The digital transformation of the steel industry promotes the development of continuous casting equipment towards networked, automated, informalized, and intelligent integrated technologies, of which intelligent mould powder-adding machines are a typical representative. The thin plate continuous casting workshop of the General Steelmaking Plant of Anshan Iron and Steel Co., Ltd. was put into operation on December 28, 2000. There are two first-class medium and thin plate continuous casting machines with a designed cross-section of 135mm (900~1550) mm and a maximum casting speed of 3.3 m/min, with an annual production capacity of 2.4 million tons. Steel types include low carbon, low silicon aluminum-killed steel, medium carbon steel, and low alloy steel. In October 2021, the casting machine was upgraded and the thickness of the mould was increased from 135mm to 150mm. The casting machine reached an annual production capacity of 600,000 tons of high-quality silicon steel. After the transformation, each continuous casting machine is equipped with an intelligent mould powder-adding machine, which not only realizes remote centralized control and unattended operation, but also reduces billet quality defects, reduces steel breakage prediction accidents, and improves the accuracy of billet quality determination. achieve better results.
1.1 Introduction of automatic slab mould powder adding machine technology
The steelmaking plant installed the first robotic automatic mould powder-adding machine in the thin plate continuous casting workshop in 2013.
The machine adopts a single-gun design and uses a robot trajectory setting to achieve crystallizer positioning, powder distribution and nozzle avoidance. The main machine includes a robot, vacuum loading tank, screw conveyor, system control cabinet, and material box, a total of 5 parts. Among them, the robot and the material box are arranged in a fixed position on the ground of the pouring platform. They can independently complete the feeding of protective powder in front of the machine, the input and control of the powder-adding machine, and the recovery during power outages.
The vacuum loading tank is installed on the bale pouring platform. Nitrogen is used as the energy medium to suck out the mould powder from the tank and lift it into the vacuum loading tank. The powder is fed to the screw conveyor through the unloading pipe relying on the gravity of the mould powder.
The feeding speed of the screw conveyor is adjusted by gears. The minimum basic value is 1kg/min, each gear level is 0.1kg/min, and the maximum feeding capacity is 2.0kg/min. The gears can be manually adjusted according to the consumption rate of protective powder in the crystallizer.
1.2 Movable and portable slab automatic mould powder adding machine
In 2015, based on the characteristics of the small slab section and high precision requirements for mould powder feeding control in the medium and thin plate workshop, a mobile and lightweight slab automatic mould powder-adding machine was developed.
The mould powder-adding machine is of rotary swing design and is installed in front of the 1# continuous casting machine. The car body uses two screw conveyors to spread slag. The maximum slag spreading width on one side is 200mm. The cumulative castings were poured from January 2016 to October 2019. There are 4.46 million tons of blanks and 2,182 tons of mould powder transported. The types of mould slag include hollow granular slag, solid granular slag, flaky granular slag, and powdered slag. The discharge port of the screw conveyor runs in an arc shape within the cross-section of the mould, and the falling point of the mould powder is biased towards the outer arc. For crack-sensitive steel types, longitudinal cracks are prone to occur at the arc nozzle of the cast slab at low pulling speeds.
1.3 Double gun transverse reciprocating motion powder adding machine
In 2017, based on the previous generation of powder-adding machines, we developed a universal automatic slab mould powder-adding machine, namely a double-gun transverse reciprocating slag-adding machine, and simultaneously developed an intelligent control system for the slag-adding machine.
The powder-adding machine is installed in front of the 2# continuous casting machine. It adopts a double-gun transverse reciprocating motion design. The maximum slag spreading width on one side is 450mm. The double-gun transverse reciprocating frequency is 0~10HZ. The transverse reciprocating design allows the screw conveyor outlet to The movement completely coincides with the y-axis of the mould. The blanking point of the mould is at the centre of the thickness direction of the mould. The distribution in the mould is more uniform, eliminating the interference of the deviation of the blanking point on the arc heat flow inside and outside the mould. The feeding rate of each screw conveyor of the slag-adding machine is 0~2kg/min, which meets the requirements of Anshan Iron and Steel Co., Ltd. for large slab continuous casting machines with various thicknesses such as 135, 150, 170, 230, and 300mm. Its control system consists of two parts: PLC and user interface, and has two modes: local and remote control. In the local control mode, the slag adding machine control system PLC executes user interface instructions, and the PLC drives the frequency converter to adjust the left/right screw conveyor speed and rotation frequency.
