When paper web exceed press section of a paper machine, it contains more than half of its weight is water. Most of this water of the paper web should be removed in the dryer section of the paper machine to ensure 4%-6% of final water content. The drying section is one of the most energy consuming parts (about 60%) of the paper machine. Consequently the role of dryer fabrics is absolutely enormous.
Function of dryer fabrics:
The dryer fabric presses the paper web against the surface of steam-heated drying cylinders. Therefore the temperature of the paper web increases and water is evaporated into and through a porous dryer fabric. Moreover dryer fabrics assist to support the paper web to shift from one cylinder to another cylinder. Dryer fabric controlled paper web shrinkage.
Selection of dryer fabrics:
The selection of dryer fabric is depending on the various paper machine parameters such as paper grades, dryers configuration, dryers temperatures, air balance in the hood etc. Dryer fabric design and materials are also very important.
For a particular paper machine, the permeability, design and materials of the dryer fabrics should be adapted to make sure optimum drying from a drying section. The air permeability of the dryer fabric has a great impact on the rate of evaporation of water. If the permeability is decreased, then it is reduction in drying capacity of the dryer fabric. The dryer fabric, whose air permeability range between 700-1000cfm is used on paper machine for producing higher gsm Kraft and board varieties. On the other hand 200-400cfm dryer fabric widely used in medium and high speed paper machine and below these rage used in lower speed paper machine. High numbers of contact areas with the drying surface ensure uniform drying. Proper chosen of dryer fabric improve paper machine runnability, increased drying rate, improved paper quality and savings energy.
Moreover the dryer fabrics should have the following parameters or characteristics: Aerodynamic Properties, Heat Transfer, Fabric Tension, Sheet Support, caliper, heat resistant, wet-resistant, should be less elongation at heat, durability, silent drive, easy to operation etc.
Classification of dryer fabrics:
Dryer fabrics can be classified depending on weaving, category and combination mode. According to the category, synthetic polyester dryer fabric can be divided into one layer, one and a half layer, double layer etc. In accordance with weaving, synthetic polyester dryer fabric or fabric can be divided into 3-shed, 4-shed etc. And in relation to the combination mode, dryer fabrics can be divided into insert, pin, pin ring and spiral ring join.