JPH1071416A - Method for cooling steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a temperature distribution at the time of the completion of cooling, and to make it possible to apply to the plate with a large taper such as a large plate thickness ratio by determining the speed of a tip part passing through the inlet and the outlet of a cooling device after calculating it preliminarily, determining a specific acceleration or deceleration after calculating it, and controlling the transfer speed of the plate. SOLUTION: Solutions to be obtained are only transfer speeds at the time of the start and the completion of cooling, and a speed pattern can be obtained in a comparatively short time. Also, by changing the transfer speed straight, a control is performed so that a cooling pattern is increased and decreased at even intervals along the longitudinal direction of the plate. Therefore, a cooling time in each position in the longitudinal direction of the plate is changed almost continuously. Consequently, for a cooling completion temperature, the continuous temperature distribution can be obtained from a tip part to a rear end, and a uniform characteristic can be obtained to the whole of the tapered plate. Also, since the transfer speed is a constant acceleration pattern, it is easily used in an actual operation. Further, according to the taper size and the plate thickness of the plate, it can cope with a plate with a large taper as well with a proper cooling pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate having a thickness gradient in a longitudinal direction (hereinafter referred to as "tapered steel plate"). The present invention relates to a method for controlling a cooling end temperature distribution in a longitudinal direction of a steel sheet to a predetermined value.

[0002]

2. Description of the Related Art Tapered steel plates can greatly reduce the costs required for member processing and on-site welding work, and are expected to expand their application to bridge materials in addition to shipbuilding materials that have been applied so far. .

With respect to the taper ratio (maximum plate thickness / minimum plate thickness) and the plate thickness difference (maximum plate thickness-minimum plate thickness), particularly for bridge materials, a steel plate having a larger taper ratio or plate thickness difference (large taper) Needs).

In general, the performance of a steel sheet for the above-mentioned applications is required to have mechanical properties such as high strength and high toughness, and to reduce preheating work to facilitate on-site welding. In order to obtain these properties, the carbon equivalent is reduced, using a material of a predetermined steel type such as adding an alloy component, and performing controlled rolling to control the rolling temperature in each pass, and then under a predetermined temperature condition. It is essential to perform cooling control. Since the above characteristics depend on the cooling start temperature, the cooling end temperature, and the cooling rate, it is important to control these temperatures accurately.

In actual on-site operation, the management point of the cooling control is easier to control the cooling start temperature and the cooling end temperature than the cooling speed, and if the equipment specifications and operation specifications are determined, the cooling speed is controlled. Can be considered relatively small. For example, when the plate thickness is small or the cooling start temperature is low, the mechanical characteristics can be adjusted by setting the cooling end temperature to be high. That is, it is most important to control the cooling end temperature on site.

In a tapered steel sheet, in addition to the requirements for the steel type, rolling, and cooling, it is important to accurately control the start temperature and the end temperature of cooling over portions having different thicknesses. It is necessary to change each part in the board.

To cope with this problem, as described in, for example, "Iron and Steel", 72 (1986) 5, S348 (hereinafter referred to as Reference 1) and JP-A-62-166013, cooling has been started in advance. Temperature, cooling end temperature, cooling water amount, cooling zone length,
Set the sheet passing speed, measure the temperature of multiple dividing points in the longitudinal direction of the steel sheet on the cooling device entrance side, find the cooling conditions at each point by convergence calculation based on this, and correct the transport speed according to the sheet thickness A method of performing cooling control by performing the control is disclosed.

[0008] "Materials and Processes" Vol.8 (1995) P1353
As shown in (hereinafter referred to as Document 2), once the steel plate is stopped in the cooling device, cooling is started by simultaneously spraying cooling nozzles over the entire length of the plate, and then the steel plate is cooled from the thinner side. The cooling end temperature is controlled by carrying out the cooling device while decelerating it from the time when the leading end (thin side) reaches the cooling device outlet to the time when the rear end (thick side) reaches the outlet. A method of doing so is disclosed.

[0009]

Although the accuracy of the cooling end temperature of the tapered steel plate is improved by the above-mentioned method, the following problems remain.

