Automation of the Bao Steel Works Hot Strip Mill

Copyright © IFAC Automation in Mining. Mineral and Metal Processing. Beijing. PRC. 1992

AUTOMATION OF THE BAO STEEL WORKS HOT STRIP MILL D. LindholT*, XU Hai Hon~", Wang Wen Rui*** and Zhang Jlan Pingt ·Siemens AG. Al4 Department. Germany ··Chong Qing Iron Steel Design Institute. PRC ···Bao Steel Hot Mill Plant. PRC tBao Steel Automation Department Hot Mill Computer System. PRC

Abstract. The automation system of the BAO STEEL Hot Strip Mill consists of four level computer system ( management .production control.process contl'ol.and basic automation). I t is an integrated automation system wi th all required functions from real-time process control up to production management and fl'om produr' t ordering up to shipping , It carries out the quality design. monitor and control according to the end use of the products. In addition. some advanced technological functions adopted in the automation system: slab yard management .I!AIYC.crown and flatness control.hot charge rolling.This paper intends to introduce its lower three levels , Keywol'ds. Computer appl ication; production control; process control; adapti ve control; multiprocessing system,

INTRODUCTION Provide a good man-machine interfacp (M M I) for operator monitoring and intervention. Save energy. Keep tl'acking of the material flow from the Continuous Casting plant to Cold Mil I plant. so that the actual position and states of materials are known at all times.

[n August 1989. one of the most advanced hot stl'ip mi [Is in the world was put into operation at the BAO STEEL. In 1990.it produced 1.200.000T hot strip.and in 1991 2.400.000 T. The automation system has already demonstrated excellent performance on the production management. product quality assurance.and hot charge rolling.

AUTOMATION SYSTEM CONFIGllRATION Plant Layout The components of automation system configuration is shown in Fig,2.

The plant layout is shown in Fig.l . The technological process includes the following advanced techniques : Hot charging. Segmented walking beam furnace. Heavy vertical edger El and short stroke control in El. E2. Automatic width control ( RAIYC ). Crown and flatness control. llYD. AGC for stands FI to F7. Minimum tension control between FI to F4 . FI'equency-modulated AC motor in R3 . Step control for fully-hydraulic coiler.

Basic Automation System (BA) The basic automation configul'at i on coml'd ses a group of microcomputers forming the cOl'e of nine separated system. SYS tern 0:

System

The designed production capacity of the plant is 4.000.000 T/year . The coil thickness is 1,2 -2?4 mm. width 600-1900 mm. and unit weight 23 kg/mm. Slab thickness is 210-250 mm, slab width 650-1950 mm. max.weight 45T. Steel grades in~ludc low-carbon steel. low-alloy steel. and API X45 - X70 .

System

System System System System System

Targets of The Automation System The automation system has been implemented to : Fulfill the needs of hot charging process. Support high production yield and product quality . ll,~ I p manager and lechn i c i ans to get produc t i on information from it and give orders to pl'oduction in a timely fashion.

System System

I t cons i s t s f on" sI'! "f SI M!\ TIC S'i PLC I inked wi Ih FLS computer ;lIld is used for equipment contI'ol in the slab yard. I: [t consists of four SIMATIC S5 I inked together by a SIEMENS industrial bus and four MOD'30 sys tl'm fOl' ('("PI i ('ment control in th e fllrll ,1<'" """,1. 2 to Sys tern 8 : Tllf'S':' s~'s t('m;; ,·t)IlS i s t of MMC'216 mul t i-lIIi lTocomput"I's I inked together by the industJ'ial bus system. 2: El/RI control. 3: E2/R2.E3/R3 . E4/R4 control. 4: Crop shear control. 5: Speed control of the fini s iling In; 11 , 6: Scrcwdown control of the finishill g mi 11. 7: LaminaI' flo" cool ing c::ontJ'ol and interstand cooling control. 8: Coiler conlrol. t)

In finish mill area a MMC 216 syst('m is used

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specially for measurement and monitoring of rolling parameters. Process

system is the optimization of setpoint calculation and adaptation contl·ol. including: .Material tracking. including segment tracking . . Heat optimization control for furnace. .Mill pacing control . . Rolling strategy for the roughing mil I. . Setpoint calculation for the roughing mill. .Adaptation control of the )'ollghing mi 11. .Rolling strategy for the finishing mi I I. .Setpoint calculation for the finishing mi I I. .Adaptation control of the finishing mi I I . . Finishing temperature control . .Cooling strategy. .Coiling temperature control. .Strip width automation control. .Strip crown and flatness control . . Interstand cooling control in case of power speed up . . Man-machine dialog and CRT display. .Data communication. . logging and report generation.

