIG. 1, inter-stand thermometers 31 to 35, a calculation section 40 and an alarm 42 are added. In the figure, 50 is a finish rolling control device.

The calculation of the scale thickness in this embodiment is executed according to the procedure shown in FIG.

That is, first, in step 200, the rolling condition of the single stand is read, and in step 205, the rolling condition of the material to be rolled is read. Next, at step 210, the measured value Tin by the inlet side thermometer and the measured value Tmea by the outlet side thermometer.
Is read, and at step 215, each physical property value is set.

Next, at step 220, the scale thickness s = 0 in the above equation (5), an appropriate assumed thickness in the above equation (2),
In the above equation (5), the contact heat transfer coefficient k is calculated with s = ∞,
From this the temperature Tcalk is calculated.

Next, in step 230, as shown in FIG. 6, of the three calculated values corresponding to each scale thickness, two combinations sandwiching the measured value Tmea are selected. Next, the routine proceeds to step 240, where as shown in FIG. 7, the intermediate value scale thickness s of the combination is substituted into the equation (2) again to obtain a new calculated value Tcalk. Then step 25
The process proceeds to 0 and it is determined whether the calculated new Tcalk has a sufficiently small error with respect to the measured value Tmea. If the determination result is negative, the process proceeds to step 260, and the value corresponding to the new calculated value Tcalk and the values of the two preceding and succeeding scale thicknesses s are set as three calculated values, and the above-described step 230 is performed.
Return to

On the other hand, if the determination result of step 250 is positive, the process proceeds to step 270, the scale thickness s at the time is output, and the calculation is completed.

In the present embodiment, since the operation of narrowing the range of the scale thickness s by half is repeated using the Newton method, it can be easily realized by a computer. The method of narrowing the range of the scale thickness s is not limited to this.

[0076]

As described above, according to the first aspect of the invention, the FD that has mainly occurred in the minimum value portion of the conventional material temperature.
Defects in internal quality (mechanical properties) due to T cracking and surface quality defects (scale flaws) that mainly occur at the maximum temperature portion do not occur, and production loss due to defective cutting is reduced.

Further, according to the second invention, it is possible to measure the scale thickness of the roll bite with high accuracy, and it is possible to control the surface quality such as burning scale flaws caused by the scale generation.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a six-stage continuous hot finishing mill to which the present invention is applied and a facility layout around it.

2 is a diagram showing an example of changes in the material surface temperature in the longitudinal direction of the material, which is measured at a fixed point by the thermometer of FIG.

FIG. 3 is a diagram showing an example of a history of changes in material surface temperature during a hot rolling process.

FIG. 4 is a diagram showing an example of estimation calculation of a change in material surface scale thickness corresponding to the temperature history in FIG.

FIG. 5 is a diagram showing an example of a relationship between a contact heat transfer coefficient between a rolling roll and a material for explaining the principle of the present invention.

FIG. 6 is a diagram showing a calculation example of the temperature change on the outlet side of the single stand when the scale thickness is assumed to be 0, 50 μm and ∞.

FIG. 7 is a diagram showing a calculation example of the temperature change on the outlet side of the single stand when the scale thickness is assumed to be 50 μm, 100 μm, and ∞.

FIG. 8 is a flowchart showing a processing procedure of an embodiment for changing operating conditions according to the first invention.

FIG. 9 is a diagram showing a comparison of material surface temperatures in finish rolling before and after the first invention is carried out.

FIG. 10 is a diagram showing an example in which a temperature upper limit is confirmed under the conditions of FIG.

FIG. 11 is a diagram showing an example in which a temperature upper limit is confirmed under the conditions of FIG.

12 is a diagram showing an example in which it is confirmed that the temperature lower limit is FDT or more at the upper limit of FIG.

FIG. 13 is a diagram showing an example of simulation in which temperature conditions are observed.

14 is a diagram showing an example in which the scale thickness is calculated under the same conditions as in FIG.

