Automatic control of strip steel production

1. Automation of hot strip rolling mill

The continuous strip rolling mill has high production efficiency, easy quality control, continuous rolling process, easy mechanization and automation, and this kind of rolling mill has great potential, as long as the rolling process is slightly improved, the output and product quality can be greatly increased. The economic benefits are very significant. Therefore, all kinds of advanced scientific and technological achievements are applied to the continuous rolling process, which greatly promotes the development of continuous rolling process automation. Among them, the development of hot continuous rolling mill automation is the most rapid and mature, and the development of hot continuous rolling mill automation can reflect the development process of the automation of the whole rolling process.

 

1) Computer control function of strip hot rolling

Hot strip steel rolling production is currently the most mature application of computer control. Its control scope includes the entire production process, from the entrance of the heating furnace, even from the continuous casting outlet to the finished product warehouse, including rolling planning and slab warehouse management. , mathematical model, equipment control and quality control, and digital control of transmission (electrical and hydraulic transmission) at various levels, it is the largest and most complex control system in the field of steel rolling automation.

 

(1) Basic automation control function

The basic automation is oriented to the unit, to the equipment and the mechanism of the equipment. With the digitalization of electrical transmission and the wide application of hydraulic transmission, digital transmission has gradually become a whole with basic automation.

The basic automation control function can be divided into rolling piece tracking and transportation control according to its nature: sequence control and logic control; equipment control and quality control.

 

a. Rolled piece tracking and delivery control

The delivery of rolled pieces (steel billet, strip billet, strip steel) is one of the basic functions required by the production process. Its basic task is to control the speed of the roller table in each section and its rotation and stop so that the rolled piece can pass from the entrance of the heating furnace at the fastest speed. It is transported to the heating furnace, rough rolling, finishing rolling, coiling, and processed in each area and then transported out by the transport chain. However, while ensuring the fastest transport, it is also necessary to ensure that the front and rear rolled pieces do not collide during automatic rolling, and maintain A certain rhythm.

In order to be able to transport and sequentially control multiple rolled pieces on the production line (from the exit of the heating furnace to the transport chain, there can be up to 7 to 8 rolled pieces) according to the process requirements, each controller of the basic automation needs to know that each rolled piece is on the rolling line. Therefore, rolling stock tracking is essentially an important program to coordinate various programs and obtain “events”.

Rolled piece tracking will be carried out in the basic automation, process automation and production control levels respectively, but the requirements of each level are different, and they are all based on the position tracking results of the basic automation. The tracking of basic automation is essentially to track the position and change of each rolled piece in the production line and provide an “event occurrence” signal for sequence control (the change of hot metal detector from OFF to ON or from ON to OFF is called an event). The location tracking results of the basic automation will be uploaded to the process automation.

The tracking of process automation is essentially to track the data of each rolled piece so that the data and the rolled piece can be numbered, and the calculation and self-learning can be set correctly. At the same time, some “events” are used to start certain programs.

Production control level tracking will be used for quality control and report printing.

 

b. Sequential control and logic control

Logic control is one of the basic contents of production process automation. In fact, all control functions of basic automation contain certain logic functions, including function interlocking, logic conditions for function execution or stop, etc., so each function will have two parts: the logic part and the control part. In addition, According to the needs of the process, some sequence control functions including only the logic part will be set up, mainly the sequence control of the operation (automatic acceleration, steady speed, deceleration and reverse) of the roller table in the furnace area and rough rolling area.

 

c. Device Control

Equipment control includes position control and speed control of equipment, including mill roll gap positioning, side guide plate positioning, roll shifting position control, pusher stroke control, main drive speed control, etc., and constant pressure control of the roll bending device. There are hundreds of equipment control loops in the whole production line, so it can be said that equipment control is the most basic control function.

The equipment control accepts the set values (roll gap, speed, bending force, etc.) calculated by the mathematical model of the process automation level, and adjusts the position and speed of each actuator. In the semi-automatic state, it accepts the operator through the man-machine Input the set value of the interface and adjusts the position and speed.

With the digitalization of electrical and hydraulic transmission, equipment control will gradually be undertaken by digital transmission control.

 

d. Quality control

For strip hot rolling, quality control includes thickness control, finish rolling temperature control, coiling temperature control (including cooling speed control), width control, shape control, and surface quality control.
The main task of the process automation setting model is to set the position and speed of each actuator to ensure the thickness, temperature and shape quality of the strip head, while the quality control function is used to ensure the thickness, Temperature, plate shape and other precision.

 

(2) Process automation control function

Process automation is oriented to the entire production line, and its central task is to set and calculate each unit and each piece of equipment on the production line. For this reason, its core function is to distribute the rough rolling and finishing rolling unit loads (including optimization calculations) and predict the mathematical model. (report) estimate, in order to realize this core function, the process control computer must be equipped with slab (data) tracking, initial data input, online data acquisition model self-learning, etc. to serve and support the model set. The main function of automatic control of the hot continuous rolling process is the mathematical model of thickness setting and shape setting mathematical model of the finishing rolling unit. After the setting value is calculated, it is sent to the basic automation and executed by the equipment control function.

