It is known to use stationary surfaces which are perforated for supporting a sheet passing over the surface. A fluid is passed through the perforations to lift the sheet off the surface as it is being advanced to thereby eliminate a frictional contact with the surface. While this structure is useful in reducing frictional contact with guide surfaces, it offers nothing in the way of helping to advance the sheet or web along its path.
If a very long web is being advanced through a bath by a pulling force the web may be damaged by the tensile forces used to move the web through the bath. Also, some webs to be treated in a bath are very delicate, such that a tensile force applied at the end of the web to pull it through a bath will almost certainly damage the web. Thus, it would be desirable to have structure in the bath which would offer a frictionless support of the web and at the same time assist in moving the web through the bath. This is what applicant's structure achieves.