Analysis of Fiber-Particle-Airflow Interaction and Its Application to the Development of a Novel Card-Spinning System

Transcription

1 F98-G15 Page 1 Analysis of Fiber-Particle-Airflow Interaction and Its Application to the Development of a Novel Card-Spinning System Investigators: Students: Youjiang Wang (leader), Mary Lynn Realff, Wallace W. Carr, Radhakrishnaiah Parachuru, J. Lewis Dorrity, Fred L. Cook, Xi Chen (Georgia Tech) Bhuvenesh C. Goswami, David A. Zumbrunnen (Clemson) Jimmy Chowdhury, Jen-te Yu, Mandy Kratus, Shumin Zheng (Georgia Tech) Kai Liu (Clemson) PROJECT GOAL The goal of this project is to create the fundamental knowledge needed to develop more efficient machines and novel processes that can potentially decrease the number of process steps by a factor of 2 to 3 in short staple yarn manufacturing. ABSTRACT Currently, the process sequence for short staple yarn manufacturing involves about ten individual steps. To develop more efficient machines and novel processes that can significantly shorten the processing line, we are currently conducting research in the following two interrelated areas: (1) To analyze the motion dynamics of fiber clumps and particles in an airflow field, especially the effect of flow pattern and barrier arrangements on fiber opening, trash removal, self-leveling, nep formation, and fiber loss in opening, cleaning and carding; and (2) To develop a single-step process (Card-Spinning) to incorporate multiple spinning heads into a carding unit. This will require a fundamental analysis and understanding of web uniformity monitoring, measurement, and regulation, web division, and feeding of web ribbons into yarn spinning heads positioned at the front end of the card. Since the start of the project in May 1998, we have conducted a state-of-the-art literature survey on airflow in yarn processing, card web uniformity monitoring and control, fiber web transport, and high speed yarn spinning. Literature on current processing machinery has also been studied. We have met with industrial partners to discuss the interactions necessary to make the project successful. Studies are underway on experimental and theoretical analysis of air flow, web uniformity detection, and spinning head design. INTRODUCTION In the past decades, yarn manufacturing has transformed from a labor intensive operation to a capital intensive one. Within this century, the operator productivity has increased by three orders of magnitude, as a result of a series of innovations, as illustrated in Figure 1. The new technologies also bring products that have different characteristics from the traditional process, one example being the different yarn structures obtained from ring, rotor, and airjet spinning technologies.

2 F98-G15 Page 2 Productivity, g/spindle-hour filament texturing open-end spinning ring spinning mule spinning 1 hand spinning Year Figure 1. Illustration of Technological Innovations in Yarn Spinning Some generic approaches toward technological development include: 1. Extrapolation of process speeds in traditional manufacturing methods (e.g., increasing speeds) 2. Innovative modification of current processes (e.g., decoupling or coupling of processes) 3. Development of radically different methods of manufacturing traditional products (e.g., friction spinning) 4. Development of radically different products to replace conventional fabrics (e.g., nonwovens) In this project, we are exploiting the first three approaches to make individual processes better, to couple carding and spinning processes, and to explore new designs for making staple yarns. Staple yarn manufacturing involves four essential operations: fiber separation, parallelization, attenuation, and consolidation. The manufacturing process must produce quality products consistently and economically. Currently, several machines (about 10) in sequence are needed for these tasks. We have obtained descriptions of machinery from the leading manufacturers. Although the systems differ, they typically include the following machines in sequence for a carded yarn: Bale opener Coarse opener/cleaner Blender Intermediate opener/cleaner Fine opener/cleaner Card Draw frame (breaker drawing)

