How to avoid long-run holdup, dead zones, gel formation, and cross-contamination during product changeover?

● Zero drift compensation: static empty-scale calibration daily before startup; dynamic calibration every 2 h with a standard weight. Example: for viscous PSf dope, error reduced from ±0.5% to ±0.1%.

● Temperature compensation: mount PT100 on the scale; build a temperature–zero drift model (ΔZ = kΔT) to correct readings in real time.

● Coriolis mass flow meter:

● Zero drift compensation: “air calibration” during downtime with dry air at zero flow to record baseline and auto-correct. Example: for PAN/DMF, flow error reduced from ±0.8% to ±0.2%.

● Temperature compensation: use internal temperature sensing with density–temperature curve ρ = ρ0[1 − α(T − T0)] to correct mass flow.

● High-viscosity specifics:

● Use low-shear Coriolis designs to minimize viscosity effects.

● For ultra-high viscosity (> 1000 cP), consider LIW + time integration as an indirect measurement.

● Online verification: periodically perform volumetric checks with a standard prover to ensure system accuracy within ±0.5%.

● Push: displace dope A under laminar flow (Re < 2000) with high-purity solvent until a clear interface forms to maximize physical displacement.

● Clean (CIP): run preset CIP using the same or compatible solvent for the next dope B for forced circulation flushing.

● Verify: inline sampling with UV spectrophotometer or inline viscometer; when key indices (e.g., absorbance) reach baseline and stabilize, cleaning passes.

● Quantification: optimize CIP time, flowrate, and solvent volume based on verification data to achieve minimal consumption with assured effectiveness.

● Anti-plugging: install low-speed bottom agitators (5–10 rpm) with ultrasonic anti-settling (28 kHz, 100 W) to prevent sedimentation. Add inline filters (50 μm) and schedule regular back-blow cleaning.

● Steady-state control: link a mass flow meter (±0.2%) with a VFD pump for real-time control, keeping flow fluctuation ≤ 1%. Example: in PVDF/DMAc, this cut spinning diameter CV from 8% to 2%.

● Dissolving area: ISO 7; 22°C ± 1°C; RH ≤ 60%; dew point ≤ 15°C. Dehumidifier with ±1°C dew point control to limit solvent-driven humidity increases.
● Feeding room: ISO 6; 20°C ± 0.5°C; RH ≤ 55%; dew point ≤ 12°C. Local laminar flow hoods (0.45 m/s) to keep the feeding process clean.

● Spinning room: ISO 5; 18°C ± 0.3°C; RH ≤ 50%; dew point ≤ 10°C. Dual-stage filtration (pre + HEPA) and constant T&RH AHU to maintain ultra-clean conditions.

● Pulsation damping: install pulsation dampers at pump outlet (N2 charge at ~60% of system pressure) to reduce flow ripple from ±15% to ±2%. For viscous PSf dopes, this markedly stabilizes spinning.
● Resonance isolation: conduct modal analysis to find natural frequencies of pump–piping; shift pump speed away from resonance (e.g., 50 Hz → 35 Hz). Add flexible compensators (length ~5× pipe ID) to attenuate vibration transmission.

● Semi-automatic: time = manual disassembly (T1) + cleaning (T2) + reassembly (T3). Example: PVDF/DMAc to PES/NMP, T1 = 45 min, T2 = 60 min (3× line volume flush), T3 = 30 min; total 135 min.
● Fully automatic: time = automatic flush (T4) + system self-check (T5). Example with integrated CIP/SIP: T4 = 20 min (1.5× volume), T5 = 10 min; total 30 min.

● Solvent consumption:
● Semi-automatic: mass = line volume (V) × flush factor (n) × solvent density (ρ). Example: V = 50 L, n = 3, ρ = 0.95 g/cm³ → 142.5 kg.

● Fully automatic: with optimized segmented/variable-flow flushing, n can drop to 1.2 → 57 kg; ~60% saving.