Basic Principles of Bleaching ① Destroy or modify the structure of chromophoric groups (delignification or alteration of lignin structure). ② Prevent or eliminate the combination between chromophoric groups and auxochromic groups. ③ Block the conjugation of chromophoric groups. ④ Inhibit the formation of new chromophoric groups. ## Auxiliaries for Hydrogen Peroxide Bleaching ① Sodium silicate: On one hand, sodium silicate buffers the pH value of H₂O₂ bleaching liquor; on the other hand, it inhibits the ineffective decomposition of H₂O₂. ② Oxygen: Introducing oxygen during H₂O₂ bleaching can strengthen the delignification process. High-consistency Oxygen Bleaching Tower The basic principle of oxygen bleaching is to utilize the strong oxidizing property of molecular oxygen to oxidize and degrade lignin in pulp under alkaline medium, so as to dissolve out lignin. Hydrogen Peroxide Bleaching During bleaching, H₂O₂ continuously releases HOO⁻ under alkaline action. HOO⁻ reacts with pigments continuously to a

Correction of felt and dryer web tracking follows the 4-character principle: Move against for inward, move with for outward. This principle means: at the felt/dryer web correction station, if the correction roll is moved against the running direction of the felt (dryer web), the felt (dryer web) will shift toward the operator. If the correction roll is moved in the same direction as the felt (dryer web) travel, the felt (dryer web) will shift away from the operator. This rule applies to top and bottom felts/dryer webs, regardless of the paper machine orientation, left-hand or right-hand machine, and whether the correction roll is on the drive side or operation side. As long as the correction roll is installed underneath the felt/dryer web, the positional relationship between felt/dryer web, correction roll and operator always obeys this principle. Loose felt or dryer web will disable the tracking system and cause web deviation. Tension the felt/dryer web to its normal tension to restore proper operation. I

1. Concept of Formation Paper formation refers to the uniformity of fiber distribution within the paper sheet structure. It is generally inspected by transmitted‑light viewing. Uniform fiber distribution indicates good fiber dispersion. Poor fiber dispersion manifests as clumpy formation, disjointed formation, wavy fiber texture, stock streaks, and cloud formation. Rules of fiber dispersion and flocculation: During sheet forming, longer fibers tend to flocculate more readily. Higher stock consistency promotes flocculation, while lower shear force also favors flocculation. Conversely, these conditions facilitate fiber dispersion. 2. Causes of Various Formation Defects Clumpy formation: Fibers flocculate into irregular lumps scattered across the paper. Under transmitted light, the lumpy areas have thicker paper layers, whereas regions between lumps are thinner, resulting in uneven light transmission across the web. Causes: Insufficient beating; improper headbox consistency; poor performance of flow‑straightenin

Paper defects refer to any flaws in paper not covered by the technical specifications for paper quality. Paper defects include certain performance‑related flaws that are invisible and intangible and can only be detected through testing or printing, such as brittleness, strike‑through, linting and dusting. They also cover various blemishes and flaws on the paper surface that can be directly seen or felt, for example dirt specks and stains. The latter category is herein defined as paper surface defects. There is a wide variety of paper surface defects, including dirt specks, spots, wire marks, felt marks, cloud formation, seersucker, wrinkles, creases, stains, shives, transparent spots, moisture spots, holes, dents, scars, pulp lumps, hard chunks, as well as basis weight variation and poor formation. Some of these surface defects originate from stock prior to papermaking; some are caused by improper or inadequate technical operations during papermaking; others stem from poor plant sanitation. Certain surface de