Suction rolls

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. 

Austenitic and duplex stainless steels are the major metallic materials of construction for white water service, particularly for the headbox, piping, and also for suction roll shells. Bronze, once widely used for forming wires and suction roll shells, is used less because of its inherently poor corrosion resistance in modern white water environments. Poor welding quality can undermine the corrosion resistance of stainless steels, especially if the thiosulfate and chloride levels are high. Corrosion under surface deposits including scales, pulp mats, or microbiological growths... 

Alloy development for suction roll shells has barely kept pace with the ever-increasing performance demands and white water corrosivity in paper machines. Bronze, martensitic stainless steels, early-generation duplex stainless steels, precipitation hardening stainless steels, and later-generation duplex stainless steels have all been used for the manufacture of suction roll shells. Today, the preferred materials for suction roll shells in severe service are duplex... 

Magar [32] evaluated inhibitors in white water by means of the linear polarization resistance technique in a search for effective inhibitors to prevent corrosion of bronze suction rolls. A galvanodynamic testing method was used by DeBerry and Ellis [33] in order to study inhibition of corrosion of a duplex stainless steel alloy. 

Significant research and testing has been devoted to corrosion fotigue resistance of paper machine suction roll shells [34]. Unfortunately, the results from the various tests used by the various manufacturers have been difficult to compare. Furthermore, their tests do not predict actual performance in the paper machines and cannot be related directly to roll loads or geometries. Experience gained over a long period of time has remained the best guide to selection of suction roU alloys. The tests used are summarized below. 

Jaske and Castillo [36] used RR Moore rotating beam fatigue machines to study several roll materials with simulated white water solutions dripped onto the test specimen surface. Castillo et al. [19] used rotating bending tests to evaluate the corrosion fatigue resistance of duplex stainless steel suction roll alloys. Yoshitake et al. [21] also used this method. 

Glogowski and Castillo [37] used the reverse plate bending test to evaluate cast bronze alloys in paper mill white waters. Rectangular bars with holes drilled to simulate those in suction rolls were tested in accordance with TAPPI Technical Information Paper 0402-08 with simulated white water containing thiosulfate wicked into the holes [33], This test is better than the rotating beam test as a simulation of the fatigue that occurs at suction roU holes, since it incorporates a drilled hole geometry. 

Yeske [40-42] investigated crack propagation in the corrosion fatigue of suction roll alloys using compact tension... 

Paper machine components other than suction rolls can experience corrosion fatigue cracking. Dorsch et al. [43] used a fuU size felt roll journal as a laboratory fatigue test specimen in simulated white waters containing thiosulfate ions. 

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. 

Danielsson, E. (1989), Evaluation of design criteria for the selection of suction rolls, 6th Int. Symp. Corrosion in the Pulp and Paper Industry, Vol. 6B, August 1989, Helsinki, Finland, 379-389. 

Moskal, M. D. (1990), Suction Roll Corrosion, in Metals Haruibook Corrosion, 3rd edition. Metals Park, Ohio American Society for Metals. 

After a web break (or at the machine start up) the web has to be threaded through the machine as fast as possible to reduce production downtime. This is done by feeding either the web at full width or just a tail , a web strip of about 20 cm, at the machine tender side which is then widened to the full machine width after completion of tail threading. The equipment for web or tail feeding includes air blowing nozzles, suction rolls, wires and felts, rope guides or vacuum-supported transfer belts. 

Suction rolls apply controlled vacuum at a certain angle to the roU circumference to dewater the web or for pick up and transfer (Section 6.2.2). 

Suction rolls, which have an open shell of different design. Vacuum is applied through the interior. They are used in sheet formation as suction breast rolls, suction formers, suction forming roUs, or suction rolls at the end of the wire section. Suction rolls accelerate drainage and increase the dry content in the web. 

The fourdrinier wire (Fig. 6.38A) is the classical method of sheet formation. Speeds up to about 1200 m min are achieved with the fourdrinier. This is a reasonable limit due to excessive turbulence on the free suspension surface and dewatering capacity. Normally, the fourdrinier is equipped with a forming board, foils and/or table rolls, suction boxes, wet suction boxes, and suction rolls. Drainage proceeds in the direction of gravity. A dandy roll is often used just in front of the water line to improve formation. This is a wire-covered open roll, with a honey-... 

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... 

Uses Boilout and wire cleaner for rapid cleaning of plastic wires, dandy rolls, suction rolls, paper machine systems, wet fells, and dryer felts, inci. food-contact paper prod. carbonate scale remover in paper slodc systems stain remover for syn. fabrics... 

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