3 F98-G15 Page 3 Draw frame (finisher drawing) Yarn formation (e.g., roving and ring spinning, rotor spinning, airjet spinning, etc.) The need for such a long processing sequence is due to the four essential operations involved. If a machine can be improved so as to accomplish multitasks, this may eliminate the need for one or more machines in the sequence. For example, the drawing process is to enhance fiber blending, parallelization, and sliver uniformity. In some rotor spun yarn processes drawing has been eliminated through the use of cards equipped with effective autolevelers. Although the productivity of current manufacturing systems continues to increase, further developments require a better understanding of the fundamental principles of the processes. This includes analyzing the motion dynamics of fiber clumps and other particles in an airflow field, and developing a single-step process (Card-Spinning) to convert fiber batt directly into yarns. OPENING AND CLEANING The opening and cleaning process is the first part in a staple yarn manufacturing line. It opens fiber bales into small tufts, removes most of the impurities, and blends fibers together. Airflow plays a very important role in determining the efficiency and quality of the opening/cleaning operations. Fiber opening, cleaning, and transport in the opening and cleaning processes are achieved through interactions among airflow, inertia forces, gravity, fiber/particle configurations, barrier arrangements (mote knives, grid bars, plates, etc.), beating actions, carding actions, among others. Although some studies have been conducted in this area (e.g., [1] on opening and cleaning and [2,3,4] on carding), the depth has been limited due to the complexity of the problem. In our discussions with the machine manufacturers, we have tried to learn about the processes and tools used to design the machines. Despite that few papers appear in recent literature on air flow in opening and carding, effective use of airflow to assist fiber opening and cleaning can be found in the latest machines such as the Trutzschler CLEANOMAT cleaners, Rieter cleaners, as well as in devices like heavy particle extractor, deduster, condenser, and chute feeder. With the availability of modern tools such as computational fluid dynamics (CFD), computational solid mechanics, and fluid flow visualization using high-speed videography, a better understanding of airflow in yarn processing is possible. We are building simulation models using the FLUENT CFD software to analyze the fluid flow in cleaners and other devices. Figure 2 illustrates the static pressure distribution and airflow streamlines in a heavy particle extractor. Airflow acceleration, deceleration, and flow separation (vortices at A and B) were observed. The flow pattern changes as fibers and particles are introduced in the flow, as the movement of solid particles is affected by the air drag and their own inertia. Because air, fibers and trash particles do not accelerate or decelerate at the same rate, these components may be separated in a properly designed flow field. To complement the analytical studies, experiments on actual machines and on laboratory models will be conducted to verify the results.

4 F98-G15 Page 4 Figure 2. Static pressure distribution and streamlines in a particle extractor CARDING In a traditional process, carding individualizes fibers, removes fine impurities and neps, and forms a sliver. We are also developing a novel process (Card-Spinning) by incorporating multiple spinning heads on the carding machine itself. This single machine will replace the card, two drawframes and the yarn-spinning machine. The elimination of the drawing processes makes it necessary for the card to assume additional responsibility in fiber alignment and straightening, and in mass regulation. To achieve this, the airflow analysis will be extended to study the interaction among fibers, airflow and cleaning/carding elements of the card. This along with improved card clothing design, altered speeds and settings, and superior mass regulating devices in the card should lead to better longitudinal and transverse web uniformity. The research team has completed a literature survey, contacted several instrumentation vendors, and conducted preliminary tests in an effort to identify instrumentation and techniques for determining card web uniformity in the cross and machine directions for web produced by current carding machines [5,6,7,8,9]. The technique for measuring card web uniformity must be capable of determining card web uniformity in the cross and machine directions for webs produced by current state of the art carding machines. The system should also be capable of measuring higher areal densities than produced on today s cards since the new process may require a heavier carded web. We have evaluated several methods that have the potential for measuring card web areal density. These include: beta gauge, gamma gauge, capacitance, laser scanning, image analysis, fiber optics, ultrasound infrared absorption, and Video Image Analysis. These methods are summarized in Table I. Our study using Video Image Analysis indicates that this technique to measure the areal density in light-weight webs has possibilities. Initial results show that using reflected light with proper calibration may be sufficient to indirectly measure weight by analyzing the pixel values form the card web. This will require careful calibration to correct for non-uniformity in illumination. Our first step is to develop the correlation between pixel intensities and actual weight for a given

5 F98-G15 Page 5 TABLE I. Techniques with Potential for Measuring Card Web Uniformity Method Principle Applicable areal weight Beta Gauge Atomic Reflectance: absorption and 5-50 g/sm scattering of Transmittence: beta radiation >50 g/sm Gamma Gauge Capacitance Atomic absorption and scattering of gamma radiation Bulk dielectric properties Reflectance: 5-50 g/sm. Transmittence: > 50 g/sm. Accurate measurements for >50 g/sm. Advantages Accurate and repeatable Accurate readings for slivers. Inexpensive Disadvantages Uses nuclear radiation. Scans rate may not be sufficient. Very expensive Poor accuracy for organic materials. Very expensive. Uses nuclear radiation. Ineffective for lightweight (5-50 g/sm.) webs Laser Scanning Image Analysis Fiber Optics Ultrasound Infrared Absorption Transmittence and intensity detection of HeNe laser beam Reflected or transmitted light with a digitized camera Usage of reflectance with optical fibers to determine thickness Time dependant thickness measurement with reflectance of ultrasound. Molecular Absorption by chemical bonds at specific wavelengths Areal density < 45 g/sm Detectable range is yet to be determined Detectable range is yet to be determined Areal density > 5 g/sm. More accurate for thicker webs (>50 g/sm). Areal Density > 3 g/sm Less then 2% error for webs less then 45 g/sm. Not as expensive as beta/gamma gauges Inexpensive Simple setup. Relatively inexpensive ($1500/unit) Better accuracy then fiber optics Fairly inexpensive. Accurate and repeatable (within 5%) measurements. Affordable testing equipment. Poor accuracy for webs with areal density > 45 g/sm Attempted analysis of basis weight has been unsuccessful. Material thickness 1.3 mm required. Not accurate for materials with high transmissivity and low reflectivity and diffuse surface, e.g., a carded web. Results are affected by surface angle, surface roughness, and temperature. Reflectivity tests are not as reliable as transmission tests.

