Method and apparatus for the drying section of a paper machine

Abstract

The surfaces of cylinders or fabrics moving in the press or drying section of a paper machine induce layers of air along with them, which layers of air produce positive and negative pressures at the pits or nips defined by the fabrics or web and the surface of the cylinder. The positive and negative pressures are detrimental to the mutual support contact between the web and the fabric. A method for eliminating the detrimental positive and negative pressures affects the pressure levels at the nips by blowing air in directions opposite to the direction of travel of the web or fabric passing close to a blowing device, and possibly also opposite to the direction of travel of the cylinder surface. As a result of the blowing of air, air is ejected from the pressurized nips or from spaces placed facing the nips of negative pressure on the opposite side of the running of the web and the fabric. Apparatus for carrying out the method includes a blow box placed in connection with the nip. The blow box is connected to devices producing pressurized air and is provided with one or several nozzle slots. A nozzle slot has a curved nozzle surface at an angle of curvature of about 30.degree. to 70.degree.. The direction of the jets of air blown out of the nozzle slots is turned via the nozzle surface due to the Coanda effect. A planar surface follows the curved nozzle surface and functions as a carrying surface stabilizing the web or fabric.

Dependencies are inferred from the claim text.