For example, reference 1 and Japanese Patent Application Laid-Open No. Sho 62-16601
In the method disclosed in Japanese Patent Publication No. 3 (1993), at a plurality of division points in the longitudinal direction of the steel sheet, a conveyance speed pattern is obtained so that a cooling time corresponding to the thickness of each point is obtained. Since it is necessary to calculate the cooling time at each point by convergence calculation while solving the simultaneous equations, a large amount of calculation time is required. Also, based on the measured temperature, the transport speed pattern is determined so that the cooling time at each point matches the value obtained from the plate thickness and cooling conditions. If f changes, the solution may not be obtained. Furthermore, since the control is only the conveyance speed control, there is a limit to the application to a large taper steel sheet, which has been increasing in needs recently.

On the other hand, in the method disclosed in Document 2, a method is used in which cooling is started and accelerated all at once in a state where the steel plate is stopped. Since the cooling capacity differs greatly between the collision point and the non-collision point, there is a problem that large temperature unevenness occurs at an initial stage, and the temperature unevenness increases with the progress of cooling. Further, when the plate length is longer than the cooling device length, there is a limit that it cannot be applied.

From the above, it is an object of the present invention to obtain uniform characteristics over the entire length of a steel sheet, thereby solving the problems of the conventional cooling method, and controlling the temperature distribution at the end of cooling by a relatively simple method. Another object of the present invention is to provide a cooling method which can be applied to a large taper steel sheet having a large thickness ratio and a large thickness difference.

[0013]

The gist of the present invention is as follows.
It is in the cooling method of steel sheet from (1) to (4).

(1) In the method for cooling a steel sheet by passing the same through a cooling device, the time from when the leading end of the steel plate reaches the inlet of the cooling device to when the rear end of the steel plate reaches the outlet of the cooling device. A constant acceleration or deceleration is added to the steel sheet conveying speed, and the speed at which the front end portion passes through the cooling device inlet is adjusted so that the temperature at the end of cooling of each of the front end portion and the rear end portion matches a predetermined temperature. Calculating and determining in advance the speed at which the rear end portion passes through the cooling device outlet, calculating and determining the constant acceleration or deceleration, and controlling the transport speed of the steel sheet, Method.

(2) The method for cooling a steel sheet according to the above (1), wherein the steel sheet to be cooled is a steel sheet having a thickness gradient distribution in a longitudinal direction.

(3) Using a cooling device equipped with one or a plurality of cooling banks capable of individually adjusting the cooling capacity as a cooling device, the rear end portion of the steel plate starts from the time when the leading end portion reaches the inlet of the cooling device. Until the point of reaching the outlet of the cooling device, for each part in the longitudinal direction of the steel plate, the number of operating cooling banks and or the cooling capacity is controlled in a preset pattern, wherein (1) or The method for cooling a steel sheet according to the above (2).

(4) When setting the number of operating cooling banks and / or the pattern of the cooling capacity of the cooling device, a plurality of types of the cooling patterns are prepared, and the cooling patterns are set until a feasible solution of the transfer speed pattern of the steel sheet is obtained. Are sequentially scanned to determine a cooling pattern to be executed.

(5) In setting a cooling pattern, a plurality of executable cooling patterns are selected, one of the most preferable cooling patterns is selected from the plurality of executable cooling patterns, and a cooling pattern to be executed is determined. 4) The method for cooling a steel sheet according to the item.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is mainly applied to a tapered steel plate. However, as a special example of the taper, the present invention can also be applied to a zero taper, that is, a constant thickness steel plate. That is, in the case of a steel plate having a constant thickness, the aim is to compensate for the temperature drop until the start of cooling at the rear end, but the calculation procedure is not different from that of the tapered steel plate. Therefore, the present invention will be described below mainly on a tapered steel plate.

As shown in FIG. 1, in the process of the present invention,
Cooling is performed by simultaneously injecting cooling water from above and below while conveying the steel sheet 2 hot-rolled by the rolling mill 1 through the cooling device 3. The cooling device is composed of a plurality of banks 4, 4 'connected in the longitudinal direction. The cooling bank is composed of one or more cooling water nozzle headers, and is the smallest unit that can control the injection of cooling water by opening and closing a valve. In order to manage and control the cooling start temperature and the end temperature in the longitudinal direction of the plate, the inlet thermometers 5 and 5 ′ and the outlet thermometers 6 and 6 ′ of the cooling device are installed on the upper surface and the lower surface, respectively.