6 F98-G15 Page 6 Web Weight (grams/m2) Sum of Pixel values (thousand) Figure 3. web weight versus camera pixel value fiber. Since the color of the fiber would also affect the reflected light, an absolute measure is not possible using this technique if visible light is used. It may however be an excellent means of measuring relative densities, which could be used for control. Figure 3 illustrates the test result of web weight versus camera pixel value with static samples and an array camera. Although a clear correlation can be observed, the coefficient of correlation R 2 (0.74) is not very high due to nonuniform illumination. Correcting for these non-uniformities should significantly improve the correlation. On-line implementation on a card would require a line-scan camera and a line source of light. The video image analysis technique may possibly be applied using infrared (IR) radiation. We have investigated the effects of web basis weight of on the IR transmissivity and reflectivity properties of the web. The infrared range studied was from 0.66 to 20 micrometers. We tested four pieces of polyester card webs, each with a different areal density, ranging from 4.8 to 21.8 g/sm. The results clearly showed that as the areal density of the web increased, reflectivity increased and transmissivity decreased for almost all wavelengths. As would be expected, IR absorbency of the web also went up as the areal density increased. The magnitude of variation in transmissivity with areal density was larger than for reflectivity. While transmissivity varied from 30 to 70 percent, reflectivity changed from 5 to 15 percent. Transmissivity tests were also repeatable with more precision than reflectivity tests. Once a suitable web monitoring device is identified, it will be modified and installed on a card for online operation. After testing for effectiveness, this will be coupled with a suitable mass uniformity regulating device to control the web mass uniformity in both the machine and cross directions.

7 F98-G15 Page 7 YARN FORMATION In a traditional staple yarn spinning system, fibers are opened and or cleaned, carded, drawn and reduced to a stand before spinning (twisting). One of the objectives of this project is to design a system where the short staple fibers in the carded web can be spun directly into a yarn before the web is consolidated into a sliver. Literature research shows that the only system where the short staple (cotton type) fibers are converted into a yarn in a shortened process is the one where sliver (carded and drawn) is processed into a ring spun, a rotor spun or an air-jet spun yarn, thus eliminating the extra step of drawing and roving. One of the short staple spinning systems that has achieved commercial success is the air jet (vortex) spinning system. Most of the published literature on air jet or vortex spinning systems is in the patent literature and deals with the design of the vortex nozzle [10,11,12,13]. In the design of the vortex nozzle, attention is directed at straightening the fibers, twisting the bundle, and providing tension and forward motion to the twisted structure with a minimum of air consumption. The yarns produced have relatively low strength; low compressive characters and consequently hard feel than the corresponding ring spun yarns. The obvious reasons for such a behavior are the arrangement of fibers in the yarn structure. Currently we are concentrating on designing a system where a ribbon from the carded web will be doffed and delivered to a vortex nozzle where the fibers will be twisted in to a yarn structure and subsequently delivered through delivery rolls to a winding unit. The primary effort is being directed at designing a "complex nozzle" where the carded fibers when fed into the nozzle will be straightened to the maximum achievable extent before being twisted (in the second part of the nozzle) into a yarn. The design of the nozzle will be such that is will minimize turbulence in the vortex to achieve maximum twisting efficiency. To accomplish this, computational fluid dynamics modeling will be use to guide the design process, and a large scale model sized using scaling laws will be built to enable the observation of fiber movement using a video camera and a still camera with a stroboscope. A prototype yarn spinning unit will then be designed, fabricated, and tested in the laboratory. SYSTEM INTEGRATION We have analyzed the effect of card web areal density and speed on card-spinning parameters. The calculations show the effects of changing the card web areal density on card web speed, required draft, and final yarn speed for three yarn counts of 2 s, 4 s, 10 s and for card web divisions of 2, 4, 8 and 16. We have varied the mass flow rate of the card from 25 to 150 lb./hr. Table II shows the analysis for a 50 lbs./hr flow rate with different numbers of web slits and final yarn count. Web speed for a card producing a one-yard wide web at a mass flow-rate of 50 lbs./hr is approximately 100 yd./min. Depending on the number of splits and draft required to produce a yarn of specified count, the final yarn delivery speed can vary greatly and may exceed the exit speed of currently available spinning systems, which is approximately 200 to 450 yd./min., as illustrated in Figure 4. It also shows that the web weight has no effect on the yarn delivery

