1.Inspect roller bearings to ensure free rotation — check the hardness and aging degree of roller shells.
2.Ensure there is no abrasive material on the supporting surface.
3.Check the straightness and correction system of the rollers.
4.Verify that there are no abrasive fillers in the pulp.
5.Ensure that no sand or other abrasive substances are present in any water spray pipes.
6.Control dewatering on the wire table to reduce traction load and traction wear — reduce vacuum pressure to prevent wear of the forming fabric on the vacuum boxes.
7.Check the setting of the forming board and leave sufficient space to achieve uniform and minimal dewatering at the breast roll.
8.Implement proper maintenance; the correct selection and adjustment of dewatering elements and forming elements can reduce traction wear.
9.Streaks are caused by solid deposits on the forming board or other fixed components. The worn areas have poorer dewatering performance than other parts, and thus such defects will show on the paper sheet.
10.Check the energy distribution between the couch roll and the drive roll.
Washing of Clogged Felt
During the production process, fine fibers, fillers, sizing agents, colorants and other substances in the paper stock, as well as impurities in the production water, are prone to adhering to the felt and clogging its pores, which impairs the absorbency and drainage performance of the felt. Therefore, felt washing is one of the key measures to ensure the good dewatering performance of the press section and extend the service life of the felt.
This is even more important for needle-punched felts, as their surface has long, dense fluff with small gaps between fibers, which are easily clogged. Moreover, it is very difficult to clean the felt thoroughly once it is contaminated and clogged.
According to surveys, over 90% of felts are taken out of service not due to wear, but due to clogging. It is evident that the key to using felts lies in proper washing.
There are two felt washing methods: continuous washing during normal production and offline washing during machine shutdown.
1.Water jet spray cleaning
The water pressure should be maintained at 1.47–2.45×10⁶ Pa. Its advantages are low water consumption and reduced need for chemical cleaning agents, thanks to the forced impact of the water jets. However, it has the disadvantage of causing relatively high damage to the felt. The cleaning surface should be the side of the felt that contacts the paper sheet. The recommended washing water temperature is around 50℃ to enhance the descaling effect, which can be adjusted according to actual production conditions.
2.Intermittent on-machine chemical cleaning
Detergents, hydrochloric acid or alkali solutions can be used for intermittent cleaning. Prepare these chemicals to an appropriate concentration and apply them evenly across the full width of the felt. After the chemical solution is consumed within the specified time, rinse the residual chemicals from the felt with clean water.When using acid for cleaning, the concentration of the dilute acid must not exceed 5%. Otherwise, the polyamide fibers of the felt will harden upon contact with concentrated acid, which will affect drainage performance.
3.Continuous on-machine cleaning
This method can keep the felt in optimal condition at all times to achieve maximum papermaking efficiency, making it the best washing option.It focuses not on removing contaminants that have already caused clogging, but on removing dirt before it adheres to the felt or just after it penetrates the felt surface. The concentration of the cleaning agent for continuous washing is generally 0.01–0.06%.Although continuous cleaning agents have higher costs, their advantages include extending the service life of the felt, maintaining the felt in optimal condition at all times, helping to reduce material consumption, minimizing breakage losses, and improving paper quality.
