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Drafting Dynamics of Fine Denier Polyester Fibers

Posted on: Thursday, 8 July 2004, 06:00 CDT

ABSTRACT

It is important to understand the role of fiber properties in the drafting process. Finer denier fibers may have different drafting behaviors than average denier fibers, such as drafting force, required roller settings, draft distribution, and velocity change zone. The objective of this work is to study the interaction of specific fiber fineness values and the drawing machine. Three different fine denier polyester fibers (0.8, 1.0, and 1.2) are run on a three-over-three roller drafting machine set at six different drafts with three roller settings. A high-speed video camera system observes fiber movements and measures fiber speeds in the drafting zone. In this study, fiber speed and variations in fiber speed are significantly affected by fiber fineness and drafting conditions. Fineness changes drafting behavior by introducing fiber clusters and fiber contact points. The acceleration process depends on the interaction of static and dynamic friction forces at the fiber contact points. Therefore, fiber movement in the drafting zone is not a continuous process, that is, it consists of local acceleration and slowing down of segments of fibers.

Different methods have been used to observe fiber drafting behavior. Taylor [9] used radio-activated wool fibers to determine the proportion of fibers that accelerate to the front roller speed at any given time. Over a large part of the drafting zone, floating fibers achieve speeds greater than back roller speeds for a limited time, and they have only two speeds during their transfer through the drafting zone. Later, from a high-speed photography experiment, Taylor [10] confirmed that floating fibers achieve speeds intermediate between those of the back and front rollers.

McVittie and Barr [5] observed the movement of colored fibers in an apron drafting system with a microscope. They reported that the motion of floating fibers was determined by frictional contact points with neighboring fibers, and the coefficient of friction between materials varied with speed.

Using treated fibers to measure fiber speed can change a fiber's surface characteristics. Moreover, placing these fibers on the sliver surface may disturb the fiber's behavior, preventing observations of actual fiber movement. In recent years, laser Doppler anemometer (LDA) has been used to measure fiber speed on different drafting systems [1, 12] with more accuracy than previously mentioned methods, but monitoring fiber interactions in the drafting zone is not possible with LDA.

In this research, we use a high-speed camera to provide very real fiber movement representations without changing the sliver structure. Limited information is available describing the effects of fiber fineness on fiber speed under different conditions. Therefore, the main purpose of our research is to investigate the effect of fiber fineness on fiber speed under various drafting conditions provided by different draft ratios and roller settings.

Experimental Procedure

The polyester (PET) fibers used in the entire experiment came from Wellman Inc., Charlotte, NC. The manufacturing company used the same processing procedures to manufacture three different deniers of the PET0.8, 1.0, and 1.2-all with the same length of 38 mm. The fibers were in card sliver form, and the sliver weight was 5 ktex.

This experiment was run at the main drafting zone of a two-zone drafting system with three top rollers and three bottom rollers. The experimental design consisted of three main factors: fiber fineness (0.8, 1.0, and 1.2 denier), six draft combinations (three total draft ratio with two break draft ratio), and roller setting (43.7, 45, and 47 mm). At the break drafting zone, the roller setting was 46 mm and break drafting ratios were 1.47 and 1.76 with a constant 1.80 m/min incoming speed. The three total draft ratios used in the study were 6.07, 6.80, and 7.73.

Four slivers were fed into the drawframe, and an Olympus Encore 2000 model high-speed camera with a motion analyzer was used to record fiber movement along the drafting zone. An endoscopie lens with its own light source connected to a high speed camera was placed directly over the drafting zone, and it was able to capture up to 1000 frames per second. In each treatment, the camera was focused between two middle slivers and placed very close to the front roller for the first two replications and to the back roller sets for the second two replications in order to collect unbiased data.

During the recording, the camera setting was 500 frames per second with 20 shutter speed. The device had a limited memory, capable of storing 2.2 seconds long, the digital recording equivalent of 2046 frames. Therefore, the recorded pictures were replayed with five frames per second and re-recorded on S-VHS videocassettes for further speed analysis.

Calibration was performed after every other four replications with a steel ruler placed between rollers, and the picture showing the ruler was recorded. This picture was later played in still mode, and the lines of the ruler were drawn on a transparency that was placed on the monitor. The screen was divided into four sections, each representing 1 mm (Figure 1). Fifty readings per replication were taken at different sections of the monitor in order to scan the whole viewing area. The actual time during which a chosen fiber traveled from the beginning of one zone to the end of the next zone (2 mm) was displayed with 0.002 second increments on the motion analyzer monitor in order to calculate the fiber speed.

Data were tested by analysis of variance (ANOVA), and mean separation was performed by the least significant difference at P = 0.05 if the F test was significant at the same level. The relative importance of each source of variation in the ANOVA, including fiber fineness, draft ratio, and roller setting, was determined by partitioning the total sum of squares for treatments into main and interaction effects and expressing the individual contributions to variation as a percentage of the total sum of squares for the model.

