Diagnose the symptom before changing the felt
Press-section problems often look similar at the reel but come from different causes. A wet streak can originate from felt contamination, uneven shower coverage, vacuum instability, nip loading, roll condition or the sheet itself. Replacing the felt without separating these variables may only reset the symptom temporarily.
Use the following workflow to document the problem, test the most likely system causes and decide whether cleaning, machine correction or a different felt design is required.
1. Plugging and loss of void volume
Typical signs
- rising sheet moisture after the press;
- increasing vacuum demand or unstable uhle-box response;
- darker or glazed felt surface;
- poorer water handling even though felt tension is unchanged;
- rapid recurrence after a normal shower cycle.
Check in this order
- Identify the contaminant: fines, filler, pitch, stickies, coating color or chemical precipitate.
- Verify shower pressure, nozzle condition, oscillation and cross-direction coverage.
- Check uhle-box slot condition, vacuum level and seal-water stability.
- Compare permeability or water-handling data across the width, not only at one point.
- Review furnish, retention chemistry and broke changes before the problem started.
If cleaning restores performance only briefly, the felt structure, batt fineness or chemical program may not match the contamination load.
2. Crushing and permanent compaction
Crushing is a loss of recoverable void volume under repeated nip loading. It is different from surface contamination, although both can reduce dewatering.
Look for a persistent caliper or water-handling loss that does not recover after effective cleaning. Then verify nip load, roll crown, felt tension, start-up procedure and whether the felt was conditioned before full load.
Do not diagnose crushing from appearance alone. Compare measurements from a healthy period and check whether the loss is uniform or concentrated in a machine-direction band.
PAPTEX's product range illustrates why construction matters: BOM press fabrics are positioned for dewatering, sheet quality and compression recovery; laminated and needle-felt designs serve different paper grades and speed ranges. The correct replacement must match nip energy, paper grade and contamination conditions, not only the previous product name.
Review BOM Press Fabric, Laminated Press Fabric and Needle Felt Press Fabric.
3. Edge wear and edge damage
Common system checks
- felt guiding and alignment;
- edge position relative to rolls, suction zones and savealls;
- damaged doctor blades, sharp hardware or contact points;
- uneven shower coverage at the edges;
- edge curl, folded batt or installation damage;
- excessive local tension or oscillation limits.
Mark the damaged edge, running direction and distance from the machine datum before removing the felt. Good photos should include a wide view, a close-up and a scale. This evidence helps distinguish abrasion, cutting, thermal damage and chemical attack.
4. Cross-direction moisture variation
Do not assume every wet streak is a felt-design problem. Build a cross-direction comparison that includes:
- sheet moisture before and after each nip;
- felt condition and water handling across the width;
- shower pressure and nozzle pattern;
- uhle-box vacuum and slot condition;
- nip loading, roll cover and crown;
- stock flow and basis-weight profile.
Change one variable at a time where production permits. A felt replacement should be considered after the machine-side causes are checked or when the moisture pattern clearly follows a documented felt condition.
Data to send with a troubleshooting request
Provide paper grade, basis weight, machine width and speed, press configuration, nip loads, current felt model and age, felt tension, vacuum levels, shower details, chemicals, service history, moisture profile and photos of the symptom. If possible, include the date when the trend began and any furnish or operating changes made at that time.
Ask a PAPTEX engineer to review the press section.
What this guide does—and does not—claim
This workflow is a diagnostic checklist. It does not assign a universal cleaning interval, service-life increase or production gain. Those values must be confirmed from the individual machine's baseline and trial data.
