Tissue

Toscotec introduces new shoe press generation design for tissue

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Toscotec has launched the new generation design of its shoe press TT NextPress, featuring superior drying performances and energy savings, resulting from R&D activities in cooperation with Voith.

TT NextPress delivers a stable after-press dryness rate of more than 47% on a tissue line operating above 2,000 mpm speed. This dryness level ensures a substantial reduction of energy consumption, as the Yankee and the hoods use significantly less thermal energy to complete the paper drying process. Toscotec, together with Voith, has sold more than 60 shoe presses for tissue machines all over the world.

Superior Dewatering delivers higher Dryness

A new shoe shape has been introduced to enhance the nip width and increase the peak pressure at the nip outlet, reshaping the outward pressure into a steeper curve. This eliminates the risk of paper re-wetting at the exit of the nip, and increases sheet dryness, without affecting the belt’s life.

Continuous Nip Control for maximum Reliability

Machine operators can now visualize on the DCS (Distributed Control System) the actual nip pressure of TT NextPress in real time. The operator can regulate the nip pressure at which the TT NextPress is loaded onto the Yankee resulting from both a theoretical and empirical system, as the nip pressure is calculated based on the shoe press loading system and also measured by the load cells installed on the press mechanical stop.

Higher Precision: the perfect fit for Rebuilds

In rebuilds, the installation of a shoe press on an old-style cast iron Yankee can compromise the lifetime of both the felt and the belt. Toscotec has designed a dedicated solution on the TT NextPress consisting of multiple independent pressure zones, up to 14 in total, of which 12 are located on the edges. This design ensures a perfect fit between the shoe and the Yankee deformation, and maximizes the clothing lifetime.

Improved Safety and Yankee Protection

TT NextPress nip pressure lines are fitted with a pressure accumulator pre-charged with nitrogen, which is installed inside the belt as close as possible to the loading pistons. The accumulators absorb instantaneous overloads or pressure increases on the line due to the presence of external elements or paper wads in the nip area. This eliminates the risk of any possible damage to the Yankee dryer.

The new TT NextPress builds on the features of its previous version which have been widely appreciated by tissue producers around the globe. These include:

  • the hydraulic loading system, which ensures top pressure uniformity and reliability
  • the extreme flexibility offered by the shoe tilting regulation during operations
  • the maximization of the belt lifetime both through the continuous digital monitoring of the heads position with regular lateral movements of the belt, and through the sleeve tensioning device actuated by hydraulic cylinders, which delivers a constant and adjustable stretching force.

Shoe Press vs Traditional Press: higher paper quality

Toscotec TT NextPress allows to have an optimum pressure distribution in machine direction (MD) with a pressure profile that gradually increases from the inlet to the outlet of the nip, which is where the highest pressure is applied. At the end of the nip, due to the geometry of the pressing shoe element, the pressure curve has a very steep decline and falls down to zero, thereby avoiding rewetting the paper.

If we compare TT NextPress technology with a standard press roll, the shoe press achieves a higher post-press dryness rate, because the time the paper stays in the nip is longer, the pressure is transferred to the paper more gently, the pressure reduction at the nip outlet is very steep and the pressure peak can be equal or higher of a standard press roll.

We should consider that in a dry crepe tissue machine, the quality properties of the paper produced including bulk, softness, absorbency, and to some extent also tensile strength, are mostly determined by the creping phase on the Yankee. The shoe press acts on the flat base sheet before the Yankee drying phase and the creping phase which allows a product to maintain its creping induced paper properties. This explains why the extent to which the shoe press affects those properties – through the regulation of the nip load and the tilting function – is less significant than the extent to which the shoe press affects paper dryness.

 

 

We should also consider that:

  • on higher basis weights, the effects on the properties listed in the table are normally even higher
  • the higher the nip load, the lower the effect of tilting on dryness out. The same is expected for all other properties.

 

 

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