The permeability of the polyester dryer fabric is a function of the weave pattern, the yarn sizes and shapes and the density of the yarns in both the machine and cross direction. Conventional practice with the selection of polyester dryer fabric permeability is that the permeability increases following the dryer curve of the machine. That is during the pre heating stage, where the sheet is most wet and requiring maximum support, a dense smooth fabric is required. Consequently this fabric is general the lowest in permeability.

As the sheet then heats and water evaporation intensifies, the removal of water vapour and steam increases in volume and therefore in order for this to escape, a higher permeable polyester mesh is required. Therefore the air permeability of the polyester mesh has a major impact upon the flow of evaporated water from the heated sheet into the pocket. Any blockages of these paths will result in this flow reducing and possibly being blocked. This will subsequently reduce the overall drying efficiency of this section. As this sheet has not then reached its optimal dryness the next section will be required to remove the remaining moisture. If this section already has inadequate drying efficiency then the problems becomes compounded. The paper maker may have to alternative but to reduce the speed of the machine. 

There are limitations on the range of permeability available per drying section. For example in the later sections care must be taken not to have too high permeability as otherwise the sheet may become unstable. For a typical paper machine permeability ranges are 75 to 110ft3/min in pre heating, single tier and uno runs, 110 to 250ft3/min for conventional top and bottom and single tier drying sections and finally 250 to 700ft3/min for final drying sections.

Another of the impacts of polyester dryer fabric permeability is the effect upon systems such as vacuum rolls and blow boxes. These elements are designed to assist with both air and sheet management. Again incorrect selection of fabric permeability may result in the inefficient function of these elements. This may subsequently force the paper maker to make machine adjustments such as increased draws or even reduced overall machine speed. 

Anna
Sales Department
Hebei Defeng Polyester Fiber Co., Ltd
Add: Jingjiu Railway west, wugong town, Raoyang County
TEL: 86-311-67699480
FAX: 86-311-67699480
Website: www.china-polyestermesh.com.
E-mail:anna@china-polyestermesh.com

Tag: polyester dryer fabric, polyester mesh