防止型材翘曲

在型材的挤出生产中，由于型材不能获得均匀的冷却而导致其发生翘曲现象。为了消除此缺陷，加工商必须使用正确的冷却方法及冷却工艺。为此，Conair的挤出下游设备专家提出了很好的建议及相关的解决方案。     

如何避免型材翘曲

更快一些!每个公司都希望可以在相同的生产线上用相同的劳动量生产出更多的产品。塑料型材挤出企业也不例外。虽然加快挤出机来推送更多的物料，甚至买一台挤出量更大的挤出机来获得更多的产出很容易。但是，当挤出塑料型材时，挤出量则通常是由型材的冷却和型材在冷却中保持正确形状的能力来控制的。     

有限差分法求解塑料挤出制品冷却温度场

应用有限差分法和传热学的基本原理对无定形塑料矩形截面型材挤出冷却过程,建立三维非稳态数学模型,并作出了数值解答,能够求出冷却时间,并据此确定了冷却水槽的长度。     

基于材料边界的挤出温度场数值模拟

利用“材料边界”概念,应用传热学、有限元法和有限差分法基本原理,用线性三节点三角形单元数值求解了挤出冷却过程的截面瞬态温度场。将定型模与型材同时进行网格剖分,忽略定型模与型材之间的几何边界,利用物性参数不同而自然形成的物理边界,解决了定型模具与型材之间边界换热系数难以确定的问题,建立了相应的数学模型。通过将同一截面不同时刻的温度场分布与不同截面相同时刻的温度场进行等价,得到了该冷却过程的三维温度场。     

中空塑料异型材挤出定型模中的应变分析

运用Ansys有限元软件，对中空塑料异型材在干湿混合式真空外定型定型模中的冷却应变状况进行了数值模拟，得到了中空塑料异型材变形的形成原因及其影响因素。指出中空型材各边即使均匀冷却，也会由于型材内外壁冷却过程中的温差所产生的热应力，使型材发生翘曲变形；影响的因素有定型模的结构和挤出时的工艺两方面，这两方面的影响因素应相互适应，才能保证稳定地生产出高品质的塑料异型材。这为挤出定型模适应挤出工艺要求合理设计提供了理论依据。     

基于CAD／CAE／ERP塑料异型材真空定型模冷却水道优化设计

热的塑料异型材通过定型模来冷却定型,因此定型模内冷却水道的设计是保证型材成型质量的重要基础。依据目标函数,对定型模冷却水道进行了初步设计,通过分析软件数值模拟,型材周边局部冷却水道进行了特殊的异型优化设计,冷却效果明显提高,并基于ERP系统和基于并行工程的CAD/CAE智能化局域网络系统数据库,使塑料异型材真空定型模冷却水道设计更合理,更好地满足客户的要求。     

了解型材挤出中的所有变量

为了解决所有类型的加工问题，你需要对构成一个给定工艺的多个变量有一个透彻的了解。在型材挤出工艺中，由于用于每种型材的特有的模头设计都非常复杂，而且用于冷却挤出型材的定型段的复杂性，使得整个挤出工艺的基本过程变得非常复杂，其中所涉及的变量的数量增加了2倍。     

浮法玻璃退火窑内传热的数值模拟

分析了退火窑内传热的基本过程,建立了一个传热的数学模拟.该模型注意到了退火窑内玻璃带、冷却风管和冷却风温度分布的不均匀性,并用数值方法进行了计算.借助所建立的数学模型和模拟方法模拟了冷却风进口温度对玻璃带出口温度和退火温度曲线的影响,研究了冷却风进口温度与冷却风风量之间的关系,探讨了冷却风管高度、玻璃带至冷却风管底表面距离和玻璃带运动速度等对所要求的冷却风进口温度的影响.     

PVC型材发黄的原因

测试了用于生产型材A（合格品）和型材B（颜色发黄）的PVC树脂的原始白度、老化白度、热稳定时间、分子质量及其分布和型材A、型材B的凝胶化度,结果表明：①与型材A相比,用于生产型材B的PVC树脂的原始白度、老化白度、热稳定时间、分子质量及其分布都合格;②型材B外壁的凝胶化度比型材A外壁高约10％,表明挤出型材B时口模处的温度偏高,从而造成型材B表面颜色发黄。另外,还进行了模拟试验,验证了分析结果。     

塑料异型材挤出用冷却定型水箱

本实用新型为一种塑料异型材挤出用冷却定型水箱，其主体是用螺钉或铰链拼接而成，从型材进口至型材出口依次间隔的设置有若干定型模板和若干汇水板，定型模板和汇水板互相平行、前密后疏布置，每块汇水板位于相邻2块定型模板的正中位置，汇水板的中部设有比型材截面外形周边大的内孔，内孔类似于型材截面形状并稍加简化，在定型模板的四周设有过水槽。     

注塑结晶性塑料平板冷却时间的讨论

对注塑结晶性塑料平板的冷却问题进行了分析。注塑结晶性塑料平板的冷却模型实质是伴有相变的不稳定一维导热。通过Neumann方法求得了这一模型冷却时间的数值解，并与其他方法进行了比较。     

Models and calculations of the effectiveness of gas and liquid cooling in foam and film apparatuses

An approach to determining the temperature profiles and effectiveness of gas and liquid cooling in the developed turbulent bubbling layer on trays in column apparatuses and film blocks of cooling towers has been considered. The approach is based on models of the flow structure for two-phase media. Diffusion and cell models with bulk heat and mass sources are used. The solutions of the system of equations of these models for various special cases of heat exchange in gas–liquid media on trays and in the packings of cooling towers have been given. The results of calculations and a comparison with experimental data have been demonstrated.     

