How Press Felt Performance Directly Impacts Your Paper Quality and Production Cost

Paper making press felt is not an ordinary textile. As one of the paper machine clothing, it is the heart of the press section and plays an important role in dehydration efficiency, paper quality and production costs. Professional paper mill technicians can feel the condition of the press felt just by touching it. Below, Sun Hong will analyze the core functions, key applications, and impact of press felts on paper making production efficiency from a technician’s perspective.

What is a Press Felt Made of?

A press felt is not just an ordinary piece of fabric. It is a key fabric used in the press section to carry wet paper and help it dehydrate. Currently, press felts are mainly divided into two categories: (1) Woven felts, which are made from a blend of wool and nylon staple fibers through processes such as weaving, raising, and drying. (2) Needle-punched felts, which are the current mainstream. Wool and nylon staple fibers are first combed into a fiber web. After multiple layers of overlap, the fiber web is pierced onto a pre-woven ring-shaped base fabric with barbed steel needles to achieve the required tightness and flatness. They are further divided into single-sided and double-sided needle-punched felts. These press felts have excellent water filtration, wear resistance, high strength, and long service life.

Core Functions of Press Felt

• Efficient dewatering and water filtration: This function is the basic function of the press felt. In the press section of the paper machine, the press felt must quickly transfer the water pressed out by the wet paper sheets, maintain a smooth drainage channel, and prevent the water from being brought back into the paper sheets (i.e., rewetting). Excellent water filtration is the basis for maintaining dewatering efficiency under high line pressure and high speed.
• Support and transfer paper: The press felt needs to steadily and safely carry and transfer the wet paper that is still in a fragile state through the press area to prevent breakage. The paper making felt needs to have good dimensional stability (shrinkage) and surface flatness.
• Paper surface quality: The surface structure and state of the press felt will be directly imprinted on the paper. If the texture of the press felt surface is too rough, it may leave obvious “felt marks” on the paper surface. Therefore, while pursuing dewatering efficiency, it is also necessary to select the felt according to the surface smoothness requirements of the paper type.
• Durability and anti-interference: Press felts need to operate for a long time in an environment of high temperature, high pressure, humidity and chemicals. Therefore, they need to have excellent wear resistance, high strength and good antibacterial and anti-corrosion properties.

Press Felt Selection, Operation, and Maintenance

There’s no such thing as the best press felt, only the most suitable one. Different paper grades and pressing methods place varying demands on paper making felts. (For example, when producing high-strength corrugated core paper, attention needs to be paid to the press felt’s dehydration efficiency and rewetting resistance. When producing high-end paperboard, higher requirements are placed on the press felt’s surface smoothness.) When selecting a press felt, it’s also important to consider its basis weight, air permeability, thickness, base fabric structure, and material formulation.

Press Felt Installation and Run-in

Before installing the press felt on the machine, thoroughly clean all contact surfaces with the rollers to ensure there are no hard objects that could damage the felt. Specialized tools are required during installation to prevent snagging and twisting. Furthermore, after installation, the press felt must be run-in at a low speed. Gradually increase the speed to process requirements, while slowly increasing the press line pressure to allow the felt fibers to fully stretch and reach optimal conditions. Sun Hong also reminds us to avoid high-speed and high-load operation, as this will severely damage the paper making felt and significantly shorten its service life.

Press Felt Operation Control

Press felt cleanliness is crucial for ensuring consistent dehydration. Appropriately utilize high-pressure water jets (high water quality is required; clean water is recommended) and chemical detergents (acid and alkaline cleaning) to regularly remove fibers, fillers, adhesives, and other materials clogged in the press felt pores and restore air permeability. In paper making production, special attention should be paid to ventilation and vacuum to ensure that the paper making felt ventilation system operates well, avoid excessively high press felt temperature, and increase the vacuum degree of the vacuum box panel to effectively ensure uniform dehydration of the press felt.

Press Felt Replacement

Press felt replacement is necessary when it becomes irreversibly clogged, experiences a continuous decrease in air permeability, significantly degrades dewatering capacity, or even exhibits localized wear and tear. When replacing the press felt, for the press section without a cantilever beam device design, a felt with seam treatment can be used. It is changed to an open-end design, which does not require a large amount of disassembly and assembly of the press section equipment, saving replacement time and labor intensity and improving work efficiency.

The Impact of Press Felt Condition on Papermaking

The dryness of the paper sheet after pressing is the most direct indicator of press felt performance. Even a 1% increase in dryness significantly reduces steam consumption in the subsequent dryer section, directly saving energy costs. Furthermore, higher dryness means greater paper strength, reducing the risk of sheet breaks in the press and dryer sections and improving paper machine efficiency.
Press felts themselves are expensive consumables. Extending their lifespan means reducing felt consumption per ton of paper. Their condition impacts energy consumption, product consumption, and yield, and their comprehensive benefits far exceed their inherent value.

Press felt is not a passive consumable, it is an important tool for us to actively manage production, optimize efficiency and control costs. Understanding the press felt’s characteristics, selecting the appropriate model based on the paper machine’s characteristics, ensuring proper cleaning and maintenance, and constantly monitoring dewatering performance and paper changes are the cornerstones of ensuring efficient, stable, and economical paper machine operation.