Modelling flow stress behaviour of aluminium alloys during hot rolling

Abstract

A mathematical model is proposed to predict the flow stress behaviour of aluminium alloys under hot rolling conditions. To do so, a dislocation model for evaluating flow stress during deformation is coupled with a finite element analysis to access metal behaviour under non-isothermal and variable strain rate conditions. Then, with the aid of the proposed model, a hot strip rolling process was simulated. In order to verify modelling results, flow stress behaviour of an aluminium alloy is studied employing hot compression tests in various temperatures and strain rates and the model was examined on this material. Non-isothermal hot rolling experiments were carried out and good agreement was found between predictions and experiments.     

Development of model to predict condition monitoring interval times

Abstract

Condition monitoring intervals are usually set at fixed intervals of length typically set by a mixture of British Standards, manufacturer's recommendations, and personal experience. These rather ad hoc methods have little scientific basis. A recently developed condition based maintenance model is described which utilises reliability data combined with condition monitoring measurements. This model provides the necessary basis to optimise condition monitoring intervals. Results obtained using artificial data, based on typical machines found in a hot strip mill, show how the model can be used as part of a condition based maintenance strategy.     

Prediction of shape defects during cooling of hot rolled low carbon steel strip

Abstract

Shape defects are found in hot rolled steel strip when unwrapping tightly wound coils. This problem is particularly acute in thin strips that were considered to be defect free while processing. A model developed to predict the occurrence and magnitude of such defects in hot rolled low carbon steel strip is described in the present paper. The model assumes that the strip is free of shape defects as it exits the last stand of a continuous mill, but, as a result of processing conditions, thermal and microstructural gradients are present across the width of the strip. It is considered that the variation of ferrite and austenite mixture is caused by the chemical composition of the steel and the actual temperature of the strip. On cooling to room temperature, the distribution of both temperature and microstructure will cause variation in the local contraction that the steel is subjected to, and will promote shape defects.     

Precision online model for prediction of strip temperature in hot strip rolling

Abstract

Investigated via a series of finite element (FE) process simulation is the effect of diverse process variables on some selected non-dimensional parameters characterising the thermomechanical behaviour of the roll and strip in hot strip rolling. Then, on the basis of these parameters, online models are derived for precise prediction of the temperature changes occurring in the bite zone as well as in the interstand zone in a finishing mill. The prediction accuracy of the proposed models is examined through comparison with predictions from a FE process model.     

Splashing mechanism in combined blowing

Abstract

In combined BOF blowing, lance parameters and the combination of bottom or side wall tuyeres have an influence on splashing behaviour. The aim of this study was to clarify the interaction of the lance jet cavity with the bottom blowing plume and the side wall blowing jet and to determine its effects on splashing. According to the water model tests, three basic axioms existed in the combined blowing. First, when the bottom tuyere (or side wall tuyere) was located exactly beneath the lance jet, the lowered cavity turned the direction of splashes to lower trajectories. Second, the total amount of splashing was constant and the splashing peak was generated on the wall above the bottom plume. Third, both the plume and the side wall jet formed a so called protected zone beyond it. The model experiments showed clearly that the combination of bottom tuyeres and interaction of cavities and plumes play a very important role in splash generation in real converters.     

Three-dimensional thermomechanical coupled FEM analysis of static recrystallisation during two-pass tube tension reducing process

Abstract

In this paper, a thermal dynamic numerical method was carried out to model the austenite static recrystallisation behaviour of steel 33Mn2V used in new non-quenched/tempered oil well tubes at different deformation temperatures, strain rates, deformation amounts and initial microstructures. Based on the MARC/AutoForge software, a three-dimensional thermomechanical coupled elastoplastic finite element model (FEM) was applied to simulate static recrystallisation amount of the two-pass tube tension reducing process of steel 33Mn2V for oil well. The distribution law of static recrystallisation inside the workpiece is analysed. It is indicated that the simulation results are much reliable through comparison with experimental data.     

碲镉汞高温中波红外探测器的制备研究

采用CdTe/ZnS双层钝化工艺制备了640×512@15 μm碲镉汞中波探测器。研究了退火温度对CdTe/MCT界面及CdTe钝化膜质量的影响。经测试表明:本公司制备的碲镉汞HOT中波探测器可以在125 K稳定工作,但与国外的先进技术相比仍存在差距,需要在MCT材料改进和器件加工工艺上继续深入研究,才能提高探测器的工作温度和稳定性。     

Inhibition of pure iron in sulphuric acid by N,N-dipropynoxymethylamine acetate and its synergism with chloride

Abstract

The inhibition mechanism of N,N-dipropynoxymethylamine acetate on pure iron in H₂ SO₄ solution and its synergism with chloride was studied by potentiodynamic polarisation and electrochemical impedance techniques. Results showed that the inhibition mechanism was the mixed deactivation mechanism. Molecules of the inhibitor blocked the active sites on the iron surface and had a distinct inhibition synergism with chloride on the surface of the pure iron. Inhibition efficiencies and synergism were related to the concentration and molecular structure of the inhibitor.     

外延型InSb(InAlSb)探测器工艺分析

结合相关文献对近年来InSb基MBE外延InSb(InAlSb)材料工艺及器件性能进行了梳理分析和总结,对还存在的问题进行了探讨.InSb基外延材料(尤其是InAlSb)确实具有低暗电流、噪声抑制、高工作温度和温度稳定性优势,但材料中存在的较多缺陷影响了探测器的信号电流、探测率、响应率和电阻.分子(原子)氢脱氧技术、生...     

PRESSURE FORCE CONTROL FOR FABRICATION OF PLASTIC MICROFLUIDIC CHIPS WITH HOT EMBOSSING METHOD

A pressure force control system for hot embossing of microfluidic chips is designed with a moment motor and a ball bearing lead screw. Based on the numeric PID technique, the algorithm of pulsant integral accelerated PID control is presented and the negative effects of nonlinearity from friction, clearance and saturation are eliminated. In order to improve the quick-response characteristic, independent thread technique is adopted. The method of pressure force control based on pulsant integral accelerated PID control and independent thread technique is applied with satisfactory control performance.