Press Section

The purpose of the press section is to increase the dry content of the paper web as much as possible by compression. This kind of mechanical dewatering reduces steam consumption in the dryer section and increases the strength of the web in order to avoid web breaks during production. 

The wet paper web is picked up from the wire section and is transported by felts through the press section which contains one or more press nips to be passed. The so-caUed press nip is formed between two opposing rolls pressed together The paper web today is usually transported either on one felt in the top or bottom position or between two felts as a sandwich. In some cases, when the paper web is strong enough compared with the applied stress in operation, the weh is trans- 

Nowadays, the dry content after a shoe press section reaches about 50 to 55%, depending on the product and the raw material used. Because of these high dry contents, less thermal energy is required in the dryer section, and the resulting increased web strength results in fewer breaks. 

Shoe presses have been standard in press sections for board and packaging grades since the 1980s. Later, they have also become state-of-the-art presses for graphic paper machines. Today modern press sections of high-speed paper machines consist of only two nips. They have for instance two double-felted nips or one double-felted nip followed by a second nip with a felt and a transfer belt 

The newest development is a single nip press section where the web is dewatered in just one nip (Fig. 6.50). With a shoe of more than 300 mm length a dryness of about 52% is reached in woodfree paper production at more than 

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Head box Fourdrinier formation table Press section... 

Steindler, M. J. et al. "Fuel Cycle Programs Quarterly Progress Report, October-December 1982 " ANL-83-19, in press Section V. 

Fig. 34.4. Anderson Expeller Press, model 55 in.TDMS. Note elevated conditioner carrying product from left to right across top of press vertical screw first-stage press section (right side) higher pressure second-stage press screw section carrying product from right to left. Some hard presses have both stages on one shaft. (Courtesy of Anderson International Corp., Cleveland, OH.)...

Figure 13.19. A papemiachine (not to scale, the dryer section is mnch longer than the Fourdrinier and wet press section).

At the end of the Fourdrinier wire a couch roll removes more water from the web before it is transferred to the press section. At this point the moisture content of the web is about 80% water (20% consistency, 200g/L). The white water from the Fourdrinier is continuously recycled 1000 kg of stock at 0.5% consistency is reduced to a 25 kg mat (5 kg fibre, 20 kg water) by the time it leaves the wire and 975 kg of white water is recycled to the make-up chest and thence back to the headbox. A 500 tonne a day papermachine recycles some 100 000 m of water a day. 

On leaving the Fourdrinier, usually the web has to travel unsupported to the felts of the press section - a distance of a few centimetres. This unsupported transfer is called open draw and its success depends on the wet-web strength with the... 

High pressure agglomeration uses two fundamentally different principles confined volume compaction (Section 4.2.2.3) and roll pressing (Section 4.2.2.4). 

See size enlargement. Section 16.11.9.14. Related topics are size reduction (Section 16.11.8.5) and dewatering rotary press (Section 16.11.5.13). 

The most recent development is hot isostatic pressing (Section 6.7.2) in ivhich forming of the part(s) from dry particulate raw materials and heat treatment are combined in one piece of equipment [B.13a, B.97]. This technology is especially used for the manufacture of high-performance ceramics and of composites containing ceramic and other (e.g., metal) components. 

Microbiological deposits may be formed in many different places in the papermaking process. However, the closer to the wet-end the more detrimental the deposits will be for the papermaking process. Mio-obiological deposits may form on submerged surfaces as well as surfaces above the water line of the paper machine. In the latter case it is a requirement for slime formation that a surface is kept moist by splashes or aerosol formation. Examples of such surfaces are the frame of the wire section and the frame of the press section. 

Dewatering - improved wire section, press section and dryer section water removal... 

Extension of fibre with filler almost always results in reduced drying demands, as minerals do not absorb water compared to fibre. However, aggregated fillers with very high surface area and internal void volume may result in a wetter web going to the press section. Figure 6.18 shows a comparison between scalenohedral PCC and GCC filler in press solids. Discrete particles, like GCC, typically drain more quickly compared to similarly sized aggregated particles, like scalenohedral PCC. 

More surprising was that lost time for press section breaks more than doubled. The web is fully supported until the final press roll on this machine. There was a... 

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