Patent GB-779577-A (GB)
Title: Improvements in or relating to silk screen stencilling machines
IPC: B41F15/08
Filed: 1956-02-23
Abstract: 779,577. Stencilling-apparatus. BLACK J. A. Feb. 23, 1956 [Feb. 24, 1955], No. 5617/56. Class 100(2) A silk-screen stencilling-machine includes a drum element and a rail element mounted on a frame in juxtaposition and providing for flat stock a supporting surface in a plane tangential to the drum element and coincident with the flat surface of the rail element, means on one of said elements for effecting adherence of flat stock thereto, means for moving said element and the stock carried thereby progressively past the continuous supporting line of tangency, a silk screen stencil mounted adjacent said flat stock for coordinated movement therewith, and means adjacent the stencil for forcing coating material through said stencil on to said stock directly opposite the stock from said tangential line of support. The stencil 46, Fig. 13, is mounted on a stencil frame 47, Figs. 2 and 13, secured by pairs of bars 49, 51 to the transverse bars 42, 43 of a stencil carriage 35 comprising pairs of bearing blocks 38, 39 slidable on guide rods 34. The bars 42, 43 are connected by rack bars 45; whose teeth are driven by gears 76 on opposite ends of the main shaft 75 of the machine, to reciprocate the stencil. The oscillating movement of the shaft 75 is produced by an electric motor 56 through a gear reducer 62, crank arm 64, sector 66 and gear train. The squeegee assembly 105, Figs. 2, 12 and 13, is mounted on inverted U-shaped supports 106, 107 guided for vertical movement by studs 108, 109, and is lowered on to the stencil during the rightward printing stroke of the latter and raised clear of the stencil during the non-printing screen stroke thereof by cams 125 of a camshaft 120 driven from the gear reducer by a chain 121. Flat stock articles 78 (e.g. sheet metal, glass, plywood or composition board) are fed by a series of laterally placed conveyer tapes 154 continuously driven from the shaft 120 through chain drives to the position shown in Fig. 13, where they are assisted by a stationary stop 188. A series of laterally spaced rails 79 for supporting an article during printing are connected at their opposite ends by bars 88, 89 secured to ports 84, 85 vertically slidable in slide bearing members 80, 81 at the four corners of the stencil carriage 35, so that the rails 79 reciprocate with the stencil. The rails are supported on rollers 90 set in laterally spaced tracks 91 mounted on posts 92 slidable in bearings 93 on a pair of fixed bars 94. The outer rails 79 carry depending control assemblies 101 having spring-cushioned buttons 100, 103. Pivotally mounted on the bars 94 are a plurality of levers 95 carrying rollers 96 supporting the track assembly. The levers 95 are connected at their upper ends by actuation bars 98 carrying stops 102, 104. On completion of the return stroke of the stencil, the buttons 103 strike the stops 104 to move the bars 98 to the left and swing the levers 95 to the vertical position, whereupon the rollers 96 raise the tracks 91 and the rails 79, which lift the article off the tapes 154 and support it in contact with the stencil during the printing stroke. At the end of the printing stroke, the buttons 100 strike the stops 102 to lower the track assembly, and the article is lowered on to take-off conveyer tapes 171 continuously driven from the shaft 120. Between the rails 79, drum elements 153 are mounted on the shaft 75 for oscillating movement therewith, so as to provide a continuous line of support to the article to be printed at printing position. A roller 189 is carried on an arm 190 pivoted at 191 to a bar secured to the stencil carriage. The arm 190 has a camming surface which during the return stroke engages a stationary roller, whereupon the roller 189 engages the edge of the article to move it into correct lateral position. Pins 198 on the track assembly engage slots 197 in latches 196 pivoted to the machine frame, so as to prevent lowering of the tracks during the printing stroke, at the end of which rollers 199<SP>1</SP> on brackets 200 depending from the stencil carriage engage the latches to release the pins. The raising of the track assembly is assisted by a lever 201 pivoted at 202 and urged counter-clockwise by a spring 203, the upper end of the lever engaging a cam plate 204 on the track assembly at the end of the return stroke to urge the assembly upwards. The stencil can be adjusted according to the thickness of the articles by inserting shims between the stencil frame 47 and the bars 49, 51 or between the bars and the stencil carriage 35. Suction is applied during the printing stroke to holes in the rails 79 to hold the articles thereon by means of twin motors 127, suction pumps 130, conduits 131, vacuum tanks 132, conduits 133, valves 134, tubular columns 135, flexible conduits 136, vacuum cylinders 137, and hollow pistons 139. The cylinders 137 are suspended from the track assembly for vertical movement therewith, and the pistons 139 are slidable in the cylinders and are connected to the rails 79. The valves 134 are controlled by cams 152 on the shaft 120, so as to open the valves during the printing stroke.