非球面塑料透镜注射型芯工艺探讨

本文来自于作者的实践。介绍了加工方法及测量问题。重点叙述了加工中的一些关键,同时也提供了国内外在这方面的进展情况。     

用裂解气相色谱法对几株霉菌的分析

本文用带有PYR-2A管式炉裂解器和C-R2AX计算机的岛津GC-9A气相色谱仪,对3株曲霉和3株青霉进行了裂解气相色谱鉴别。通过对指纹图的分析,能够较好地区分出两属之间和各菌株之间的差异,证明了裂解气相色谱分析法用于霉菌鉴别的可能性。     

Analysis of the filling capability to the microstructures in micro-injection molding

Micro-injection molding is an important fabrication process for polymer plastics with micro-features. In micro-injection molding of products with microstructures, the ability for the polymer melt to flow into the microstructures is a crucial factor for successful molding. An analytical model in micro-injection molding is constructed in this research. It has been reported that most of the filling in microstructure is done during the packing pressure. In this analytical model, the temperature of the polymer melt near the entrance of the microstructure at the end of mold filling is estimated first. With the temperature, we can calculate the injection distance into the microstructures of the mold insert during the packing stage. The model is compared with experimental results, and shows the feasibility. The experiment uses the LIGA-like lithography process to define the micro-feature and a micro-electroforming method to form the mold insert with the replicated micro-feature. The injection distance into the microstructures predicted by this analytical model shows reasonable result as compared to the experimental measurement.     

Effect of solidification temperature of lead alloy grids on the electrochemical behavior of lead-acid battery

One of the main electrochemical characteristics of a lead-acid battery is amount of water consumption. The effect of solidification temperature on electrochemical behavior (mainly hydrogen overvoltage) of Pb–Ca–Sn–Al (0.09%, Ca; 0.9%, Sn; 0.02%, Al) and Pb–Sb–Sn (1.7%, Sb; 0.24%, Sn) alloys, which are used in making the grid of lead-acid batteries, has been studied by cyclic voltammetry (CV) and linear sweep voltammety for different concentrations of sulfuric acid (ranging from 0.5 mol L^–1 to 4.0 mol L^–1). The morphology of the grid at some solidification temperatures was studied by optical microscopy. After one sweep of CV the surface of the electrode was investigated by using scanning electron microscopy.The results show that the potential of hydrogen evolution depends on the solidification temperature of the grids during production (mold temperature of grid casting). Also, at different solidification temperatures, different passivation phenomena, electrode surface constituents, and structure were observed.     

Finite element analysis of flow and heat transfer with moving free surface using fixed grid system

A numerical study was performed on flow and heat transfer involving moving free surfaces that occurs in mold filling processes such as casting and injection molding. In these problems, the calculation domain changes continuously and the numerical treatment of the moving interface tends to cause artificial diffusion. Among the solution algorithms based on the Eulerian method, the volume-of-fluid (VOF) method was used because the method is simple and efficient in handling the complex flow patterns inside the cavity. To solve the transport equation of free surface without artificial smearing of the interface the baby-cell method was employed in the geometric reconstruction of the free surface. Furthermore, a predictor–corrector method was adopted in the time integration of volume-of-fluid (VOF) transport equation to increase the accuracy. The proposed scheme was verified through several benchmark problems. In order to show the capability of the proposed method, several three-dimensional mold filling processes were solved. The current algorithm was applied to the floating body problem. Three-dimensional floating body problems were tested.     

In-depth analysis of the mathematical model of polyester thermosets curing

In many areas of chemical engineering applications we have to deal with thermosetting polymer structures. One of the major processing techniques for producing such structures is the curing process. This process may be accompanied by undesirable thermal spiking phenomena during which the released energy may be trapped inside the structure. In order to predict the onset of this phenomenon models that couple reaction kinetics and heat transfer are required. The numerical model was constructed by taking into account the heat transferred by conduction through the resin, as well as the kinetics of heat generated by the cure reaction. The contributions to the rise in temperature from heat conduction and chemical reactions are different in different parts of the composite, which can be explained by the temperature–time, or conversion-time histories. The temperatures were measured in the center of a cylindrically shaped mold. Initiator concentration varied from 0.5% to 2.0% of mass fraction throughout the experiments, which governed the reaction kinetics. Introduction of the carbon base filler reduced the amount of heat generated in the composite, and as a result lowered the temperatures of the resin. The analysis of parameter sensitivity and model simulation was performed with data obtained. A good agreement was observed between experimental data and the mathematical model of the curing process in the mold.     