 

(3) Production control level function

The production control level mainly completes the adjustment and issuance of the production plan, the collection, processing and uploading of the actual production results to the production management level, manages the slab warehouse, steel coil warehouse, and finished product warehouse, and performs tasks such as product quality control.

 

(4) Production management level

The production management level mainly completes contract management, preparation of production plans, mutual coordination of each production line, application materials according to the contract, dispatches the operation plan to the production control level, collects the actual production performance of the production control level, tracks the production situation and quality situation, and organizes Finished products are shipped out of the factory, as well as financial management and other tasks.

 

2. Basic content of computer-controlled rolling process

 

1) 3/4 continuous hot rolling mill equipment layout

The rolling line equipment layout of a 1700mm 3/4 continuous hot strip rolling mill is shown in the figure. The main equipment includes a walking heating furnace, a rough rolling unit, a finishing rolling unit, a laminar flow cooling device, a coiling unit, and a finishing unit. work line etc. The slab with a thickness of 150~250mm is rolled into strip steel coils with a thickness of 1.2~12.7mm through the rough rolling and finishing rolling mills, part of which can be shipped as finished products, and the other part can be supplied to cold rolling plants and silicon steel plants. As a blank for reprocessing.

The production process under computer control is basically the same as that of manual operation, but the operation method and content of the operator have changed. More is to use the man-machine interface (display and keyboard, etc.) to understand the actual rolling situation and carry out Certain ancillary operations and necessary interventions. Therefore, the operator should have a deep understanding of how the computer control system of each piece of equipment works and how the computers communicate with each other.

When the strip hot rolling production line performs automatic steel rolling, the raw data of the slab and rolling plan are transmitted from the production control level computer to the process control level computer. The raw data of the slab includes steel type, chemical composition, slab thickness, width, slab length, slab weight, slab position in the warehouse, coil thickness, width, etc. If there is no production control level computer, they can be directly input into the process control level computer through the initial data input (PDA) terminal.

 

hot strip rolling mill, strip rolling mill automation

 

2) Automated process in the heating zone

According to the sequence stipulated in the rolling schedule, after a certain slab is hoisted by a crane to the feeding A roller table, it is under the tracking of the process control computer.

The slab is on roller table A and is tracked by the cold metal detector, which controls the operation of the roller table and the position of the slab on the roller table. In order to avoid misoperation of the computer, no matter whether it is a long slab or a short slab, only one slab can be placed on a set of roller tables during feeding, and it cannot be placed across groups, and two slabs cannot be placed on the same set of roller tables.

After the slab is on the A-roller table, the length and weight should be measured. After the measuring device automatically completes the measurement, the measured data will be transmitted to the computer. The computer will check the data and output an alarm message if any abnormality is found, requesting the operator to deal with it accordingly. The computer compares the slab number in the PDA with the number marked on the actual slab input by the operator through the man-machine interface MMI device and performs slab confirmation or slab identification. If an abnormality is found, reorder, do “missing number processing” or revoke the slab.

For the slabs that have been measured and confirmed, the slab movement and furnace front positioning control is carried out according to the specified furnace number and furnace row, and the slab is controlled to stop at the centre of the furnace front, which is completed by the APC program of the automatic position control system of the B roller table. When the slab is to be pushed into the heating furnace, the computer determines the moving stroke of the steel pusher and checks the rationality of the set calculation value. When the steel loading conditions are met, the steel pusher is controlled by the APC program to load the slab into the furnace. Predetermined position in the heating furnace.

The position where the slab moves in the furnace uses the cold metal detectors 31, 32, and 33 as the starting point for tracking. The slab is moved to the discharge end step by step by the walking beam in the heating furnace, and the normal step-forward stroke of the walking beam is 600mm. In order to prevent the front slab in the furnace from being offside and hitting the discharge furnace door, or even falling down, a gamma ray detector is installed on the side wall 1450mm away from the discharge end wall to control the walking beam to stop go ahead. In order to ensure the normal operation of the extractor, when the γ-ray detector fails, the walking beam can be controlled by the computer to stop advancing. The repeated cyclic actions of the walking beam rising, advancing, falling, and retreating, and the stepping action of the walking beam rising and falling when the tapping time is longer than the specified time, are all controlled by the computer. The combustion control of the heating furnace is set and calculated by the computer, and the corresponding temperature and flow regulator is used to perform its control function.

The computer predicts the running time of the rolled piece in the rough rolling area, finishing rolling area and coiling area according to the size of the rolled piece and the “kinematic equation” of the rolled piece, and determines the plate The time when the billet is pulled out from the heating furnace is controlled by the mill pacing. In addition to the automatic steel drawing method, there are also timed steel drawing and forced steel drawing methods.

When there is a steel drawing request, the computer first checks whether the various conditions for steel drawing are satisfied then calculates the set value of the steel drawing machine stroke and controls the steel drawing machine to advance and retreat through the APC program, and puts the heated slab on the speed of the outlet roller table is determined according to whether there is a billet on the centre line of the outlet roller table in the forward direction, and the slab is moved into the rough rolling area.

