CN102343367B - Control method for lowering head and tail undercooled sections of steel plate in pressure jet cooling process - Google Patents

Abstract

A control method for reducing the supercooling section at the head and tail of a steel plate in the process of pressure spray cooling, including setting water cooling equipment on a rolling line and configuring an automatic control system, which is characterized in that the speed of the head and tail of the steel plate passing through the cooling zone is controlled separately, so as to The cooling time of the head and tail of the steel plate is shortened by passing through quickly; the cooling zone is divided into several zones in the control program, and the designed passing speed of the steel plate in each cooling zone is executed by the process control system. Zone A is the head speed shielding section, and the steel plate speed After entering the cooling zone from 1.4m/s, it starts to decelerate to 1.138m/s. Zone B is a transition zone, which serves as a connection between the head shielding section and the normal cooling section, and decelerates from 1.138m/s to 0.826m/s s, Area C is the normal cooling section of the non-head and tail velocity shielding section, and Area D is the tail velocity shielding section, where the speed increases from 0.879m/s in normal cooling to 1.23m/s. The invention can ensure the head-to-tail temperature hit rate of the steel plate in the cooling process, obtain a cooling effect with uniform temperature in the length direction of the steel plate, has a simple adjustment method, is stable and reliable, and is suitable for medium-thick plate production occasions.

Description

A control method for reducing the head and tail subcooling section of the steel plate in the process of pressure spray cooling

technical field

The invention belongs to the technical field of steel rolling automation, and relates to a method for controlling the target temperature in the longitudinal direction of a steel plate, in particular to a method for controlling the hit ratio of cooling head and tail temperature after rolling of medium and thick plates. the

Background technique

The temperature uniformity control in the cooling process is an important issue in the cooling process of medium and thick plates. Especially the head and tail of the steel plate generally have the problem of overcooling of the head and tail. The existence of the supercooled section at the head and tail will cause uneven temperature and performance in the longitudinal direction of the steel plate, which will seriously affect the yield of steel rolling production. the

The reasons for analyzing the head and tail supercooling of the steel plate are as follows:

1. During the cooling process of the steel plate, it mainly includes the internal heat conduction process and the convective and radiation heat exchange process between the surface of the steel plate and the outside world. Since the heat dissipation in the length direction is much smaller than the heat dissipation in the thickness and width directions, the heat conduction in the length direction can be ignored, and the heat transfer process can be regarded as a two-dimensional heat transfer process along the thickness and width directions of the steel plate. However, there are convective and radiation heat transfer processes in the head and tail of the steel plate in the length direction, so there is a head and tail supercooling section when the steel plate enters cooling after leaving the rolling mill.

2. According to the characteristics of the ultra-fast cooling equipment (ADCOS-PM), when the head of the steel plate enters cooling, since most of the spraying direction of the nozzle is along the running direction of the steel plate, and the drainage effect of the head and tail of the steel plate is better than other positions (During the cooling process of the steel plate, there is a large amount of cooling water on the surface of the steel plate, which seriously affects the heat transfer effect of the steel plate), so the cooling effect of the head and tail parts is stronger than that of other positions, resulting in supercooling of the head and tail of the steel plate. the

3. The cooling water sprayed by the lower nozzle is much higher than the surface of the roller table. Generally, when the steel plate enters the cooling zone, the lower header water has been opened, so when the head and tail of the steel plate pass through the cooling zone, a large amount of cooling water from the lower nozzle is retained (the spray height is on the part of the roller surface), causing the head and tail of the steel plate to be overcooled. the

At present, the commonly used method of reducing the head and tail subcooling section in the cooling system after rolling of medium and heavy plates is generally realized by the method of head and tail water shielding control. According to the different configurations of the control valve group, it is divided into two types: head and tail water cutting control and head and tail flow control. Head and tail water cutting control can be realized by adjusting the opening time of the header. When the head of the steel plate passes through the cooling water injection interval, the header will spray water. Similarly, when the tail reaches the cooling water injection interval, the header will stop spraying water. Head and tail water cutting control depends on the cooperation of accurate micro-tracking and quick response of opening and closing valves. The head-to-tail flow control can be realized by adjusting the header flow when the head and tail of the steel plate pass through the cooling water injection interval. The shielding coefficient (shielding length and shielding flow) is set according to the length and temperature of the low-temperature section of the steel plate head. The head-to-tail flow control depends on Precise and fast response of the flow regulating valve. At the same time, the above two control methods have high requirements on the stability of the water supply system. If the post-rolling cooling system uses a high-level water tank (or high-level water tower) for water supply, the water supply pressure is relatively stable. , the above two methods can be used to achieve head and tail shading to a certain extent, but the accuracy of shading (shading section length and temperature accuracy) is difficult to guarantee. the

