Numerical Simulation for Effects of Injection Mold Cooling on Warpage and Residual Stresses

Abstract

The dimensions quality of the injection‐molded parts is the result of a complex combination of material, part, and mold designs and process conditions. In this article, warpage prediction relies on the calculation of residual stresses developed during the molding process. The solidification of a molten thermoplastic between cooled parallel plates is used to model the mechanics of part warp in the injection‐molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The warp and residual stresses numerical simulation with finite element method (FEM) is time dependent. At each time step, the material properties can be temperature and pressure dependent. Mold temperature or mold‐cooling rate effects on part warp have been numerically predicted and compared with experimental results. By showing the mold‐cooling effects, it was concluded that mold cooling has a significant effect on part warpage, and mold‐cooling parameters, such as mold temperature, resin temperature, cooling channels, etc., should be set carefully.     

闭式冷却塔的计算模拟

分析了闭式冷却塔的传热传质机理,建立了其数学计算模型,求解沿塔高度方向的温度分布,采用一维和二维模型对比分析,一维模型每排管为一个单元,二维模型每排管分别划分4个、10个单元,利用Matlab编写圆管型闭式冷却塔程序,与Hasan的结果对比,管内冷却水沿塔高度的温度分布采用二维模型每排管划分4个单元和10个单元相比相差较小,二维模型比一维模型的管内冷却水温度分布更接近Hasan的结果;按二维模型每排管划分10个单元,采用Matlab编写圆管模拟程序,采用分段计算的方法预测冷却水出口水温,与实验结果相比,一致性较好。该模型可用来预测不同流速和不同室外空气状态下闭式冷却塔的出口水温和喷淋水水温。     

空气冷却结晶塔工艺设计计算

空气冷却结晶塔是以空气作为冷却介质直接与溶液混合换热,以使溶液冷却并结晶析出晶体的高效换热节能设备.以20 kt/a硝酸钾冷却塔的设计计算为例,介绍了冷却结晶塔的工作原理、主要工艺参数确定方法和有关工艺计算过程.     

循环冷却水系统中逆流湿式冷却塔的特性研究

以循环冷却水系统中的逆流式湿式冷却塔为研究对象,详细阐述了空气湿球温度、水流量和进塔水温对冷却塔热力学性能的影响。水温降低幅度越大,冷却塔冷却效能越好。结果表明:增加进口空气湿球温度或水与空气进料质量比,冷却塔冷却效能降低;水进口温度的变化对塔冷却效能影响较小;水与空气进料质量流量比高时,沿塔高显热交换潜力降低,质量流量比低时,沿塔高显热交换潜力增加。     

机械通风逆流冷却塔节能降耗设计实例

在能源比较紧缺的今天，循环水站冷却塔的节能降耗设计显得十分重要。结合化工厂循环水站冷却塔的设计，介绍了通过对机械通风逆流冷却塔的热力和通风阻力的计算，求得冷却塔的最佳工艺参数，在满足正常生产要求的情况下，达到节能节电、取得较好的经济效益的目的。     

浅谈冷却塔塔体结构的分类与特点

在水资源和环境问题日益突出的今天,在工农业生产和人民生活中广泛应用的冷却设备——冷却塔对于节省水资源和保护环境发挥了重要的作用.从冷却塔塔体结构材料的角度对不同塔体结构的特点进行了阐述和分析,并对其进行了比较,以供在冷却塔选型、设计时参考.     