 

3) Automated process in the rough rolling area

In order to meet the requirements of process automation, hot metal detectors are installed at the corresponding equipment to track the rolled piece, so that the computer can detect the hot metal according to the detector and the position of the slab, strip, and sets and controls the corresponding equipment on the rolling line.

When the next slab is to be pulled out, the process control computer calculates the set values of the roughing mill through the mathematical model, such as the pressing position of each stand of the horizontal rolling mill for each pass, that is, the roll gap before rolling, and each stand of the vertical rolling mill. The opening degree of each pass, the position of the side guide plate, the biting speed of each frame of the horizontal rolling mill, the rolling speed, the steel throwing speed, the vertical rolling mill speed, the front and rear roller table speeds, the descaling method, the reference value of the measuring instrument, and the reduction compensation Values, etc., there are two calculations for the setting of the roughing mill. The time is when the steel is drawn from the heating furnace and when the slab reaches the entrance of the roughing mill. The second time is more accurate than the first time.

After accepting these set values, each computer at the basic automation level, through its own automatic position control system APC program and its own speed control system, within the specified time, the position of the work roll of the horizontal mill, the speed of the roll, the opening of the vertical roll mill, the side The actual value of each setting item required by the normal rolling process such as the position of the guide plate is adjusted to the allowable deviation range from the set value.

After the slab is released from the furnace, the operation of the roller table is controlled by a hot metal detector, and the slab is sent to the large vertical roll (VSB), which gives the slab a certain side pressure/amount, on the one hand, it reduces the slab The width; on the other hand, it is used to break the furnace-generated iron oxide scale attached to the surface of the slab. A high-pressure water nozzle is installed behind the large vertical roller to break the iron oxide scale on the surface of the slab.

In order to further improve the surface quality of the slab, before the slab enters the two-roll irreversible rolling mill R1, the iron oxide scale is sprayed with high-pressure water. The rolled piece is only rolled once on the R1 rolling mill, and then immediately and automatically sent to the four-high reversing rolling mill R2 for further rolling. ~ 5 or 7 passes, some can also be rolled 9 passes.

Since the R2 reversible rolling pass can be selected, in order to adapt to the rolling of multi-variety and specification rolled pieces, a semi-automatic setting is designed on the operating table. The so-called semi-automatic setting means that the operator uses the human-machine interface to set the process parameters of each pass of the R2 rolling mill, and outputs the set signal to the basic automation controller, which performs the control.

When the R2 rolling mill performs reciprocating rolling, in the case of an odd number of passes, the guide plate on the entrance side centres the rolled piece, and the small vertical roll Ez gives side pressure to the rolled piece. Before the rolled piece enters R2, it is further descaled with high-pressure water. In the case of even-numbered passes, the side guide plate behind R2 moves the rolled piece to the right. At this time, the side guide plate in front of R2 (i.e., the entrance side guide plate) is opened, and the small vertical roller E2 does not give side pressure. The R2 rolling mill forward and reverse and high-pressure water nozzle settings are controlled by signals from the hot metal detectors 34 and 40 at the entrance and exit sides. Due to the poor working environment conditions before and after the R2 rolling mill, there is water mist interference, in order to ensure that the hot metal detectors 34 and 40 can work reliably, gamma ray detectors are used.

The rolled pieces continue to enter the R3 Hefeng four-high irreversible rolling mill for twin-machine continuous rolling. The fan rolling mill is driven by an AC synchronous machine, while the R3 rolling mill is driven by a DC motor, and its speed is variable. The speed setting of the rolling mill is calculated based on the equal relationship between the speed of the R4 rolling mill and the metal flow rate per second. Considering the changes in the properties of the rolled metal and the process parameters during the rolling process, in order to ensure that the continuous rolling process can be carried out stably, The strip steel between R3 and R4 rolling mills adopts tension-free control.

There are high-pressure water descaling nozzles on the entrance sides of R3 and R4 rolling mills. Whether to spray water is determined according to the specifications of the finished products. During rolling, high-pressure water is used to further descale. On the intermediate roller table at the exit side of the R4 rolling mill, there are gamma-ray thickness gauges, photoelectric width gauges and optical pyrometer RT4. The measured thickness, width and temperature values are sent to the computer, which is used to calculate the temperature drop when the finishing mill is threaded, to set the exit thickness of each stand, and to control the width of the rough rolling unit.

In summary, the automation objects and contents of the rough rolling area are as follows:

 

(1) Basic setting items of each piece of equipment of the roughing mill

The pressing positions of R1, R3 and R4 mills;

The rolling passes of the R2 rolling mill and the pressing positions of each pass;

Openings of large vertical rolls (VSB) and small vertical rolls E3 and E4, and openness VSB of odd-numbered passes of Ez small vertical roll stands, positions of entrance side guides of R1 and R4, and positions of front and rear side guides of R2 rolling mill ;

The biting and throwing speed of the R2 rolling mill, the rolling speed of the R1, R2, and R4 rolling mills, the setting of the rolling time and reversal time of the R2 rolling mill;

The setting of the high-pressure water descaling nozzles on the front and rear sides of the R2 rolling mill and the entrance sides of the R3 and R4 rolling mills;

The setting of the thickness gauge, width gauge and temperature gauge on the exit side of the roughing mill and others.

