Strip tracking measurement and control in hot strip rolling

It is well known that poor strip tracking can lead to reducedproduct quality but also to mill delays. The resultingcosts for internal rejects, customer complaints and yieldlosses have historically been significant. Moreover, the severityof these issues increases dramatically when stripsbecome wider, thinner and harder. Ultimately the rollingprocess becomes completely unstable. Hence, to reducecost of poor quality for the current product mix as well asto enable product development it is vital that strip trackingis improved.Most strip tracking issues arise at the head or the tail ofthe strip. In the rougher mill the main issue is head camber,a shape defect of the bar where the head is curved. Aclear example of this shape is shown in Fig 1. Large headcamber of the transfer bar may result in further problemsdownstream in the finishing mill and should ideally thus beprevented.Another notorious problem closely related to strip trackingis tail pinching in the finishing mill. This is a phenomenonwhere the tail of the strip suddenly moves sideward’s andgets damaged right after it has left the previous stand. AnPoor strip tracking is one of the notorious problems threatening process stability in a hot strip mill. Theseissues often lead to tail pinching and in the worst cases even to cobbles. The main pillars of the strategy setout to tackle these issues for the Hot Strip Mills in IJmuiden are rougher mill camber control and finishing millstrip steering and tail control. For such applications, a camera based measurement system has been developedin-house that is simple, cost-effective and yet both accurate and robust. Moreover, as we show in this paper,the system has proven its merits both as a finishing mill interstand centerline deviation measurement aswell as a rougher mill camber measurement. In the latter application the measurement data can be used forautomatic levelling in the rougher mill. The results of production tests presented in this paper demonstrate thatthe camber measurement in combination with a basic rougher mill tilt set-up model is sufficient to reduce thetransfer bar camber significantly

Stability analysis of a general class of singularly perturbed linear hybrid systems

Motivated by a real problem in steel production, we introduce and analyze a general class of singularly perturbed linear hybrid systems with both switches and impulses, in which the slow or fast nature of the variables can be mode-dependent. This means that, at switching instants, some of the slow variables can become fast and vice-versa. Firstly, we show that using a mode-dependent variable reordering we can rewrite this class of systems in a form in which the variables preserve their nature over time. Secondly, we establish, through singular perturbation techniques, an upper bound on the minimum dwell-time ensuring the overall system's stability. Remarkably, this bound is the sum of two terms. The first term corresponds to an upper bound on the minimum dwell-time ensuring the stability of the reduced order linear hybrid system describing the slow dynamics. The order of magnitude of the second term is determined by that of the parameter defining the ratio between the two time-scales of the singularly perturbed system. We show that the proposed framework can also take into account the change of dimension of the state vector at switching instants. Numerical illustrations complete our study

Strip tracking in hot strip mills

In the finishing mill, steel strip is rolled from thick slabs through pairs of rollers housed in a continuous train of seven roll stands. As the strip is rolled, unwanted lateral movement, known as strip tracking, can cause the strip to collide with the edge of the mill. Strip tracking control is currently a manual operation, relying on the skill of the operators. When tracking is observed, the stand tilt is adjusted asymmetrically, causing a camber in the strip, steering it towards the centreline. Tracking control can be automated if a reliable measurement of position is available. A vision-based system was developed to measure strip position. Cooling water, steam, high temperatures and electrical noise create a hazardous environment for electronic equipment and hamper image analysis. Hardware was specified to protect all equipment against the environment. A novel image analysis method combining predictive elements, filtering and Bezier curve fitting was created to allow measurements to be made with large amounts of cooling water obscuring the strip edges. The measurement system was designed to integrate with the existing mill systems, using the OPC protocol for communication. The system was created as a development system with only two cameras included, but allowed for additional cameras to be easily added and automatically detected. The results of the system showed that the image analysis techniques were effective, providing an estimated final resolution of 3.5mm/pixel, with measurements ±2mm within 60% confidence. Hardware performance provided good protection of the equipment against the environment but poor quality installation limited overall system performance. A computer model was developed to simulate tracking behaviour in the mill with non-linear variations of strip properties across the strip. The model was not completed to a satisfactory standard capable of producing useful results but the theories described could be developed further.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

On-line diagnostic tool for hot strip mill

TCC(graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Engenharia de Controle e Automação.A indústria siderúrgica está em constante evolução. O processo de laminação a quente, introduzido no início do século XX, revolucionou a indústria do aço, tornando o custo de produção de laminas de aço significativamente menores. O processo consiste em transformar grandes barras de aço em chapas extremamente finas através de uma série de rolos. Com o advento dos sistemas de controle, a automatização do processo de laminação a quente deixou o processo ainda mais eficiente e rápido. Novas tecnologias trazem novos desafios, nos processos de laminação a quente atuais, os rolos compressores chegam a uma velocidade de 120 metros por minuto. Nessas condições, qualquer defeito ou falha no sistema deve ser detectado o mais rápido possível, para evitar danos ou produtos defeituosos. O presente trabalho apresenta diferentes métodos para implementar um sistema de detecção de falhas. Primeiramente é desenvolvido um sistema para detecção de falha nos "loopers". Esse sistema consiste em analisar os sinais adquiridos nas fábricas com diferentes métodos de processamento de sinal, notadamente estatística descritiva, STFT e EMD, e usando técnicas de aprendizado de máquina, classificar as informações extraídas dos sinais em dois grupos: nominal (quando o sistema está em seu funcionamento normal) e falho (quando há alguma falha no sistema). Esse método provou-se eficaz na detecção de falhas. Em seguida, foi proposto um método baseado em modelo para identificação de falhas no subsistema de "strip steering". No entanto, a implementação desse método pode ser terminada devido a ausência de dados experimentais, necessários para a validação do modelo matemático do sistema.The steel industry is constantly evolving. The hot strip mill process, introduced in the early twentieth century, reshaped the steel industry, making the cost of producing steel sheets significantly lower. The process consists in transform thick steel slabs into thin coils using a series of compressing rolls. With the advent of control systems, the automation of the hot rolling process has made it even more efficient and faster. Nowadays, the rolling speed can reach 120 meters per minute. In this condition, any default or failure must be detected as soon as possible to avoid damages and non-quality products. This document present different method to implement a fault detection system. First, it is developed one fault detection system on loopers. This system analyses the signals recorded by the plant’s data acquisition system with data processing methods, notably descriptive statistics, STFT and EMD. By using machine learning techniques, the features extracted from the signals are separated into two groups: the nominal (when the system has no default) and the fault (when the system has a fault). This method proved to be efficient for fault detection on loopers. Then, it was proposed a model-based method for fault detection on the strip steering subsystem. Although, the method implementation wasn’t possible due to the lack of experimental data. Those data are necessary to validate the mathematical model of the system

