Formation of β-cylindrites under supercooled extrusion of isotactic polypropylene at low shear stress

Formation of β-cylindrites of isotactic polypropylene under various wall shear stress (σ_w), supercooled temperature of melt (T_e) and crystallization temperature (T_c) has been investigated by polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). To have better control over the thermomechanical history, instead of a reciprocating screw, the samples were prepared by extruding supercooled melt through capillary die. β-cylindrites can be observed by PLM in the extruded specimen even at a lower σ_w (0.020 MPa), and the number of β-cylindrites nuclei increases rapidly with the lowering of T_e. The nucleation density of β-cylindrites increases with the raising of wall shear stress under a given T_e of 160 °C. Furthermore, at lower supercooled temperature of melt (145 °C), the radius of β-cylindrites decreases with the increasing of σ_w, and the number of β-cylindrites nuclei almost remain invariant. At relatively higher σ_w (0.090 MPa), a saturation of β-cylindrites nuclei is observed with decreasing T_c. A modified model based on above results has been proposed to explain the effect of the original structure of quiescent supercooled melt on the formation of β-cylindrites under low shear stress.     

低碳环保型碱性镀锌自动生产线工艺设计

阐述了某军工企业无氰镀锌工艺设计秉持的原则和依据.介绍了2699型碱性镀锌智能化生产线的工艺流程,其主要包括:化学除油,除锈,阳极电解除油,浸碱液,镀锌,硝酸出光,彩色钝化或三价铬厚膜钝化,热水洗,烘干,检验,装箱.给出了各工序的溶液组成及工艺条件.从槽液带出损失及废水处理方面,比较了该工艺与高氰镀锌工艺的运行成本.实...     

低发泡聚氯乙烯结皮板材生产技术

分析了低发泡聚氯乙烯结皮板材的挤出生产技术。在低发泡聚氯乙烯结皮板材生产中,选用螺杆特性硬的双螺杆挤出机、无发泡死角的模头,选用聚合度700~800,K值55~68的PVC原料,以及复合型发泡剂,挤出温度控制在140~160℃,可以生产性能比较优异的制品。     

多螺杆挤出机的研究与应用

对三螺杆挤出机的结构、混合机理和挤出特性进行了分析,重点论述了三螺杆挤出机的研发及应用现状,并对四螺杆挤出机的研发现状进行了简要介绍,指出多螺杆挤出机发展的不足之处,对多螺杆挤出机的研究与应用具有一定的指导意义.     

高熔体强度聚丙烯/低密度聚乙烯共混体系的挤出发泡行为研究

利用熔体流动速率测试仪和转矩流变仪对不同比例的高熔体强度聚丙烯(HMSPP)/低密度聚乙烯(PELD)共混体系的流变行为进行研究,并对共混体系的流变数据进行分析.随后采用超临界CO2作为发泡剂进行了HMSPP/PE-LD共混体系的挤出发泡研究,并通过真密度计和扫描电子显微镜表征了发泡材料的表观密度和泡体结构参数.结果表...     

蒸汽加热模具及模具变温辅助控制装置的研制

对高光无痕注射成型工艺的成型装置和辅助控制系统进行了研究和开发,介绍了蒸汽加热注射成型工艺原理。通过辅助系统来控制蒸汽加热模具的型腔温度,特殊的水道设计使模具型腔的温度能够迅速升至熔体的热变形温度以上,进而获得高光表面制品。同时指出了蒸汽加热模具在模具材料的选择、测温点的分布等方面的设计思想,阐述了辅助控制装置的组成部分及控制原理。结果表明,蒸汽加热模具可加工高表面光洁度、无熔接痕、无流痕的塑料制品,可免除后续喷涂工艺,降低了生产成本,成型周期由120 s 缩短到43 s。     

高岭土尾矿对亚甲基蓝的吸附行为的研究

文章探索了高岭土尾矿对亚甲基蓝溶液的吸附性行为,测定了高岭土尾矿的粒度与用量、亚甲基蓝溶液的pH与浓度、吸附时间及吸附温度等因素对亚甲基蓝吸附性能的影响。结果表明：在碱性条件下,高岭土尾矿对亚甲基蓝溶液有较好的吸附能力,亚甲基蓝浓度增加,高岭土尾矿对其脱色率减小,而随着高岭土尾矿用量的增加,则脱色率不断提高。高岭土尾矿对亚甲基蓝的等温吸附服从Freundlich方程式。高岭土尾矿对亚甲基蓝吸附的随时间的增加、温度的升高而增加。通过对这些参数的探索和测定,高岭土尾矿的吸附能力可以达到98%以上,高岭土尾矿能有效除去溶液中的亚甲基蓝。     

高线机组轧制急停控制系统的开发应用案例

介绍安钢高线机组生产急停控制系统的开发应用过程。     

辊式挤压成型机机架设计与有限元分析

介绍辊式挤压成型机的工作原理和产品特点,重点阐述了机架设计中的要点与细节问题,并以φ800 mm×340 mm挤压成型机为例计算得到侧臂支架的应力与变形分布,验证了机架结构设计的合理性。     

Impedance of reinforcing steel with disbonded dual polymer–zinc coating

Dual polymer/zinc-coated concrete steel reinforcing bar (rebar) is a novel material intended to improve corrosion related durability in marine and deicing salt environments. Severe fabrication bending induces coating breaks and separation from the steel substrate, creating a crevice where some zinc corrosion takes place. EIS measurements to characterize that corrosion revealed spontaneous fluctuations that included variations in the size of the high frequency loop and sometimes strong intermediate frequency dispersion. This investigation examined the underlying causes for that behavior. The fluctuations were explained by formation and episodic release of hydrogen gas in the crevice underneath the disbonded coating, as a product of the cathodic reaction in corrosion of the zinc layer. The gas caused partial occlusion of the crevice and the crevice opening at tears in the coating. Gas occlusion increased the effective electrolytic resistance inside the crevice, and contributed to an enhanced transmission line configuration with associated frequency dispersion, especially notable in the intermediate frequency part of the impedance spectrum. A radial transmission line model was adopted as a simplified abstraction of the system. Properties of the radial transmission line impedance behavior are discussed. The model output replicated the key features of the measured impedance spectrum and its fluctuations, and permitted isolating the low frequency response as the most representative to evaluate corrosion conditions inside the crevice in subsequent research.