模压法制备微孔发泡聚碳酸酯片材

为制备采用微孔挤出法、微孔注射法及常规发泡方法难以制备的薄型微孔发泡聚碳酸酯(PC)片材,首次采用具有制备周期短、工艺简单、操作容易、制备价格低廉等优点的模压法,通过快速降温降压制备了薄型微孔发泡PC片材,并探讨了加工参数对泡孔结构的影响,利用显微镜对泡孔结构进行了表征.实验结果表明:随着发泡时间的增加,泡孔尺寸先增加后恒定不变,泡孔密度先增加后降低;随发泡压力的增加,泡孔尺寸快速减小后变化不大,泡孔密度先快速增加后变化较小;随着发泡温度的增加,泡孔尺寸快速增加,泡孔密度快速降低;随活化比的增加,泡孔尺寸先减小后增加,泡孔密度则先增加后降低.通过控制发泡时间、发泡压力、发泡温度、活化比等加工参数可以控制微孔发泡PC的泡孔结构.     

Fabrication of concave and convex potassium bromide lens arrays by compression molding

A new simple and cost-effective method has been developed for the fabrication of both plano-convex and plano-concave lens arrays with potentially important sag heights. The process is based on the use of potassium bromide (KBr) powder. At ambient temperature and under pressure, KBr powder is compressed on a molding die with the desired shape to form a solid lens array. The quality of the lens arrays has been assessed, and we present the first image produced by a converging KBr lens array.     

Bamboo fiber reinforced thermoplastic molding made of steamed wood flour

To improve the mechanical property of moldings made of steamed wood flour, layered wood moldings reinforced with steam-exploded bamboo fiber was prepared. Setting the bamboo fiber weight fractions at 25, 50, and 75%, and number of layers at three-, five-, and seven-layered wood moldings were prepared by compression molding. The results of tensile test showed that the tensile strength as well as Young’s modulus increased along with the increase in the bamboo fiber fractions. Where the bamboo fiber content was 75%, the tensile strength became approximately 3.8 to 5.8 times greater, and the tensile Young’s modulus became approximately 2.5 times greater when compared to moldings of 100% wood flour. This fact shows that bamboo fiber is effective to improve the mechanical property of wood moldings. In addition, the tensile strength also increased as the number of layers increased. This result suggested that interfacial shear stress was produced between the layers of bamboo fiber and wood flour.     

Processing of cardanol resin with CSP using compression molding technique

This paper exhibits the synthesis of a cardanol-based polymeric resin (CR) from cashew nut shell liquid as a composite matrix along with coconut shell (CS) as reinforcement utilizing poly-condensation technique. In the proposed method, the provincially gathered CSs are dried in an oven in order to expel dampness content. With an average diameter ranging from 25 to 75 µm, the dried CSs are then grated into small particles and in the compression molding method these particles are made into two sets for untreated and treated (5% NaOH) biocomposites with varying concentration of 0%, 10%, 20%, 30%, and 40%. The thermal properties are assessed by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) whereas the chemical formulation is reckoned by the assistance of Fourier transforms infrared spectroscopy. The microstructures of the composites are portrayed by scanning electron microscopy to scrutinize the morphological and surface characteristics of CR and CS. The TGA and DTA results revealed that the treated CS particle at 25 and 75 µm thermal stability (484° and 459°) with untreated CS particle (466°C and 449°C) at 30% particle loading condition. The 25-µm CS particles are thermally more stable than 75 µm particles. Veritably it is unveiled that, a polymeric matrix composite combined with untreated and treated CS particles might be a good alternative remembering the ultimate goal to nab an eco-friendly product.     

Numerical simulation of injection/compression liquid composite molding. Part 2: preform compression

In the injection/compression liquid composite molding process (I/C-LCM), a liquid polymer resin is injected into a partially open mold, which contains a preform of reinforcing fibers. After some or all of the resin has been injected, the mold is closed, compressing the preform and causing additional resin flow. This paper addresses compression of the preform, with particular emphasis on modeling three-dimensional mold geometries and multi-layer preforms in which the layers have different mechanical responses. First, a new constitutive relation is developed to model the mechanical response of fiber mats during compression. We introduce a new form of nonlinear elasticity for transversely isotropic materials. A special case of this form is chosen that includes the compressive stress generated by changes in mat thickness, but suppresses all other responses. This avoids the need to model slip of the preform along the mold surface. Second, a finite element method, based on the principle of virtual displacement, is developed to solve for the deformation of the preform at any stage of mold closing. The formulation includes both geometric and material nonlinearities, and uses a full Newton–Raphson iteration in the solution. An open gap above the preform can be incorporated by treating the gap as a distinct material layer with a very small stiffness. Examples show that this approach successfully predicts compression in dry preforms for three-dimensional I/C-LCM molds.     

