GB957533A - Improvements in or relating to lithographic printing machines - Google Patents

Abstract

957,533. Printing apparatus. METAL BOX CO. Ltd. Aug. 17, 1962 [Nov. 30, 1961], No. 42947/61. Heading B6C. A lithographic plate on the printing cylinder 37, Fig. 2, of a rotary machine is dampened by wetting liquid exuding from the absorbent cover 35 of a rotating hollow damping cylinder 1 which has a porous peripheral wall and is mounted on a partially hollow rotating shaft 3, Fig. 1, to which the wetting liquid is supplied from a reservoir 12 through a feed line 13. Liquid issuing from the axial bore 7 of the shaft 3 is distributed throughout the interior of the cylinder 1 by a perforated tube 9 axially coincident with the shaft. The reservoir 12 comprises compartments 14 and 15, the former containing the wetting liquid and having a stoppered and filtered liquid filling opening 17, whilst the latter is associated with a spring- loaded air-pressure control valve 26. The liquid from the compartment 14 is forced into the cylinder 1, and from thence through the peripheral wall and the covering, by increasing the air pressure in the reservoir through pumping air into the compartment 15 from a pump 25 via a reducing valve 28, feed line 27 and a two-way and " off " valve 34. The liquid may be withdrawn from the plate and cylinder by a suction pump 30 which is connected to the compartment 15 through a reducing valve 32, a feed line 31 and the valve 34. These suction means may be used to control the rate of liquid flow from the cylinder 1 on to the printing plate, appropriate actuation of the valve 34 cutting off the air supply from the pump 25 whilst connecting the compartment 15 to the pump 30. By manually holding the valve 26 in a closed position the air pressure in the reservoir may be rapidly built up when the apparatus is started. If the compartment 11 is filled with a cleaning liquid the printing plate and the cylinder 1 and its wall and covering may be cleaned, the pump 25 being used to apply the liquid throughout the apparatus to the plate whilst the pump 30 is used to withdraw the contaminated liquid. Alternatively, the compartment 15 may be emptied, the plate and cylinder being cleaned by placing a tray of water under the cylinder 37 and then applying subatmospheric pressure to the reservoir through the pump 30. The liquid flow rate to the cylinder 1 is controlled by the reducing valve 28 usually within the range 0-5 lb. per square inch. The peripheral wall of the cylinder may be of porous ceramic material, carborundum or a polyvinyl copolymer. In use, excess liquid and/or ink is removed from the cylinder 1 by a scavenger roller 38 and the liquid may be indirectly applied to the plates on the printing cylinder, one or more fabric-covered dampener rollers being placed between the latter and the cylinder 1.