Some typical fiber configurations in vortex yarns are given in Figure
3-6. As seen from figures vortex yarn structure varies along the yarn
length. The configuration of each tracer fiber was studied and grouped
according to the classification illustrated in Table 3. Results of fiber
configuration classification showed that the percentage of straight,
hooked(trailing) and hooked(both ends) is very close to each other.
Migration in Vortex Yarn
The images captured during analysis of yarn structure suggest that the fiber migration in vortex yarns differs from that in both air jet and ring yarns. A close look to the twist insertion mechanisms in these spinning technologies reveals the reason behind this discrepancy. In ring spinning, twist is inserted a thin ribbon shape fiber bundle coming from the front roller of drafting device by the traveler. As fibers are transformed to roughly circular shape most of them are grasped at the nip of the front rollers and in already formed yarn structure. During yarn formation fibers on the edges are subjected to the tension and fibers in the core are subjected to “compression”. The edge fibers try to lessen the stress by migrating to the inner layer while the core fibers are displaced to the outer layers and these now become edge fibers. This process of fiber movement in the cross section (migration) is repeated. As a result fibers leave their helical path and give an interlocking structure. This structure includes fibers migrate periodically, going inward from the surface into the center of the yarn and then back out, with some random fashion[10]. In air jet spinning, fibers leaving the front roller of the draft zone advance to the two contra-rotating nozzles. The second nozzle imparts a false twist to the fiber strand that migrates back to the front roller. The first nozzle, which has lower intensity than the second one prevents edge fibers from receiving false twist. Therefore as the fiber strand enters the second nozzle only core fibers have full twist; edge fibers either do not have any twist or have twist in opposing direction. When the fiber strand leaves the nozzle core fibers become untwisted and edge fibers receives twist and wrap around the core fibers. The resultant yarn has a central core of mostly parallel fibers wrapped with wrapper fibers[12,15]. In air jet spinning the great majority of the wrapping fibers are
leading-end fibers since the control of aprons prevents a trailing end from becoming an effective and long free end [5]. Unlike ring yarn structure, in air jet yarn the “migration” does not repeat. Although vortex spinning can be considered as the modification of air jet spinning there are key differences between the principles of yarn formation in these spinning technologies. In vortex spinning fibers emerging from the front rollers are sucked into the spiral orifice at the inlet of the air jet nozzle and move towards the tip of the needle protruding from the orifice. In the meantime, these fibers are subjected to whirling air flow and receive twist. Twist tends to move upwards, but the needle prevents this upward twist penetration. Therefore, the upper parts of some fibers are kept open as they depart from the nip line of front rollers. After these fibers have passed through the orifice, the upper parts of the fibers spread out due to the whirling air flow and wind over the hollow spindle. Subsequently these fibers are wrapped around the fiber core and turned into yarn as the already formed yarn part is pulled trough the spindle [4,14,17]. The main difference between the air jet and vortex yarn is the number of wrapper fibers which is much higher in vortex yarns. In air jet spinning only the edge fibers (fibers lying at the edges of the ribbon like fiber bundle as it leaves the front roller) become the wrapper fibers. In vortex spinning, on the other hand, the fiber separation from the bundle occurs everywhere in the entire outer periphery of the bundle. It is very likely that during yarn formation the leading part of fibers will not be able to escape from the false twist penetrating upwards and eventually located in the core. The trailing parts, on the other hand, won’t receive twist and become wrapper. The images captured during analysis of yarn structure confirmed this assumption. Most of tracer fibers first showed core fiber
Structure and Properties of Vortex Yarns
Yarn Properties
Statistical analysis of the data from yarn testing showed that in 50/50 polyester/cotton blended yarn the shorter front roller to the spindle distance gave lower irregularity, imperfection and hairiness values. The imperfection values also were low but hairiness was high at the low nozzle angle and large spindle diameter. The high nozzle pressure produced less hairy yarns. The yarn speed affected yarn evenness, hairiness and the number of thick places. The low yarn speed resulted in more regular yarns with fewer thick places and low hair. The interaction of the front roller to the spindle distance and the spindle diameter had a significant effect on elongation and the number of thick places. When the front roller to the spindle distance was short the smaller spindle diameter resulted in the higher elongation; on the other hand when the front roller to the spindle distance was large the large spindle diameter produced the higher elongation. The tenacity values were affected by the interaction of the spindle diameter and nozzle angle. While at the high nozzle angle, the large spindle diameter caused higher tenacity at the low nozzle angle it was opposite. The interaction of the nozzle pressure and nozzle angle, and the interaction of the spindle diameter and nozzle angle had a significant effect on hairiness. The combination of the high nozzle pressure and angle, and the combination of the small spindle diameter and high nozzle angle produced yarns with less hair.
