Guide for Cleaning and Conditioning Forming Fabrics for Paper Machines

Maintaining the cleanliness and conditioning of forming fabrics is one of the most critical yet often misunderstood aspects of maximizing runnability and paper quality in modern paper machines. In the high-speed and high-contaminant environment of today’s furnish — particularly with the increased use of recycled fibers — forming fabric performance directly influences drainage efficiency, sheet formation, fiber retention, runnability, and ultimately the economic performance of the machine.

This comprehensive guide unpacks all of the key principles, best practices, and expert tips for cleaning, conditioning, and controlling contamination in forming fabrics — based primarily on ExpertTips, expanded with practical insights and extended context for papermakers and machine clothing engineers.

Table of Contents

1. Introduction: Why Forming Fabric Cleanliness Matters

2. Understanding Forming Fabric Contamination

 2.1 What Contaminants Are and Where They Come From

 2.2 How Contamination Impacts Fabric Performance

3. Contamination Resistance: Material Choices and Coatings

4. Cleaning and Conditioning Systems Explained

 4.1 Chemical Cleaning

 4.2 Shower Systems

 4.3 Mechanical Cleaning

5. Best Practices for Shower Cleaning

 5.1 Shower Positioning

 5.2 Pressure, Coverage, and Synchronization

 5.3 High-Pressure vs Low-Pressure Showers

6. Practical Guidelines for Chemical Cleaning

 6.1 Choosing the Right Chemicals

 6.2 Safety Precautions and Chemical Compatibility

 6.3 Application Protocols

7. Mechanical Cleaning: When, Why, and How

8. Monitoring Cleanliness: Metrics and Inspection Techniques

9. Conditioning Strategies That Extend Fabric Life

10. Common Pitfalls and How to Avoid Them

11. Integrating Cleaning into Fabric Maintenance Plans

12. Conclusion: Clean Fabrics Drive Better Paper

1. Introduction: Why Forming Fabric Cleanliness Matters

Forming fabrics are the workhorses of the wet end of a paper machine. Their primary role is drainage — removing water from the fiber slurry while supporting the forming paper web. The efficiency of this drainage process is largely determined by the porosity and void volume of the fabric structure. When these pathways are blocked by contaminants, the fabric’s ability to drain water and release the sheet deteriorates rapidly.

Over time, contaminants such as pitch, stickies, adhesives, coatings, and recycled fiber fines accumulate in the yarns and voids of forming fabrics. Left unaddressed, this buildup leads to reduced drainage capacity, increased formation problems, web breaks, felt plugging, higher vacuum draw risk, and reduced overall runnability. The result: lower quality paper, compromised machine stability, and increased operating costs.

To combat this, paper mills must adopt a proactive, repeatable cleaning and conditioning approach that addresses contamination at its source, removes deposits before they bond or “lock” into the fabric structure, and maintains the fabric’s designed drainage performance throughout its service life.

2. Understanding Forming Fabric Contamination

2.1 What Contaminants Are and Where They Come From

Contaminants in forming fabrics typically originate from one of the following sources:

Raw furnish components: Natural pitch, resin, waxes, and extractives inherent in pulp fibers, especially softwood grades.

Recovered fiber streams: Recycled furnishes bring coatings, adhesives, hot-melt binders, and printing inks. These materials readily adhere to polyester monofilaments and can build up quickly over time.

Chemical additives: Sizing agents, retention aids, and coating components can interact with fiber fines, exacerbating deposit formation.

Paper machine contaminants: Fibers shed from press felts or dryer fabrics, shower residue, and roll oils can all contribute to internal fabric contamination.

These contaminants adhere to the yarn surface and fill the interstices in the fabric structure — especially around yarn crossovers where mechanical locking and capillary forces trap deposits.

2.2 How Contamination Impacts Fabric Performance

Contaminant buildup affects forming fabrics in several detrimental ways:

Reduced drainage: Blocked voids limit airflow and water removal capacity critical to formation efficiency.

Poor release: Deposits interfere with the clean separation of the paper web from the fabric, increasing the risk of rewetting and sheet defects.

Increased sheet marks: Uneven contamination creates localized drainage variations that manifest as streaks or MD/CD irregularities.

Accelerated wear: Abrasive contaminants increase mechanical wear on yarns, reducing fabric life.

Understanding these mechanisms is the first step in selecting the right cleaning and conditioning strategies.

