1 Introduction

With the advancement of technology and the increase of production rhythm, Shouqin Company's converter steelmaking system decides to introduce Siemens' advanced secondary control model to upgrade the existing control system, and the PLC program adds the secondary model control mode on the basis of the original automatic control. The converter steelmaking system consists of three converters, and the alloy charging system is divided into a common part shared by the three converters and a private part serving only a single converter, as shown in Figure 1. There are 10 bins in the common part, each two adjacent to each other as a group, sharing a hopper scale, a total of 5 hopper scales. Below the hopper scales, the alloy charge is transported via 4 belts and 2 electro-hydraulic 3-way valves to the alloy aggregate hoppers at the back of each converter. Each converter has 2 private bins with 1 hopper scale, and the weighed alloy is discharged directly into the alloy hopper at the back of the furnace. Since there is only one manual valve at the bottom of the hopper, which is normally normally open, the weighed alloy will be poured directly into the ladle. In both the public and private parts, there are 2 silos sharing 1 hopper scale. Due to the production process and equipment, two kinds of raw materials can not be mixed in the same hopper scale, so when the two neighboring bins need to release materials, the hopper scale can only weigh one kind of alloy material first, and then continue to weigh another kind of alloy material after the hopper scale is empty. With the introduction of a secondary dosing control system, the alloying system automatically completes the process from preparation to discharge according to the alloying commands issued by the secondary system. Considering that the common 10 alloy silos are shared by three converters, the raw material stored in each silo is not fixed, and there is also a situation that the same raw material is stored in more than one silo, in order to speed up the production rhythm, shorten the preparation and discharge cycle, and try to avoid the phenomenon of "hopper scale scrambling" (two adjacent silos are required to prepare the material, and scrambling to use the same hopper scale). Therefore, the weighed alloy material is directly unloaded into the alloy summary hopper after the furnace. The requirement of "optimized bin selection" is put forward for the primary feeding system.

2 System environment

This transformation project, for the alloy feeding part, continue to use the original environment: the first level of control system hardware is Schneider's Quintessence series of CPU 43412, PLC programming software using ConceptV2.6, monitoring screen using iFix v3.5 software programming.

3 control requirements and difficulties

The operation process of the alloy loading system before the modification is as follows: the operator inputs the set weight of the material to be prepared for each hopper scale on the monitoring screen in advance, and then notifies the PLC of the bin from which the material will be prepared by the selection buttons on the monitoring screen, and then triggers the "Alloy Preparation Start" button to complete the process from preparing to discharging the material to the ladle. Since the alloy charging system is shared by three converters, it is necessary to obtain operating privileges before operation, and then release the privileges for other converters after the operation is completed.

After the modification, the parameters such as raw material name, raw material code, raw material description and priority stored in each bin are all controlled by the secondary system and the data is sent to the primary control system. The operator can change the raw material type, code and other parameters of each bin in the secondary control system according to the actual production and production demand.

In the secondary control mode, the secondary control system will also calculate the type and quantity of alloy to be added according to the composition of molten steel before the steel is discharged and send it to the primary control system for execution. After receiving the instruction from the secondary control system, the primary control system will judge which silo will perform the preparation operation according to the equipment conditions, and then transfer the set weight corresponding to the raw material with higher priority to the corresponding hopper scale to carry out the weighing operation. After weighing, the alloy materials in the hopper scale will be put onto the conveyor belt, and then the alloy materials will be discharged to the ladle through the alloy summarizing hopper after the furnace by the belt conveyor. The primary control system also sends the status of each silo equipment and the actual feeding weight to the secondary control system as an important parameter to participate in the model calculation. In the secondary control mode, the whole process of feeding alloy into the ladle is actually divided into two steps: weighing and preparation and feeding into the ladle. To facilitate the operation, the operator only needs to obtain the corresponding operating privileges in advance, and then triggered by the "Work 2 feed preparation start" button on the monitoring screen, the whole process from feed preparation to discharge can be completed.

In the process of programming the PLC, it was found that the following factors existed that made programming difficult.

(1) The type of raw material in each bin is not fixed and is determined by the secondary control system with the possibility of change.

(2) The type of alloying material added to the ladle and the data are not fixed and are calculated by the secondary control system model and the results are transmitted to the primary control system for execution. Prior to the retrofit, the operator entered the weighing setup data for each hopper scale and manually specified which silo would be used to prepare the material. After the modification, only the set weight and priority of each type of material to be prepared are known, and the first-level automatic dosing system judges which bin to prepare the material and transmits the set data to the hopper scale.

(3) Each alloy material is not necessarily stored in only one silo, and there is a possibility that the same raw material is stored in more than one silo.

(4) Considering that there are 10 alloy bins shared by the three converters, and due to the production process and equipment requirements of the hopper scale can not be mixed, so we should try to avoid the phenomenon of "hopper scale contention", that is, to avoid sharing the same hopper scale of the two silos at the same time need to prepare the material situation. When the occurrence of "hopper scale", in accordance with the secondary control system to send a variety of raw materials to allocate the priority of the bin to prepare the sequence of raw materials, high priority raw materials are weighed first, and then the implementation of all hopper scales in the raw materials through the belt transportation discharge to the ladle process; and then, then lower priority raw materials are weighed, and once again the implementation of the discharge through the belt discharge to the ladle of the discharge process. In this case, the system has to go through two cycles of preparing and discharging to complete the instruction to add alloy, which is bound to extend the time of preparing and discharging, which may affect the production of the other two converters, and will also have an impact on speeding up the pace of production and improving productivity.