TURBULENT VARIABLE PROPERTY GAS FLOWS

The surface renewal model of wall turbulence is coupled with the classical eddy diffusivity/mixing length approach for the turbulent core to analyze turbulent variable property gas flows with moderate heating and cooling. The analysis indicates that the mean frequency of wall turbulence is decreased by heating and increased by cooling, with the heating effect being significantly greater than the cooling effect. The analysis also gives rise to mean velocity and temperature distributions, friction factors and Stanton numbers that are consistent with most of the experimental data for both heating and cooling.     

大方钢坯连铸二冷区传热与凝固过程数值模拟

采用改进的波动冷却法(FCA-I)对大方坯连铸二冷区传热与凝固过程进行数值模拟,并与单调冷却法、波动冷却法(FCA)的计算结果进行比较. 结果表明,3种方法计算所得铸坯矫直前温度及液芯长度均与实测值相近,但FCA-I法计算结果更准确,可实时预测拉速变化时铸坯表面温度分布与液芯长度变化. FCA-I法既保留FCA法能准确反映铸坯足辊间温度、凝固壳厚度变化的优点,同时也克服了其难以适应变拉速的缺点. FCA-I法模拟所得结晶器内和二冷区凝固壳厚度dshell与凝固时间t的关系分别满足dshell=19.62t1/2-2.52和dshell=29t1/2,模拟值与文献结果基本一致.     

Modelling of crystallization process and optimization of the cooling strategy

To obtain a uniform and large crystal in seeded batch cooling crystallization, the cooling strategy is very important. In this study, an optimal cooling strategy is obtained through simulation and compared to linear and natural cooling strategies. A model for a crystallization process in a batch reactor is constructed by using population balance equation and material balance for solution concentration, and a prediction model for meta-stable limit is formulated by the dynamic meta-stable limit approach. Based on this model, an optimal cooling strategy is obtained using genetic algorithm with the objective function of minimizing the unwanted nucleation and maximizing the crystal growth rate. From the simulation results, the product from the optimal cooling strategy showed uniform and large crystal size distribution while products from the other two strategies contained significant amount of fine particles.     

Long-term failure of transversely loaded glass/iPP

Herein, temperature-dependent long-term behavior of polypropylene and its transversely loaded unidirectional glass fiber reinforced composite is investigated and a lifetime prediction method is proposed, which is based on the observed long-term failure mechanisms. Furthermore, the effect of cooling rate during processing on the time-dependent behavior is addressed. The composite is revealed to exhibit multiple molecular deformation mechanisms, similar to neat polypropylene, which is modeled using the Ree–Eyring approach. Failure kinetics under constant-strain-rate and creep tests are found to be identical and switching from creep to cyclic loading decelerates the failure, which are signs of plasticity-controlled failure. Hence, lifetime is predicted well by using a lifetime prediction methodology for the plasticity-controlled failure which combines the Ree–Eyring approach and the concept of critical strain. A change in the cooling rate alters the deformation and failure kinetics: lower cooling rates promote embrittlement.     

循环冷却水系统处理用的专家系统方法(续)

本文首先介绍了敞开式循环冷却水处理中四个方面:腐蚀结污、沉积结垢、悬浮颗粒结污和微生物结污的概况、特点、产生原因、控制方法和监测项目.在此基础上介绍了计算机应用于水处理咨询用的专家系统方法及其运行概况.本文以两个实例分别介绍了专家系统知识库中的故障树,并以此分别说明其专家系统:(1)如何对一个读数有问题的电导率控制器进行故障分析;(2)如何证实冷却水中的聚磷酸盐系缓蚀剂是否发生了降解的分析过程.     

The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

In a previous work a master‐curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro‐hardness, crystallinity) by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. For this purpose three semi‐crystalline polymers were studied [iPP, polyamide‐6 (PA6) and poly(ethyleneterephthalate) (PET)], which exhibited remarkably different behaviour when crystallized under pressure and high cooling rates Copyright © 2003 Society of Chemical Industry     

Improving the energy efficiency of cooling towers on the basis of information technology

The basic principles for the reconstruction of sectional cooling towers are considered on the basis of current information technology. In reconstruction, a group of cooling microtowers is installed on a special reference grid. The air parameters that must be monitored so as to permit automatic control of the reconstructed tower are noted. This approach improves the energy efficiency of the evaporative cooling of circulating water at industrial enterprises and reduces pollution emissions to the surroundings with the discharged steam.     

基于ATR-UV实时浓度检测的扑热息痛冷却结晶过程研究

以无水乙醇-扑热息痛为模型物体系,对基于衰减全反射紫外光谱(ATR-UV)分析的结晶过程实时浓度检测进行了研究。采用偏最小二乘法进行结晶过程浓度关联,建立了ATR-UV实时浓度检测模型,该模型实时分析结果与重量法测量结果一致,均方根平均偏差为0.0075。通过ATR-UV实时浓度分析关联结晶过程的过饱和度变化,并结合聚焦光束反射测量技术分析了不同降温方式对结晶产品的影响。结果表明:相对于自然冷却和线性冷却温度控制方式,受控冷却过程能获得尺寸更大、分布更均一的晶体产品。