Effect of screw design on fiber damage in extrusion compounding and composite properties

The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine design are extremely important in discontinuous fiber reinforced composites. Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet quality, wet-out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions in the screw are determined to identify regions of higher fiber interaction. The fiber damage during subsequent injection molding has also been determined. The tensile, flexural, and impact properties of the tensile bars are compared. It is found that the residence time, fill-up, and the intesity of mixing during extrusion compounding have a predominant effect on fiber length degradation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass-filled polymer than the 30 wt% glass-filled polymer. However, the mechanical properties of the 30 wt% glass-filled polymer showed an increasing trend compared to the 40 wt% glass filled polymer. A screw design that provides a balance of the fiber length, wet-out, and fiber dispersion was noted to give consistent mechanical properties.     

Intermediate temperature oxidative strength degradation of a SiC/SiNC composite with a polymer‐derived matrix

The article describes an experimental investigation of oxidative degradation in mechanical performance of a SiC fiber‐reinforced composite with a SiCN matrix produced by polymer infiltration and pyrolysis. Tensile stress rupture and retained strength tests were performed at 800°C in dry air and in water vapor. Fracture surfaces were examined to determine the degree of fiber pull‐out and constituent oxidation and to measure radii of representative fiber fracture mirrors. The results indicate that degradation in tows adjacent to cut surfaces occurs equally rapidly in water vapor with or without application of stress; regions in the composite interior and near as‐processed (uncut) surfaces appear far less affected. Similar effects are evident but less pronounced in dry air. Although oxidation of fiber coatings is observed in some cases, collectively the results suggest that fiber degradation is the main mechanism leading to reduced composite strength.     

HYDRAULICS AND EFFICIENCY OF SCREEN TRAYS FOR DISTILLATION

Screen trays are proprietary devices similar to sieve trays which are used in distillation and absorption applications. The pressure drop, liquid holdup and entrainment are measured for screen trays in an air/water column and compared to results obtained with sieve trays. The effciencies of both types of trays were compared in a distillation column using systems of various physical properties (methanol/water, acetic acid/water and cyclohexane/n-heptane mixtures). It was found that the screen tray has a lower dry pressure drop, higher liquid holdup, lower entrainment and weeping, and higher jet flooding capacity than the sieve tray. However, the effciencies of both trays are similar for the systems studied. A model was developed for predicting total pressure drop for screen trays using an air/water column. The model was tested using results for methanol/water, cyclohexane/n-heptane and acetic acid/water systems at total reflux. The deviations are within +/- 20% for 90% of the data points. The effect of a bed of mesh packing on the screen tray was also studied. It was found that the packing led to a higher tray effciency, but resulted in a higher tray pressure drop.     

小化纤厂自建干空气站的探讨

介绍了该厂自建干空气站的工艺流程及干空气生产过程中应注意的事项,并比较了干空气站使用前后涤纶切片含水及产品质量,认为小型涤纶厂自建干空气站可以防止干燥后的切片回潮,是稳定生产和提高产品质量的一项行之有效的技术改造措施。     

超高分子量聚乙烯纤维 第一讲 超高分子量聚乙烯纤维发展概况

冻胶纺是一种新颖纺丝技术,用此法制取超高分子量聚乙烯纤维(UHMW-PE)的工艺过程包括:溶解UHMW-PE在适当的溶剂中,制成半稀溶液,经喷丝孔挤出,以空气或水骤冷纺丝溶液,将其凝固成冻胶原丝。从大分子观点出发,在溶液中聚乙烯大分子处于解缠状态并在冻胶原丝中保持这种大分子的解缠状态。拉伸冻胶原丝使大分子链取向和高度结晶,进而使呈折叠链的大分子转变为伸直链,从而制得高强、高模纤维。本讲座分以下五讲:第一讲超高分子量聚乙烯纤维发展概况;第二讲超高分子量聚乙烯冻胶纺工艺过程剖析;第三讲超高分子量聚乙烯的溶解和冻胶纺,第四讲聚乙烯冻胶原丝的萃取和干燥;第五讲聚乙烯冻胶原丝的超拉伸。     

Well-developed mass transfer in axial flows through randomly packed fiber bundles with constant wall flux

An analysis of the effects of fiber packing on mass transfer coefficients for axial fluid flow through fiber bundles with uniform wall flux in the well-developed limit is presented. The finite element method is used to solve the governing momentum and conservation of mass equations. The effective mass transfer coefficient depends strongly on fiber packing. Randomly packed fiber bundles have much lower mass transfer coefficients than regularly packed fiber bundles. Mass transfer rates are controlled by the lowest fiber packing regions through which most of the flow occurs.     

