Experimental and analytical study on filling of nano structures in micro injection molding

Nano technology is attracting more attention and has increasing applications in the recent years. Among the products with nano technology, many of them are made of polymer plastics. Micro injection molding is one of the critical processes for polymer plastics. In micro injection molding, the ability for the polymer melt to flow into the micro/nano structures is a crucial factor for successful molding. The flow behavior of polymer in nano structures needs to be explored further to facilitate the molding process. In this study, we investigated the effects of the processing parameters on the filling of nano structures analytically and experimentally. Firstly, mold inserts with nano channels were constructed by LIGA-Like process. Secondly, an analytical model was developed to model the filling of polymer melt in the nano channels. Molding experiments were performed to verify the analytical filling model. With this verified model, a theoretical penetration distance can be obtained, and the suitable processing parameters can be estimated for different product geometries.     

A simplified transient three-dimensional model for estimating the thermal performance of the vapor chambers

The vapor chambers (flat plate heat pipes) have been applied on the electronic cooling recently. To satisfy the quick-response requirement of the industries, a simplified transient three-dimensional linear model has been developed and tested in this study. In the proposed model, the vapor is assumed as a single interface between the evaporator and condenser wicks, and this assumption enables the vapor chamber to be analyzed by being split into small control volumes. Comparing with the previous available results, the calculated transient responses have shown good agreements with the existing results. For further validation of the proposed model, a water-cooling experiment was conducted. In addition to the vapor chamber, the heating block is also taken into account in the simulation. It is found that the inclusion of the capacitance of heating block shows a better agreement with the measurements.     

Study on the electrical and mechanical properties of phenol formaldehyde resin/graphite composite for bipolar plate

With phenol formaldehyde resin (PF) powder and graphite powder as raw materials, a kind of conductive composite for bipolar plate is obtained by hot-pressure molding. The effects of PF resin content, molding temperature and time on conductivity and bending strength of the composite were investigated in this paper; and the optimum PF resin content, molding temperature and time were obtained. The results show that: the conductivity decreases and bending strength increases with the increasing of PF resin content; the conductivity varies wave-like and bending strength increases firstly and then decreases with the increasing of molding temperature; the effects of molding time on properties of the composite are similar to that of molding temperature; and the best conductivity and bending strength of the composite are 142 s cm⁻¹ and 61.6 MPa, respectively, when its PF resin content is 15% molded at 240 °C for 60 min.     

Fabrication of multi-filler thermoset-based composite bipolar plates for PEMFCs applications: Molding defects and properties characterizations

The bipolar plate (BP) material should possess contradictory properties. They should also manufacture from low-cost methods and materials. In the current investigation, thermoset-based composite materials reinforced with conductive fillers, and the compression molding process is implemented. In addition to fabricating the bipolar plates (BPs) with and without the flowing channels, alleviating the defects during the molding process is performed. The channels are perfectly formed on the plates with the designed depth of 0.65 mm and 0.5 mm of width. In the meanwhile, we alleviate different molding defects, which spoil the surface appearance and part properties. Regarding the physical properties, the water contact angle is measured to be around 85°. The through-plane electrical conductivity of molded plates showed high values up to 38 S/cm, and the interfacial contact resistance measured to be 18–24 mΩ cm². The mean value of the flexural strength of the produced samples was equal to 47 MPa, which is almost twice the DOE target (>25 MPa).     

木屑颗粒燃料冷态压缩成型参数试验研究

对杉木屑进行不同成型直径、含水率及压缩速度条件下的冷态压缩成型试验,分析多个影响因素对木屑成型试样的松弛密度、抗压强度及比能耗的影响。通过单因素影响试验分析表明,在含水率为16%和成型直径为10 ~ 12 mm时能获得较好的成型参数,压缩速度为40 mm/min时,可获得较大的松弛密度和抗压强度,但比能耗相对较大。通过设计三因素三水平正交试验,运用多指标综合加权评分法对试验结果进行分析,权重系数综合考虑松弛密度、抗压强度和比能耗的重要与次要程度,结果表明：木屑最佳成型因素水平组合为成型直径10 mm、含水率16%、压缩速度40 mm/min,此时木屑试样松弛密度、抗压强度和比能耗分别为0.91 g/cm³、315 N和30.20 J/g,综合加权评分值最高。     

