基于正交试验的PET瓶拉伸吹塑优化设计

针对部分聚对苯二甲酸乙二醇酯（PET）成型瓶靠近底端壁厚较小的缺陷，采用Polyflow仿真软件对PET瓶拉伸吹塑成型过程进行数值模拟。重点采用交互作用的正交试验方法，对瓶坯的加热温度、拉伸杆拉伸速度、预吹压力、延迟时间和高吹压力等工艺参数进行优化组合，使瓶子的最小厚度增大，瓶体更加均匀。结果表明，较优组合工艺参数分别为：延迟时间0.06 s、拉伸速度为1.6 m/s、预吹压力0.7 MPa、瓶坯温度110 ℃；优化后最小壁厚增大了28 %，瓶体壁厚均匀度提高了63 %。     

橡胶沥青搅拌罐内混合过程的数值模拟

针对橡胶粉与基质沥青混合过程中出现的漂浮、沉底、粘壁及挂料现象,建立了橡胶沥青搅拌罐的几何模型,基于计算流体力学软件对罐内混合过程进行非定常固液两相流数值模拟,分析了影响混合均匀性的因素,如桨叶直径、桨叶位置、挡板及搅拌速度等. 结果表明,尺寸适宜的桨叶直径与合适的桨叶位置有利于形成循环的轴向流,并减少定常流现象,安装挡板有效减少了切向流,搅拌器转速不影响内部流场的基本形态,但适宜的搅拌转速提高了混合均匀性. 混合均匀度与模拟结果印证,且当搅拌器直径800 mm、桨叶距离罐底680 mm、桨叶宽100 mm、搅拌速度280 r/min时,优化后橡胶粉的分布较均匀,混合均匀度为0.24,处于完全离底悬浮状态,模拟结果与实验结果较吻合.     

Analysis of the effects of internal heating and cooling during the rotational molding of plastics

In rotational molding, shortening the cycle time is one of the most important requirements for increasing production rates and reducing product cost. A characteristic feature of the process is that the mold and plastic powder are heated from room temperature to the melting temperature of the plastic and then back to room temperature. In addition, in the vast majority of cases the heat input and subsequent heat extraction occur at the outside surface. In order to improve the heat transfer, this paper considers the effects of internal heating and cooling. A mathematical model has been developed in which an internal heating term can be incorporated. The experiments with rotomolding powders show that the predictions made by the model are accurate. In particular, it is found that the introduction of internal heating is very effective in shortening the cycle time and that the introduction of internal cooling in rotational molding provides a more uniform structure and less likelihood of warpage.     

Research on a New Variotherm Injection Molding Technology and its Application on the Molding of a Large LCD Panel

The polymer injection products produced by using the current injection molding method usually have many defects, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers. These defects have to be eliminated by using post-processing processes such as spraying and coating, which will cause environment pollution and waste in time, materials, energy and labor. These problems can be solved effectively by using a new injection method, named as variotherm injection molding or rapid heat cycle molding (RHCM). In this paper, a new type of dynamic mold temperature control system using steam as heating medium and cooling water as coolant was developed for variotherm injection molding. The injection mold is heated to a temperature higher than the glass transition temperature of the resin, and keeps this temperature in the polymer melt filling stage. To evaluate the efficiency of steam heating and coolant cooling, the mold surface temperature response during the heating stage and the polymer melt temperature response during the cooling stage were investigated by numerical thermal analysis. During heating, the mold surface temperature can be raised up rapidly with an average heating speed of 5.4°C/s and finally reaches an equilibrium temperature after an effective heating time of 40 s. It takes about 34.5 s to cool down the shaped polymer melt to the ejection temperature for demolding. The effect of main parameters such as mold structure, material of mold insert on heating/cooling efficiency and surface temperature uniformity were also discussed based on simulation results. Finally, a variotherm injection production line for 46-inch LCD panel was constructed. The test production results demonstrate that the mold temperature control system developed in this study can dynamically and efficiently control mold surface temperature without increasing molding cycle time. With this new variotherm injection molding technology, the defects on LCD panel surface occurring in conventional injection molding process, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers were eliminated effectively. The surface gloss of the panel was improved and the secondary operations, such as sanding and coating, are not needed anymore.     

