Patent GB-774764-A (GB)
Title: Silk-screen printing machine
IPC: B41F15/08
Filed: 1955-09-23
Abstract: 774,764. Stencilling-apparatus; feeding sheets. FRANK'SCHE EISENWERKE AKT.-GES. Sept. 23, 1955 [Sept. 24, 1954], No. 27223/55. Classes 100(1) and 100(2) A silk-screen printing machine comprises a screen frame and a printing table, both of which are pivotally mounted so that they can be brought into and out of a printing position in which they lie against each other. The screen frame 3, Fig. 1, is pivoted at 2, and moved downwards and upwards by a piston in a cylinder 35, Figs. 1 and 6. A doctor 10 is carried on a tube 7 reciprocated by pistons 6 in cylinders 5. The screen 11 is carried on a sub-frame 15 held by clamping rails 16, 17, the latter being adjustable for rise of format by a spindle 18. The tube 7 carries a cam 110 which in the rightward position opens a switch 111 to release a relay 102 and raise the screen, and closes a switch 112 to energize a relay 105 and reverse the doctor. The printing table 20 is pivoted at 29 to columns 21 adjustable in height according to the thickness of the material to be printed on by spindles 23 adjusted by a handoperated worm 24. The other end of the table is pivoted at 30 to a threaded spindle 26 adjustable in height by a hand-wheel 28. The column 27 containing the end of the spindle 26 is mounted on a support 31 connected at each end to a two-armed lever 33 pivoted at 32, the other arm of which is connected to a rod 34 connected to the screen frame, so that as the latter is lowered, the table is raised so that they come together. One end of the lever 33 actuates switches 38, 39, 40 when the table is in lower intermediate and upper positions respectively. Below the table 20 are also mounted front lay stops 48 actuated by a piston in a cylinder 50, and side lay stops 49 actuated by a piston in a cylinder 51. The angular position of the stops 48 when raised is adjustable according to the size of the sheets to be printed, and if only one stop 49 is needed, the rest can be rendered inoperative. Below the table is a, chamber 42 connectable to a source of compressed air or vacuum. The piston in the cylinder 51 actuates a switch 91. Pile tables. A pile of sheets rests on a table 60 connected to one end of each of four chains 58, having weights 59 at their other ends and passing over sprockets 57 on shafts 56, 56<SP>1</SP> mounted in a frame 55, the shafts being rotated intermittently to raise the pile by a ratchet mechanism 64 on a shaft 61, the ratchet being actuated by a rod 65 connected to the table 20. The top of the pile engages a feeler switch 67 operating a magnet 68 to engage or disengage the ratchet teeth and keep the height of the top of the pile constant. The sheets are placed on the table 60 between side plates and are urged by an adjustable end plate 73 against a plate 70 carried by columns 69 and adjustable vertically to be aligned with the edge of the table 20 by hand-operated spindles 71. The plate 70 carries a blower- 72 for separating the upper sheets. Sheet-separators. Secured to the table 20 so as to form an extension thereof is a frame 75 moving therewith and carrying a cylinder 76 in which slides a piston 77 connected to a transverse hollow tube having suction cups 78 spaced therealong to engage the top sheet, the hollow tube carrying hollow tubes 81 in which are slidable hollow tubes 81<SP>1</SP> connectible to a source of vacuum, stuffing boxes 82 preventing leakage of air. The cups 78 are thus reciprocated by the piston 77. A transverse feeler arm 84 rises on the top sheet to further its engagement by the suction cups. At the leftward end of the stroke, an opening 90 is exposed to release the sheet. On leftward movement of the suction cups, a control rail 110 actuates a switch 99 to open a valve 101 and operate the lay stop cylinders 50, 51, and to close a valve 120 and cut off the suction. Reverse movement of the cups is caused by compressed air through a valve 98 controlled by the switch 91. Electrical and pneumatic control system. A motor 44 drives a generator 47 for the electric control circuits, and also drives a compressor 43 which produces a vacuum in a vessel 45 controlled by a valve 85, and pressure (6 atmospheres), in a vessel 46, controlled by a valve 87, the air to the vessel 46 passing through an oil purifier 86. In the position shown in Fig. 6, regarded as the initial part of a machinecycle, the stops 48 are raised, but the stops 49 are not yet raised owing to a delay valve 89. A sheet 88, freed by the exposure of the opening 90, drops on to the stops 48, and the stops 49 being by then raised, the sheet is accurately located. Compressed air through valve 95 passes to the chamber 42 and through holes 41 in the table 20. The piston i ncylinder 51 operates the switch 91 to release a relay 92, thereby closing valve 95 to release the pressure in the chamber 42, opening valve 116 to producesuction in the chamber and hold the sheet on the table, closing valve 97 and opening valve 98 to reverse the movement of the sheet feeder. The switch 91 also energizes a relay 102 through the switch 38, whereupon valve 104 is closed and valve 119 opened, to lower the screen frame and to supply compressed air to the blower 72 through an adjustable hand valve 114. A holding circuit for the relay is established through switch 111. On downward movement of the screen frame, the switch 39 is inoperative, its circuit being interuppted at 103. On movement of the sheet feeder to the right, the switch 99 opens valve 120 and produces suction in the feeder, and closes valve 101 to lower the stops 48, 49 and releases the switch 91. At the lowest position of the screen frame, the switch 40 releases relay 105 to close valve 107 and open valve 108 and cause the doctor to move to the right. At the rightward end of the stroke of the doctor, the switch 111 releases the relay 102 to put the switch 39 in circuit, open valve 104 and close valve 119 to raise the screen frame, and the switch 112 energizes the relay 105, whereupon valve 107 is opened and valve 108 closed to reverse the doctor. During the upward movement of the screen frame, the switch 39 energizes relay 92 through a vacuum supervising device 115, and a holding circuit for the relay is established through the switch 91, whereupon valve 116 is closed and valve 95 opened to shut off the vacuum and admit compressed air to the chamber 42, so that the sheet is lifted off the table and slides on to a drying conveyer belt. The relay 92 also closes valve 98 and opens valve 97, so that the sheet feeder moves to the left. The switch 99- then closes valve 120 to cut off the suction to the sheet feeder, and opens valve 101 to operate cylinders 50, 51 and raise the stops 48, 49, thereby completing the cycle. For laying-on by direct copying with the screen frame and table 20 horizontal, a hand switch 118 is opened to inimobilize the doctor. If no sheet is seized by the cups 78, the vacuum supervisor device 115 brushes the circuit to the relay 92.