Levelness in the Dyeing of Wool Yarn and Fabric

In experiments with a thin bed of cloth, the maximum rate of uptake of dye by a wool yarn has been found to be limited by the concentration gradient of the dye across the yarn. A type of unlevelness observed in a conventional cross-wound package is attributed to the same concentration gradient.     

Influence of Substrate Type on Level Dyeing of Acrylic Yarn Packages

In an earlier paper [1], the influence of flow rate, ramp (constant rate of temperature rise) and package density on the rates of dyeing of two basic dyes on Ex/an, and on the levelness obtained in the resulting dyeings, was investigated, and a relationship was derived to link these factors quantitatively. This work has now been extended to cover the behaviour of various basic dyes on Exlan and other acrylic fibres, under conditions expected to give borderline levelness. It has been shown that the shape of the rate–of–dyeing curve depends on the type of acrylic fibre and, to a lesser extent, on the cationic retarder used, but not on dye type within the group of CV2. 5–3. 5 basic dyes examined. The response of dyeing rate and degree of unlevelness to deliberate variations of ramp, as demonstrated in the previous work on Exlan, is now confirmed on Cashmilon. Evidence of a different type of random unlevelness, not related directly to dyeing rate, was also obtained from dyeings on the various fibres at a slow ramp.     

A new image‐based unlevelness index

A new quantitative unlevelness index based on the Fourier transformation frequency component is introduced for evaluation of the degree of unlevelness of a set of dyed fabrics with different surface colour uniformities. A series of dyed denims with different degrees of unlevelness were prepared, and the degree of uneven appearance of fabrics was ranked by a group of observers. The surfaces of fabrics were imaged by a conventional scanner, and the Fourier transform was employed to compute the spectrum of desired images. It was found that the low‐frequency components of the computed matrix were stronger than the others, while its DC component, which related to the mean of the desired image, was too large. By this method, it was demonstrated that the fraction of the sum of the maximum of the second to sixth columns of the Fourier components of the captured image to the maximum of the first column component varied with the degree of unlevelness of the desired surfaces. The performance of the method was compared with five spectral and image based instrumental levelness–unlevelness indices, as well as those reported by visual ranking. Based on the results, the Fourier transformation method and the singular value decomposition technique show the best agreement with visual evaluation results, but the singular value decomposition method requires a longer computation time.     

An analysis of the factors influencing unlevelness of a direct dye on a pilot-scale jet dyeing machine

The investigation used a pilot-scale jet dyeing machine to examine the relationship between the dye exhaustion rate per contact and dye unlevelness on the fabric. It was found that a commercially acceptable degree of unlevelness could be obtained for a direct dye on pure cotton fabric as long as the exhaustion rate did not exceed 1.0% per contact, independent of the dye amount used. Bath contacts and fabric contacts influenced unlevelness in equal manner. Non-ionic surfactants, which had been selected so as not to influence the dye exhaustion rate or its equilibrium uptake, appeared to have little or no influence on unlevelness. Control of the dye uptake by electrolyte addition proved to be a more efficient dyeing strategy than controlling it by dye addition, as unlevelness in the first case was much lower at the same exhaustion rate.     

Package Dyeing of Acrylic Fibre Yarn: Important Parameters which Influence Level Dyeing

Flow rate, ramp (constant rate of temperature rise), and package density are recognized to be particularly important for obtaining uniform uptake in the package dyeing of acrylic fibre yarns. This paper is concerned with the contribution of these three parameters to levelness in this system. An attempt is made to define empirical mathematical relationships between these variables and the observed rate of dyeing, in order to be able to specify those values of these parameters which would be expected to give rise to unlevel dyeings. Linear relationships were found between these parameters and the rate of exhaustion per circulation of the dyebath, expressed either as the overall rate or as separate rates for the two successive stages of the exhaustion process (attributed to adsorption at the surface of the fibre and diffusion into the interior). The equations relating rate of exhaustion to package density, ramp and the reciprocal of the rate of liquor flow can be combined into a single equation. This enables the relative effects of these variables to be calculated. For example, the equation can be used to decide which combination of ramp and flow rate will give a pre–determined rate of exhaustion by a package of given density. In a similar way, the corresponding equation relating the instrumental criterion of degree of unlevelness to package density, ramp and rate of flow forms a convenient means of predicting the effects that these three variables will have on the possibility that unlevel dyeing will occur.     

Dye demand/supply ratio as a predictor for the unlevelness of disperse‐dyed polyester

The ratio of the demand for dye by the fibre and the supply of dye by the dyebath is a useful indicator to predict unlevelness in the exhaust dyeing of polyester with disperse dyes, provided that dispersion breakage is small. The ratio can be calculated from the dye exhaustion curve, the dye solubility and the flow rate in the machine. The findings suggest that unlevelness can be successfully controlled by ensuring that dye demand never exceeds dye supply at any moment during the dyeing process.     

