Optimum web stabilization and tail threading
Voith web stabilizers ensure
- stable web pickup from the dryer
- the best sheet stabilizing
- safe and fast ropeless tail threading
- good pocket ventilation
Stabilizers – stainless steel
Stable and crease-free web run
By means of an ejector effect, the Bubble Sucker generates a vacuum of up to -150 Pa under the press felt in the stabilization zone. This enables a stable and crease-free web run, and the frequency of breaks is noticeably reduced.
Creation and maintenance of the vacuum in the entire stabilization zone are achieved by blowing air at high speed in the nozzle geometries at the entry and outlet and by means of side air knives on the Bubble Sucker. The vacuum can be set manually by means of a hand flap in the air supply duct. The design of the Bubble Sucker is easy to maintain.
Web stabilization between press and dryer section
The DuoTransferFoil with drilled roll stabilizes the web on the dryer fabric. With its use, problems such as edges peeling away, fluttering and the formation of wrinkles on the paper web are eliminated.
Web stabilization with the DuoTransferFoil is done by means of a vacuum (up to -350 Pa) that is set via the fan speed. For ropeless threading of the transfer tail, a threading zone can be separated in the system from the entire operating zone. In the threading process, suction is concentrated on the threading zone. The stabilization zone is sealed using lateral air knives and a machine-wide nozzle at the transition to the first dryer cylinder, which are provided with supply air from the DuoTransferFoil.
The DuoTransferFoil with a drilled roll is inserted between the DuoCentri NipcoFlex presses and the first dryer cylinder in order to hold the paper web on the dryer fabric. The difference compared to the TransferFoil with dryer fabric suction roll is that the drilled roll does not have an internal box, and its suction mechanism works according to the DuoStabilizer principle. This design without an internal box saves costs and no back-up roll is required.
Stabilization of paper web between press and dryer section
By means of an ejector effect, TransferFoil creates a vacuum (up to -350 Pa) behind the dryer fabric in the stabilization zone. The supply air is connected to the supply air system of the downstream stabilizers’ air knives. Use of TransferFoil after a dryer fabric suction roll facilitates ropeless threading to the nip between the drying cylinder and dryer fabric. No air bubble forms between the dryer fabric and paper web during feed-in. Due to TransferFoil’s multi-part design, an adjustment of the bodies to the fabric deflection can take place by means of the vacuum.
TransferFoil is used to hold the web after a dryer fabric suction roll between the press and the first drying cylinder.
Stabilizers – painted steel
Stable web pickup and increased speed
The sealing system consisting of MultiSeal forms the release zone and in a targeted fashion provides for a high vacuum in the area where the paper web is picked up from the cylinder. This reduces the stresses that act on the still relatively wet and sensitive paper web when it is being removed from the cylinder. In addition, runability is improved in the particularly sensitive area of the first dryer groups. Fewer breaks and an increase in speed at the same draw are the results.
ProRelease+ is used in the first dryer groups of single-tier dryer sections and provides for stable web pickup.
Upgrade for ProRelease+
The upgrade for ProRelease+ consists of the new sealing strip holder MultiSeal Plus, which is installed with a sliding device. This allows the adjustment of the holder’s position according to the best operating position. With MultiSeal Plus, the high vacuum conditions can be optimized and constantly maintained over a longer period or the production speed can be increased. Another benefit is that the lifetime of the strips can be extended to more than a year. For the perfect fit, we recommend the installation of SkySeal Plus or SkySeal Flex sealing strips.
Increased runability due to web stabilization
With web stabilization, the stabilizer roll is suctioned via the DuoStabilizer, and the stabilization zone is placed under pressure with a vacuum via the bypass of the roll. Sealing of the zone is done with a cost-effective and energy-saving sealing concept called MultiSeal, comprised of lateral air knives and a Teflon seal toward the roll. The MultiSeal is a mechanical seal that prevents the boundary air layer carried along with the dryer fabric from getting into the stabilization zone. For ropeless threading of the transfer tail, a threading zone can be separated in the system from the entire operating zone.
Separation is carried out with a securely installed separation disk in the roll, an additional air knife in the stabilization zone, and a flap that separates the suction area of the operating zone from the threading zone. In the threading process, suction is concentrated on the threading zone. The additional air knife is fed with supply air, and the operating zone is switched off. After threading, the air knife is depressurized, and the operating zone is activated. The negative pressure of the DuoStabilizer is set with the fan speed. Manual alignment of the individual DuoStabilizers can be done with a manual flap in the suction line.
The DuoStabilizer allows a stable and wrinkle-free web run in the dryer section from dryer cylinder to dryer cylinder. Web tension and shrinkage are thus reduced; in addition, the speed can be increased.
Web stabilization in the single-tier dryer section
In the scope of rebuilds to paper machines with a single-tier dryer that 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 runability 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 transfer tail, 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 transfer tails 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.
Stabilization with unsteady web run or web flutter
The S-Stabilizer stabilizes the paper web in the area of the dryer fabric. The dryer fabric guide roll is moved asymmetrically until it dips into the paper web. The number of breaks can therefore be reduced and machine availability increased. The paper web is stabilized through the use of a vacuum. It is created by means of an ejector effect behind the dryer fabric in the stabilization zone. The vacuum can be set manually through a hand flap in the air supply duct. The MultiSeal mechanical seal prevents the boundary air layer carried along with the dryer fabric from getting into the stabilization zone. Air knives seal on the sides to compensate for the deflection of the dryer fabric. In addition, there is a seal toward the roll.
The S-Stabilizer is used in two-tier dryer sections and allows an increase in speed due to stabilization of the web run.
Hood air supply
Improved removal of air moisture
The VentiPipe hot air blow pipe improves ventilation in the fabric loops of the dryer group and removes moisture more efficiently. Hydrolysis on the dryer fabrics is prevented.
VentiPipe is connected to the air supply system of the dryer section. Hot, dry air is brought into the dryer group via exhaust openings. More air is blown out in the center of the machine; a transverse flow thus arises from the center of the machine to the edges. The hot, dry air absorbs the water vapor and removes it. The number of VentiPipes used depends on the number of drying cylinders in a dryer group and the hood balance. Taken as a whole, VentiPipe contributes to improved conditioning of the dryer fabric, since less dirt remains due to continuous drying.
The VentiPipe hot air blow pipe is placed in single-tier dryer groups in the upper fabric loop above the drying cylinders.
Improved removal of air moisture
The VentiBox hot air blow box is connected to the air supply system within the machine frame or with a two-sided dryer section, also from the drive side. Via exhaust openings, hot, dry air is brought into the dryer fabric and the pocket that absorbs the water vapor and reduces the air moisture. The air supply is increased in the center of the VentiBox, and the moist air is transported from the center of the machine to the edges. This transverse flow prevents the edges of the paper web from turning up. Condensation and hydrolysis are also prevented by the VentiBox.
The VentiBox hot air blow box is used in single-tier and double-tier dryer groups.
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Engineered for success
Rebuild of Jass Schwarza PM 1
Production increase thanks to web stabilization and "Clean Design"
In September 2015, Voith rebuilt the dryer section of PM 1 at the Adolf Jass paper mill in Schwarza, Rudolstadt. The aim of the rebuild was to increase the maximum production speed for low grammages from 1,400 to 1,500 m/min and at the same time maintain the already excellent machine efficiency.