8 F98-G15 Page 8 Yarn Speed vs. # of Web Splits (for 50lbs/hr mass flowrate) 4,000 3, grains/yd web 240 grains/yd web 480 grains/yd web 3,000 Yarn Exit Speed (yd/min) 2,500 2,000 1,500 1, # of Web Splits Figure 4. Effect of number of web splits and web weight on the delivery speed of a 10 s yarn speed, although it affects the draft ratio required. This analysis provides a guideline for the section of processing variables, and possibly points to a need for developing faster yarn spinning systems that can extend the range of yarns to be produced on the system. Additional effort is needed to develop technologies to split the web into ribbon strips and to transport them to the spinning units. SUMMARY To develop more efficient machines and novel processes that can significantly shorten the processing line, we are currently conducting research on the motion dynamics of fiber clumps and particles in an airflow field and on the development of a single-step process (Card-Spinning) to incorporate multiple spinning heads into a carding unit. We have conducted a state-of-the-art literature survey on airflow in yarn processing, card web uniformity monitoring and control, fiber web transport, and high speed yarn spinning. The project has received significant interest from the textile and the machinery industries, and we have interacted with industrial partners for collaborative approaches to make the project successful. Progress has been made in the various fronts of the project, and the results to date are very encouraging. Continuing effort is underway

9 F98-G15 Page 9 on experimental and theoretical analysis of air flow, web uniformity detection, and spinning head design. Table II. Relationship among Web Weight, Number of Splits, Yarn Count, Draft Ratio, and Yarn Delivery Speed for a 100 lb./hr Flow Rate Web Weight Web Linear No. of Web Ribbon Yarn Required Yarn Delivery Speed Splits Count Count Draft Speed grains/yd yd/min Ne Ne yd/min , , , , , ,

10 F98-G15 Page 10 References 1 W. Bostock, S.M. Freeman, S.A. Shorter and T.C. Williams, An aerodynamical study of the opening and cleaning of cotton by existing machinery, J. Tex. Inst., 1955, T P.M. Strang, Air shearing force separates fibers, Am. Wool & Cotton Reporter, August 1949, p12. 3 G. Merenyi, Methods of control of strips and effect of air currents in carding, Tex. Manufacturer, 1957, p27. 4 A.L. Miller, R.S. Brown, and R.A. Ruca, An investigation of air pressures in the cotton carding machine, Tex. Res. J., July 1958, p P. Boeckerman, Meeting the Special Requirements for On-line Basis Weight Measurement of Lightweight Nonwoven Fabrics TAPPI Nonwovens Conference, L. Crook, and K. Staats, Carded Webs An Overview of Methods Used to Produce Parallel and Random Webs for Print Bonding and Thermal Bonding TAPPI Nonwovens Conference, 1984, p21. 7 T.R. Wan, G.A.V. Leaf, C. Iype, A New Objective Method for Assessing Fibre Arrangement in Fibrous Webs. J. Text. Inst. 86 No. 4, 1995, p A. Cherkassky, Analysis and Simulation of Nonwoven Irregularity and Nonhomogeneity. Textile Res. J. 68(4), 1998, p R.K. Aggarwal, W.R. Kennon, and I. Porat, A Scanned-laser Technique for monitoring Fibrous Webs and Nonwoven Fabrics. J. Text. Inst. 83 No.3, 1992, p E. Pallay, "Method of and apparatus for spinning yarn in an air vortex in a Spinning tube", USA patent: , Nov, 20, S. Didek, L. Fajt, M. Reymanova, M. Markova, "Method of and apparatus for spinning yarn from staple fibers in an air vortex", USA patent: ,nov 19, D. A. Bahov, H. A. Bahov, "Vortex air nozzle for yarn spinning from staple fibers". USA patent: ,Sep, 1, H. Stadler, R. Ammann, "Method of producing a rotating air layer and false-twist air jet nozzle for practicing such method", USA patent: , Jun 19,1990.