The PLC communication port is connected to the HMI of the casting machine, and the powder-adding machine can be remotely operated in remote control mode.
Compared with the previous two powder-adding machines, this slag-adding machine has a wide range of cloth width, high reciprocating frequency, small amount of slag added in a single time at the same feeding rate, little interference to the three-layer structure of the protective slag, and stable thickness of the liquid slag layer.
The two guns reciprocate in the same direction and the cloth movement is highly symmetrical and has the function of spontaneously suppressing the bias flow.
The residence time of the screw conveyor outlet in the nozzle area is controllable, which increases the supply of protective powder around the nozzle and indirectly promotes the renewal of protective powder before and after the nozzle. Therefore, the lubrication state of the area around the nozzle is effectively improved, and the occurrence rate of steel breakage prediction is significantly reduced. The central crack on the inner arc surface is effectively suppressed.
In October 2019, the 1# continuous casting machine was also upgraded to this type of powder-adding machine, realizing unified management of this machine.
In order to ensure the operability of the powder-adding machine process, three equipment testing standards have been formulated based on actual production, and are tested once a quarter.
(1) Detection of pulverization rate during granular powder transportation.
This test is to add 30kg of protective slag with complete particles into the material box. After it is discharged through a single screw conveyor of the powder-adding machine at the maximum speed, the powdering rate is <8%. Otherwise, the screw conveyor blades must be replaced to ensure slag addition. The machine does not destroy the original physical properties of granular powder (such as density, specific gravity, and fluidity), so as not to affect its melting state in the crystallizer.
(2) Conveying capacity and control accuracy testing.
Adjust the feeding rate of the screw conveyor of the powder-adding machine to 0.4, 0.5, and 0.6 kg/min, and record the speed of the frequency converter. There should be a linear relationship between the speed change and the feeding rate.
(3) Detection of feeding speed deviation of two screw conveyors.
Adjust the speed of the screw conveyor of the powder-adding machine to the maximum, and weigh the feeding volume of each screw conveyor in 30 minutes. The weight deviation should be <2% to prevent the occurrence of biased flow in the crystallizer.
1.4 Billet continuous caster powder-adding machine
In 2019, the General Steelmaking Plant developed a crystallizer powder-adding machine for billet continuous casters. It is mainly used on six-machine and six-stream billet continuous casters. It can realize automatic feeding, intermittent powder supply, remote control, and powder thickness display. and other functions.
The system is independent of the powder-adding machine and includes the host machine, crystallizer slag thickness collection equipment, silo weighing scale, communication network and powder-adding machine PLC. The host consists of three parts: database, user interface, and analysis program. The functions are introduced as follows
2.1 Automatic control function of mould powder thickness
This function is a necessary condition for the implementation of the intelligent control system of the slag adding machine. The automatic control function of mould powder thickness keeps the slag thickness in the mould always within the set value range and is not affected by changes in casting machine speed or online mould width adjustment. This function compensates for mould liquid level fluctuations and powder surface burning and tumbling. It has 4 intelligent algorithms including smoke filtration, foreign object-blocking filtration, and manual powder compensation correction. There are two ways to generate the mould slag thickness setting value. The first is generated by input through the host user interface, and the intelligent control system generates the second through the “mould powder optimal thickness iteration function”.
2.2 Cloth powder shape control function
This function meets the needs of the mould flow field. Based on the “automatic control function of mould powder thickness”, the required powder shape can be obtained by changing the feeding amount of a certain area of the powder-adding machine. There are two ways to generate the cloth powder shape control setting value. The first one is generated through input from the host user interface, including the centre distance of the marking area, the thickness of the marking area, and the thickness system setting value.