Combined these factors, the first level of control system is not only the second level of the system instructions in the raw material code and the silo code for simple judgment to match, but should choose a reasonable silo for the preparation of materials, so that the two adjacent silos try to avoid the simultaneous request for preparation of the material occurs, so as to shorten the cycle of preparation and discharge, that is, to achieve the "optimization of the selection of silo". Algorithm steps in order to facilitate the integration with the original program, we optimize the selection of the entire function is designed as a custom function block. Since there is a possibility of "hopper scale contention", the case of two cycles of material preparation is considered.

We divided the optimization of bin selection into three steps. First, the secondary instructions are sorted by priority and the results are stored in the variable ZL_PX; then, in the second step, the available bins are searched for one by one according to the priority for each of the data in the sorted variable ZL PX, and the results are sent to the internal variables SPWt1 (set weight for bins of the first stocking cycle) and spWt_2 (set weight for bins of the second stocking cycle), so as to ensure that the raw materials with higher priority are prepared first. This is a key step in optimizing bin selection. Finally, in the third step, the data of SPWt 1 and SPWt_2 are organized into output variables HopWt1 (the weighing setting of each hopper scale for the first round of stockpiling), HopWt_2 (the weighing setting of each hopper scale for the second round of stockpiling), and Sel-Bin_1 and SelBin_2 (the markers for selecting the two partner bins of the first and second rounds of the hopper scales, respectively, with 1: odd bin, 0: even bin, and 1: even bin). bin 0:even bin) are assigned.

4.1 Interface Data Design

In order to facilitate the calling of the function block, we design the input data, output data and internal variables of the function block as an array type, and the data type is named starting with "A".

4.2 Specific Steps and Processes

Feeding system consists of control, control, bucket machine and other weighing control system; electromagnetic vibrating feeder is used to provide granule or powder ingredients from storage warehouse or hopper to belt conveyor, bucket machine and other batching system. Especially in automatic batching, automatic control, etc., to realize the production process automation control and centralized management.

To ensure weighing speed and weighing accuracy, use a floor scale real-time weighing system with all controls to speed up and slow down the two-stage dosing system. Weighing is done first using the fast method, and as the weighing approaches the setting using the slow addition method until the setting is reached and the batching system is stopped.

Powder is measured using weighing and then placed into the mixer for periodic mixing before opening the mixer's exhaust gate and placing the mixer into the transition warehouse. The powder in the transition warehouse and the well known crushed residue are simultaneously and uniformly placed into the formulation dosage extractor, which feeds the dosage into the reaction tank.

The central control system can be divided into three control managers: Engineer Operator Workstation, Manual Control Center and Remote Control Center. The Engineer Operator Workstation system monitors site status and enables automated control in the form of an intuitive HMI platform. Clear illustration describes the industrial control site. Specialized software development platform is applied to complete the real-time monitoring of temperature, pressure, flow, etc. in the workshop, record the historical data, complete the record of production parameters, manual/automatic status, dosage system status, and the protection status system displays the alarms in the form of acoustic and visual alarms to ensure the stable operation of the system.

(1) Engineer operator station. Mainly responsible for the whole raw material handling and dosage process, on-site weighing data, dosage status monitoring. Batching operation control; adjusting and printing the way of material parameters, warning, recording, displaying and printing parameters.

(2) Manual control layer. Mainly used for dosage process monitoring, manual intervention. Workstation and control cabinet button operators can operate the on-site dosage system directly by detaching from the automatic process according to the on-site situation and process scheduling requirements.

(3) Field control. Completion of the batching production process key electromechanical system field control function configuration machine-side control, faster and flexible control of field circuits; fully alleviate the complexity of the field control circuits, help to improve the performance of field control of the batching and improve work efficiency.

In order to optimize the horizontal collaboration of process batching, the system connects the reaction tank stages to complete the seamless connection between raw material batching and production, eliminating miscalculation of production status and reducing stalls, failures, disturbances and energy efficiency. First, the control system integrates storage, management and sharing of the integrated network integrated mode dosing data. Among other things, the parameters related to process batching are updated in real time by the process control station, and the updated data parameters are stored in the PLC master data card. The system introduces monitoring of the current dosage operating parameters into the production process, which is automatically modified at each process changeover point, so that each process dosage system maximizes the use of accuracy improvements over unit time for best fit throughout the system's production process.

5 Conclusion

After the above analysis, we can conclude that the optimized bin selection function can be a good solution to practical problems in production. Taking the above assumption as an example, if we do not consider optimal bin selection, but simply match the code in the instruction with the raw material code of each bin, we will get the result that both the bin and the control need to be prepared. Such a result will lead to "hopper scale competition" phenomenon, will inevitably extend the preparation, discharge cycle, affecting the efficiency of production.