GB683800A - Improvements in and relating to screen or stencil printing machines - Google Patents

Abstract

683,800. Stencilling-apparatus. GROAK, J. April 25, 1950 [Jan. 25, 1949], No. 2067/49. Class 100 (ii). In a screen or stencil printing machine comprising a hollow work table 18 and a movable support 43 for a screen, stencil or mask, the work table 18 has a work-receiving surface 19 provided with a large number of distributed slit apertures 20, and means, including a valve, is provided for reducing the pressure within the table to hold the material thereon by suction, the valve being arranged to operate in such a way that the suction can be reduced to zero substantially instantaneously, whereby a back pressure surge is induced in the interior of the work table. The slits 20 are about 2 inches long and 1/64 inches or less in width. The interior of the table is connected through a short tube 24 (Fig. 6) and a flexible conduit 23 with an exhaust fan 22. The valve referred to above is between the tube 24 and conduit 23 and comprises an apertured plate 26 fixed to the conduit 23 and pivotally attached at 27 (Fig. 4) to a similarly shaped apertured plate 25 fixed to the tube 24. When in the position shown in Fig. 6 the apertures in the two plates are in register and the fan communicates with the interior of the hollow table. The plate 26 is connected by a bar 34 to a foot pedal 39 pivoted at one end and by depressing the foot pedal against the action of a spring 36 the vacuum within the table may be suddenly reduced to zero. The resulting inrush of air positively disengages the printed material from the table, and with this arrangement the slits 20 are self-cleaning. The value of the maximum suction can be controlled by the amount of overlap between circumferential slots 38 and 40 in the tube 24 and a rotatable sleeve 39 mounted thereon, respectively (Fig. 6). The screen frame support 43 is pivoted at one end on a rod 54 carried by cranks 52, 53 which are adjustable vertically to vary the height of the screen to suit the thickness of the material being printed on. This adjustment is provided by pivotally attaching the cranks 52, 53 at their ends 58, 59 to the machine frame. Threaded rods 62, 63 (not shown) passing through vertical slots in the cranks 56 are received in tapped holes in downwardly extending members (as 61). Handwheels 65, 66 enable the rods 62, 63 to be screwed inwardly to hold the cranks 52, 53 in a desired position. The screen frame support 43 is biased away from the printing position by means of springs 67, 68 but held in printing position by a quick-release catch 71.