During manual operation of continuous casting tundish, temperature measurement, sampling, addition of protective slag and shroud loading and unloading work, the operator will be exposed to high temperature and dust environment, labor intensity, accidental reaction splashing or ladle formation in the tundish There is a certain danger when the shell falls. Working in this environment, these indispensable operational tasks must be completed to ensure the stability of the continuous casting process and the quality of the slab. By using two robots to realize automatic tundish operations, safety and operating efficiency can be greatly improved, and process reliability can be improved. This article introduces the layout, composition, characteristics and operation of the tundish robot project in detail.
Industrial robots have been used in the automotive industry for many years, but so far, robots are rarely used due to the harsh environment of steel plants. The main problem is that industrial robots and their auxiliary systems (such as material magazines or tool warehouses) must adapt to this Challenging environment, work that meets customer requirements for reliability. However, in the past 10 years, more and more robot systems have been successfully installed worldwide to perform sampling, measurement and processing tasks in the fields of oxygen converter steelmaking, electric furnace steelmaking and continuous casting. [1~3]
In the area of the continuous casting machine, most of the robots are installed in the tundish area, because during the manual operation of the tundish, the operator will be exposed to high temperature and dust. The labor intensity and the internal reaction and splashing of the tundish or ladle are dangerous. , There is even a danger of crusting slag falling from the ladle. Working in this harsh environment, the following important operational tasks must be completed to ensure continuous casting process stability and product quality:
- Temperature measurement.
- Determination of hydrogen.
- Covering agent for tundish.
- Loading and unloading operation of ladle long nozzle.
- Long nozzle oxygen cleaning.
- Burn the oxygen bow when it is not automatic pouring|flow blow open the ladle nozzle.
First of all, the introduction of robots can greatly improve the safety of the operators, because the operators operate remotely and avoid dangerous areas, and there is a sufficient safety distance between the operators and the molten steel.
The second important factor in the use of machines is to improve production efficiency and maintain the stability of product quality. The robot can add covering agent to the tundish according to the set program timing, quantification and positioning, which ensures that the tundish starts and repeats various actions quickly and safely. It installs, disassembles, oxygenates and checks the ladle nozzle, reducing the time for ladle replacement During the replacement, no molten steel falls into the tundish, which improves the safety. At the same time, because the height of the molten steel level in the tundish is quickly maintained, the quality of the castings related to the inclusions caused by the change of the drawing speed and the drop of the liquid level can be avoided problem.
In addition to adding the covering agent, the continuous casting tundish robot can also repeat and accurately complete the temperature measurement and sampling according to the production process steps, and the temperature measurement and sampling position and the immersion depth of the molten steel are executed at a predetermined time according to the production specifications. Therefore, The automatic operation of the tundish further improves the reliability of the entire continuous casting process. All data of the robot operation and the quantity of consumables are recorded, and further analysis and process optimization are carried out through the secondary automation system or the manufacturing execution system (MES), so the process operability has also been enhanced.
The current work describes the use of two robots in the tundish area of two continuous casting machines of Ternium, Brazil, to implement robot operations, and introduces the main components, characteristics and operating performance of the system in detail.
In August 2017, the Brazilian steel mill of Dexing Company’s Tener Group (the former Thyssen-Krupp steel mill) awarded Vesuvius a turnkey project. The project is a robot system (robot continuous casting technology Or RCT), can perform 7 related operations in the tundish area of the two-strand slab caster.
In the first phase of the project, four functions were implemented (temperature measurement, hydrogen determination, sampling and addition of covering agent). Since the replacement of the ladle nozzle requires the replacement of a new casting slide mechanism (LTC), it was implemented in December 2018. From January to March 2019, the ladle opening pouring mechanism was transformed, and all functions were completed in the second project phase.
The robot system was put into operation on the No. 1 continuous casting machine in May 2018 and on the No. 2 continuous casting machine in November 2018, with four new functions. The tundish. The upper platform must be reinforced and reconstructed during the five-day planned maintenance shutdown period. System optimization, thermal commissioning and operator training do not require additional downtime. Finally, all 7 functions of the robot were fully put into use on two continuous casting machines in April 2019.
