Audio acoustic plant condition monitoring of spiral bevel gearbox

Abstract

Plant condition monitoring (PCM) is widely used by a variety of industries as part of a condition based maintenance programme. This replaces the previous ‘schedule’ based maintenance programme, in which individual components of a machine are replaced at specified intervals. With PCM the condition of the individual components is monitored, and they are only replaced when their performance is deemed unsatisfactory. PCM techniques are often capital and/or labour intensive, and their use limited to critical machines only. The objective of the present research is to develop a system comprised of microphones and accelerometers which is able to screen industrial environments, such as the hot rolling mill at Corus's Port Talbot plant, for machine faults. The system would use the minimum number of transducers to remotely screen the maximum number of machines, but is not required to provide detailed diagnostic information. To date, an omnidirectional microphone has been used successfully to detect badly damaged gear teeth. The method does not require the use of a soundproof enclosure to filter out background noise. A finite element analysis model of the test rig has been created to determine the eigenfrequencies and eigenmodes of the test rig and to improve the understanding of the vibration behaviour of the faults.     

旋转机械设备状态预警与维修优化

旋转机械设备的维修策略对于维护机械设备运行状态,保障产品生产质量有着重要意义,并且直接影响企业经济效益.频繁维修虽可以保障设备状态,但随之会带来高昂的维修成本;检修周期过长虽然可以降低维修次数,减少维修成本,但是设备状态却难以保证.本文提出了一种基于峭度指标的故障预警方法以及基于模糊C均值方法的实时维修策略优化方法.通过监测峭度指标变化,可以成功捕捉机械设备的早期故障特征,再使用模糊C均值方法,评估设备状态,将其结果视为设备运行可靠性指标,根据企业效益最优化的维修建议准则,对设备的维修策略做出实时建议.对某钢厂的设备状态监测数据分析验证,结果表明,本文提出的基于实时维修策略优化方法的维修建议更加适用于现场设备的管理,节约了监测成本,使得企业效益更优.      

Criterion to control self-propagation high temperature synthesis for porous Ti–Al intermetallics

Abstract

The criterion to control self-propagation high temperature synthesis for the fabrication of porous Ti–Al intermetallics was established from the prereaction model and the thermal balance condition. The criterion equation reflecting the relation between the solid reaction layer thickness correlation parameter and the ignition temperature was deduced to be p³?=?C₁/(T_ad?T₀)+C₂, according to which the near net shaping synthesis of porous Ti–Al intermetallics was realised, which was significantly important for the industrial productions and applications of this high performance novel porous material. The slight difference between theoretical predictions and experimental data was analysed according to the model analysis.     

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

A physically based model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the η- and the S-phase solvus (using a regular-solution model), taking account of the capillary effect and η coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles, and precipitates) and solute-depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr-containing alloys and Cr-containing alloys under various aging conditions, achieving an accuracy of about 1 pct in predicting unseen conductivity data from this set of alloys.     

Optimization of the johnson-mehl-avarami equation parameters for <Emphasis Type="Italic">α</Emphasis>-ferrite to <Emphasis Type="Italic">γ</Emphasis>-austenite transformation in steel welds using a genetic algorithm

A nonisothermal Johnson-Mehl-Avarami (JMA) equation with optimized JMA parameters is proposed to represent the kinetics of transformation of α-ferrite to γ-austenite during heating of 1005 steel. The procedure used to estimate the JMA parameters involved a combination of numerical heat-transfer and fluid-flow calculations, the JMA equation for nucleation and growth for nonisothermal systems, and a genetic algorithm (GA) based optimization tool that used a limited volume of experimental kinetic data. The experimental data used in the calculations consisted of phase fraction of γ-austenite measured at several different monitoring locations in the heat-affected zone (HAZ) of a gas tungsten arc (GTA) weld in 1005 steel. These data were obtained by an in-situ spatially resolved X-ray diffraction (SRXRD) technique using synchrotron radiation during welding. The thermal cycles necessary for the calculations were determined for each monitoring location from a well-tested three-dimensional heat-transfer and fluid-flow model. A parent centric recombination (PCX) based generalized generation gap (G3) GA was used to obtain the optimized values of the JMA parameters, i.e., the activation energy, pre-exponential factor, and exponent in the nonisothermal JMA equation. The GA based determination of all three JMA equation parameters resulted in better agreement between the calculated and the experimentally determined austenite phase fractions than was previously achieved.     