Three-dimensional numerical and experimental investigations on polymer rheology in meso-scale injection molding

Three-dimensional simulation and experimental investigation of polymer rheology in a miniature injection molding process is presented. The material used in the study is ABS plastic, Toyolac 250-X10 and tests are carried out at different temperatures of the molten thermoplastic which is injected into the mold cavity. FLUENT 6.3 software is used in the simulation to verify the viscosity model (Cross model) and the Volume of Fluid (VOF) method is applied for the melt front tracking. The model is validated by means of experiments performed by using Davenport High Shear Viscometer with injection nozzle. It has been observed that there exists an optimum combination of temperature viscosity and shear rate for the selected injection molding process. Accordingly, the temperature range 200–260 °C and shear rate 10²–10⁴ s^− 1 are found good for the process. The mold flow profiles for various temperatures and time steps are also presented. The experimental and the simulation results are in good conformity and the strength of FLUENT 6.3 in handling injection mold filling problems is proved to be excellent.     

Pumping characteristics of a thermosyphon applied for absorption refrigerators with working pair of LiBr/water

A thermosyphon with a separate heating chamber was taken into consideration as a model device for a high-temperature generator in a small capacity absorption refrigerator with LiBr/H₂O solution. Quantitative measurements of operating characteristics of the thermosyphon were made as functions of pipe diameter, pumping height and heating power. It was found that vapor production rate is mainly affected by the heating power, and the flow rate of pumped liquid is limited by the pumping height. It was also observed that, as the pipe diameter increases, dependency of liquid flow rate on the pumping height becomes stronger. For a LiBr/H₂O solution system, ratio of vapor production rate to liquid flow rate was found to be well correlated as a function of the power input. Present experimental data are expected to provide useful information for determination of design parameters of a thermosyphon.     

高频感应加热弯板成型温度场的有限元分析

在船外板等板结构的热弯曲成型工艺中 ,用高频感应加热取代传统的火焰加热方法正得到人们的广泛重视。针对高频感应加热的特点 ,提出了感应加热热源的有限元模型。用该模型分析了高频感应加热温度场 ,并通过实验结果的比较验证了本模型的有效性。最后运用确定的热源模型对高频感应蛇形移动加热的温度场进行了有限元模拟计算 ,并对温度场进行了分析讨论     

生物质固化成型的微观机理

通过对生物质固化成型微观机理的研究,建立了生物质固化成型的微观接触几何模型,确定了压辊对原料的正压力与生物质颗粒表面斜角之间的数学关系,正压力F的大小与颗粒表面斜角a_i的余弦成正比关系。通过对固化成型分子微观机理的研究,说明了固化成型燃料燃烧点低的原因。建立了生物质固化成型的能量微观机理,并从表面能角度揭示了固化成型燃料能量密度增加、燃烧值提高的机理。     

Feasibility evaluation of gas-assisted heating for mold surface temperature control during injection molding process

Dynamic mold surface temperature control has the advantage of improving molded part qualities without significant increases in cycle time. In this study, a gas-assisted heating system combined with water cooling and different mold designs to achieve dynamic mold surface temperature control was established. The feasibility of using gas-assisted heating for mold surface temperature control during the injection molding process was then evaluated from experimental results. The effect of mold design as well as heating conditions including hot gas temperature, gas flow capacity, and heating time on the heating efficiency and the distribution uniformity of mold surface temperature were also studied. Results showed that as hot gas temperature and gas flow capacity increased, as well as increasing heating times from 2 s to 4 s, mold surface temperature increased significantly. Fan shaped gas channel design exhibits better mold surface temperature distribution uniformity than tube shaped gas channel design. During gas-assisted heating/cooling, it takes 2 s to increase mold surface temperature from 60 °C to 120 °C and 34 s for mold surface to return to 60 °C. In addition, under specified heating conditions and using the best composite mold designs, the heating rate can reach up to 30 °C/s, a rate well-suited to industrial applications.     

