Abstract: Air knife designed to be used in coating machines or equivalent to finish and smooth the coating by blowing air onto it, e.g. to remove excess coating material, said air knife comprising a main channel into which the air is blown in the axial direction of the channel at least from one direction, the main channel being so constructed that there are two air jets flowing in opposite directions and having equal and constant velocities over the whole length. Thus the air jets discharged from slits next to a partition between the two main channel sections, after being merged, flow in a direction perpendicular to the slit and the air flow is evenly distributed over the whole length of the slit. By using a construction in which the partition is movable, the location of the point at which the two jets mix can be varied, thus allowing the turbulence of the air jet blown at the web to be controlled and, consequently, an influence to be exerted on the properties of the coating surface.

Abstract: A method and an apparatus for reducing moisture differentials of a moving web, for instance, a paper web, containing longitudinal wet streaks, by applying high-frequency electromagnetic energy to bar-formed electrodes, which are located close to the surface of the web. In accordance with the invention, the longitudinal axes of the electrodes are aligned approximately parallel to the machine direction of the web and the electrodes are located over each wet streak of the web. The apparatus in accordance with the invention comprises a beam extending in the cross direction essentially over the web, with each electrode fitted to the beam so as to align the longitudinal axis of the electrode in the home position approximately parallel to the machine direction of the web and provided with a means of transferring each electrode in the aforementioned cross direction onto an assigned wet streak in the web. The invention provides an economical and effective solution for reducing moisture differentials in the web.

Abstract: A method for providing in a web of sheet material, particularly a paper web, a predetermined moisture content which is uniform throughout the web. The web which has been dried so as to be within the hygroscopic range is directed through an enclosure which is closed off from the outer atmosphere while lapping in the enclosure a perfusion roll having a foraminous wall through which a treating gas, such as air of a given humidity or steam with predetermined properties, can pass into the interior of the roll after first passing through the web which laps the roll. By way of a suitable gas-circulating structure, the treating gas is circulated so as to travel out of the interior of the perfusion roll along a given path back to the web at the exterior of the perfusion roll to pass again through the web and into the perfusion roll, this gas-circulating structure providing the treating gas with predetermined properties for achieving in the web a desired moisture content which is uniform throughout the web.

Abstract: A method and apparatus for providing in a web of sheet material, particularly a paper web, a predetermined moisture content which is uniform throughout the web. The web which has been dried so as to be within the hygroscopic range is directed through an enclosure which is closed off from the outer atmosphere while lapping in the enclosure a perfusion roll having a foraminous wall through which a treating gas, such as air of a given humidity or steam with predetermind properties, can pass into the interior of the roll after first passing through the web which laps the roll.