Quantifying Primary Trim Scrap in Rapier Weft Insertion
Primary rapier trim scrap depends on insertion geometry rather than fabric width, requiring exact tail length modeling to prevent yarn yield deficits.
Active Reed Width
Weave Dimension
Woven width boundary defines the maximum lateral distance across a loom where warp yarns are threaded through the reed to form the fabric structure. Adjusting the active reed width allows the mill to control the final selvedge-to-selvedge dimension of the linen cloth. It represents the active section of the reed that contains the drawing-in of the warp ends, excluding empty outer dents.
Mechanical Constraint
Looms operate within strict physical limits that prevent damage to the reed or the insertion mechanism during the weft propulsion. The active reed width must align with the travel of the rapier or gripper to avoid collision with unthreaded dents. If this setting is too wide, the weft carrier may lose guidance at the edge of the warp, which causes yarn breakage or fabric defects.
In pneumatic looms, the placement of the relay nozzles must match this width exactly to maintain the air pressure required for stable yarn flight. Adjusting these parameters ensures that the yarn runs smoothly during high-speed insertion.
Shrinkage Calculation
Loom-state fabrics undergo contraction when the tension of the weaving process is released during finishing. The active reed width is calculated by adding the target finished fabric width to the estimated warp and weft shrinkage, along with the expected takeup and edge trim margin. In linen weaving, flax fibres exhibit high moisture absorption, which leads to substantial wet shrinkage during bleaching or dyeing.
Because of this behaviour, the active reed width is typically set five to eight percent wider than the desired finished width to compensate for these dimensional changes. This adjustment ensures the final linen delivery meets the specified commercial width.