 

(2) Control of strip width

According to the width of the finished strip measured at the exit side of the finish rolling unit, it is fed back to the rough rolling unit E3 and x4 for resetting to control the width of the strip. When the required width of the finished strip is When the difference from the actual measured width is less than 2.0mm, it is considered that the requirements of the technical standard have been met, and at this time, the correction of the required rough rolling strip width can be stopped.

 

(3) No tension control between R3 and R4 racks

In order to ensure that the continuous rolling process can be carried out stably, no-tension control is adopted on the R3 and R4 stands. The so-called no-tension does not mean that there is no tension on the rolled piece but only means that the tension level is limited to a small and constant within range. The tension-free control is realized by the hardware circuit. When the rolled piece is bitten by the R4 rolling mill, the tension-free control process is quickly established between the R3 and R4 stands. At this time, the computer only outputs the cross-sectional area data of the rolled piece.

 

(4) The rolled piece is controlled to wander and wait on the roller table (D6~D11 group roller table) between the R2 and R3 rolling mills.

In order to prevent this piece of the strip from colliding with the previous piece of the strip (strip that has entered the finishing mill) before the first stand F1 of the finishing mill, before the rolled piece is bitten by the R3 rolling mill, the anti-collision inspection calculation should be carried out, when the rolled piece is allowed to enter the R3 rolling mill, it can be bitten by the R3 rolling mill, otherwise the rolling piece should be controlled to wander and wait on the roller table in front of the R3 rolling mill.

 

4) Automated process in the finishing area

The roller table from the exit of the rough rolling mill to the entrance of the finishing mill is called the delay table (Delay Table) and is also called the E roller table according to the number of the roller table. On the left side of the advancing direction of the E-roller table, there is a waste product pusher, and on the right side, there is a fixed stand for processing the waste strip.

The speed of the roller table is controlled by the computer, which not only shortens the running time of the intermediate strip blank but also avoids the collision between the front and rear pieces. When the strip comes out of the last roughing mill R4, the speed of the E roller table is synchronized with the R4 stand. When the tail of the strip leaves the R4 rack, the computer checks the collision conditions. If there is no collision, the E roller table is controlled to run at a high speed, otherwise, the E roller table is controlled to run at a low speed until there is no collision before turning to a high speed operation. When the current strip arrives at the hot metal detector HMD54 before the cutting head flying shear, if the leading strip is still in the situation of the first finishing mill F1ON, that is, the leading strip is still rolling in F1, the computer has to judge whether it will Collision with the preceding strip, if F1OFF, that is, there is no rolling piece in it, check whether the roll gap and speed of the rolling mill reach the set value, if there is a possibility of collision, or the inspection fails, a swing command is issued to make The E-roller table reverses and delays for 10s before moving forward, swinging back and forth in this way (repeat the check every time HMD54 is turned on), until it is qualified and the computer issues a command to release the swing.

When the strip blank advanced to the hot metal detector 55, the speed measuring roller descended to measure the actual running speed of the strip blank at this moment, so that when the strip blank advanced to the hot metal detector 60, the speed of the strip blank was completely reduced to the same speed as the flying shear The cutting speed is the same. When the strip head reaches the hot metal detector 61, the flying shears start to automatically cut off the irregular or low-temperature head of the strip. Then the speed of the strip should be further reduced to be compatible with the biting speed of the first stand F1 of the finishing rolling group, that is, the reduction compensation should be considered.

The speed of the billet during tail cutting is detected by the upper roll of the second pair of pinch rolls in the descaling box before finishing rolling, and then the speed of flying tail cutting is determined according to this speed, and hot metal is still used for detection during tail cutting Device 61 starts flying shears. In order to prevent the cut head and tail from resting on the blank, the speed of the flying shears should be slightly higher than that of the blank when cutting the head, and the speed of the flying shear should be slightly lower than that of the blank when cutting the tail.

The control of the flying shear by the computer includes the cutting mode, the selection of the cutting length and the starting of the flying shear. There are 3 cutting methods: head cutting, tail cutting and half splitting (Half). Generally, the strip should be trimmed to make the head neat, which is convenient for the finishing mill and coiler to bite into. Whether to cut the tail depends on the thickness and width of the finished product. When the thickness is more than 2.4mm and the width is less than 1000mm, the tail of the blank will not be cut. The cutting method can be set by the computer or decided by the operator. The accident shear is controlled by the operator. In the past, the length of the cutting head and tail was generally set by the operator, and the cutting length was fixed. In order to improve the yield, a system for cutting to the optimum length according to the different head shapes of the strip was developed.

After cutting the strip, the secondary iron scale formed on the intermediate roller table is broken by high-pressure water through the descaling box. In order to further remove the secondary oxide scale on the surface of the rolled piece, there is also high-pressure Water nozzles, they not only play the role of removing the secondary oxide scale but also play the role of adjusting the temperature of the finished strip steel, so the selection of the high-pressure water nozzles before the descaling box, F1 and F2 should be based on the thickness of the finished strip steel, selected by the computer.

