Headbox case study – Overcoming newsprint mill speed limit

Aug 9, 2022

Headbox profilerValmet has a strong technological background as a headbox design innovator and manufacturer, including decades of experience in on-site servicing and advanced paper and board process expertise. Valmet service specialists have what it takes to analyze and service all types of headboxes, in any condition.

Concern about speed limitation

A newsprint mill in the Unites States wanted to speed up their machine. Mill personnel were concerned about speed limitations due to the current status of the headbox. They asked Valmet to diagnose their situation and recommend a course of action.

Survey and recommendations

After preliminary discussions, Valmet headbox service experts came to the mill and performed a survey of the headbox. After the survey, Valmet recommended a number of headbox service actions, including the following:

  • The gravity deflection in the pivot location could be reduced with pivots at the quarter point of the headbox.
  • Add 0.25 thick STST316L plate to area of corrosion above headbox pivot - to stop corrosion.
  • Weld the joints in the tapered header across the machine to prevent the joints from opening.
  • Use the keyed flow plate from the #2 PM headbox. This would reduce the high stress in the bolts and carry the stress across the keyed joint, as well as help eliminate the stock build-up at this location.
  • Install a new slice body with all stainless steel construction and internal heated compartments using 3” centers and Valmet Automation actuators. This would eliminate this high stress area due to thermal bowing.
  • Cover the header and tube bank area with 0.25 stainless steel to stiffen the structure and limit future corrosion.
  • Add new ribs added at the front and back of the apron support.
  • Add new ribs added to the inlet transition piece to support the 0.312 skin and lower plate stress levels.

Results achieved

The mill then chose which items to pursue and gave Valmet the go-ahead to do them. Most of the items were performed, and, after restarting the machine and giving the headbox a thorough test, the mill was satisfied.

So, what were the results?

  • The headbox will now allow for a speed increase from 4000fpm to 4500fpm.
  • Basis weight profiles have improved.
  • The headbox, which was close to failure due to corrosion, is now good to go for several years.

A sampling of headbox services

The most typical headbox service actions are:

  • Replacement of the slice lip
  • Reconditioning of the apron
  • Reconditioning and tuning of the slice control system
  • Headbox realignments
  • Reconditioning of the top slice movement mechanism
  • Reconditioning of rectifier rolls
  • Cleaning and special treatment of headbox flow surfaces
  • Replacement of headbox seals

MX06 coatingMX06 coating

This new coating method can help reduce dirt-related problems on paper machines, especially in the humid conditions at the wet end. Coating can be applied on-site at the customer mill. Surface treatment MX06 leaves a very thin and unnoticeable protective coat that is nevertheless a very long-lasting and effective dirt repellent.

Cleaning & polishing internals

Sometimes the simple things get overlooked–like proper cleanliness and condition of headbox internal surfaces. Rough surfaces with pulp scabs and other stuck materials contribute to increased corrosion, stock hang up, and improper flow characteristics in the head-box. Every maintenance program should include a thorough cleaning, inspection, and if necessary, polishing of the surfaces that contact stock.

Headbox process and condition test

The service concerns the mechanical condition, automation and process aspects. The testing is carried out in a separate shutdown or in the same shutdown with the service work and testing typically takes from 6 to 12 hours depending on the type and width of the headbox. A small service could be done in a one day shutdown, but larger services are usually done in an annual maintenance shutdown. All types of headboxes are serviced by Valmet headbox service specialists.

Headbox structural analysisHeadbox structural analysis

The headbox often stands in the way of higher machine speeds. Structural analysis helps to reveal the limitations and bottlenecks of a headbox, determine any modifications needed for the planned higher speeds, and to minimize the cost of the upgrade.

Valmet IQ Slice Profiler

The distribution of dry solids in the paper, i.e., fibers and fillers, lays the foundation for overall paper uniformity. The need to correct profile deviations mainly arises from flow or mechanical disturbances in the head box and from the greater shrinkage of the paper web at the edges. Valmet IQ Slice Profiler, a control system for slice profile, offers the best possible profiles with minimum manual operation and less maintenance.

Apron work

Apron workThe headbox apron performs a simple function: provide a flat and true surface for stock to exit the headbox. A critical area of the apron is the edge. Any unevenness or localized damage on the apron edge makes it impossible to maintain an even sheet profile. Valmet technicians can repair minor damage to your apron edge, grind, and then polish it to like-new condition. And it can all be done on-site with the apron in the machine. Alternatively, Valmet can replace the beam or entire headbox apron.

Having headbox problems? Contact your Valmet representative today to schedule a headbox expert to visit your mill!