Today the screening room is one of the key elements for top quality mechanical pulp and good runnability at the paper machine.
Pulp and paper quality is highly dependent on the function of the screening room, and a good performance in the screening room is an absolute necessity when manufacturing value added（提升附加值） paper grades. One single harmful shive（碎片） in the accept pulp（良浆） can cause runnability or quality problems at the paper machine.
The mechanical pulping screening room includes several subprocesses, most notably screening, cleaning, and reject handling（渣浆处理）. Each of them has its own specific task in pulp processing, such as separation and/or retreatment of various impurities like sand, bark, shives, and coarse fibers（粗纤维，纤维束）.
The cleaner's primary task is to remove inorganic debris, mainly sand, from the system. Today's screens usually are slotted pressure screens（缝压力筛）, and their task is to separate wood originating impurities from fibers and to divide the feed pulp（进浆，来浆） into different fractions, which will be further processed separately.
The main functional difference between screening and cleaning is that screens reject debris on the basis of fiber dimensional properties (length and width), whereas cleaners mainly do it based on density（密度） and specific surface area.
Separated undefibrated wood components and undeveloped (unfibrillated) fibers will be refined in the reject handling until suitable for further processing. Screening and cleaning technologies are both subject to complex fluid mechanics.
The best configuration（布置，排列） for the screening room depends on the desired accept pulp （良浆）quality, on the raw material, and on the pulping process. For example, the use of cleaners is questionable if the feed pulp （进浆）is sufficiently clean from sand. If there are cleaners in the process, they are coupled（并列，排列） together in 2~6 stages and are usually situated after the fine screening（精筛） or in the reject line.
The fine screening with pressure screens is typically done in 2~3 stages, and the accepts from each stage are combined. The screens rejects are further treated in the reject refiner（渣浆再磨机）, after which the refined reject pulp is screened in a reject screen from which the accept is usually led forward and rejects are led back to the reject handling feed.
With modern equipment, there is no need for cascade connections（串联）in the screening room; screening efficiency has improved remarkably（已经显著改善了） during the last decade.
Quality improvements of mechanical pulp can be done mainly in two ways: Either by changing the process conditions in grinding or refining or by improving the undeveloped fibers separation efficiency in screening and cleaning.
An improved efficiency in screening means that the screening will be more selective and the reject refining can be directed only at those components, which need more treatment. The efficiency of screening and cleaning depends on the design of the screening room.
The screening room has become a more important part of the pulping processes, and its importance tends to（趋向，朝向） grow. The biggest challenges for the screening room equipment and design will in the future be higher screening consistencies for cost reduction reasons and higher fractionation efficiency for pulp quality reasons.（由于成本和质量原因，趋向高浓）