The taper of the steel sheet may be tapered such that the thickness increases from the front end portion to the rear end portion, or conversely, the taper may be such that the front end portion is thicker and the rear end portion becomes thinner. In the cooling control method of the present invention, as shown in FIG. 1, the time when the steel plate front end portion 21 (strictly, the taper start portion) reaches the inlet 31 of the cooling device is defined as the cooling start point, and the steel plate rear end portion 22 (taper end). Part)
A speed pattern in which the transfer speed is changed at a fixed rate (acceleration or deceleration = a) from the cooling start point to the end point is given as the cooling end point at the point when the motor reaches the outlet 32 of the cooling device.

The parameters necessary for the speed pattern are the speed Vin at the start of cooling, the speed Vout at the end of cooling, and the acceleration a. These parameters are two points, a front end portion and a rear end portion, and the front end temperature Ttc and the rear end temperature Tbc after cooling are within the allowable error range (± ΔT) for the respective target cooling end temperatures Tts and Tbs. It is characterized in that it is calculated so as to match.

FIG. 2 shows an example of the transport speed pattern in the case of the present invention. Here, an example is shown in the case where the taper is thick at the front end and thin at the rear end.

FIG. 4 shows an example of a flow chart for calculating the transport speed pattern according to the present invention. The calculation procedure is as follows.

(1) First, the plate thickness (maximum and minimum), taper direction, plate length, length of the constant thickness portion at the front and rear ends, steel type, rolling end temperature, front and rear ends The cooling conditions such as the target cooling end temperature, the set flow rate of the nozzles in the cooling bank, and the setting pattern of the cooling bank are read. (Step 4 in FIG. 4)
p1) (2) Assume the initial value of the cooling bank pattern number. (S
Step 2) (3) Assume the cooling start temperature at the rear end. (Step 3) (4) Assuming the initial values of the transport speed Vin at the start of cooling and the transport speed Vout at the end of cooling, the acceleration (or deceleration) a is obtained from Vin, Vout and the plate length, and the speed pattern is determined. calculate. (Step 4) (5) Based on Steps 1 and 3, the cooling start temperature of the front end portion and the rear end portion is determined.

Here, the cooling start temperature at the tip is
Based on the measured temperature at the time of completion of rolling or a standard temperature determined from a technical standard, it may be a calculated temperature in consideration of a temperature drop due to a transport time to the cooling device, or as a measured temperature of a thermometer provided on the cooling device inlet side. Is also good. The transfer time may be obtained from a table of standard values, or the actual transfer time may be used.

The cooling start temperature at the rear end is based on the measured temperature at the end of rolling or a standard temperature determined from a technical standard, and the transfer time from the end of rolling to the cooling device, and the above-mentioned Vi.
The temperature may be calculated taking into account the temperature drop due to the time until the start of cooling of the rear end determined from the speed pattern of n, Vout and a, or the measured temperature of the rear end at the time of measuring the temperature at the inlet of the cooling device at the front end. Is calculated, the calculated temperature may be set in consideration of the temperature drop until the start of cooling of the rear end determined by the speed pattern during cooling based on the temperature. (Step
5) (6) Based on the speed pattern condition in Step 4, the cooling start temperature of the front end and the rear end in Step 5, and the cooling bank setting pattern, the cooling end temperature Ttc and the rear end of the front end using the cooling model. The temperature Tbc at the end of the cooling of the unit is calculated. (Step 6) (7) Ttc obtained in Step 6 and target cooling end temperature Tts
Is in the allowable error range ΔT. (Step 7) (8) In Step 6, if | Ttc−Tts |> ΔT, that is, if convergence is insufficient, Vin is corrected, and the process returns to Step 5 again. As a method of correcting Vin, for example, assuming that the corrected value of Vin is Vin * and the cooling start temperature of the tip portion obtained in Step 5 is Tt0, Vin * = Vin × (1−α (Ttc−Tts) / (Tt0−) Tts)) と し て (1) Where α is the relaxation coefficient (0.1 to 1.0),
The gain is appropriately adjusted according to the stability of the solution of the convergence calculation.
(Step 8) (9) Tbc obtained in Step 6 and target cooling end temperature Tbs
Is in the allowable error range ΔT. (Step 9) (10) In Step 9, if | Tbc−Tbs |> ΔT, that is, if convergence is insufficient, Vout is corrected and the process returns to Step 5 again. As a method of correction, as in the equation (1), assuming that the corrected value of Vout is Vout * and the starting temperature of the rear end obtained in Step 5 is Tb0, Vout * = Vout × (1−α (Tbc−Tbs) / (Tb0-Tbs)) 求 め る (2) (Step 10) (11) As described above, Vin and Vout that simultaneously satisfy | Ttc−Tts | ≦ ΔT and | Tbc−Tbs | ≦ ΔT are obtained.