Between F2 and F3, F3 and F4, F4 and F5, F5 and F6, and F6 and F7, there are nozzles for cooling the strip steel between the racks, The purpose is to adjust the final rolling temperature of the finished strip steel, and their selection is also based on The thickness of the finished steel strip and the final rolling temperature are controlled by the computer. In addition to changing the water quantity by changing the water spraying method, the water quantity can also be controlled by dynamically adjusting the opening of the valve.

In order to ensure that the continuous rolling process of the rolled piece in the finishing rolling unit can be carried out stably and reliably when the front end of the strip reaches the thermometer RT4 behind R4 2s, the temperature should be determined according to the specifications of the finished strip (such as steel type, material and size, etc.) ), rough rolling result information (such as strip thickness, width and temperature, etc.), to determine the load distribution, reduction regulation and speed regulation of each stand of the finishing rolling unit, and determine the reduction position according to the rolling load. Each stand of the finishing mill is set for the first time.

After the first setting calculation, because the strip blank will produce a certain temperature drop as the running time goes by, when the strip blank passes through the thermometer FT10 at the flying shear, the computer should use the temperature model again according to the measured temperature at this time The setting calculation is performed, which is the so-called second setting. It is especially effective for the setting of the second half of the strip that needs to be rolled on the intermediate roller table when a failure occurs in the process after the finish rolling, and when the strip is cut in half. After the strip is bitten by the F1 and F2 racks, it is necessary to compare the measured rolling pressure and pressing position with the set value and then set the third time for the F3 to F7 racks.

After the strip is bitten by the finish rolling mill, the thickness automatic control device (i.e. AGC) of the corresponding stand will be put into work one by one.

When the strip is bitten by the two racks in the finishing mill, the load relay of the latter rack will activate the looper supporter between them. According to the principle of equal flow of metal per second, the load relay of the former rack is adjusted. Speed, to maintain the speed balance relationship between the two racks. In addition to supporting the weight of the strip between the racks, the looper support also plays a role in adjusting and maintaining a constant small tension on the strip between the racks.

In order to make the temperature of the finished strip steel at the outlet of the finishing rolling mill uniform along the length direction of the strip steel, an accelerated rolling method is adopted in the continuous rolling process, that is, the speed of the last stand of the finishing rolling mill is 600m when the strip is threaded. /min, after the strip threading process is completed, rolling is carried out at different accelerations according to the thickness specifications of the finished strip steel. When rolling thin-gauge strip steel, in order to ensure the stability of the strip steel running on the output roller table when the strip is threaded, two-stage acceleration is generally adopted, which is divided into the first acceleration and the second acceleration. Since thickness gauges, width gauges and other equipment are arranged on the exit side of the finishing mill, the distance between the rollers of the roller table is large, and the stability of the strip running in this area is very poor. The first acceleration starts after the rack exits 50m.

During the rolling process, the required acceleration range is adjusted according to the temperature of the steel strip at the exit of the finishing rolling mill. The highest rolling speed used by the finishing rolling unit is set according to the table stored in the computer in advance, but it can also be set by the operator through the man-machine interface according to the actual rolling situation. When the rolling process of a steel strip in the finishing mill is about to be completed, in order to avoid jumping or discounting the tail of the strip when throwing steel after the tail of the strip leaves the P7 stand, the machine should be started according to the pre-determined deceleration The deceleration frame can be decelerated, and the deceleration start frame can be specified as F1, F2 or F3, that is to say, after the tail of the strip leaves the frame, the throwing speed of the strip from the F frame should be reduced (controlled at 900m / rain or so). After the tail of the strip leaves each frame, the frame should reduce its speed to the speed of the next threading with the maximum deceleration, so as to get ready for the rolling of the next strip.

During the rolling process, the speed adjustment system of each stand of the finishing mill is controlled by a computer with the F7 stand as the reference stand. In the operating room of the finishing rolling unit, there is also a semi-automatic setting control. If necessary, the operator can set the speed of the finishing rolling unit, and send the signal to the computer for control.

In order to ensure uniform thickness along the length direction of the strip, in the automatic thickness control system, various methods are used to control the thickness of the strip at the exit of the finishing mill. The basic thickness control method is the thickness gauge AGC (GM-AGC), which is equipped with a thickness gauge AGC on each frame. In addition, there is a feed-forward AGC for the F2 to F6 frames, and the seventh frame is equipped with a feed-forward AGC. Equipped with monitoring AGC.

In order to control the transverse thickness difference and shape of the strip, the positive and negative roll bending devices for the work rolls are installed on the 7 stands of the finishing rolling unit, and the hydraulic cylinders used for the positive roll bending are set on the bosses of the archway windows, There is a hydraulic cylinder for negative bending rolls in the support roll chock. As for the bending device of which frame to choose, whether to use positive bending rolls or negative bending rolls, it is up to the operator to choose reasonably according to the different conditions of the plate shape. Positive and negative bending rolls can only be formed in the rolling state. When the roll bending device is not used, the hydraulic cylinder of the positive roll is used as the balance cylinder of the work roll. At this time, the hydraulic cylinder works under low pressure.

