Solving Plastic Clogging in Pulper Screens
In many paper manufacturing machine lines, soft plastic contaminants are a persistent challenge. The typical symptom is a screen plate with 8.0 mm holes becoming plugged by plastic sheets, reducing accept flow and requiring frequent cleaning stops.
The primary reasons are fourfold. High proportion of plastic film, hot melt adhesive, and pressure‑sensitive labels in the waste paper furnish: these materials do not disintegrate easily; they form flat or clumped pieces that easily wedge into round holes. The 8.0 mm hole diameter is too small for many plastic pieces, especially when they are not fully broken down. Low pulping consistency or insufficient residence time: when the paper mill machinery runs at 4‑5 percent consistency, the fiber mass lacks enough rubbing action to tear plastics apart. A rotor‑to‑screen gap that is too wide fails to create the hydraulic shear needed to push plastics through the openings. Finally, a conventional screen plate without reverse taper or cleaning features allows plastics to become firmly stuck, and the blockage accumulates over time. These issues directly affect the reliability of your paper production line.
Short‑term measures that can be implemented quickly include raising the pulping consistency to 6‑7 percent, which increases fiber‑to‑fiber friction and helps break plastic aggregates. Extending the pulping cycle by a few minutes allows more time for plastic dispersion before the stock reaches the screen. If your system has the capability, use high‑pressure water above 20 bar directed from the outside of the screen plate to blow out lodged particles. Stricter sorting of incoming waste paper to reject bales with high plastic content will also reduce the load.
For permanent fixes, the most effective change is to replace the screen plate with a larger aperture – 10‑12 mm round holes or slotted plates like 12×40 mm elliptical openings. These geometries are much kinder to soft plastics. A screen plate with reverse‑tapered holes where the outlet is slightly larger than the inlet prevents wedging. Some advanced plates incorporate serrated or knife edges that cut plastic strips as they pass. Installing an additional coarse screen with 12‑15 mm holes upstream of the pulper discharge catches large plastics before they reach the fine screen. Ensure the Conic Drum plastic cleaner operates correctly to avoid recirculation. When all else fails, consider replacing the whole paper processing line pulping stage with a drum pulper, which is inherently more tolerant to plastics.
Leizhan’s ZG series drum pulper is the ultimate solution for mills struggling with plastic clogging. It operates at 14‑18 percent high consistency, gently separating fibers while keeping plastics whole, so they are easily removed by downstream screens. The drum design provides long retention time and efficient coarse screening in one unit, lowering energy consumption and maintenance cost. With models covering 70 to 1800 t/d, our drum pulper fits any scale of paper making line. Choose Leizhan for a turnkey paper production line that runs smoothly without plastic‑related downtime. Contact us to discuss your specific furnish and get a tailored recommendation: leizhanworld@gmail.com