Results

The average fiber speed in the main drafting zone depended significantly on fiber fineness, which accounted for 22% of total variation in fiber speed (Table I). Each fiber fineness level significantly differed from the others. The average fiber speed increased with increasing fiber fineness. The microfiber had a speed of 9.95 m/min, while the 1.2 denier fibers had 7.64 m/min as an average (Table I).

FIGURE 1. Tracking a single fiber movement between the two roller sets.

The draft combination had a significant influence on fiber speed, accounting for 18% of the total variation in average speed. In general, the average fiber speed increased with increasing total draft ratio. In addition, 16% of the total variation was attributed to the fiber fineness and draft combination interactions (Table I). The general trend for 0.8 and 1.0 denier fibers was that higher average speeds were measured at the draft combinations with 1.76 breaking draft (Table II). However, the draft combinations with 1.47 break drafting ratio yielded higher fiber speed readings for 1.2 denier fibers.

The interaction of setting and draft ratio was a significant factor, which accounted for 7% of the total variation, even though the main effect of setting was not significant (Table I). For each draft combination, fiber speed remained generally unchanged with increasing roller settings from 43.7 to 47 mm. However, within each roller setting, increasing the total draft ratio from 6.07 to 7.73 increased fiber speed regardless of back drafting ratio (Table III).

Fiber fineness and draft ratio significantly affected the CV% of speed, accounting for 10% and 9% of the total variation, respectively (Table I). In addition, fiber fineness significantly interacted with total drafting ratio, and this interaction accounted for 13% of the total variation in CV% speed. The other factor that had a significant effect on the CV% of speed was setting: increasing the setting from 43.7 to 47 mm increased the variation in speed.

TABLE I. Sources of variation in the analysis of variance (ANOVA) for the effect of fiber fineness, draft ratio, and setting on the speed and CV% speed at the main drafting zone.

TABLE II. Interaction of fiber fineness and total drafting ratio on speed and CV% speed at the main drafting zone.

TABLE III. Interaction of roller setting and total drafting ratio on speed and CV% speed at the main drafting zone.

Discussion

In this study, we intend to show how different fiber fineness levels behave at different drafting conditions. The statistical analysis reveals that fineness has a significant effect on the average fiber speed at the main roller drafting zone. Fineness introduces the clustering effect and different numbers of fiber contact points.

In roller drafting, several researchers have reported fiber grouping behaviors [2, 3, 4, 8]. The size and number of clusters depend on several factors such as fiber length, crimp, spin finish, etc. In this study, these factors were constant, except for the number of fibers in the cross section of a sliver, and fiber fineness, which can change the number of fiber contact points. The number of fibers in the cross section of microfiber card sliver was 50% more than that of a 1.2 denier fiber card sliver. Hence, the crowded structure of the mic\rofiber sliver obviously increased the number of fiber contact points.

The more direct effect of fiber fineness on the cluster structure is bending rigidity, which depends on the shape factor of the fibers and proportional to the fourth power of diameter for round fibers [UJ. Microfibers have a lower bending rigidity, which allows them to bend or wrap more easily than coarser fibers. Thus, the clusters formed by microfibers are more compact than the coarser fiber clusters due to the higher compression forces on the fibers created by flexible fibers [8]. The closer packing of microfibers results in a higher number of contact points.

Drafting is a highly complex transformation of fibers between roller sets. As the fibers leave the back roller, the pressure on them starts to drop. The moment they leave the back roller, internal tension in the fibers starts to restore crimp, which results in expansion of the sliver's cross section in the drafting zone and formation of new interfiber contact points. At first, sections of fibers in a slack position are straightened by opening crimps with applied tension (Figure 1). The friction forces at different directions cause fibers to stretch until they lose contact with the other controlling contact points. Subsequently, fiber sliding begins for a period of time during which the forwarding force is higher than the retaining static friction force. During sliding, internal tensions begin to restore crimp, creating new contact points (step 3 in Figure 1). This forward acceleration movement is usually interrupted by either slow moving, unoriented fibers or other fibers in the clusters.

Each fiber contact point is exposed to a different magnitude of friction force; the forces determine the local fiber acceleration and the drafting force. Between the roller sets, friction forces on the different sections of fibers vary because normal forces on the fibers are affected by the cluster structure and position in the drafting zone. Some fibers can be held firmly in clusters due to high entangling, which promotes higher static friction force by increasing normal forces at the fiber contact points. Additionally, the stick slip motion occurs at the fiber contact points when fibers are transferred from one set of rollers to the next during drafting because the friction coefficient varies as a function of load, velocity, and viscosity [6]. As a result, fiber movement in the drafting zone is not a continuous process, but consists of local acceleration and slowing down of parts of fibers. This can explain the drafting behavior of different fiber fineness levels and what has been observed and reported in this experiment and other studies.