The objects and content of automation in the finishing rolling area are as follows:

 

(1) The setting of each piece of equipment in the finishing rolling area

The setting of the opening degree of the guide plate on the inlet side of the flying shear and the setting of the cutting method;

The setting of the water spraying system between the high-pressure water descaling box and the rack;

The setting of the opening degree of the entrance guide plate of each stand of the finishing mill;

The setting of the pressing position of each frame when threading the belt;

The setting of the strip threading speed and acceleration of the final stand of the finishing mill and the rolling speed in the stable rolling stage;

The calculation of the rolling pressure of each stand and the setting of the pressing position;

The setting of the balancing force, height and tension of the looper support;

Setting of thickness gauge, width gauge, crown gauge and flatness gauge, setting of bending force of work roll and axial movement of work roll, etc.

 

(2) Automatic thickness control during finish rolling

Selection of thickness automatic control mode; calculation and setting of process parameters (rolling pressure, roll gap value, rolling mill rigidity coefficient, oil film thickness, speed, tension, etc.) in various thickness automatic control systems.

 

(3) Automatic temperature control during finish rolling

Automatic control of the temperature at the exit of the finishing mill; adaptive control during strip threading, the first setting calculation when the head of the strip reaches the thermometer behind the R4 rack about 2s; detection of the hot metal when the head of the strip reaches The second setting calculation of the HMD54; when the head of the strip is bitten by the F1 and F2 racks, according to the measured rolling pressure and the pressing position on the F1 and F2 racks, for F3 to F7, the racks The original set value is corrected, which is the belt self-adaptation or the third set calculation.

 

5) Automated process in laminar cooling and coiling zone

After the steel strip enters the Fl, the computer calculates the settings of the coiler and calculates the reference value required for the control of the coiling area.

From the time the head of the strip leaves the finishing stand of the finishing mill until the head is drawn into the coiler, the speed of the hot run table (Hot Run Table) is controlled by the computer to be higher than the speed of the finish stand of the finishing mill (i.e. leading), so that the roller table gives Strips a forward pull that prevents wrinkling of the head.

After the strip head bites into the coiler, the speed of the roller table is synchronized with that of the finish rolling unit. When the tail of the strip leaves the deceleration stand of the finishing mill, the computer controls the speed of the roller table to make it slower than the throwing speed of the finishing mill, so that the roller table can give the strip a backward pulling force to prevent the tail of the strip from wrinkling.

When the strip runs on the roller table at the exit side of the finishing mill, the computer controls the coiling temperature of the strip by presetting and dynamically adjusting the number of cooling water sections and water spraying methods of the laminar cooling device.

The rolled steel coil is placed on the transport chain by the coil unloading trolley, and transported to the downstream process. The computer judges whether the operator has issued a “steel coil inspection request” for the steel coil, and if so, sends the steel coil to the inspection line, the inspection results are input into the computer through the man-machine interface device, so as to print the report.

After the steel coil is weighed, the weighing machine transmits the measured weight of the steel coil to the computer, and the computer checks the weighing result, judges whether the weight is reasonable, and generates an alarm message. If the weighing is normal, the computer will set the “weighing completion flag” output the print command and coil number to the printer, and print the report.

At this point, the control of the rolled piece by the process computer is over, and the control and management of the steel coils in the coil warehouse and the finished product warehouse are completed by the production control computer.

The automation objects and content of the laminar cooling and coiling area are as follows:

 

(1) The setting of each piece of equipment, the setting of the lead rate, lag rate, deceleration rate and deceleration start point of the output roller table; The setting of the lead rate of the auxiliary winding roller and the reel; the tension torque, bending torque and acceleration torque of the reel; the lifting amount of the unloading trolley, etc.

(2) Automatic control of coiling temperature.

(3) Control of side water spray and cooling water on the output roller table.

 

3. Types of control systems

There are many ways to classify control systems. According to the variable control and information transmission methods, they can be divided into open control, closed control, semi-closed control, and compound control.

 

1) Open control

The principle of this control method is that the signal is transmitted from the given value to the controlled quantity in one direction, so it is also often called open-loop control. The accuracy of an open-loop control system then depends on the accuracy of the initial calibration of the system and the accuracy of the system components.

This type of control is simpler but has major drawbacks. When the control device is disturbed or the controlled object is disturbed, it will directly affect the controlled quantity and cannot be compensated. The steady-state performance index and dynamic performance index of the system cannot be guaranteed, so they can only be used on occasions with low requirements.

 

2) Closed control

The principle of this control method is that what is measured is the controlled quantity. Whether it is caused by interference or the change of the structural parameters of the control device, as long as there is a deviation in the controlled quantity of the controlled object, the system will correct the deviation by itself, so this kind of control is often called closed-loop control or adjustment according to deviation. feedback control system.

Since the signal obtained from the detection is fed back to the input terminal for comparison with the given amount, the deviation obtained is not to control the position at the detected point, but to control the subsequent position, so the feedback control has a hysteresis effect. However, since the condition of the raw material cannot change suddenly, the control signal also has a reference function for the subsequent parts, so the feedback is widely used in the automatic control system.

