Patent GB-625108-A (GB)
Title: Improvements in and relating to screen printing apparatus
IPC: B41F15/42
Filed: 1946-04-29
Abstract: 625,108. Stencilling-apparatus. WALKER, D., and EVANS & CO., Ltd., D. April 29, 1946, Nos. 12884/46 and 10147/47. [Class 100 (ii)] A squeegee is mounted in a holder supported by guides on a cross - head adapted to reciprocate along parallel guides, the holder is movable in the guides towards and from a stencil and can turn wholly or in part and with or independently of the guides about an axis parallel to the operative edge of the squeegee, spring means acting on the holder provides a resilient pressure of the squeegee on the stencil, stops arrest the turning movement of the holder at angles such that the squeegee will overhang the stencil in the direction of cross-head travel, and mechanism is provided for moving the holder away from the stencil near the limit of travel of the crosshead along its guides. In the form shown in Figs. 2 and 6a, a screen A is attached to a frame B fixed to a steel, aluminium, &c. carriage E comprising L-section side bars 3 bolted to channel-section front and rear bars 1, 2; the frame B is adjustable relatively to the carriage by means of screws 43 at one end and a clamp 46 at the other. A squeegee blade 24 is detachably secured to a bar 23 slidable between guides 21 fixed to a bar 16 pivoted to plates 14 secured to channels 13 slidable in channels 5 fixed to the side bars 3, the channels 13 being filled with lubricant. The blade is pressed downwardly by a spring 25, the pressure of which can be adjusted by turning a screw 27. Longitudinal movement of the blade is prevented by pins on the bar 23 engaging slots in plates attached to the bars 16; the arrangement allows a blade to adjust itself to irregularities in the work. The squeegee is operated by means of a handle 33 pivoted to the slotted plates, and the rocking movement of the squeegee is limited by stop-screws 18. To wards the end of each stroke, pins 36 projecting from the bar 23 ride up ramps 8 and drop down on to the stencil behind the paint &c. On the return stroke, the pins rock the ramps about pivots 9 and ride under the ramps. Stops 58 arrest the squeegee at each end of the stroke while the operator turns the squeegee to an angle on the other side of the vertical. If the squeegee is set vertically, the pins 36 turn cams 59 which lower the stops 58 and allow the squeegee-slides to pass beyond the stops. The carriage E is movable to different positions along the table and for this purpose carries V-shaped rollers 50 riding on a rail 51, the carriage being lifted about a hinge or about the rail prior to movement. A spring-pressed plunger 53 carried by the bar 2 engages a notched plate 52 at each position; the plunger is operated by a Bowden cable 56. The members 13 may be replaced by rollers mounted on the plates 14, and the bar 2 may be bolted to the bars 3 at several positions to vary the effective length of the carriage E. In a modified construction, a squeegee blade 24a, Figs. 9 and 10, is carried by a bar 16a pivoted to slides 13a engaging guides 5a and retained in normal position by clips 65 movable inwardly to free the bar which can then be turned into positions for exchanging the squeegee. The blade 24a is attached by a keyhole slot arrangement to a rod 74 seated in the loop 97 of a U-shaped member 9S movable vertically in guides 99 fixed to the bar 16a. Levers 82 pivoted at 85 to the bar 16a rest on half bearings 72 which slide vertically between brackets 70 depending from the bar 16a and engage the rod 74, the inner ends of the levers 82 being connected to a block 88 carrying a screw 92 on which is a nut 96, a spring 95 between the bar 16a and the nut pressing the inner ends of the levers upwardly to apply downward pressure to the outer ends whereby the squeegee is pressed resiliently on to the stencil. The blade 24a can rock to an extent determined by telescopic members comprising rods 103 connected to the member 98 and tubes 104 connected to a bar 107 fixed to the rod 74. Towards the end of each stroke of the squeegee, an eccentric pin 111 on each end of the rod 74 runs up an incline 10a, Fig. 11, on a ramp 8a, whereby the blade is turned so that by the time the pin rides over a curved surface 63 the blade slopes in the opposite direction ready for the return stroke during which the pin rides under the ramp and lifts it about a pivot 9a against the action of a spring 61. The stencil is stretched in a frame B, Figs. 18 and 20, attached at one end to a cross-member 2a of a carriage by clips, one of which comprises a plate 144 pivoted at 143 to the frame B and connected by a bolt 150 engaging a slot 149 in the plate 144 and carrying a bolt 145, a nut 146 on which engages a slot 142 in the member 2a, this arrangement allowing a lateral pivotal -adjustment of the stencil frame B within the carriage; a second clip is similar but is not pivoted. At the other end of the frame there is a central clamp comprising a pad 156 on an arm 155 pivoted at 154 to a bracket 152 and carrying a screw 157 engaging an extension of the bracket, the latter being pivoted at 153 to a cross-member 1a of the carriage and pressed clockwise by a pin 158 on a spring 159. To adjust the frame B longitudinally, lock-nuts 146, 147 and the screw 157 are slackened, the stencil is moved to a new position and the nuts and screws are tightened up. A spring 161 forces the adjacent end of the frame up to the carriage, and a slight upward movement of the clamp H has the same effect at the other end.