Chapter 5. Improving condition monitoring and maintenance framework for refractory linings in induction melting furnaces through continuous improvement methods

86 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS ABSTRACT The service life and reliability ofrefractory linings incoreless induction crucible furnaces are essential factors influencing the efficiency, safety, and cost-effectiveness ofmetallurgical melting processes. Premature wear oflinings, caused bythe combined effects ofslag composition, molten metal temperature, crucible geometry, electromagnetic stirring intensity, and cooling conditions, inevitably leads toincreased maintenance frequency, unplanned production downtime, and higher operational costs. Inthe context ofthe global steel industry’sdecarbonization strategy and the growing demand for resource-efficient technologies, the issue ofextending refractory lining durability ininduction melting units gains particular relevance. This study presents animprovement ofthe lining condition monitoring and maintenance decision-making system through the integration ofa continuous improvement methodology and heuristic engineering tools, including TRIZ, morphological analysis, the method ofcontrol questions, the method offocal objects, the theory ofinventive problem solving, and functional–value analysis. The research incorporates both areview ofexisting industrial practices and anexperimental evaluation ofinnovative technical solutions. Acomparative evaluation ofmonitoring technologies was carried out, with the criteria including measurement accuracy, implementation complexity, cost, and adaptability toharsh metallurgical environments. This assessment resulted inthe selection oflaser-based 3D profilometry asthe most appropriate solution for high-precision wear assessment and digital surface modelling, providing areliable basis for predictive maintenance planning. The proposed approach combines technical and organizational measures, including optimization ofslag formation processes, adjustment ofcrucible geometry toreduce thermomechanical stresses, improvement ofcooling regimes, and systematic wear tracking supported bydigital data analysis. Anindustrial case study involving EGES-type furnaces atZaporizhzhia Foundry and Mechanical Plant confirmed the applicability and efficiency ofthe developed framework under real production conditions, ensuring timely maintenance planning, reducing the risk ofemergency lining failure, lowering specific energy consumption, and supporting stable quality ofthe produced steel. The findings demonstrate the potential ofcombining continuous improvement principles with modern monitoring technologies tocreate anintegrated refractory lining management strategy that enhances durability, minimizes environmental footprint, and strengthens the competitiveness ofelectrometallurgical production. KEYWORDS Induction crucible melting, refractory wear mechanisms, furnace lining durability, 3D laser scanning systems, automated condition monitoring, continuous improvement methodology, digital profiling technologies, TRIZ methodology, morphological analysis, method ofcontrol questions, method offocal objects, DOI: 10.15587/978-617-8360-14-6.CH5 Oleksandr Povazhnyi, Volodymyr Kukhar, Oleksiy Koyfman, Khrystyna Malii, Volodymyr Pashynskyi 5 87 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS theory ofinventive problem solving, functional-value analysis, slag formation optimization, crucible geometry adjustment, cooling regime improvement. One ofthe approaches toreducing greenhouse gas emissions inthe fight against climate change, within the framework ofthe steel production decarbonization strategy, isthe transition toelectrometallurgical steelmaking technologies, including the production ofsteel ininduction furnaces[1]. Induction heating asa physical principle isuniversal for awide range ofmetallurgical operations– from melting incrucible furnaces[2, 3] topre-deformation (pre-forming) billet/blank heating and heat treatment offinished products[2, 4]. The principles ofcurrent induction are identical: the electromagnetic field ofthe inductor induces eddy currents inthe conductive material, which, due tothe Joule effect, heat its volume, and, under certain conditions, also ensure significant electrodynamic stirring ofthe molten metal[3]. Such intensive circulation isbeneficial for achieving chemical homogeneity, but atthe same time imposes additional thermomechanical stresses onthe refractory lining. Given the global decarbonization agenda, increasing the operational efficiency and durability ofkey components ininduction furnaces becomes acritical factor for ensuring the competitiveness and sustainability ofmetallurgical enterprises. Improving refractory lining management directly contributes toboth energy efficiency and production reliability. One ofthe main limitations hindering the potential full-scale transition tosteelmaking ininduction furnaces isthe relatively low durability ofthe refractory lining. Atthe same time, induction steelmaking units are characterized byhigh productivity and, asdemonstrated inpractice, are successfully used for the production ofrelatively small volumes (from 5 kgto 60 tonnes) ofhigh-quality steels inboth industrial (foundry shops) and laboratory conditions. The technical literature reports the use