FIG. 15 is a diagram showing the configuration of an apparatus for carrying out the second invention.

FIG. 16 is a flowchart showing a processing procedure in the embodiment of the second invention.

[Explanation of symbols]

 8 ... Rolled material 10 ... Continuous hot finish rolling mill 12, SB ... Scale breaker 14 ... Cooling device 16 ... Winding device 18, Sin ... Finishing material surface temperature gauge FET ... Finishing material temperature 20, Sout ... Finishing Outgoing material surface thermometer FDT ... Finishing outgoing temperature 31-35 ... Inter-stand thermometer 40 ... Calculation unit 42 ... Alarm device 50 ... Finishing rolling control device

Claims (4)

[Claims] 1. A hot finish rolling method for rolling a material to be rolled by a plurality of continuous rolling mills, wherein the temperature of the material to be rolled on the finishing rolling mill entrance side and a model of a heat transfer phenomenon on the surface of the material to be rolled, In calculating the temperature of the rolled material after rolling based on the heat generation / endothermic phenomenon model of the rolled material, when the thickness of the scale between the rolled material and the work roll is set to zero or the minimum value, Using the heat transfer coefficient between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the surface of the rolled material, the minimum value of the temperature at the exit side of the finishing mill is calculated, and the material between the material to be rolled and the work roll is calculated. Calculate the temperature between stands using the heat transfer coefficient between the work material and the work roll used in the model of the heat transfer phenomenon on the work material surface when the scale thickness is infinite or maximum. And then the finish rolling calculated If the minimum value of the exit side temperature is less than or equal to the predetermined value, change the operating conditions to increase the finish rolling mill exit side temperature above the predetermined value, and if the calculated temperature between the stands is above the predetermined value, The hot finishing rolling method is characterized in that the operating conditions are changed to make the temperature between the stands smaller than a predetermined value. 2. A hot finish rolling method for rolling a material to be rolled by a plurality of continuous rolling mills, the temperature of the material to be rolled on the inlet side of the finishing rolling mill, and a model of a heat transfer phenomenon on the surface of the material to be rolled, When calculating the post-rolling temperature of the rolled material based on the exothermic / endothermic phenomenon model of the rolled material, when the thickness of the scale between the rolled material and the work roll is set to zero or the minimum value, Using the heat transfer coefficient between the material to be rolled and the work roll used in the model of the heat transfer phenomenon on the material surface, the minimum value of the temperature at the exit side of the finishing rolling mill is calculated, and the scale between the material to be rolled and the work roll is calculated. The temperature between the stands is calculated by using the heat transfer coefficient between the work material and the work roll used in the model of the heat transfer phenomenon on the work material surface when the thickness of the material is infinite or maximum. , Calculated between the stands The scale thickness between the stands is calculated based on the temperature of the stand, and when the calculated minimum value of the finish rolling mill outlet side temperature is less than or equal to a predetermined value, the operating conditions are changed to set the finish rolling mill outlet side temperature to a predetermined value. If the calculated scale thickness between the stands is larger than a predetermined value, the hot finish rolling method is characterized in that the operating conditions are changed to make the scale thickness between the stands smaller than the predetermined value. . 3. A hot finish rolling method for rolling a material to be rolled by a plurality of continuous rolling mills, wherein a measured value of the temperature of the material to be rolled at the entrance side of any rolling mill,
In calculating the temperature after rolling of the rolled material based on the model of heat transfer phenomenon on the surface of the rolled material and the model of heat generation / endotherm of the rolled material, it was used as a model of the heat transfer phenomenon on the surface of the rolled material. Change the heat transfer coefficient between the rolled material and the work rolls, and obtain the heat transfer coefficient when the calculated temperature substantially matches the measured value of the rolled material temperature at the rolling mill outlet side. A hot finish rolling method, characterized in that the scale thickness of the material to be rolled is calculated based on the value of. 4. The hot finishing rolling method according to claim 3, wherein an alarm is issued when the calculated scale thickness is a predetermined value or more.