An experimental investigation of class A surface finish of composites made by the resin transfer molding process

Achievement of high class surface finish is important to the high volume automotive industry when using the resin transfer molding (RTM) process for exterior body panels. Chemical cure shrinkage of the polyester resins has a direct impact on the surface finish of RTM molded components. Therefore, resins with low profile additives (LPA) are used to reduce cure shrinkage and improve surface quality of the composite parts. However, little is known about the behaviour of low profile resins during RTM manufacturing and their ultimate effects on the surface quality of molded plaques. In this work, the effects of controlled material and processing parameters on the pressure variations, process cycle times and ultimately on the surface quality of RTM molded components were investigated. Taguchi experimental design techniques were employed to design test matrices and an optimization analysis was performed. Test panels were manufactured using a flat plate steel mold mounted on a press. Pressure sensors were inserted in the mold cavity to monitor pressure variations during different stages of cure and at various locations in the mold cavity. It was found that a critical amount of LPA (10%) was required to push the material against the mold cavity and to compensate for the resin cure shrinkage. A significant increase in pressure was observed during the later stages of resin cure due to the LPA expansion. The pressure increase had a significant effect on the surface roughness of the test samples with higher pressures resulting in better surface finish. A cure gradient was observed for low pressure injections which significantly reduced the maximum pressure levels.     

Refractive index variation in compression molding of precision glass optical components

Compression molding of glass optical components is a high volume near net-shape precision fabrication method. In a compression molding process, a variation of the refractive index occurs along the radial direction of the glass component due to thermal treatment. The variation of refractive index is an important parameter that can affect the performance of optical lenses, especially lenses used for high precision optical systems. Refractive index variations in molded glass lenses under different cooling conditions were investigated using both an experimental approach and a numerical simulation. Specifically, refractive index variations inside molded glass lenses were evaluated by measuring optical wavefront variations with a Shack-Hartmann sensor system. The measured refractive index variations of the molded glass lenses were compared with the numerical simulation as a validation of the modeling approach.     

Precision compression molding of glass microlenses and microlens arrays--an experimental study

An innovative manufacturing process utilizing high-temperature compression molding to fabricate aspherical microlenses by using optical glasses, such as BK7, K-PG325, and soda-lime glass, is investigated. In a departure from conventional approaches, a unique hollow contactless mold design is adopted. Polished glass substrates and the mold assembly are heated above the glass transition temperature first, followed by initial forming, then annealing. The forming rate is controlled in real time to ensure mold position accuracy. Mold materials used include tungsten carbides, 316 stainless steel, 715 copper nickel, and aluminum alloys. The geometric control of the microlenses or microlens arrays can be precisely controlled by the forming temperature, forming speed, mold design, and annealing time.     

杭氧大型化工型内压缩流程空分技术现状

介绍了杭氧设计制造的、典型的大型化工型内压缩流程空分设备,并从应用场合、设计参数和流程形式等方面进行了论述。最后总结了杭氧对于不同类型的化工型内压缩流程空分设备在流程组织和系统配置等方面的经验。     

Investigations into the mechanical strength anisotropy of Sorbitol Instant compacts made by uniaxial compression

Powder compacts manufactured by the pharmaceutical industry are usually produced by uniaxial compression of powders or granules. This process results in compacts that are anisotropic in their mechanical strength, but this hypothesis has received little attention in the past. In this work, compacts were produced from sorbitol granules using two distinctively different particle size fractions, two compaction speeds and a range of different tablet porosities. The compact tensile strength was assessed by diametral and biaxial compression and by flexural bending. Fracture mechanics, i. e. the critical stress intensity factors in mode I and II loading, and the construction of the fracture envelope were used to investigate failure mechanisms and strength anisotropy. The strength results were also analyzed statistically employing Weibull analysis and analysis of variance. Granule size and compaction speed were identified as major influence factors on tensile strength. The magnitude of the effects found, however, varied between the individual test configurations. Further processing of the Weibull moduli obtained from the different tests confirmed the anisotropy of powder compacts made by uniaxial compression. They also showed that the commonly used diametral compression test to obtain tensile strength values is the least sensitive measure to assess the influence of particle properties on mechanical strength. Biaxial testing was found to be able to detect small changes in crack and flaw structure as a result of small changes in the particle characteristics of sorbitol.     

Strength of structural elements made of glass-reinforced carbon in compression

Experimental data for the structural strength in axial compression and bending of monolithic composite specimens of glass-reinforced carbon grade SU-2000 and also the supporting capacity of multilayer structural elements having the shape of a bar or hollow truncated cone loaded by an axial force and external hydrostatic pressure are analyzed.Translated from Problemy Prochnosti, No. 5, pp. 73–79, May, 1990.The authors thank G. S. Pisarenko and Yu. M. Rodichev for helping to carry out the present work.     

Development of a compression molding process for three-dimensional tailored free-form glass optics

Because of the limitation of manufacturing capability, free-form glass optics cannot be produced in a large volume using traditional processes such as grinding, lapping, and polishing. Very recently compression molding of glass optics became a viable manufacturing process for the high-volume production of precision glass optical components. An ultraprecision diamond-turning machine retrofitted with a fast tool servo was used to fabricate a free-form optical mold on a nickel-plated surface. A nonuniform rational B-spline trajectory generator was developed to calculate the computer numerical control machine tool path. A specially formulated glass with low transition temperature (Tg) was used, since the nickel alloy mold cannot withstand the high temperatures required for regular optical glasses. We describe the details of this process, from optical surface geometry, mold making, molding experiment, to lens measurement.     