Here, the lower limit speed of the transfer equipment for Vin and Vout is checked. That is, since there is often a facility limitation in the control of the steel sheet transfer speed control, particularly in the stable speed control at a low speed, the control by the transfer speed control alone requires the control of the large taper steel plate having a large taper ratio or a large thickness difference. This is because, in such a case, uncontrollable cases may occur. (Step
11) (12) If Vin and Vout are equal to or lower than the transport lower limit speed in Step 11, change the cooling pattern and return to Step 5 again.
Perform the calculation again.

The criterion for changing the cooling pattern is, for example, Vin,
If any of Vout is equal to or lower than the lower limit speed, a cooling pattern for a larger taper is selected. If both Vin and Vout are equal to or lower than the lower limit speed, a cooling pattern of higher cooling is selected. (Step 12) Here, as shown in FIG. 5, the cooling pattern includes a pattern for turning on / off the bank with the transfer of the steel sheet, a thinning pattern for always turning off the specific bank, a thinning pattern for always turning on the specific bank, and the like. is there. Although not shown, there is also a pattern in which ON / 0FF of the bank during cooling is kept fixed.

FIG. 6 shows the conveying speed of the steel sheet and ON / O of the cooling bank.
The relationship of the timing of the FF is shown. Here, FIGS. 5a and 6a
In a pattern corresponding to
This is a pattern of cooling from the first half of the cooling device. FIG.
d represents a pattern for cooling the tapered taper in the latter half of the cooling device.

The line SS 'in FIGS. 6a and 6d indicates the timing of turning on / off the cooling bank corresponding to the position of the steel sheet. By drawing such a straight line SS ′, it is possible to control so as to minimize and equalize the temperature step caused by ON / OFF of the cooling bank. This SS '
The cooling bank from ON to OFF or OF
Various cooling patterns can be created by selecting ON from F. FIG. 7 shows the difference between the plate lengths due to the same cooling pattern. FIG.
Represents the relationship between the cooling pattern and the corresponding plate thickness and taper. Here, for example, "The higher the cooling in the second half, the greater the heat transfer coefficient due to nucleate boiling, the lower the temperature of the thicker and thinner parts in the same way, the less the temperature difference becomes, and the smaller the cooling pattern Suitable for taper ".

Thus, after preparing a number of cooling patterns, these are stored in a table in the computer. As shown in FIG. 9, these cooling patterns are numbered, and are two-dimensionally arranged and arranged in the order of weak cooling to strong cooling and small taper to large taper. Therefore, Step 12
In order to select a cooling pattern for a larger taper, an adjacent pattern on the left side of FIG. 9 may be selected. To select a more intense cooling pattern, an adjacent lower pattern may be selected.

(13) Based on the cooling pattern changed in Step 12, the calculations in Step 5 to Step 9 are performed to obtain Vin and Vout that do not fall below the lower limit speed of conveyance.