Effect of a severe form of initial gas maldistribution on pressure drop of a structured packing bed

The results of an experimental study devoted to establishing the relation between a severe form of initial gas distribution, as created by a chordal blockage set-up used in a recent FRI study, and the hydraulics of a structured packing bed are presented. Both dry and wet bed experiments were conducted with air/water system under ambient conditions, using a 1.4 m i.d. Plexiglas column in conjunction with Montz-pak B1-250 packing bed of the approximately same length, employing liquid loads corresponding to that from the FRI study. From dry and wet experiments it appeared that chordal blanking of 30% of cross-sectional area at gas inlet can influence the pressure drop significantly, particularly that in the lower part of the bed.     

DRYING OF SUGAR BEET FIBER WITH HOT AIR OR SUPERHEATED STEAM

A comparative study of drying thin layers of sugar beet fiber with hot air or with superheated steam in a specially designed pilot dryer is reported. Our present interests are focused on drying rate and on the quality of the dried product. Steam superheated at 130-150°C yields 90 % of dry matter (DM), however steam condensation on the cold product at the beginning of the process may penalize the drying time. The color of the fiber is not modified until reaching 80 % DM. Drying with air heated at temperatures lying in the 40 to 105°C range does not alter the white color up to 90 % DM. The water retention capacity of the original fiber, 14 g water/g DM remains unchanged whatever drying agent is used. The scaling up of the primary hot air drying set up to a ten times larger experimental dryer introduce no modification of drying time, water retention capacity or fiber color. Thick layer drying experiments permit to define parameters of a belt dryer for an industrial fiber processing plant.     

DRYING OF SUGAR BEET FIBER WITH HOT AIR OR SUPERHEATED STEAM

A comparative study of drying thin layers of sugar beet fiber with hot air or with superheated steam in a specially designed pilot dryer is reported. Our present interests are focused on drying rate and on the quality of the dried product. Steam superheated at 130-150°C yields 90 % of dry matter (DM), however steam condensation on the cold product at the beginning of the process may penalize the drying time. The color of the fiber is not modified until reaching 80 % DM. Drying with air heated at temperatures lying in the 40 to 105°C range does not alter the white color up to 90 % DM. The water retention capacity of the original fiber, 14 g water/g DM remains unchanged whatever drying agent is used. The scaling up of the primary hot air drying set up to a ten times larger experimental dryer introduce no modification of drying time, water retention capacity or fiber color. Thick layer drying experiments permit to define parameters of a belt dryer for an industrial fiber processing plant.     

中,高压浇注成型坯体的特性

卫生陶瓷中，高压浇注成型工艺是当今世界上的最新工艺，而该工艺在我国目前处于研究阶段未被广泛应用。本文在实验的基础上，对压力浇注成型坯体的特性（干燥粒子的堆积密度、坯体的残留水份、干燥收缩与坯体的结构等）进行了研究，得出了一些有价值的结论。     

干法腈纶纺毛条过程中的挤并丝问题

讨论分析了干法腈纶长丝纺毛条生产过程中产生的挤并丝问题,结果表明：通过提高聚合物的相对分子质量,相对降低第二单体含量,提高第三单体含量及降低沸水收缩率,并控制长丝的含油率、含水率及拉断机的相关参数,降低了挤并丝的产生。     

短切原丝毡用乳液粘结剂专用乳液的合成

为了提高乳剂毡的粘结性,尤其是毡的浸透性、力学性能,研究了粘结剂配方中丙烯酸、丙烯酸丁酯、丙烯酸异辛酯、自制特殊单体以及乳化体系、单体配比等对粘结剂性能的影响。其主要是在合成过程中尽量调整最佳单体配比、乳化剂用量,尽量减小毡在苯乙烯中浸透速度、浸透终态的影响。     

Hydraulics and efficiency of screen trays for distillation

Screen trays are proprietary devices similar to sieve trays which are used in distillation and absorption applications. The pressure drop, liquid holdup and entrainment are measured for screen trays in an air/water column and compared to results obtained with sieve trays. The effciencies of both types of trays were compared in a distillation column using systems of various physical properties (methanol/water, acetic acid/water and cyclohexane/n-heptane mixtures). It was found that the screen tray has a lower dry pressure drop, higher liquid holdup, lower entrainment and weeping, and higher jet flooding capacity than the sieve tray. However, the effciencies of both trays are similar for the systems studied. A model was developed for predicting total pressure drop for screen trays using an air/water column. The model was tested using results for methanol/water, cyclohexane/n-heptane and acetic acid/water systems at total reflux. The deviations are within +/- 20% for 90% of the data points. The effect of a bed of mesh packing on the screen tray was also studied. It was found that the packing led to a higher tray effciency, but resulted in a higher tray pressure drop.     