3. Contamination Resistance: Material Choices and Coatings

One of the first lines of defense against contamination is fabric design and material selection:

Contaminant-resistant finishes and coatings applied to yarns during manufacturing reduce the adhesive attraction between contaminants and polyester monofilaments. These finishes can be engineered to minimize surface energy and slow initial deposit buildup.

Surface-active chemical passivation (applied via shower passivation cycles) can create a temporary protective layer that reduces deposit bonding during production.

Higher mesh counts and lower caliper fabrics often have more open and straight-through drainage paths, which facilitate easier cleaning by online shower systems and reduce the tendency for contaminants to bridge and lock in place.

However, coatings and finishes must be selected carefully — considering environmental concerns, compatibility with chemical cleaning agents, and the specific furnish chemistry encountered on a given machine.

4. Cleaning and Conditioning Systems Explained:

To successfully manage contamination, mills rely on a combination of cleaning technologies:

4.1 Chemical Cleaning

Chemical cleaning involves applying solvents or detergents that dissolve or emulsify contaminants. Effective chemical cleaners can soften and detach pitch, waxes, glues, and other non-water soluble deposits. Key points include:

Avoiding concentrated acids or alkalis and highly aggressive oxidizers, which can damage polyester yarns.

Using soft bristle brushes or rags with chemical agents — avoiding metal brushes that can scratch or damage fabric surfaces.

Chemical cleaning is most effective when fabrics are stopped or on crawl speed and when contaminants are still pliable — not fully hardened.

4.2 Shower Systems

Shower cleaning systems are the most widely used method online. They work by directing jets of water (or water with additives) at the fabric to dislodge and flush contaminants away:

Stationary fan showers provide broad coverage.

Oscillating needle showers deliver targeted kinetic energy to penetrate deep into fabric voids.

High-pressure showers (carefully controlled) can remove stubborn deposits.

Effective shower systems must deliver uniform coverage, sufficient energy, and be synchronized to match fabric travel speed. Shower nozzle positions, angles, and flow rates all influence cleaning effectiveness.

4.3 Mechanical Cleaning

Mechanical cleaning includes using suction rolls, doctor blades, and specially designed fabric cleaners that physically scrape or vacuum contaminants. While less common than shower systems, these can be beneficial in targeted situations — particularly where heavy deposits resist other methods.

5. Best Practices for Shower Cleaning

Shower cleaning is the backbone of forming fabric conditioning. To make the most of this approach:

5.1 Shower Positioning

Position nozzles close enough to the fabric surface to impart sufficient kinetic energy without damaging yarns. Typically:

Sheet side showers focus on dislodging surface and near-surface deposits.

Non-sheet side showers target internal void contamination.

Monitor flow uniformity across the width, and be sure nozzles are free of clogs.

5.2 Pressure, Coverage, and Synchronization

Balancing pressure is critical:

Too low — cleaning is ineffective.

Too high — risk of fabric movement or damage increases.

Synchronize oscillation rate to fabric travel speed so each area receives consistent exposure. Uneven coverage leads to MD streaks and localized plugging.

5.3 High-Pressure vs Low-Pressure Showers

High-pressure showers deliver deep cleaning but require careful control to avoid excessive vibration or premature seam wear.

Lower pressure fan showers excel at general flushing and distributing water evenly across the fabric.

Most modern machines use a combination of shower types staged strategically throughout the forming section for optimal removal of diverse contaminants.

Refer to standard recommendations for shower types, pressures, and flows (adapted from industry benchmarks):

