Functions of the Press Felt
Functions of the Press Felt:
1. Filtration: Acting as a dewatering medium, the felt absorbs and filters out moisture from the paper web during the pressing process. 2. Smoothing: During the conveyance and dewatering of the paper web, the felt serves to smooth and refine the surface of the paper. 3. Conveyance: It supports the wet paper web as it enters the drying section and drives the rotation of the rollers within the press section. The moisture squeezed out of the wet paper web by the press unit must pass through the felt to be effectively removed. If the felt possesses poor water permeability, the expelled moisture will re-enter the paper web after it exits the press nip, thereby reducing the web's dryness. Consequently, this increases the moisture content of the paper web entering the drying section, leading to a significant rise in energy consumption for drying. Furthermore, the increased moisture content of the paper web necessitates a reduction in the paper machine's operating speed, which in turn results in a decrease in overall production output.
Furthermore, if the performance of the press felt is substandard, it can lead to various paper defects, thereby compromising product quality. It is evident, therefore, that the press felt is a critical factor influencing the rate of dewatering in the press section, as well as the dryness and quality of the paper web. It directly impacts the dewatering efficiency of the press section, both the internal and external quality of the paper, and the overall production efficiency of the paper machine. Precautions for Using Press Felts:
1. Selecting the Appropriate Felt
Choosing the right press felt is no simple task; with numerous manufacturers currently producing felts, the sheer variety of product types and models can be overwhelming. The "best" felt is not necessarily the *most suitable* felt. The selection of a felt depends on various factors, including the grade, basis weight, and surface finish requirements of the paper being produced; the properties of the pulp; the type of press section; the operating environment of the felt; and the available cleaning conditions. 2. Expediting Felt Replacement
Press felts have a finite service life. When a felt's operational performance no longer meets production requirements, it should be replaced with a new one as soon as possible; failure to do so will prevent the paper machine from operating at its normal speed and will have an adverse effect on product quality.
① Schedule felt replacements judiciously, ideally coinciding them with scheduled machine shutdowns for maintenance. ② The design of components within the press section-such as the machine frame, press rolls, and housing units-should be scientifically sound and rational, ensuring sufficient clearance and spatial access. Furthermore, platforms, frames, and roll housings should be designed to facilitate easy disassembly and hoisting. ③ Whenever possible, increase the number of guide rolls supporting the outer run of the felt while reducing those supporting the inner run; simultaneously, minimize the total number of guide rolls used, provided that the operational requirements of the press felt are still met. ④ When replacing felts that are particularly hard, stiff, or thick, consider utilizing specialized "bear-claw" clamps or sewing a dedicated traction strap onto the drive-side edge of the felt to assist operators in pulling the felt into position from the drive side. 3. Minimizing the Initial Break-in Period
Once a newly installed felt is mounted on the machine, its performance characteristics-including surface flatness, the orientation of surface fibers, moisture content, and air permeability-may not yet be sufficient to support the paper machine's operation at normal production speeds while yielding high-quality products. Consequently, a new felt typically requires a certain period of "dry running" (running without paper) or operation at reduced machine speeds before it reaches its optimal operational state.
