Troubleshooting Common Paper Defects in The Paper Machine Forming And Press Sections

Part I: Typical Paper Defects in the Forming Section (Wire Section)

1. Poor formation, cloudiness/mottling, and uneven basis weight Causes originating in the forming section: 1. Clogged stock distributor or branch pipes, resulting in uneven stock flow distribution;

2. Inconsistent slice opening (front-to-back or side-to-side), or stock accumulation and clumping on the slice lip;

3. Headbox consistency too high or too low; mismatch between stock jet speed and forming wire speed (excessive speed differential);

4. Misalignment of the breast roll or forming fabric; localized surface irregularities or pitting/wear on the fabric;

5. Uneven suction across vacuum boxes; clogged vacuum box covers; vacuum leaks due to worn sealing strips;

6. Imbalanced dosage of retention aids or flocculants, leading to fiber flocculation and clumping;

7. Fluctuations in headbox liquid level, unstable pressure, or excessive pulsation.

 

Factors Related to Pressing Pressing-related issues-such as felt clogging or uneven local dewatering capacity-can exacerbate "cloudiness" (uneven formation), making thinner areas highly susceptible to crushing. Troubleshooting Steps

1. Shut down the machine to check the slice lip for stock buildup and calibrate the full-width gap o

f the apron board;

2. Measure the flow rate in each branch pipe and clear any blockages in the headbox distributor;

3. Verify the stock jet speed, forming wires speed, and headbox consistency;

4. Inspect each vacuum box for vacuum level, cover condition, and sealing strips;

5. Sample and analyze stock flocculation, then adjust chemical additives accordingly. 2. Holes, pinholes, and "insect eyes" (micro-pinholes)

 

Causes Originating in the Forming Fabrics Section

1. Damage to the forming fabric, such as loose threads, broken filaments, or sharp protrusions on the fabric surface;

2. Impurities in the pulp, such as bark fragments, foam clumps, slime/decayed pulp, plastic strands, or metal debris;

3. Resin flakes or accumulated deposits detaching from the headbox interior and depositing onto the forming fabric, puncturing the wet paper web;

4. Failure of cleaners or pressure screens (due to clogging), allowing coarse rejects to flow back;

5. Excessive pressure of the forming fabrics shower, causing the high-pressure water jet to pierce the thin paper web.

 

Factors Aggravated by Pressing Holes in the wet sheet expand under the pressure of the press section, resulting in large, irregular ruptures. Troubleshooting Steps

1. Conduct a thorough visual inspection of the entire wire for damage or loose strands (jumpers);

2. Check the reject discharge operation of the screens and cleaners in each section;

3. Clean out resin and pulp deposits from the headbox and slice;

4. Reduce the spray water pressure in the forming wires section and switch to fan-shaped atomizing nozzles. 3. Wire marks, mesh impressions, and grid patterns

 

Factors Related to the Forming Fabric

1. Excessive service life of the forming fabric, leading to clogged mesh openings and filler accumulation;

2. Excessive vacuum box suction, causing the wet sheet to adhere too tightly to the forming fabric surface and transferring mesh marks;

3. Improper selection of forming fabric type or mesh count, resulting in pronounced marks from coarse forming fabrics;

4. Inadequate paper machine fabric cleaning/spraying, leading to the deposition of calcium carbonate and starch in the mesh openings.

 

Press Section-Related Issues A dirty press felt or uneven dewatering can cause wire marks to persist in the finished paper. Troubleshooting and Corrective Actions

1. Activate online high-pressure cleaning; perform an alkaline wash of the forming fabric during machine downtime.

2. Reduce the vacuum level in the vacuum boxes in stages.

3. Replace the forming fabric at the scheduled interval; select a fine-mesh fabric with high uniformity.

4. Seersucker-like defects, air bubble marks, and transparent bubble spots.