Dewatering Mechanism
Liquid removal by rotary suction rolls involves the continuous withdrawal of water from a wet paper web through a perforated shell under negative pressure. This rotary vacuum extraction takes place primarily in the forming and press sections of the paper machine, where the web must be rapidly consolidated before entering the dryers. The vacuum level is carefully controlled to prevent fiber carryover into the suction system while maximizing water extraction.
Web Consolidation
Effective dewatering improves wet web strength, which allows the machine to run at higher speeds without breaks. If the rotary vacuum extraction is inefficient, the paper web enters the press section with too much water, causing sheet crushing and surface defects under the rolls. Consistent vacuum pressure helps maintain a uniform moisture profile across the width of the machine, which is critical for subsequent coating applications.
Suction Efficiency
Suction roll maintenance is essential to prevent hole clogging and vacuum leaks that reduce the efficiency of the dewatering process. When holes become blocked by paper fines and scale, the local rotary vacuum extraction drops, leading to wet streaks in the finished paper. These wet streaks cause uneven caliper and can lead to puckering when the paper is wound into rolls or printed on high-speed presses.
High-pressure showers and periodic chemical washing are used to keep the suction rolls clean and ensure uniform drainage across the entire forming table.