Three-dimensional analysis and design of petal-like mould for continuous casting of steels

Abstract

Understanding the shrinkage behaviour of a steel billet is very important for designing the continuous casting mould, and conversely, a well designed mould is beneficial when matching the shrinkage behaviour of the billet. The shrinkage behaviour of a billet is hard to measure in situ during continuous casting but can be calculated by numerical simulation. A three-dimensional finite element model has been built to simulate the thermal and stress fields of the billet in the mould. The dynamic thermal boundary condition, the effect of ferrostatic pressure and the temperature dependent thermophysical parameters have been considered in the model. The shrinkage of billet when considering ferrostatic pressure is on average 0·08 mm smaller than when not considering ferrostatic pressure. The temperature and stress distributions are analysed in the present paper, and based on this analysis, a novel petal-like mould was designed and its taper determined. The designed mould has been tested in industrial practice showing better lifetime and billet quality.     

基于Copula函数的热轧支持辊健康状态预测模型

热轧支持辊的健康状态在带钢板形质量和轧制稳定性控制中起着关键作用,非线性、强耦合、少样本等特点使得热轧支持辊健康状态的预测复杂,目前各大钢厂仍以定期维护和事后维修为主。本文提出了一种支持辊虚拟健康指数的构建方法以及基于Copula函数的复杂工况健康状态预测模型。首先结合支持辊弯窜辊数据表征支持辊健康状态,再使用K-means聚类方法对支持辊工况进行划分,将各工况下过程数据分别构建Copula预测模型,最后根据实际轧制计划的排布顺序融合各工况模型的预测结果。提出的基于Copula函数的预测模型在某钢厂1780热连轧产线得到应用,结果表明,该模型能够准确有效的按照轧制计划实现支持辊的健康状态预测,以更科学的策略指导支持辊更换维护。      

Continuous-cooling-precipitation kinetics of Nb(CN) in high-strength low-alloy steels

Although isothermal precipitation has been frequently studied with respect to industrial hot deformation processing, the temperature decreases continuously under these conditions so that isothermal data cannot be applied directly to predict the precipitation kinetics. This study therefore was concerned with the continuous-cooling-precipitation (CCP) behavior of Nb carbonitride in austenite. In the present work, the Liu-Jonas (L-J) model was used to calculate the precipitation start (P _s) time at a given temperature from experimental data. A new calculation method for predicting the precipitation finish (P _f) time, based on reaction kinetics and classical nucleation and growth theory, was also developed. The additivity rule was then used to calculate the extent of precipitation during continuous cooling. Isothermal precipitation rates for 0.04 pct Nb steels were measured experimentally by the stress relaxation method. The CCP behavior was then calculated from the model, and the accuracy of the predictions was evaluated by carrying out continuous-cooling tests using a deformation dilatometer. The precipitate size distributions were determined by the transmission electron microscopy of specimens quenched after increasing intervals of cooling at various cooling rates. TheP _s andP _f times estimated from the particle size data show good agreement with the calculated CCP behavior.     

Comparison of four methods to evaluate flow fields in CSP casting mould

Abstract

Commercial flow analysis tools are widely used in industry, but their capacity, efficiency and accuracy to solve complex flows are not so clear. In the present paper, first, three-dimensional computations are performed to calculate the flow field in the mould region of compact strip production (CSP) casting using a conventional finite volume method program, CFX4, with laminar model, standard k–? model, renormalisation group k–? model and low Reynolds number k–? model with default model parameters for handling turbulence. Next, these were compared with the flow pattern in a 1 : 1 scale water model by other investigations and quantitative comparisons were made for the flow velocities. Finally, the four numerical simulation models were evaluated in detail. Each method has its own merits and disadvantages, so model verification is always necessary for a highly accurate numerical analysis of complex flows. Under the situation of lacking experimental data, the standard k–? may be a good choice to evaluate liquid steel in a CSP mould.     

Prediction of shape defects over length of cold rolled sheet using artificial neural networks

Abstract

A model based on an artificial neural network (ANN) has been developed for prediction of flatness of cold rolled (CR) sheet in a tandem cold rolling mill for white goods applications. Various process parameters including roll bending, roll shifting, tensions between stands etc., which affect flatness of CR sheet are considered in the model. Substantial amounts of data are obtained from level II automation of PL-TCM of TATA Steel to develop the prediction model. The developed ANN model, based on back propagation algorithm, is able to predict the flatness defects like edge buckles, centre buckles for a given set of rolling parameters. The model involves a large number of process parameters and application of ANN to such kind of problems is successfully demonstrated in the present study. The model is in good agreement with the observed flatness values at different locations across the width. High coefficient of determination close to 0·919 is achieved for the prediction of flatness at edges.     

