Yarn Performance During Weaving

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C92C2Material and Machine Interaction During Weaving

(i) Structure Property Relationship in Ring/Rotor/Air Jet Spun Yarns

(ii) Yarn Performance During Weaving

PI(s): Clemson:

Bhuvenesh C. Goswami, Professor (Team Leader)Rajesh D. Anandjiwala, Research Associate/Asst. ProfessorTony Shan, Ph. D. StudentS. Yellambalse, Ph. D. Student P

NCSU:William Oxenham, Professor, Graduate Student (will join program in the 3rd year)

Relevance to NTC Goals:

Staple yarns form the bulk of the manufacturing activity of the U.S. textile industry. Staple fiber yams areutilized in the making of apparel, upholstery and industrial fabrics. Yarns may be made from natural staple fibersor from a variety of synthetic fibers or from the blends of different fibers. As a matter of fact, blends constitute abulk of the staple yarns manufactured in the U.S. Although both natural (primarily cotton) and synthetic fibers(primarily polyester) have geometric and physical properties that meet most, if not all of the end-use requirementsfor a variety of applications. However, the limits in the utilization and translation of the physical and mechanicalproperties of fibers into yarns are strongly influenced by the system of manufacturing. We believe that by delineating

the role played by the fiber/machine interactions in determining the characteristics of the final products, i.e. yarns

that the U.S. textile industry will be able to better utilize the raw materials and improve the product quality. Theproposed work in this project is concerned with the fundamental aspects of studying the factors that influence theyarn structure and consequently the properties of the resultant yarns spun with various spinning systems especiallythe air jet and rotor systems.

Spun yarns, especially the blends made from cotton and polyester are consumed in large quantities both bythe weaving and knitting industry. The yarn structure has a very profound influence on the physical and mechanicalproperties of yarns and fabrics but also determines the processing efficiency during knitting and weaving. Theintroduction of tine synthetic fibers in the apparel and industrial yarns coupled with the high speed air jet spinningand weaving has created problems but at the same tile opportunities for the textile manufacturers in the U.S. SinceU.S. textile industry is the only country at the present that has any significant activity in the air jet spinning,consequently, a thorough understanding of the material and machine interaction can only help the U.S. industrycompete with the imports. The emphasis in this project has been to understand the structure development in existing

systems. The proposed work in this area will be concerned with studies on how twist flows in the twisting zone,modification of already twisted yarns to achieve higher strength in the air-jet yarns and high draft during spinning

on the structure and properties of both cotton and blended yarns. Air jet spinning is the fastest system of producingstaple yarns. Rotor spinning and ring spinning follow air jet in that order in terms of productivity of the systems.However, ring spun yarns are the strongest followed by rotor spun yarns and the air jet yarns are the weakest,provided all other factors are constant. The rotor and the air jet systems are amenable to automation and the yarnsthat can be produced on these systems cover a very wide range of yarn linear densities customarily produced in the

U.S. Process and better material utilization will enhance the capabilities of the textile industry. The productcharacteristics that meet the end use requirements will give the industry an added strength in meeting globalcompetition. The information generated in this project will help the entire textile industry in improving the processof twisting in staple yarn spinning thus meeting the goals of National Textile Center.

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Objectives

The objectives of this study are to understand the dynamics of the interaction of fibers and yarns with themachines during processing. To achieve these objectives it is important to have a theoretical understanding of the

process of yarn formation and how the processing factors influence the disposition of fibers in the yarn structure.Also, it is important to understand the behavior of the yams structure and characteristics during the subsequentprocesses such as in winding and weaving.

Technical Approach and Experimental

To achieve these objectives simultaneous studies on the structure property relationship in yarns made on

different spinning systems and the performance of these yarns during weaving are being studied, The spun yarnsmade from 50:50 blends of micro denier polyester (0.7 denier, low and high tenacity) and cotton have ken spunon ring, rotor and air jet systems. The yarns have been spun at three different twist levels on each spinning system.Fiber distribution in yarns cross sections and the blend homogeneity have been studied. The mechanical propertiesof these yarns have been determined at different strain rates, e.g. 10, 50. 100 and 200 % per minute to simulatevarious conditions of subsequent end use such as winding, weaving etc. The fatigue behavior of sized and unsizedyarns has been studied on the Sulzer-Ruti Webtester where all the forces that a yarn experiences during weaving aresimulated.