Control System (PCC)

It includes six sets of SICOMP 70 minicomputers. They are: One set for furnace control. One set for the roughing mill. One set for the finishing mill.laminar flow cooling and coiler. One set for standby. Four computers are linked by optical fibers. In addition. two sets are used for the equipment monitoring and fault alarm system. To assure the data safety. data is simultaneously stored on both the main and a parallel image disk. In case the main disk malfunctions. the parallel image disk will be used for data access immediately.

The main functions of the preprocessing computers are' .Material image and segment image . .Acquisition. processing. and classification of measured value.

In addition. three MMC-216 are used for preprocessor of the PCC system. Production Control System (FLS)

The detai Is about setpoint calculation for the finishing mill are as follows:

The production control system has four sets of SICOMP M70 minicomputers. They are: One set for the slab yard and rolling area. One set for the coil yard. finishing area and finished product storage. One set for standby. One set for program development. Similar to the PCC.optical fiber and parallel image disk are used. In addition.it supports also the communication with the slabbing mill.continuous casting. and cold mill computers .

It comprises: .Pre-calculation . . Entry correction . .Post-calculation . 1. Pre-calculation: The pre-calculation is set in operation if a rolling has reached the measurement position after stand R4 and the target va lues. m,~ asured values and the boundary condi tions of the process become available.According to the nominal flow time from the measurement point to FI. a calculation is performed to get the following setpoints and control reference values for the finishi ng mi 11: .Roll ing for·ce. tOI'que.screwdown posi tions. speeds of FI to F7 . . AGC amplification factor. . CVC position . . Bending force . . Spray between stands.etc.

All MMls are designed with an industrial control keyboard and CRT. SUMMARY OF THE AUTOMATION FUNCfIONS Basic Automation System (BA) The basic automation has cute dynamic closed-loop control according to the and material position at main functions are:

the main task to execontrol and sequence setpoints from PCC the mill line. The

The precalculation will be initiated again if the following conditions appear : .The hold time on the intermediate roller table prescribed in the first precalculation was exceeded. .when the strip arrives at the hot metal det ector before thp. CI'OP shear. a set of new adaptation coefficients has been detel'mined by the post-calculation for the previous strip with similar quality and same finished thickness class . . The request from operator.

Material tracking. Automatic combustion control. Sequence control of the roller table and mi 11. Master control. Automatic posi tion control ( APC ). Crop shear control and cutting optimization control. Short stroke control. width dynamic feedback control (AWC) and feedforward width control (PWC) in the width automation control (RAWC) . Torque calculation of the looper and looper control. Speed control and minimum tension control. Full HYD. automatic gauge control (AGC) . Laminar flow cooling spray valve control. Control of interstand spray. Setup calculation and control of the coiler. Coiler step control. Scanning and processing of measured value. Man-machine dialog and CRT display. Data communication.

2. Entry correction: ImmediatelY following a stl'ip head entry to a stand the entry correction compares the mea s ured value acquired at the stand with th e calculated value from measured value anrl the' inher i ted data to correct the ro 11 i ng ( nl',' e and the screwdown for the stands not yet loaded. 3. Post-calculation: The post-calculation detp.rmines adaptation coefficients from measured values and the model equations used in the pre-calclIlation . using a variable amplification factor . Adaptation coefficients are determined for: Stand speeds. Stand exit thickness. Roll forces .

Process Control System (PCC) The main function of the process automation

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Rolling torques. Temperatures. Screwdown zero points, etc .

From the continuous casting plant (CC) via the transfer table . From the slabbing mill plant (SM) by truck. As a returned slab from the rolling area . As a returned slab from the area in front of furnaces.

The adaptation coefficients are then used in the "short time" and "long time" inheritance loops . Adaptation coefficients for short time inheritance are made available to the next strip with the similar quality and same dimension class, and have a greater amplification factor . The long time adaptation coefficients become effective when a large change in quality and/or dimensions occurs .

If the slab comes from the CC or SM. the FLS will execute the following input management functions: Announcement of a slab input from CC or SM . Identification of a slab at the entr'y of the HM area. Allocation of a position in slab yard for the slab. Selection of a transfer route . Transmission of transfer information of the slab to crane terminal and PLC . Material tracking on the roller table and starting of the roller table to transfer the slab . Lifting of the slab to the position in the slab yard by crane . Return actual location of the slab by the crane terminal.

