,

1)Tube&Bar Division,Baoshan Iron &Steel Co.,Ltd.,Shanghai 201999,China;

2)Research Institute,Baoshan Iron &Steel Co.,Ltd.,Shanghai 201999,China

Abstract：The function,features,and architecture of a robot that performs automatic temperature measurement and sampling applied on a 150-t AC electric arc furnace (EAF) production line of Baosteel were presented,and the key points of design and revamping experience on the site layout,device protection,lance tool,probe container,measuring position control,and system safety were summarized.Furthermore,a valuable reference for the application of automatic temperature measuring and sampling robots in EAF steelmaking plants will be provided.

Key words：robot; electric arc furnace (EAF); temperature measuring; sampling

1 Introduction

Temperature measurement and sampling oper-ations in the process of electric furnace steelmaking are mainly used to sample and measure the tem-perature and composition of liquid steel in the electric furnace to determine whether they meet the require-ments of process standards,which is an indispensable part of the electric furnace smelting process and quality control.

Temperature measurement and sampling in the process of electric furnace smelting have long been conducted manually.However,several problems are encountered.

(1) Safety issues are encountered due to the harsh operating environment.Manual temperature measure-ment is substantially close to the furnace door,and high temperatures and steel slag splash burns are possible.

(2) The operation is labor intensive.The temper-ature measurement and sampling operation of each furnace must generally be conducted 1-2 times,and workers must repeat such operations dozens of times daily.

(3) Low efficiency.Electric furnaces must be turned off,and the smelting process must be suspended during manual time measurement temperature and sampling,which extends the smelting cycle.

(4) The success rate is unstable.Individual work-er skill levels and responsibility heavily affect the success rate,while workers may make mistakes and repeat measurements due to psychological and physical factors.

With the development of intelligent manufacturing technology,the usage of robots to replace manual completion of liquid steel temperature measurement and sampling[1-4]has become the trend of intelligent technology development in the field of steelmaking.Furthermore,such a replacement has good value and significance in terms of safety and productivity im-provement in steel making.LiquiRob[5]installed in the electric arc furnace (EAF) of the Neuves Maisons branch in France in 2010 and Q-ROBOT-MELT[6]developed by Danieli in 2013 have achieved tem-perature measurement and sampling of electric furnaces.However,cases of stable,reliable,and long-lasting applications are limited,and successful cases are even scarce in China[7].The electric furnace automatic temperature measurement and sampling robot in the 150-t electric furnace plant of Baosteel breaks the long-term history of manual operation of temperature measurement and sampling and has achieved good practice results.

2 System functions and components

2.1 Main functions of the system

The robot system for automatic temperature mea-surement and sampling of electric furnaces mainly has the following functions.

(1) Automatic temperature measurement and sam-pling of liquid steel

A robot grips a lance tool loaded with a tem-perature measuring and sampling probe and auto-matically inserts the liquid steel according to a preset trajectory.Temperature and oxygen determination (with oxygen probe),sampling (with sampling probe),and temperature and carbon determination (with carbon probe) can be realized with different kinds of probes.The oxygen probe is used to determine the temperature and oxygen level of low- and medium-carbon steel.The carbon probe is utilized to identify the temperature and carbon level of high-carbon steel.The sampling probe is used to obtain and send a sample of the liquid steel to the analysis room for accurate chemical composition analysis.

(2) Storage,automatic loading,and removal of probes

The robot equipped with a lance tool can auto-matically load the new probe from the probe magazine and unload and place the used probe in the recycling bin.The probe magazine can store a certain number of various probes to meet the needs of continuous steelmaking,and an alarm can be issued when the number of probes is insufficient to prompt the timely replenishment of probes.

(3) Security protection and fallback

The robot has a safe and reliable interlock protection function.Once a person enters the operation area of the robot or other equipment or an abnormal situation interferes with its operation,the robot can automatically stop its operation or fall back to a safe position to avoid personal injury and equipment damage.

The main technical performance parameters of the automatic temperature measurement and sampling robot system of the electric furnace are shown in Table 1.

Table 1 Main parameters of the robot system

2.2 Main equipment

The automatic temperature measurement and sam-pling robot system of an electric furnace comprises the following:robot body,lance tools,probe magazines,probe unloading frame,control system,heat protection device,detection instrument,safety device,and other parts.

Robot body:The robot is an ABB IRB6700 series,which is a casting-type 6-axis high-reliability industrial robot,and its protection level is IP67.The robot uses a brushless low inertia servo motor to drive each joint.Gas purge cooling can be used at the joint,and each axis is controlled and positioned by a high-precision encoder.

