Continuous Pad Dyeing Liquor Volume Control Methods for High Speed Ranges
High-speed pad dyeing liquor control requires ultra-low volume troughs and closed-loop radar dosing to eliminate tailing and shade drift across bulk runs.
Hydrodynamics in Squeeze Nip
Fluid Pressure
Hydrodynamic forces generated within converging roller gaps control liquid transfer and penetration during continuous wet processing operations. The phenomenon of hydrodynamics in squeeze nip governs how fluid velocity, viscosity, roll diameter, and applied pressure interact as fabric moves through saturated dye liquor between elastomeric rolls. High fluid pressures develop in the entrance zone ahead of the narrowest gap clearance, forcing chemical liquor into internal yarn structures before mechanical compression reaches maximum levels.
Liquid transport splits at the exit side, where cavitation bubbles form as liquid surface tension pulls excess liquor back toward roll faces. Peak hydrodynamic pressure occurs ahead of the nip centerline and drops rapidly across the exit point.
Wedge Profile
Geometry of the converging gap creates a liquid wedge that pushes against elastomeric roll coverings during continuous operation. Dynamic roll deformation broadens the contact footprint, which reduces local hydrodynamic pressure peaks while extending pressure duration across the moving fabric. Viscous chemical liquors increase hydrodynamic drag, pushing the liquor bank upstream and generating surface turbulence at elevated line speeds.
Inadequate roll hardness allows liquor film thickness to vary across the working width.
Roll Boundary
Boundary layer drag pulls fluid into the nip entry zone at speeds matching the rotating roll surfaces. Elastomeric roll covers deform under applied load, altering fluid film thickness across the contact zone. Hydraulic resistance within dense fabric structures resists rapid liquor displacement, generating fluid backflow away from the nip entrance.
Excessive line speed produces a hydraulic lifting force that partially separates roll faces and increases pick-up levels above specified target limits.
Residence Time
Duration of liquor exposure within the high-pressure zone determines liquid absorption into hydrophobic fiber matrices. Extended contact under peak pressure drives air out of filament interstices and forces dye molecules onto available surface sites. Insufficient residence time leads to superficial surface coating rather than deep fiber core penetration.
Squeeze nip fluid mechanics cease to dictate liquor pick-up once fabric exits the mechanical contact zone.