Examining the video recordings, we saw sudden acceleration and deceleration of fiber sections. Additionally, in roller drafting some of the fiber movements were not perpendicular to the rollers. These phenomena have been observed by other researchers. Taylor [9, 10] confirmed that fibers sometimes show sudden increases and decreases in speed. Cherif et al. [1] reported that some fibers at the vicinity of the front roller have slower speeds. Furthermore, some fibers have higher speed than the front roller speed, and fibers sometimes show sudden acceleration in the middle of the drafting zone [1, 12].

In our experiment, microfibers had the highest average speed, which decreased with increasing fiber denier. However, variations in speed increased with increased fiber denier. Clusters formed by coarser fibers have large void spots because of lower compression force and numbers of fibers inside the clusters. This can ease fiber acceleration and increase the variation in speed. On the other hand, most microfibers in clusters move together without changing their relative positions, resulting in a decrease in the speed variation.

The drafting combination had a significant influence on fiber speed. Increasing the drafting ratio from 6.07 to 7.73 resulted in higher fiber speeds. The draft combinations with a break drafting ratio of 1.47 had relatively lower average speeds but higher variation values compared to the 1.76 break drafting ratio. This can be explained by the fact that higher numbers of fibers supplied into the main drafting zone at the lower break drafting ratio increased the number of fiber contact points and therefore speed variation.

From the statistical analysis, the 43.7 mm setting had the lowest average speed, whereas 47 mm showed the highest speed. Moreover, the variation in speed increased with increases in setting. At the 47 mm setting, the spacing was large enough to release fibers from clusters, allowing them to have enough distance to accelerate and form new contact points, making more local acceleration possible.

In conclusion, even though the differences between fiber fineness levels were small, the interaction of fineness with drafting conditions was highly important. We found that microfibers had the highest average speed but the lowest variation compared to the other fineness levels. This change in denier was enough to change the fibers' drafting behavior. Therefore, machine adjustments should be carefully made, especially when working with fine denier fibers in order to spin high quality yarns.

ACKNOWLEDGMENTS

We would like to thank Wellman Inc. for supplying the test material and lending the high speed camera. Thanks are also due to Dr. Ahmet Korkmaz for critically editing the manuscript.

Literature Cited

1. Cherif, Ch., Achnitz, R., and Wulfhorst, B., New Drafting Process Data on High Performance Cotton Drawframe, Melliand Textilber. 6, E-102-103 (1998).

2. Dehghani, A., Lawrence, C. A., Mahmoudi, M., Greenewood, B., and Iype, C., Fibre Dynamics in a Revolving Flat Card: An Assessment of Changes in the State of Fibre Mass during the Early Stages of the Carding Process, J. Textile Inst. 91, Part 1 (3), 359-373 (2000).

3. Grover, G., and Lord, P. R., The Measurement of Sliver Properties on the Drawframe, J. Textile lnst. 83, 560-572 (1992).

4. Komori, T., A Modified Theory of Fiber Contact in General Fiber Assemblies, Textile Res. J. 64, 519-528 (1994).

5. Mc Vittie, L, and Barr, A. E., Fibre Motion in Roller and Apron Drafting, J. Textile Inst. 52, T147-T156 (1961).

6. Nachane, R. P., Hussain, G. F. S., and Krishna Iyer, K. R., Theory of Stick-slip Effect in Friction, Ind. J. Textile Res. 23, 201-208 (1998).

7. Persson, B. N. J., "Sliding Friction-Physical Principles and Applications," 2nd ed., Springer, Berlin, 2000.

8. Schoppee, M. M., A Poisson Model of Nonwoven Fiber Assemblies in Compression at High Stress, Textile Res. J. 68,371-384(1998).

9. Taylor, D. S., Some Observations on the Movement of Fibres during Drafting, J. Textile Inst. 45, T 310-322 (1954).

10. Taylor, D. S., The Velocity of Floating Fibres During Drafting of Worsted Slivers, J. Textile Inst. 47, T 233-236 (1956).

11. Warner, S. B., "Fiber Science," Prentice Hall, Englewood Cliffs, NJ, 1995.

12. Wulfhorst, B., Weber, M., Phoa, T., and Lauber, M., Measurement of Fibre Velocity on a High-draft Drafting System, ITB Yarn Fabric Form. 2, 37-39 (1994).

Manuscript received September 18, 2002; accepted January 23, 2003.

YASEMIN AYDOGMUS KORKMAZ1 AND HASSAN M. BEHERY

School of Material Science, Clemson University, Clemson, South Carolina 29634, U.S.A.

1 Corresponding author: present address, Kahramanmaras Sutcu Imam University, Faculty of Engineering, Dept. of Textiles, 46100, Kahramanmaras, Turkey, email: ykorkmaz@ksu.edu.tr

Copyright Textile Research Institute Jun 2004

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