Lance tool:This tool is mounted on the 6th axis flange of the robot,including a clamping tube in the front and a rear support rod in the back.The clamping tube,which matches the size of the probe,is used to plug in the probe and prevent heat from the probe.The rear support rod is used to extend the robot arm to reach the measurement position.This rod is a hollow pipe body structure with a water gap between the inner and outer pipe walls and is protected by water cooling.

Lance tool calibration device:This calibration device has a switch.Each time before loading the probe,the lance tool carried by the robot will touch the calibration device and determine whether the gun barrel is too bent and whether the positioning error exceeds the standard range upon receipt of the switch signal.This condition guarantees that the robot can accurately and reliably perform subsequent positioning and loading probe actions.

Probe magazines:According to different types and sizes of probes,three independent probe storage bins are available,which are used to store and distribute probes for temperature and oxygen mea-surement,temperature and carbon measurement,and sampling.Each bin has a low number of probes and probe distribution detections.The probe stored in the bin can be sent to a fixed loading position step by step through the cylinder-driven rotary rod transmission mechanism,and the guide mechanism with gripper type located at the entrance of the bin can facilitate the guidance and centering of the lance tool.

Probe unloading frame:A V-shaped unloading claw is adopted,and the lance tool is separated from the probe by pressing the probe on the unloading claw.

Heat protection device:This device includes protective clothing and shields and is used to protect the robot from high-temperature radiation and slag sprayed in the furnace.

Control system:This system includes an onboard operation panel,remote control console (including an HMI),PLC controller,and robot controller (including teach pendant),as shown in Fig.1.The robot controller is ABB IRC5,and the PLC controller is IM151-8 PN/DP CPU in the Siemens-distributed ET200S series.The PLC controller supports data networking communication with the main control system of the electric furnace through PROFINET and remotely monitors the robot through the HMI terminal of the remote control console.

Fig.1 Composition of EAF temperature sampling robot control system

Detection instrument:It is a multifunction tool to measure temperature,oxygen,and carbon,and acts as a signal indication device.The signal measured by the probe is sent to the multifunction instrument through a special compensation cable for measuring high-temperature resistance.The instrument pro-cesses these signals and sends temperature values,oxygen levels,and carbon levels to the control system for display.

Safety devices:These devices mainly include safety emergency stop devices and electronic safety fences.The robot operation area is protected by a fence.Workers can walk in and out of the area through electronic keys or personnel access requests,ensuring the safe stopping of the robot in an emergency situation.

3 Issues that require attention

3.1 Equipment layout

The probe usually enters the electric furnace through the slag hole in front of the furnace.The electric furnace will produce slag splash during the smelting process,and the furnace body is surrounded by a closed hood for dust removal (commonly known as a dog kennel).The slag hole is not only for tem-perature measurement and sampling but also for slag cleaning and the spraying of resistant materials inside the furnace,resulting in a remarkably com-plicated layout of the robot equipment.The design should not only consider whether the robot can reach the target measurement position in the furnace but should also focus on the impact of the harsh and complex working conditions on the reliability and interference of the robot.

The layout generally has the following choices,as shown in Table 2.

Table 2 Comparison of EAF temperature sampling robot layouts

The first choice is the arrangement of the robot outside the hood,which has radiation and splashing shielding effects.Thus,this layout can reduce the impact of harsh smelting conditions on the robot and improve the working environment.However,the distance between the robot and the measurement position in the furnace is simultaneously increased,and the travel distance and load requirements of the robot will increase significantly.If the robot arm encounters difficulties in reaching the measurement position,then this arm needs a seventh-axis turn-table or a slide.However,such a requirement will markedly increase the cost and maintenance work-load of the robot system.

The second choice is the arrangement of the robot inside the hood.The advantage of this scheme lies in its relative proximity to the measurement position in the furnace,which reduces the arm travel and load requirements of the robot.Therefore,a small robot can be used to reduce the cost.However,the disadvantage is that the environmental conditions at the robot location are suboptimal due to high tem-peratures and a dirty environment,and the splashed liquid residue is critical.As precision equipment,robots easily break down,and online maintenance is complicated.