Robot system (RCT)
The equipment position on the upper platform of the tundish has been carefully designed and reinforced to ensure safe operation, optimize the operating procedures of the robot, and minimize changes to the continuous casting machine. Since the operating space of the two robots is very limited, in order to optimize the position of the robot and the auxiliary system of the cargo magazine, the whole project was simulated in a virtual three-dimensional environment. In addition, the movement of the robot, the accessibility of all material magazines, storage racks and tools are all simulated and verified in this virtual environment for collision detection.
Despite extensive 3D simulations, the robot was assembled and tested in Vesuvius, Belgium, along with all tools, material magazines and consumables. In this controlled environment, the programming of the robot trajectory and the testing of the complete automation package (tool function, shroud and safety mechanism, including all failure scenarios) are completed. The Brazilian Ternium project team members participated in several factory tests, reviewed functions and requirements, and received extensive operation and maintenance training. The following figure shows some pictures of these workshop tests. (Picture 1)
The figure below shows the layout of the robot system and all its main components. Generally speaking, the design of robot system should meet some safety standards, such as EN ISO 12100:2010 (General Principles of Mechanical Safety Design), ISO/TR 202218 -1:2018 (Safety Design of Robot-Industrial Robot System), ENISO 10218-2 :2011 (safety requirements for robotic systems and integration) and IS013849-1:2006 (machine safety-part of the safety control system). (Figure II)
The design of the robot system uses two industrial six-axis robots (Robot No. 1 (1) and Robot No. 2 (2), these two robots are specially modified for the harsh conditions of the casting platform. Both robots have-a special The sleeve is protected to deal with the environment of the steel factory, that is, to prevent molten steel splashing, heat radiation, and dust from entering. Because these two robots are standard industrial robots of KUKA⑧, they are widely used in the automotive industry and can provide spare parts and 24 Hours of technical assistance.
Robot No. 1 completes all the shroud replacement operations and the addition of the tundish covering agent at the two positions of the tundish. However, this robot does not need to support it for a long time during casting after installation of the shroud, because the ladle shroud has a supporting structure in the new LTC mechanism. The layout of the robot allows to retain the existing shroud manipulator as a backup solution, allowing a smooth transition from manual operation to fully automatic operation during commissioning.
The second smaller number two robot (2) handles different probes: temperature measurement, hydrogen determination and sampling. In the case that the automatic pouring cannot be started, the oxygen-burning top opens the ladle nozzle for drainage, and the tundish-one position with covering agent. Both robots are equipped with special fixtures (tool converters) to grasp different tools, and transmit the required media or signals through the tool (with and without argon sampling, hydrogen measurement, molten steel temperature detection or any Other specific media such as oxygen). As a safety measure, the tool changer remains clamped (self-locking) to prevent air pressure leakage failure.
The robot system is installed in place after dismantling the existing cabinets and operating tables, rearranging the current operating panels, power, fluid and gas pipelines, and installing on the existing tundish platform (3). Since both robots will generate additional static and dynamic loads on the continuous casting platform, the structure of the existing platform must be reinforced. It can be seen from Figure 2 that due to the realization of the robot system, the casting platform is expanded into two movable platforms (4), which can be easily removed when the casting machine repairs and replaces parts.
All robot movements occur in a closed robot space, separated by fences on the platform, and the operator enters intelligently through the door (5) and the door (6). According to IS013849-1:2006 automatic i door lock mechanism, connected to A safety programmable logic controller (PLC), which allows or denies the operator access according to the actual operating state of the robot system.
During normal continuous casting operations, the operator usually does not need to enter this enclosed space because all consumables are provided to the system from outside the robot space. The robot obtains the detection head and the sampling head from the material magazine (7). After use, the robot puts them into the sampling head scrap box or the sampling sample box (8), and the operator processes them.