ofinduction furnaces for melting high-alloy heat-resistant steels[5], structural and low-carbon steels[6], non-ferrous metals[7] and special-purpose alloys[8, 9], aswell aswidespread examples ofcombined technologies inwhich, following melting, processes ofsevere plastic deformation are implemented toimprove the mechanical properties ofthe final products[10, 11]. Induction melting provides intensive stirring ofthe melt flows and active slag formation, contributing tometal purification. The effect ofreducing segregation and modifying non-metallic inclusions can befurther enhanced through the use ofspecial additions based onrare-earth metals[12]. Adistinctive feature ofthe operation ofan induction crucible furnace isits similarity toa transformer, where the inductor serves asthe primary winding and the metal inthe crucible– located atthe center ofthe inductor and powered bya high-frequency alternating current generator– acts asthe secondary winding. Due tothis design, the molten metal, heated byeddy currents, issubjected toradial forces directed towards the center ofthe molten bath[13]. These forces cause acirculating motion inthe vertical plane, which, onthe one hand, facilitates the attainment ofchemical homogeneity and the flotation ofnon-metallic inclusions[14, 15], but, onthe other hand, increases the intensity ofcontact between the molten metal and the refractory lining[13, 16, 17], leading toits accelerated wear. Active circulation ofmolten metal positively affects the uniformity ofthe chemical composition ofthe produced metals, but has anadverse effect onsuch aparameter asthe durability ofthe refractory lining 88 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION ininduction furnaces. The lining islocated between the molten metal and the inductor (Fig. 5.1), and itis evident that the thicker the furnace lining (orits thickening due tobuild-up deposits), the smaller the magnetic flux penetrating the metal, and consequently the lower the efficiency ofelectrical energy utilization during melting. Therefore, the lining thickness issubject tocertain limitations[18]. The general design ofan induction melting furnace isshown inFig. 5.1. pouring spout support axis shell crucible refractory concrete plate a b inductor coil slag molten metal Fig. 5.1 Schematic (a) and general view (b) ofa typical coreless induction crucible furnace (modified bythe author based onan open-source illustration from KEMA educational resource) Source: [17] The crucible ofan induction furnace (Fig. 5.1) ismanufactured orrepaired byramming orlaying with refractory material (bricks). The crucible ispositioned directly inside the inductor, which isa water-cooled coil made ofcopper tubing with adefined number ofturns. Arammed crucible made ofrefractory powder material isfixed inthe furnace shell and placed ona base plate made ofrefractory con crete[17, 18]. The discharge ofmolten metal isperformed through aspout bytilting the furnace together with the shell relative tothe support axis. Due tothe physical characteristics ofheat generation directly within the metal, the maximum melting temperature ismainly limited bythe durability ofthe crucible itself. Toincrease thermal resistance and reduce thermal stress, water-cooling systems and refractory lining temperature monitoring devices[17, 18] are employed, which may integrate measurement sensors[19] and computer modelling oftemperature fields using numerical methods[11, 14]. Such solutions not only extend the crucible’sservice life but also ensure the stability ofthe melting process[20]. The crucible ismade ofrefractory materials, which may include ceramics, graphite, orchamotte-graphite[17, 18]. The melting temperatures ofsteel grades produced ininduction furnaces determine the use ofthree types ofcrucible linings: a) acidic; b) basic; c) neutral. 89 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS Acidic linings (a) are made from refractories based onsilicon oxide (90–98% SiO2), boric acid (1–1.5%), and small amounts ofmetallic oxides such asAl2O3, Fe2O3, MnO, and others. The service life ofacidic crucibles istypically 80–100 heats. Basic linings (b) are mainly produced from magnesite (upto 85% MgO), water glass, and additives ofoxides such asCaO, SiO2, and others. The durability ofsuch crucibles decreases with increasing furnace capacity and ranges from 20 to50 heats. Neutral linings (c) are based onAl2O3 with magnesite additives. The durability ofneutral linings isgenerally higher than that ofthe previous two types[17, 18]. Research shows that the behavior ofthe refractory lining isdetermined both bythe composition ofthe refractory material and bythe nature ofits interaction with the molten metal and non-metallic inclusions[12, 21, 22]. Modelling the processes ofinteraction between the lining, slag, and metal[11, 14, 17] allows for predicting its wear rate and scheduling maintenance ina timely manner. Inthe conditions ofthe intense electromagnetic field ofan induction furnace, safety aspects must betaken into account– including personnel electrical safety, the effects ofelectromagnetic radiation, and the safe operation ofpower systems[20, 23]. Addressing these issues involves the implementation ofrisk control and protection systems based onthe principles ofindustrial safety and occupational health standards. Sources[24, 25] also