Suction Press Roll

This type of roll is an open press roll vdth vacuum application at part of the circumference. The vacuum removes the air between the web and the felt ahead of the press nip and holds the web on the felt. It enables the water squeezed out in the press nip to flow from the web and felt to the roll void volume where it is stored and released after leaving the vacuum zone. 

Shell thickness and open area define the amount of air to be removed constantly during vacuum build up which affects the amount of energy consumption. Hole diameters (about 4 mm, open area about 15 to 30%) in the metal shell are larger than those in the cover (about 2.5 to 4 mm, open area about 10 to 20%). The holes in the cover are drilled after the coating has been applied. The coating holes have to match the pattern in the shell which is easier -with smaller hole diameters in the coating. 

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With vacuum application and line load as suction press rolls in press rrips. 

Fig. 6.6 Multilayer design for suction press roll cover (source Voith).

As the machine speed has continuously has increased the dynamic forces to the web have increased and it has forced to support the web with felts to avoid web breaks. Before 30 s typically the web had open draw between press and wire section which was soon replaced with pick-up suction roll arrangement. In this arrangement web is picked up with a suction roll from wire and supported by press felt to the first nip. Most recent fast paper machines are using the same principle of suction roll and supporting fabric not only through press but also through dryer section. 

A briquetting plant (Figure 17.1) typically consists of the mixer-dryer with drive, the fan, and the gas ducts. From the mixing chamber, flue gas at 300°C-500°C (570°F-930°F) passes through the coal-binder mixture, suction being provided by the fan. After cooling, the material enters the roll presses from the mixer-dryer. 

Wensley, D. A. and Moskal, M. D., Paper Machine and Suction Roll Corrosion, Chapter XXIH of Pulp and Paper Manufacture, Vol. 7, Paper Machine Operation, TAPPI Press, Atlanta, 1991, pp. 594-614. 

In the press section the individual rolls are hard or soft covered. The press nip (Fig. 6.7) is created either by two profiled rolls or by a combination of one profiled and one plain roll. Covers with high open surface area, similar to tyre technology, offer the necessary storage capacity for the water squeezed out in the press nip. The various surface designs include grooves, blind drilled holes or suction holes as well as combinations of these. 

Polyurethane roll covers were introduced to the paper industry at the end of the 1980s. The outstanding mechanical and dynamical properties make polyurethane the most suitable material for soft elastomeric covers in press positions. Depending on paper quahty and press design, high open surfaces up to 45 % with grooves, blind drilled holes or suction holes, as well as combinations thereof are used. An example of surface design is shown in Fig. 5.11. 

The state-of-the-art dryer section for a high-speed paper machine has a singletier configuration with steam heated cylinders in the top row and suction rolls in the bottom row. The paper web is always supported by the dryer fabric and runs jointly around the drying cyHnders and suction roUs (Fig. 6.55). In the top row the paper web is pressed against the drying cyHnders by the dryer fabric. In the bottom... 

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