Continuous Annealing Furnace Research Articles

Numerical study on temperature and thermal stress behaviors in silicon carbide heating elements within high-temperature annealing furnaces

In response to global sustainability goals, the transition from fossil fuel-based to electric silicon carbide (SiC) heating elements in continuous annealing furnaces is critical for reducing emissions, enhancing safety, and improving operational environments in the steel industry. This study investigates the cross-sectional temperature profiles and the resultant thermal stress of hollow cylindrical SiC heating elements under varied design conditions. To independently analyze the complex effects of multiple factors, both theoretical and numerical analyses were conducted using simplified boundary conditions in two dimensions, which closely simulate the actual temperature profiles observed in heaters within a continuous annealing line. The results indicate that the radial temperature gradient and resulting thermal stress in these elements are directly proportional to the surface heating load, with the maximum axial tensile stress occurring at the outer surface of the heater. Scenarios involving closely spaced multiple heaters or the introduction of cold steel strips lead to increased axial thermal stress due to additional circumferential temperature gradients. Conversely, the application of shield tubes, despite increasing the heater’s temperature, reduces thermal stress by homogenizing radiation within the tube. Consequently, optimizing heater configuration and operational conditions is essential in furnace design to effectively manage heaters’ temperature and thermal stress, thereby ensuring both efficiency and service longevity of the heating elements.

PSO-FDM (Particle Swarm Optimization-Finite Difference Method)-Based Simulation Model of Temperature and Velocity of Full-Scale Continuous Annealing Furnace

Improving the accuracy of the temperature field prediction model for continuous annealing line strips and enhancing the model’s adaptability to full-size strips are key technical challenges in continuous annealing lines. This paper developed a continuous annealing temperature prediction model based on a variable step-size strategy for the heating section, even-heat section, slow-cooling section, and fast-cooling section of the continuous annealing line. To improve the prediction accuracy for different strip sizes, the PSO optimization algorithm was employed to determine the optimal heat transfer coefficient for each strip size. Additionally, due to the limited production of certain strip gauges, providing insufficient data for optimization, this study introduces a combined file approach to address gauge vacancies. The experimental results indicate that the optimized model with variable step size can control the absolute prediction error to less than 4 °C, improving prediction accuracy by 61.9% and prediction speed by 26.8% compared to the traditional equal-step prediction model. This study verified that the merger method is effective for addressing side gauge vacancies, while the proposed method is suitable for resolving middle gauge vacancies. The main technical contribution of this study is the establishment of a high-precision prediction model for continuous annealing temperature of variable step length strips, ensuring high temperature control accuracy for full-gauge strips when passing through the continuous annealing production line.

Predictive Modeling of Strip Temperature in Continuous Annealing Furnace: An Improved Optimization Algorithm

Predictive Modeling of Strip Temperature in Continuous Annealing Furnace: An Improved Optimization Algorithm

Numerical analysis of the radiant heating effectiveness of a continuous glass annealing furnace

• A modeling approach for industrial-scale continuous radiative heating furnaces was developed. • The spacing between the glass bottle rows affects the radiative heating effectiveness of the furnace. • Optimum row spacing was found to be 35 % of the bottle diameter. • Operating the furnace at the optimum row spacing, furnace length could be reduced by 8.5%. Radiative heat transfer is the dominant mode of heat transfer in glass annealing furnaces. Especially in electrically heated furnaces due to the nonparticipating nature of the furnace atmosphere the radiative heat transfer predominantly occurs between surfaces. In this regard, in container glass manufacturing the layout of the container glasses inside the furnace can considerably affect the radiative heating effectiveness of the furnace. In this numerical study, the effect of the spacing between the bottle rows on the radiant heating effectiveness of the furnace was numerically investigated. An industrial scale continuous annealing furnace model was used and the combined conduction – radiation heat transfer modes in the furnace were solved with the in-house developed transient solver. The convective heat transfer inside the furnace was not taken into account due to its relatively lower contribution in heat transfer. The computational cost of the numerical model is reduced with the use of a computational domain consisting of 7 bottle rows instead of full 29 bottle rows. Reverse Monte Carlo Ray Tracing method is used to solve for the surface-to-surface radiative heat transfer inside the radiant heating zone and integrated into GPU to reduce its computational cost. Further computational speed-up was achieved with the use of a 2nd order accurate radiation boundary condition implementation. It allows a time step increase of 2.5x in comparison with the first order accurate implementation for the same level of accuracy. Finally, a parametric study on the effect of the spacing between the bottle rows on the radiative heating of the bottles have been conducted. In this regard, the spacing between the bottle rows and the conveyor speed have been altered in a way that the throughput of the furnace, the number bottles processed per unit time, is kept constant. The study shows that there is an optimum spacing value between the bottle rows. For the particular bottle geometry considered in this study, the optimum row spacing value is found to be 35% of the bottle diameter. Running the furnace at this optimum value, the length of the heating zone could be reduced by 8.5% compared to the case when the furnace was operated with the bottles almost in touch with each other.