highlight, among the advantages ofinduction crucible furnaces, their broad potential for automation using controllers, aswell asthe high environmental performance ofthese units, while citing the low durability ofthe refractory lining asa disadvantage. According tothe author of[26], animportant part ofmaintenance, ensuring equipment efficiency and reliability, and maintaining process safety during melting, isthe automated monitoring oflining wear. Atthe same time, the low durability ofthe refractory lining once again appears among the main drawbacks, which iswhy current research focuses ondeveloping methods toimprove it, including the application ofheuristic approaches, functional value analysis (FVA), and TRIZ tools tooptimize the monitoring and maintenance ofmelting units[27, 28]. Based onthe above, the analysis ofindustrial experience inimproving refractory lining durability and the development ofrecommendations for enhancing the efficiency oflining wear monitoring ininduction crucible melting furnaces isa relevant scientific and practical task. The aim ofthe study isto substantiate and implement amethodological approach tothe synthesis and improvement ofa condition monitoring and maintenance system for refractory linings ininduction melting furnaces, based oncontinuous improvement methods, inorder toenhance the reliability, durability, and operational stability ofthe induction melting process. 5.1 TECHNICAL BACKGROUND AND METHODS FOR IMPROVING LINING DURABILITY Induction steelmaking furnaces are widely used inthe metallurgical industry, inglass production, and inwaste processing. Considering the prospects and the objective necessity for the development ofelectrometallurgical technologies, the scope and volume oftheir application are expected toincrease. For example, atZaporizhzhia Foundry and Mechanical Plant LLC, aninduction steelmaking furnace manufactured byEGES (Turkey) with acapacity of3.0 tonnes has been installed. Fig. 5.2 shows the furnace inoperation, and Fig.5.3 – during tapping. The technical specification s ofthe furnace equipment are presented inTable 5.1. 90 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION a cb Fig. 5.2 Melting ina 3-tonne induction furnace produced byEGES (Turkey): a– overall appearance ofthe unit; b– the crucible isenclosed tominimize heat loss and limit the escape ofmetal vapors into the work area; c– the interior ofthe furnace visible after tapping a cb Fig. 5.3 Steel casting using a3-tonne induction melting furnace from EGES (Turkey): a– pouring molten metal from the furnace into aladle; b– skimming slag from the surface ofthe melt; c– filling molds during the casting stage Table 5.1 Specifications ofEGES induction furnaces (Turkey) with crucible capacities of1 tonne and 3 tonnes Furnace Electric converter Melting rate, kg/h Melting time, min Model Capacity, kg Power, kW Frequency, Hz Cast iron at1450°C Steel at1600°C Cast iron at1450°C Steel at1600°C EGP 1000 SE 1000 600 1000 1137 1043 53 58 EGP 3000 SE 3000 1750 500 3305 3062 54 59 91 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS Among the main causes ofcrucible failure inan induction steelmaking furnace, the following should behighlighted: –thermal stress: during the steel melting process inthe crucible, significant heating and cooling occur. These heating and cooling cycles induce thermal stresses inthe crucible material, leading toits damage and wear; –mechanical impacts: during the charging ofthe charge material and scrap, impacts occur when the material falls onto the refractory lining. The steel melting process isaccompanied bymechanical effects, such asthe intensive movement ofmetal inthe crucible. This also causes crucible damage and wear; –corrosion (erosion): certain constituents ofsteel oradditives used during melting may becorrosively active towards the crucible material, resulting inits wear; –uneven heating: uneven heat distribution within the crucible during melting also generates thermal stresses, which may cause cracking ofthe refractory lining; –contact with metal: direct contact with unmelted metal (atthe beginning ofmelting) and with molten metal during the process leads tomechanical wear ofthe lining through friction. Fig. 5.4 shows the process oframming a3-tonne crucible ofan induction furnace under the operating conditions ofZaporizhzhia Foundry and Mechanical Plant LLC. a cb ed Fig. 5.4 Relining ofa 3-tonne capacity induction furnace (produced byEGES, Turkey): a– inductor workspace prepared for lining; b– meconite being readied for application tothe furnace lining; c– lining the furnace bottom; d– placing the furnace lining machine inside the unit using acrane; e– charging the furnace for the sintering stage 92 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION 5.2 METHODSFORIMPROVINGTHEDURABILITYOFREFRACTORYLININGS Improving the durability ofthe crucible requires acomprehensive approach, which includes both the selection ofappropriate materials and the proper management ofthe operating process. The general methods and strategies used toenhance the durability ofthe refractory lining inindustrial and laboratory induction furnaces, identified asa result ofthe analysis ofliterature sources and practical experience, are summarized inTable 5.2. Table 5.2 Systematization ofmethods for improving the durability ofrefractory linings