Mycotoxins from Mold Fungi — Weapons of Uninivited Fellow-Boarders of Man and Animal: Structures,Biological Activity,Biosynthesis, and Precautions

In addition to the antibiotics, mycotoxins represent a second large group of biologically active substances of microbial origin. Over 300 mycotoxins are so far known and can be subdivided into 25 structural types. They are formed by approximately 350 molds of which there are 10 000 different strains. As mycotoxin-producing molds tend to spread aggressively on foodstuffs, they can cause epidemic mycotoxicoses.—The mycotoxins have been isolated, their structures determined, and their biological activities investigated; their biosynthesis has now also largely been elucidated. Accordingly, mycotoxins are derived from only three groups of key biogenetic building blocks: polyketides, isopentenyl pyrophosphate, and amino acids. Mycotoxins are mainly non-polar, chemically stable, are formed in high concentrations, and do not contain—unlike antibiotics—any sugars. Mycotoxins display an enormous variety of toxic-pharmacological activities, e.g. liver degradation, hemorrhages, carcinomas. The identification of mycotoxicoses is impeded by their long incubation periods and the fact that the mycotoxins tend to accumulate in the mammalian organism, which means that even very low concentrations in food are a potential danger. The particularly dangerous aflatoxin B₁ 1 may not exceed a limit in food of 5 ppb (5 μg/kg), which is difficult to control.     

Production planning and warehouse management in supply networks with inter-facility mold transfers

This paper, considers with the problem of production capacity and warehouse management in a supply network in which inter-plant mold transfers are enabled. The supply network has a limited number of very expensive molds which can be transferred from a plant to another making it possible for each plant to produce the entire product gamut. It is assumed that warehouses in this supply network can be activated and deactivated as required, and that material transfers from a warehouse to another are also possible. The objective is to develop a capacity and warehouse management plan that satisfies the expected market demands with the lowest possible cost. A mixed integer programming model for the problem is suggested and its properties are discussed. A linear programming-based heuristic that combines Lagrangian relaxation and linear programming duality to generate lower and upper bounds for the problem is proposed. Finally, based on a designed experiment the performance of the heuristic on a set of generated test problems is reported and discussed.     

Simulations of fibre orientation in dilute suspensions with front moving in the filling process of a rectangular channel using level-set method

The simulation of fibre orientation in dilute suspension with front moving is carried out using the projection and level-set methods. The motion of fibres is described using the Jeffery equation, and the contribution of fibres to the flow is accounted for by the configuration-field method. The dilute suspension of short fibres in Newtonian fluids is considered. The governing Navier–Stokes equation for the fluid flow is solved using the projection method with finite difference scheme, while the fibre-related equations are directly solved with the Runge–Kutta method. In the present study for fibres in dilute suspension flow for injection molding, the effects of various flow and material parameters on the fibre orientation, the velocity distributions and the shapes of the leading flow front are found and discussed. Our findings indicate that the presence of fibre motion has little influence on the front shape in the ranges of fibre parameters studied at the fixed Reynolds number. Influence of changing fibre parameters only causes variation of front shape in the region near the wall, and the front shape in the central core area does not vary much with the fibre parameters. On the other hand, the fibre motion has strong influence on the distributions of the streamwise and transverse velocities in the fountain flow. Fibre motion produces strong normal stress near the wall which leads to the reduction of transversal velocity as compared to the Newtonian flow without fibres, which in turn, leads to the increased streamwise velocity near the wall. Thus, the fibre addition to the flow weakens the strength of the fountain flow. The Reynolds number has also displayed significant influence on the distribution of the streamwise velocity behind the flow front for a given fibre concentration. It is also found that the fibre orientation is not always along the direction of the velocity vector in the process of mold filling. In the region of the fountain flow, the fibre near the centreline is more oriented across the streamwise direction compared to that in the region far behind the flow front. This leads to the fact that the fibre near the centreline in the region of fountain flow is more extended along the transverse direction. As the fibre orientation in the suspension flow and the shape of the flow front have great bearing on the quality of the product made from injection molding, this study has much implications for engineering applications. These results can also be useful in other fields dealing with fibre suspensions.     

注射成型聚碳酸酯厚度截面的残余应力分析

通过光弹法定量测量了注射成型聚碳酸酯(PC)试样在厚度截面上的残余应力,并结合模具温度的变化与不对称分布,对厚度截面上的残余应力分布进行了详细的研究.结果表明,在厚度截面上,试样边缘分布较高的流动残余应力,芯部分布较高的热残余应力,两区域界面处为流动应力与热应力相互耦合而形成的低应力过渡区;模具温度低于120?C时,PC的残余应力随模具温度的变化并不明显;模具温度高于120?C时,PC的残余应力随模具温度的升高显著降低;不对称模具温度会导致在低模温侧高热残余应力区分布宽,在高模温侧高热残余应力区分布窄.此外,试样的翘曲随模具温度的升高而逐渐增加,不对称模具温度会导致较大的翘曲.