Steel annealing furnace robust neural network model

Abstract

In this day and age, galvanised coated steel is an essential product in several key manufacturing sectors because of its anticorrosive properties. The increase in demand has led managers to improve the different phases in their production chains. Among the efforts needed to accomplish this task, process modelling can be identified as the one with the most powerful outputs in spite of its non-trivial development. In many fields, such as industrial modelling, multilayer feedforward neural networks are often proposed as universal function approximators. These supervised neural networks are commonly trained by the traditional, back-propagation learning format, which minimises the mean squared error (mse) of the training data. However, in the presence of corrupted or extremely deviated samples (outliers), this training scheme may produce incorrect models, and it is well known that industrial data sets frequently contain outliers. The process modelled is a steel coil annealing furnace in a galvanising line, which shares characteristics with most of the furnaces used in galvanised lines all over the world. This paper reports the effectiveness of robust learning algorithms compared to the classical mse-based learning algorithm for the modelling of a real industry process. From this model an adequate line velocity (the velocity set point) for a coil, depending on its characteristics and the furnace condition to receive this coil (temperature set points), can be obtained. With this set point generation model the operator could set strategies to manage the line, i.e. set the order of the coil to be treated or preview the line's speed conditions for the transitory situations.     

Model based optimisation of continuous annealing operation for bundle of packed rods

Abstract

A typical industrial thermal processing operation has multifold complexity, with varying charge dimensions, multiple grades and inconsistent loading patterns as well as the absence of in situ sensors. These operational characteristics and restrictions invariably lead to empirical design for the temperature time cycles, which often results in suboptimal operation in terms of higher energy consumption, inconsistent quality and lower productivity. In the present work, a process model is proposed for designing the heating cycles for bundles of packed rods with different rod diameters, bundle diameters and packing fractions in a continuous annealing furnace. The process model has the capability of predicting spatial and temporal evolution of temperature and hardness in the bundle as it traverses through the furnace. Interestingly, the model based process cycles are found to be counterintuitive as compared with the empirically designed cycles normally employed in the plant. It is shown that instead of designing the process cycles on the basis of rod diameters, which is the general practice in the plant, it should be based on bundle characteristics, such as bundle diameter and packing fraction. These concepts have been implemented in an industrial operation resulting in around 20% energy reduction and 15% productivity enhancement.     

Coupled reaction kinetics of duplex steelmaking process for high phosphorus hot metal

Abstract

The duplex steelmaking process has been proven to be an effective solution for the utilisation of high phosphorus iron ore, yet systematic analyses of the dephosphorisation rate and mechanism of duplex process for high phosphorus hot metal are seldom reported. Comprehensive exploration and discussion on the kinetics of duplex steelmaking process for high phosphorus hot metal are thus required. First, based on the kinetic model proposed by Robertson et al., a modified coupled reaction kinetic model was formulated and employed to analyse the dephosphorisation process of duplex melting for high phosphorus hot metal. Furthermore, a series of experiments were carried out to validate the accuracy of the established model, and the calculated results showed good agreement with the experimental data. Finally, a parametric study was conducted to perform a further discussion of the mechanism of duplex steelmaking process for high phosphorus hot metal.     

Numerical simulation of fluid flow and solidification in continuous slab casting mould based on inverse heat transfer calculation

Abstract

A mathematical model based on an inverse heat transfer calculation was built to determine the heat flux between the mould and slab based on the measured mould temperatures. With K–? turbulence model, a mathematical model of three-dimensional heat transfer and solidification of molten steel in continuous slab casting mould is developed. Solidification has been taken into consideration, and flow in the mushy zone is modelled according to Darcy’s law as is the case of flow in the porous media. The heat flux prescribed on the boundaries is obtained in the inverse heat conduction calculation; thus, the effect of heat transfer in the mould has been taken into consideration. Results show that the calculated values of mould temperature coincide with the measured ones. Results also reveal that the temperature distribution and shell thickness are affected by the fluid flow and heat transfer of slab which is governed by the heat flux on the mould/slab interface.     

Recalculation of Flow Stresses from Industrial Process Data for Heavy Plate Rolling Using a 2D Finite Element Model

In hot rolling, the quantities rolling load, torque, and power consumption are important measurable process parameters. For the determination of rolling loads in hot flat rolling processes, like heavy plate rolling, Sims's model 1 is a well‐known approach represented by an analytical formula. The solution of Sims's equation leads to the multiplier Q, which is a function of the roll gap geometry. The rolling load is then computed by applying the width of the plate, the contact length, the multiplier, and an average material flow stress called k_fm. This flow stress is commonly recalculated from process data as a function of temperature, pass strain, and a mean strain rate, applying the Sims model itself. One question arises from this method: Are the recalculated flow stresses physically based values or in other words, what is the (physical) meaning or interpretation of these values? The present paper tries to give an answer to this question by determining the influence of the roll gap geometry alternatively by means of a simple 2D FEM model which gives a corresponding multiplier referred to as Q_FE. Flow stresses are recalculated from a set of process data using both factors. The results are compared to experimental flow stress data from hot compression tests. It is shown, that the recalculated flow stresses using Q_FE are in better agreement with the laboratory data than the recalculated values using Sims's Q.     