 

3) Semi-closed control

The principle behind this type of control is that disturbances that disrupt the normal operation of the system are measured. Use the control function generated by the interference signal to compensate for the influence of the interference on the control quantity. Therefore, this kind of control is also often referred to as a control system based on disturbance compensation. This kind of control is conditioned on the measurable disturbance of the system, so it can only compensate for the measurable disturbance. The system will not be able to compensate for the impact of unmeasurable disturbances and changes in the structural parameters of the control device on the controlled quantity. Therefore, the steady-state performance index and dynamic performance index of the system are still not guaranteed, and the application is limited.

 

4) Duplex control

Integrating a closed control system and a semi-closed control system, it is more reasonable to combine these two kinds of control. For interference, use appropriate control devices to compensate for disturbances; in addition, use closed-loop negative feedback to adjust according to deviations to eliminate the impact of other disturbances and changes in structural parameters of control devices on the controlled variables. In this way, since the main disturbance has been compensated or approximately compensated, the disturbance received by the system is greatly reduced, so the part adjusted according to the deviation is easier to design. The main steady-state performance index and dynamic performance index of the system are guaranteed, and a better control effect can be achieved. This kind of control is widely used in engineering.

 

4. Various testing instruments

There are many detection instruments on the automated steel rolling production line, with many models, different functions and principles. The following is a brief introduction to the working principles of some typical instruments.

 

1) Temperature measuring instrument

Contact thermometers include thermocouples and thermal resistors. The principle of temperature measurement is that the measured object and the detection element are in contact. When the temperature reaches the same value, the temperature change of the detection element causes the electrical parameter to change, and the electrical parameter change is used to calculate the temperature of the measured object. Thermocouples and thermal resistance thermometers are suitable for measuring the temperature of fixed objects. The thermocouples that are recognized as representative or more commonly used include platinum-rhodium-platinum thermocouples, nickel-chromium-nickel-aluminium thermocouples, and nickel-chromium-nickel-copper thermocouples.

Non-contact thermometers include radiation thermometers, optical pyrometers and scanning thermometers. The detection elements for radiation pyrometers mainly include silicon photocells and stacks. The medium and object blackness coefficient changes between the measured object and the thermometer sensor Will affect the measurement accuracy. Radiation pyrometers are used in places where it is not suitable to install thermocouples for temperature measurement, especially for temperature measurement of moving objects, such as the detection of steel plate temperature in controlled rolling, and temperature correction when measuring steel plate thickness, width, and length. Optical thermometers are measured by human eyes. In addition to the change of the medium and object blackness coefficient between the measured object and the thermometer sensor, which will affect the measurement accuracy, it is also affected by the subjective factors of the observer. The measurement accuracy is low, generally only It is used to temporarily detect the temperature of the steel plate, and its advantage is that it is easy to carry. The scanning thermometer is used to measure the lateral temperature distribution of the steel plate.

 

2) Rolling pressure measuring instrument

The pressure measuring sensor (also known as the pressure head) has several types such as piezomagnetic type, resistance strain type, capacitive type and inductive type, and sometimes the rolling force is indirectly measured by detecting the oil pressure in the hydraulic cylinder.

The piezo-magnetic indenter is a force-electric converter made of the phenomenon that the distribution of magnetic force lines will change when a force is applied to the silicon steel sheet. It has three series of rectangle, circle and ring to choose from. Its key components are composed of many silicon steel sheets overlapped and bonded together, similar to the iron core of a transformer. The piezoelectric indenter has the characteristics of good anti-interference, reusable, large output signal, good overload performance and high measurement accuracy, but it is expensive and only used in necessary places. The domestic application is mostly made by ASEA Electric Company in Sweden The piezomagnetic indenter.

The resistance strain indenter is made by using the phenomenon that the elastic element is elastically deformed under the action of pressure, causing the strain gauge (internal wire) close to its surface to deform (elongate or shorten) and the resistance will change accordingly. , it is generally used in racks that do not require very high accuracy of rolling force detection.

The pressure head generally has 3 installation positions: between the pressing screw and the bearing seat of the upper roller, between the bearing seat of the lower roller and the lower beam of the frame, and on the pressing nut. The specific installation position of the pressure head depends on the condition of the rolling mill.

 

3) Thickness gauge

There are two types of thickness gauges: contact type and non-contact type. The contact-type thickness gauge has a long measurement period, low measurement accuracy and wide measurement range. It is used for measuring the thickness of rolled pieces under low-speed and cold rolling conditions. Non-contact thickness gauges are widely used due to their fast response, high measurement accuracy, continuous detection, easy computer networking, and automatic thickness control.

Non-contact thickness gauges include X-ray thickness gauges, γ-ray thickness gauges (mainly americium and caesium), ultrasonic, infrared and laser thickness gauges. The first two are radiation thickness gauges, which are based on certain When the energy ray passes through the steel plate, the attenuation intensity of the ray has a certain relationship with the thickness of the steel plate. After the ray is emitted by the ray source, it is generally absorbed by the steel plate from bottom to top, and the rest is accepted by the detector. When there is no steel plate in the measured space, use a reference plate of known thickness for calibration.

