Thixotropic Rebuild Kinetics Governing High Speed Slot Die Coating Instabilities
Thixotropic rebuild delay shifts slot die bead rupture limits during high speed web acceleration.
Progressive Cavity Pump Ripple
Meaning
Low-frequency flow pulsation caused by the eccentric rotation of a metallic rotor within an elastomeric stator introduces cyclic pressure variations into a fluid feed line. When delivering slurry to a coating die, progressive cavity pump ripple appears as periodic variations in the wet film thickness along the continuous substrate. This pressure fluctuation arises from the changing cavity volumes at the discharge point of the pump.
Managing these pulsations requires damper units or downstream flow controllers to maintain dry coat weight consistency.
Pulsation Cause
Rotational eccentricity of the internal pump parts creates moving sealed cavities that discharge fluid in a continuous but non-uniform manner. As each cavity opens and closes, it generates a tiny pressure peak and valley.
Thickness Impact
Cyclic flow changes produce a wavy surface on the wet electrode foil, with alternating bands of high and low active material loading. These regular variations lead to uneven current density during battery use, creating hot spots that accelerate aging and increase the risk of internal short circuits. In addition, the uneven thickness makes it impossible to achieve a uniform density during the calendering process.
Attenuation Mechanism
Minimizing these waves involves installing a pulsation dampener close to the slot-die inlet to absorb the pressure spikes. Choosing a multi-lobe rotor-stator configuration also reduces the amplitude of the ripple by spreading the pressure changes over more frequent, smaller discharge events.