At present, there are no related reports at home and abroad on the method of adjusting the speed of the head and tail passing through the cooling zone to control the head and tail supercooling section. the

Contents of the invention

The purpose of the present invention is to provide a control method for reducing the supercooling section of the steel plate head and tail in the pressure spray cooling process, by adjusting the speed when the steel plate head and tail pass through the cooling zone, the temperature hit rate of the steel plate head and tail of the jet flow is improved. the

The control method for reducing the supercooling section at the head and tail of the steel plate in the pressure spray cooling process of the present invention includes setting water cooling equipment on the rolling line and configuring an automatic control system for controlling the rolling line on the rolling line. The length of the cooling zone is 8m. A total of 9 groups of nozzles are set up, and the initial section is a strong cooling zone; it is characterized in that the head and tail of the steel plate pass through the cooling zone to implement separate speed control, so as to shorten the cooling time of the head and tail of the steel plate by passing quickly; the cooling zone is controlled in the control program. Divided into several zones, the designed passing speed of the steel plate in each cooling zone is implemented by the process control system. Zone A is the head speed shielding section. After the steel plate enters the cooling zone from 1.4m/s, it starts to decelerate to 1.138m/s. It is a transition area, which plays the role of connecting between the head shielding section and the normal cooling section, decelerating from 1.138m/s to 0.826m/s, the C area is the normal cooling section (not the head and tail speed shielding section), and the D area is In the tail speed shield section, the speed is increased from 0.879m/s in normal cooling to 1.23m/s. the

Since the water stabilization time in the pressure injection process is long, which is lower than the control response requirements, on the other hand, the method of adjusting the cooling time of the head and tail parts of the steel plate is used to reduce the head and tail supercooling section. the

During the steel plate cooling process, before entering the cooling zone, the process control system sends the cooling rules (nozzle opening mode, nozzle flow rate, roller speed of the steel plate passing through the cooling zone, etc.) to the basic automation control, and the basic automation control system implements the cooling rules on the cooling equipment . During the cooling process, the opening mode of the nozzles, that is, the number and position of openings, and the water volume of the nozzles will generally not change due to the constraints of the water system. Therefore, the only way to reduce the cooling temperature drop in the supercooling section of the head and tail of the steel plate is to adjust the cooling time, that is, Adjust the speed when the steel plate head and tail pass through the cooling zone. In the cooling process of the medium and thick plate, in order to realize the uniform cooling of the whole length direction of the steel plate, the initial temperature and the acceleration of a roller table are generally used, but the present invention lies in the independent speed control of the head and tail, that is, the speed of the head and tail sections passing through the cooling zone It has nothing to do with other positions of the plate. the

Description of drawings

Fig. 1 is the velocity curve when the steel plate passes through the cooling zone;

Fig. 2 is the temperature distribution when no head and tail shielding is put in;

Fig. 3 is the temperature distribution situation when putting into head and tail shielding;

Figure 4 shows the PDI parameters of the steel X70 cooling steel plate.

Detailed ways

A control method for reducing the supercooling section at the head and tail of the steel plate in the process of pressure spray cooling. The cooling setting adopted is that the length of the cooling zone is 8m, and there are 9 groups of nozzles in total. The high-strength cooling zone is characterized by using the automatic control system configured on the rolling line to control the rolling line to adjust the speed of the steel plate passing through the cooling zone to change the cooling time of the head and tail of the steel plate, thereby controlling the cooling temperature drop at the head and tail of the steel plate , in order to achieve the purpose of controlling the cooling temperature uniformity between the head and tail of the steel plate and the whole plate. the

The specific implementation of the head and tail subcooling section of the control steel plate of the present invention is as follows:

For the cooling steel plate used in the embodiment and the process requirements, see the PDI parameters of the cooling steel plate shown in FIG. 4 . When the steel plate is rolled to the penultimate pass, the cooling process control system automatically gives the cooling schedule, including nozzle configuration, nozzle flow rate and roller table speed, where the roller table speed includes initial speed, roller table acceleration and different positions of the steel plate The speed of the roller table when passing through the cooling zone; at the same time, head shielding measures are taken on the rolling line.