Failure Analysis of Inconel 601 Radiant Tubes in Continuous Annealing Furnace of Hot Dip Galvanizing Line

Metallurgical investigation was conducted to establish the genesis of crater-like defects and perforations in Inconel 601 radiant tubes used in Radiant Tube Heating/ Radiant Tube Soaking (RTH/RTS) section of the Continuous Annealing Furnace in Hot Dip Galvanizing Line (HDGL) of an integrated steel plant. The radiant tubes, several of them, had undergone catastrophic damage after only about 70 days of service under mixed gas firing inside the furnace. Visual examination, chemical analysis and secondary electron imaging (SEI) coupled with energy-dispersive x-ray spectrometry (EDS) were concomitantly utilized for the investigation of failed radiant tube samples. Based on the findings, the unprecedented failures were attributed to the high temperature sulphidation attack experienced by the tubes on their inner walls, owing to sulphur dioxide (SO2) resulting from combustion of hydrogen sulphide (H2S) in the mixed gas (2H2S + 3O2 → 2H2O + 2SO2). The investigation also pointed toward the apparent formation of low-melting nickel-nickel sulphide (Ni-Ni3S2) eutectic because of sulphidation, which led to unique spherical manifestations of the defects and served to highlight the deleterious influence of sulphur-bearing compounds on nickel-base alloys at high temperatures. Suitable alternative materials of construction are proposed for the radiant tubes operating under such environments.

Failure analysis of a furnace roller in continuous annealing line after long-term service at high temperatures

The rollers used to convey steel strips in a continuous-annealing furnace were deformed after about 12 years of service, resulting in an unevenness of the rolled strips. In this study, failure causes of the furnace rollers were investigated in terms of degradation of microstructure and mechanical properties of the roller material. After a long period of high temperature service, the microstructure of the material has changed significantly. A large number of network-like carbides precipitated at the grain boundaries, and these carbides have been greatly coarsened. It was also found that a great number of σ-phase have formed on the coarsened carbides, and that the volume fraction of the σ-phase on the grain boundaries has exceeded 50%. In addition, creep cavities have been found in the grain boundaries. Especially in regions with dense grain boundaries, the cavities formed at the intersection of grain boundaries have been linked into chains, which tend to develop into cracks. The grain boundaries of the furnace roller material after service has been severely embrittled. Both tensile and impact fracture surfaces show brittle intergranular fracture characteristics. Compared to the unused material, the tensile strength and impact toughness of the failed roller decreased significantly due to the deterioration of the microstructure. Because of the degraded mechanical properties, the rollers are prone to deformation under the service loads, thus cannot guarantee the normal production of strip steels. The results of this study provide a reference for evaluating the remaining life of furnace rollers after long-term service at elevated temperatures.

Unsteady‐state lumped heat capacity system design for tube furnace for continuous inline wire annealing process

AbstractA continuous annealing furnace is developed, which incorporates the principle of electric resistance heating for obtaining the desired temperature in the furnace. The concept of lumped heat capacity system is applied for the determination of annealing time of a continuously moving wire through the refractory tube. Also, the heat transfer inside the system and heat losses to the atmosphere are considered using the principles of conduction, convection, and radiation. The parameters related to the dynamics of moving wire are also designed. The designed furnace is fabricated and tested for its working, the observations of which show that 30 minutes are required to reach about 400°C furnace temperature and 30 seconds for annealing 1 m length of wire. The morphological testing of annealed and nonannealed wire is done to study the microstructure, which shows more traces of pearlite in annealed wires than in nonannealed wires. Thus, continuous annealing furnaces are more effective for inline annealing of wires; so as to relieve the internal stresses, induced by the step cold rolling process.

Monte Carlo calculation of view factors between some complex surfaces: Rectangular plane and parallel cylinder, rectangular plane and torus, especially cold-rolled strip and W-shaped radiant tube in continuous annealing furnace

View factor plays an important role in evaluation of radiative heat transfer. This paper gives a detailed account of setting up the Monte Carlo calculation models of view factors between some complex surfaces. Main purpose is to calculate view factor between cold-rolled strip and W-shaped radiant tube in continuous annealing furnace. Given advantages of Monte Carlo method, it has been used to calculate view factor between the strip and radiant tube. Firstly, the Monte Carlo calculation models for view factor between rectangular plane and parallel cylinder and for view factor between rectangular plane and torus are established and verified, respectively. Then, according to reciprocity and superposition rules of view factors, the Monte Carlo calculation model for view factor between the strip and radiant tube is established by the above models. By comparing with analytical expression, or checking reciprocity after performing the Monte Carlo analysis in each direction between surface pairs, the calculation errors of above Monte Carlo models are analyzed and the results show that the Monte Carlo method is effective and reliable in calculating view factors between some complex surfaces.

