加热时间对滚塑制品性能的影响

使用滚塑级线型低密度聚乙烯(LLDPE)粉末,研究了加热时间对滚塑制品性能的影响。结果表明:在滚塑成型工艺中,存在最佳加工温度区间,且该区间位于凝结段;对于滚塑制品的断裂伸长应变和弯曲模量,在消泡段存在"加热陷阱",应尽量避免在这一温度区间进行加工。     

快速发展中的滚塑工业 慈溪市德顺容器有限公司总经理罗宏裕先生专访

<正>谈到滚塑工业,也许许多人了解得并不多,主要原因在于其属于塑料行业很小一个分支。塑料滚塑工艺起源于英国,第一台商用滚塑机问世于上世纪30年代,50年代滚塑工业在欧洲得到很大发展。随着时间推移以及聚乙烯粉末化技术的成熟,滚塑工艺成为塑料成型工艺中不可缺少的一种,在全世界不断发展。     

滚塑发泡成型技术及其发展方向

介绍了一种新型的发泡成型技术———滚塑发泡成型技术。该技术既继承了传统滚塑成型的众多优点,同时又具有其独有的特点,即:具有发泡的芯层的同时又有光滑的表面,能大大提高产品的力学性能,弥补传统滚塑成型技术的缺点。主要从滚塑发泡成型技术的发展历程、工艺流程、加工原理、影响因素以及技术特点等几个方面,详细地介绍了如何利用滚塑发泡成型技术加工具有非发泡外壳和发泡内芯的塑料制品,并且着重介绍了一步法滚塑发泡成型工艺原理及影响因素,展望了滚塑发泡成型未来的发展方向。     

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。     

LLDPE/PA6滚塑专用料的应用研究

制备了线性低密度聚乙烯／尼龙6(LLDPE／PA6)滚塑专用料,考察了增容剂马来酸酐接枝聚乙烯(PE-g-MAH)、PA6含量及抗静电剂含量对LLDPE／PA6滚塑专用料性能的影响。结果表明,适当含量的PE-g-MAH可以增加LLDPE与PA6的相容性,提高材料的综合力学性能;适当含量的PA6可以提高材料的刚性,同时其熔体流动性满足滚塑成型工艺的要求;适量的抗静电剂可以满足材料抗静电的要求。用该滚塑专用料成型的制品可满足高低温、密封性、跌落、振动等试验的环境适应性要求。     

220L塑料桶滚塑成型技术

主要讨论了利用滚塑成型方法生产220L塑料桶的成型工艺，模具设计和生产工艺对制品性能的影响，提出了要获得优异的制品，模具设计是关键，是佳的工艺条件也是成型的重要因素。     

一步法滚塑发泡成型新技术

介绍了一种用于加工具有非发泡外壳和发泡内芯的塑料制品的新方法——一步法滚塑发泡成型技术,包括一步法滚塑发泡成型工艺原理、加工流程及影响因素。     

滚塑成型聚乙烯制品的冲击强度

滚塑是成型中空塑料制品的方法之一。此工艺40年代发展于美国,50年代传到英国。在早期,滚塑没有受到重视,被认为成型慢,应用仅限于少量塑料品种。在最近十来年,由于工艺控制及塑料粉末化的发展,使其得以广泛发展。现在,它比吹塑成型和注射成型更具竞争力,能够成型形状复杂、无应力制品。1　引言　　滚塑,又称旋转成型,工艺较简单。将备好的常温粉末塑料放入常温模具的一半,模具通常是钢板或铸铝的。然后合上模具,在高温下双轴旋转,如图1。当金属模具非常热时,塑料粉末在模具内熔化流动,黏附在模具内表面。当所有的粉末都熔化时,将模具移到冷…     

高温封闭环境下无线测温装置的工作性能的实验研究

滚塑成型是一种热塑性塑料中空成型方法,而温度是滚塑成型过程中不能缺少的因素。在滚塑成型过程中烘箱内的温度很高,无法利用现有的温度测量装备对其实施在线测量,进而为恰当的温度调控提供必要的参考。提出一种应用于高温封闭环境下的无线测温装置,并且介绍其组成结构和工作原理,然后对其工作性能进行试验验证和调试,从而为优化滚塑工艺及提高滚塑设备的工作效率和能源利用率提供一种理论工具。     

磨粉温度对交联聚乙烯滚塑加工性能及其力学性能的影响

考察了磨粉温度对自制滚塑级交联聚乙烯材料粉体特性和力学性能的影响,分析和比较了不同磨粉温度下粉体颗粒形貌、流动性、松装密度、粒径分布、流变特性、滚塑加工性能以及制品冲击强度、弯曲模量等,以筛选合适的磨粉温度区间。研究结果显示,随磨粉温度升高,粉体流动性提高、松装密度增加、颗粒形貌改善,滚塑加工性能逐渐提高;但冲击性能逐渐降低,流变测试的复数黏度及交联度逐渐下降。结合粉料的各项性能,选择磨粉温度在45~55℃,所制交联聚乙烯粉料兼具较高流动性(滚塑加工性能)、较优力学性能(使用性能)。     

