AIR SEAL DEVICE FOR A SPRAY APPARATUS IN A PAPERMAKING MACHINE
A non-contacting air seal device is provided in order to reduce or minimize the ingress of external air into a fluid spray apparatus for applying a fluid coating to a moving web in a papermaking machine. The air seal device includes two air seal assemblies located in tandem with convexly curved web facing surfaces arranged offset in a direction of travel of the web and in opposing relation to one another to define an S-shaped sinusoidal path along which the web travels as it passes through the seal device and wraps a portion of each of the convexly curved web facing surface as it either enters into or exits from the fluid spray apparatus. Each air seal assembly includes a roll, a rod, or a shoe that forms the convexly curved surface over which the web passes in a non-contacting manner on an air cushion which also minimizes ingress of both ambient and boundary layer air external to the fluid spray apparatus.
1 . A non-contacting air seal device for at least one of an entry or an exit in a spray apparatus for applying a fluid coating to a moving web in a web forming process, the sealing device comprising:
a. first and second air seal assemblies each including a convexly curved web facing surfaces over which the web passes;
b. he convexly curved web facing surfaces arranged offset in a direction of travel of the web and in opposing relation to one another define an S-shaped sinusoidal path along which the web travels as it passes through the seal device and wraps a portion of each of the convexly curved web facing surface;
c. an air cushion is provided at each of the convexly curved web facing surfaces, the air cushion being adapted to support the web; and
d. the air seal assemblies comprising one of: a perforated or slotted stationary pipe, a slotted stationary shoe, or a rotating roll, that include the convexly curved web facing surfaces.
2 . The device according to claim 1 , further comprising a pressurized air source connected to the first and second air seal assemblies that forms the air cushion.
3 . The device according to claim 2 , wherein the first and second air seal assemblies comprise the perforated or slotted stationary pipe or the slotted stationary shoe, and each include a series of nozzles, perforations or discontinuous slots arranged linearly parallel to a longitudinal axis of the respective first and second air seal assemblies.
4 . The device according to claim 2 , wherein each of the first and second air seal assemblies includes a porous material located in a linearly oriented slot.
5 . The device according to claim 1 , wherein the air seal assemblies comprise the rotating roll that is driven by a drive and entrains a layer of boundary air to form the air cushion.
6 . The device according to claim 1 , further comprising adjustable supports that mount the first and second air seal assemblies to the spray apparatus, the adjustable supports providing at least one of vertical, horizontal, and rotational positioning of the first and second air seal assemblies.
7 . The device according to claim 6 , wherein the adjustable supports are positionable to form a bowed orientation of the first and second air seal assemblies.
8 . The device according to claim 1 , wherein a angle of wrap of the web about a surface is from 0° to 25°; preferably 5° to 15°.
9 . The device according to claim 1 , wherein the air cushion provides to the web a pressure P=T/R±25% where T is a web tension and R is a radius of the curved surface.
10 . The device according to claim 9 , wherein P≧T/R .