滚塑成型技术

随着滚塑成型工艺的发展，滚塑制品的应用范围不断扩大，目前滚塑制品的应用已经十分广泛。本文详细介绍了滚塑成型工艺的原理、优势、工艺、设备等。[编者按]     

滚塑成型的进展

滚塑成型是用粉末塑料或液体塑料来生产中空制品。本文阐述了它的成型特点，对原料的要求以及加热、冷却方法等。并详细介绍了最近几年关于滚塑成型的一些研究。     

滚塑成型技术及发展趋势

概述了滚塑成型技术的基本原理、工艺特点,介绍了滚塑成型的设备和模具,展望了滚塑成型技术的发展趋势。     

滚塑成型的现状与未来

随着滚塑成型规模的进一步扩大,将需要开发更加适用的,高性能的工程塑料,以满足该工艺的苛刻的性能要求。滚塑成型是一种非常适合于生产中空制品的独特的塑料成型工艺。无接缝塑料制品小可到玩偶的眼睛,大可至７９５００升的贮存罐。不能用其它中空成型工艺生产具有复...     

滚塑成型用聚乙烯专用树脂的性能

研究了滚塑成型用聚乙烯专用树脂DNDC7150A的基本物性、耐紫外光老化性能、耐环境应力开裂(ESCR)性能和加工性能.结果表明:DNDC7150A经过1 176 h紫外光老化实验后,拉伸断裂应变保留率仍在50%以上:ESCR超过6 000 h:具有良好的加工性能.     

滚塑成型技术及应用进展

滚塑成型是塑料加工工艺的一个分支,近几年来,全球滚塑行业的发展很快,其发展速度高于整个塑料行业的平均发展速度,越来越受到塑料加工商的青睐,应用领域不断拓展。滚塑成型是塑料加工工艺的一个分支,与其他塑料加工工艺相比,具有设备投资少、模具成本低、产品设计形式灵活多样、可一体化成型等优势。近     

Reactive rotational molding

In order to identify the major fluid mechanical effects and catalog their domains of influence, an extensive study of flow behavior of reactive polyester resin systems in uniaxial, horizontal rotating systems has been undertaken. Four general flow phenomena are identified: cascading, where resin is withdrawn from the recirculating pool arid drains back; rimming, where resin is taken around the top of the cylinder by viscous forces; stable hydrocyst formation, where rings of fluid perpendicular to the axis of rotation are formed; and solid body rotation, where the resin on the mold wall is quite uniform and time-independent. For most flow conditions, the desired region of solid body rotation apparently can be reached only by passing through each of the other flow regimes. Experimental work on polyester resin systems is compared with theoretical studies on flow stability, hydrocyst formation, and withdrawal from quiescent pools, and suitable correlations are developed. It is noted that the current correlations for stable hydrocyst formation are invalid for polyester resins and a simpler correlation is proposed.     

Motion control for uniaxial rotational molding

Motion control parameters of rotational molding can affect process efficiency and product quality. Different motion control schemes will lead to varied powder flow regimes exhibiting different levels of mixing and temperature uniformity. The change in nature of powder flow during a molding cycle suggests that varying the rotational speed could improve the powder mixing and temperature uniformity, therefore potentially reducing processing time and energy consumption. Experiments completed investigating powder flow under uniaxial rotation show that savings of up to 2.5% of the heating cycle time can be achieved. This validates the hypothesis that altering the rotational speed to maintain the ideal powder flow throughout the heating cycle can be utilized to reduce the time taken for all the polymer powder to adhere to the mold wall. The effect of rotational speed on wall thickness uniformity and impact strength were investigated and discussed. Results show a strong influence of rotational speed (and powder flow) on the wall thickness uniformity of the moldings with wall thickness uniformity deviations of up to 50% found (within the 2–35 RPM speed range tested).     