The tundish insulation bag (10 kilograms of synthetic powder or carbonized rice husk) is loaded into the movable insulation shelf (9) and (10); the robot is taken by tools. The ladle shroud rack (11) provides storage for up to 6 shrouds, which can be used for continuous casting for a long time without the need for manual handling of shrouds in the robot motion space unit during shift operation.
Both robots grab tools from specific shelves (12), (13) and (14). Figure 3 shows the robot system assembled before the start of the hot test phase of the continuous casting machine in May 2018.
Ladle opening mechanism (LTC)
Before the implementation of this project, the downward flow of molten steel between the ladle and the tundish was controlled by the pouring slide mechanism. The upper part of the conventional shroud is an upper wrist aligning with the pouring mechanism with a taper nozzle, which is flushed with argon gas to protect and seal ( See Figure 4a). However, robot automatic replacement of the shroud requires different methods, and there is no way to use a manipulator to keep the shroud fixed on the ladle opening mechanism. The LTC mechanism of Vesuvius is a ladle pouring slide device with an integrated shroud device to load and keep the shroud fixed on the ladle pouring mechanism. During the casting of the LTC mechanism, the integral ladle shroud is pressed to the lower plate, and the robot only needs to load and unload the shroud from the LTC (Figure 4b). Because there is no physical connection between the ladle and the platform during the casting process, it is guaranteed that the turntable can rotate freely in an emergency situation.
Compared with the conventional ladle slide pouring mechanism, two hydraulic cylinders are used to operate the LTC mechanism, and the larger hydraulic cylinder (1) controls the movement of the slide plate, thereby controlling the speed of the ladle steel underwater flowing into the tundish (see figure) 5). The smaller hydraulic cylinder (2) switches between the conical upper end (3) of the shroud (the conventional shroud operation uses a manipulator), and the robot operates the shroud (4). The good switching between these two operation modes can make the machine debugging stage flexible, and also can use the backup manual operation manipulator to install and remove the shroud. In the first phase of the implementation of LTC, the hydraulic system and hydraulic cylinder support of the ladle turret were improved to operate the new LTC mechanism and the original pouring mechanism at the same time. After these modifications, the LTC structure was gradually installed on each ladle. The modification of the ladle is limited, and is limited to the adjustment of the radiation protection plate and the assembly of the intermediate adapter plate.
As mentioned above, in the first stage of implementation, LTC was used as a conventional ladle slide mechanism, using a manipulator to cover the long nozzle on the taper of the pouring mechanism. After the first implementation phase, only a few adjustments (replace a few parts) are required to allow the robot to replace the shroud in a full LTC operation.
The possibility of switching between the two operating modes provides huge benefits for the non-self-opening state. In this case, the oxygen-burning drainage needs to continue the casting sequence. In the full-time operation, the oxygen blast tube is inserted into the taper nozzle, and the integral ladle long reservoir is still installed in the pouring mechanism. Therefore, the time interval between the drainage and the use of the long nozzle (and therefore the The negative impact of steel quality) is reduced to a minimum. Therefore, after successfully completing the task of oxygen burning and drainage, the overall ladle nozzle is ready to quickly change the casting position at any time.
From the perspective of slab quality, the traditional long nozzle is connected with the taper nozzle of the pouring mechanism. (1) The use of the LTC mechanism can better protect the secondary oxidation and nitrogen absorption of the steel flow (Figure 6). After the improvement, the long nozzle (2) is in flat and sealed contact with the upper pouring mechanism slide block (3). The spring compression force is about 1.5 tons, and there is an argon-blowing annular seam to keep the positive pressure and shield the atmosphere from entering (4). The idea of plane connection can perfectly align the shroud vertically and provide a symmetrical stream of molten steel into the tundish, so the product quality and the cleanliness of molten steel can be maintained.
Another advantage of the LTC mechanism is that the bottom slag detection ring is integrated on the bottom plate, which improves the reliability of the bottom slag detection, thereby improving process stability and product quality.
