Disc Thickener Technology for Consistent Coating Board Production
In coating board production, consistency control is the hidden variable that determines everything: formation quality, drying efficiency, coat weight uniformity, and machine speed. The disc thickener — sitting between the screening system and the paper machine approach flow — is often the bottleneck that limits your entire line.
Why Consistency Stability Matters for Coating Board
Coating board is typically manufactured in multi-ply configurations with three to five layers. Each layer requires precise basis weight control because:
- The top layer (usually 20–40 g/m² bleached chemical pulp) must be thin enough for economy but thick enough to receive coating without strike-through
- Filler layers (30–80 g/m² each) carry the bulk of the sheet weight and require stable fiber-to-filler ratios
- The back layer provides bending stiffness and smoothness for the reverse side coating
A consistency swing of just ±0.3% entering the headbox can cause basis weight variations of 3–5% across the web. For a 250 g/m² board, that’s a 7.5–12.5 g/m² deviation — enough to fail quality specifications and generate off-grade production.
The Disc Thickener Advantage
Leizhan’s Disc Thickener uses a series of rotating disc sectors covered with fine-mesh filter screens to dewater low-consistency stock (typically 0.8–1.5% inlet) to a stable discharge consistency of 8–12%. The key technical features:
- Filtration surface area: 20–150 m² depending on model (LDX series)
- Screen mesh: 40–80 mesh (350–180 micron) polyester or stainless steel
- Disc diameter: 1500–3000 mm
- Number of discs: 4–16 per unit
- Throughput capacity: 15–200 TPD per unit
- Drive power: 2.2–11 kW (low-energy operation)
Key Technical Specifications — LDX Series
| Model | Discs | Filtration Area | Capacity (TPD) | Motor (kW) |
|---|---|---|---|---|
| LDX-4 | 4 | 20 m² | 15–25 | 2.2 |
| LDX-8 | 8 | 50 m² | 40–60 | 4.0 |
| LDX-12 | 12 | 90 m² | 80–120 | 7.5 |
| LDX-16 | 16 | 150 m² | 140–200 | 11.0 |
Consistency Control Strategy
To achieve the tight consistency control coating board demands, pair the disc thickener with:
- Inlet flow control valve with automatic PID control tied to a consistency transmitter at the outlet
- Vat level sensor to maintain stable submergence of disc sectors (typically 40–55%)
- Variable frequency drive on the disc rotation motor for fine-tuning discharge consistency
- Filtrate turbidity monitoring — rising turbidity signals screen damage or blinding
With this control architecture, discharge consistency can be held within ±0.5% of target, providing the stable feed conditions that coating board headboxes require.
Fiber Recovery and White Water Management
The disc thickener also serves as a fiber recovery device. With 40–60 mesh screens, fiber retention exceeds 95%. The clear filtrate (typically 50–150 ppm TSS) can be reused as shower water on the paper machine, reducing fresh water consumption and effluent treatment load.
For a coating board mill producing 400 TPD, reusing thickener filtrate in place of fresh water saves approximately 200–300 m³ of water per day — a meaningful sustainability and cost benefit.
Maintenance Schedule
- Daily: Check filtrate clarity and vacuum gauge readings on disc sectors
- Weekly: Inspect screen surface for tears, pinholes, or blinding
- Monthly: High-pressure spray cleaning of disc screens (use 20–40 bar water jets)
- Every 3 months: Check disc sector seals and bearings; lubricate per manufacturer specification
- Annual: Replace screen mesh — typical service life is 10–14 months under normal conditions
Stable consistency is the foundation of quality coating board. A properly sized and maintained disc thickener delivers that stability at remarkably low operating cost.
📧 Contact us at leizhanzhang@gmail.com for sizing calculations, throughput projections based on your furnish, or a complete stock preparation line design.