Like 50/50 polyester/cotton blend yarns, in 100% cotton yarns the short front roller to the spindle distance produced more even yarns with fewer imperfections and less
hair. The nozzle angle had a significant effect on evenness and hairiness values. The high nozzle angle caused more even and less hairy yarns. The interaction of the high nozzle angle and short front roller to spindle distance led to improved evenness. Nozzle pressure and spindle diameter only affected hairiness. Hairiness was low at the high nozzle pressure and the small spindle diameter. The yarn speed had a significant effect on the number of thick places and hairiness. A low yarn delivery speed caused fewer number of thick places and low hairiness. The interaction of the yarn speed and nozzle angle had a significant effect on hairiness as well.
In vortex spinning fibers coming from the front rollers are first sucked into the spiral orifice at the entrance of an air jet nozzle by the air jet stream. Following the air jet nozzle the fiber bundle enters a hollow spindle. The false twist insertion starts at the inlet of the spindle. Twist tends to propagate towards the front rollers, but this penetration is prevented by the needle protruding from the orifice. Therefore the upper portions of some fibers are kept open as fibers move towards the spindle. When the fiber bundle leaves the orifice the upper portion of the fibers begin to expand and wind over the spindle. These fibers are whirled around the core and form into MVS yarn as they are drawn into the hollow spindle (See section 2.3.2)[14]. The distance between the front roller and the spindle is critical since it determines the number of wrapping fibers. If this distance shorter both ends of fibers are tightly assembled resulting in fewer open ended fibers, in turn, a yarn consisting of mostly parallel core fibers held with fewer wrapper fibers as in the case of air jet yarn. In the mean time yarn evenness and imperfections are better since there is less chance to lose control of fibers during the bundling of the parallel core fibers which forms the main part of the yarn with a few wrapper fibers. Waste is less because
of better fiber control as well. The yarn has less hairiness and a leaner appearance. If this distance is longer the number of wrapper fibers increases, but also less fiber control is present. The resultant yarn is softer due to increasing wrapper fibers and has more hairiness with longer hair. The waste fiber rate, however, is higher compared to that in short setting [16].
When nozzle pressure increases, both the axial and the tangential velocity increase. As a result the fiber bundle receives more twist and yarn becomes stronger but stiffer. The nozzle angle plays critical role on characteristic of the air flow as well. A high nozzle angle causes higher tangential velocity, in turn, higher twist. Surprisingly results showed that neither the nozzle angle and nor the nozzle air pressure had any effects on yarn tenacity and elongation. Another surprising result was in 100% cotton yarn, the high nozzle angle caused better evenness, which was the opposite of what would be expected. A lower nozzle angle should result in better yarn evenness due to the increasing axial velocity of air flow. Probably the levels used in this study were too close to show the real effect of these parameters. Hairiness values, on the other hand, were low at high nozzle angle and high air pressure supporting that twist increases as nozzle angle and pressure go up, and fibers are integrated more tightly into the yarn structure.
Spindle diameter determines the tightness of the wrappings [16]. A small spindle diameter gives less freedom to the fiber bundle to expand as it enters the spindle. This generates higher friction between fibers and results in tighter wrappings, higher twist and in turn denser yarns with less hair. With a large spindle diameter the fiber bundle has more freedom to move inside the spindle and therefore some twist is lost, wrappings
become looser and yarn becomes bulky and more hairy. Results supported that a small spindle diameter resulted in low hairiness.
Yarn Structure
Results from 434 individual tracer fibers were obtained through the computer analysis. Statistical analysis of results showed that none of the process parameters had any significant effects on the mean fiber position, r.m.s. deviation, helix angle or helix diameter. Mean migration intensity and equivalent migration frequency, on the other hand, were influenced by yarn speed and nozzle angle. Both were high at the low yarn speed and high nozzle angle. The possible reason for this at low speed the movement of fiber bundle inside the nozzle chamber is slower so that the fibers in the bundle are subjected to whirling air current at a longer period of time, and at high nozzle angle twist increases due to rising tangential velocity and this might cause an increase in the values of the mean migration intensity and equivalent migration frequency. The nozzle pressure and the interaction of nozzle pressure, speed and front roller to spindle distance also had a significant effect on the mean migration intensity. The mean migration intensity was high at the high nozzle pressure. The interaction of the high nozzle pressure, low yarn speed and short front roller to spindle distance gave the highest mean migration intensity values. Yarn diameter was mainly affected by yarn speed. It was smaller at the low delivery speed. Again this can be attributed to the fiber bundle being exposed to the whirling air force for a longer period time at the low yarn speed.
