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Air-flotation ovens are widely used for noncontact support and drying of coated paper and plastic films (generically called webs). The main components in typical air-flotation ovens are air bars which have slot nozzles or holes through which hot air jets are ejected. Problems in air-flotation drying techniques include sideward motion of the web, web flutter, and contact between the web and air bars. The key to analyzing these problems is to determine the aerodynamic forces on the web. This paper discusses the aerodynamic forces generated by pressure-pad-type air bars, each of which has two slot nozzles. Ground-effect theories, which were originally developed for the design of hovercraft, are re-examined. The theories are compared with the measured values of the aerodynamic forces for typical air bars. It is shown that ground effect theories can be applied to pressure-pad-type air bars if we properly define the equivalent values of the ground effect variables, which include thickness of the air jet, flotation height, ejection angle of the air jet, and the effective total pressure of the air jet. [S0021-8936(00)02801-4]

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A long web span supported by many, regularly spaced, alternating air-bars is studied. The focus is on the lateral forces on the web due to the interaction of lateral curvature with out-of-plane deflections. The effect of stretching of the elastic web material is included, and the effect of high web speed is handled by distinguishing between the tension in the material Tmat and the apparent tension Tapp=Tmat−μv2. The governing partial differential equations for a continuous representation of the web’s lateral deflection, stability, and control is developed for both straight and cambered webs. The dimensionless parameters for web-tension effect, web-camber effect, and stretching effect are identified. The influence of tilted air-bars is studied, towards developing a control mechanism to compensate for camber.