挤出吹塑制品冷却和固化阶段的模拟及优化方法

在挤出吹塑过程中,冷却和固化是一个非常重要的阶段,它对挤出吹塑制品的性能及生产效率均有很大影响。本文从挤出吹塑制品冷却和固化阶段聚合物的相变、吹塑制品的微观结构与宏观性能之间的关系、模具与制品间传热系数对吹塑制品冷却和固化的影响以及吹塑制品冷却和固化阶段的温度场及结晶度的模拟四方面综述了这一复杂过程的研究进展。     

冷却水系统中军团病的防治

综述了军团病的历史和它的爆发与冷却水化学处理的关系。讨论了冷却塔的设计、安置和维护,冷却水处理,系统的记录与报告,员工的培训等因素所起的作用,推荐了冷却水系统军团病防治的应对措施。     

A proposed technique to improve the filling of the mold cavity by polymer during injection molding

In this study, a technique is proposed to improve the filling process of the injection molding and minimize the solidification during the filling to achieve a complete filling of the mold cavity. Two methods are proposed: stopping the flow rate of the cooling fluid or passing cooling fluid inside the cooling channels at higher temperature during a period of the injection molding cycle. The configuration studied consists of the mold with cuboids‐shape cavity having two different thicknesses. A validation of the numerical model used by an experimental work is presented. The results show that, stopping of cooling fluid on a period of injection cycle has not great effect on the improvement of injection cycle. The results indicate that passing coolant fluid at higher temperature during the ejection stage decreases the solidification of the polymer during the filling stage by about 40%. © POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

复杂冷却循环水系统的建模与优化

建立了新的复杂冷却循环水系统的费用模型。利用优化软件GAMS求解了各冷却塔的最佳进出塔水温、用户进出水温、分配系数、循环水量、风量和循环水泵及风机功率等参数。通过工程实例验证了其可行性,并将其与原模型相比较。结果表明,新模型的操作费用减少了13%左右。因此,当处理复杂循环水系统时,应选取新模型。     

循环水凉水塔性能优化

介绍了延安石油化工厂循环水凉水塔存在的问题,通过对问题的分析,采取一系列整改措施,如对凉水塔填料层进行粘泥剥离、改造填料等方法,使循环水冷后温度≤30℃,循环热水和循环冷水温差达到10℃左右,确保了全厂装置的平稳长周期运行。     

A simple method for forecast of cooling time of high‐density polyethylene during gas‐assisted injection molding

Gas‐assisted injection molding (GAIM) is an innovative plastic processing technology, which was developed from the conventional injection molding, and has currently found wide industrial applications. About 70% of the whole gas‐assisted injection molding cycle is actually occupied by the cooling stage. The quality and production efficiency of molded parts are considerably affected by the cooling stage. Hence, it is necessary to study the solidification behaviors during the cooling stage. In this work, a simple experimental method was designed to simulate the solidification behaviors of high‐density polyethylene during cooling stage of GAIM. The enthalpy transformation approach, coupled with the control‐volume/finite difference techniques, was adopted to deal with the transient heat transfer problems with phase change effects. In situ measurements of the temperature decreases in the cavity were also carried out. Reasonable agreements between the experimental values and the simulated results such as cooling time, cooling rates, and temperature curves were obtained, which proved that this simple experimental method was effective. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

气淬高温熔渣颗粒运动和换热特性的数值分析

建立了高炉渣颗粒运动与换热过程的数学模型，利用FORTRAN语言编写程序，通过四阶Runge?Kutta方法求解其动力学和传热方程，计算时充分考虑熔渣与冷却空气主要热物性参数随温度的变化，采用温度回升法计算熔渣凝固过程释放的潜热，提出在气淬空气中添加喷雾强化熔渣冷却，考察了渣粒尺寸对换热过程的影响。结果表明，飞行过程中渣粒速度受气淬空气影响先增大后减小；温度降低趋势随运动距离增加而减小，主要受对流换热系数影响，凝固过程持续时间较短；喷雾使渣粒在飞行过程中整体冷却速率明显升高，最终温度明显降低，而对熔渣的运动影响较小；相同初始工况下，熔渣粒径越小，运动越易受流场影响，渣粒整体冷却速率较高，换热效果越好。     

Impac塔填料在冷却塔中的应用

在对比国内外冷却塔填料现场应用情况的基础上，总结了Impac塔填料及喷嘴应用的优势及存在的问题，说明了Impac塔填料热力性能传质传热效果及Lantc喷头的布水情况，通过经济效益对比分析表明，该填料及喷头具有良好的应用前景；同时，该填料具有施工安装方便等特点，对解决冷却塔冬季结冰也有好处，为冷却塔改造填料喷嘴的选型提供了新途径。     

