Narrow Fabric Needle Loom

Overview

A narrow fabric needle loom weaves tapes, webbing, elastics and ribbons, fabrics too narrow to justify a full-width loom. Instead of a shuttle that carries a weft package back and forth, it uses a curved, eyed needle that swings the weft across the warp and back every pick. Because the weft never leaves the needle, it goes in as a doubled strand and returns as a loop at the far edge; that loop is caught by a small latch needle and chained into the previous loop, giving the characteristic knitted selvedge of needle-loom webbing. One machine usually carries two to eight identical weaving heads side by side on a common drive, so a single 1.5 kW loom can produce eight tapes simultaneously at up to 2,000 picks per minute each.

Needle looms make most of the world's seat-belt webbing, cargo and lifting slings, elastic waistbands, zip tapes, hook-and-loop base tape and shoe laces. Seat-belt webbing alone, 47 mm polyester tape woven to ECE R16 and FMVSS 209 strength requirements of roughly 27 kN, is almost exclusively a needle-loom product.

How it works

Each pick begins with the Shedding Motion motion: cams on the bottom shaft lift up to eight Heald Frame units, raising and lowering groups of warp ends threaded through Heald Wire eyes to open the shed. Swapping the Shedding Cam set changes the weave, plain, twill, or the multi-layer constructions used in lifting slings.

With the shed open, the Weft Needle swings in. Driven by its cam-actuated Needle Lever, the needle carries the weft through its tip eye across the full tape width and immediately withdraws, laying two weft strands per pick and leaving a loop standing at the far selvedge. There the Selvedge Latch Needle, a latch needle reciprocated by its own Knitting Cam, hooks the new loop and draws it through the loop of the previous pick, building a chain-stitch edge that cannot unravel in service. Variants use an auxiliary locking thread fed to the knitter for a stronger two-thread selvedge on safety-critical webbing.

The Reed & Sley follows: conjugate cams rock the Sley so the Reed packs the doubled pick against the cloth fell, then dwells back long enough for the needle to pass on the next cycle. Warp is supplied by the Warp Let-Off, small per-head beams with friction Let-Off Brake bands and sprung Tension Bar rollers, while a Warp Stop Motion drop wire on every end and a Weft Detector on every weft halt the loom within a revolution of any break.

Finished tape is pulled off by the Tape Take-Up: knurled rollers advance the tape a fixed increment per pick, with the increment set by interchangeable Pick Change Gears. Pick density is therefore a gear ratio, not an electronic setting, on mechanical machines; electronic models replace the change gears with a stepper drive.

Drive and timing

Everything runs off one shaft. The Main Motor belts to the Main Shaft, which carries the needle cams and beat-up cams for all heads and gears down to the shedding camshaft. Needle entry, shed crossing, knitter motion and beat-up are all fixed phase relationships machined into the cams, which is why a needle loom holds its timing for decades with only lubrication. The Control Box box is correspondingly simple: a counter board totals picks for cut-length control, latches stop-motion signals and drops the motor relay, with an Encoder on the shaft providing position for the counter and for inch-mode jogging.

Capabilities and limits

The doubled weft and knitted edge distinguish needle-loom tape from shuttle-woven tape, whose selvedge is a continuous weft turn on both edges. For most applications the knitted edge is acceptable and the productivity difference is decisive: a needle loom inserts weft an order of magnitude faster than a narrow shuttle loom and needs no weft replenishment, since the weft feeds continuously from a stationary spool through the Weft Guide train. Where both edges must be identical, some military and medical tapes, shuttle looms or special two-needle locked-edge heads are still used. Jacquard heads can replace the cam shedding for woven labels and patterned ribbons, raising individual ends instead of whole frames.