Principles of rotational molding

Rotational molding is a process by which powdered or liquid plastics are converted into hollow articles. This paper is devoted to the theoretical understanding of the process of rotational molding. There are seven sections: The Art, wherein we describe the process, discuss previous attempts at understanding the process, and mention processes that are similar in principle to rotational molding. Transient Heating of Mold Surface, wherein we show that the criterion for selection of mold materials is the ratio of the thermal diffusivity to the thermal conductivity, and present the heating curve for a mold in a rotational mold machine. Melting of Plastic Powder in a Rotating System, wherein we discuss in detail those physical powder characteristics that are necessary for good flow within the mold cavity. Fluid Flow During Rotational Molding, wherein we discuss the velocity profiles within the melt film, point out that there is very little bulk polymer flow possible within the mold cavity under normal processing conditions, and consider capillary flow forces and surface wetting. Sinter-Melting, wherein we compare the Kuczynski-Neuville empirical sintering model with the Lontz viscoelastic model, conclude that the latter is correct for the sintering of materials such as ABS, and apply the Frenkel glass densification theory to the prediction of void disappearance in sinter-melt polymers. Degradation, wherein we compare our experimental tensile strengths of polystyrene, obtained at varying oven cycle times and oven set point temperatures, with values obtained from degradation models given in the literature. Laboratory Simulation of Rotational Molding, wherein we propose two series of experiments, the first series being carried out without using rotational molding equipment, and the second using rotational molding equipment with molds having relatively simple geometries.     

New models for rotational molding of plastics

We present a detailed theoretical model of the rotational molding process, and identify the key dimensionaless groups affecting the process cycle time. This theoretical model is employed to create differential and lumped parameter numerical models, as well as a simple closed form estimate for the time required for complete powder deposition. Both numerical models give results that are in very good agreement with experimental data available in the literature. The closed form solution gives good predictions over a wide range of processing parameters. In addition, the effects of variations in the dimensionaless groups on processing time are evaluated.     

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.     

Bubble removal in rotational molding

Closed form solutions have been obtained for bubble dissolution in typical polymer melts encountered in rotational molding. The solutions are in excellent agreement with experimental data available in the literature. Using these solutions, it is shown that under typical rotational molding conditions the polymer melts may be almost saturated. As a result, bubble shrinkage occurs over long periods. Depending on the degree of saturation, surface tension may contribute substantially to the concentration gradient that drives bubble shrinkage. It is also shown that a pressure increase imposed on a nearly saturated polymer melt leads to a steep concentration gradient at the bubble/melt interface that can cause extremely fast bubble shrinkage. Applied to the rotational molding process, such a pressure increase can result in substantial cycle‐time shortening through elimination (or reduction) of the currently used excessive heating. A further benefit may be that additional resins, which at present cannot be used because of oxidation at sustained high‐temperatures, can become available to the rotational molding industry. Under the under‐saturated conditions created by a pressure increase, the effect of surface tension on the rate of bubble shrinkage is negligible.     

浅谈滚塑工艺在钢衬塑储罐方面的技术与应用

随着滚塑工艺的成熟发展,特别是在滚塑钢衬塑储罐以及化工防腐设备等领域的应用非常广泛,并具有强力的市场需求。这一技术的应用凸显了它的工艺结构、特点、原材料、生产设备等方面的独特优势,对产品性能、质量的稳定有了很大提高。本论文以滚塑成型工艺技术在钢衬塑产品方面的应用为分析对象,在理论与实践的基础上,对滚塑钢衬塑工艺技术、特点、原材料、成型设备、衬塑方案以及常见问题的解决方法,逐一进行了论述和总结,可为相近类型企业生产提供参考。     

旋转成型专用树脂MLPE-8050的开发

通过研究抗氧剂和光稳定剂的协同作用,提出了合理的添加剂配方,并将该配方应用到中密度聚乙烯旋转成型专用树脂MLPE-8050的生产中。采用该专用树脂制备的制品能够达到长期使用的特殊要求,其氧化诱导期可达142.0 min,光老化时间大于2 000 h。