The set of Vin and Vout obtained here may not always be optimal values. That is, even if Vin and Vout are obtained by a weak cooling type cooling pattern, the efficiency is not improved if these are small. On the other hand, in a transfer facility such as a roller table, a slip of a steel sheet is likely to occur during deceleration. Therefore, acceleration (Vin <Vout) is desirable as much as possible. There may be. Therefore, it is necessary to search for a higher-efficiency pattern or a pattern with higher accuracy. (Step 13) (14) In order to obtain a pattern of this improved solution, the cooling pattern is further changed and St is obtained until a plurality of cooling patterns are obtained.
Repeat ep5-9. In this pattern selection, as shown in FIG. 9, a feasible solution is selected near the solution obtained first. In addition, an operator may manually intervene to assist the computer in searching for a cooling pattern. (Step1
4) (15) When a plurality of feasible solutions are obtained, they are evaluated in terms of operation (comprehensive evaluation of efficiency, quality, ease of operation, etc.) and one optimal solution is selected. To end the calculation. (Step 15) (16) In addition, when assuming an arbitrary cooling pattern in Step 2, the cooling pattern No. 1-1 in FIG. 9 may be used as a starting point, or the sheet thickness and the sheet length may be set in order to shorten the calculation time. It is also possible to start from a cooling pattern of an appropriate number, judging from operating conditions such as a taper degree, a cooling start temperature and an end temperature.

As described above, in the method according to the present invention, the solution to be obtained is only the transport speed at the start and end of cooling, and the speed pattern can be obtained in a relatively short calculation time. In addition, since the transport speed is changed linearly and the cooling pattern is controlled to increase and decrease at equal intervals along the plate longitudinal direction, the cooling time at each position in the plate longitudinal direction changes almost continuously. As a result, the cooling end temperature can obtain a continuous temperature distribution from the front end to the rear end, and uniform characteristics can be obtained over the entire tapered steel plate. In addition, the transport speed has a characteristic that it is easy to use in actual operation due to the constant acceleration pattern. Furthermore, the bank cooling capacity is controlled with an appropriate cooling pattern according to the taper size and thickness of the steel sheet, so it can be used for large taper steel sheets, and the cooling pattern selection is automated, contributing to automation and labor saving. can do.

The present invention can be applied to equipment of a type in which the speed control of the transport equipment is not continuous, but is changed stepwise. In this case, the actual acceleration is not constant, and a slip may occur between the steel plate and the transfer table during acceleration / deceleration.However, if the speed setting stage is divided so as not to be practically permissible. For example, the present invention can be applied by calculating Vin and Vout and the acceleration a assuming that the speed control is of a continuous type, and performing a stepwise speed control closest to this speed pattern.

Further, in the case of a tapered steel plate, a constant thickness of about 0.5 m to 2.0 m may be provided in order to provide a space for bolt fastening at the front end and the rear end depending on the order specification. If this part is not so long, the transport speed is Vin until the leading end of the thickness taper comes to the cooling device inlet, and Vout after the trailing end of the thickness taper exits the cooling device outlet. The cooling bank applied to the rear end
There is no problem if the ON / OFF state is applied as it is.

[0038]

When cooling was performed with the speed control pattern obtained by the method of the present invention shown in FIG. 2 and the speed control pattern obtained by the conventional method shown in FIG. Shown in

Here, the steel sheet has a thickness of 40 mm at the front end, a thickness of 20 mm at the rear end, a length of 20 m, and a width of 3000 mm. The rolling end temperature is 850 ° C., and the target cooling end temperature is the thick part at the front end. 550
The target was 600 ° C in the thin portion at the rear end.

The cooling device has a total length of 20 m and the number of banks is one.
0 is Bank, 1 the cooling water flow rate per bank upper bank 6 m ³ / min, and a lower bank 10 m ³ / min.

Because of the thick taper at the tip, the cooling pattern selected by the computer was such that the cooling banks as shown in FIG.

In the case of the prior art shown in FIG. 3, the acceleration is started when the leading end reaches the outlet of the apparatus, and the speed control is performed at a constant acceleration until the trailing end reaches the outlet. This method is based on manual cooling control. After passing through the cooling device to control the end temperature of the front end, the method is accelerated to further secure the end temperature of the rear end.

As shown in FIG. 10, in the case of the prior art, the acceleration was increased, so that the accuracy of the conveyance speed control was deteriorated, and the fluctuation of the end temperature tended to be increased. In addition, since the tip is conveyed at a constant speed until reaching the outlet of the cooling device and then rapidly accelerated, the cooling time at each position in the longitudinal direction is not continuous, and the gradient of the end temperature distribution is not uniform.