Adaptive control The adaptation function adjusts the inaccuracy of the existing model by means of global adaptation coefficients after the post-calculation has been completed for the strip, thereby ensurring that the specified accuracy is achieved in the second strip of a order. It is very effective when the rolling batch or rolling condition has a larger change. Production Control System (FLS)

Slab slab slab data

In addition to real-time data processing,the production control system mainly executes production schedule dispatch and storage management. Its main functions include: Issue, dispatch.and optimization of the produc tion schedule. comprising the rolling schedule.shearing schedule. and shipping schedule . Execution of the hot rolling schedule. Material tracking . Slab yard management . Coil yard management . Finishing material storage management . Roll shop management. Quality control . Production data acquisition . Logging and report generation. Data communication .

yard mapping. The FLS keeps in memory each location in the slab yard and makes up a yard map . The operator can then change. upor query it . and print it out .

Crane operation management. There are three kinds of operation modes for the cr·an,,,, . l'Ii th the following priority : I. Output of slabs to the furnaces. 2. Restore of a slab from a pile to other pile in the slab yard . 3. Slab entry into storage. Cranes can be al located by the dispatcher by means of FLS t e rmlnai ana the operation direct! ve is thcn sen l lo lhe u ·ane . Slab out ut 0 eration man a emcnt. After the rolling schedule is optimize . t e FLS sends the slab output operation directives to the cranes in order of the rolling sequence . These directives are displayed on the crane t e rminal. After a slab has been loaded on the roller table. the FLS informs the PLC to control the charging roller table carrying the slab to furnace entry .

The control range of the production control system encompasses the entire hot rolling plant from the entry of a slab into the mill to the shipment of the finished product . SOME ADVANCED TECHNOLOGICAL FUNCfION

Generally, the crane loads the slab directly onto the roller table from the pile . In special cases. the slab is moved to a temporary holding area.

Slab Yard Management

Restoring slabs in storage. FLS suggests an appropriate position for thc slab . The slab yard manager can decide if it is adopted . The directive is then sent into the crane . After restoring the new position is fead back to FLS through the crane terminal.

The slab yard is a "buffer" area between steel making. continuous casting. slabbing mill. and the hot strip mill plant. Its management level has a great effect on production in front of or behind the process. The management target is to realize: Material flows smoothly. To minimize the storage of slabs satisfying the requirement of HM production. To support hot charging rolling. To keep the data safety of slabs. To simplify operator's work.

!lot buffer pi t operation. Opening and clos ing of the cover of the hot buffer pits can be controlled from the crane terminals. as we ll as from FLS and PLC terminals. Data communication pulpit is equipped that executes data inductive wireless

The main functions of the slab yard management are : Slab yard organization . FLS needs to set up some basic parameters of slab yard management via the terminal . All parameters can be input . changed.and updated. These parameters include: Slab yard layout . Crane allocation. Slab yard management strategy.

of c rane terminal. The c rane with an operation t e rminal communication with FLS by an communication devi ce .

Data inquiry. Through the terminal. th e ope r'ator and manager can inquit'e the location of any slab and any pile in the slab yard . and make a print out. Optimization process. The system makes optimal selection of slabs for the rolling schedule . In the rolling schedule . every rolling item is given a coil number. a slab number and corresponding slab data . FLS redistributes the slabs

Slab input operation management. There are four possible ways for a slab to enter the slab storage area :

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to the coils according to their positions in piles to minimize the repiling times. After processing. the piles are blocked and the roIling schedule is sent to process computer.

Where Fi : Pre-calculated rolling force . Fbi: Bending force . ' fl(W). f2(W) : functions of the strip width .

The optimization of process mentioned above has the following feature: The average repile rate for output slabs from slab yard into furnace is decreased about 30 to 50 % on the basis of actual production data statistics . During optimizing or after optimizing. only a small amount of the piles is blocked. so that the slab input into slab yard is not be hindered.

The stroke setpoint of eve roll is calculated according to the calculated Ccvci . The thermal expansion on the roller by temperature increa se and the wear of roller during the rolling, process are also taken into consideration. Dynamic crown control. Based on the strip crown measured by the static gamma-ray crown gauge. width. thickness and rolling force. the roll bending devices are dynamically adjusted to obtain the required crown. In addition . a laser flatness gauge is installed to monitor strip flatness . the crown and flatness control block diagram is shown in Fig.4.

Strip Width Automation Control (RAWC) Following are the main purposes of width automatic control: To decrease or eliminate the narrowing of strip head and tail due to bigger width reduction . To decrease or eliminate the influence of the "dog bone" part due to bigger width reduction to the target width. To decrease or eliminate the influence of the skidmark and width defects.