ininduction steelmaking furnaces No. Method for improving durability Essence ofthe method 1 2 3 1 Selection ofappropriate crucible material Use ofhigh-quality materials with high thermal resistance and mechanical strength that meet the requirements ofthe specific process. Application ofspecial materials, such assilicon carbide orzirconium oxide, which may offer improved thermal and chemical resistance[18, 29] 2 Thermal insulation Ensuring effective thermal insulation ofthe refractory lining toprevent heat losses, overheating, and wear under high-temperature conditions. Applied toconcentrate heat inthe required areas. Thermal insulation coatings are used toreduce heat losses and retain heat within the inner region ofthe crucible. These materials can help maintain stable temperature conditions and reduce energy consumption[20, 26, 30] 3 Cooling systems Use ofcooling systems tocontrol the temperature ofthe refractory lining and prevent overheating[18, 31, 32]. This includes lining with integrated channels for water cooling, pumping and circulating acoolant (water), introducing acooling medium (cold gas) directly into the crucible, and employing additional active cooling methods (e.g., using Peltier elements[33]) 4 Temperature regime monitoring and automated control Installation oftemperature monitoring systems for continuous tracking ofoperating parameters and timely detection ofanomalies toavoid sudden temperature changes that may cause thermal shock tothe crucible. This includes maintaining astable temperature regime and ensuring gradual heating and cooling. The method involves installing thermocouples and sensors for continuous crucible temperature monitoring and prompt response toany changes, aswell asusing automatic temperature control systems capable ofadjusting the supply ofcooling liquid orgas asrequired[19, 25, 26, 34] 5 Optimisation ofmelting processes and crucible design Analysis and optimization oftechnological processes toreduce excessive hydrodynamic friction and thermal impact onthe refractory lining. This involves studying the hydrodynamics ofmelting toidentify areas where excessive friction occurs, and using computer modelling toanalyze and improve hydrodynamic processes and thermal models inorder todetermine heat distribution and identify zones with excessive thermal impact. Modifications tothe shape and configuration ofthe lining are introduced toreduce frictional resistance. Ensuring proper crucible design takes into account parameters such aswall thickness, shape, and dimensions. The risk ofthermal shock isminimized byselecting optimal design parameters[35] 93 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS 1 2 3 6Expert assessment, monitoring ofwear and deformations Engagement ofspecialized experts for systematic assessment ofthe refractory lining condition and identification ofany signs orrisks ofwear. This includes conducting visual inspections todetect any traces ofwear ordeformation, aswell asusing non-destructive testing methods (e.g., ultrasonic inspection) toidentify internal defects[13, 18, 26, 36] 7Regular maintenance and repair Regular maintenance ofthe refractory lining toensure timely detection ofwear signs ordefects and tomaintain its durability. This includes scheduled repairs, refurbishment, orreplacement ofthe crucible[26, 37] 8Application ofprotective coatings Application ofprotective coatings toreduce the effects ofchemical reactions and wear onthe crucible surface[30, 38, 39]. Graphite coatings are used toprotect the crucible from erosion and oxidation athigh temperatures, asgraphite ischemically stable and withstands high temperatures, making itan effective material for crucible protection. Ceramic coatings are applied tocreate athermally and chemically resistant layer that shields the crucible from aggressive environments (some types ofceramic coatings have high thermal shock resistance). Oxide-ceramic materials, such asaluminum oxide orzirconium oxide, are employed toprotect the crucible from oxidation and aggressive reactions atelevated temperatures. Some manufacturers offer specialized coatings designed specifically for metallurgical applications and induction melting, which can beoptimized for particular operating conditions. Enamel and ceramic coatings with alow coefficient offriction may also beused toreduce frictional resistance and improve crucible performance 9 Electromagnetic field management Optimization ofcrucible design and positioning toreduce the impact ofthe electromagnetic field onits durability[40, 41]. Transition toinnovative electromagnetic cold crucible (EMCC) solutions[40], i.e., the use ofa segmented, water-cooled copper crucible for induction melting ina vacuum orcontrolled atmosphere without the use ofrefractory materials. EMCC technology isbeing adopted intwo types ofindustrial applications: (a) asbatch crucibles for melt preparation, and (b) asbottomless cylindrical molds for continuous casting. The advantages ofEMCC include: reduced friction effects inthe forming system (minimized contact between the melt and the crucible), which significantly increases crucible durability; absence ofcontamination and inclusions inthe melt; creation offluid flow conditions that can control grain structure and accelerate online chemical treatment (resulting inhigh-quality castings); and reduction ofcycle time[41] The selection ofthe optimal solution isrecommended tobe carried out after consultation with manufacturers orspecialists inmetallurgical equipment. 