高密度聚乙烯滚塑皮划艇变形的解决方案

针对高密度聚乙烯滚塑皮划艇的变形问题,对皮划艇的滚塑工艺进行了研究,发现壁厚均匀度差、壁内存在大量气孔和模内温度不均匀是造成皮划艇变形的重要因素。首先通过增加预热程序以及延长摇摆停留时间来提高壁厚的均匀度;然后通过预热及提高加热室温度来调节模内温度,达到消除壁内气孔的目的;最后,通过采用自然冷却并在冷却阶段再次加热等手段,进一步平衡模内温度。经过上述工艺的调整和改进,最终解决了皮划艇的变形问题,获得了合格的皮划艇产品。     

不饱和聚酯树脂旋转模塑成型工艺试验研究

应用正交实验方法研究了引发剂、促进剂及二氧化硅（SiO2）粉末的加入量对旋转模塑成型制品壁厚和壁厚均匀程度的影响，测定了不同配比黏度变化曲线，找出了树脂体系黏度变化对成型制品质量的影响规律。试验表明，树脂体系的初始黏度对制品最终壁厚影响较大，体系的凝胶速率对制品壁厚均匀性影响较大。在本试验条件下，不饱和聚酯琊烷酸钴／过氧化甲乙酮／SiO2配比为：50g／0．4g／0．5g／0．5g时制品壁厚均匀程度最高。     

连续化双螺杆混合机混合均匀性调控研究

针对高分子复合材料粉体混合均匀性和工艺可重现性难以调控的行业共性技术瓶颈,模拟研究了粉体混合均匀性和工艺可重现性相对标准偏差(RSD)与入口粉体配方比的组分含量、粉体内聚特性和螺杆转速的协同演化规律.结果表明,RSD与组分含量、螺杆转速呈现负关联关系,而与粉体内聚能量密度呈现正关联关系,可以通过提高螺杆转速强化超细超低...     

Global efficiency of innovative rotational mold directly heated by thermal fluid

The article is focused on analysis of global efficiency of new mold for rotational molding of plastic parts, being directly heated by thermal fluid. The overall efficiency is based on several items such as reduction of cycle time, better uniformity of heating–cooling and low energy consumption. The new tool takes advantage of additive fabrication and electroforming for making the optimal manifold and cavity shell of the mold. Experimental test of a prototype mold was carried out on an experimental rotational molding machine, developed for this purpose, measuring wall temperature, and internal air temperature, with and without plastic material inside. Results were compared with conventional mold heated into an oven and to theoretical simulations done by Computational Fluid Dynamic software (CFD). The analysis represents considerable improvement of cycle time related to conventional methods (heated by oven) and better thermal uniformity to conventional procedures by direct heating of oil with external channels. In addition to thermal analysis an energetic efficiency study was done. POLYM. ENG. SCI., 52:1998–2005, 2012. © 2012 Society of Plastics Engineers     

直接电加热滚塑工艺的传热分析

通过实验测量了直接电加热的滚塑模具在加热阶段的表面温度和模内温度以及所消耗的电能。然后根据实验数据对该滚塑工艺的加热阶段进行了传热分析,计算了有效热能和无效热能,并提出了评估该滚塑工艺的3个指标参数——热能利用率、加热每单位质量粉料所消耗的电能、加热每单位质量粉料所需的时间。结果表明,该滚塑模具的表面温度具有一定的不均匀性,不同位置处的最大温差为8 ℃。3种实验情形下的最高热能利用率为37.5 %,另外在相同的模内加热温度下,热能利用率随模内粉料质量的增大而减小。     

单轴滚塑成型传热过程的数学建模

阐述了滚塑成型技术的基本原理、工艺特点。以单轴滚塑成型实验为依据,对工艺过程进行了适当简化和假设,着重对粉料在加热及熔融状态下的物理过程进行了分析,详细提出了单轴滚塑成型传热过程的数学模型,对模具加热时间、粉料熔融时间、熔融温度场时间函数、半径函数及温度场分布进行了求解。     

Simulation of non‐isothermal melt densification of polyethylene in rotational molding

Rotational molding involves powder mixing, heating and melting of powder particles to form a homogeneous polymer melt, as well as cooling and solidification. The densification of a loose powder compact into a homogeneous melt occurs over a wide range of conditions as the material passes from a solid state into a melt state. The numerical simulation of the non‐isothermal melt densification in the rotational molding process is presented in this work. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in general agreement with experimental observations presented in the literature for the rotational molding of polyethylenes. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density. Results indicate that the densification process is primarily affected by the powder characteristics, which are accounted for in terms of the particle size and the particle packing arrangement. The material rheological properties become increasingly important as the powder characteristics lessen in quality. The simulation demonstrated that while certain combinations of processing conditions help reduce the molding cycle, they have a detrimental effect on the densification process.     

