Yarn production challenged due to the strip-back effect and strategies to deal with them

Also known as the Barbelpole Effect, the Strip-Back Effect is a critical defect in the production of core-spun yarns, particularly on the ring spinning frame. It occurs when the continuous filament core slips relative to the staple sheath fibers, leaving sections of the core exposed. This slippage severely compromises yarn quality and processability.

Issues spinners face

The Strip-Back effect presents several challenges for spinners attempting to produce high-quality core-spun yarns:

• Quality defects
• Incomplete core coverage: Often having a different color or shade, the core filameny (especially in dyed yarns or stretch yarns with spandex core), becomes visibly exposed. This creates a major aesthetic defect.
• Reduced abrasion resistance: The exposed core filament is vulnerable to abrasion, which can easily strip the remaining staple fibers away during subsequent processing (like winding, warping, or weaving), leading to further quality degradation.
• Uneven yarn properties: The inconsistent wrapping of the sheath fibers causes variations in yarn thickness, hairiness, and strength, resulting in poor unevenness (CV per cent) and appearance.
• Processing and production issues
• Frequent end breaks: The bare, exposed filament is weaker than the fully covered core-spun yarn. This leads to frequent end breaks during high-speed subsequent processes, significantly reducing production efficiency and increasing waste and labor costs.
• Higher twist requirement: To ensure sufficient cohesion and prevent slippage, spinners often must use a higher twist coefficient. While this helps mitigate strip-back, it reduces the maximum production speed of the ring frame and can negatively impact the yarn's final properties (e.g., making it harder or less soft).
• Fundamental cause
• The core challenge is the lack of sufficient cohesion and friction between the filament core and the staple sheath fibers during the high-speed twisting and wrapping process. This is often exacerbated by a nonconformity between the core filament's linear density and the core-spun yarn's linear density.

How to deal with the strip-back effect

Mitigation strategies focus on enhancing the binding force, friction, and control of the sheath fibers around the core filament during and after the spinning process.

1. Process parameter optimization

Twist coefficient:  Increasing the twist level helps   increase the radial pressure and binding force between the sheath and the core, significantly improving cohesion and reducing slippage.

Core filament pre-tension: Optimizing the pre-tension helps keep the filament precisely centered within the staple fiber bundle, promoting uniform wrapping and better axial alignment.

Core feed-in position: Adjusting the core filament's feed-in angle/position ensures the staple fibers fully enclose the core filament before the twist is inserted from the spinning triangle.

Draft ratio: Optimize the drafting ratio of the staple roving ensures the sheath fibers are properly aligned and controlled, creating a uniform, cohesive fiber bundle for wrapping.

Export to Sheets

2. Machine and system modifications

• Compact spinning technology: Using compact spinning modifications results in a more compact and tighter sheath structure with lower hairiness. This naturally reduces the tendency of the sheath to slip away from the core and provides better coverage.
• Modified core feed systems: Employing specialized core stabilizers, guides, or V-grooved rollers at the front roller nip point ensures the core filament is held securely and centrally for optimal wrapping.
• Alternative spinning systems: Some advanced techniques, like the Siro core spinning system or the three-strand modified method, have been shown to produce yarns with better strength, unevenness, and less strip-back compared to conventional ring core-spun yarns.

3. Core material treatment

• Core coating: An advanced strategy involves coating the core filament (e.g., with a Methyl Methacrylate (MMA) binder via a pad-dry-cure system) before spinning. This increases the surface friction of the core filament, significantly enhancing the adhesion and resistance to slippage of the sheath fibers.

4. Raw material selection

Core/sheath ratio: Adjusting the ratio of sheath to core can improve coverage. A higher proportion of sheath fibers generally ensures better core coverage and helps minimize strip-back problems.