Pick Up Felt Stripping Failure During Paper Making

From the forming section to the press section, the pick up felt bears the critical responsibility of picking up and conveying the wet paper web. 

Particularly in high-speed paper machines, where the high operating speed makes open-draw sheet transfer difficult, the vast majority of such machines employ a closed-draw system (the vacuum sheet transfer device) to facilitate the transfer of the paper web from the forming section to the press section.

After learning what pick up felt is, it is important to note that during this transfer process, the wet paper web may exhibit phenomena such as edge shedding, localized adhesion failure with the felt, or even complete detachment across the entire web width. This leads to operational faults involving creasing, web breaks, and dewatering issues.

Causes of Paper Edge Detachment Due to Pick Up Felt

Here are numerous causes of paper edge drop-off, such as the surface properties of the pick up fabric being too poor. If the surface of the pick up felt is not sufficiently smooth and dense, it will result in insufficient adhesion of the felt itself. Furthermore, this issue often arises during the initial stages of the felt’s use, which will tend to improve after a period of operation.

But the root cause lies in the lack of sufficient adhesion between the pick up felt and the wet paper web to counteract the combined forces of gravity, centrifugal force, and vibration that otherwise cause the wet sheet to detach.

The Solutions

• Perform a dry run before starting the paper machine, or after installing the pick up felt, to ensure a smoother felt surface.
• Increase the water flow within the felt shower system to raise the moisture content of the pick up felt, thereby increasing its surface tension.
• Reduce or even shut off the pick up felt suction box, and refrain from using high-pressure showers to prevent the felt fibers from standing erect.
• Apply a rosin sizing solution to the area of ​​the pick up felt where edge dropping is occurring.
• At the wire section, spray water from the underside of the wire directly onto the corresponding area of ​​the pick up fabric where edge dropping is observed.

Other Paper Stripping Failure Causing Factors

Pick Up Felt Speed Ratio Control

During the wet paper web conveying via the pick up felt, strict control over the speed ratio between the forming section and the press section is essential to ensure a smooth transfer and maintain paper quality. Generally, the speed ratio of the pick up felt should be maintained at 0.3% to 0.5% or less. If the speed ratio is excessive, it leads to increased elongation of the wet web, reduces its tensile strength, and may even result in web breaks. Conversely, the speed of the press section must not fall below that of the forming section; otherwise, the wet web will exhibit curling and wrinkling.

Pick Up Felt Adsorption Capacity

Factors such as the surface texture, degree of looseness, structural stability, flatness, and air permeability of the pick up felt directly influence its adsorption capacity. Furthermore, the cleanliness of the felt, particularly the condition of its edges and its moisture content, are also critical factors that directly affect the paper sheet adsorptivity of the felt.

Basis Weight of the Pick Up Felt

The basis weight of the pick up felt used on a paper machine falls within a specific range. If the basis weight of the felt is excessively high, the surface tension of the fabric will be insufficient to effectively hold the paper web, and it will also be difficult to sever the web using edge-trimming water jets.

If edge dropping is a localized issue, you must consider whether the basis weight of the pick up felt is uniform. Moreover, if edge dropping frequently occurs along the edges of the pick up fabric, it is most likely caused by an excessive basis weight.

Pick Up Felt Clogging

The pick up felt requires periodic cleaning and replacement to eliminate clogging issues caused by pulp fibers, fillers, sizing agents, or impurities that may become embedded within their fabric structure.

Such clogging of pick up felt can lead to problems such as poor adhesion to the paper sheet and unstable conveyance, which, in turn, may cause edge breaks, wrinkling, stretching, or tearing of the paper web.

Accumulation of Paper Scraps

As the pick up felt conveys the wet paper web from the forming section to the press section, the paper stock may accumulate and agglomerate at the entrance of the press nip. This generates instantaneous and intense friction between the paper stock and the pick up felt. Under the combined influence of this immense frictional force and the internal pressure within the nip, the synthetic fibers on the felt’s surface—along with the pulp fibers being squeezed and dragged into the nip—rapidly heat up and melt. This results in the formation of a dense layer on the surface of the pick up felt fabric, thereby compromising the felt’s subsequent operational performance and disrupting the paper web production process.