Weft Insertion on Air-jet Looms: Velocity Measurement and Influence of Yarn Structure Part II: Effects of System Parameters and Yarn Structure

An investigation of the effects of different weft–insertion–system parameters on yarn velocity is reported. Increasing the air–supply pressure, initial loop length, and running speed decreases the total insertion time and hence increases the average yarn velocity.

To examine the effects of yarn characteristics on yarn velocity, several yarns were tested under the same laboratory conditions. For every yarn, relations between total insertion time, yarn velocity, and air velocity and distance were obtained. It was found that open–end–spun (OE) yarns had a higher yarn velocity than ring–spun (R) yarns owing to the bulkier structure. However, R yarns had a higher initial acceleration than OE yarns. Murata air–jet–spun yarns had a higher velocity than R yarns.

Increasing the yarn linear density and twist increased the insertion time. Texturing of continuous–filament yarns increased the yarn velocity by comparison with straight continuous–filament yarns.     

JAT 710型喷气织机引纬系统的实际应用及性能分析

阐述了JAT 710型喷气织机引纬系统主要部件的结构特点，并对关键技术参数进行了分析，为提高织机生产效率、正确选择喷气引纬工艺参数、减少织疵、实现高速优质生产提供了依据。     

喷气织机引纬工艺参数的设定

探讨喷气织机引纬工艺参数的设定方法。以GA708-280型喷气织机为例,分析了主喷嘴、辅助喷嘴电磁阀的开闭时间、主喷嘴和辅助喷嘴的喷气压力、储纬器挡纱针的释放时间等引纬参数的设定方法及一般原则。认为:喷气织机引纬喷射时间参数要根据不同的织物组织结构及品种来设定;喷气压力应采用先由高压(如4×105Pa)开始,再逐渐降低的方法来设定。     

喷气织机综框高度对纬向停台的影响

降低纬向停台是提高喷气织机效率的重要课题。根据不同的开口形式及在引纬过程中不同的阶段对综框高度的要求，进行合理的综框高度设定。降低纬向停台，提高开台效率。     

喷气织机引纬筘槽内气流状态的影响因素

由于测量引纬筘槽内的气流速度可用于分析各工艺参数对引纬过程的影响,为此通过自行设计的测试装置,采用毕托管测试引纬筘槽内不同位置的气流速度,并研究喷向角和辅助喷嘴间距等工艺参数的适调范围。结果表明:引纬筘槽内不同位置具有不同的气流速度;供气压力在(2～4)×105 Pa范围内,辅助喷嘴喷射角不宜设置为5°,否则将导致引纬气流速度过低;辅助喷嘴间距缩短有利于提高引纬筘槽内的平均流速,当辅助喷嘴间距为65 mm时,引纬筘槽内的气流速度完全能够满足100 m/s的引纬要求。     

纱线气流指数测试仪

纱线气流指数仪是一种类似喷气织机引纬系统脱机操作的测试装置，用于测试喷气织造纬纱的速度（平均值和变异系数）。文章综述了诸如纱线气流指数与喷气织机耗气量、织机速度之间的关系等，同时还介绍了会对纱线气流指数值产生影响的某些纱线品质。     

筘槽内引纬气流场分布及其对纬纱飞行的影响

为了解喷气引纬纬纱的实际运动状态和筘槽内引纬气体流场的分布变化与纬纱运动状态的关系,采用高速摄影系统,对喷气引纬时纬纱在异型筘槽内飞行的实际状态拍摄记录,可以看出纬纱在筘槽内呈旋转螺旋状前行。通过气体流场测试装置,对筘槽内喷气引纬的气体流场进行测试分析,认为因筘槽内引纬气体流场的特殊动态分布变化使纬纱作旋转螺旋状前行。对第1辅助喷嘴喷向角做适当调整,可以降低第1、第2辅助喷嘴间段上引纬气体流场的波动变化。     

