In the paper press section, especially for high-speed paper machines, the press felt is a key component that affects paper quality and production efficiency.
During the pressing process, the paper sheet is mechanically compressed by a series of press rolls while being supported and conveyed by the press felt. This process alters the fiber network structure and physical properties of the paper in multiple ways. Its primary function is to strengthen the bonds between fibers, thereby increasing the paper’s strength. At the same time, the compaction reduces the paper’s porosity and further affects key physical properties such as bulk density and air permeability.
The press felt plays a crucial role in this process, as its parameters directly influence the quality of the resulting paper.
Press Felt Parameter Influence
Press Felt Air Permeability & Porosity
The air permeability of a press felt is its most critical parameter. measuring the rate of airflow and directly related to dewatering efficiency.
Porosity, on the other hand, refers to the proportion of pore volume within the press felt, determining its water storage and conduction capabilities. High porosity promotes faster dewatering and prevents paper from becoming damp again, but may affect felt strength.
These two factors are key to determining paper dewatering efficiency. Press felts with high air permeability and porosity can quickly guide water away from the paper, significantly improving dewatering efficiency and enhancing paper web folding endurance.
Press Felt Compression Resilience
Compression resilience refers to the ability of press felts to quickly rebound after being compressed in the press zone to regain their ability to absorb moisture. A high resilience rate (>85%) ensures long-term stable dewatering performance, promotes the formation of uniform press zones, and prevents compaction.
High-resilience felt cushions printing pressure effectively, thus maintaining the three-dimensional structure and bulk of the paper, and preserving its feel.
Press Felt Pore Size Distribution
This is a key performance indicator for papermaking press felt. It not only affects the felt’s water retention and dewatering capabilities but also influences the flow path of moisture during the pressing process.
Its pore size (such as O95 pore size) must be precisely matched to the dimensions of the pulp fibers. Otherwise, it may lead to fiber loss or uneven dewatering, which affects paper uniformity. Therefore, when selecting a press felt, it is essential to choose or customize it appropriately based on the type of paper being produced.
Uniform pore size distribution helps improve dewatering efficiency, not only saving resources but also ensuring uniform dewatering, which is crucial for paper strength. Uniform dewatering allows fibers to interweave more effectively, thereby improving paper uniformity, mechanical strength, and overall physical properties.
Press Felt Surface Contact Area
Surface contact area, also known as fiber support index (FSI), refers to the percentage of surface area that press felt fibers actually contact and support the wet paper web. A higher support ratio provides more uniform support to the wet paper, preventing it from loosening or leaving marks due to uneven local pressure. Conversely, a lower support ratio can lead to the formation of localized high-pressure points, making it easier to leave indentations or spots on the paper.
 |  |
Other Influencing Factors
Papermaking is a continuous process, including in the press section. Press felts are an important factor affecting paper shape, but not the only one.
Pulp Type
Different pulps have different fiber properties, and their responses to pressing will vary accordingly. Even using the same press felt and undergoing the same pressing steps, different characteristics will emerge. For example, chemical pulp shows a more significant reduction in bulk after compression than mechanical pulp. Furthermore, pulp fibers with higher freeness are more easily crushed, making them more sensitive to pressing.
Press Felt Size
The press felt size not only affects whether it can be successfully installed on the paper machine, but also affects the stability of the paper machine’s operation, dewatering efficiency, and paper quality. Its length influences the tension adjustment range and operational stability, while its width affects factors such as paper sheet shrinkage and lateral deviation.
Pressure Zone Location
In multi-press processes, the pressure of the first pressing zone (when the wet paper sheet has the highest moisture content and the lowest strength) often has a more significant impact on the final paper structure than that of subsequent pressing zones.
Press Type
Different pressing technologies have different effects. For example, shoe pressing can apply higher linear pressure without increasing the risk of crushing, achieving better dewatering and strength improvement. Hot pressing, on the other hand, can improve strength while better maintaining the porosity and permeability of the paper.
Pressing Pressure
The pressure applied to the press felt is a key variable that directly affects the magnitude of changes in all performance indicators.
All these factors, including the press felt and other related factors, together determine the paper’s smoothness (the smoother the surface), uniformity (the more even the fiber distribution), and double-sided difference (the smaller the difference between the front and back sides, the better).
Chinese (Simplified)
Arabic
Dutch
English
French
German
Italian
Portuguese
Russian
Spanish