The second type is generated by the intelligent control system through the “optimal thickness iteration function of mould powder”, such as low-carbon, low-silicon aluminum-killed steel, with a cross-section of 150mm*1290mm and a manually set parameter value for the powder thickness at a drawing speed of 2.4m/min.
Table 1 Manually-set Parameter Values for Thickness of Mould Powder
|Marking area center distance/mm
|Marked area mould powder thickness/mm
2.3 Abnormal alarm function
The system abnormality alarm module is managed by the user interface. The triggering conditions of the alarm value can be set according to the production situation, which mainly includes: the execution of alarms. For example, during the slag shape control process, the actual powder surface shape is out of control, and the height of a certain part is not up to standard, triggering the Alarm, the system displays the cause of the alarm through the user interface.
Quality event alarms, such as left and right powder consumption deviation alarms in the crystallizer.
An alarm will appear if the weight of the protective powder silo is less than 30kg, it will prompt the need to add protective powder.
Equipment failure alarm, such as the data value fed back to the intelligent control system by the crystallizer powder surface height collection equipment is interrupted or continues not to be updated.
2.4 Optimal thickness iteration function of mould powder
The optimal thickness iteration function of the mould powder belongs to the core module within the system. It means that when the steel type, cross-section, drawing speed, and mould powder are the same, all operating settings of the powder-adding machine will be used for scoring and sorting, and the crystallizer status evaluation. The highest mould powder thickness setting is implemented as the optimal thickness. This function is based on operating values and technical evaluation. As production proceeds, the optimal thickness of mould powder is always updated and iterated. Under the condition that the intelligent control system and the powder-adding machine work together, the optimal mould powder thickness generated by the system is directly sent to the “mold powder thickness automatic control function module”, which controls the powder-adding machine PLC to perform operations.
Under the working conditions of the intelligent control system and manual powder pushing, the workflow of the system remains unchanged. The intelligent system will generate the optimal powder thickness and also send it to the “automatic powder thickness control function module”. This module monitors the current powder in the crystallizer. Thickness, when the optimal powder thickness cannot be met during operation, the module will feedback to the intelligent control system and activate an audible and visual alarm to prompt for correction. This function always works. In the manual control mode of the powder-adding machine, the manual thickness setting mode of the powder adding machine, and the manual powder-pushing mode, the current mold powder thickness can be evaluated and the optimal value of the iteration is updated. The operator can use the user The interface can be consulted at any time.
3.1 Standardized management of mould powder thickness
Standardized management of protective powder thickness is to use a powder-adding machine to achieve uniform powder thickness and powder distribution in the mould under the same production conditions such as steel type, protective powder, cross-section, and drawing speed, eliminating differences and non-repeatability of manual operations, and making the technology management and process behaviours are consistent. When quality objections occur, the current state of the crystallizer can be reconstructed and analyzed. The intelligent control system of the powder-adding machine has completed the operation of 2.45 million tons of steel in the thin plate continuous casting workshop of the main steelmaking plant, forming an operation mode that combines “standardization of process operations” and “standardization of protective powder thickness”.
3.2 Mold powder material management
There are 6 mould powder suppliers in the thin plate continuous casting workshop of the General Steelmaking Plant, with 11 models. Each model has 1 to 2 batch numbers, and the inventory of each batch number is 10 to 15 packages. Before the intelligent control system of the powder-adding machine works, it first collects the company name, model, batch number, production date of the protective powder in the current silo, the number of packages in stock of the batch number and the weight of the material in the silo (usually 1 package, weight 1 ton, No mixing allowed). After the batch number inventory is consumed, the powder-adding machine intelligent control system synchronizes the list statistics of the batch number’s mold slag consumption cycle, the usage of each powder-adding machine, the usage of each team, the cumulative amount added, the cumulative length and weight of the cast slab, and the average ton comprehensive steel mould powder consumption, cumulative breakout forecast times, and scrap information. Based on the future production plan and the “average comprehensive powder consumption per ton of steel”, the purchase amount of mould powder can be accurately calculated, thereby effectively compressing the consumption cycle of mould powder and realizing the digitalization of material management.