Research on process parameters in a novel drafting system

To overcome the shortcomings existing in the roller drafting system of air jet spinning, a set of combing roller-drafting system has been introduced to substitute the roller drafting system in air jet spinning. Moreover, a funnel-shaped fibre conveyer, a disc fibre collector and a swirl twister have been designed to accomplish the spinning process, which was named disc swirl spinning. Experimental spinning proves that combing roller drafting device wears little. Its remarkable advantage lies in the high efficiency of drafting. The rotational speed of jet stream in nozzle can be well utilized, which promises a high productivity. The relationship between the drafting process parameters of disc swirl spinning and yarn properties, such as tenacity and peeling-off-resistance, has been investigated and the data suggest that yarn properties keep stable when combing roller speed is 6000–7000 rpm, feeding quantity is 1.695–2 g/min, sliver linear density is 2–2.58 g/m, feeding tension is 0.012 N and the unwinding tension of the core filaments is 0.06 N. Furthermore, the appearance of disc swirl spun yarn is compared with that of air jet spun yarn. The scanning electron microscope (SEM) photos show that yarn structure of disc swirl spun yarn is similar to that of air jet spun yarn. The core is bound by the outer fibres and it is nearly parallel and no twist. However, the outer fibres of disc swirl spun yarn cover yarn body totally, which is different with that of air jet spun yarn.     

减少喷气织机断纬的工艺实践

分析喷气织机引纬过程中断纬产生的主要原因,介绍减少断纬的工艺改进措施。     

喷气织机辅助喷嘴流场特性与耗气量分析

为研究辅助喷嘴几何结构对喷嘴喷射效果及耗气量的影响,采用CFD软件Fluent对喷气织机辅助喷嘴流场进行数值模拟,获得了辅助喷嘴在不同供气压力、出口截面积、出口形状及喷射角下的纬纱飞行轴线气流速度分布。结果表明:随压力增大,射流速度的提升逐渐变弱,耗气量随压力呈正相关变化;喷嘴出口截面积影响射流速度和持续性,随截面积增加耗气量不断增大;截面积一定时,出口形状变化对筘槽内流场影响较小;纬纱飞行方向上气流速度及峰值位置随喷射角而变化,在实验范围内,喷射角越大耗气量越小,选择合适的辅助喷嘴和引纬工艺,是实现喷气织机高质低耗目标的关键。     

宽幅纯棉特细号高密直贡缎的织造实践

为了在双织轴宽幅喷气织机上顺利生产纯棉特细号高密直贡缎,选用100%长绒棉为经纱,50%长绒棉为纬纱,而且在织造工序采用中开口、低后梁、早开口、迟引纬、合理配置主辅喷嘴气压及引纬工艺、确保探纬器作用良好等技术措施,使织疵减少,织机效率达85.7%,入库一等品率达99.87%.     

PZK500型喷气织机控制系统的设计及应用

探讨PZK500型喷气织机控制系统的工作原理及应用效果。针对PZK303系列喷气织机控制系统存在的问题及缺陷,根据喷气织机五大运动,把相对独立的各部分运动采用相对独立的控制单元进行控制,采用可抢占型任务调度设计方法,实现了纬纱制动功能、防止开车档功能、辅喷开启时间独立设定功能等,提高了无故障运转时间,稳定了产品质量。     

Recent progress in food processing applications of air impingement technology: A review

Air impingement method has been widely used in a variety of industrial applications, such as textile and paper drying, turbine cooling, and glass quenching, because it is an efficient technology with high heat and mass transfer rates. This technology has received increasing interest in the field of food processing over the last two decades, such as drying, baking, blanching, freezing, and thawing. In a food processing equipment using air impingement, jets of high-velocity air (with speeds of 10–50 m/s) are directed at a food product. The performance of the system is influenced by several critical elements, including jet velocity, nozzle array diameter and layout, jet distance, and boundary layer characteristics. The use of computational fluid dynamics, an emerging tool, has been shown to be valuable in the analysis of fluid flow and heat and mass transfer in jet impingement systems. The physical properties of impinging jets, such as turbulent mixing in the free jet zone, stagnation, boundary layer formation, recirculation, and their interactions with food products in terms of heat and mass transfer, have been discussed in this article. The benefits and disadvantages of air jet impingement technology in different food processing applications together with potential trends for improving impingement technology performance were identified and discussed. This review not only contributes to a better understanding of the research status of impingement technology on food processing but also triggers new research opportunities in this field in order to provide more healthy and nutritious food in a more sustainable way to the world's growing population.     

