The role of the press section of the paper machine

The main function of the paper machine press section is to use mechanical extrusion to remove moisture from the paper web as much as possible, evenly and stably. The dryness of the wet paper web from the forming section is usually 18%-20%, and the dryness of the wet paper web can be increased to 40%-50% after dewatering in the press section, depending on the paper type and press form.

As much dehydration as possible in the press section is required because the cost of mechanical extrusion dehydration is much lower than that of steam drying. Improving the efficiency of press dewatering plays an important role in increasing the output of the paper machine and reducing the production cost. To this end, some new press technologies have been continuously developed, including new press rolls, new press roll combinations, new press roll structures and materials, and new blankets.

The dewatering of the press section of the paper machine should be uniform along the width of the paper web, and the instantaneous dewatering amount should be stable, because when the paper web is partially over-dried or over-wet, defective products or post-feeding may occur. The process brings operational obstacles. For example, if the paper web enters the dryer section with uneven moisture, it will cause uneven shrinkage during drying, which may cause the paper web to wrinkle or break.

In addition, pressing can improve the surface quality of the paper, increase the tightness of the paper, and also improve the strength of the paper to a certain extent. In the pressing process, the surface of the wet paper web is in contact with the smooth surface of the press roll or the smooth felt surface, which can reduce the net marks on the surface of the paper web and increase the smoothness of the paper. After the pressed wet paper, the contact area of the fibers in the wet paper sheet increases, and the bonding points increase, and the tightness and strength of the finished paper will increase, but the air permeability and absorption performance of the paper will decrease. When the back press and smooth press are used properly, the difference in the performance of the two sides of the paper web can be more effectively controlled.

In addition, the press section of the paper machine is also responsible for peeling the paper web from the forming wire and transporting the paper web after dewatering by pressing to the drying section.