The speed masking control process of the head and tail subcooling section is as follows: the steel plate starts to travel from the rolling mill to the control cooling device at the steel throwing speed (v=4.0m/s) and gradually decelerates. When the steel plate head travels to the position 8m before the cooling zone At this time, the speed of the steel plate is 1.4m/s, as shown in Figure 1, and then it starts to run to the A area according to the speed given by the process machine of the control cooling system. Compared with the speed given by the process machine of the control cooling system at this time as 20 points, the speed curve from the first point to the 20th point can be seen in Figure 1, that is, the speed of each position of the steel plate in the active cooling interval (the normal speed set by the process machine The cooling speed is the speed at the 8th point in the speed curve, and the acceleration section is from the 8th point to the 14th point, which is the normal cooling section for removing the head and tail of the steel plate. The speed values from the 8th point to the 14th point can be seen in Figure 1, and the speed range It is 0.835～1.038m/s. When the steel plate runs from the position of 8m before the cooling to the entrance of the cold zone device, the steel plate is decelerating. The head of the steel plate enters the cooling device from the second point, and the head speed shielding process begins. At this time The speed of the roller table is 1.17m/s. The range of speed adjustment is given by the process control system. The process control system is based on the temperature of the steel plate head detected by the pyrometer at the exit of the rolling mill and the pre-calculated temperature drop caused by water penetration at the head Give speed compensation, speed compensation is generally 1.3~1.8 times of normal cooling speed, the shielding position is the steel plate head in the interval from point 2 to point 5, and the speed of each point set at this time is: point 2~3 1.149m/s, 1.139 m/s at the 3rd to 4th points, 1.138 m/s at the 4th to 5th points. When the head of the steel plate passes through the 5th point, it enters the transition zone between the head shielding section and the normal cooling section, and the first The speed setting from point 5 to point 8 needs to take into account the degree of head and tail shielding and the connection with the normal cooling start speed, decelerate from 1.138m/s to 0.826m/s, and start the normal cooling speed at point 8. Area C is the normal cooling section (non-head-to-tail speed shielding section), and area D is the tail shielding section. The passing speed of the steel plate increases from 0.879m/s for normal cooling to 1.23m/s. When the tail of the steel plate reaches the 14th entrance of the cooling device At point 1, the tail shading process starts, that is, the tail quickly passes through the cooling zone. Between the 14th and 20th points is the tail shading section. At this time, considering the ability of the cooling device to convey the roller table, the strength of the head and tail shading, etc., set the The speed curve of the section. In this example, the speed of the 14th point is 0.879m/s, and the speed of the 15th point is increased to 1.038m/s. This speed increase is related to the process characteristics of the cooling device, and the front end of the cooling device is a high-intensity cooling zone , so in the process of the 14th to 15th point, the running acceleration of the steel plate is relatively large. In the process of the D zone of the 15th to 20th point, the steel plate passes through the cooling device at a relatively small speed, and the set speed at this time is 1.066 m/ s, 1.085 m/s, 1.133 m/s, 1.172 m/s, 1.230 m/s). The tail of the steel plate leaves the cooling device at the 20th point, and the entire cooling process ends. the

A special explanation is needed here: the above-mentioned term "shelter area" is only borrowed, and there is no measure to shield the water flow in this section of the cooling section of the method. Although the shielding measure still adopted in the industry to alleviate the overcooling problem of the steel plate head and tail is to block to reduce the flow of cooling water on the steel plate, the method of the present invention only changes the speed to allow the steel plate head and tail to pass through the cooling zone quickly, and is set in the control program. "Speed Mask". "When the head of the steel plate enters the cooling zone, the temperature uniformity control in the length direction is started. In order to avoid the violent fluctuation of the speed of the roller table and the large temperature fluctuation in the length direction of the steel plate, the B area is set before the temperature uniformity control in the length direction. It is the transition area, and this area is also the head shielding area, so that the steel plate is reduced to the target initial speed. After that, it enters the temperature uniformity control area C in the length direction. Because under normal circumstances, the overcooling of the tail is not as obvious as the head , so the accelerated passage of the tail shielding measures is relatively moderate, as shown in area D in Figure 1.

