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Process Control of Sizing
Subrata Majumder
Department of Textile Engineering
Daffodil International University
Email: eng.smder@yahoo.com
Contact: +8801710541657
Sizing of Warp Yarn:
The sizing of yarn absolutely essential to render it weavable; without sizing the end breakage rate of warp, particularly in the case of single yarns, is so high that weaving becomes impossible. The objective of sizing, however, sizing cannot be looked upon as a process that improves the basic quality of yarn. The fact is that by endowing the yarn with abrasion resistance, proper sizing bring out the full potential of a yarn to weave. A properly sized yarn should have adequate improvement in abrasion resistance, indirectly indicated by the increase in tensile strength, minimum loss of extensibility and required amount of moisture. For satisfactory weaving the quality of the beam also important; the beam should be firm and it should not have excessive missing ends, crossed ends, taped ends (sticky ends) etc., so that it unwind smoothly in the loom shed.
We also want that in the sized yarn there should be:
The process control program in sizing should, therefore, comprise of the following aspects:
1. Selecting the correct size recipe and size pick -up level.
2. Ensuring correct ratio of size paste.
3. Control of the followings:
The following properties of yarn are affected by sizing:
Viscosity of size paste in size box: Any variation in the concentration or temperature alters the viscosity of the paste which in turn affects both the level of size pick up and extent of penetration. Initially as the viscosity increases, the size pick-up also increases. But as the viscosity increases beyond a point, the size pick up is reduced.
Squeezing pressure and condition of squeezing nip: The squeezing pressure determines the extent of penetration of the size paste between the fibers of the yarn and also of the removal of excess size paste and hence the level of the size pick up.
Speed of the sizing machine: Other sizing conditions remaining unchanged, the size pick up increases with increasing sizing speed and vice versa. This is because the time available to squeeze the surplus size from the yarn is less at high speeds.
Depth of immersion roller in size paste: the depth of immersion roller in the paste determines the duration for which the yarn remains immersed in the paste. This duration in turn influences both the level of size pick up and the extent of size penetration.
- Some increase in tensile strength in the yarn
- Minimum loss of extensibility in yarn ( about 4.4-4.6% elongation at break is required for cotton)
- Required moisture content ( 8-10% of cotton)
- Good quality of sized beam (neither too soft nor too firm + free from yarn defects)
- Good productivity and efficiency
- Reduced Cost
Some Important Parameters for the Process Control of Sizing:
Process Control in Sizing: The process control program in sizing should, therefore, comprise of the following aspects:
1. Selecting the correct size recipe and size pick -up level.
2. Ensuring correct ratio of size paste.
3. Control of the followings:
- size pick up
- stretch
- moisture content
- quality of beam
- machine speed
- machine efficiency
- a method to calculate the expected level of productivity
The following properties of yarn are affected by sizing:
- Yarn elasticity decreases.
- Yarn strength increases.
- Hairiness of yarn increases.
- Flexibility of yarn decreases.
- Smoothness of yarn increases.
- Irregularity of yarn decreases.
- Yarn diameter increases.
- Yarn weight increases.
- Composition of yarn
- Yarn count
- Total no. of ends
- Weight of yarn
Viscosity of size paste in size box: Any variation in the concentration or temperature alters the viscosity of the paste which in turn affects both the level of size pick up and extent of penetration. Initially as the viscosity increases, the size pick-up also increases. But as the viscosity increases beyond a point, the size pick up is reduced.
Squeezing pressure and condition of squeezing nip: The squeezing pressure determines the extent of penetration of the size paste between the fibers of the yarn and also of the removal of excess size paste and hence the level of the size pick up.
Speed of the sizing machine: Other sizing conditions remaining unchanged, the size pick up increases with increasing sizing speed and vice versa. This is because the time available to squeeze the surplus size from the yarn is less at high speeds.
Depth of immersion roller in size paste: the depth of immersion roller in the paste determines the duration for which the yarn remains immersed in the paste. This duration in turn influences both the level of size pick up and the extent of size penetration.
Level of size paste in the size box: Variation in the level of size paste is an important source of size pick-up variations both within and between beams.
Density of ends: When the density of ends is high, difficulties are encountered in obtaining adequate and uniform size penetration. Therefore size pick up may vary at these fabrics.
Yarn tension: In case of higher tension during sizing the set of warp yarns encounter a stretch of comparatively higher tension and thus the set of yarn increases in length. If this increase is too high then the elongation property of the yarn will be decreased. So the yarn will face comparatively higher breakage in subsequent processes. On the other hand lower yarn tension leads to uneven sizing. So the yarn tension must be optimal.
Yarn twist: In case of high twisted yarn penetration time should be increased in order to obtain the optimal pick up %.
Dia. of the yarns: Yarn with greater dia consumes higher size paste. Therefore, the higher the dia of yarn, the higher the pickup will be added.
Density of ends: When the density of ends is high, difficulties are encountered in obtaining adequate and uniform size penetration. Therefore size pick up may vary at these fabrics.
Yarn tension: In case of higher tension during sizing the set of warp yarns encounter a stretch of comparatively higher tension and thus the set of yarn increases in length. If this increase is too high then the elongation property of the yarn will be decreased. So the yarn will face comparatively higher breakage in subsequent processes. On the other hand lower yarn tension leads to uneven sizing. So the yarn tension must be optimal.
Yarn twist: In case of high twisted yarn penetration time should be increased in order to obtain the optimal pick up %.
Dia. of the yarns: Yarn with greater dia consumes higher size paste. Therefore, the higher the dia of yarn, the higher the pickup will be added.
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