Aug 9, 2022
Valmet 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.
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.
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 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 most typical headbox service actions are:
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.
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.
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.
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.
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.
The 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!