Computer-aided multivariable control system design for processes with time delays

A computer-aided control system design package is described which handles processes with multiple time delays and allows subsequent design of interaction compensators. The package synthesizes control system designs for complex problems in a short time while also providing dynamic simulation for the purpose of evaluating controller performance. Example problems are presented along with a case study on sensitivity to errors in the delays.     

Optimisation of the disperse dyeing process using dyebath analysis

A competitive market forces textile manufacturers to continuously look for ways to increase productivity and resource efficiency. Taking the exhaust dyeing of polyester with disperse dyes as an example, it is shown that detailed process analysis using, among other methods, dyebath monitoring can yield considerable benefits. In the case examined, process cycles for a typical trichromic set of dyes could be shortened by 13% and dye unlevelness on the substrate reduced by 45%. The study confirmed that for optimum performance, process profiles need to be machine-specific since the maximum temperature gradient that yielded commercially acceptable unlevelness varied significantly from one machine to another machine. Received: 4 April 2005; Accepted: 14 June 2005.     

Bulk–scale Dyeing of Acrylic Yarn Packages

Bulk–scale dyeing trials on three different types of acrylic fibre are described. Basic dyes were applied under conditions predicted to give a borderline degree of unlevelness, following earlier laboratory work [1–3] intended to determine the relative importance of different factors which control level dyeing in this system. The results of the dyeing trials are discussed in this context and an attempt is made to attribute the effects observed to specific causes of unlevel uptake of dye.     

Optimal control and operation of drum granulation processes

Process optimisation and optimal control of batch and continuous drum granulation processes are studied in this paper. The main focus of the current research has been: (i) construction of optimisation and control relevant, population balance models through the incorporation of moisture content, drum rotation rate and bed depth into the coalescence kernels; (ii) investigation of optimal operational conditions using constrained optimisation techniques; (iii) development of optimal control algorithms based on discretized population balance equations; and (iv) comprehensive simulation studies on optimal control of both batch and continuous granulation processes. The objective of steady state optimisation is to minimise the recycle rate with minimum cost for continuous processes. It has been identified that the drum rotation-rate, bed depth (material charge), and moisture content of solids are practical decision (design) parameters for system optimisation. The objective for the optimal control of batch granulation processes is to maximize the mass of product-sized particles with minimum time and binder consumption. The objective for the optimal control of the continuous process is to drive the process from one steady state to another in a minimum time with minimum binder consumption, which is also known as the state-driving problem. It has been known for some time that the binder spray-rate is the most effective control (manipulative) variable. Although other possible manipulative variables, such as feed flow-rate and additional powder flow-rate have been investigated in the complete research project, only the single input problem with the binder spray rate as the manipulative variable is addressed in the paper to demonstrate the methodology. It can be shown from simulation results that the proposed models are suitable for control and optimisation studies, and the optimisation algorithms connected with either steady state or dynamic models are successful for the determination of optimal operational conditions and dynamic trajectories with good convergence properties.     

Mechanistic investigations on the action of levelling agents in reactive wool dyeing

Although levelling agents for reactive dyes have been on the market for more than twenty years, there still remains some uncertainty as to their mode of action. Therefore an investigation has been carried out, using Albegal B as a typical levelling agent and reactive dyes from the Lanasol range. There are three mechanisms proposed to describe how auxiliaries such as Albegal B can act to overcome tip/root unlevelness when dyeing wool fibres: a dye complex mechanism, a surface mechanism and a fibre mechanism. These are discussed in the light of the experimental results.     

文丘里型气液分布器的实验与数值研究

以一种文丘里型气液分布器为对象,在直径为28 cm的冷模装置中考察了其流体力学性能。气、液流量分别在5~25 m³·h^-1、0.2~0.6 m³·h^-1范围内,使用激光粒度仪测量了液滴Sauter平均粒径（D₃₂）,并测定了其分布均匀性和抗塔板倾斜性能。结果表明：文丘里结构加强了气液混合,与泡罩型分布器相比,此分布器具有更好的液滴破碎性能;气速增大会使出口液体从伞状流变为喷射流,但仍能在直径约为出口直径10倍的区域内均匀分布;在气、液相负荷分别为10~20 m³·h^-1、0.4~0.6 m³·h^-1时,液位在进液口和进气口之间,此时分布器具有优异的抗塔板倾斜性能。采用计算流体力学软件模拟了分布器内部气液流动过程,得到了相含率和速度矢量图,所得结果有利于分布器的分析与改进。     

Chemical engineering aspects of reactive dyeing

The process of dyeing with reactive dyes was formulated on the basis of diffusion of dye species in the pores of polymer phase accompanied by fixation reaction with fiber substrate on the pore wall incorporating hydrolysis of dye species. The effect of the hydrolysis on the fractional fixation was numerically analyzed under various levels of bath ratio and degree of mixing in the dyebath. The simulation model was presented to yield the unlevelness arisen from lack of uniformity of degree of mixing in the dyebath.     

