Web stabilization in the single-tier dryer section
In the scope of rebuilds to paper machines with a single-tier dryer, which use suctioned rolls (known as dryer fabric suction rolls, DFSR), the DuoFoil can be installed over the DFSR in order to stabilize the web. With stabilization zones the DuoFoil supports wrinkle-free sheet edges from dryer cylinder to dryer cylinder. The negative pressure in the stabilization zone is created via the "pre-suction" zone in the DFSR. This increases the runnability of the paper machine.
The web is stabilized by means of negative pressure (-100 to -200 Pa) in the stabilization zone. The DuoFoil does not have its own connection to the vacuum system, but rather is supplied through the vacuum of the DFSR. The negative pressure of the DuoFoil therefore depends on the vacuum setting of the DFSR. The stabilization zone is sealed off by the MultiSeal and the lateral air knives. The MultiSeal is a mechanical sealing system that ensures high negative pressures with low energy requirements. With this system the seal strips can be replaced quickly and easily (including parts set behind the framing). Air knives are used for sealing on the sides in order to compensate for the deflection of the dryer fabrics and to prevent wear of the dryer fabric. There is also a seal (Teflon plate) to the roll provided.
For the ropeless threading of the transfertail, a threading zone can be separated in the system. This separation is created using flaps that are activated automatically during the threading. As a result, the transfertails are held securely on the dryer fabric with negative pressure in the threading zone during the ropeless threading. This increases the reliability of the machine and reduces the threading time.