| Due to higher cooling intensity and better cooling uniformity, medium roller quenching machine has become the first choice of plate quenching all over the world. In order to control quenching machine automatically and precisely, automatic control system must be applied. Therefore, based on plate quenching machine developed by the state key laboratory of rolling and automation(RAL), considering the characteristic of quenching machine multi-cooling function, mathematical model of water cooling process, spray cooling process and forced air cooling process have been established. At the same time, hardening thickness forecast model and quenching machine process control system have also been established. According to these, domestic roller quenching machine developed by RAL could accomplish automatic and precise control. The main work and the results are as follows:(1) Roller quenching machine with slot, double spraying and other forms of water spray requires comprehensive segment water cooling model and cooling strategies to achieve temperature and microstructure precise control during quenching process. Based on jet impinging heat transfer theory, through analyzing steel plate surface Nusselt number(Nu) distribution regularity in different nozzle forms, researching on the relationship among steel temperature drop, cooling intensity and cooling time, and then importing interactive influence function, water cooling comprehensive heat transfer coefficient model is established finally. Therefore, multi cooling section assembly and quenching machine jet impinging cooling model are built up. Different from the traditional model, water cooling model has improved calculated accuracy through external causes(parameter measurement accuracy) and internal causes(thermal parameters rational choice).(2) With better cooling uniformity, spray cooling could relieve thin steel plate cooling deformation effectively. Through establishing water-gas impinging jet model and heat transfer model, spray cooling is introduced to the field of plate off-line heat treatment for the first time. In this thesis, the method which through gas-water two phase coupling calculation to establish injection angle and injection parameters model is proposed, and then according to analyze plate surface heat transfer regularity, steady film boiling is considered as the main spray cooling heat transfer pattern. On this basis, after comparing spray heat transfer coefficient with plate thickness, roll speed and water volume, spray heat transfer coefficient calculation model is built up according to tank film boiling theory. Finally, combining with spray cooling strategy, spray cooling model system and reasonable cooling process is established, and this provides a new approach to accomplish thin steel plate quenching.(3) Forced air cooling technology is applied to realize stainless steel and superalloy solution treatment in this thesis, after constructing forced air cooling calculated model, air cooling room automatic control is achieved. Through analyzing air cooling room structure characteristic, air-impingement heat transfer is regarded as the main heat transfer pattern, and then using process discretization analysis method, cycling medium impinging parameters calculation and steel surface heat transfer calculation is solved. Meanwhile, gas jet heat transfer coefficient distribution regularity is gained by means of comparative analyzing the relationship among distribution of steel plate surface Nu, Reynolds number (Re), gas injection and nozzle arrangement. Considering the difficulty of Nu measurement, lumped parameter method is used to calculate heat transfer coefficient, and this lay a foundation for forced air cooling stable application.(4) Due to the traditional hardening thickness forecast methods is not suitable for medium plate roller quenching machine, the concept of medium plate hardening thickness is put forward. And then, based on modify Grossmann method, medium plate hardenability forecast model is established through analyzing different steel grade ideal critical diameter influential factors, such as carbon content, austenite grain size and alloy element. In the meantime, combining with CCT curve and C curve, critical cooling rate is calculated adopting modify Maynier method, Eldis method and isothermal curve method respectively. The superior model is picked out to calculate hardening thickness with hardenability forecasting model. The construction of hardening thickness forecast model provides an effective method for forecasting steel performance after quenching machine cooling.(5) Combining with the related model which has been built up in above paragraphs, quenching machine PLC control system is modified and then process control system is constructed. To be more specific, improved water spraying control system which adopts Fuzzy-PID control method possesses several characteristics, such as rapid response, anti-interference ability, good stability; Automatic quenching function consists three aspects, that is, steady and rapid communication function, precise tracking function and data automatic store, send and receive functions; Process control system is based on mathematic model, through allocating quenching schedule, triggering functions and calculating quenching parameters, high precise temperature control, plate profile control and model self adaption are realized. The established control system has been successfully applied in Baosteel, Nansteel and other medium plate plants, quenching problems such as quenching machine complex control and low control accuracy have been basically solved.According to the application of medium plate roller quenching machine cooling model and control system, series of control system softwares are developed with independent properties. As part of research results, some conclusions gained metallurgy science and technology prize(first prize) in2010. |
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