Thermophysics characteristics and densification of powder metallurgy composites

Abstract

An analytical densification model describing the final stages of hot pressing and sintering has been developed and found to be consistent with empirical findings. The behaviour of composite powders for the matrices of diamond tools has been studied under hot pressing conditions. Differential scanning calorimetry was used to determine the heat capacity at constant pressure C _p of pure Co, 663Cu, and composite iron- and cobalt based powders (also containing WC, Ni and 663Cu). The relationship between C _p and composite densification has been analysed, and it has been found that optimised rare earth additions to the iron based composite powders can produce C _p characteristics close or equivalent to that of pure Co powders. This modified composite powder has been used to hot press diamond drill and saw bits that show good properties. Employing a densification regime guided by the dynamic model has been found radically to improve stability in service (bend strength, hardness, impact, ductility and porosity).     

Simulated effects of martensite start temperature,thermal conductivity and pore content on end quench cooling rate

Abstract

Process modelling, based on finite difference methods, is used to show that the thermal conductivity increases, which typically attend the martensite transformation in steel, affect the cooling rate in the Jominy end quench test. A one-dimensional model, which includes the effects of material property variations, is presented that predicts slightly increased cooling rates with increases in the M _s temperature for fully dense steels and significantly increased rates for powder metallurgy (PM) steels. The model is based on earlier studies of the end quench test that initially showed increased cooling rates in PM steels versus fully dense ones and then went on to show water penetration of the pores as a causative mechanism. In the present study, it is shown that by combining a simple theory of this mechanism with the aforementioned M _s effects, it is possible to obtain cooling curves that display a marked resemblance to the experimentally observed ones of these earlier studies.     

Calcium deoxidation equilibrium in liquid iron

Calcium-oxygen equilibrium was studied at 1873 K under normal pressure by the method of immersing a pure iron capsule containing calcium metal into liquid iron, which was equilibrated with CaO-Al₂O₃ slags in Al₂O₃ and CaO crucibles. On the basis of these and previous results obtained in the equilibrium experiments between liquid iron and CaO-containing slags, the equilibrium constant,K _Ca, for the reaction, CaO (s) =Ca +O, and the first-order interaction parameter,e ₀ ^Ca , were estimated. The measured value forK _Ca reported in previous experiments, which was found to be significantly different from that calculated from the reliable thermodynamic data, was discussed. Nitrogen distribution ratios between CaO-Al₂O₃ slags and liquid iron were also measured. Formerly Graduate Student, Department of Metallurgical Engineering, Tohoku University     

Single strand continuous caster tundish furniture comparison for optimal performance

Abstract

Analysis of a single strand 36 t thin slab caster tundish has been conducted with different sets of furniture using a three-dimensional computation fluid dynamics model taking heat losses into account. Five distinct and optimised cases and a base case were used for simulation. The cases were built considering tundish furniture that is readily and economically available and provides ease of maintenance, thus targeting an optimal set of furniture. The performance of different sets of furniture was assessed based on residence time parameters like plug volume fraction, mixed volume fraction, dead volume fraction, etc. Other performance indicators used in the analysis were temperature distribution, observing cold spot, surface velocity and nature of flow in the tundish. Insight from the base case reveals the desired flow characteristics that help to achieve the target performance. Inferred results suggested the use of a turbulence inhibitor in combination with a dam as the optimal set of furniture. Use of a non-isothermal model is important, as it was found that even a small change in temperature (2·3°C) plays a vital role in the fluid flow inside the tundish.     

Simplified thermochemical functions for tabulation

A set of thermodynamic functions for the tabulation of thermochemical data is proposed which seems to offer a satisfactory basis for the calculation of chemical equilibria and heat balances in metallurgy. The selection and evaluation of these functions are based on simple definitions which follow directly from the basic relationships in chemical thermodynamics. Apart from the temperature,T, and the heat capacity,Cp, the following functions are used: the enthalpy,H, the entropy,S, the Gibbs energy, G, and the betafunction, β, butH, G andβ not in the form most commonly employed, for instance in the JANAF tables. No use is made of the so-called free energy function, nor the parameters for the formation of the substance in question from the elements at a temperatureT. As is shown in an example, the form chosen by JANAF for the tabulation of,e.g., the enthalpy may in special cases not produce the optimum presentation for the evaluation of energy balances.