On the other hand, when the present invention is applied, the gradient of the end temperature distribution has a relatively small variation, and a distribution that changes at a substantially constant rate from the front end to the rear end is obtained.

FIG. 11 shows a speed pattern (set speed) when the present invention uses a transfer facility having stepwise speed control. It is possible to set the speed of the transfer equipment from 5 m / min to 150 m / min by dividing the speed into 15 at substantially equal intervals. When the cooling control according to the present invention was carried out in this case, almost the same results as in the continuous speed control were obtained.

[0046]

According to the present invention, the cooling control of the tapered steel sheet is relatively easy, the calculation time is short, and the temperature distribution at the end of cooling over the entire steel sheet can be controlled more accurately. As a result, it is possible to provide a cooling method that can reduce variation in mechanical properties of the entire steel sheet and can also be applied to a steel sheet having a large taper, and thus has a great industrial effect.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a steel plate cooling facility.

FIG. 2 is an example of a transfer speed control pattern in the cooling method of the present invention.

FIG. 3 is an example of a transfer speed control pattern in a conventional cooling method.

FIG. 4 is a flowchart illustrating a procedure of calculating a transport speed according to the present invention.

FIG. 5 is an example of various cooling patterns in the present invention.

FIG. 6 is an example of a control timing and a transfer speed pattern of a cooling bank according to the present invention.

FIG. 7 is an example of cooling bank control timing when the same cooling pattern of the present invention is applied to a short steel plate and a long steel plate.

FIG. 8 is an example showing a relationship between a cooling pattern, a plate thickness, and a plate thickness taper of the present invention.

FIG. 9 is an example showing a layout of a cooling pattern table and a situation of searching for a feasible solution according to the present invention.

FIG. 10 shows the measurement results of the cooling end temperature of the present invention and the prior art.

FIG. 11 is an example showing a speed pattern when the present invention uses transport equipment having stepwise speed control.

[Explanation of symbols]

 1: Rolling mill 2: Steel plate 21, 22: Front end and rear end of steel plate 3: Cooling device 31, 32: Inlet and outlet of cooling device 4, 4 ': Upper surface of cooling bank, lower surface 5, 5': Inlet side Upper and lower surfaces of thermometer 6, 6 ': Upper and lower surfaces of outlet thermometer

Continued on the front page (72) Inventor Michiharu Hariki 4-5-33 Kitahama, Chuo-ku, Osaka-shi

Claims (5)

[Claims] 1. A method for cooling a steel sheet by passing the steel sheet through a cooling device, wherein the time from when the leading end of the steel sheet reaches the inlet of the cooling device to when the rear end of the steel sheet reaches the outlet of the cooling device, Add a constant acceleration or deceleration to the steel sheet transport speed,
The speed at which the front end portion passes through the cooling device inlet and the speed at which the rear end portion passes through the cooling device outlet so that the temperature at the end of cooling of each of the front end portion and the rear end portion matches a predetermined temperature. A method for cooling a steel sheet, comprising calculating and determining in advance, determining and determining the constant acceleration or deceleration, and controlling a conveying speed of the steel sheet. 2. The method of cooling a steel sheet according to claim 1, wherein the steel sheet to be cooled is a steel sheet having a thickness distribution in the longitudinal direction. 3. A cooling device equipped with one or more cooling banks capable of individually adjusting cooling capacity as a cooling device.
From the time when the leading end of the steel sheet reaches the inlet of the cooling device to the time when the rear end reaches the outlet of the cooling device, the number of operating cooling banks and / or the cooling capacity for each longitudinal portion of the steel sheet. 3. The method for cooling a steel sheet according to claim 1, wherein the temperature is controlled by a preset pattern. 4. When setting the number of operating cooling banks and / or the pattern of the cooling capacity of a cooling device, a plurality of types of the cooling patterns are prepared, and the cooling patterns are set until a feasible solution of the conveying speed pattern of the steel sheet is obtained. 4. The method for cooling a steel sheet according to claim 3, wherein scanning is performed sequentially to determine a cooling pattern to be executed. 5. When setting a cooling pattern, a plurality of executable cooling patterns are selected, one of the most preferable cooling patterns is selected from the plurality of cooling patterns, and a cooling pattern to be executed is determined. The method for cooling a steel sheet according to the above.