Repeated web breaks in the press section can significantly affect paper machine stability. While poor sheet formation, inappropriate process settings and unstable moisture conditions are common contributing factors, mechanical problems must also be considered.

Once basic process checks have been completed, a detailed examination of press rolls, their alignment and the associated drive components can help identify defects that are not immediately visible during normal operation.

1. Evaluate Press Roll Crown and Nip Pressure Distribution

The crown profile of a press roll is designed to compensate for roll deflection under operating load.

Check whether the crown, particularly on granite or stone press rolls, is appropriate for the machine's current speed and nip loading.

An unsuitable crown can produce nonuniform pressure across the machine width. This may cause localized poor dewatering, sheet crushing, cross-direction moisture variations and recurring web breaks.

Roll crown should therefore be assessed together with actual nip loading and deflection compensation rather than as an isolated design parameter.

For relevant equipment configurations, see Huatao Group's Press Roll product information.

2. Inspect Press Roll Surface Quality

The surface condition of a press roll influences sheet release and transfer.

Inspect rubber-covered rolls, suction press rolls and other rolls installed in the press section for:

• Surface scratches and mechanical damage

• Corrosion and pitting

• Irregular wear

• Coating defects

• Stock deposits and contamination

Even localized defects can affect contact conditions and cause the sheet to adhere unevenly to the roll.

When these problems are suspected, review the condition of the roll covering and determine whether cleaning, maintenance or component replacement is necessary.

Additional information is available in the Suction Press Roll technical article.

3. Measure Roll Runout and Investigate Vibration

Excessive radial runout may produce periodic variations in nip pressure.

Where appropriate, use a dial indicator to measure press roll runout and compare the results with the machine's applicable tolerances.

Potential mechanical contributors include roll imbalance, bearing defects and damage to rotating components.

Inspect the roll journals, bearings and bearing housings. If abnormal vibration is observed, vibration measurements can provide further diagnostic information.

Mechanical irregularities may result in unstable sheet transfer even when the average nip loading appears correct.

4. Verify Roll Alignment and Parallelism

Correct alignment is essential for distributing press loading evenly between the drive side and tending side.

Check the parallelism of adjacent press rolls and the alignment of the press section relative to the forming and dryer sections.

Misalignment can contribute to:

• Uneven cross-machine nip pressure

• Nonuniform sheet dewatering

• Paper web wandering

• Irregular press felt wear

• Increased web-break frequency

These effects should be evaluated together because a single alignment problem can influence both the sheet and the felt.

Huatao Group provides additional information about Paper Making Rolls for press-section applications.

5. Examine Bearings, Gearboxes and Couplings

The mechanical condition of the drive system can influence roll rotation and press stability.

Inspect bearings, gearboxes, couplings and related components for abnormal wear or damage.

Potential symptoms include vibration, speed fluctuations, unstable rotation and inconsistent nip loading.

Routine inspection and preventive maintenance help reduce the likelihood of unexpected mechanical failures.

When evaluating maintenance or upgrades, equipment should be selected according to the actual paper machine configuration and operating requirements.

See the Paper Machine Equipment range.

6. Analyze the Location and Appearance of Each Web Break

The pattern of a web break can provide important diagnostic clues.

First, identify where the break occurs. It may happen after the first press nip, after the second nip or after the smoothing press.

Next, determine where the failure begins across the machine width.

Does tearing start at the sheet edge, near the center or repeatedly at the same cross-machine position?

The appearance of the damaged sheet also matters.

Localized tearing may indicate weak areas. Crushing may suggest inappropriate nip conditions. Tensile failure may be associated with excessive draw, while irregular release may indicate dewatering or roll-surface problems.

Record machine speed, press loading, break location and other relevant operating data to identify recurring patterns.

7. Apply a Five-Stage Troubleshooting Procedure

A reliable investigation should progress from accessible checks toward detailed mechanical inspection.

Stage 1: Paper Machine Clothing

Inspect press felts, forming fabrics and dryer fabrics for contamination, wear, damage, reduced permeability, improper tension and tracking problems.

Stage 2: Vacuum and Doctoring Equipment

Review suction box conditions, vacuum levels, shower performance, blade loading and roll cleanliness.

Doctor blades, holders and shower systems should operate correctly to support consistent roll cleaning and sheet release.

Stage 3: Process Parameters

Check nip loading, machine speed, draw settings, web tension and press-section dewatering performance.

Stage 4: Stock and Incoming Sheet Quality

Evaluate furnish composition, refining conditions, formation, wet-web strength and sheet dryness before the press section.

Stage 5: Mechanical Components

Investigate roll crowns, roll surfaces, bearings, alignment, parallelism and vibration.

8. Compare Current Conditions with Previous Stable Operation

When web-break frequency increases, review any recent changes to the production process.

Examples include installing a new press felt, modifying furnish or chemical dosage, increasing machine speed, adjusting nip loading or draw, and replacing or servicing press rolls.

Where technically appropriate and safe, compare current settings with previously stable operating conditions.

Change one variable at a time whenever possible and evaluate the result.

Controlled comparative trials provide a practical way to confirm suspected causes rather than relying on assumptions.

9. Consider the Entire Papermaking Process

A web break observed in the press section may originate elsewhere.

Unstable sheet dryness, poor formation, unsuitable refining or inconsistent stock preparation can produce a weak web before pressing begins.

A complete investigation should therefore follow the production sequence:

Stock Preparation → Approach Flow → Forming Section → Press Section → Dryer Section

This system-wide approach helps prevent repeated adjustments to equipment that may not be responsible for the actual problem.

Huatao Group — Paper Machine Equipment and Spare Parts

Since 2008, Huatao Group has been engaged in the production and international supply of pulp and paper machinery, equipment and spare parts.

Our product range includes press felts, forming fabrics, dryer fabrics, suction press rolls, blind-drilled press rolls, jumbo press rolls, pickup rolls, dewatering elements, suction boxes, doctor blades, doctor holders and shower systems.

Appropriate component selection and operating conditions can contribute to improved dewatering efficiency, stable sheet transfer and reliable machine operation.

For technical discussions, equipment upgrades or spare parts inquiries, contact:

Huatao Group

Website: https://www.huataolover.com

Email: service@huataogroup.com

WhatsApp / WeChat: +86 177 7825 5675  

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