How Forming Fabric Problems Cause Paper Breaks in the Forming Section

The forming fabric section is the stage in the papermaking process where paper breaks occur most frequently and are most easily overlooked.

Many times, paper breakage is not sudden but is caused by fabric parameters, equipment status, and slurry conditions.

Improper Headbox Settings

This is the most common cause of paper jams in the forming section. 

Improper headbox settings will cause uneven distribution of slurry on the forming fabric, including fluctuating concentration, inconsistent headbox lip openings, and excessive jet-to-wire speed differences. All of these can directly result in uneven basis weight across the web and inconsistent wet paper sheet strength.

Causes

Common causes include fluctuations in pulp fineness, unstable pressure in the pulp feed pump, abnormal throttling of the pulp feed valve, drift in the headbox liquid level control, and localized pulp buildup or blockages at the lip.

Results

These problems can cause localized areas of the wet paper sheet on the forming fabric to become too thin, too dry, or too wet, resulting in poor strength. 

As a result, the sheet may break as soon as it enters the press section, or it may tear or rupture directly on the forming fabric.

Solutions

Maintain the slurry concentration on the forming fabric within the process range. At the same time, keep the jet-to-wire ratio within the standard range and avoid making arbitrary, drastic adjustments.

Regularly check the uniformity of the lip opening on the headbox.

If slurry is detected, stop the machine immediately and clean it.

Forming Fabric Contamination

Forming fabric is an important carrier for transporting wet paper sheets. As soon as the forming fabric becomes dirty or clogged, its dewatering performance suffers.

Causes

The main causes of fabric plugging and wear include excessive fillers in the stock, fine fiber buildup, chemical residues, insufficient cleaning water pressure, clogged cleaning agent nozzles, worn or poorly fitted doctor blades, and extended forming fabric service periods.

Results

Slow localized dehydration of the forming fabric leads to high moisture content and low strength in the wet paper sheet.

If localized dewatering on the forming fabric occurs too rapidly, it can cause the paper sheet to become dry and wrinkled, with brittle edges, making it highly prone to tearing along the sides.

The moisture content of the web varies significantly, causing the paper to tear immediately upon entering the press section.

Solutions

Ensure the high-pressure spray water pressure meets the forming fabric cleaning standards required. 

Periodically check the contact between the chest roll, table roll, and water deflector doctor blade. If the forming fabric surface becomes dirty or clogged, please immediately intensify cleaning efforts.

Abnormal Vacuum Level

Vacuum is the most critical control item in the forming section, even slight fluctuations can cause paper breaks.

Abnormal vacuum levels are typically caused by air leaks in the piping, water buildup in the steam water separator, reduced vacuum pump efficiency, clogged filters, or poor seals at the edge.

Results

Improper vacuum settings can cause the wet paper sheet to adhere poorly to the forming fabric, making it susceptible to disturbance from water flow. This can also result in insufficient localized dewatering, leading to uneven moisture distribution in the paper sheet as it enters the press section and increasing the risk of paper breaks.

Solutions

Check for leaks section by section.

Clean the steam-water separator regularly.

Check the vacuum pump’s operating current and oil temperature.

Ensure the vacuum in each section is stable according to the process gradient, without sudden increases or decreases.

Forming Fabric Tracking and Tension Instability 

If the forming fabric shifts, vibrates, or wobbles due to the influence of the corrector, the wet paper sheet cannot be formed stably.

Causes

The main causes of unstable forming fabric operation include sluggish correction roll movement, abnormal tension roll operation, pulp buildup on the roll surface, drive misalignment, and foundation vibration.

Results

This causes the paper sheets on the forming fabric to stretch and twist, resulting in hidden tears. 

Consequently, the paper sheets are highly prone to breaking the moment they enter the press. In severe cases, they may even tear apart directly on the forming section.

Solutions

Ensure that the forming fabric’s automatic alignment system is sensitive and effective. 

Maintain stable forming fabric tension.

Clean pulp residue from the roll surfaces at the end of each shift.

Check the parallelism of the rolls.

Immediately reduce speed and investigate if wire vibration is detected.