Porosity is an extremely important property for almost all paper types and grades. It plays a crucial role in the production of papers for sacks, filters and cigarette wrappers, where air permeability is an essential characteristic. In addition, correct porosity is a key factor in paper printability. Paper porosity has been measured for a long time, but until now, measuring porosity CD profiles in real-time has been impossible. The fixed position online porosity measurement system has been used for several years. In some cases paper mills have measured porosity profiles from samples with manual testing equipment or by means of automated paper testing systems.
Honeywell's new Porosity Sensor is the first online profiling measurement sensor that offers the capability to control the porosity MD and CD profiles. This means it is possible to have more uniform paper quality, and tools to better meet the quality expectations of customers. Papermakers have knowledge and experience about factors affecting the air permeability profile. The same CD profiling units that affect other profiles also affect the air permeability profile : water removal elements, the press section nip pressure, the run model of the steam box, the condition of the paper machine fabrics, the drying shrinkage profile, and calendering are known to affect the porosity profile.
The scanning porosity measurement improves control over the grinding phase, the wet end chemical dosage, the wire section vacuum, and the calender. Optimal porosity also improves the coating result and reduces consumable coating agent volumes. Furthermore, improved paper machine control shortens grade change times, thus minimizing related downtimes and waste.
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