GB1008668A - Method and apparatus for dewatering paper machinewet felts - Google Patents

Abstract

1,008,668. Drying felts in paper-making machines. HUYCK CORPORATION. March 3, 1964 [March 18,1963], No. 8891/64. Heading D2A. A method of dewatering a wet press felt comprises blowing air at substantial pressure through the felt so as to force the water therefrom. Water is transferred from the web of paper 10 to a felt 11 on passage of the felt and web through the nip of press rolls 12, 13 and is removed from the felt by air supplied at a substantial superatmospheric pressure to the surface of the felt by cylinders 16, 23. The air is supplied to the felt at a pressure between 4 and 100 lbs. per square inch and preferably between 4 and 20 lbs.per square inch and for a sufficient period to reduce the moisture content of the felt to between 10% and 40% of the weight of the wet felt. The felt 11 may be supported in its passage over the openings 16b, 23b in the cylinders 16, 23 by porous supporting fabric or wire belts 25, 26 and bars or rollers 17, 18, 23d, 23c urge the supporting belts and felt into contact with the respective cylinders to ensure a satisfactory seal. In addition the supporting belts may serve to compress the felt in the region of the air supply to improve the removal of water. The degree of compression of the felt is preferably between 30% and 50% of its normal thickness. The belt 26 may be arranged to pass with the felt through the nip of press rolls 12, 13. The latter may be plain rolls or the lower may be a suction roll. In an alternative arrangement (Figs. 2, 2a not shown) an air supply hood is arranged to cover a portion of the surface of the felt and transverse partitioning elements in the hood make sliding contact with the surface of the felt. The edges of the hood are sealed by bars of low friction material in sliding contact with the surface of the felt or supporting belts or by belts which make contact with the felt or supporting belts and travel therewith (Figs. 2-9 not shown). The felt may be sandwiched between two moving belts of supporting fabric (Fig. 10 not shown) this arrangement facilitating the compression of the felt which is desirable for effective water removal. The supporting belt may itself be subjected to a separate drying treatment by blowing air through it, or by other, conventional, methods. In an alternative embodiment (Fig. 11 not shown) the felt travels around a major proportion of a rotating perforated cylinder or roll to the interior of which compressed air is supplied, the air passing outwardly through the felt to carry water into a surrounding casing from which the air and water are then removed. In yet another embodiment (Fig. 13 not shown) the felt passes to the interior of a pressurised rectangular casing and travels around a succession of perforated rolls mounted in the casing, the compressed air passing through the felt and through the perforations into the interior of the rolls and thence through hollow shafts on which the rolls are mounted. In a still further embodiment (Fig. 15 not shown) the felt passes through the nip of a pair of perforated press rolls having respectively internal air supply and suction boxes which serve to force air through the felt in the region of the nip. The spacing of the rolls may be adjustable to accommodate varying thicknesses of felt and the air supply box may be arranged to supply air only in the region from the beginning of compression of the felt to the line of maximum compression. Details are given of the results of drying tests using compressed air on a variety of conventional paper machine felts.