模压成型的杨木纤维/高密度聚乙烯复合材料蠕变性能和蠕变模型

采用长为850~2 000 μm的杨木纤维(PWF)增强高密度聚乙烯(HDPE), 利用模压成型法制备了PWF/HDPE复合材料, 对其进行了弯曲力学性能测试、无缺口简支梁冲击强度测试、24 h弯曲蠕变-24 h回复性能测试、1 000 h蠕变性能测试及蠕变后残余弯曲力学性能测试, 并利用两参数指数模型、Findley指数模型及四元件Burgers模型拟合蠕变曲线。结果表明: PWF/HDPE复合材料的弯曲强度为21.14 MPa, 弹性模量为2.31 GPa, 无缺口冲击强度为6.77 kJ/m2;24 h形变为0.803 mm, 24 h回复率为78.46%, 蠕变后弯曲强度下降了6.45%, 而弹性模量增加了8.95%;1 000 h形变为0.809 mm, 蠕变后弯曲强度保留了72.35%, 弹性模量增加了10.67%;3种模型中, 四元件Burgers模型拟合PWF/HDPE复合材料蠕变性能的效果较好。      

Relaxation of residual stresses in plastic cover lenses with applications in the injection molding process

The quality of molded parts made of clear thermoplastic polymers is determined by the absence or presence of residual stresses. In this work we analyzed the flow-induced residual stresses, which cause serious damage to plastic parts used in automotive and optical applications. Plastic cover lenses (PCLs) are important components of LED and bulb headlights that are produced by the injection molding process (IMP). However due to multiple characteristics of PCLs as, complex geometry, size and wall thickness residual stresses are difficult to keep under control during the IMP, causing cracking under chemical attack, ultraviolet radiation, abrasion and other environmental conditions. These residual stresses in PCLs were characterized by a chemical attack and photoelasticity method in the present work, and the methods were compared and validated. A stress-relieving technique was then successfully applied, implementing a thermal treatment for prototypes, and after its validation in the laboratory it was applied in a series production. These experiments were based on a design of experiments (DOE) for the annealing process considering the glass transition temperature (Tg) of the polycarbonate and allowing the relaxation of the internal microstructure of PCLs without causing degradation, helping us to increase the production efficiency and improve the component performance in the plant.     

Grain-size dependence of anhysteresis in iron oxide micropowders

The low-field anhysteresis of small equidimensional multidomain particles of Fe3O4is found to be surprisingly large. For particle sizes below about 0.075 μm the anhysteretic susceptibility equals or surpasses that of elongated or doped equidimensional single-domain γFe2O3particles used in conventional recording tapes.     

Polymeric micropowders from thermal reversible crosslinking of oligomers

Polymeric microparticles provide great potentials for applications originated from their high surface area and functionalities and thus have attained many attentions in various fields. Here, we attempt to fabricate polymeric micropowders based on the reversible thermal crosslinking (Diels-Alder reaction). Initially, poly(FEEMA) obtained from the radical polymerization of furan functionalized monomer and partially crosslinked poly(FEEMA) respectively. The physical properties of base-polymer for fabrication of microparticles have changed in order to control thermal responsible property of final micro particles. Based on Diels-Alder reaction, microparticles in the size range of 200 nm–2 μm were successfully prepared using polymer precursors and cross-linker in oil-in-water emulsion. Controlling the molecular weight as well as crosslinked density of polymer precursors makes it possible to adjust the thermal properties (glass transition temperature and retro-Diels-Alder temperature) of the microparticles. These series of method can provide thermal triggered, selective meltdown microparticles for several application fields such as selective gluing, patching, filling or healing by applying external heat.     

Numerical simulation of injection/compression liquid composite molding. Part 1. Mesh generation

This paper presents a numerical simulation of injection/compression liquid composite molding, where the fiber preform is compressed to a desired degree after an initial charge of resin has been injected into the mold. Due to the possibility of an initial gap at the top of the preform and out-of-plane heterogeneity in the multi-layered fiber preform, a full three-dimensional (3D) flow simulation is essential. We propose an algorithm to generate a suitable 3D finite element mesh, starting from a two-dimensional shell mesh representing the geometry of the mold cavity. Since different layers of the preform have different compressibilities, and since properties such as permeability are a strong function of the degree of compression, a simultaneous prediction of preform compression along with the resin flow is necessary for accurate mold-filling simulation. The algorithm creates a coarser mechanical mesh to simulate compression of the preform, and a finer flow mesh to simulate the motion of the resin in the preform and gap. Lines connected to the top and bottom plates of the mold, called spines, are used as conduits for the nodes. A method to generate a surface parallel to a given surface, thereby maintaining the thickness of the intermediate space, is used to construct the layers of the preform in the mechanical mesh. The mechanical mesh is further subdivided along the spines to create the flow mesh. Examples of the three-dimensional meshes generated by the algorithm are presented.