On the Influence of Felt Structure Details on Water Removal in a Press Nip, 1993 Papermakers Conference Proceedings

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Pressing experiments were performed in an pilot PM, using six different felts having the same base, but differing in batt layer thickness and fiber coarseness of the batt surface layer.

Thin wet webs (ca. 35 g/m-squared, some 20% solids were formed and reeled, to ensure uniform web material independent of PM operating conditions. Sheets were passed through the press using different felts. Speed range 5 - 40 m/min. Solids content 30 - 35% after one press nip.

For a given batt layer thickness, the solid content after pressing varied by 4 - 6% dependent on the coarseness of the surface batt fibers; fine fibers giving the higher readings. A similar variation in solids was found between felt with varying batt layer thickness, however the same surface batt fibers. The thicker the batt layer, the higher the solids level. For thicker paper webs, the effect of the felt structure was reduced.

Replicas of the felt, on thin tin foils give a good illustration of the non-uniformity of the felt structure.