Pulp Paper & Logistics
HEIMBACH 15 Laminat - Gewebe Multiaxial - Gewebe
Figure 2: Improved covering of suction holes by an Atrojet base design.
throughput than smaller ones. Therefore large holes lead to higher water flow speeds than smaller ones and cause shadow marks to be much more likely.
Felt designs that reduce hydraulic marks The appearance of hydraulic marks can be influenced by using suitable felt designs. Practical experience shows that Atrojet felts, due to their multi-axial non-woven structure, are excellent diffusors and are able to reduce hydraulic problems effectively. Particularly for speciality paper
grades, where flawless paper is especially important, Atrojet felts improve the paper quality significantly, as shown in Figure 2 and Photo 2.
Standard- laminatfilz
Durchlichtaufnahme Bildanalyse / inverse FFT
Atrojet-Filz
Photo 2: Significantly improved quality by using an Atrojet for producing a coating base paper grade
Press felts under pressure
In the press section the felt and the paper sheet are compressed. First the air is extracted until the felt/paper entity is 100 per cent water saturated. Then water is expelled, first from the felt because the flow resistance here is less than in the paper. The paper is pressurised. The differential pressure, that is, higher pressure above the land area than in the groove, ensures that water is ‘pressed out’ of the paper and starts to flow. Initially the water flows against the running direction and, in doing so, has to overcome the flow resistance of the felt, so that the hydraulic pressure in the press nip rises again. The pressure of the felt to the paper can cause crushing, hydraulic marks such as shadow, groove and felt marks, and it can create vibrations and even felt bursts.
Schematic simplified diagram of the nip July/August 2019
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36