Strip tracking in hot strip mills

In the finishing mill, steel strip is rolled from thick slabs through pairs of rollers housed in a continuous train of seven roll stands. As the strip is rolled, unwanted lateral movement, known as strip tracking, can cause the strip to collide with the edge of the mill. Strip tracking control is currently a manual operation, relying on the skill of the operators. When tracking is observed, the stand tilt is adjusted asymmetrically, causing a camber in the strip, steering it towards the centreline. Tracking control can be automated if a reliable measurement of position is available. A vision-based system was developed to measure strip position. Cooling water, steam, high temperatures and electrical noise create a hazardous environment for electronic equipment and hamper image analysis. Hardware was specified to protect all equipment against the environment. A novel image analysis method combining predictive elements, filtering and Bezier curve fitting was created to allow measurements to be made with large amounts of cooling water obscuring the strip edges. The measurement system was designed to integrate with the existing mill systems, using the OPC protocol for communication. The system was created as a development system with only two cameras included, but allowed for additional cameras to be easily added and automatically detected. The results of the system showed that the image analysis techniques were effective, providing an estimated final resolution of 3.5mm/pixel, with measurements ±2mm within 60% confidence. Hardware performance provided good protection of the equipment against the environment but poor quality installation limited overall system performance. A computer model was developed to simulate tracking behaviour in the mill with non-linear variations of strip properties across the strip. The model was not completed to a satisfactory standard capable of producing useful results but the theories described could be developed further

Chinese sectoral industrial policy shaping international trade and investment patterns - Evidence from the iron and steel industry

In the three decades since China's economic opening to the world, the country's integration into the global economy has progressed by leaps and bounds. Especially after joining the WTO in 2001, international trade and investment flows have been on a steep upward trajectory. This process was not only driven by market forces but heavily influenced by government intervention in commodity and financial markets. While government authorities are strongly determined to promote closer economic integration with the rest of the world, they seek to supervise and control the process in order to carve out maximum benefits for domestic enterprises and the economy as a whole. Balancing market forces and industrial policy strategy, political decision makers have worked out an elaborate framework of measures to create an environment conducive to the development of several sectors deemed backbone or pillar industries. As one of them, the steel industry is subjected to numerous measures steering its development both in the home market and at the global market interface. By examining these mechanisms, this article aims to illustrate that sectoral industrial policy in China does not push for expanding exports and investments across the board but carefully and discretionarily promotes global integration in some areas while delaying it in others. --Economic integration,industrial policy,trade policy,trade restrictions,foreign direct investment,steel industry

Exports and Invoicing: Evidence from the 2015 Swiss Franc Appreciation

The Swiss National Bank's (SNB) elimination of the lower bound on the EUR/CHF exchange rate on January 15 2015 provides a unique setting to study how prices and quantities respond to changes in nominal exchange rates. In this paper, we complement the study of imports in Auer et al. (2020) by looking at how the response of Swiss export prices and export values varies across products according to the currency of invoicing at the border. The rate of pass through (measured in CHF) into export prices was much lower in industries with a higher share of CHF-invoiced export border prices. We show that industries with higher CHF-invoicing shares experienced substantially weaker export growth in the two-year period after January 2015. At short horizons, however, export quantities did not respond across industries as much as prices to the exchange rate shock

Implementing an on-line bond quality inspection system for cold roll bonded Al/Al-Sn/Al/steel strips using guided wave EMATs

A prototype on-line bond inspection system for Al/Al-Sn/Al/steel strips is introduced to detect bond defects that occur in the cold roll bonding (CRB) process of strips. The transmitting and receiving ElectroMagnetic Acoustic Transducer (EMAT) probes inspect 100% material volume whilst the strip is processed continuously. The inspection signals are processed in real-time and are stored for post-processing. Serial production strips with good bond as well as with defects along the bond line were inspected for rigorous testing of the prototype machine. The inspection results were statistically analysed to determine an alarm threshold for serial inspection. The most important results are that the guided waves are sensitive enough for practical non-destructive testing (NDT) to detect all bond defects with only 0.5% false alarm rate, which nowadays can only be detected with a destructive peel-off test. The detection of all kinds of bond defects would lead to unreasonable levels of scrap due to false alarms. The application of this prototype EMAT inspection system to an industrial strip processing line shows that on-line detection of significant defects in CRBed Al/AlSn/Al/steel strips in a harsh serial production environment is possible. Design improvements are proposed to address the issues that occurred during inspection trials to design a more robust mechanical machine for the industrialisation of an EMAT inspection system

Commonwealth Times 2003-10-23

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