Headbox profile settings, hydrodynamic condition, and profile control directly influence sheet formation, uniformity, and machine runnability. Our practical checklist helps you quickly pinpoint the most significant improvement opportunities.
Process performance
The headbox is designed to dampen disturbances from the short circulation, although in some cases it may actually contribute to their amplification.
Improved Runnability and Profiles
More uniform web formation, fewer disturbances, improved profiles, and smoother runnability — particularly during speed transitions.
Potential Benefits
Reduced waste and quality fluctuations — lowering the consumption of energy, chemicals, and raw materials.
Where do the improvements come from? – Every result has a logical explanation.
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Feed points for wire water circulations (white water and dilution systems) should be located away from the suction line of the headbox feed pump to avoid pressure fluctuations.
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Poor mechanical cleanliness — in channels, dilution valves, the slice lip area, or the headbox in general — leads to increased need for profile adjustment and makes it difficult to achieve the desired sheet uniformity.
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Optimization of the jet/wire speed ratio and jet impingement point improves tensile strength control and enhances sheet formation (formation quality).
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If the headbox damping control responds too slowly, leading to critical oscillations in the 2–12 second range, the control system should be reviewed carefully.
For example, when implementing combined control of two valves (supply and discharge) for the headbox, pressure fluctuations can be significantly reduced.
The key factors are the correct placement of control valves (order of pressure reducer and control valve) and a well-defined control operating range (typically 30–70%). -
Actuator condition and setpoints should be checked regularly. Flow surfaces that are critical for quality — such as the lip area — must be inspected, cleaned, and, if necessary, refurbished carefully.
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Differential pressure measurements may not always provide accurate values during transient conditions, such as grade changes. Properly tuned controls and the use of flow measurements help stabilize process regulation.
Checklist for Ensuring Stable Headbox Performance
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Critically review the implemented automation.
Check all measurements, their calibrations, as well as control loops and tuning parameters.
Prefer flow measurements over differential pressure readings to achieve stable control performance. -
Measure or assess pressure and consistency variations entering the headbox.
Variations that are too large cannot be compensated for by the headbox and must be corrected at their source. -
Relocate chemical and white water circulation intake and feed points away from unstable areas such as the suction line of the headbox feed pump or other sources of pressure fluctuations.
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Clean and inspect the headbox thoroughly, paying special attention to profiling devices and dilution valves.
Ensure the slice lip area is clean and in good condition. -
Optimize the jet/wire speed ratio and jet impingement point on the wire according to formation and strength index requirements
Practical Aspects of Profile Control and Operation
Profile Control and Practical Operating Methods
Stable headbox operation alone is not enough if profiles and operating practices are not properly adjusted.
The following measures help ensure that the benefits of headbox stability are transmitted throughout the process.
Slice Lip Adjustment and Zeroing
Regular mechanical zeroing of the slice opening (±0.02 mm accuracy) is essential.
Electrical zeroing of the actuators alone is not sufficient.
Avoid overbending of the slice lip, check for clearances, and replace worn actuators.
Controlled temperature adjustment of the upper and lower lips prevents profile distortion.
Optimization of Profile Controls
Monitor all basis weight, orientation, and ash profiles.
Avoid slope and edge deviations across the sheet by using correct operating methods and control settings.
Ensure consistency between online and laboratory measurements, and calibrate profile measurements frequently enough.
Operating Practices
Proper flow rate, jet/wire speed ratio, jet impingement point, and impingement angle improve retention and formation, while reducing defects such as white spots.
Edge feed adjustments must be correctly tuned.
Condition of Actuators
Regular cleaning, zeroing, and maintenance of dilution and profile control valves are vital.
Valves that move freely and operate within their correct range keep the profile under control.
Identifying faulty devices among hundreds of actuators can be difficult, but it is critical.
Only fully functional edge feed valves enable proper control of fiber orientation profiles.
Dilution Water Management
Use white water taken from the correct location and maintain dilution at 10–15%.
Excessive dilution reduces stability and sheet formation quality, while increasing the consumption of retention chemicals and energy.
Cleanliness
The condition of flow surfaces directly affects profile control and production stability.
Keep all critical components clean to maintain uniform profiles and consistent operation.
Who Is This For?
For mills aiming to improve product quality and production efficiency without major investments.
Our audit delivers a prioritized action plan, and in many cases, improvements can be implemented in just a few steps during a scheduled shutdown
Author
ProBoreal’s headbox expert has been involved in numerous audits, start-ups, and machine speed upgrades. Get in touch to evaluate and improve the performance of your own production line.