Pressure and cooling rate‐induced densification of atactic polystyrene

The exact knowledge of postprocessing polymer‐specific volume is often a factor of enormous strategic importance from an industrial point of view. The subject is complicated by the fact that the specific volume of solid polymers at a constant temperature and pressure is not only a function of the current temperature and pressure, but is also a consequence of the whole formation history from the melt. In this work, specific volumes of samples solidified in different conditions are analyzed and related to their formation history. A wide range of cooling rates (from 5 × 10^?3 to 300 K/s) and solidification pressures (from 0.1 to 80 MPa) are examined. The results show a synergic effect of the cooling rate and solidification pressure: Lower cooling rates result in a much higher pressure‐induced densification with respect to higher cooling rates. A simple phenomenological model which essentially links the densification effect to the dependence of the glass transition temperature upon the cooling rate and solidification pressure is adopted to describe the experimental data. Starting from the densification effect, the effect of the pressure and cooling rate on the glass transition temperature is evaluated. Furthermore, some conclusions about the dependence of the volume relaxation time on the temperature and pressure in the glass transition range are achieved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 184–190, 2003     

Control of Lamellae Spacing During Freeze Casting of Ceramics Using Double-Side Cooling as a Novel Processing Route

A processing route for freeze-casting of particle suspensions is presented, where the microstructure development during the solidification process can be controlled precisely. For this purpose, the single-side cooling and double-side cooling methods are compared. A procedure will be shown to control the freezing process using the double-side cooling method. Our approach was to determine the freezing conditions in order to forecast the freezing velocity and to carry out an advanced directional solidification setup for the experimental realization. Using this setup and the theoretical knowledge, the microstructure development can be controlled during the whole freezing process over a length of several centimeters.     

Analysis of Optimal Heat Transfer in a PEM Fuel Cell Cooling Plate

An analysis of three‐dimensional computational fluid dynamics (CFD) is conducted to investigate the coupled cooling process involved in fluid flow and heat transfer between the solid plate and the coolant flow for optimization of the cooling design of a fuel cell stack. A conception of IUT (Index of Uniform Temperature) across the entire area is presented to evaluate the degree of uniform temperature profile across the cooling plates. Six cooling modes, including three serpentine‐type modes and another three parallel‐type modes, are presented and analyzed for optimization of the cooling mode of fuel cells. The prediction finds that the cooling effect of serpentine‐type cooling modes could be better than that of parallel‐type cooling modes.     

Cooling water treatment by ozonization

Ozonization of water in a cooling tower was investigated. A laboratory experimental set-up was employed to study changes in water quality during ozonization. Measured data were analyzed in the context of cooling water's resistance to corrosion, scaling and biofouling. A method is proposed for determining the suitable dosage of ozone for maintaining the necessary water quality. It has been found that ozonization is very effective in maintaining the correct water quality for the required purpose and provides an attractive alternative to the conventional multiple chemical method of cooling water treatment.     

冷却塔风筒缺陷分析及处理

冷却塔风筒由于几何缺陷存在,破坏了双曲线外形,影响了钢筋混凝土的设计载荷分布,使结构强度降低。通过缺陷的检测,对冷却塔风筒的应力改变、结构配筋进行计算与分析,同时对冷却塔风筒初始几何缺陷的产生原因进行探讨,并提出相应处理措施。     

400kt／a硫磺制酸装置中循环水冷却系统加硫酸除垢的实践

某公司400kt／a硫磺制酸装置循环水冷却系统的冷却塔填料结垢,使其换热通道堵塞严重,造成干吸塔的酸温、循环水的温度较高,采取了间断性向循环水池添加硫酸,控制循环水pH值,加大循环水排污量等措施,生产实践证明除垢效果、可操作性和经济性良好。