(i) Structure Property Relations in Ring/Rotor/Airjet Yarns

Literature Review

The engineering design of a yarn involves, in essence, the investigation of its mechanical response in termsof constituent fiber properties and yarn structure which is decided by the distribution of fibers in a cross section andlongitudinal fiber migration along the yarn axis [l]. The complex interrelationship of fiber and yarn structure isdecided by the process of yarn formation, i.e. the interaction of material with the spinning system [Z]. The structureproperty relationships have been investigated for ring spun [2,3]. open-end rotor [4-61 open-end friction [7,8] andfor air-jet-spun [9-l 11 yarns.

All the published research work cited above pertains to the yarns made from single component fiber eitherof natural origin or synthetic of normal denier (1.2 to 1.6). The micro fibers provide better handle, drape, luster,

smoothness and comfort [121. Micro fibers are expected to yield uniform yarn because they can be easily wrappedaround the core due to their low bending rigidity [13]. Therefore, to understand the final yarn behavior, which inturn affects the machine performance in the subsequent process, it is important to understand the structure propertyrelationship of blended yarns made from such micro fiber polyester and cotton.

Experimental

The experimental part of the study is concerned with the establishment of structure-property relationship

in spun yarns made from 50:50 blend of micro denier polyester and cotton on various spinning systems viz. ring,rotor and air-jet. To pursue this objective yarns were spun at three different twist levels for each spinning methodto understand the effect of twist on yarn structure. Tensile response of these yams was tested at various strain rates

(10, 50, 100 and 200 % per minute). Fiber distribution in yarn cross-section was studied along with blendhomogeneity for yarns spun from all three spinning systems under study. Further work on longitudinal migrationusing digital image analysis technique is under progress.

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Two different micro-denier polyesters. both with same denier (0.7) but with different tenacity and elongationwere selected for blending with Upland cotton (3.9 micronnaire). The blending was carried out at the draw framestage. Ring spun yarns were spun at twist levels of 3601. 3791 and 3980 texsi. Yarns were spun on rotor spinningsystem at twist levels of 3601.3980, and 4731 texsi. In air jet spinning yarns were spun at second nozzle pressuresof 4.0, 4.5 and 5.0 kglcm.

Yam cross-sections were prepared by standard microtome technique [14] as used in our previous work [2].Evenness of various yarns were measured using an Uster evenness tester. Tensile properties of yarns at various strain

rates were measured on an Instron tensile tester at a gauge length of 10 inches.

Results

Fiber density distribution was carried out according to the method suggested by Driscoll and Pestle [151.From the fiber distributions obtained it is seen that in both ring and rotor spun yarns, fiber packing density decreasesparabolically with the increase in yarn radius. Typical fiber packing density distributions are shown in Figures 1 and2 for ring and rotor spun yarns, respectively. In air-jet spun yams the fiber packing density distribution tends to belinear for all yarns as shown in Figures 3 an 4. These findings are consistent with our earlier published results [I].Tables 1 and 2 show the coefficients of parabolic fit to fiber packing density distribution for all yarns under study.The technical significance of the variations in the values of coefficients for different types of yarns is being studiedin terms of the stress-strain behavior of these yarns.

The range of twist studied in the present program did not seem to have any influence on fiber packingdensity. The blend homogeneity characterized by Hamiltons method [163. as shown in Table 3, indicates that cottonfibers migrate towards surface of yarn for both ring and air-jet spun yarns, whereas in rotor spun yarns it tends tomigrate towards the core of the yarn. From the tensile properties studies it appears that , in the absence of anyclusters, the yarn tenacity increases with the increase in strain rate as shown in Tables 4 and 5. Presence of fiberclusters in the yarn structure tends to decrease the yarn tenacity at the increasing strain rates. The findings in thisstudy agrees well with some reported results by other authors [171. Figure 5 shows the presence of clusters as seenin ring yarn spun at twist multiplier of 3980 tex.(ii) Yarn Performance During Weaving

Literature Review

In the traditional approaches to the problem of assessing warp yarn performance on the loom, researchershave investigated tensile strength of sized yarn and attempted to correlate it with weavability [18,19]. However, theuse of such tensile strength approach has not shown consistent correlations to weavability because the process ofweaving is far more complex and several authors have raised doubts as to this approach [20,21]. The failure of sizedyarns on a loom is attributed to the cumulative damage caused by cyclic fatigue of relatively small forces combinedwith abrasion [22].The failure of warp yarns on a loom is caused by repeated cyclic elongation at small stresses well below the breakingpoint applied under static load [23,24]. The phenomenon commonly known as fatigue [25], is caused by the graduallydiminishing resistance of the material, attributable to cumulative damage. Earlier attempts to characterize the fatigueperformance of various materials, including textiles, were made in terms of average, median, or logarithmic lifetimes[26-281. Fatigue behavior of sized staple yam under cyclic loading follows three parameter Weibull distribution[23,26-281. However, some studies have reported unimodal [29] distribution whereas other studies have shownbimodal distribution 1301. This poses a formidable problem in understanding the mechanism of yam failure undertensile loading, since the mechanism involved in bimodal behavior is inherently different from that in unimodalWeibull distribution [23].

