Patent GB-673895-A (GB)
Title: Stencilling machine
IPC: B41F15/08
Filed: 1949-06-29
Abstract: 673,895. Stencilling apparatus. FORDYCE, R. G. June 29, 1949, No. 17260/49. Class 100 (ii). [Also in Group XXVIII] Stencilling apparatus comprises a screen, paint spreading and forcing means on one side thereof, and work carrier means on the other .side thereof, means for causing the paint spreading and forcing means, the screen, and the work carrier means to assume two separate fixed relative positions, 'and means for moving the paint spreading and forcing means over the screen, to effect a complete sweep thereof, at each of the fixed positions, so that paint is spread on to the screen when the parts are in one of the positions, and forced through the screen on to the work when the parts are in the other of the positions. General organisation.-In a machine for stencilling luminous indicia on watch, clock or other dials, there is provided a stencil screen 52, Fig. 1, a rotatable squeegee 56, and a turntable 36, Figs. 1 and 3, carrying three work-holders 38. The machine is driven by a <SP>1</SP>/ 3  H.P. electric motor 30 which drives a main shaft 32, Figs. 1, 2 and 3, through a one-revolution clutch 34. The machine comprises a lower unit, Fig. 1, containing the motor 30, shaft 32, and work-holder mechanism, and an upper unit, Fig. 2, containing the mechanism for operating the squeegee and dispensing the luminous paint, and contained in a housing 48, the upper unit being tiltable rearwardly on the lower unit to allow access to the interior. The mechanism in the upper unit is driven by an upper drive shaft 60 coupled to the shaft 32 by a universal joint so as to be rotatable in all positions of the upper unit. Blank work 164 is placed on a holder 38 at a loading station 40, the turntable rotated 120 degrees to bring the holder to stencilling station 42, while finished work is removed at unloading station 44. The squeegee is rotated 180. degrees in a position out of contact with the screen, to spread paint over the screen. The holder 38 at station 42 is then raised while the squeegee is lowered so that the work 164 and squeegee are in contact with the screen, and the squeegee again rotates through 180 degrees to force the paint through the screen on to the work, the holder and squeegee then moving away from the screen. Driving mechanism.-The motor 30 drives the shaft 32 through a variable pitch diameter pulley 78, a V-belt 76, a speed reducer, chain, and sprocket 122 on the driving element 102 of the clutch 34, the element 102 being loose on the shaft 32. The driven element 104, keyed to the shaft 32, comprises a hub 106 carrying a trip cam 108. A trip lever 112 pivoted to the frame is spring-urged against the cam 108 to engage a step 120 thereof. A solenoid 116, Fig. 29, when energised draws the lever 112 clear of the step 120, mechanism in the clutch automatically engaging the elements 102, 104 to drive the shaft. The solenoid is immediately de-energised, and the lever 112 rides on the cam until it reengages the step and releases the clutch. To adjust the tension in the belt 76 when the pitch diameter of the pulley 78 is changed, the motor is transversely adjustable by means of a handwheel on a threaded rod 82. One stencilling operation is performed while the shaft 32 makes one complete revolution. Turntable and work-holders.-The turntable 36 is mounted on a shaft 128 and is rotated in 120 degrees steps, one step for each revolution of the shaft 32. A lug 202 on the shaft 32 engages one of six slots in a Geneva wheel 172 which drives the shaft 128 by sprocket 174, chain and a sprocket 192. The sprocket 174 is angularly adjustable on the Geneva wheel by means of slots 180 on the sprockets engaging screws 176 on the Geneva, to adjust the position in which the turntable stops. Minute angular adjustment of the turntable with respect to the Geneva can also be made by lateral adjustment of two idler sprockets 194 over which the chain also runs. The turntable is held in its correct position by means of a pin 208 engaging apertures 206 in bosses 204 on the table, the pin being projected into the apertures when the turntable is stationary and controlled by a cam 222 on the shaft 32. To ensure that the Geneva stops in correct position to be engaged by the lug 202, a roller 880 on a spring-urged pivoted arm 874 engages in one of the Geneva slots to urge it into said correct position, and when the roller is not so engaged in a slot, a micro-switch 888 in the circuit of the solenoid 116 is allowed to open by an extension of the arm 874 to prevent engagement of the clutch 34. Each workholder is mounted in the turntable by screws 156 through brackets 158, being spring-urged downwardly flush with the turntable. Each holder carries four dials 164 by means of two pins 166 and recesses 168 to receive the rims of the dials, recesses 170 facilitating removal of the dials. When at the stencilling station 42, a workholder can be raised against the screen 52 by means of a plunger 46 slidable in a guide sleeve 226 and reciprocated by means of a roller 264 on a rocker arm 250 pivoted at 260, the rocking strokes of the arm being limited by adjustable stops 274. A cam 294 on the shaft 32 vertically reciprocates a bar 296 which reciprocates a sleeve 278 and thereby the outer plates 280 of a spring assembly 280, 286, 282, which actuates a roller on the end of the cam 250, whence the strokes of the rocker are cushioned by the springs 286. The cam 294 is adjustable along the shaft 32 to adjust the axial positions of the work-holder. A work-holder at the stencilling station can be removed through a hole in outer sheet metal' coverings provided over the frame. Upper unit housing.