Crabbing stabilises wool fabric in a hot-liquor bath, preparing a flat piece with the required handle for subsequent processing. QL’s WPF-ZN uses two reciprocating rollers in one bath for batch treatment; its position before scouring, after scouring or after dyeing depends on the route.
Where this machine sits in the line, and what comes before and after
WPF-ZN is the batch-crabbing choice in wet finishing. Worsted routes usually scour first, with crabbing-before-scouring available for selected qualities. Woollen routes complete milling and scouring first; the piece-dyed route then dyes before crabbing. Wool-blend knits complete tubular wet processing and any required dyeing, are slit, and then enter crabbing.
At the same station on worsted and woollen routes, the continuous crabbing section of WPF-LXZH is another choice. Woollen fabric leaves crabbing wet for WPF-SSMDX wet brushing and WPF-CG teasel raising, followed by squeezing and drying. Review crabbing position together with delivery condition.
What it changes in the fabric, top or yarn: handle, dimensional stability, lustre, cleanliness
Crabbing holds the fabric under tension and pressure in a hot-liquor bath, giving the piece a stable form, lasting lustre and a soft, resilient hand. The hot liquor breaks a large share of the wool fibre's hydrogen bonds and opens its disulfide crosslinks, releasing internal stress; the crosslinks re-form in new positions, and on cooling, together with the new hydrogen bonds, they lock the fabric's form in place — a permanent set, not the temporary, tension-held cohesive set. The WPF-ZN keeps the fabric fully immersed throughout, so the set forms while the fibre is at its most saturated. Placed after singeing, it also washes the fabric clean of singeing ash.
Why this machine is necessary: what happens without it, or with another method
WPF-ZN places two crabbing rollers in one bath. Fabric travels back and forth between them, changing its position so sections of the piece are treated alternately in the same liquor. QL’s reciprocating arrangement combines setting, layer exchange and a compact batch layout.
Whether crabbing comes before scouring depends on the route. Worsted qualities prone to distortion can use pre-setting; woollen fabric first completes the required milling, and the piece-dyed route also dyes after washing and milling before crabbing. Establish the process position before comparing WPF-ZN with the continuous crabbing section of WPF-LXZH.
Setting the parameters: temperature, tension, speed, time
The WPF-ZN's single 1,500-litre bowl loads 6 to 8 pieces of worsted fabric at a running speed of 60 metres per minute, heated by direct steam. Wrapper tension is held constant by torque control throughout, so tension acts on the wrapper, not directly on the fabric — low tension, zero elongation, so knitted wool is processed as readily as woven, and tension-sensitive qualities set without distortion. Setting temperature and dwell time are fixed by trial against the fabric in question — ask QL for the process sheet.
The questions customers ask most
- A single-bath machine runs uneven end to end and has to be stopped to turn the piece — what can be done about output?
- A twin-bath machine takes floor space and water we do not have — what then?
- Knitted wool cannot take tension — can it still be crabbed?
- Should crabbing come before or after scouring, and how do worsted and woollen routes differ?
- Should I choose batch crabbing (WPF-ZN) or continuous crabbing (WPF-LXZH) — and is continuous crabbing deep enough?
- Why must there be a cooling bath — can it be skipped?
Which process routes it appears on
Read WPF-ZN in the context of these routes: worsted top-dyed, worsted piece-dyed, woollen stock-dyed, woollen piece-dyed, wool-blend knitted fabric. Follow each branch to understand the equipment choice; a required process does not mean every quality uses the same model.
Give QL the fabric or top sample, existing upstream and downstream stations, and target finish to review configuration and process connections together.