Designing control system with entropic modeling

Contributions of entropic modeling to the performance of reactive process control have been investigated. Modeling has been developed based on mass, energy and entropy balances and thermodynamic relations, resulting in a model for the entropy production rate. Using the conventional optimization technique, a minimum for the entropy production rate was found when a given relationship between the temperatures of the inlet stream and of the reaction is satisfied for a particular residence time in the reactor. A new class of nonlinear controller is proposed by means of introducing entropic models into the classical algorithms designed from a synthesis of the reference system. The results indicate that such a controller yields a superior performance when compared with classical feedback control strategies.     

An objective method for the assessment of levelness of dyed materials

An objective method for the assessment of levelness of dyed materials has been established. The relative unlevelness index developed takes account of the coefficients of variation of reflectance measured over the visible spectrum, with appropriate consideration of human vision sensitivity. It was found that the index demonstrated good correlation with the visual levelness assessment.     

Time-optimal control of mmama copolymerization in a CSTR for grade change

The time-optimal control of MMA-MA copolymerization in a CSTR is treated for a grade-change operation. The control objective is to bring system specifications, such as polymer production rate and polymer composition, to desired values in minimum time. The initiator concentration is chosen as a manipulated variable. Two cases are considered: One is to get the time optimal control for both a desired polymer production rate and a desired weight composition of MA in dead copolymer; the other is only for a desired polymer production rate. In numerical calculation, the final t(ⁱ)_f is chosen at each iteration as the time at which the system reached steady-state. This allows us to use a more easily manipulatable form of the performance index and at the same time not directly use the free final time boundary condition.     

Integrated design and control of semicontinuous distillation systems utilizing mixed integer dynamic optimization

Semicontinuous distillation systems are notoriously difficult to design and optimize because the structural parameters, operational parameters, and control system must all be determined simultaneously. In the past 15 years of research into semicontinuous systems, studies of the optimal design of these systems have all been limited in scope to small subsets of the parameters, which yields suboptimal and often unsatisfactory results. In this work, for the first time, the problem of integrated design and control of semicontinuous distillation processes is studied by using a mixed integer dynamic optimization (MIDO) problem formulation to optimize both the structural and control tuning parameters of the system. The public model library (PML) of gPROMS is used to simulate the process and the built-in optimization package of gPROMS is used to solve the MIDO via the deterministic outer approximation method. The optimization results are then compared to the heuristic particle swarm optimization (PSO) method.     

COMPUTER AIDED OPTIMAL HEAT EXCHANGER NETWORK SYNTHESIS BY A TWO-STAGE METHOD

This paper presents a two-stage method for the optimal heat exchanger network synthesis.In the firststage based on the study of the pinch point properties,a network minimizing the utility consumption and thenumber of exchangers is developed.Usually,this network is close to the optimal.In the second stage,anonlinear programming formulation is developed,and its solution with features of minimum capital andannual operating costs provides an improvement on the network obtained in the first stage.An integratedsoftware package for heat exchanger network synthesis has been developed.This package consists of a sp-readsheet,a graphics program,a data base management system,a menu program,an application networksynthesis program,a network simulation program and a data base of standard size exchangers.The appli-cation of this method is illustrated with several examples which include a complex crude oil preheating heatexchanger network.     

多阶段间歇过程无穷时域优化线性二次容错控制

针对具有输入时滞的多阶段间歇过程,考虑执行器故障影响,提出了无穷时域优化混杂容错控制器设计方法。该方法首先将给定具有输入时滞的模型转化为新的无时滞的状态空间模型,接着再将此模型转换为包含状态变量误差和输出跟踪误差的扩展状态空间模型,并用切换系统模型表示,然后引入有限时域的二次目标函数,利用最优控制理论,设计出在无穷时域中容错控制器。为获得最小运行时间,针对不同阶段设计依赖于Lyapunov函数的驻留时间方法。创新之处在于,控制律设计简单,计算量小,且每一阶段时间求取不需要引用任何其他变量,简单易行。最后,以注塑成型过程为例,仿真结果证明所提出方法具有可行性和有效性。     

大型化直立炉DCS控制系统

介绍了大型化连续式直立炉自动化系统的主要组成和各工艺的控制功能。针对现有直立炉装备水平低、人工操作效率低、劳动强度大、操作环境差等问题,采用Web Field ECS-100控制系统和Advan Trol-Pro软件包实现对工艺过程的监视控制和设备的连锁运行。该系统的运行,为规范大型化直立炉自动化系统的设计做出了有益的探索。