Hot Charging Rolling (HCR) In this system. there are two hot charging operating modes: Hot buffer pit mode . All hot slabs in the lIell schedule are put in hot buffer pit beforehand. Then. according to the rolling order. the hot slabs are taken out from the hot buffer pit and put into furnace .

Width automation control mainly includes the following : Pre-calculation. recalculation. post-calculation. and new-calculation for the vertical edgers . Calculation of strip natural spreading in the finishing mill. Adaptation control of width. Short stroke control of El and E2. Feedback control according to edger rolling force of E2 and E3(AWC). Width feedforward control of E3(PWC).

Mixed HCR. Partial hot slabs are taken out from hot buffer pi t and others come di rectly fr'om continuous casting plant. The following new techniques are used for hot charging . Refining process in the ladle. Width-adjustable mold. Non-defect slab casting . In the plant layout. the slab produced by continuous casting can be transferred directly to the hot strip rolling mill via the table.

Its control block diagram is shown in Fig . 3.

Specific technology has been used to satisfy the needs of the hot charging pr' ocess. For example: Hot buffer pit in the slab yard Segmented walking beam furnac e. Heavy vertical edger eve roll in the finishing mi 11. which wi 11 able to perform free rolling in the future. Optimized cutting equipment .

Crown and Flatness Control In order to control strip crown and flatness. the evc (Crown Variable Control) roll device and bending roll device are equipped for FI to F7. Through the bending roll device. the strip crown can be dynamically controlled. Precalculation of setpoint for crown and flatness control . The control has two related parameters: crown and flatness. The following principles are used to control flatness: It minimizes the load of the last stands. To equalize the crown to thickness ratio at all stands. Cl/HI

= C2/H2 = C3/H3 = ..... = C7/H7

In this automation system. the hot buffer' pi t hot charging is implemented as follows: MS computer system makes the hot charge schedule. The operators decide when to begin hot charging and reserve the hot buffer pi t posi tion for the hot slabs according to the process state of steel making and continuous casting. When the hot slab arrives at the hot mill plant entry from the continuous casting plant. the production control system assigns ita hot buffer pi t number and posi lion . and then sends this information to the crane terminal and the basic automation s~' st e m. After receiving the hot slab. FLS s end it's actual data to M S system, According to the hot slab data recei ved. MS system corrects or remakes the hot charge rolling schedule and sends it to production control system (FLS). The FLS optimizes the hot charge 1'01 ling sc hedule and sends it to the process automation system. According to the optimized hot charge rolling schedule. FLS sends a command for hot slab charging to the crane terminal and the basic automation system. and the HCR is then started.

(I)

During pre-calculation of the crown and the flatness. the above formula is used to calculate the target crown at each stand exit. The calculation steps are as follows : Strip target crown at each stand exit. Ci*

(2)

Cfi + Ccvci + Cfbi .

Where Ci* Cfi

strip target crown caused of stand i. Ccvci : crown caused stand i. Cfbi : crown caused of stand i.

From above calculation : Ccvci = Ci* - Cfi - Cfbi. Cfi = Fi * f1 ( W ). efbi = Fbi * f2 ( W ).

crown of stand i by rolling force by evc roll of by bending roller

(3)

(4) Hot charging rolling is a comprehensive new

(5)

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techniq ue. More experie nce and further develop ment will be required to bring the hot chargin g rate up to a higher operatio n level.

Strip Crown. Strip crown curve is shown in Fig . B. Mi II Pacing.

OPERATIONAL RESULTS.

The deviatio n of the mill pacing control is 3 seconds

Accordi ng to product statist ics, the typical curve of operatio nal results is as follows :

CONCLUSION

lfulih..

Although the system has been in operatio n for two years, some functio ns. such as rolling strateg y, flatnes s control and hot chargin g is still to be improve d . Followi ng the continuo us increase in product ion and system improvement. however, this system should be enhanced to satisfy fully product ion requirem ents .

Width control accurac y : within 6 - 10 mm Width deviatio n distribu tion curve is shown in Fig.5 . Thickne ss. The preset accurac y : within 0.05 mm. Thi ckness deviatio n distribu tion curve is shown in Fig .6.

REFERENCES

Finishin g and Coiling Temper ature.

Wilms,W . ,and L.Vogtman(1985) .Profile and flatnes s control in hot strip mills . Metallu rgi ca l Plant and Technology . Vol . 6 . pp .74-90.

Finishin g tempera ture accurac y: -20 - +20~C. Coiler tempera ture accurac y : -15 - +15-C . Finishin g and coiler tempera ture deviatio n distribu tion curve is shown in Fig .7.

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