Where this machine sits in the line, and what comes before and after
The WPF-ZN crabbing machine sits at the setting station in the wet-finishing stage. In common domestic practice it follows rope scouring and milling, clearing the running marks that rope processing leaves behind. It is also placed after singeing, to wash the fabric clean of singeing ash. It can equally sit before rope scouring and dyeing as a pre-set, so the piece does not distort or crease once wet processing begins. At the same station, a mill can instead choose the continuous route — the crabbing section of the WPF-LXZH continuous line — the two are alternatives at one decision point, not a sequence.
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
Worsted fabric leaving the loom still carries considerable weaving stress. Left unset before rope scouring or dyeing, that stress releases uncontrolled, and the piece is prone to cockling and running marks, plain weaves especially. Conventional crabbing machines force a choice here: a single-bath machine sets deeper and takes less floor space, but runs uneven end to end and needs the piece turned by hand, which slows output and can leave water marks; a twin-bath machine runs even and marks-free, at the cost of setting depth. The WPF-ZN carries the fabric back and forth between two crabbing cylinders inside one bath, exchanging position with every pass — each pass does the work a manual turn would do. The piece gets one heat history end to end, without giving up the single bath's setting depth or its smaller footprint.
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?
- Why must crabbing come before rope scouring or dyeing, rather than after?
- 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
The WPF-ZN appears on five process routes at the batch crabbing station: the Worsted finishing, top-dyed route, the Worsted finishing, piece-dyed route, the Woollen finishing, stock-dyed route, the Woollen finishing, piece-dyed route, and the Wool-Blend Knitted Fabric Process Route. For the process sheet for this station, contact QL — WhatsApp +1 380 900 2442, or +86 189 2110 8080.