Challenges spinners face in producing core-spun yarns due to the strip-back effect
The Strip-Back or Barberpole Effect is a significant challenge for spinners producing core-spun yarns. This defect occurs when the staple sheath fibers (e.g., cotton, polyester staple) slip relative to the continuous filament core (e.g., spandex, nylon, PET), leaving a length of the bare filament exposed with a clump of sheath fibers at one end.
This defect severely compromises the yarn's quality, appearance, and processability.
Challenges faced by spinners
The core challenge is the lack of sufficient cohesion between the sheath and the core during the high-speed spinning process, leading to the following specific problems:
- Incomplete core coverage: The core filament (which is often different in color, luster, or property from the sheath) becomes visible, creating a major visual defect and potentially reducing the desired aesthetic qualities (like the cotton-look of a stretch yarn).
- End breaks in processing: Exposed, bare filament is weaker than the fully covered core-spun yarn and can cause frequent end breaks during subsequent processes like winding, warping, weaving, or knitting, leading to lower production efficiency and higher costs.
- Reduced abrasion resistance: The sheath, which is meant to protect the core, is not fully secured, making the yarn highly susceptible to abrasion, which can easily strip the remaining fibers off the core, especially in high-speed applications like sewing threads.
- Need for higher twist: To prevent slippage, spinners often have to increase the twist level, which, while mitigating strip-back, can reduce production speed and negatively impact the hand feel (softness) and overall strength of the yarn.
- Uneven yarn properties: The inconsistency in the wrapping of the sheath fibers causes variations in yarn thickness, hairiness, and strength, leading to poor yarn unevenness
Strategies to mitigate Strip-Back (Barberpole effect)
Mitigation strategies focus on enhancing the friction, binding, and control of the sheath fibers around the core filament during and after the spinning process.
- Process parameter optimization
Increase the twist coefficient:This is the primary solution, as higher twist increases the radial pressure and binding force between the sheath and the core, improving cohesion.
Optimize the core filament's pre-tension: Higher pre-tension helps to keep the filament precisely centered in the staple fiber bundle, promoting a better axial arrangement and more uniform wrapping. However, too much tension can cause filament breakage or affect elongation.
Adjust the core feed-in angle/position: Feeding the core filament closer to the nip point of the front rollers, or using V-grooved rollers, helps to ensure the staple fibers fully enclose the core filament before twist is inserted.
Optimize the drafting ratio: Proper drafting of the staple fiber roving ensures the fibers are aligned and controlled, creating a uniform, cohesive fiber bundle to wrap around the core.
- Machine and system modification
- Modified spinning systems: Using modified systems like Siro-Spun Core Spinning or Dual-Core Spinning (where two core filaments are used) can provide better control over the sheath fibers compared to conventional ring spinning, significantly improving core coverage.
- Use compact spinning technology: Using compact spinning modifications (e.g., RoCos or Suessen systems) results in a more compact and tighter sheath structure with lower hairiness, which naturally reduces the tendency of the sheath to slip away from the core.
- Core material treatment
- Core coating/binding: This is a highly effective, though complex, solution. The core filament (e.g., PET) can be coated with a binder like Methyl Methacrylate (MMA) using a Pad-Dry-Cure (PDC) system before it is spun. This coating increases the surface friction of the core, thereby enhancing the adhesion and resistance to slippage of the sheath fibers.
- Raw material selection
- Adjust core/sheath Ratio: Adjusting the ratio of sheath to core can help. A higher proportion of sheath fibers (lower core-to-sheath ratio) generally ensures better core coverage and helps minimize strip-back problems.