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

Excessive hydraulic pressure within the press nip damages the web structure by over-draining water, resulting in sheet crushing. Inspect the felt tensioning and felt guiding devices. Wash or replace dirty, clogged press felts; check felt design and wear conditions. Check for blockages in felt Uhle boxes and/or raise vacuum level. Test pulp freeness; lower beating degree or adjust fiber furnish to improve freeness. Reduce press nip load to prevent rewetting between nips; inspect shower water and clean clogged spray nozzles. Consider revising the felt design or lowering machine speed to extend dwell time in the press section. Clean or replace suction press rolls; inspect Uhle box seals for air leakage; check pulp buildup on press roll surfaces, which may trigger crushing. Verify camber and crown curvature of press rolls; replace rolls if necessary. Excessively hard roll covers can cause sheet crushing. Likewise, check vacuum level of suction press rolls. Check and adjust load distribution evenly across the pres

How to Fix Wire Marks on Paper Adjust the slice lip toward the apron to reduce dewatering on the breast roll. If feasible, adjust the curvature of the apron slice lip so that the ejected pulp travels further forward along the forming wire. Reduce refining for pulp with slow dewatering performance. Gradually increase the vacuum level of vacuum boxes and put all vacuum boxes into service. Tighten the forming wire if it is too loose. Raise the headbox consistency to lower the moisture content of the paper web. Inspect the position and alignment of forming boards, dewatering elements and vacuum boxes. Raise the position of the dandy roll. Reduce the load of press rolls. Evaluate the feasibility of adopting a higher-mesh forming wire. Wire marks are sometimes related to the degree of fiber penetration through the forming wire. Excessive dewatering during initial forming will cause fiber ends to stand upright and embed into the forming wire. Excessive dewatering without turbulence may seal the paper web. This resul

Excessive dilution water is added to the vacuum broke chest. Especially when the chest only processes paper trims, check the spray water control and water pressure. Overflow from the wire pit flows into the vacuum broke chest. Adjust the overflow of the wire pit to prevent excessive dilution water from entering the broke handling system. The vacuum broke chest has insufficient capacity to process wet broke. Modify the dispersing equipment to meet the dispersion requirements for full-width broke. Inspect all pumps and control systems equipped for the broke handling system. Verify whether the pump capacity can meet high flow demands, and check the length of the pump suction line. Check the control configuration of the vacuum broke chest. Broke floats in the pulper. The pulper shall submerge the broke and defiber it promptly. Adjust the position of the spray pipe. Check the circulation system. Ensure sufficient agitation to draw the broke into the rotor area. Liquid level fluctuation occurs in the broke pulper.