What Is a Fabric Press? — “Squeezing Water Out of a Sponge”
As you surely know, when the paper web comes off the wire section, it’s like a sponge soaked with water—with a moisture content of around 80%. If it were sent directly to the drying cylinders, the steam cost would skyrocket. The core task of a fabric press is simple: use mechanical force to squeeze out as much water as possible, increasing the dryness of the paper web before it enters the drying section (the target is to raise it to 50% or even higher). Every 1% increase in dryness saves a significant amount of steam costs in the drying section. So, our work is directly tied to the workshop’s costs.
The press section may seem complex, but it essentially relies on the coordination of three key components:
1. Press rolls (including pressure rolls, vacuum rolls, etc.): These are the "workhorses" that do the heavy lifting. They provide the pressure to squeeze out water. We need to pay attention to their crown (how much thicker the middle of the roll is than the ends), hardness, and surface condition. If the crown is incorrect, the pressure will be uneven, resulting in paper that’s dry on one side and wet on the other—all wasted.
2. Fabrics (or BOM paper fabrics): These are the most critical yet delicate "partners," with three key roles:
Web transfer: Like a conveyor belt, they smoothly receive the wet web from the wire section, safely move it through the nip, and pass it on to the next process.
Dewatering and water drainage: Themselves like large sponges, they absorb the water squeezed out of the paper web in the nip. Then, with the help of vacuum boxes and water spray pipes, the water is removed, allowing the fabrics to dry out and prepare for the next dewatering cycle.
Web support: Prevent the wet web from being crushed or embossed under high pressure.
3.Nip: This is the "gap" where the press rolls and fabrics make contact—it’s where the "miracle of dewatering" actually happens. The core parameters here are pressure, linear pressure, and dwell time.
Operators’ “Eyes, Ears, and Hands” — Daily Monitoring Points
Looking:
Fabric operation: Is the fabric running straight? Are there signs of arching or wrinkling? Is the surface dirty? Check the fabric’s wet-dry line to assess its dewatering performance.
Vacuum level: Is the vacuum level of the fabric’s vacuum box stable? A sudden increase indicates the fabric may be dirty or clogged; a sudden drop suggests a leak.
Spray effectiveness: Can the high-pressure moving spray pipes thoroughly clean the fabric? Are the water jets uniform? Does the low-pressure spray adequately moisten the fabric?
Web exiting the nip: Is the paper web crushed or embossed? Is it sticking to the rolls? How does the dryness feel?
Listening:
Are there abnormal friction sounds from the fabric operation? Are there harsh scraping sounds from the vacuum box doctor blades?
Is there any blockage in the spray pipe nozzles (the sound will change)?
Feeling (Safety first!):
When the machine is stopped, feel the fabric to check its elasticity, thickness wear, and for any hard lumps or oil stains.
Common Issues and Troubleshooting
1. Embossing/Crushing
Symptom: The paper surface has marks similar to the fabric’s texture; in severe cases, it looks tattered like a map.
Causes: This is the most typical issue, rooted in poor water drainage. Either the fabric is dirty or clogged (fillers, sizing agents, or fibers
blocking its pores, reducing water permeability); or the linear pressure is too high/speed is increased too quickly, leaving no time for water to drain; or the vacuum box panel is worn, leading to poor sealing and insufficient suction.
Troubleshooting: Strengthen fabric cleaning (adjust the concentration and frequency of chemical cleaning agents); inspect and optimize the vacuum system; appropriately reduce linear pressure or machine speed.
2. Web Breakage
Most web breaks in the press section are caused by the web sticking to the rolls.
Causes: Uneven surface or small cracks on the press rolls (especially stone rolls) that adhere to the web; defects in the fabric surface leading to poor web transfer; changes in process parameters (e.g., pH value, pulp ratio) increasing paper stickiness.
Troubleshooting: Inspect and grind the press roll surface; ensure the fabric is clean and intact; coordinate with the process department to adjust pulp parameters.
3. Poor Dewatering Efficiency
Symptom: The web dryness after pressing fails to improve, leading to a sharp increase in steam consumption.
Causes: The fabric is aged and has lost elasticity; the press roll crown is worn away, causing uneven pressure; the vacuum system has leaks or the vacuum pump efficiency has decreased.
Troubleshooting: Check the fabric’s operating hours and replace it if necessary; contact the mechanical department to verify and restore the press roll crown; conduct a comprehensive inspection of the vacuum pipes and seals.
4. Fabric Misalignment, Arching, or Wrinkling
Causes: Improper adjustment of the tension roll; defects in the fabric’s weaving or uneven local wear; dirty guide rolls with pulp lumps attached.
Troubleshooting: Carefully adjust the tension and alignment devices; keep all rolls clean; if a new fabric misaligns, contact the manufacturer immediately.
Key Takeaways
1. Treat fabrics well: Fabrics are the "lifeline" of the press section. A set of fabrics costs tens of thousands of yuan, and their service life varies greatly depending on how they’re used. The nine-character mantra for extending fabric life is: "Clean frequently, tension gently, speed up slowly." If the machine is stopped for an extended period, always relax the fabrics.
2. Water quality is critical: The pressure and quality of the water used to clean the fabrics are essential. The pressure must be sufficient to thoroughly clean the fabric, and the water must be clean—otherwise, the fabric will get more clogged instead of cleaner.
3. Collaborative operation: The press section is not independent. The dryness and vacuum level of the web from the wire section, as well as the tension from the drying cylinder section, all of which directly affect the operation of the press section.