However, the biggest advantage of LTC is that the spring locking force of about 1.5 tons can ensure safety and reliability in the continuous casting process, while the locking force provided by the taper connection between the nozzle ladle nozzles of the conventional pouring mechanism is limited, while LTC The flat surface sealing connection provides enough locking force to withstand and protect the flow of air during casting. During the ladle replacement process, the flat seal maintains good quality, thereby avoiding quality degradation caused by molten steel inhalation, which is beneficial to the production of high-quality steel plates.
As mentioned earlier, the commissioning phase is divided into two phases, and in the first phase, the robot system has four functions available:
- Molten steel temperature measurement
The temperature is measured through the hole on the right side of the tundish cover. For the No. 1 continuous caster, it is near the second flow stopper, and for the No. 2 continuous caster, it is near the 4 flow stopper. Robot No. 2 grabs the temperature measuring tool from the specific tool rack, takes out the temperature measuring probe from the material magazine, and dips it into the molten steel in the tundish through the hole on the tundish cover. Since the material bomb warehouse has temperature probes, fixed hydrogen heads and samplers (Figure 7a), it must be designed to correctly extract “error-proof” to prevent shutdowns with the wrong probe. After the temperature measurement system evaluates the temperature measurement data normally or after the maximum immersion time has elapsed, the robot removes the probe and discards it in the probe waste box. After each temperature measurement, use a bag of tundish covering agent to cover the exposed point of molten steel caused by temperature measurement. This is a better method of operation. In order to make the smallest possible opening when the temperature measuring gun is immersed in the covering agent and molten steel during temperature measurement, and to avoid the formation of crusts on the tundish cover hole, it is a good way to use a probe with a cardboard structure with a splash-proof coating. 7b shows the temperature measurement of the tundish of No. 1 continuous casting machine.
- Tundish molten steel hydrogen determination
From the program point of view, the indirect hydrogen measurement is very similar to the temperature measurement, except that the tool and probe type are different, and the immersion time into the molten steel is much longer than the temperature measurement.
Sampling is also very similar to temperature measurement, the probe is replaced with a sampler, and the sampling time is immersed in the molten steel for a long time. After sampling, the robot places the sampler in the sample box, cools and processes it by the operator, and then sends the sample to the laboratory. According to the requirements of steel type, in the casting process of a ladle, at most three tundish samples are taken for a given ladle molten steel weight. Sampling and measurement tasks are automatically triggered by the actual ladle weight signal (automatic ladle mode) to ensure that the required measurement sampling is accurately timed. The task list and bribes of different steel grade families through the human-machine interface (HMI) stored in the robot PLC Set up within the casting time.
- Tundish covering agent
Two robots can add covering agent to the tundish at the same time. Robot No. 1 is responsible for adding the left and middle holes of the tundish cover, and Robot No. 2 is responsible for adding the right hole of the tundish cover. The robot uses a tool for adding covering agent. Enable the robot to pin and grab the cover pack stored on the shelf (Figure 8a). The operator puts a sufficient number of bags of covering agent on the shelf according to the regulations. Robot No. 1 can put up to 6 bags of covering agent into the tundish at a time; Robot No. 2 can handle up to 4 bags at a time. Figure 8b and Figure 8c show the application of the cover hole on the left side of the cover agent tundish on the No. 1 continuous casting machine. At the beginning of the pouring process or after the tundish is replaced, a large amount of covering agent must be added in a relatively short period of time. The precise time and rapid addition of the covering agent are essential to prevent secondary oxidation of the molten steel and maintain the temperature of the molten steel in the tundish. The task of adding and adding the tundish covering agent is performed by the tundish electronic scale according to the actual molten steel weight according to the program (automatic sequence start function).