Atmosphere Dynamics Modeling and Hydrogen Ratio Control of Horizontal Continuous Annealing Furnace

Atmosphere Dynamics Modeling and Hydrogen Ratio Control of Horizontal Continuous Annealing Furnace

Simulation of the Temperature, Microstructure and Mechanical Properties of Cold-Rolled Stainless Steel Sus430 During Continuous Annealing

Mathematical models of variation of the temperature, microstructure and mechanical properties of cold-rolled steel SUS340 in a continuous annealing furnace are derived using experimental results and numerical methods. The results obtained are used for computing the mechanical properties of SUS340 under continuous annealing and for developing new annealing modes with the help of the model suggested.

Analysis of thermal energy performance in continuous annealing furnace

In this paper, the effects of several parameters such as the strip width and thickness, strip velocity and also heating power produced by radiant tubes and its distribution on the overall efficiency of continuous annealing furnace were analyzed. A mathematical model was developed to compute the total heat absorbed by the strip. Then, the overall efficiency was calculated. It was recognized that the strip with lower thickness and width may reduce the thermal performance of continuous annealing line. According to this study, both of strip velocity and heating power should be carefully adjusted in each heating schedule. One of the greatest benefits of this work rather than other previous studies is that both strip velocity and heat power are simultaneously considered such that the operator can make a better sense of setting parameters among tangible choices for a predetermined schedule. The results showed despite more heat provided at the entry of the furnace, the effect of adjusting the heating power at the exit of furnace on overall efficiency was remarkably more.

Comprehensive optimisation technology of roller profile in continuous annealing furnace

ABSTRACTSeveral problems, such as strip deviation and buckling, are encountered in the continuous annealing process. In this study, equipment and process features of continuous annealing, as well as the advantages and disadvantages of single taper roller and double taper roller in the prevention and treatment of the buckling and strip deviation were considered. Basing on a number of field experiments and theoretical studies, a new set of furnace roller profile curve was proposed and a set of optimisation model suitable for furnace roller was established, with travelling stability of the strip as the objective function. Test results of field production showed that the strip exhibited high speed and stability after optimisation, and the service cycle of the furnace roller was considerably improved. The results of this study provide an important economic benefit for the site and are valuable for further popularisation and application.

富氧掺烧在镀锌连续退火炉上的应用

八钢冷轧镀锌连续退火炉年设计产能15万吨，由于市场需求量增大，产能已不能满足市场需求，将富氧掺烧新技术应用到镀锌连续退火炉中取得了良好效果，目前退火炉已具备年产18万吨钢的能力。 The original yearly capacity of the cold rolled galvanized continuous annealing furnace in Bagang is 150,000 tons of steel. With the increasing market demand, this capacity cannot meet the need. Applying the new technology of burning with enriched oxygen to the cold rolled galvanized con-tinuous annealing furnace obtains a good effect. The present annual capacity of annealing furnace has been increased to 180,000 tons.

Heating and Flow Analysis in Hot‐Rolled Stainless Strip Continuous Annealing Furnace Based on CFD Modeling

AbstractA three‐dimensional mathematical model was found for a continuous annealing furnace, the temperature field, and flow field of the furnace and the temperature of the stainless strip could be calculated by using this model. The simulation results were compared with measured data and the accuracy of the model was proved by the predicted temperature distribution. By using this model, the convective heat transfer coefficient and equivalent radiation heat transfer coefficient of the strip surface were also analyzed.

Mathematical modelling and parameter identification of a stainless steel annealing furnace

A new, comprehensive mathematical model of continuous annealing furnaces is developed, under consideration of both the radiative and convective heat transfer of the furnace components. Based on measured normal operating data from an industrial stainless steel plant, parameter identification is basically carried out using a nonlinear least-squares optimization algorithm for the whole annealing furnace, to estimate optimal values of uncertain parameters, such as emissivities. Due to the complexity of the model, a sequential approach for parameter identification is proposed and implemented, i.e. the parameter set is divided into different subsets, and the parameter estimation is carried out sequentially in several steps and iterations. The performance of the model with the estimated parameters is then evaluated on a different test data set. It is shown that the obtained model can predict temperature evolutions along the furnace in good agreement to measured data, under both steady-state and transient conditions. The presented model is suitable for controller design and process optimization.