5.3 METHODSFORMONITORINGTHECONDITIONOFREFRACTORYLININGS Regular and comprehensive monitoring ofthe refractory lining condition allows timely detection ofany changes and helps toavoid potential accidents orproduction issues. Based onpractical experience and the analysis ofinformation from the sources listed inTable 5.2, the methods for monitoring the condition ofrefractory linings ininduction steelmaking furnaces have been systematized. The results ofthis systematization are presented inTable 5.3. Itshould benoted that the effectiveness ofwear monitoring depends onthe systematic nature, accuracy, and timeliness ofthe measurements and inspections performed. Continuation of Table 5.2 94 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION Table 5.3 Methods for monitoring the condition ofrefractory linings ininduction steelmaking furnaces No. Monitoring method Type ofwork under the monitoring method 1 Visual inspection Conducting regular inspections ofthe refractory lining for the presence ofcracks, spalling, orany signs ofmechanical damage. Checking for uniform wear ofthe lining and identifying any possible unevenness that could lead toa loss ofdurability 2 Measurement ofcrucible thickness and geometric parameters Carrying out regular measurements ofthe refractory lining thickness todetect wear (areduction incrucible wall thickness may indicate the need for replacement). Monitoring other geometric parameters ofthe crucible (height, diameter) todetect deviations from standard values. The use ofappropriate equipment isrequired toensure precise measurements 3 Thermal (thermographic) monitoring Using thermal imaging cameras toidentify potential overheating zones orareas ofuneven heat distribution, which may indicate problems inthe refractory lining. Measuring the temperature onthe lining surface and inthe contact zone with molten metal when monitoring thermal parameters 4 Tracking offurnace operating parameters Tracking operating parameters such asoperating time, power, and temperature regime todetect anomalies that may indicate problems with the refractory lining. Sudden temperature changes oroverheating can accelerate lining wear 5 Non-destructive testing Using non-destructive testing methods, such asultrasonic inspection orradiography, todetect internal defects inthe refractory lining. Magnetic testing methods can also beeffective for identifying cracks and defects inthe lining structure 6Petrographic analysis ofrefractory lining material composition Sampling refractory lining material for subsequent petrographic analysis toidentify structural changes inthe material and determine the degree ofageing, which affects strength and thermal resistance 7Testing ofrefractory lining material properties Measuring the elastic characteristics ofthe refractory lining material toassess the degree ofageing and durability. Conducting strength tests onthe lining todetermine its mechanical properties and strength reserve 8Vibration monitoring Installing avibration monitoring system todetect potential vibrations, impacts, orother anomalies that may affect the condition ofthe refractory lining 9 Scheduled maintenance Establishing aregular schedule for planned maintenance, including inspection and monitoring ofthe refractory lining 5.4 HEURISTIC METHODS APPLICATION Toaddress the problem ofimproving the durability ofthe refractory lining ofan induction furnace, heuristic methods[42, 43] were used, including: a) method ofcontrol questions (MCQ); b) morphological analysis / focal objects method (MO/FOM); c) algorithm for solving inventive problems (ASIP); d) functional value analysis (FVA). 101 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS Table 5.5 Numbers and names ofinventive principles and proposed solutions No. Name ofPrinciple Solution (Idea) (VII, Fig. 5.4) 1 2 3 N=5 2 Extraction a) establishment ofa dedicated service (outsourcing[50]) ortraining one orseveral specialists tooperate the laser system and maintain several furnaces (possibly not only induction furnaces but also basic oxygen converters, blast furnaces, electric arc furnaces, etc.); b) relocation ofthe laser system outside the unit (furnace), ensuring mobility ofthe measuring device N=4 10 Preliminary action a) focus the sensors and laser scanning onareas ofmaximum wear and dimensional changes inthe refractory lining, asidentified from operational experience; b) perform measurements only inareas subject tomaximum wear, deformation, and changes; c) take measurements several heats before the known critical number that characterizes the minimum durability ofthe lining; d) pre-scan the initial shape ofthe lining (crucible) orits critical shape and periodically compare with the actual condition todetermine wear 13 Inversion (reverse, the other way round) Reorient the sensors and embed them “inthe armor” outside the refractory lining, directing the laser (oran acoustic system, ultrasonic testing[51], etc.) not from the outside onto the lining, but rather from beneath the lining outward 35 Parameter changes (changing the physical orchemical parameters) a) controlling slag build-upon the refractory lining[52] byadding fluxes during the melting process; b) modifying