Migration in Vortex Yarn
The images captured during analysis of yarn structure suggest that the fiber migration in vortex yarns differs from that in both air jet and ring yarns. A close look to the twist insertion mechanisms in these spinning technologies reveals the reason behind this discrepancy. In ring spinning, twist is inserted a thin ribbon shape fiber bundle coming from the front roller of drafting device by the traveler. As fibers are transformed to roughly circular shape most of them are grasped at the nip of the front rollers and in already formed yarn structure. During yarn formation fibers on the edges are subjected to the tension and fibers in the core are subjected to “compression”. The edge fibers try to lessen the stress by migrating to the inner layer while the core fibers are displaced to the outer layers and these now become edge fibers. This process of fiber movement in the cross section (migration) is repeated. As a result fibers leave their helical path and give an interlocking structure. This structure includes fibers migrate periodically, going inward from the surface into the center of the yarn and then back out, with some random fashion[10]. In air jet spinning, fibers leaving the front roller of the draft zone advance to the two contra-rotating nozzles. The second nozzle imparts a false twist to the fiber strand that migrates back to the front roller. The first nozzle, which has lower intensity than the second one prevents edge fibers from receiving false twist. Therefore as the fiber strand enters the second nozzle only core fibers have full twist; edge fibers either do not have any twist or have twist in opposing direction. When the fiber strand leaves the nozzle core fibers become untwisted and edge fibers receives twist and wrap around the core fibers. The resultant yarn has a central core of mostly parallel fibers wrapped with wrapper fibers[12,15]. In air jet spinning the great majority of the wrapping fibers are
leading-end fibers since the control of aprons prevents a trailing end from becoming an effective and long free end [5]. Unlike ring yarn structure, in air jet yarn the “migration” does not repeat. Although vortex spinning can be considered as the modification of air jet spinning there are key differences between the principles of yarn formation in these spinning technologies. In vortex spinning fibers emerging from the front rollers are sucked into the spiral orifice at the inlet of the air jet nozzle and move towards the tip of the needle protruding from the orifice. In the meantime, these fibers are subjected to whirling air flow and receive twist. Twist tends to move upwards, but the needle prevents this upward twist penetration. Therefore, the upper parts of some fibers are kept open as they depart from the nip line of front rollers. After these fibers have passed through the orifice, the upper parts of the fibers spread out due to the whirling air flow and wind over the hollow spindle. Subsequently these fibers are wrapped around the fiber core and turned into yarn as the already formed yarn part is pulled trough the spindle [4,14,17]. The main difference between the air jet and vortex yarn is the number of wrapper fibers which is much higher in vortex yarns. In air jet spinning only the edge fibers (fibers lying at the edges of the ribbon like fiber bundle as it leaves the front roller) become the wrapper fibers. In vortex spinning, on the other hand, the fiber separation from the bundle occurs everywhere in the entire outer periphery of the bundle. It is very likely that during yarn formation the leading part of fibers will not be able to escape from the false twist penetrating upwards and eventually located in the core. The trailing parts, on the other hand, won’t receive twist and become wrapper. The images captured during analysis of yarn structure confirmed this assumption. Most of tracer fibers first showed core fiber
Structure and Properties of Vortex Yarns
Yarn Properties
Statistical analysis of the data from yarn testing showed that in 50/50 polyester/cotton blended yarn the shorter front roller to the spindle distance gave lower irregularity, imperfection and hairiness values. The imperfection values also were low but hairiness was high at the low nozzle angle and large spindle diameter. The high nozzle pressure produced less hairy yarns. The yarn speed affected yarn evenness, hairiness and the number of thick places. The low yarn speed resulted in more regular yarns with fewer thick places and low hair. The interaction of the front roller to the spindle distance and the spindle diameter had a significant effect on elongation and the number of thick places. When the front roller to the spindle distance was short the smaller spindle diameter resulted in the higher elongation; on the other hand when the front roller to the spindle distance was large the large spindle diameter produced the higher elongation. The tenacity values were affected by the interaction of the spindle diameter and nozzle angle. While at the high nozzle angle, the large spindle diameter caused higher tenacity at the low nozzle angle it was opposite. The interaction of the nozzle pressure and nozzle angle, and the interaction of the spindle diameter and nozzle angle had a significant effect on hairiness. The combination of the high nozzle pressure and angle, and the combination of the small spindle diameter and high nozzle angle produced yarns with less hair.