滚塑成型工艺加热阶段的数值研究

为一个球形中空塑料制品的滚塑成型工艺的加热阶段建立了一种新的流动与传热理论模型,并采用Fluent软件对其进行数值计算。该理论模型将模具的导热、塑料层的导热和随后的熔融以及内部空气的自然对流换热耦合起来求解。数值计算所得的加热时间、模具外壁面温度和内部空气温度都与实验结果吻合较好,从而证明了本理论模型的有效性。最后采用该理论模型分别计算了在不同外部加热温度、外部对流换热系数以及塑料粉末层厚度下的加热时间,从而确定了这些参数对加热时间的影响,并得出了提高外部对流换热系数比提高外部加热温度能更有效地缩短加热时间等结论。     

一种简单的用于滚塑工艺加热阶段的传热模型

对从滚塑模具开始受热到其内部粉料开始熔融之间的加热阶段建立一个简化的传热理论模型,通过混合物与模具内壁面接触时的非稳态导热方程来计算这二者之间的表面传热系数,然后采用MATLAB软件求解模型中的常微分方程组。将计算所得的内部空气温度与实验结果相比较,证明了传热模型的准确性;应用该传热模型分别研究了烘箱内加热温度、外部表面传热系数以及塑料制品的厚度对加热时间和加热效率的影响,发现加热效率随时间的延长而增大,较厚的塑料制品比较薄的塑料制品具有更高的加热效率。     

间隙对电热变模温高光注塑模具加热效率的影响

采用电热方式的高光注塑模具可以有效消除传统注塑成型过程中塑件的熔接痕、浮纤、银纹等缺陷。高光注塑成型技术要求对模具温度的快速动态控制,然而在电加热高光注塑成型中,电加热棒与模具安装孔之间不可避免地存在间隙,间隙层内的空气大大阻碍热量向模具传递。研究了电加热棒与模具安装孔之间的间隙对电热变模温加热效率的影响,构建了电加热高光注塑模具的三维热响应分析模型,利用有限元分析软件ANSYS进行了三维瞬态传热分析,得到了在不同间隙下的模具表面和电加热棒内部的热响应曲线,并通过大量实验证明了理论分析和模拟方法的正确性。结果表明,加热相同时间,间隙量越小,模具表面温度越高,电加热棒内部温度越低,加热效率越高,相较于间隙在0.32 mm,间隙在0.05 mm加热到60 s的模具表面温度至少高出50%,电加热棒内部的温度至少低55%。隙量对模具加热效率的影响并非成线性关系,而是间隙量在越小的区间,加热效率对间隙更加敏感,研究结果为电热变模温高光模具结构设计和电加热棒的选用提供依据。     

PA12双腔医用导管挤出成型工艺实验研究

在实验的基础上,分析了聚酰胺(PA)12双腔医用导管挤出过程中机头温度、螺杆转速、牵引速率和注气流量对导管截面形状精度的影响。采用椭圆度和壁厚均匀度对导管截面形状进行表征,得到了较为合适的工艺参数,即机头温度范围205～210℃,螺杆转速16～18r/min,牵引速率450cm/min左右,月牙腔和圆腔的注气流量分别为10mL/min和8mL/min。     

黄姜废渣发泡陶瓷的制备及其性能研究

发泡陶瓷作为一种新型建筑墙体材料,具有轻质保温的优良特性,有利于实现建筑节能。以黄姜废渣为主要坯料,掺加适量麻城石粉优化坯料组分,并以SiC为发泡剂,通过混料、压片、烧结等工艺实现了一种新型闭孔发泡陶瓷的制备。主要研究了烧成制度、成型压力、发泡剂掺量、石粉掺量对黄姜废渣发泡陶瓷宏观性能及其微观特征的影响。试验结果表明,在烧成温度1 130 ℃、升温速率5 ℃/min、成型压力1 MPa、SiC掺量0.5%、麻城石粉掺量40%(均为质量分数)的工艺条件下,黄姜废渣发泡陶瓷制备效果最佳,综合性能最优。     