Rapid mold temperature control in injection molding by using steam heating

The rapid heating cycle has the advantage of improving product quality in injection molding. In this study, steam heating was combined with cool water on the same mold design to achieve dynamic mold surface temperature to establish control. By applying the steam system on a TV housing mold, the advantage of using steam heating for injection molding was then evaluated and compared with water heating by experiment and simulation. The effect of steam on the quality of the part was also studied. Results showed that as steam was used, the heating time of the simple mold plate can be reduced from 18 s to 8 s with the heating rate of 9 °C/s, and the cooling time is reduced over water heating. When the target temperature is changed from 70 °C to 110 °C, the heating time of the TV housing mold plate varies from 7 s to 19 s. For the product quality, steam heating showed an improvement in both the gloss and hardness of the TV housing.     

The dimensional stability of a microcellular injection molded gear shaft

There are several benefits of using the supercritical fluid microcellular injection molding process. One of the benefits of microcellular injection molding is that the dimensional stability can be improved. In this study, the mechanical properties of the material Polyamide(PA) 66 (glass fiber (G. F.) 33% wt.) and the dimensional stability of a microcellular injection molded gear shaft were investigated. L₉ experimental tests based on Taguchi's method were performed and a Tokyo TF 40 gear experiment machine was used to measure gear profile and to determine the optimal process conditions. The gear diameter of the gear shaft molded by conventional and microcellular injection molding were compared. The results showed that dimensional stability was improved by microcellular injection molding. The microstructure of cells at the weld-line and flow end is clearly observed from the micrographs.     

Using differential mold temperatures to improve the residual wall thickness uniformity around curved sections of fluid assisted injection molded tubes

Fluid assisted injection molding technology, including gas assisted injection molding and water assisted injection molding, has been used to manufacture plastic tubes in recent years, due to the light weight of molded parts, relatively lower resin cost per part and faster cycle time. However, the non-uniform residual wall thickness distribution usually occurs around curved sections and can significantly affect the molded product quality. This aim of this report was to improve the uniformity of residual wall thickness distribution at curved sections of fluid assisted injection molded tubes by adopting differential mold temperatures. Experiments were carried out on an 80-ton injection molding machine equipped with gas and water injection units. The material used was semi-crystalline polypropylene. It was found that the water assisted molded parts exhibit a more uniform thickness distribution at curved sections than the gas assisted molded parts. The uniformity of residual wall thickness in fluid assisted injection molded parts could be improved by adopting differential mold temperatures. In addition, a numerical simulation using commercially available software was carried out to simulate the melt temperature distributions during the filling process, so as to better interpret the fluid penetration behavior in fluid assisted injection molded parts.     

A visualized study of micro-bubble emission boiling

Experiments were designed, and experimental equipment was built, to study the characteristics of micro-bubble emission boiling (MEB) in water contacting a copper heating surface 10 mm in diameter. The behavior of bubbles on the heating surface was captured by a high-speed video camera. The results of these experiments indicated that after subcooling exceeded 25 K, MEB occurred and was accompanied by the emission of numerous extremely small bubbles. During the initial stage of MEB, two different bubble behaviors were observed: a film of vapor on the heating surface expanded and shrank periodically, emitting micro-bubbles, and the film of vapor expanded unevenly before condensing or collapsing into many micro-bubbles. During fully developed MEB, the film of vapor exhibited irregular changes at its surface and partially collapsed in several milliseconds. Nearly simultaneously, a new vapor film layer formed on the heating surface. MEB never occurred during water subcooling when the heating surface was embedded 0.5 mm within a ceramic thimble.     

Shrinkage study of textile roller molded by conventional/microcellular injection-molding process

One of the advantages of microcellular conventional injection molding over conventional injection molding is that the shrinkage of the part can be reduced. This project investigated the effect of the process parameters on the shrinkage of the textile roller by conventional/microcellular injection-molding process. Polybutyleneterephthalate (PBT) materials with 30 wt.% glass and Wollastonite fiber were used. The results showed that the shrinkage by microcellular injection molding is less than that of conventional injection molding. Glass fiber filled PBT has more shrinkage than Wollastonite fiber filled PBT due to the non-uniform cell size of the glass fiber filled PBT.     