GA-PARSIMONY: A GA-SVR approach with feature selection and parameter optimization to obtain parsimonious solutions for predicting temperature settings in a continuous annealing furnace

This article proposes a new genetic algorithm (GA) methodology to obtain parsimonious support vector regression (SVR) models capable of predicting highly precise setpoints in a continuous annealing furnace (GA-PARSIMONY). The proposal combines feature selection, model tuning, and parsimonious model selection in order to achieve robust SVR models. To this end, a novel GA selection procedure is introduced based on separate cost and complexity evaluations. The best individuals are initially sorted by an error fitness function, and afterwards, models with similar costs are rearranged according to model complexity measurement so as to foster models of lesser complexity. Therefore, the user-supplied penalty parameter, utilized to balance cost and complexity in other fitness functions, is rendered unnecessary. GA-PARSIMONY performed similarly to classical GA on twenty benchmark datasets from public repositories, but used a lower number of features in a striking 65% of models. Moreover, the performance of our proposal also proved useful in a real industrial process for predicting three temperature setpoints for a continuous annealing furnace. The results demonstrated that GA-PARSIMONY was able to generate more robust SVR models with less input features, as compared to classical GA.

Thermal anti-oxidation treatment of CrNi-steels as studied by EXAFS in reflection mode: the influence of monosilane additions in the gas atmosphere of a continuous annealing furnace

Surface sensitive, reflection mode EXAFS spectroscopy at the Cr and Fe K-edges was used to study the surfaces of stainless steel (EU alloy grade 1.4301 X5CrNi18-10) after different heat treatments. The thermal treatments were performed in a conveyor belt furnace at temperatures between 600 and 900 °C in different gas atmospheres containing inert carrier gases (N2 or Ar) and different additives such as hydrogen (H2) and monosilane (SiH4). The ex-situ EXAFS results show that the iron and chromium in the steel can only be reduced to a metallic state, if SiH4 was used as a reducing additive for temperatures of 900 °C. Lower temperatures and process atmospheres without silane always result in strongly oxidized steel surfaces.

Simulation of Taper Roll Deviation Rectification Ability in Continuous Annealing Furnace

Running deviation of cold strip affects smooth operation in continuous annealing furnace, and the taper roll technology has positive significance for the prevention of strip deviation. In this paper, a finite element model of cold strip in continuous annealing furnace is established, and it can be used to analysis deviation rectification ability of single taper roll with different conical height and straight section length, double taper roll with different total conical height, straight section length and taper ratio. The calculation results show that the conical height is the most important factor for deviation rectification, and the deviation rectification ability of double taper roll is better than single taper roll. The results provide reference for taper roll optimization design in continuous annealing furnace.

Overall models based on ensemble methods for predicting continuous annealing furnace temperature settings

The prediction of the set points for continuous annealing furnaces on hot dip galvanising lines is essential if high product quality is to be maintained and energy consumption and related emissions into the atmosphere are to be reduced. Owing to the global and evolving nature of the galvanising industry, plant engineers are currently demanding better overall prediction models that maintain accuracy while working with continual changes in the production cycle. This paper presents three promising prediction models based on ensemble methods (additive regression, bagging and dagging) and compares them with models based on artificial intelligence to highlight how good ensembles are at creating overall models with lower generalisation errors. The models are trained using coil properties, chemical compositions of the steel and historical data from a galvanising process operating in Spain. The results show that the potential benefits from such ensemble models, once configured properly, include high performance in terms of both prediction and generalisation capacity, as well as reliability in prediction and a significant reduction in the difficulty of setting up the model.

Methodology based on genetic optimisation to develop overall parsimony models for predicting temperature settings on annealing furnace

Developing better prediction models is crucial for the steelmaking industry to improve the continuous hot dip galvanising line (HDGL). This paper presents a genetic based methodology whereby a wrapper based scheme is optimised to generate overall parsimony models for predicting temperature set points in a continuous annealing furnace on an HDGL. This optimisation includes a dynamic penalty function to control model complexity and an early stopping criterion during the optimisation phase. The resulting models (multilayer perceptron neural networks) were trained using a database obtained from an HDGL operating in the north of Spain. The number of neurons in the unique hidden layer, the inputs selected and the training parameters were adjusted to achieve the lowest validation and mean testing errors. Finally, a comparative evaluation is reported to highlight our proposal’s range of applicability, developing models with lower prediction errors, higher generalisation capacity and less complexity than a standard method.