The modern thickness gauge is a set of computer data detection and processing systems, which has computing functions (such as calculating and outputting the measured thickness deviation according to the input target thickness and measured thickness), self-calibration, self-diagnosis and maintenance and other intelligent functions.

Gamma rays are more penetrating than X-rays, but it is difficult to achieve high radiation doses compared with X-rays. A large radiation dose enables low noise and high response speed. The X-ray thickness gauge is suitable for thickness measurement of high-speed production lines such as thin plates and medium plates, and can be installed between the exit of the hot-rolled strip mill, the exit of the cold-rolled strip mill, and the racks. The americium 7-ray thickness gauge is mainly used for thickness measurement of medium and low-speed production lines of thin plates. Since the energy of the 7-ray radiated by the americium isotope is lower than that of the gamma-ray radiated by the caesium isotope, it is easy to shield and can be used as a small thickness gauge for cold rolling lines. The caesium gamma ray thickness gauge can be installed at the exit of the hot strip rough rolling mill, the exit of the thick plate hot finishing mill and its finishing line.

 

4) Roll Gap Measuring Instrument

The roll gap value is affected by factors such as roll diameter changes. It is a relative value relative to a certain zero point (or reference point). Generally, the pressing force of the upper and lower work rolls is 1/5~ of the usual maximum rolling load. The position at 1/10 o’clock is set as the zero position of the roll gap, and zero adjustment operation is required after changing rolls or when the machine stops abnormally.

Generally, the roll gap cannot be directly measured. The commonly used method is based on the measured rotation angle of the pressing motor shaft, the rotation angle or displacement of the pressing screw (such as the top hat detector), and the displacement of the hydraulic cylinder piston or roll-bearing seat. The amount (such as measured with a magnetic ruler) is used to calculate the roll gap.

Since the roll gap cannot be measured directly, the change of the roll gap caused by factors such as roll wear, thermal expansion, oil film thickness change of the oil film bearing, and roll eccentric operation will not be measured, and measurement errors will inevitably occur, and various compensation measures need to be taken to solve it.

 

5) Rolling piece position detector

There are several types of rolling position detectors:

 

(1) Hot Metal Detector HMD

When the hot-rolled piece reaches the detector position, the infrared rays radiated by the hot-rolled piece are focused by the objective lens, pass through the filter that blocks visible light, and enter the photoelectric conversion element (silicon solar cell, etc.) placed at the focal point for photoelectric conversion. The output of the photoelectric conversion element is amplified by a DC amplifier and used as a control signal. The influence of the temperature of the rolled piece or water vapour should be considered when using it.

 

(2) Gamma-ray detector

It is used for the detection of rolled pieces or plate edges in heating furnaces and rough rolling processes. The gamma-ray source and gamma-ray detector are respectively placed on both sides of the plate. When the steel plate arrives, the signal from the detector changes sharply, and the signal is amplified as a control signal. The work of the γ-ray edge detector is not affected by the temperature change of the rolled piece and water vapour.

 

(3) Cold Metal Detector CMD

The light emitted by the light emitter or laser source with frequency conversion by the oscillation circuit is received by the light receiver, becomes the output voltage of the phototransistor, and then becomes the output signal after amplification and detection. When the head of the plate arrives or the tail leaves the detector position, due to the radiation, reflection or shading of the plate, the amount of light received by the light receiver changes, causing the output signal to change, thereby detecting the position of the edge of the plate.

 

6) Width measuring instrument

The detection part is installed above the steel plate, and two sets of scanners are installed inside. The distance between the scanners is preset according to the width of the steel plate, and the position of the edges on both sides of the steel plate is scanned continuously. In order to make the edge of the steel plate have a strong contrast, a light source is installed below, that is, a back-illuminated light source is used to form an image of the edge on the rotating slit through the optical system, which is converted into a signal corresponding to time through the rotating slit. The light passing through the rotating slit is converted into an electrical pulse signal in the photomultiplier tube, and a reference clock signal is applied on the basis of the pulse signal. According to the digital measurement value and the width setting value, the width deviation and the lateral swing of the plate centre are obtained.

 

7) Flatness measuring device

At present, the laser-type flatness measuring instrument is widely used. The laser beam emitted by the three laser generators deviates from the reference point with the height of the surface wave of the strip, so that the waveform size of the edge (middle) of the plate can be measured. and. However, when the strip enters the coiler, tension will be formed between the pinch roll and the finishing stand to distort the wave shape (in general, the wave shape will disappear), so the flatness measurement is only valid before the strip enters the coiler.

 

8) Convexity measuring device

In order to measure the change in thickness along the strip width, mobile thickness gauges have been used. Due to the limited moving speed, the measurement signal cannot be used for feedback in real-time and can only be used for the next piece of steel. In addition, the jitter that occurs when the thickness gauge moves will affect the thickness measurement accuracy. The multi-point X-ray source and the array X-ray receiver introduced in recent years make the crown of the strip steel can be measured instantaneously, so it can be directly used for crown feedback control.

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