环氧树脂/碳纤维复合材料模压制品表面质量影响因素分析

通过正交试验研究了模压温度、模压压力、保压时间、合模速度对环氧树脂/碳纤维片状模塑料模压成型制品表面质量的影响,通过方差分析,表明各因素对表面粗糙度影响程度的主次顺序为：模压温度T>保压时间t>模压压力P>合模速度v。通过邓肯法多重比较进一步探讨了各影响因素中不同水平之间平均值的差异性,并绘制了各因素所对应的表面粗糙度实测平均值关系图。发现随着模压温度的增加,制品表面粗糙度先缓慢后急剧增大;保压时间与模压压力对表面粗糙度的影响作用相反;随着合模速度的增大,表面粗糙度不会发生明显的变化。获得最佳工艺参数为：模压温度T=130℃、模压压力P=600 kN、保压时间t=720 s、合模速度v=15 mm/s。通过模压成型实验验证：在最佳工艺参数下,表面粗糙度相对于正交实验结果中的最小值减小了19.3%,有效提高了模压成型制品表面质量。     

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。     

热塑性塑料流动性能测定方法的研究

用一定注射成型条件下的流动长度来表征热塑性塑料注射成型的流动性能。主要介绍阿基米德螺旋线法测定热塑性塑料流动性能的原理、测定方法和工具,对注射成型系数的影响因素进行了探讨,可供指导生产实践参考。     

Powder‐shape analysis and sintering behavior of high‐density polyethylene powders for rotational molding

The quality of rotational molded products is strongly affected by the sintering behavior of the powders used in the process. In turn, for a given material, the sintering behavior of polymer powders is dependent on the size and the shape of particles obtained in the milling apparatus. The quality of powders for rotational molding is usually determined by means of size distribution, dry flow, and bulk density tests. However, these tests do not provide insight into the relationship between the shape of powders, the milling conditions, and the sintering behavior during the rotational molding cycle. Nevertheless, the application of mathematical tools to powder analysis can significantly improve the efficiency of the grinding process, looking not only at the size but also at the shape of the powder. This can in turn result in a higher reliability of rotational molding and in better performances of the products obtained in processes dominated by the sintering behavior of polymer powders. In this work the grinding process of recycled high‐density polyethylene was analyzed using a quantitative approach to the shape and size of the powders. In particular, shape factors, capable of characterizing powders obtained in different milling conditions, were studied. Finally, the influence of the powders' shape and size on sintering behavior was studied by thermomechanical analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 449–460, 2004     

Rotational molding of plastics: Comparison of simulation and experimental results for an axisymmetric mold

We present a validation study comparing the mold wall temperature estimates from an axisymmetric thermal finite element simulation of the rotational molding process with temperature data obtained during experiments conducted on industrial‐grade rotational molding equipment. The finite element model simulates the heat transfer processes involved in rotational molding through the end of powder deposition, and uses an Arbitrary Lagrangian Eulerian technique to track the growing molten plastic layer. The experiments were conducted with nine different operating conditions on a single axisymmetric mold shape. The simulation results for mold wall temperature agreed well with the experimental data under all of the conditions tested.     

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。     

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.     

Characterization of polymer powder motion in a spherical mold in biaxial rotation

As rotational molding of thermoplastic parts become more and more complex, understanding the fundamental processing aspects such as powder flow becomes important for good and uniform part quality. In this work, an image analysis technique is used to determine the effect of polymer powder particle size and distribution in a biaxially rotating spherical mold. Experimental parameters such as particle diameter (d), ratio of larger over smaller particles diameters (d_r), and initial powder position inside the mold and camera viewing position were studied. From the results obtained, conditions leading to homogeneity and segregation are discussed. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

影响可再分散聚合物乳胶粉性能的因素分析

采用喷雾干燥法制备可再分散聚合物乳胶粉。探讨了干燥室进口温度、喷雾液黏度、雾化轮转速及喷雾液进料速率对制备可再分散乳胶粉及其性能的影响,并用扫描电镜对乳胶粉进行表征。结果表明:进口温度为120～140℃、喷雾液黏度在15～20 s、雾化盘转速24 000 r/min、进料泵转速为30～35 r/min时,制备的乳胶粉流动性好、无结块,再分散性优良,满足制备乳胶粉的性能要求。     

Application of citric acid as natural adhesive for wood

The development of natural adhesives derived from nonfossil resources is very important for the future. Besides, it is desirable to be safe adhesives without using harmful chemical substances. In this study, application of citric acid as a natural adhesive was investigated. Citric acid powder and bark powder obtained from Acacia mangium were used as raw materials. Citric acid powder was mixed with the bark powder, and the resulting powder mixture was poured into a metal mold. The mold was hot‐pressed at 180°C and 4 MPa for 10 min, and a bark molding was then obtained. The specific modulus of rupture and modulus of elasticity values of the molding containing 20 wt % citric acid were 18.1 MPa and 4.9 GPa, respectively. The molding did not decompose during a repeated boiling treatment. To clarify the effect of tannin on the adhesiveness of molding, bark was separated into tannin and residue. The molding was not obtained while using the tannin due to the marked fluidity, whereas it was obtained while using the residue, the same as while using the bark. It was considered that components other than tannin contributed to the adhesiveness. Based on the results of Fourier transform infrared spectra, the formation of ester linkages between carboxyl groups derived from citric acid and hydroxyl groups in the bark was confirmed. Accordingly, citric acid brought an adhesion by chemical bonding, and it could be used as a safe natural adhesive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012