Step air foil particularly for one-sided flotation of a running web, and web dryer incorporating the same. The air foil includes two discharge slots which allow for increased draw down force, which flattens machine direction wrinkles in a floating web. The air foil includes a primary discharge slot and a second discharge slot spaced from and stepped down from the primary discharge slot, a first web support surface between the primary discharge slot and the secondary discharge slot, and a second web support surface downstream of the secondary discharge slot in the direction of web travel. The air foil is in communication with an air supply which provides a supply of air that is uniformly distributed to the primary and secondary slots. Air discharged from the primary slot is gathered into the air stream of the secondary slot and creates an increased air cushion to provide greater support to the moving web and thereby remove machine direction web wrinkles caused by higher tension in light weight webs.
1. An air foil for floating a web of material, comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein said secondary discharge slot discharges air parallel to the web.
2. An air foil for floating a web of material, comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein air discharged from said primary discharge slot is gathered into the air stream of said secondary discharge slot in a direction parallel to the web transport direction.
3. An air foil for floating a web of material, comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein said second web support surface comprises a wing portion that slopes downwardly as it extends away from said secondary discharge slot.
4. The air foil of claim 1 , 2 or 3 , further comprising a diffuser for uniformly distributing air to said primary discharge slot and to said secondary discharge slot.
5. The air foil of claim 1 , 2 or 3 , wherein said second web surface is an elongated wing having a series of bends.
6. The air foil of claim 5 , wherein said elongated wing terminates in a downwardly extending flange.
7. the air foil of claim 5 , wherein one of said bends is at an angle of 30°.
8. A web dryer, comprising a web inlet and a web outlet spaced from said web inlet, a plurality of air discharge nozzles in said dryer for drying said web, and at least one air foil in said dryer, said air foil comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein said secondary discharge slot discharges air parallel to the web.
9. A web dryer, comprising a web inlet and a web outlet spaced from said web inlet, a plurality of air discharge nozzles in said dryer for drying said web, and at least one air foil in said dryer, said air foil comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, ana a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein there are a plurality of air foils in said dryer, all positioned on the same side of said web.
10. An air foil for floating a web of material, comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, a first web support surface between said primary discharge slot and said secondary discharge slot, a second web support surface downstream of said secondary discharge slot in the direction of web travel, said second web support surface comprising a bent plate, wherein said secondary discharge slot is defined by said first web support surface and said bent plate, wherein air discharged from said primary discharge slot is gathered into the air stream of said secondary discharge slot in a direction parallel to the web transport direction.
11. the air foil of claim 10 , wherein said bent plate comprises a plurality of apertures to allow air flow to said secondary discharge slot.
12. The air foil of claim 10 , wherein said secondary discharge slot discharges air parallel to the web.
13. A web dryer, comprising a web inlet and a web outlet spaced from said web inlet, a plurality of air discharge nozzles in said dryer for drying said web, and at least one air foil in said dryer, said air foil comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein air discharged from said primary discharge slot is gathered into the air stream of said secondary discharge slot in a direction parallel to the web transport direction.
14. A web dryer, comprising a web inlet and a web outlet spaced from said web inlet, a plurality of air discharge nozzles in said dryer for drying said web, and at least one air foil in said dryer, said air foil comprising a primary discharge slot and a secondary discharge slot spaced from and stepped down from said primary discharge slot, said secondary discharge slot being downstream of said primary discharge slot in the direction of web travel, a first flat web support surface between said primary discharge slot and said secondary discharge slot, and a second web support surface downstream of said secondary discharge slot in the direction of web travel, wherein said second web support surface comprises a wing portion that slopes downwardly as it extends away from said secondary discharge slot.