涤纶短纤维引进线原料单耗考核研讨

剖析了涤纶短纤维引进线原材料单耗等７２ｈ考核的验证方法存在的缺陷。建议以后纺拉伸批数划定考核验证时间，包装环节设置计量复称，对科学合理的验证具有积极的作用。     

THE INFLUENCE OF OXIDATION OF THE FIBERS ON THE TRIBOLOGICAL PROPERTIES OF CARBON FIBER-REINFORCED NYLON COMPOSITES

Three-dimensional braided carbon fiber-reinforced nylon composites (C_3D/MCN) were prepared in order to investigate the influence of oxidation of carbon fibers on the tribological properties of the C_3D/MCN composites. Friction and wear tests of the C_3D/MCN composites with untreated and treated carbon fabric were conducted. The characteristics of the carbon fiber, the interface strength, the hardness, and the worn surface morphologies of the C_3D/MCN composites were analyzed. The results show that the specific surface area of treated carbon fiber was far higher than that of untreated carbon fiber and there formed a functional group of -C=O on the carbon fiber surface after air oxidation. The oxidation of the carbon fibers improved the interface strength between the carbon fibers and the matrix and had little effect on the hardness of the composites. The friction coefficient and wear rate of C_3D/MCN composites with oxidized carbon fibers were apparently lower than those with untreated carbon fibers. In conclusion, the oxidation of the fibers showed good effects on the improvement of the interface strength and the tribological properties of the composites.     

填料加盘管型闭式冷却塔的性能试验研究

通过设计和搭建填料加盘管型闭式冷却塔对其进行了性能测试。试验结果表明,对于结构和设计参数确定的填料加盘管型闭式冷却塔,空气湿球温度和空气流量对其冷却性能的影响最为显著,冷却水流量和进口温度则有较大影响,而喷淋密度在达到最佳值后对其冷却性能的影响基本保持不变,空气干球温度只有较小影响。由于填料的加入,填料加盘管型闭式冷却塔的最佳喷淋密度相对偏小,可以在0.025～0.035kg/(m·s)之间取值。     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

Drying kinetic curves and modelling for cassava chips were determined using a pilot-size air dryer. Operating conditions involved temperatures ranging from 35 to 90 ° C, air flow velocities from 0.5 to 2.0 m/ s, and air moisture content from 0.005 to 0.060 kg water/ kg dry air. Sorption isotherms at temperatures of 23, 45 and 60 ° C were obtained. Results for the drying experiments can be used to calculate the optimal drying conditions for dehydration of cassava roots in multilayers     

THE INFLUENCE OF OXIDATION OF THE FIBERS ON THE TRIBOLOGICAL PROPERTIES OF CARBON FIBER-REINFORCED NYLON COMPOSITES

Three-dimensional braided carbon fiber-reinforced nylon composites (C_3D/MCN) were prepared in order to investigate the influence of oxidation of carbon fibers on the tribological properties of the C_3D/MCN composites. Friction and wear tests of the C_3D/MCN composites with untreated and treated carbon fabric were conducted. The characteristics of the carbon fiber, the interface strength, the hardness, and the worn surface morphologies of the C_3D/MCN composites were analyzed. The results show that the specific surface area of treated carbon fiber was far higher than that of untreated carbon fiber and there formed a functional group of –C=O on the carbon fiber surface after air oxidation. The oxidation of the carbon fibers improved the interface strength between the carbon fibers and the matrix and had little effect on the hardness of the composites. The friction coefficient and wear rate of C_3D/MCN composites with oxidized carbon fibers were apparently lower than those with untreated carbon fibers. In conclusion, the oxidation of the fibers showed good effects on the improvement of the interface strength and the tribological properties of the composites.     

电子玻纤布生产过程中的开纤

对电子玻纤布开纤后能提高其与树脂的浸透性、PCB的耐热性、PCB的可靠性进行分析；总结了在电子玻纤布的生产过程中，如何进行电子玻纤布开纤的方法。     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

ABSTRACT

Drying kinetic curves and modelling for cassava chips were determined using a pilot-size air dryer. Operating conditions involved temperatures ranging from 35 to 90 ° C, air flow velocities from 0.5 to 2.0 m/ s, and air moisture content from 0.005 to 0.060 kg water/ kg dry air. Sorption isotherms at temperatures of 23, 45 and 60 ° C were obtained. Results for the drying experiments can be used to calculate the optimal drying conditions for dehydration of cassava roots in multilayers