the crucible shape during repairs, taking into account slag buildup(“freezing-on”), incombination with Principle 10 (Preliminary action); c) adjusting the relative position ofthe inductor coil and the crucible toanticipate slag deposits; d) inthe case ofacidic linings, avoiding the use offluorspar (CaF2) and borax (Na2B4O7) inthe slag toprevent asharp decrease inlining durability; e) reducing the porosity ofthe lining and selecting appropriate raw materials, e.g., using high-quality quartzite linings with boron anhydride for alternating melting ofcast iron and alloyed (corrosion-resistant, chromium–nickel) steels N=3 19 Periodic action a) operating the sensors (laser system) not ina continuous mode, but only when measurements are required, for example, before the predicted critical heat corresponding tothe minimum durability ofthe lining; b) effective when applied incombination with Principle 13 (Reverse– The other way round); c) alternating melting ofcast iron and alloyed steels 27 Cheap short-living instead ofexpensive long-living The use ofinexpensive laser sensors ishardly feasible. Replacing the laser system with mechanical measurement isunproductive, unsafe, outdated, and contradicts the task requirements 102 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION 1 2 3 28 Replacement ofa mechanical system (with anoptical oracoustic one) Incertain cases, itis reasonable toconsider replacing acostly laser system with amore affordable ultrasonic system[51] for measuring the lining thickness 32 Change ofcolour Changing the color ofthe laser beam depending onthe lining thickness (the color changes together with the thickness). This ispossible when using anionic liquid (molten salts, sodium chloride at800°C)[53] and controlling the state ofthe ionic liquid via feedback (“laser– lining thickness– laser”) N=2 3 Local quality Differentiated gunning during repairs 11 Cushion inAdvance Disabling orpreventing the start-upof afurnace, which lining thickness isbelow orabove the critical value 29 Use ofpneumatics and hydraulics Application ofgas, liquid, and other types oflasers[53, 54]. Liquid lasers enable continuous adjustment ofemission wavelengths, i.e., beam color (used inconjunction with Principle 32 – color change) N=1 1 Segmentation a) perform measurements not ina continuous mode, but atspecific time intervals (see also Principle 19 – Periodic Action); b) since the lining thickness changes unevenly, more detailed measurements should betaken inareas ofintensive thickness variation (see also Principle 10 – preliminary action) 6 Universality Use lasers capable ofvarying their power over awide range, both for scanning the lining profile asits thickness changes and for performing repair work such asoverlaying aprotective glaze onworn areas and/orselectively melting slag deposits. Inthe future, apply laser melting for metal processing (“laser furnaces”), considering current developments inlaser sintering and casting[55] 21 Skipping Following earlier proposals, use ahigh-power laser for both repair[56] and scanning[57] ofthe lining condition ina “skip” mode, allowing much shorter measurement times 24 Intermediary Apply acontrollable laser amplifier[58] toenable seamless switching between “scanning-measuring” and “repair-modification” modes 26 Copying Study lining wear using photocopies and scanned images. Create aholographic model ofthe crucible for further analysis 38 Use ofstrong oxidants Employ laser ionization methods[59]. Although oxidation isharmful toboth the metal and the lining (crucible material), future laser technology could ionize the layer between the lining and the molten metal[60], preventing direct contact. Combining this with Principle 6 – Universality, one can envision melting units based onvariable-power lasers that can: a) scan the lining condition; b) repair and modify the lining; c) ionize the contact layer; d) melt metal  Continuation of Table 5.5 103 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS Itshould benoted that some ofthe ideas presented inTable 5.5 are formulated with consideration for the innovative development ofscience and technology, demonstrating the prospects ofusing laser systems for monitoring the thickness ofthe lining and expanding their technological capabilities. 5.5 FUNCTIONAL VALUE ANALYSIS Functional Value Analysis (FVA orABC-Method) isa method for evaluating the efficiency ofa technical system interms ofits functionality and cost. Inorder tooptimize the expenses for the technology ofrepairing worn-out linings ofinduction crucible furnaces, FVA isexpedient toapply for determining the relationship between the functionality ofcost components (materials) used for repair and their price. The main stages ofFVA for evaluating the effectiveness ofmaterials for repairing the worn lining ofan induction crucible furnace are given inTable 5.6. Table 5.6 Main stages ofFVA inevaluating the effectiveness ofmaterials for repairing the lining ofan induction crucible furnace No. FVA stage Description ofthe FVA stage 1 Identification ofthe functions ofthe repair materials See Table 5.7 2 Evaluation ofthe importance offunctions Determining the degree ofimportance ofeach function for restoring the lining and ensuring the efficient operation ofthe induction crucible furnace, using the ABC principle. Assessing the impact ofeach function