Gas-assisted mold temperature control for improving the quality of injection molded parts with fiber additives

A rapid heating cycle has the advantage of improving product quality in injection molding. In this study, gas-assisted mold temperature control (GMTC) was combined with cool water to achieve dynamic mold surface temperature control. By applying the GMTC system on the mold of a rectangular plate, the advantages of using GMTC for injection molding were evaluated and compared with the traditional injection molding process using different gas gap sizes and gas flow capacities. The effect of GMTC on the quality of the part was also studied. Results showed that when GMTC was used, the heating rate can reach 28 °C/s. For an initial mold temperature of 60 °C, and an air gap size of 8 mm, after 6 s heating, the mold surface temperature can reach 147.8 °C, 167.2 °C, and 229 °C with gas flow capacities of 100, 200, and 300 l/min, respectively. When the gas gap size is changed from 4 mm to 8 mm, the uniformity of temperature distribution shows a clear improvement. When GMTC was used for injection molding of parts with fiber additives, the part surface was clearly improved.     

Development of optical naphthalene sublimation method

The naphthalene sublimation technique is one of the most convenient mass transfer methods to determine local heat transfer coefficient by using the heat and mass transfer analogy; however, it has difficulties in molding the naphthalene and measuring the naphthalene thickness in arbitrary shapes. This study introduces a new naphthalene thickness measurement technique using an optical method to be applied to arbitrary shapes. Naphthalene coating is made on an arbitrarily-shaped glass substrate using vapor plating. Later, collimated laser light is illuminated onto it and a CCD camera detects the scattered light to measure the thickness before and after the sublimation process. The correlations between the naphthalene thickness and the signal strength of the CCD image are preliminarily found. With the correlations, four wind tunnel experiments with flat plate, wedge, plate-wedge and cylinder flow are performed. The results demonstrate the capability of accurately measuring the naphthalene thickness in a fast optical manner, which eventually enables a more universal naphthalene sublimation technique.     

油品损耗与油气回收测试系统的研制开发

为了深入研究油品蒸发损耗的机理和规律,减少油品蒸发的污染和危害,研制开发出一套油品损耗及油气回收测试系统,可以模拟油品储存和装卸过程中的蒸发损耗,并可利用活性炭吸附法和常温常压吸收法实现对蒸发油气的回收处理,为研究和开发高效的油气回收技术和工艺提供技术支持和研究平台。该系统取得的研究成果和技术已成功应用于石化企业铁路装车过程,回收效果显著,效益明显。     

感应加热电源在注塑机料筒加热上的应用研究

介绍感应加热电源在注塑机料筒加热上的应用,设计一种半桥式串联谐振电路拓扑结构的电磁感应加热电源,通过在一个内直径40mm、外直径100mm的注塑机料筒上实验,得出谐振电容和谐振电感参数的变化与电源输出功率之间的关系。设计1台样机,实验结果表明该电源工作稳定可靠,对进一步研究具有一定的参考价值。     

Temperature measurements near a heating surface at high heat fluxes in subcooled pool boiling

In previous papers (Int J Heat Mass Transfer, 2008;50:3481–3489, 2009;52: 814–821), the authors conducted measurements of liquid–vapor structures in the vicinity of a heating surface for subcooled pool boiling on an upward‐facing copper surface by using a conducting probe method. We reported that the macrolayer dryout model is the most appropriate model of the CHF and that the reason why the CHF increases with increasing subcooling is most likely that a thick macrolayer is able to form beneath large vapor masses and the lowest heat flux of the vapor mass region shifts towards the higher heat flux. To develop a mechanistic model of the CHF for subcooled boiling, therefore, it is necessary to elucidate the effects of local subcooling on boiling behaviors in the vicinity of a heating surface. This paper measured local temperatures close to a heating surface using a micro‐thermocouple at high heat fluxes for water boiling on an upward‐facing surface in the 0 to 40 K range of subcooling. A value for the effective subcooling, defined as the local subcooling during the period while vapor masses are being formed was estimated from the detected bottom peaks of the temperature fluctuations. It was established that the effective subcooling adjacent to the surface remains at considerably lower values than the bulk liquid subcooling. This suggests that, from nucleation to coalescence, the subcooling of a bulk liquid has a smaller effect on the behavior of primary bubbles than the extent of the subcooling would appear to suggest. An empirical correlation of the effective subcooling is proposed to provide a step towards quantitative modeling of the CHF for subcooled boiling. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20277