Excess Water Carry-Over in Forming Fabrics: A Comprehensive Guide for Paper Makers and Fabric Manufacturers
- Snehes Dasgupta
- Nov 13
- 5 min read
Introduction:
In the forming section of paper machines, excess water carry-over represents a pervasive challenge that undermines efficiency, escalates energy consumption, and compromises sheet quality. This phenomenon occurs when forming fabrics retain or transport surplus water into subsequent sections, such as the press and dryer, leading to higher steam demands, reduced machine speeds, and increased operational costs. For paper makers, it manifests as hidden energy drains and runnability issues; for fabric manufacturers, it translates to customer dissatisfaction and premature fabric replacement. By addressing root causes through targeted monitoring, design optimization, and maintenance, both stakeholders can achieve substantial improvements in dewatering performance and overall process stability.
This blog post synthesizes insights from PMC Centre's recent LinkedIn series, offering actionable strategies tailored to paper makers and forming fabric manufacturers. Drawing on established papermaking principles, we explore diagnostic factors, corrective actions, and design innovations to minimize water carry-over.
Understanding the Impact: From Forming to Dryer Efficiency
Excess water in the forming fabric directly correlates with elevated web moisture entering the press section, where each 1% increase in incoming moisture can amplify steam usage in the dryer by approximately 4%. Restricted drainage in the forming zone—often due to fabric fouling, compaction, or suboptimal vacuum application—forces reliance on evaporative drying downstream, inflating energy costs and limiting production rates. Paper machines operating at high speeds (over 1000 m/min) are particularly vulnerable, as centrifugal forces exacerbate water retention in coarser fabric structures.
For paper makers, early indicators include inconsistent couch moisture profiles (varying across sheet center, edges, and back) and declining solids consistency post-forming. Fabric manufacturers must recognize that mismatched designs exacerbate these issues, potentially shortening fabric life by 15-20% through accelerated wear from uneven loading. Proactive collaboration between the two groups is essential: paper makers benefit from customized fabrics, while manufacturers gain from field data to refine weaves.
Key Factors and Corrective Actions for Paper Makers:
Paper makers can mitigate water carry-over by focusing on operational diagnostics and maintenance protocols. Below are critical areas, with emphasis on monitoring and intervention.
1. Restricted Fabric Drainage and Permeability Loss:
Forming fabrics degrade over time through fouling (e.g., pitch, fibers) or mechanical compaction, reducing permeability by 20-25% and trapping water that overloads the press. This leads to higher web moisture and steam loads in the dryer.
Action: Conduct regular permeability audits using air flow tests; target showers with high-pressure oscillating nozzles (optimized at 4-6 bar) to restore openness. Replace fabrics if permeability drops exceed 20%. Monitor couch moisture uniformity to benchmark forming efficiency.
2. Wet Press Overload from Inadequate Dewatering:
A saturated sheet entering the press limits mechanical water removal, shifting dewatering to thermal methods and reducing press efficiency. Vacuum imbalances or excessive fabric voids compound this, retaining water in fabric channels.
Action: Optimize press loading and felt conditioning; verify incoming solids consistency (aim for 15-18% post-forming). Adjust foil angles and main header vacuum levels based on real-time readings to enhance initial drainage.
3. Vacuum and Shower System Imbalances:
Misaligned showers or unstable vacuum boxes create uneven drainage, fostering water pockets and sheet defects. Up to 10% of process water can be lost to carry-over in poorly tuned systems.
Action: Perform routine vacuum audits and shower alignments; employ low-pressure, high-volume showers to prevent fabric saturation. Clean vacuum boxes quarterly to maintain suction stability.
4. Contaminated Fabric Surfaces:
Chemical carry-over, pitch buildup, and fiber residues block drainage pathways, directly elevating steam demand by impairing water release.
Action: Implement proactive cleaning with oscillating nozzles and periodic chemical soaks (e.g., enzymatic cleaners for pitch). Schedule shutdown washes to recover full permeability, potentially cutting energy use by 5-10%.
5. Inadequate Monitoring and Early Trend Detection:
Water carry-over often builds gradually, appearing as rising steam/ton ratios or output drops. Without baseline tracking, issues escalate unnoticed.
Action: Log key metrics like forming solids, post-press dryness, and vacuum profiles weekly. Use data analytics to spot drifts early, integrating with PMC Centre's AI tools for predictive insights.
Design Strategies for Forming Fabric Manufacturers
Fabric manufacturers play a pivotal role in preventing carry-over at the design stage. By engineering for machine-specific needs, products can deliver consistent dewatering and longevity.
1. Tailoring Designs to Machine Variability:
No two paper machines are identical—variations in furnish, grade, speed, type, and drainage profile demand attention to select fabric designs. Generic designs lead to mismatched permeability, trapping water and causing press overloads.
Strategy: Partner with clients during specification to align fabric openness with vacuum dynamics and flow profiles. Validate through pilot simulations for seamless installation performance.
2. Balancing Caliper and Void Volume:
Excessive caliper or void volume retains surplus water, delaying release and amplifying carry-over risks like sheet breaks.
Strategy: Engineer targeted void volume suited to furnish density, confirmed via lab drainage tests. For high-speed applications, prioritize lower-caliper structures to minimize internal voids without sacrificing wear resistance.
3. Ensuring Uniform Air Permeability:
In multilayer fabrics, imprecise stacking from weaving to heat-setting creates permeability gradients, promoting localized water retention and fouling.
Strategy: Integrate inline sensors during production and mandate post-heat-setting audits. This sustains even flow across the width, extending fabric life.
4. Optimizing for High-Speed Operations:
At speeds exceeding 1000 m/min, coarser fabrics succumb to centrifugal water trapping, eroding fines retention and uniformity.
Strategy: Favor finer structures with durable monofilaments for rapid dewatering. Consider Shute Support Binder (SSB) designs or warp binders for reduced voids; incorporate non-sticking materials to deter contamination.
5. Embedding Cleaning Guidance in Product Support:
Even superior designs require maintenance to combat permeability loss from operational contaminants.
Strategy: Provide clients with protocols for low-pressure oscillating showers and chemical regimens, referencing field data to underscore maintenance's role in curbing carry-over buildup.
Conclusion: Collaborative Optimization for Sustainable Gains:
Excess water carry-over is not inevitable—it's a solvable inefficiency through vigilant monitoring by paper makers and innovative design by fabric manufacturers. By integrating these strategies, the industry can unlock 5-15% energy savings, enhanced sheet quality, and prolonged asset life.
Empower Your Operations with PMC CENTRE AI – our free 24/7 AI assistant for PMC troubleshooting, delivering instant, data-driven guidance on water carry-over and beyond. Access it anytime at www.pmccentre.com/pmc-centre-ai.
PMC Centre offers unbiased consultancy tailored for both paper makers and forming fabric manufacturers, optimizing Paper Machine Clothing for superior efficiency, reduced energy costs, and proactive troubleshooting.
Contact us at www.pmccentre.com to schedule a customized audit and unlock sustainable gains in your forming section.
Citations:
1. Paper Machine Water Efficiency - Paper360 -
2. Designing of Forming Fabric Considering Paper Making - IPPTA
3. A study in how rewetting can be reduced in the paper machine.
4. Paper Machine Water Efficiency - TAPPI.org
5. PAPERMAKING BEST PRACTICES WITH VACUUM-DEWATERING
6. Rate-limiting mechanisms of water removal during the formation
Comments