Choose press felts: is achieving 55% dryness after pressing no longer just a dream ?

The selection of press felts depends on factors such as the paper grade, basis weight, machine speed, surface finish requirements, paper machine type, operating environment, and existing felt cleaning equipment. Particular attention must be paid to the relevant technical parameters of the paper machine during the design and selection process; only by appropriately adjusting the felt's specifications and technical parameters based on actual operating conditions can the felt effectively meet the machine's requirements.

1. Line Pressure and Mechanical Load:

The line pressure and mechanical load in the paper machine's press section are directly proportional to the strength requirements of the press felt. Higher line pressure demands superior compression resistance from the selected felt throughout its service life, as well as excellent elastic recovery to maintain effective water drainage and void volume over time. Greater mechanical load requires the felt's base fabric to possess superior elastic recovery and high tensile (breaking) strength for power transmission, alongside minimal elongation and shrinkage rates.
2. Vacuum Level:

The vacuum level and the configuration of the vacuum system directly determine the moisture content, cleanliness, and dewatering performance of the press felt-particularly the base fabric. Insufficient vacuum leads to poor sheet dewatering, high felt moisture content, inability to achieve target nip pressure, difficulties in sheet threading, and inadequate felt cleaning. Conversely, excessive vacuum increases the drive load, accelerates wear on the fabric, and results in energy waste.
3. Washing Conditions:

Washing conditions encompass the configuration of the washing equipment, water quality requirements, and settings for water pressure and vacuum; the quality of these conditions directly correlates with cleaning effectiveness. When selecting a press felt, it is crucial to consider the paper machine's washing conditions. Ideally, every paper machine should have optimal washing conditions to meet the felt's requirements; however, in reality, conditions vary between machines and even for the same machine over time. Therefore, when selecting a felt, it is essential to adjust parameters-such as felt type, basis weight, structural composition, manufacturing process, and heat-setting-within appropriate limits to suit the specific needs of the paper machine.
4. Pulp Characteristics:

The quality of the pulp not only affects the quality of the paper being produced but also plays a crucial role in the water drainage performance and service life of the paper machine clothing (felt). Pulp freeness, filler viscosity, and impurity content are inversely related to the felt's water drainage performance; additionally, since synthetic fiber felts are resistant to weak alkalis but sensitive to acids, the pH level of the pulp also impacts the felt. When selecting a suitable paper machine felt, it is essential to consider parameters such as pulp composition, freeness and wet weight, the use of chemical additives, and pulp pH; these factors directly influence the felt's water drainage performance and service life, as well as the tendency for pulp to adhere to the felt's surface.
5. Dewatering Method:

The press configuration of the paper machine determines the dewatering method for the wet paper sheet, and different press configurations require different types of felts. Generally, for paper machines relying primarily on horizontal dewatering, felts with higher compressibility and lower basis weight are preferred; for machines utilizing vertical dewatering-combining press dewatering with vacuum suction-felts with lower compressibility, good elasticity, and higher basis weight should be selected. The choice of the number of base fabric layers in the press felt is also determined by the parameters of the press section mentioned above; under favorable operating conditions, felts with more layers can be chosen to extend service life, increase machine speed, and improve paper quality.