Figure 2 shows the temperature curve in the longitudinal direction of the steel plate before adopting the patented method. It can be seen that there are large supercooled sections at the head and tail of the steel plate, especially the temperature point in the frame, which is obviously lower than the temperature in the middle of the steel plate Many, which seriously affect the temperature uniformity in the longitudinal direction of the steel plate, resulting in a lower yield. When adopting the method of the present invention to control the cooling process, the temperature distribution in the longitudinal direction of the steel plate is as shown in Figure 3, as seen in Figure 3, the supercooled section of the steel plate head and tail is obviously much shorter than Figure 2, indicating that the control method starts When it comes to the effect, this is of great significance to the improvement of performance uniformity and yield in the steel plate production process. the

Claims (5)

1. A control method for reducing the supercooling section at the head and tail of the steel plate in the pressure spray cooling process, including setting water cooling equipment on the rolling line, configuring an automatic control system for cooling control, the length of the cooling zone is 8m, and a total of 9 groups of nozzles are installed , the initial section is a strong cooling zone; it is characterized in that the control cooling system process machine gives a 20-point speed curve, and implements separate speed control for the head and tail of the steel plate passing through the cooling zone, so as to shorten the cooling time of the head and tail of the steel plate by passing through quickly; In the control program, the cooling zone is divided into several zones. The designed steel plate passing speed in each cooling zone is executed by the process control system. Points 1 to 5 in zone A are the head speed shielding section. After the steel plate speed enters the cooling zone from 1.4m/s , start to decelerate to 1.138m/s, and the 5th to 8th points in area B are transitional areas, which serve as a connection between the head shielding section and the normal cooling section, decelerate from 1.138m/s to 0.826m/s, and the 8th point in area C Points ~ 14 are the normal cooling section of the non-head and tail velocity shielding section, points 14 to 20 in D area are the tail velocity shielding section, and the speed increases from 0.879m/s in normal cooling to 1.23m/s. 2. the control method for reducing the supercooled section of the head and tail of the steel plate in the pressure spray cooling process according to claim 1, is characterized in that the process control system detects the temperature of the head of the steel plate according to the outlet pyrometer of the rolling mill and the pre-calculated due to Speed compensation is given to the temperature drop caused by water penetration on the head, and the speed compensation is 1.3 to 1.8 times the normal cooling speed. 3. The control method for reducing the supercooling section at the head and tail of the steel plate in the pressure spray cooling process according to claim 1, wherein the steel plate speed is 1.4m/s when the head of the steel plate advances to a position 8m ahead of the cooling zone , and then start to decelerate and run to zone A according to the speed given by the process machine of the control cooling system. The head of the steel plate enters the cooling device and starts the head speed shielding process from the second point. At this time, the speed of the roller table is 1.17m/s, and the shielding The position is that the head of the steel plate is in the interval from point 2 to point 5. At this time, the set speeds of each point are: 1.149m/s for points 2~3, 1.139m/s for points 3~4, 1.138m/s at 5 points. 4. The control method for reducing the supercooled section of the head and tail of the steel plate in the pressure spray cooling process according to claim 1, wherein when the head of the steel plate passes through the 5th point, it enters the transition zone B between the head shielding section and the normal cooling section , The setting of the speed from the 5th point to the 8th point in the B area should consider the degree of head and tail shading and the connection with the normal cooling start speed, decelerate from 1.138m/s to 0.826m/s, and start to execute normally at the 8th point cooling rate. 5. The control method for reducing the supercooling section at the head and tail of the steel plate in the pressure spray cooling process according to claim 1, characterized in that the D zone between the 14th and 20th points is the tail shielding section, when the tail of the steel plate reaches the cooling device At the 14th point of the entrance, the tail shading process starts. At this time, considering the capacity of the cooling device’s conveying roller table and the strength of the head and tail shading, set the speed curve of this section: the speed of the 14th point is 0.879m/s, and the speed of the 15th point Raise to 1.038m/s, in the zone D of points 15-20, the set speeds are 1.066m/s, 1.085m/s, 1.133m/s, 1.172m/s, 1.230m/s; Leave the cooling device at the 20th point, and the whole cooling process ends.