Do You Know What is Dryer Felt ?

Dryer Felt Used in Paper Machine Dryer Section

Dryer felt, together with polyester dryer fabric, are called dryer cloth and are essential dryer equipment for the dryer section. They transfer the wet paper sheets from the press section to the dryer section, where they are dried before being transported to the calendering and reel section. During the process of transferring wet paper sheets, one of the most basic tasks of a dryer felt is to help and promote uniform drying of the sheets in order to achieve normal moisture content.

The dryer cloth initially used in the dryer section was called dryer woven canvas, which is a flat woven cotton canvas. Later, with the demand for papermaking and the improvement of fabric production technology in the dryer section, fully synthetic needle punched dryer felt made of 100% polyester fibers using needle punching were widely used in the dryer section of paper machines. The dryer felt has significantly better temperature resistance, moisture resistance, and corrosion resistance than woven canvas, and its service life is several times longer. But now the widest used dryer cloth is polyester dryer fabric.

The Function of Dryer Felt

The functions of a dryer felt include the following aspects:

(1) Pass the paper sheet through the dryer section.

(2) Drive the operation of the felt dryer cylinder and other rollers in the dryer section (including dryer felt rollers, adjustment rolls, tension rolls, etc.), that is, transmit power.

(3) The dryer felt tightly presses the paper sheet onto the surface of the dryer, which can enhance the contact between the paper and the cylinder surface and improve heat transfer efficiency.

(4) Dryer felt can also absorb the water vapor and moisture on the surface of wet paper that evaporates during drying, increasing the evaporation area. After the dryer felt is dried by the felt dryer cylinder, it comes into contact with the wet paper and enters a new drying cycle. Both are beneficial for improving drying efficiency, while also avoiding wrinkles and folds on the paper during drying, and endowing the paper with some properties such as flatness, smoothness, and glossiness.

Performance of Dryer Felt

In order to meet the above requirements, the dryer felt must have the following properties:

(1) Good Durability

It is necessary to require the fibers and structure of the dryer felt to have good durability under high tension in the dryer section, high humidity and heat environment, chemical corrosion, machine component wear, and continuous repeated bending state.

(2) Dimensional Stability

When the dryer felt is running at high speed in the dryer section, it must maintain a tension of not less than 3kg · cm-1. In such a high tension state and high temperature environment, it must be able to maintain longitudinal and transverse dimensional stability and smooth organizational structure, so that the wet paper can be tightly adhered to the cylinder surface under the strong and uniform tension of the dryer felt to achieve the best drying effect.

(3) Breathability and Water Absorption

In the drying process of wet paper sheets in the dryer section, during the initial stage of drying, the activity of water molecules is activated under the action of thermal energy in the preheated state of the dryer, and some of them enter the dryer felt; The water molecules activated by thermal energy in wet paper sheets change from liquid to gas as the drying temperature increases and continue to enter the dryer felt. Some of the steam passes through the dryer felt and is discharged, while the remaining steam is reduced to water and taken away by the dryer felt. The water molecules taken away need to be further heated by the dryer felt cylinder or other heating devices such as hot air guide rollers during the return journey of the dryer felt, and then turned into gas and discharged. Such a drying cycle requires the dryer felt to have good breathability and water absorption performance in order to improve the drying efficiency of wet paper sheets in the dryer section.

(4) Smoothness and Softness

Dryer felt should have good smoothness and softness, so as not to leave felt patterns (surface imprints of dryer felts) on the surface of the paper, and to evenly press wet paper tightly onto the surface of the dryer, improving heat transfer efficiency and drying efficiency.