- long nozzle
During the casting process, 6 integral shrouds are placed on the storage rack, and each position of the storage rack has an optical sensor to identify the existence of the shroud. After using the pneumatic tool to grab the shroud from the storage rack, the robot arm stretches to the LTC machine, the ladle turning head is already in place, and the pouring mechanism is already in the casting position. The installation of the shroud requires precise knowledge of the exact position of the pouring mechanism (fixture tool). Because the machining accuracy and positioning of the ladle rotary head cannot meet the requirements for automatic installation of the shroud, optical measurement technology is used to detect each time the shroud is disassembled and assembled. At a precise location, the three-dimensional laser measurement system installed on the robot arm measures the characterization topography of the specially designed three-dimensional body installed on the LTC mechanism (see Figure 9a). The topography of the measured LTC provides the exact installation of the shroud Position and positioning provide complete three-dimensional information for the robot fixture. This method of determining the location of the ladle pouring mechanism has strong resistance to interference from changes in dust and light conditions. According to the information of the location of the LTC, the robot moves to the vicinity of the LTC with the shroud and is ready to be inserted. The installation of the integral shroud only needs to move vertically and is automatically locked by spring loading. Figure 9b shows the installation of the ladle shroud. (Picture 9 a, b)
When the robot returns to its original position, the ladle lifting mechanism of the turntable moves, and the ladle descends under the action of the hydraulic cylinder, and the shroud is immersed in the tundish molten steel to open the pouring mechanism.
Before disassembling the integral ladle shroud, the precise position of the LTC mechanism was determined again by laser measurement technology. The ladle shroud was clamped by the robot, and the nozzle was released from the LTC and rotated 45 degrees. Finally, when the robot arrives at the starting position with the nozzle, it checks the nozzle and uses oxygen to clean the cavity of the nozzle, or adze it in the trash can of the nozzle.
- Cleaning of the long nozzle
To remove the ladle nozzle from the LTC and clean it requires two robots to operate jointly. In this operation task, robot 1 is responsible for blessing the nozzle, robot 2 is responsible for oxygen purging and cleaning, and the purge oxygen flow is controlled by RCT PLC during the cleaning process. In the middle, the ladle nozzle faces the tundish to minimize the safety and operational risks caused by molten steel splash (see Figure 10).
Oxygen burning and drainage.
If the ladle nozzle cannot open automatically, the operator can request the robot system to use the oxygen-burning opening function. As mentioned earlier, the design of the LTC opening and sliding mechanism takes this into consideration, and the overall shroud remains attached to the LTC mechanism. Therefore, after successful oxygen firing, it quickly switches to the shroud protection casting mode and opens the casting time. (This has a negative impact on the quality of steel) is reduced to a minimum. After grabbing the retractable oxygen blowing tube, the robot positions the end of the oxygen blowing tube directly below the tapered drain of the LTC. The operator can use the joystick in the console to adjust the position of the pipeline. During this adjustment process (Usually only minor adjustments are needed to align the end of the oxygen blowing pipe with the drain). The actual position of the oxygen blowing pipe port can be monitored through the camera installed on the robot and the screen of the console. After the inside of the drain, the operator activates the oxygen switch to perform the oxygen-burning top boiling procedure. The oxygen blowing tube itself is used as a telescopic pipe. The pressure of oxygen is applied to the inner cavity of the nozzle, and the effect of oxygen burning and the force of oxygen pressure are added to push out the molten molten steel. After the ladle is successfully drained, the robot moves the oxygen lance tool back to the frame, and the hydraulic cylinder of the LTC mechanism immediately moves to switch the pouring position to the overall shroud. The ladle lifting mechanism of the ladle turntable begins to descend.
The robot system is not a completely independent system, but is fully integrated into the continuous casting machine automation system, which is essential for handling emergency situations, tracking the operations performed through the secondary automation system and MES, measurement results, and the quantity of consumables.
In an emergency situation, the rotating ladle and the tundish need to leave the casting position, and the robot must also perform the corresponding tasks at the same time to make a full and rapid response. The “emergency signal” sent by the continuous caster PLC is directly sent to the robot PLC, so there is no delay in the movement of the robot back to its original position. In order to minimize the movement time, a number of simulations were carried out during the I-program design stage. The results show that in the emergency evacuation process, it is advantageous to disassociate the probe and the tool from the robot, and to leave the tool in place before starting the escape action. When performing this kind of emergency task, the robot decoupling tool will not cause an increase in time. The time from receiving the emergency signal to reaching the original position is only 6 to 9 seconds. It needs to be pointed out again that the use of the LTC mechanism does not require a fixed ladle nozzle manipulator, so during the pouring operation, there is no physical connection between the ladle and the pouring platform, which ensures the freedom of the ladle turning head during emergency evacuation. Rotation, in an emergency, in order to save time, the ladle does not need to be raised when the ladle is evacuated and rotated, and the shroud is directly collided on the tundish cover and ruptured to continue rotating the ladle and evacuate the tundish.
