SHEET STABILIZERS AND POCKETS VENTILATION
Paper sheet stabilizing is an extremely important factor for modern paper machine.
The continuous increasing of production speed requires systems able to assure the best support of the paper sheet in the machine drying section.
Here below you can find a list of the main advantages that can be obtained thank to a modern and efficient drying section ventilation system:
• Improving of paper quality thanks to the elimination of defects due to paper flattering, edges curling, bubbles formation , wrinkles formation and striations.
• Improving of cross machine direction CD paper moisture profile, thanks to the proper drying section ventilation system that avoids dangerous stagnations into the pockets.
• Improving of drying capacity of the machine thanks to the better paper evaporation conditions in the drying section.
• Reduction of cross machine direction CD paper shrinkage thanks to the better paper support.
• Reduction of paper breaks thanks to the better web sheet stability, to the reduction of open draws and to the perfect control of air flows inside the pockets.
• Possibility to have drying sections with no rope system of tail threading.
The specific characteristics of each paper machine drying section require to study the most suitable solutions to solve problems of sheet stabilization and pocket ventilation.
Thank to our complete range of blowing boxes and sheet stabilizers, we can realize specific solutions for each different type of paper machine drying section.
Configuration of paper machine drying section is different relating to products range and to operating speed.
Press Transfer Sheet Stabilizer PTSS is used to prevent bubbles formation on the web entering in the press section.
Bubbles could have a negative effect on the press operating conditions.
Increasing the machine speed, the air has the tendency to be trapped in the contact nip between paper and the press bottom fabric, this eventuality causes the formation of bubbles on the web surface.
The sheet stabilizer creates a negative pressure by blowing air in a proper way that keeps the paper against the press fabric.
There is no contact between the PTSS stabilizers and the fabric wire.
The alimentation of the box with high pressure air keeps clean and free the blowing slots.
Sheet stabilizer DTSS, for paper transfer from press section to drying section, is a valid solution to eliminate paper instability in this machine area.
These blowing boxes guarantee a paper proper support creating a suction effect through the fabric wire and contrasting air flow due to the fabric pumping action.
Thanks to this effect it is possible to reduce the open draws, to eliminate sheet detachment and to reduce wrinkles and paper breaks.
In order to completely eliminate the open draws in the drying section, we developed this new sheet stabilizer that combines the web stabilization, obtained by blowing hot air, with a suction effect in the box bottom part.
The suction action needs the presence of a grooved bottom roll, in order to allow the web support on the complete wrapping angle of the bottom grooved roll.
The SFDX stabilizer has a connection for suction air and a second one for blowing air, consequently it is possible to assure, at the same time, stabilization effect between top and bottom roll and suction effect from the grooved bottom roll.
By means of on-off automatic dampers, SFDX stabilizer assures a ropeless tail threading.
passage is automatically controlled by means of these dampers, that concentrate the stabilization effect due to suction air and the blowing air in the tail passage area.
SFDX slalom fabric double stabilizer allows to design drying sections completely without open draws and with ropeless tail threading.
Thanks to these characteristics, SFDX can be installed on high speed paper machines, where runnability and web stabilization are factors of primary importance.
The complete web support of SFDX stabilizer assures an improvement of paper quality and mechanical performances.
The SFHV version have a separate section with high level vacuum for ensure the detachment of the paper from the upper dryer roll.
The stabilizing box for slalom fabric is used to eliminate paper sheet detachments at leaving of the top cylinder and entering of bottom cylinder.
This event is particularly harmful and it compromises drying section runnability.
The air pumping effect creates instability on the sheet and paper breaks.
The stabilizer box generates a negative pressure in the paper detachment area behind the fabric, supporting it until entering of bottom cylinder.
The suction effect is produced by the particular box shape and by the pocket air flow control.
The stabilizer box is designed to adapt itself to drying cylinder, rolls and fabric profile.
The main advantages offered by using these boxes are : increasing of machine speed, possibility of paper width increasing, paper wrinkles reduction and easier tail passage.
A second blowing box ( SFCB Slalom Fabric Conditioning Box ) located below the top cylinder doctor, allows the control of the air flow coming from the machine basement, by means of hot air flow blown in the direction of paper sheet detachment from the drying cylinder.
These sheet stabilizers are installed in the double fabric new drying groups, when the fabric roll is tangent to the fabric itself.
This solution is frequently used in new design high speed drying sections.
Paper leaving the drying cylinder is supported by the fabric in order to reduce the free draws, hence is not possible use a conventional blowing box in this position, because the paper should be detached by the air flow.
These stabilizers assure in the same time paper stability and good ventilation of the pocket.
Two blowing slots, located on the top of the box, produce a negative pressure which keeps the paper against the fabric.
A third slot, in the bottom part of the TFSS box, works like a pocket ventilation eliminating wet air.
With similar design can be supplied a special stabil
The twin slots shape of this blowing box allows to achieve a proper ventilation of the pocket and to prevent the wet air dragging effect due to fabric roll rotation.
Hot air flow crossing the fabric gets in touch with the paper just leaving the drying cylinder, increasing evaporation rate.
The use of special three directions adjustable brackets, allows a perfect setting of the blowing box in the pocket area.
Cross machine moisture profile can be controlled using manual or automatic special dampers, subdividing in three or more zones the blowing profile.
This blowing box is particularly suitable for machine producing at speed higher than 200 m/min, where the effects of dragging air due to cylinder rotation, create problems of drying efficiency.
The blow box shape and the blowing slots design are studied on the base of the pocket configuration.