Abstract: In this paper， daily production scheduling is studied based on the Third Steelmaking Plant of Wuhan Iron and steel corporation (WISCO). To make sure the daily production plan is feasible， method of casting group is established， and the compatibility between two converters and three continuous casting devices in the Third Steelmaking Plant of WISCO is analyzed. The process flow chart of daily production scheduling is given in this paper. Then， algorithms and procedures for the simulation of daily production plan is developed. Using the actual data from the Third Steelmaking Plant， the feasible daily steelmaking plan and cast plan are given. The plan contains 7 groups of cast plan， figured out 54 converters， and about 13，500 tons steel.

Key words: Production Plan Simulation; Steelmaking; Continuous Cast

doi:10.3969/j.issn.1673-0194.2009.15.036

CLC number: TP224;F275Article character:AArticle ID:1673-0194（2009）15-0120-04

1 INTRODUCTION

Consisting of two converters， three refining furnaces， and three continuous casting devices， the Third Steelmaking Plant (3rd SMP) of Wuhan Iron and Steel Corporation (WISCO)， P. R. China is a modern steelmaking plant， which has the most advanced technology for both production and management in the world. The 3rd SMP has be equipped with desulphurization installations. Its refining process consisting of two argon blowing stations， one ladle furnace， and vacuum degassing system. The 3rd SMP has three dual-line bow type continuous casters.

The 3rd SMP mainly satisfies the slab requirement from the Second Hot Rolling Mill. The main production method of the Second Hot Rolling Mill is Direct Hot Charging Rolling (DHCR). For the steelmaking-continuous casting-rolling production system which main charging method is DHCR， continuous casting process is the bottleneck. The jointed pull and push production method should be adopted［1］. According to the production scheduling problem in the dual-line continuous casting production of thin slab continuous casting and hot rolling， which is similar to the equipments of WISCO， two production organization modes were proposed. A simulation model was designed to analyzed the execution process of scheduling［2］. For theoretical study， mathematics models and algorithms are developed for the steelmaking-continuous casting production process［3，4］.

While formulating the feasible daily steelmaking-continuous casing production plan， the daily cast plan must be given firstly， then based on the pull production method， the daily steelmaking plan should be given according to the capacity of converters and the continuous casters， finally， the match between the converters and the casting machines should be verified. Because the 3rd SMP has two converters and three continuous casters， mismatch between the converters and the continuous casters occurs sometimes.

To make sure the daily steelmaking plan and cast plan is feasible， this paper developed the method how to simulate the match between the two converters and three continuous casters. The flow chart of daily charging production plan and the flow chart of daily charging production plan were built in this paper. In addition， the process flow charts of simulation of daily production plan was given. By using the actual data from the 3rd SMP， the feasibility of the draft daily steelmaking plan and cast plan was analyzed. The draft plan contains 7 cast plan， figured out 54 converters， and about 13，500 tons steel.

2 FROM 5-DAY PRODUCTION PLAN TO DAILY PRODUCTION PLAN

2.1 Daily casting production plan

When the 5-day charging and casting production plan is given， the daily casting production plan must be created. Based on WISCO’s conditions， to create the daily casting plan， 5-day production and equipment maintenance plan must be inputted. Then casting time can be calculated according to slab section table and cycle time of casting. The flow chart of daily casting production plan is shown as figure 1.

Fig.1 Flow chart of daily casting production plan

2.2 Daily Charge Production Plan

Based on daily casting production plan， the daily charging production can be developed. Firstly， based on daily casting timetable and equipment maintenance plan the daily charge plan can be developed. Then， the refine route can be determined according to code of process and steel grade table. Finally， the daily charging timetable can be developed through calculating metal adding time. The flow chart of daily charging production plan is shown as figure 2.

Fig.2 Flow chart of daily charging production plan

3 MATCH BETWEEN CONVERTERS AND CASTING MACHINES

The main outputs of daily steelmaking-continuous casting production plan are authorized daily charge and cast production plan. To achieve these results， daily cast schedule， daily charge schedule， and the smelting cycle， which is the main inputs of daily steelmaking-continuous casting production plan must be established.

To be sure the daily charge and cast production plan is feasible， plan simulation must be carried out based on the compatibility of converters and continuous casting machines. For the 3rd SMP， when mismatch occurs， the following strategies are established: if three casting machines must be operated simultaneously to finish one cast plan， but no converters is idle， or having no time to prepare the cast machines， the cast must be postponed; if only two cast machines operated simultaneously and one converter is idle， the time for metal founding should be moved up.

Fig.3 Flow chart of daily steelmaking-continuous casting production plan simulation

When daily steelmaking-continuous casting production plan is passed， the authorized daily charge and cast production plan is achieved. Then， the panel data interface (PDI) can be released.

Based on the inputs-process-outputs logic above， flow chat of daily steelmaking-continuous casting production plan can be drawn shown as figure 3.

