Dynamic modelling of die melt temperature profile in polymer extrusion: Effects of process settings,screw geometry and material

Extrusion is one of the major methods for processing polymeric materials and the thermal homogeneity of the process output is a major concern for manufacture of high quality extruded products. Therefore, accurate process thermal monitoring and control are important for product quality control. However, most industrial extruders use single point thermocouples for the temperature monitoring/control although their measurements are highly affected by the barrel metal wall temperature. Currently, no industrially established thermal profile measurement technique is available. Furthermore, it has been shown that the melt temperature changes considerably with the die radial position and hence point/bulk measurements are not sufficient for monitoring and control of the temperature across the melt flow. The majority of process thermal control methods are based on linear models which are not capable of dealing with process nonlinearities. In this work, the die melt temperature profile of a single screw extruder was monitored by a thermocouple mesh technique. The data obtained was used to develop a novel approach of modelling the extruder die melt temperature profile under dynamic conditions (i.e. for predicting the die melt temperature profile in real-time). These newly proposed models were in good agreement with the measured unseen data. They were then used to explore the effects of process settings, material and screw geometry on the die melt temperature profile. The results showed that the process thermal homogeneity was affected in a complex manner by changing the process settings, screw geometry and material.     

Principal Components in Time Series Forecast

Abstract

This article describes a time series forecast method based on the principal component analysis applied to the data matrix derived from the initial time series.     

Mixed Model-Based Hazard Estimation

This article proposes a new method for estimation of the hazard function from a set of censored failure time data, with a view to extending the general approach to more complicated models. The approach is based on a mixed model representation of penalized spline hazard estimators. One payoff is the automation of the smoothing parameter choice through restricted maximum likelihood. Another is the option to use standard mixed model software for automatic hazard estimation.     

An anisotropic enhanced thermal conductivity approach for modelling laser melt pools for Ni-base super alloys

Ni-base super alloys are extensively used in high temperature gas turbine engines and energy industries. Due to the high replacement costs of these components, there are huge economic benefits of repairing these components. Laser direct metal deposition processes (LDMD) based on laser cladding, laser fusion welding, and laser surface melting are some of the processes which are used to repair these high value components. Precise control of these processes is important to achieve the desired microstructure, stress distribution, distortions due to thermal stresses and other important output variables. Modelling of these processes is therefore an extremely important activity for achieving any degree of control/optimisation. However, modelling of these processes is not straight-forward due to melt pool flows dominated by Marangoni and buoyancy driven convection. Detailed CFD models are required for accurate prediction of melt pool geometry. But these models are computationally expensive and require greater expertise. To simplify and speed up the modelling process, many researchers have used the isotropic enhanced thermal conductivity approach to account for melt pool convection. A recent study on mild steel has highlighted that isotropic enhanced thermal conductivity approach is not able to accurately predict the melt pool geometry. Based on these findings a new approach namely anisotropic enhanced thermal conductivity approach has been developed. This paper presents an analysis on the effectiveness of the isotropic and anisotropic enhanced thermal conductivity approaches for laser melting of Inconel 718 using numerical technique. Experimental melt pool geometry has been compared with modelling results. It has been found that the isotropic enhanced thermal conductivity approach is not able to accurately predict the melt pool geometry, whereas anisotropic enhanced thermal conductivity approach gives good agreement with the experimental results.     

神光Ⅲ主机搭载平台双光路自动瞄准系统

神光Ⅲ主机靶室中用来搭载多种物理诊断设备(条纹相机、分幅相机等)的平台要求具有很高的定位精度和工作稳定性,能方便、可靠地实现对靶室内打靶目标的瞄准,为此设计了一种双光路自动调整与瞄准装置,其位置精度可以保证20μm范围内。搭载平台采用了一套双光路成像系统和一套三自由度运动部件构成瞄准系统。在瞄准系统中,应用视觉伺服控制技术,实现了搭载平台对打靶目标的高精度自动瞄准。搭载平台已经安装到神光Ⅲ主机装置上进行了自动瞄准精度检测,得到径向(z)和指向(x,y)的瞄准调整精度分别为14,11,12μm;实际搭载了分幅相机进行激光打靶考核验证,通过物理实验得到了X光焦斑图像,表明该自动瞄准调整系统满足工程使用要求。     

自复叠制冷系统工质成分分析

分析了多级自动复叠制冷系统中非共沸混合工质的运行特点。针对系统运行过程中由于相分离、积液和工质积存等原因引起的混合工质组分发生变化的问题,在气相色谱仪的辅助下,对多级自动复叠制冷系统中混合工质实际运行成分进行取样、检测以及分析。通过对运行工质不同位置点的采样分析,发现自动复叠制冷系统实际运行时各个位置的组分含量与理论分析的差别较大。     

Spectral K-Ratio Spectrophotometry

A method called “Spectral K-ratio spectrophotometry” was proposed. The method takes the K-coefficient dual-wavelength spectrophotometric method as the mathematical model in order to resolve the different nth-derivative spectral data at one wavelength to determine certain two components systems that their zeroth- (absorption) and nth-derivative spectra were all interfered seriously. Examples of the application of the proposed method were given.     

Optical microfiber passive components

Optical microfiber waveguides with diameters close to the wavelength of light possess an intriguing combination of properties, such a tight modal confinement, tailorable dispersion, and high nonlinearity, which have been utilized in many passive applications. Here, the key fabrication techniques and optical properties of microfibers are introduced, followed by a discussion of the various passive microfiber devices and sensors. Applications exploiting their strong confinement are reviewed, including harmonic generation, supercontinuum sources, gratings, tips for optical trapping and intracellular sensing and subwavelength light sources, as well as devices based on large evanescent fields such as couplers, interferometers, optical manipulators, sensors, and resonators. Furthermore, the properties and practical intricacies of manufacturing various microfiber resonators are evaluated, with a focus on their applications in sensing ranging from temperature monitoring to current, pressure, refractive index and chemicals detection.     

Novel waveguide components based on complementary electrically small resonators

In this paper, we present a new class of waveguide components based on the use of complementary electrically small resonators etched on metallic sheets. We first show a rectangular-to-circular waveguide transition that allows to effectively match waveguides with different cross-sections and to transform the linearly polarized TE₁₀-mode of a rectangular waveguide into a circularly polarized TE₁₁-mode of a circular waveguide. Then, using similar structures, we present the design and the numerical results of two power dividers and of an orthomode transducer. All these components, employing only thin metallic sheets with properly shaped slits, can be integrated in waveguide transmission systems without increasing their space occupancy. A proper set of full-wave numerical simulations proves the validity of the proposed approach.     

水驻极熔喷非织造材料的制备与性能研究

口罩的核心功能层是熔喷非织造材料,为了满足高效低阻要求,需要对其进行电晕驻极和水驻极处理,但有关驻极机理方面的研究却鲜见报道,特别是水驻极.本文对比测试了电晕驻极和水驻极熔喷非织造材料的过滤效率和表面电荷分布,模拟了水驻极实验,并对水驻极机理进行了探索.结果 发现,相对于电晕驻极,水驻极能显著提高熔喷非织造材料的过滤效...