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A data capturing board (model DT2801. Digital Translation) capable of converting singleended/differential/mu/bipolar analog signals to digital output is used. The board is set, calibrated and programmedto carry out required analog/digital translation. The software sets the data capturing boards clock to 10 Hz (0.1set).The clock rate used is slightly slow because of the slow speed of interpreted BASIC language, however, it issufficiently accurate for the purpose of the tension measurement of the yarn on the loom. The computer programprepared requests the user to specify A/D input channels, the gain rate and the total number of A/D conversions. The

block of A/D conversion at the rate of internal clock frequency takes place and it calculates the input values fromthe converted data and prints out the A/D input for the entire block. A graphic program is incorporated to plot the

values of signals recorded against time at an interval of 0.1 second. We have just completed this part of the workand now the instrument set-up is ready for actual measurement of tension on the loom. After necessary refinements,we shall collect dynamic tension profiles, which will be reported in the next report period.

Proposed Work

So far one student has finished work for a masters thesis and a part of his work has been presented in the

annual report. Three Ph. D. students, two at Clemson and one at NC state have chosen the area of material/machineinteraction for their thesis topic. (1) One topic is the twist distribution in the spinning zone in air jet spinning, (2)a second thesis topic is the translation ofyam structure and fiber properties in yarn properties spun from fine denierfibers on ring, rotor and air jet yarns. (3) The third thesis topic will be the influence of drafting conditions on thequality of air jet yarns. Our previous results have shown that drafting has a tremendous effect on the clustering offibers in the yarn and consequently on the structure and properties of resultant yarns. A possible (4) fourth topicwhich has come about as a result of the experience of one of the investigators is the post treatment (use of crossbelttwisting of air jet yarns) to modify the distribution and disposition of surface fibers in the air jet yarns to improvethe strength of cotton yarns. The literature on the development of structure and twist geometry in air jet spun yarns

is scarce [10,11,31,32]. The kinematic approach suggested by Grosberg et al [ill does not agree with the actual twistdistribution and there are presumably some contradictions that occur between the theoretical and the experimentallyobserved results. Similarly, the kinematic approach suggested by Miio and Chen [33] (M = KT, a simple linearapproach to the relationship between moment and twist) does not agree with the experimental work. A modifiedapproach which combines both the aforementioned approaches is proposed and is currently being analyzed. In themodified approach it is postulated that the twist in the strand is minimum at the two extremities of the fiber bundleand it is maximum in the middle which corresponds to the position of the air jet (nozzle). All three approaches areshown in Figure 6.

The instrument set-up and preparation of necessary softwarefor measuring the dynamic tension variationhave just been completed. After necessary calibration of this instrument, dynamic tension variation profiles during

actual weaving trials will be studied. Actual break data on working of open-end yarn beam will be commenced

shortly. The analysis and correlation of the warp stops to laboratory evaluation will be reported in the subsequentreports. To assess the microscopic damage that the yarn experiences during the process of weaving, the broken endswill be examined under the electron microscope. The type of breakage will be correlated with the distribution of

fibers in the yarn. This exercise will help in engineering yarns where the fibers will contribute the desiredcharacteristics needed in the winding and weaving operations.

References

HIPI[ 3 1

B.C. Goswarni, R.D. Anandjiwala and M. Carrnical, Engineering of Fiber Properties for Spinning on Various

Systems, J. Appl. Poly. Sci.: Applied Polymer Symposium 47, 464-485, pp 463485 (1991).J.W.S. Hearle, in Tomorrows Yarns, Conference at UMIST, June 1984.

J.W.S. Hearle, On the Theory of the Mechanics of Twisted Yarns, J.Text. Inst., 60, T95-101 (1969).

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EgUre 5 Dirlribulion or Fibcn in Yam Ours Sodon :Ring Spun, Yarn f r o m Dlend or 915WPolyu~u and COIIOII 11 Twirl Mulliplicr

0f3980 .

nclx)bI

0 r TN(b) Kinetic analysis

(a) Kincmahc analysis

(c) Modifted rppmach

Figure 6: Twist distribution by vsrious mclhodr

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Yarn Performance During Weaving

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