Processing enhancers for rotational molding of polyethylene

Rotational molding is a zero shear process used to manufacture hollow plastic parts. One disadvantage of this process is long cycle times, which are significantly affected by the sintering rates of thermoplastic powder. The objective of this work was to evaluate low molecular weight additives as sintering enhancers for polyethylene and to validate the results in rotational molding. The following additives were blended with linear low‐density polyethylene: mineral oil, glycerol monostearate and pentaerythritol monooleate. The additives resulted in decreased melt viscosity and/or elasticity at low shear rate. The reduction in melt elasticity was particularly significant. Sintering studies confirmed that the additives resulted in significantly faster coalescence. In uniaxial rotational molding, the decreased melt viscosity and elasticity obtained with mineral oil were observed to result in much faster densification and bubble removal. Part thickness was uniform and there was no warpage. Adding mineral oil to polyethylene reduced the cycle time in uniaxial rotational molding and the peak impact strength was identical to that obtained without any additive. Biaxial rotational molding experiments confirmed that the use of mineral oil resulted in shorter cycle time without sacrificing peak impact strength.     

注水参数对水辅助注射成型充填过程影响的数值模拟

建立水辅助注射成型二维、瞬态、非定常流动模型,采用黏度幂律模型,在k ω湍流模型下,充分考虑注射水的湍流特性以及熔体前沿的喷注效应,采用有限体积法（VOF）对充填过程中的注水速度、注水温度和注水延迟时间等注水控制参数的影响进行数值模拟。结果表明,注水速度的增加会增加水在熔体中的穿透长度,并且会减小残余壁厚;注水温度对水的穿透长度和残余壁厚的影响均不显著;随着注水延迟时间的增长,水的穿透长度和残余壁厚均有增加的趋势。     

A Diffusion Model for a Drum Dryer Subjected to Conduction, Convection, and Radiant Heat Input

Drum dryers are commonly used for production of a flaky dry powder from thick suspensions. This article presents results of a simple diffusion-based model to predict the drying performance of a pilot-scale twin-drum dryer. Numerical results are compared with experimental data obtained for a biological sludge whose initial moisture content varied from 1.0 to 2.3 kg/kg db. The agreement of model predictions with the pilot-scale experimental data is favorable. Effects of film thickness, drum rotational speed, external air flow velocity, and its humidity are examined parametrically. Sludge film thickness is identified as the most critical operating parameter to control the final moisture content and productivity of the dryer. The validated model is used to predict performance of a drum dryer subjected to heat input by convection and radiation along with conduction through the drum wall. It is shown that dryer output can be enhanced significantly by increasing the film thickness and applying radiant heating in the initial period of drying. A simple mathematical model of this type can be used for the purpose of design and analysis as well as scale-up of industrial drum dryers based on simple laboratory-scale experiments.     

Influence of processing conditions in small‐scale melt mixing and compression molding on the resistivity and morphology of polycarbonate–MWNT composites

Polycarbonate (PC) composites containing 1 wt % multiwalled carbon nanotubes (MWNT) were produced in a small‐scale DACA microcompounder under variation of mixing temperature and mixing speed at fixed mixing time according to a two‐factor and three‐level factorial design. The extruded strands were compression molded under comparable conditions, and their volume resistivity values indicated differences of about 14 orders of magnitude as well as big differences in the state of MWNT agglomerate dispersion (evaluated as macrodispersion index) are observed. The results indicate that mixing at high melt temperature and high speed can lead to the composites having low resistivity and high dispersion index at low mixing energy input. The influence of compression molding parameters was investigated on precompounded PC composites containing 1 and 2 wt % MWNT. Compression molding parameters such as temperature, time, and speed were varied according to a three‐level and three‐factor factorial design. By adjusting compression molding parameters, the volume resistivity of PC with 1 wt % MWNT composites can be varied over eight orders of magnitude, whereas for 2 wt % MWNT, the variation was within one decade. The electrical volume resistivity results indicate the highest influence of the compression molding temperature followed by time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009