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Thursday, 24 February 2022 11:25

How to preserve paper bulk thanks to our SMARNIP® mini shoe press

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The bulk is an important characteristic for many types of paper, capable of determining the softness of the papers for hygienic-sanitary use or the dimensional stability of the paper sold in sheets. In these cases, where it is essential to implement a correct and effective pressing process, our SMARNIP® mini shoe press is the ideal solution to optimize the dryness and mechanical properties of the paper.

The shoe press is a Beloit invention dating back to the 1980s aimed at the production of packaging paper. It is an extended nip press (ENP) where a concave stationary shoe, opposed to a cylinder, is used to substantially expand the nip, thus allowing the application of a high linear load while keeping the specific pressure low.

Since the first installations, it was possible to highlight advantages in terms of sheet drying compared to traditional cylinder presses, guaranteeing excellent results in terms of increased production and energy savings. The interest aroused by this innovation has led to the application of the concept also in the production of graphic papers, but we had to wait until 2003 to have a shoe press specifically designed for applications where paper bulk was a priority.

It was in that year that PMT, a company part of the A.Celli Group since 2020, patented the SMARNIP® mini shoe press. Let's see the characteristics of this solution in detail.

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Why PMT developed the SMARNIP® mini shoe press

The experience deriving from applications in production lines of graphic papers and papers with specific bulk needs has led to the conclusion that, for these products, the "standard" load exerted by a conventional shoe press (about 1,000 kN/m) is excessive.

Furthermore, even the size of this shoe press itself is disproportionate to the real needs, for which a smaller and more manageable solution is sufficient also from the point of view of the overall dimensions.

The installation of a conventional shoe press also requires significant interventions on the paper machine and, often, on its surroundings, such as the strengthening of the overhead crane and the reinforcement of civil structures, with an increase in installation costs and a reduction of the profitability of the investment.

To overcome these limitations and find an appropriate balance between the desired degree of dryness and the qualitative properties of the paper, we have developed and patented the SMARNIP® mini shoe press.

The characteristics of the SMARNIP®

The SMARNIP® is a relatively compact and light solution, with diameter from 700 mm to 1000 mm, shoe width from 70 mm to 125 mm and overall dimensions similar to a variable-crown roll.

Our mini shoe press is capable of exerting a linear load from 100 to 700 kN/m and has the same characteristics as a conventional shoe press, i.e. a pivoting concave shoe loaded by two rows of transverse pistons and a commercial polyurethane sleeve.

The aforementioned loading system gives the SMARNIP® an operational flexibility such as to guarantee an optimal ratio between dryness and bulk. Furthermore, the distribution of the hydraulic pressure applied to the pistons can be easily set while the machine is running to facilitate optimization even in the event of frequent production changes.

SMARNIP® advantages

The numerous references and the positive experiences accumulated have shown that our SMARNIP® mini shoe press is able to increase dryness up to 2% more than a roll press with the same bulk (this result can obviously vary based on the composition of the mixture of the specific case).

Considering the advantages obtained also in relation to the small dimensions of our solution, it is often interesting to consider the installation of two SMARNIP® in the same press section. This possibility opens the way to a completely new approach in evaluating the possible investments to be made in the press section itself.

The installation of the SMARNIP® is particularly recommended for paper machines of limited width and, in general, for the production of all types of paper in which a high bulk is sought

Among the many advantages we can mention:

  • Increase in production, thanks to an increase in the degree of dryness and a consequent reduction in the evaporation load on the dryer
  • Greater efficiency of the paper machine, as it is possible to obtain a drier, more resistant sheet
  • Greater bulk
  • Better control of paper smoothness, both in absolute terms and relative terms (between the two sides of the paper)
  • Easy installation, thanks to the limited dimensions
  • Less interventions on the building due to the reduced weight of our mini shoe press
  • Interchangeability with conventional cylinder, unlike a traditional shoe press which has a greater distance between bearings than roll presses

Ultimately, the SMARNIP® embodies all the advantages of the shoe press while preserving the simplicity and compactness of traditional presses.

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