onfurnace productivity and operational safety 3 Cost analysis offunctions Considering the costs ofmaterials, their manufacturing, and installation. Evaluating the efficiency ofdifferent materials interms ofservice life extension, resistance toaggressive environments, and lining cost 4 Identification ofalternatives Reviewing various types ofthermal insulation, structural, and heat-resistant materials that may beused for lining repairs. Comparing their technical characteristics and cost 5 Selection ofthe optimal option Selecting the material that ensures the highest efficiency atan affordable cost 6Optimization and continuous improvement Implementation ofthe selected material. Monitoring the material’sperformance. Adjusting the material specification ifnecessary The wear ofthe crucible lining inan induction furnace isinfluenced bythe severe operating conditions itis subjected to: thermal, erosive, and corrosive impact ofthe hot molten metal; the chemical corrosion processes caused byslag; the effect ofthe static pressure ofthe molten metal column (upto 40–80kPa[18]); the effect ofdynamic friction during molten metal stirring; mechanical impacts during charging ofscrap and alloying elements; aswell asduring the collapse ofbridges formed during melting. 104 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION The object ofimprovement considered isa 3t induction crucible furnace operated inthe melting department ofthe foundry shop ofZaporizhzhia Foundry and Mechanical Plant LLC. Thus, FVA makes itpossible toselect the optimal material for repairing worn lining, ensuring process efficiency and economic feasibility inresource utilization. The furnace lining must typically bereplaced ona monthly basis. The following components are required for the repair: refractory mass, refractory concrete, ramming mass, amold for furnace ramming, and acrucible (which has its own service life and requires replacement after wear). The functionality ofthe materials was assessed interms oftheir significance for achieving the goal (effect) ofextending the intervals between repairs. Anexpert assessment method was applied toevaluate the functionality ofthe elements. Following the Eisenhower-Pareto principle, functions (see item 1 inTables5.6 and 5.7) were categorised bytheir contribution toachieving the goal, assigned tospecific ABC classes, denoted asfollows: A– main functions, B– secondary functions, C– unnecessary orredundant functions. Table 5.7 Distribution ofrepair material functions for furnace lining (asper item 1 inTable 5.6) according tothe ABC principle for the target objective ofextending the inter-repair period No. Components Functions F1 F2 F3 F4 F5 F6 Total bycomponents 1. Crucible B AAAAB 4A–2B 2. Refractory mass B B – A– B A–3B 3. Refractory concrete – B B A– C A–2B–C 4. Ramming mass¹ AC – C – – A–2C 5. Furnace ramming mould² A–––––A Note: 1 mineralizers and binding agents; 2 welded from sheet material. F1 – restoration ofthe lining’sdimensions and shape; F2 – recovery ofthe lining’sthermal insulation properties operating across the entire working temperature range (200…1650°C); F3 – provision ofmechanical strength toretain the melt and withstand impacts; F4 – ensuring resistance tohigh-temperature exposure; F5 – protection against erosion, aggressive media, and wear caused byhydrodynamic stirring ofthe molten metal; F6 – restoration ofheat-reflective characteristics Source: [61] Thus, the materials are considered according tothe expenditure incurred for furnace repair. Owing tofluctuating prices, nondisclosure policies, and the likelihood oftrade secrecy affecting the repair cost, Table 5.8 presents the distribution ofrepair expenditures asresulting percentage values. The costs for items 2–3 inTable 5.8 are given per tonne ofmaterial. Inaddition, the materials used for furnace repair were evaluated interms oftheir functional significance for achieving maximum lining durability. The evaluation was performed ona tenpoint scale. Asurvey was conducted among employees ofvarious shop departments, namely: the section foreman, representatives ofthe procurement department, and repair crews. The average expert scores for significance are provided inTable 5.8. Based onthe obtained results, asignificance coefficient was calculated for the constituent materials used torepair the induction crucible furnace (Table 5.8). The data obtained are presented graphically inFig. 5.8 asa functional-value diagram. 105 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS Table 5.8 Calculation ofcost coeffi cients for constituent materials used torepair aninduction crucible furnace No. Components Repair costs Expert assessment ofthe signifi cance Cost ratio Share intotal costs, STC (%) Class Average score (10-point scale) Signifi cance, SIG (%) Cost coeffi cient, CC=STC/SIG 1 Crucible 81 A7.6 21 3.85 2 Refractory mass 6.2 A8.3 24 0.25 3 Refractory concrete 3.5 B 720 0.17 4 Ramming mass 5 A7.6 21 0.20 5 Furnace ramming mold 4.3 C 5 14 0.30 Total 100 – 35.5 100 – Crucible Crucible Refractory mass Refractory mass Refractory concrete Share in total cocts, STC (%) Significance, SIG (%) Cost coefficient, CC - STC/SIG Refractory concrete Ramming mass Ramming mass Furnace ramming mould Furnace ramming mould 100 80 60 40 20 0 81 3.5 4.3 14 21 20 0.3 0.2 24 21 0.17 0.25 3.85 5 6.2 Fig. 5.8 