3.3 Defect cause analysis and production traceback
The mould powder-adding machine intelligent control system database provides slab defect cause analysis and production traceability support. The user searches the defective billet ID through the database and queries the mould powder manufacturer, model, production date, batch number, mould powder thickness, powder cloth shape, mould liquid level fluctuations, left/right powder consumption rate, Left/right motor speed, use the billet ID to retrieve the converter number, steel type, refining and blanking records, process ingredients, process temperature, tundish number, number of uses, tundish weight, tundish covering agent model in the secondary system, Information such as tundish temperature, pulling speed, plug rod opening, secondary cooling curve of the casting machine, production operation event notes, etc. can be used to trace back the entire production process of the slab.
3.4 Evaluation of Mold Powder Quality
When the powder-adding machine completes the emptying operation of the silo, the intelligent control system of the powder-adding machine simultaneously generates a quality evaluation of the “package” of protective powder, and the system quality evaluation mark is divided into “qualified” or “unqualified”. The evaluation criteria include comprehensive powder consumption, powder strip conditions, molten layer thickness, steel breakage prediction, and scrap information. If these five parameters are all normal, it is qualified.
Abnormality in any item is considered unqualified. Automatically generate “defect cause analysis” mark instructions for unqualified mould powder batch numbers and archive records.
In December 2021, Anshan Iron and Steel Production Execution System (“PES” for short) was put into operation, covering the entire production process of the enterprise. The continuous casting process can directly check the quality defects of the slab in the subsequent processing process through the system, including hot-rolled scrap, and cold-quality feedback information on key processes such as rolling scrap and galvanizing lines. The intelligent control system of the powder-adding machine realizes reverse tracing of defect causes and current status determination through PES system information, that is, intelligent evaluation of powder-adding status and slab quality forecasting functions. The intelligent evaluation of slagging status is based on “standardization of process operations” and “standardization of mould powder thickness”. By collecting the parameters of the casting machine, the intelligent system conducts a comprehensive evaluation. The evaluation results are fed back to the “optimal thickness of mould powder iteration module” and Mark the billet length information. After the billet is cut to a fixed length, this information is simultaneously converted into the ID information of the fixed length and stored in the database of the intelligent control system of the powder-adding machine. During the subsequent processing of the slab, the PES system enters the returned quality information into the database of the powder-adding machine intelligent control system through the ID number. After receiving the quality objection information of each coil, the intelligent control system conducts a defect characteristic evaluation on the powder-adding status evaluation parameter of the ID. Through big data statistics of 10,000 tons of cast slab production, the defect characteristics of this parameter are included in the “abnormal alarm” “Function” module—quality event alarm. The intelligent control system of the powder-adding machine issues an audible and visual alarm, and the alarm reason is displayed on the user interface.
With the support of the PES system, the intelligent powder-adding machine system realizes comprehensive traceability of process operations, material quality, and slab defects. From January to October 2022, the quality evaluation of 21 batches of 6 models of mould powder was completed, and 3 batches were judged to be unqualified.
Generated 144 slab-quality prediction prompts with an accuracy of 86.9%
The number of 10,000-ton steel breakout forecasts sent decreased by 0.02 times compared with 2021.
The surface defect rate of the cast slab decreased by 0.012%
The intelligent technology of the continuous casting powder-adding machine realizes process operation control, material quality management, comprehensive traceability of slab quality defects, and remote centralized control of continuous casting. The number of predicted steel breakouts per 10,000 tons has been reduced by 0.02 times, and the surface defects rate of the slab has dropped by 0.012%, meeting the development needs of intelligent and centralized control of Anshan Iron and Steel’s continuous casting equipment.