GB890943A - Improvements connected with rotary photogravure printing apparatus - Google Patents

Abstract

890,943. Printing machines. HALLEY & SONS Ltd., JAMES. July 4, 1958 [July 6, 1957], No. 21467/57. Class 100(2) In a rotary photogravure printing apparatus comprising a printing cylinder supported in a pivotally mounted cradle which can be rocked by fluid-operated ram means to determine the printing pressure, the ram means comprises at least two rams which exert relatively light and heavy printing pressures when energized by the same relatively high pressure of a fluid supply line, and valve means for selectively energizing the rams to produce the light or heavy printing pressure. The machine is of the type described in Specification 586,986, the rectangular cylinder-supporting cradle being pivoted at two corners and having each of its free corners supported by a pair of pneumatic rams. Each pair of rams comprises concentric hollow cylinders 12, 13 disposed between end closure plates 14, 15 and in which pistons 10, 11 respectively are slidable. The pistons 10, 11 are fastened together by bolts 16 and a connecting rod 21, having a ball and socket type mounting in the piston 10, connects them to the cradle. A high pressure air supply line is connected through a manually controlled changeover valve and branch air lines to chambers 17, 18 beneath the pistons 10, 11. One branch line is permanently connected to the chamber 17 through a port 19 and a low pressure thrust is thus transmitted to the cradle by the piston 10. If air is also fed into the chamber 18 through a port 20 the pressure on the cradle is increased owing to the fact that the combined pistons 10, 11 offer a greater cross-sectional area to the pressurized air than does the piston 10 alone. The pressure of air in the supply line is regulated by a pressure reducing valve and is registered by a gauge which may have a low range and a high range scale to indicate the thrust imparted to the cradle in either position of the changeover valve. In a modification a pair of separate rams supports each side of the cradle, the piston of that ram of each pair which is furthest away from the cradle pivot being of greater cross-sectional area than that of the other ram. High pressure is exerted on the cradle when the large pistoned ram of each pair is connected to the supply of pressurised air and low pressure when the other ram is so connected. In a further modification a pair of oppositely acting rams is connected to the cradle at each of its two free corners, the upward thrusting rams having larger pistons than the downward thrusting rams. A high pressure on the cradle is obtained when only the upward thrusting rams are connected to the air supply and a low pressure when both upward and downward thrusting rams are operated.