Press Felt Design and History

At the beginning of industrial paper making, simple cloths made out of wool were used. In the early sixties these felts were replaced by improved designs based on high-tech textiles. This replacement was necessitated due to the increasing demands (life time more than six days, use of abrasive fillers, higher machine 

Seamed felts, in contrast, are used mainly in the production of board and packaging and are not endless. They are closed in the paper machine with a seam, produced in a special variation of the weaving process. They are very common in North America (about 60% of all press felts in NA are seamed felts) and are easier 

B first base weave, C second base weave, D paper side fiber layer (source Voith). 

The nonwoven layers on the top and bottom of the base weave consist of staple fibers vdth different yarn count (3.3 to 100 dtex which means a diameter of 20 to 100 gm). The nonwoven layer on the bottom is in contact with the roll covers and protects the press felt against abrasion. The nonwoven layer on top is in contact with the paper surface and ensures a low and uniform water flow resistance during dewatering of the paper web. A coarser nonwoven layer is used in the first press nips with a higher amount of water removed from the paper web, finer nonwoven layers have use in the further press nips with a lower amount of water extraction. 

Polyamide 6 and polyamide 66 are the raw materials used for both the base weave and nonwoven layers. In some cases polyamide 6.10 is used to increase the cross machine stability during the felt lifetime, due to its reduced water absorption. 

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