Application	Type	Nozzle Spacing (in/cm)	Distance (in/cm)	Pressure (psi/kPa)	Flow Rate (GPM/in / LPM/cm)	Orifice (in/mm)
Headbox Rotary	Fan Spiral	10-20” (25–50cm)	8” (20cm)	20-40 (140-280)	0.075-0.204 (0.111-0.303)	0.1” (2.5mm)
Headbox Apron	Stationary Fan	6-8” (15-20cm)	16” (40cm)	30-40 (200-280)	0.120-0.133 (0.178-0.198)	0.080” (2.0mm)
Dandy	Oscillating Needle	1-1.5” (2.5-4cm)	2-4” (5-10cm)	100-200 (700-1,400)	0.130-0.290 (0.19-0.433)	0.031 (0.8mm)
Lump Breaker	Stationary Fan	6-8” (15–20cm)	12” (30cm)	20-30 (140-200)	0.028-0.043 (0.042-0.064)	0.060” (1.5mm)
Non-Sheet Side HP	Oscillating Needle	3” (7.5cm)	3-4” (7.5–10cm)	100-250 (700-1,700)	0.130-0.238 (0.19-0.355)	0.031-0.040” (0.8–1.0mm)
Sheet Side HP	Oscillating Needle	3” (7.5cm)	3-6” (7.5-15cm)	200-450 (1,400-3,100)	0.135-0.238 (0.20-0.355)	0.031-0.040” (0.8–1.0mm)
Multi-Head Cleaner HP	Traversing Head	0.080” (0.2cm)	0.6-2” (1.5–5.0cm)	1595-2540 (11,000-17,500)	0.008-0.014 (0.012-0.021)	0.008” (0.2mm)
Sheet Knock-off (Slow Machines)	Stationary Fan	3” (7.5cm)	4-7” (10–18cm)	150 (1,030)	0.75-1.77 (1.12-2.678)	0.12-0.16” (3-4mm)
Flooded Nip Knock-off	Stationary Fan	3” (7.5cm)	11-14” (28-36cm)	80-200 (550-1,400)	Fill Fabric Void Volume	0.16-0.24” (4-6mm)
Wash Roll/Sheet Wetting	Stationary Fan	3” (7.5cm)	4-7” (10–18cm)	80-120 (550-830)	0.75-1.77 (1.12-2.678)	0.12-0.16” (3-4mm)
Doctor Lube	Stationary Fan	6-8” (15–20cm)	8” (20cm)	30-40 (200-280)	0.150-0.163 (0.223-0.242)	0.1” (2.5mm)
Suction Rolls Cleaning	Oscillating Needle	3-6” (7.5-15cm)	4” (10cm)	350-500 (2,400-3,500)	0.18-0.250 (0.27-0.373)	0.031-0.040” (0.8-1.0mm)

6. Practical Guidelines for Chemical Cleaning

Chemical cleaning is a powerful but often misunderstood tool in forming fabric maintenance. When applied correctly, it can restore drainage capacity, remove stubborn deposits, and significantly extend fabric life. When misused, however, it can damage yarns, weaken seams, and accelerate wear.

6.1 Choosing the Right Chemicals

The first rule of chemical cleaning is match the chemistry to the contaminant. No single chemical is effective against all deposit types, and over-reliance on aggressive products often causes more harm than good.

Common contaminant–chemical pairings include:

Pitch, waxes, and resins: Solvent-based or emulsifying cleaners

Stickies and adhesives: Specialty adhesive dispersants

Coating residues and fillers: Alkaline detergents with dispersing agents

Organic fines and bio-slime: Oxidizing or enzymatic cleaners

It is critical to verify that any cleaning chemical is compatible with polyester monofilament yarns and approved for use on forming fabrics. Highly concentrated acids, strong alkalis, or uncontrolled oxidizers can embrittle yarns and permanently alter fabric geometry.

6.2 Safety Precautions and Chemical Compatibility

Chemical cleaning must always be performed with strict safety controls in place. Operators should follow plant safety protocols and chemical supplier guidelines, including:

* Proper personal protective equipment (PPE)

* Adequate ventilation

* Controlled dilution and application rates

From a fabric standpoint, compatibility testing is essential. Repeated exposure to aggressive chemicals can degrade yarn surfaces, increase abrasion, and reduce seam strength over time. Chemical cleaning should therefore be viewed as a targeted corrective tool, not a substitute for consistent mechanical and shower cleaning.

6.3 Application Protocols

Chemical cleaning is most effective when:

* Fabrics are stopped or running at crawl speed

* Deposits are still soft or semi-plastic, not fully hardened

* Chemicals are allowed sufficient dwell time to penetrate deposits

Mechanical assistance — such as soft nylon brushes or low-abrasion pads — may be used to loosen deposits, but metal brushes and aggressive scraping tools should always be avoided. Following chemical application, thorough rinsing with clean water is essential to prevent residual chemical buildup within the fabric.

7. Mechanical Cleaning: When, Why, and How

Mechanical cleaning methods physically remove contaminants through scraping, vacuuming, or doctoring actions. While not always necessary on every machine, they can be highly effective under specific conditions.

Mechanical cleaning approaches include:

* Suction boxes and vacuum rolls that extract water and loose contaminants from the fabric

* Doctor blades designed to skim surface deposits

* Dedicated fabric cleaning devices that combine mechanical agitation with flushing water

These systems are particularly useful when dealing with heavy surface contamination or when chemical and shower systems alone cannot maintain fabric openness.

However, mechanical cleaning must be carefully controlled. Excessive blade pressure, misalignment, or vibration can accelerate yarn wear, damage seam loops, or induce fabric instability. Mechanical cleaning should be integrated into an overall conditioning strategy — not used as a standalone solution.

