Loom Mechanisms and Motions
This domain tests the primary, secondary and auxiliary motions of a loom, their timing, and how loom speed and efficiency convert into production.
Core rules
- Primary motions: shedding, picking and beat-up. They form the shed, insert the pick and push it to the fell.
- Secondary motions: let-off and take-up. They maintain warp tension and wind the cloth at the required pick density.
- Auxiliary motions: warp stop, weft stop, temples, selvedge devices and brakes. They reduce defects and damage after a stoppage.
- Shedding types: crank or tappet for simple repeats, dobby for medium repeats, jacquard for large figure control.
- Picking systems: shuttle, projectile, rapier, air-jet and water-jet. Each has a different yarn range and insertion rate.
- Loom timing covers shed opening, pick release and beat-up. Early or late shedding changes yarn strain and fabric appearance.
Worked example
A loom runs at 600 picks/min with 90% efficiency and inserts 40 picks per cm. Picks per hour = 600 × 60 = 36,000. At 90% efficiency, effective picks = 32,400. Picks per metre = 40 × 100 = 4,000. Production = 32,400 / 4,000 = 8.1 m/h.
Traps
- Classifying let-off or take-up as primary motions.
- Mixing picks/min with loom rpm on shuttle looms.
- Applying efficiency twice in a production chain.
- Using picks per inch when the calculation is in picks per cm.
- Ignoring stoppage time when calculating actual output.