Functional-value diagram for the repair ofan induction crucible furnace For anoptimal technical system, the ratio ofthe specifi c weight intotal costs tothe signifi cance ofeach individual parameter (component) should not exceed 1.0. Based onthe obtained results, itwas established that the cost coeffi cient (CC) for crucible replacement is3.85, which indicates the need tosearch for alternative crucible suppliers with lower prices. Itshould benoted that crucible replacement does not take place during every repair. Therefore, inthe future, itis advisable torefi ne the above-mentioned FVA methodology torecalculate costs per tonne ofsteel produced. Asan organizational optimization measure, recommendations have been developed toensure compliance with crucible operating rules toextend the intervals between repairs and tocarry out maintenance byre-ramming the furnace without crucible replacement. The cost coeffi cient for other components isconsidered favorable (<1.0). 106 PROCESSES AND CONTROL SYSTEMS: SYNTHESIS, MODELING, OPTIMIZATION CONCLUSIONS Inthe context ofglobal decarbonization, this study addresses the improvement ofelectrometallurgical steelmaking processes, particularly the operation and reliability ofinduction melting furnaces used for high-quality steel and alloy production. These units combine high productivity with stable process control and lower environmental impact, yet the durability ofthe refractory lining remains alimiting factor for operational efficiency and reliability. The improvement ofinduction furnace performance primarily depends onoptimizing the crucible design and refractory lining properties, including resistance tothermal shocks, slag corrosion, and mechanical stresses, aswell asmaintaining minimal wear during melting. Based onthe operational experience ofZaporizhzhia Foundry and Mechanical Plant LLC, amethodological framework for systematic condition monitoring and maintenance decision-making ofrefractory linings was developed and tested. This framework integrates engineering practice with heuristic analysis and continuous improvement principles toidentify actionable measures for enhancing lining durability and stability ofmelting processes. The application ofthe method ofcontrol questions (MCQ) enabled identification ofcritical operational and design factors affecting refractory wear. These findings formed the basis for the monitoring logic, linking observed wear symptoms with preventive and corrective actions– selection ofoptimal refractory materials, implementation oflocal hot repairs, control ofslag quality and chemical composition, and optimization ofcrucible geometry and cooling zones. Using the focal objects method (FOM), innovative technical concepts were generated, particularly the feasibility ofintroducing alaser-based system for real-time monitoring ofthe residual lining thickness. This system, functioning asa diagnostic element ofthe proposed monitoring framework, allows continuous tracking ofthe lining profile and thickness, enabling early detection ofcritical wear areas and precise scheduling ofmaintenance operations. The TRIZ/ARIZ methodology contributed tothe synthesis ofthe overall monitoring and maintenance framework byconnecting heuristic problem-solving with the structural definition ofdecision-support stages– data acquisition, condition assessment, and corrective planning– within acontinuous improvement loop. Inturn, the Functional–Value Analysis (FVA) enabled the evaluation ofthe cost-efficiency ofmaintenance and repair operations for a3-tonne induction crucible furnace, identifying cost drivers and establishing decision criteria for supplier selection, resource allocation, and maintenance optimization. Organizational improvements were also proposed, focusing onstandardized maintenance protocols and adherence tooperational parameters toextend crucible service life. These measures facilitate the transition from reactive topredictive maintenance strategies, improving process stability and the overall efficiency ofthe equipment. The integration ofthe developed condition monitoring and maintenance decision-making framework, grounded incontinuous improvement principles, enables asystematic increase inprocess reliability, reduction ofunplanned downtime, and improvement ofrefractory lining durability. The obtained results confirm the effectiveness ofcombining analytical, heuristic, and managerial methods inadvancing electrometallurgical process control systems and serve asa practical foundation for further development ofdecision support tools for maintenance planning and optimization ofrefractory management ininduction melting furnaces. 107 5 IMPROVING CONDITION MONITORING AND MAINTENANCE FRAMEWORK FOR REFRACTORY LININGS IN INDUCTION MELTING FURNACES THROUGH CONTINUOUS IMPROVEMENT METHODS REFERENCES 1. Zhang, J., Guo, H., Yang, G., Wang, Y., Chen, W. (2025). Sustainable Transition Pathways for Steel Manufacturing: Low-Carbon Steelmaking Technologies in Enterprises. Sustainability, 17 (12), 5329. https:// doi.org/10.3390/su17125329 2. Mariani, A., Malucelli, G. (2023). Insights into Induction Heating Processes for Polymeric Materials: An Overview of the Mechanisms and Current Applications. Energies, 16 (11), 4535. https://doi.org/10.3390/ en16114535 3. Hauck, A., Schmitz, W. 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