8. Monitoring Cleanliness: Metrics and Inspection Techniques

Effective cleaning programs rely on measurement and observation, not assumptions. Mills that monitor fabric cleanliness consistently are far better positioned to intervene early — before performance declines significantly.

Key monitoring techniques include:

* Visual inspection: Regular inspection of both sheet and non-sheet sides for discoloration, streaking, or visible buildup.

* Air permeability testing: Tracking changes in airflow provides quantitative insight into void blockage and drainage loss.

* Vacuum and drainage performance: Increasing vacuum demand or slower dewatering rates often signal contamination issues.

* Formation and sheet quality trends: MD/CD streaks, pinholes, or inconsistent formation can be downstream symptoms of fabric plugging.

Establishing baseline measurements early in the fabric’s life allows mills to track degradation trends and evaluate the effectiveness of cleaning interventions over time.

9. Conditioning Strategies That Extend Fabric Life

Cleaning removes contaminants; conditioning prevents them from bonding in the first place. Conditioning strategies aim to maintain a low-adhesion fabric surface that resists deposit buildup.

Effective conditioning practices include:

* Surface passivation treatments applied through shower systems to reduce surface energy

* Consistent low-level cleaning cycles rather than infrequent aggressive cleaning

* Balanced furnish chemistry**, minimizing excess stickies and pitch at the source

Well-conditioned fabrics maintain more stable drainage, reduce the need for harsh chemical cleaning, and exhibit longer service life with more predictable performance.

Importantly, conditioning should be viewed as a **continuous process**, not a one-time event. Small, frequent interventions are far more effective than reactive deep cleaning after performance has already declined.

10. Common Pitfalls and How to Avoid Them

Despite best intentions, many forming fabric cleaning programs fall short due to avoidable mistakes:

* Waiting too long to clean: Once contaminants harden and lock into the fabric, removal becomes far more difficult.

* Overusing high-pressure showers: Excessive pressure can damage yarns, seams, and fabric stability.

* Incorrect nozzle alignment or coverage: Uneven cleaning leads to streaking and localized plugging.

* Using incompatible chemicals: Short-term cleanliness gains can result in long-term fabric damage.

* Treating symptoms instead of root causes: Without addressing furnish chemistry or upstream contamination sources, cleaning becomes a constant battle.

Avoiding these pitfalls requires coordination between operations, maintenance, wet-end chemistry, and PMC expertise.

11. Integrating Cleaning into Fabric Maintenance Plans

The most successful mills integrate forming fabric cleaning into a structured maintenance plan, rather than treating it as an ad-hoc activity.

An effective plan includes:

* Defined inspection intervals

* Documented shower settings and chemical protocols

* Clear trigger points for corrective cleaning

* Collaboration with PMC suppliers and independent consultants

* Ongoing operator training and awareness

By embedding cleaning and conditioning into standard operating procedures, mills reduce variability, improve repeatability, and protect fabric investment.

12. Conclusion: Clean Fabrics Drive Better Paper

Forming fabric cleanliness is not merely a housekeeping task — it is a fundamental driver of paper machine performance, product quality, and operational efficiency.

Clean, well-conditioned fabrics deliver:

* Consistent drainage and formation

* Improved sheet release

* Lower vacuum demand

* Reduced break frequency

* Longer fabric life and lower total cost of ownership

As furnishes become more complex and machines operate at ever higher speeds, proactive cleaning and conditioning strategies are no longer optional. By understanding contamination mechanisms, selecting appropriate cleaning tools, and monitoring performance over time, papermakers can unlock the full potential of their forming fabrics — and produce better paper, more reliably, every day.

Ready to optimize?

PMC Centre provides unbiased consultancy to optimize Paper Machine Clothing performance—independent of fabric sales. Our expertise resolves forming fabric challenges with precision.

👉 Try our expert PMC Troubleshooting – Now Powered by GPT-5

(100% free): https://www.pmccentre.com/pmc-centre-ai-gpt

Built for papermakers and PMC pros—faster, smarter, 24/7 support for every fabric issue.

🚀 Get instant guidance: www.pmccentre.com/pmc-centre-ai-gpt

For a customized audit or deeper dive, contact us today. Stay tuned for more insights on our blog!

#FormingFabrics #PaperIndustry #FabricMaintenance #ManufacturingExcellence

Reference: https://www.astenjohnson.com/media/1759/expertip-cleaning-conditioning-forming-fabrics-0620.pdf