Like 50/50 polyester/cotton blend yarns, in 100% cotton yarns the short front roller to the spindle distance produced more even yarns with fewer imperfections and less
hair. The nozzle angle had a significant effect on evenness and hairiness values. The high nozzle angle caused more even and less hairy yarns. The interaction of the high nozzle angle and short front roller to spindle distance led to improved evenness. Nozzle pressure and spindle diameter only affected hairiness. Hairiness was low at the high nozzle pressure and the small spindle diameter. The yarn speed had a significant effect on the number of thick places and hairiness. A low yarn delivery speed caused fewer number of thick places and low hairiness. The interaction of the yarn speed and nozzle angle had a significant effect on hairiness as well.
In vortex spinning fibers coming from the front rollers are first sucked into the spiral orifice at the entrance of an air jet nozzle by the air jet stream. Following the air jet nozzle the fiber bundle enters a hollow spindle. The false twist insertion starts at the inlet of the spindle. Twist tends to propagate towards the front rollers, but this penetration is prevented by the needle protruding from the orifice. Therefore the upper portions of some fibers are kept open as fibers move towards the spindle. When the fiber bundle leaves the orifice the upper portion of the fibers begin to expand and wind over the spindle. These fibers are whirled around the core and form into MVS yarn as they are drawn into the hollow spindle (See section 2.3.2)[14]. The distance between the front roller and the spindle is critical since it determines the number of wrapping fibers. If this distance shorter both ends of fibers are tightly assembled resulting in fewer open ended fibers, in turn, a yarn consisting of mostly parallel core fibers held with fewer wrapper fibers as in the case of air jet yarn. In the mean time yarn evenness and imperfections are better since there is less chance to lose control of fibers during the bundling of the parallel core fibers which forms the main part of the yarn with a few wrapper fibers. Waste is less because
of better fiber control as well. The yarn has less hairiness and a leaner appearance. If this distance is longer the number of wrapper fibers increases, but also less fiber control is present. The resultant yarn is softer due to increasing wrapper fibers and has more hairiness with longer hair. The waste fiber rate, however, is higher compared to that in short setting [16].
When nozzle pressure increases, both the axial and the tangential velocity increase. As a result the fiber bundle receives more twist and yarn becomes stronger but stiffer. The nozzle angle plays critical role on characteristic of the air flow as well. A high nozzle angle causes higher tangential velocity, in turn, higher twist. Surprisingly results showed that neither the nozzle angle and nor the nozzle air pressure had any effects on yarn tenacity and elongation. Another surprising result was in 100% cotton yarn, the high nozzle angle caused better evenness, which was the opposite of what would be expected. A lower nozzle angle should result in better yarn evenness due to the increasing axial velocity of air flow. Probably the levels used in this study were too close to show the real effect of these parameters. Hairiness values, on the other hand, were low at high nozzle angle and high air pressure supporting that twist increases as nozzle angle and pressure go up, and fibers are integrated more tightly into the yarn structure.
Spindle diameter determines the tightness of the wrappings [16]. A small spindle diameter gives less freedom to the fiber bundle to expand as it enters the spindle. This generates higher friction between fibers and results in tighter wrappings, higher twist and in turn denser yarns with less hair. With a large spindle diameter the fiber bundle has more freedom to move inside the spindle and therefore some twist is lost, wrappings
become looser and yarn becomes bulky and more hairy. Results supported that a small spindle diameter resulted in low hairiness.
Yarn Structure
Results from 434 individual tracer fibers were obtained through the computer analysis. Statistical analysis of results showed that none of the process parameters had any significant effects on the mean fiber position, r.m.s. deviation, helix angle or helix diameter. Mean migration intensity and equivalent migration frequency, on the other hand, were influenced by yarn speed and nozzle angle. Both were high at the low yarn speed and high nozzle angle. The possible reason for this at low speed the movement of fiber bundle inside the nozzle chamber is slower so that the fibers in the bundle are subjected to whirling air current at a longer period of time, and at high nozzle angle twist increases due to rising tangential velocity and this might cause an increase in the values of the mean migration intensity and equivalent migration frequency. The nozzle pressure and the interaction of nozzle pressure, speed and front roller to spindle distance also had a significant effect on the mean migration intensity. The mean migration intensity was high at the high nozzle pressure. The interaction of the high nozzle pressure, low yarn speed and short front roller to spindle distance gave the highest mean migration intensity values. Yarn diameter was mainly affected by yarn speed. It was smaller at the low delivery speed. Again this can be attributed to the fiber bundle being exposed to the whirling air force for a longer period time at the low yarn speed.