One prior art type of basic air cushion drum is known from DE-PS 1,561,043. The casing of this prior art drum is made of a porous material so that the air issues radially to atmosphere from a large number of pores uniformly distributed over drum length and forms on the drum periphery a thin air cushion inhibiting contact between the printed sheets and the drum and thus preventing ink set-off. As also disclosed, this known drum is double-walled and the between-walls cavity or space is divided by ribs into discrete chambers which extend parallel to the drum axis and which by means of control elements are supplied consecutively with air as the drum rotates. Although drums of this kind have proved satisfactory for air cushioning purposes, the noise caused by the airstreams is a serious disadvantage.
USPTO Backgrounds
USPTO Backgrounds