Before the start of this project, only two types of intermediate package operation data were sent to the Level 2 system and MES, which is the result of manual temperature measurement and hydrogen determination. So far, the exact time of sampling and the weight of the corresponding ladle molten steel have not been recorded, and the type and quantity of the tundish covering agent and the replacement operation of the shroud are also not recorded. After the robot is adopted, since all the intermediate package operations are recorded in the robot PLC, it is easy to send the data to the secondary computer and MES to prepare for further processing of the data.
The introduction of robot systems in continuous casting is not only a technological advancement, but to a certain extent, it has also completely changed the daily work experience of operators, which is a worrying issue before the start of the project. However, before the implementation of the robot system in the steel plant, practical training in the workshop of the Vesuvius plant in Belgium will help all those involved in this project adapt to this new technology. A very important factor controlling the robot and its operation is the various panels and man-machine interfaces in the console. The new air-conditioning and noise prevention console is shown in Figure 12.
The new operating table has the operating panels of the existing operators: ladle slewing head (1), slag detection (2), communication system (3), and the new panel includes a tundish robot operating panel (4), oxygen burning and drainage The joystick (5) and oxygen panel (6) of the camera system. The robot operating panel allows the traditional button operation mode to perform measurement and sampling operations, but all operating functions and their adjustments can also be performed through the HMI using a 30-inch touch screen.
In the first few weeks of the operation of the No. 1 continuous casting machine, the robot RTC carried out 152 cover agent additions, 192 temperature measurements, 20 constant hydrogen measurements and 89 samples. As shown in Figure 13, the robot system proved the high efficiency, practicality and excellent performance (execution success rate) of four different tasks during this period, and achieved the required 95% availability and performance during the first few weeks of continuous operation.
During the start-up phase, it can be observed that the different ladle has obvious deviations when the lifting mechanism lowers it to the lowest pouring position. These deviations are caused by the different positions of the ladle on the ladle arm of the turntable and the inevitable deformation of the ladle during the service period. Therefore, in order to ensure that the covering agent is added to the tundish, the distance between the central hole cover of the tundish cover and the ladle opening mechanism must be optimized to allow enough space for the robot to add the covering agent to the motion trajectory. The gradual optimization process reduces the workload of the initial testing phase.
During the first few weeks of operation, crusts were formed in the tundish and molten steel splashed into the lid hole of the tundish, which affected the temperature measurement and sampling of the robot. When the detector has been immersed in molten steel during temperature measurement and sampling, when the detector collides with these crusts, the collision detection function of the robot will start and stop the task. The collision detection function monitors the torque of each drive to prevent damage to the robot and its detection tools.
By optimizing the amount of covering agent, adding a bag of insulating powder or synthetic slag after each measurement or sampling, to prevent the formation of a solid slag shell on the liquid surface of the refractory steel slag in the tundish. By applying “splash-proof” material coatings on different probes, the splashing of molten steel can be significantly reduced and the formation of crusts at the hole of the tundish cover can be significantly reduced.
The LTC mechanism is still being continuously tested and improved. By the end of May 2019, 8 out of a total of 23 ladles have been transformed into LTC pouring mechanisms, and in the first test phase, the shroud robot was successfully replaced , Oxygen cleans the shroud nozzle and burns the oxygen to open the ladle nozzle.
The introduction of the robot system in continuous casting is not only a major advancement in technology, but also a major change in the daily operation of continuous casting. The implementation of the robot system on the pouring platform and the new ladle slide plate pouring mechanism of Brazil’s Taina continuous casting machine has a profound impact on the safety of operators, process reliability, process operability, productivity and product quality. influences.