喷气织机织造色织物的色差分析与研究

文章用实验的方法分析得出:用喷气织机织造纯棉色织物时产生色差的主要原因是布面上织缩率和捻度的分布不均匀。为了避免色差的产生,需要运用合理的引纬工艺参数和优化上机工艺。     

喷气织机纬停原因分析

根据喷气引纬的特点,分析说明了织造过程中造成纬停特别是阻挡性纬停的原因是纱线的毛羽、织轴质量和经纱的织缩等,并提出了正确设置引纬参数等防治措施。     

HEAT TRANSFER COEFFICIENT FOR COOKIE SHAPED OBJECTS IN A HOT AIR JET IMPINGEMENT OVEN

Correlations for average heat transfer coefficient for cookie shaped objects in a hot air jet impingement oven were obtained using aluminum cookie models. The study was carried out in a pilot plant scale hot air jet impingement oven. The effects of individual cookie position, presence of surrounding cookies, air velocity, air temperature and rotation of the oven plate on average surface heat transfer coefficient were investigated. The value of the heat transfer coefficient ranged between 100–225 W/m²K and was found to be a strong function of jet air velocity. The impact of surrounding cookies on the heat transfer coefficient was more for smaller cookies, which had larger cookie‐to‐cookie spacing.     

辅助喷嘴结构对喷气织机异形筘内合成流场特征的影响

为提高喷气织机引纬系统的引纬速度和稳定性,采用雷诺时均方程中的k-ε双方程湍流模型分别对单圆孔、正三角形孔和星形孔3种不同的典型喷嘴与异形筘的合成流场进行模拟仿真,得到在0.2~0.4 MPa供气压力下不同辅助喷嘴间距合成流场中心轴线气流速度和流场速度云图。结果表明:当压力相同时,正三角形孔辅助喷嘴合成流场中心轴线气流速度最高,对纱线牵引力最大;星形孔辅助喷嘴合成流场中心轴线气流速度变化幅度最小,引纬稳定性最好;单圆孔辅助喷嘴中心轴线气流速度波动最大,间距超过70 mm,不适合引纬;在全幅织物接力引纬时,各组喷嘴射流的喷射时间互相衔接,喷嘴间距不宜太长。     

多圆孔辅助喷嘴喷孔结构参数灵敏度分析北大核心CSCD

为探究多圆孔型结构喷孔对喷气织机辅助喷嘴喷射性能的影响规律,获得更好的喷嘴结构和引纬质量,文章以多圆孔辅助喷嘴为研究对象,进行多圆孔辅助喷嘴结构参数灵敏度分析。首先,采用拉丁超立方采样(LHS)抽取所需实验样本并建立各样本的流场模型,获得最大出口速度作为性能评定指标。其次,基于支持向量回归机(SVR)建立辅助喷嘴结构参数与最大出口速度间的数学代理模型。最后,采用Sobol全局灵敏度分析法求解结构参数的灵敏度,得到结构参数对其最大出口速度的一阶灵敏度系数和全局灵敏度系数。结果表明:喷孔直径和孔心距对最大出口速度的影响较大,喷孔位置和喷孔锥度的影响较小。     

喷气织机中压缩空气的泄漏评估及其修复优化

为探究喷气织机中压缩空气泄漏情况,以便对泄漏原因及参数影响进行评估,在织布车间从喷气织机引纬系统入手,对输送及使用过程中的压缩空气进行泄漏检测。结果发现,泄漏主要来源于管路输送、连接附件以及使用点设备3 方面,原因主要为使用过程中零部件老化及破损而没有及时修复更换。数据分析表明,压缩空气在使用过程中泄漏量、能耗随压降及温度变化的增加而增大。通过实验、数值及理论分析相结合揭示了压缩空气在喷气织机中泄漏情况及压降、温度等因素的影响机制。以此为基础,对泄漏进行了探讨并提出了修复优化。结果表明,通过对喷气织机引纬专件定期管理维护、检修保养,可有效减少甚至消除泄漏,从而达到降耗要求。     

如何提高喷气织机的效率

喷气织机的适应范围越来越广，引纬速度飞速提高，为了充分发挥其优势，实行高速、高效运转，则要充分做好经纱和纬纱的准备、附件的选择工作，改善生产环境。