From a practical viewpoint,a 6-axis robot arranged outside the hood provides superior results considering safety and reliability.To satisfy such a layout scheme,robot simulation software is used to establish a 3D virtual environment consistent with the real working environment for design verification (Fig.2).First,determining the position reference line of structural parts,such as the furnace body,base platform,and closed hood,is necessary.Then,RobotStudio simulation software is used to design and adjust the equipment layout.The robot’s work trajectory,attitude,and accessibility in the simul-ation environment are repeatedly checked.Finally,the possibility of collision interference with other objects in the robot path is verified to form the best layout scheme in the design stage.

Fig.2 Virtual simulation model of the robot system

3.2 Heat protection design

During robot operation,the robot heat protection design is crucial to the safe and stable operation of equipment.This condition is due to the relative proximity of the body to the slag hole.Thus,a lance tool must be inserted into the liquid steel when the temperature is higher than 1 500 ℃;this not only demonstrates high-temperature radiation but also shows vulnerability to the slag splash from the slag hole.

In addition to the selection of a casting-grade robot with an IP67 or higher protection level,the design scheme must consider the thermal protection of the robot’s various heated parts,mainly in the form of insulated splash guard steel plate,insulated protective clothing,and insulated shields (Fig.3).

Fig.3 Heat protection of the robot

The insulated splash guard steel plate is a frame structure formed by welding a steel plate coated with resistant material on one side,which provides protection for the lateral,top,and bottom sides of the nonworking surfaces.This plate is mainly used to block slag splashing from the furnace and is produced by adding scrap metal and liquid iron to the furnace.

Insulated protective clothing is a closed protection material for robots.The material of this clothing is Kevlar fabric,and some pieces of clothing are covered with high-strength aluminum foil in the outer layer.This clothing is characterized by its high-temperature resistance,high strength,heat insulation,flame retardant,wear resistance,dust prevention,and anti-static capability.The clothing also has a certain degree of elasticity,easy dis-assembly,and good flexibility,effectively isolating the external high-temperature environment up to 1 000 ℃.Insulated protective clothing is the most widely used protective material for high-temperature robots.

Insulated shields aim to enhance the protection provided by protective clothing.Adding metal housing to the robot joints that follow the movement of the axis joints is possible;thus,InsufraxS insul-ation fibers are added to the inner wall.This shield can withstand a temperature of 1 100 ℃ and effec-tively protect the robot joints from heat radiation and slag splash.The largest advantage of this clothing lies in its good heat insulation shielding effect,long life,low wear rate,and occasional replacement.

From the actual application of the project,the protective clothing is easy to use and maintain.However,in the usage process,wearing this clothing in the angular parts is easy;it must also be checked and replaced regularly.Meanwhile,the heat shield and splash guard plate can play superior roles in blocking the slag spatter and extending the life of the protective clothing,respectively.Therefore,these protective measures must be used jointly to achieve successful protection.

In addition,the protection of the robot base should not be overlooked.Various cables and pipe-lines have interfaces at the robot base,which can easily burn the interfaces and cable pipelines once the electric furnace slag hole is spattered with liquid slag.Therefore,in project practice,building a pro-tection wall for the robot base can effectively improve the protection level of the robot.

3.3 Lance tool design

The design of the lance tool focuses on the layout of the tool end of the entire system and is crucial to ensuring stable and reliable measurements inside the furnace.Because the robot carries the tool inside the furnace from the side and inserts it below the liquid steel level to a certain depth,the entire length of the tool must be relatively long and should have a certain degree of rigidity to maintain sufficient stability during motion (Fig.4).The tool is typi-cally separated into two parts:the clamping tube in the front and the rear support bar in the back.The layout of the two parts has an angle to facilitate liquid steel insertion and maintain convenience.The rear support bar is long and is connected to the flange of the robot’s sixth axis,which is air- or water-cooled to prevent heat deformation after frequent entry into the high-temperature environ-ment.The front clamping tube is short and is used for inserting all types of probes.This tube is equipped with a removable connector at the front end for easy maintenance and replacement,and it also provides protection against heat through the probe when taking measurements from inside the furnace.

Fig.4 Lance tool

The size of the clamping tube usually depends on the probe size.Unlike the small size of the manual tool,rather than the large diameter specification,the clamping tube of the automatic tool can be used,which improves the deformation resistance of the front clamping tube and effectively extends its life.

3.4 Probe magazine design

Depending on the loading type,the probe magazine of a temperature measurement and sam-pling robot system is generally available in two different forms:probe fixed racks and probe distri-bution magazines.The fixed rack comprises a num-ber of slots without mechanical moving parts.Therefore,this type is characterized by its small area,simplicity and reliability,and short downtime.However,the following limitations are encountered:the probes must be manually placed into each slot of the rack,and the number of programming points must be taught for each slot.Therefore,realizing tool alignment and probe position detection is difficult.

