Needle Punching Process Overview
Needle punching is a mechanical process used to create non-woven fabrics. Barbed needles pass repeatedly through a fibrous web, entangling the fibers to give the web strength and integrity.
Understanding Punch Density
Punch density refers to the number of needles striking the fabric per unit area, typically measured in needles per square inch or square centimeter ($N/cm^2$). A higher punch density means more needles are impacting the fabric within a given area.
Impact of Higher Punch Density
Increasing the punch density generally leads to greater mechanical action on the fiber web. Let's analyze its effects:
- Web Thickness: More needles cause increased compaction of the fiber web. This results in a lower web thickness. Thus, higher punch density causes lower web thickness.
- Fabric Dimensions: The intensified mechanical action associated with higher punch density can cause fibers to shift and rearrange, potentially leading to changes or instability in the overall fabric dimensions (e.g., shrinkage or stretching). Thus, higher punch density can cause changes in fabric dimensions.
- Fiber Damage: With a higher number of needle penetrations per unit area, the likelihood of individual fibers being damaged, cut, or broken increases. Therefore, higher punch density can lead to higher damage of fibres.
- Fabric Permeability: Permeability measures how easily fluids (like air) can pass through the fabric. Higher punch density compacts the web more intensely and increases fiber entanglement. This closes the interstitial spaces between fibers, reducing pore size and increasing the tortuosity of the flow paths. Consequently, higher punch density typically leads to lower fabric permeability, not higher.
Conclusion
Based on the analysis, higher punch density causes increased compaction (lower thickness), potential changes in dimensions, and increased fiber damage. However, it leads to reduced pore size and increased entanglement, resulting in lower, not higher, fabric permeability.
Therefore, higher punch density CANNOT cause higher permeability of the fabric.
Important Questions from FABR Nonwoven Fabric Technology Bonding Methods
- The bonding process followed for production of highloft nonwoven is
Consider the following components of a needle:
P. Shank
Q. Beard
R. Barb
S. Latch
The combination of correct components of a needle in a needle punching nonwoven machine isA needle loom, having a needle board with 2000 needles/m, is operating at a stroke frequency of 2000 strokes/min and producing a needle-punched nonwoven fabric at 5 m/min. The punch density, in number of punches per $cm^2$, is ______________
- The punch density of a needle-punched nonwoven fabric is 50 punches/cm². If the stroke frequency of needle bed is doubled and the fabric delivery speed is halved, then the punch density (punches/cm²) would be
Consider the following assertion [a] and reason [r] and choose the correct alternative from amongst A, B, C, and D.
[a] Cross-laid needlepunched nonwoven fabrics demonstrate higher tensile strength in machine direction.
[r] In cross-laid nonwoven fabrics, the fibres are randomly oriented.