-The upper unit is made gas-tight to prevent the escape of radio-active gases from the luminous paint, a vent 348, Fig. 14, being provided, and connected to a vacuum pump. The top of the housing is closed by a plate 336. The lower edge of the housing is sealed by a strip 332. An inclined front plate 330 has an opening with a leaded glass plate 338 to permit observation of the squeegee operation. The rear of the housing is closed by plates 322, 324, 326, being recessed so as to allow tilting without interference with the upper plate 94 of the main frame 64. Squeegee shaft operation.-A bearing cage 430 secured to the squeegee shaft 58 is reciprocated by a rocker arm 404 pivoted at 414. The pivot 414 is vertically adjustable by rotating a shaft 422. A cam 462 on the shaft 60 reciprocates a cam follower bar 446, which has a resilient connection through springs 456 with the rocker 404. The vertical strokes of the shaft 58 are limited by abutments 492 on bell-cranks 480, 482 whose rocking movement is limited by stopscrews rotated by hand-wheels which can be locked by spring fingers. Alternatively, the squeegee shaft could be vertically fixed, the work-holder and screen being raised into paintforcing position. The shaft 58 is rotated by means of a cam 508 on the shaft 60, Figs. 2 and 8, follower 516, arm 518 engaging one of six notches 536 in a cam gear 520, pinion 504 driven by the cam gear, inner star wheel 564 riveted to the pinion, outer star wheel 566, driven by inner star wheel through springs 572, base member 556 riveted to outer star wheel and rotatable on shaft 58, worm wheel housing 560 screwed to the base member, and worm wheel 562 splined to the shaft 58. The shaft revolves through 180 degrees twice during each revolution of the shaft 60. The cam 518 is biassed outward by springs 549 and 546. The wormwheel 562 is secured against rotation with respect to the housing 560 by engagement with a worm 630 on a shaft 632 journalled in a part of the housing. The position of the squeegee shaft when stationary is adjustable by rotating shaft 632, and by means of an eccentric bushing the worm can be moved into binding engagement with the worm wheel to avoid back lash. The base member 556 has two projections 592 engaged by a forward stop pawl 596 and return stop pawl 594 to limit the rotation of the squeegee. The pawls are spring-urged into locking position and are pivoted on lugs 598 adjustable by screws 600. When the shaft 60 begins to rotate, the pawl 596 is moved out of locking position by a spring link 612 actuated by a lever 512 from the cam 508. During rotation of the squeegee shaft, the pawls 596, 594 are held out of engagement by cams 620, 624. Squeegee assembly.-Blades 670, Fig. 15, of rubber or like synthetic material are clamped between L-shaped body members 668 and clamping plates 672, and have forwardly-reaching extensions at either end to confine the paint within the blade limits. The leading edge is vertical and the trailing edge inclined. For lateral and rotational adjustment, to let the outer end of the blade precede the inner end to direct the paint inwardly, the body members 668 are secured to a supporting member 638 by means of screws 664 passing through elongated slots in the member 638. The member 638 is adjustably mounted on a hub 646 of the shaft 58 by means of a pair of screws passing through any of three pairs of holes in the member 638. The hub is frictionally secured on.the shaft 58 by a capstan 652. Paint agitating and dispensing means.-Rotatably mounted in a fixed shell 704, Fig. 14, is a shell 702 carrying a cylindrical reservoir 680 for the paint. The shell 702 and reservoir are rotated to agitate the paint by an electric motor 722 of 1/2000th H.P. In the reservoir is a manually operated piston rod 692 having a piston 694 spring-urged forwardly to force paint into a metering bore 684, and a piston 700 to force the paint through a ball valve 686 and out of a nozzle 688 against a deflector which guides it towards the screen. Stencil screen supporting and adjusting means.-Hinged to the frame 64 is a table 50 having an aperture 54 for the squeegee assembly, Figs. 1, 2, 18 and 24. The housing 48 can be clamped to the table 50 by means of lugs 352, Fig. 14, having slots to rece