4 SIMULATION ALGORITHM OF DAILY PRODUCTION SCHEDULE

4.1 Constraints of daily production schedule

While dealing with the production schedule， there are four constraints in the 3rd SMP as follows.

a. Three continuous casting machines are served by two converters. The output capacity of each converter is 250 tons. The smelting cycle is 40 minutes. Load should be allocated to each converter proportionately. The average casting speed is from 1.5 to 1.8 meter per minute. The average casting cycle is 50 minutes.

b. The time between current tapping of current charge schedule and metal adding of the next charge can not be less than 10 minutes.

c. The time between the end of the current cast and begin of the next cast can not be less than 60 minutes.

d. The output capacity of the converters and casting machines should be maximized. Theoretically， the 3rd SMP can produce 56 (56=24*60/50) converters according to the average smelting cycle， which is 50 minutes.

4.2 Simulation Steps of Daily Production Schedule

According to the flow and constraints of daily production schedule， steps of daily production schedule can be given as follows.

a. Read three daily cast schedules， which is foregoing in each day.

b. Read the number of the continuous casting machines， which will carry out the three cast schedules.

c. Read or compute the four time of each cast schedule: FC-metal cast-on time of first tapping; FA-metal adding time of first tapping; LC-metal cast-on time of last tapping; LA-metal adding time of last tapping. So， FCi-the ith cast metal cast-on time of first tapping， and so on.

d. Validate whether the following relation is correct or not:

LA3≥min{FC₁， FC₂}

e. If the relation is correct， carry the following steps; otherwise， adjust the value of LA3， FC1， or FC2 until the relation is correct.

f. Read the ith cast schedule and the number of continuous casting machine， which will carry out the three cast schedules.

g. Within the three daily cast schedules foregoing， find the cast schedule which continuous casting machine number is similar to the number of ith cast schedule， denoted by jth cast schedule.

h. Validate whether both of the following two relations are correct or not:

a) LAi≥min(FCi-1， FCi-2)，

b) LCi>FAj+150.

i. If one of the above relations is not correct， or both of them are not correct， adjust the LCi， FAi， FCi-1 or FCi-2， so that the two relations are correct.

j. Let i=i+1

k. Make sure the whole cast schedules are read， otherwise repeat the step g， h， i， j.

l. Give the authorized cast and charge time table.

4.3 Simulation Data and Results of Daily Production Schedule

The data applied to stimulating is shown as table 1.

Table 1 Cast schedule of No. 3 steelmaking plant of WISCO

Serial NumberNumbers of ConvertersNumber of Continuous Casting MachinePrimary finish time of the castFeasible finish time of the cast

162#05:3005:40

281#07:3007:30

373#11:0011:30

482#14:0014:10

581#18:0018:10

663#23:0023:10

7112#23:0023:20

Total54

For the first cast in the above table， subject to the smelting cycle， can’t be finished by 05:30， but can be finished by 05:40. For the second cast in the above table， If the cast requirement is not for the DHCR， it can be moved up 10 minutes to finished. Here， remain the time 07:30 unchanged.

Obviously， the finish time of the third cast is not feasible. The two casts which start before the cast must be finished until 04:40. In addition， the third cast contains 7 converters， so， based on the constraints above， the early start time of this cast should be 11:30， shown as figure 2.

So， the finish time of other casts can be determined， shown as the last column in the table 1.

The simulation result shown as figure 4. This feasible daily production plan amounts to 13， 500 tons metal. Specially， the time span of the cast that day is from 300 minutes to 550 minutes， indicating the daily production plan is flexible.

Fig.4 Simulation Result of Daily Production Scheduling

5 SUMMARY

The results of this paper is the subsequent ones of the paper titled “DHCR Scheduling Management System of Wuhan Irion and Steel (Group) Corporation (WISCO)”［1］ which is from same author. That paper studied the DHCR production management method in WISCO， designed process of subdividing 5-day production schedule in the form of flow chat， gave the solution of grouping the cast of steelmaking-continuous casting.

In accordance with the conditions of the 3rd SMP， this paper gives the method how to developed the daily casting and charging production plan based on 5-day production scheduled. In addition， the process flow chart of daily production scheduling， develops algorithms and procedures for the simulation of daily production plan is established in this paper. The time span applied to simulate is from 300 minutes to 550 minutes， so the daily steelmaking-continuous casting production plan is feasible.

References

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［2］ LV Zhimin， MU Weiheng， XU Jianhua， Jinwu. Production Organization Method and Simulation of Dual-line Thin Slab Continuous Casting and Hot Rolling ［J］. Journal of University of Science and Technology Beijing， 2005， 27(3): 256-359.

［3］ LIU Qing， BAI Suhong， LU Junhui， Production Plan Schedule for the Casting-rolling Process in BOF Special Steel Plants ［J］. Journal of University of Science and Technology Beijing， 2008， 30(5): 566-570.

［4］ YU Lihua， TANG Qiuhua. Establishment of Steelmaking-continuous Casting Production Plan and Simulation Test ［J］. Industrial Control Computer， 2008， 21(11): 39-41.