The lance tool is relatively long and is easily misaligned.Thus,this project has adopted the solu-tion of a probe distribution magazine to ensure the accuracy and reliability of each probe loading.Under this situation,accurately placing each probe and teaching each probe separately at multiple points are no longer necessary because each probe has a fixed loading position,simplifying the work for manually teaching robots.In particular,each probe magazine is equipped with a clamping guide at the entrance,which leads the tool and facilitates probe position detection,increasing the success rate of automatic loading.The failure rate is relatively low.

3.5 Method of controlling measurement position

If the robot could help in measurements com-pletely,then ensuring accurate and repeatable measuring positions every time is necessary.One of the key points to achieving this goal is to insert the lance tool into the furnace along a suitable trajectory without collision to the optimum depth under the liquid steel for accurate results.If a collision occurs or the measuring position is too deep,then the tool is easily damaged;if the measuring position is too shallow,then the measurement results are inaccurate.

According to the actual operating experience,the measuring position is suitable when the horizontal distance is 500-1 000 mm from the inner side of the furnace hole edge and the depth is 300-400 mm below the surface of the steel,as shown in Fig.5.

Fig.5 Measuring position inside the furnace

In addition to the multipoint teaching,evaluating the impact on the trajectory of the lance tool into the furnace,considering the angle of the electric furnace in the steel-making process is also necessary.The trajectory into the furnace must be corrected depending on different furnace angles to avoid the furnace entrance obstacles and reach the target measuring position.Simultaneously,the cap-ability of sensing sudden temperature changes by the probe thermocouple and the measuring instrument is used to detect the liquid level and determine the depth of the target measurement position.Thus,the accuracy and reliability of the robotic lance insertion into the liquid level are improved.

3.6 System security design

The robot system is located in harsh working conditions,and a considerable amount of human-machine crossover work is observed in the front area of the furnace.Therefore,the primary goal of the system safety design is to ensure the safe operation of the robot and avoid damage to personnel and equipment.System security design is based on a strategy in which an emergency stop occurs and a fallback strategy emerges in the event of abnormal conditions.

A two-stage emergency stop strategy is applied:a GS-level general emergency stop and an AS-level automatic emergency stop (Fig.6).The general emergency stop signal is triggered by manually tapping the emergency stop button,which is located on the machine control panel,remote control console,robot controller,and teach pendant.When the general emergency stop is triggered,all robot axes are disabled,and axes are immediately clamped.Power-up can only be resumed when the emergency stop button is restored and reset is pressed.The system automatically triggers the auto-matic emergency stop signal in response to an inter-lock signal,and it is normally used for automatic interlock protection when a person breaches the security fence.Robot motion control is disabled in automatic mode but remains valid in manual mode.

Fig.6 Emergency stop logic

The fallback function under abnormal conditions considers accidental collisions and power failures.In the event of an accidental collision,the robot can automatically move back via the collision detection function,which is effective protection in the case of slag piled up at the furnace door and cold steel existing in the furnace.This function can prevent lance tool damage from collisions and burnout from staying in the furnace for a long time.In the event of an accidental power failure,the robot can be continuously powered by the UPS uninterruptible power supply.Even in the operating cycle,this function ensures that the robot immediately falls back and returns to a safe standby position to avoid burnout in the furnace.

4 Conclusions

Through the design and improvement of the site layout,equipment protection,lance tool,probe storage magazine,measuring position control,and system safety,the automatic temperature measurement and sampling robot of the 150-t electric furnace in Baosteel has maintained a functional commissioning rate of over 98% since online usage.This robot has a high degree of automation and is considerably safe and reliable,resulting in the effective replacement of the manual work in the front furnace area under severe and dangerous working conditions.This condition not only significantly reduces the labor intensity of the operators but also essentially reduces the safety risk of the electric furnace plant.Moreover,the robot can complete the temperature measurement and sampling operation during the charging of the electric furnace,avoiding the impact of the furnace smelting inter-ruption during manual work.This causes an impro-vement in the production efficiency of the electric furnace and plays a crucial role in energy saving and reducing consumption.This solution has remarkable prospects for promotion and application of automatic temperature measurement and sampling robot for electric arc furnace and provides a valuable reference for the development and transformation of similar temperature measurement and sampling equipment in China.