Patent GB-802728-A (GB)
Title: Improvements in or relating to screen printing machines
IPC: C09B44/08
Filed: 1953-12-14
Abstract: 802,728. Stencilling-apparatus. WHITEBIRK WEAVING CO., Ltd., and BLAIR, J. T. Aug. 24. 1955 [Dec. 14, 1953], No. 34699/53. Class 100(2) In a screen printing machine, operating mechanism for the squeegee mounting comprises support means reciprocated longitudinally at different heights during the forward and backward strokes, two squeegees being, provided and one of them brought into register with the screen at the beginning of each stroke. The screen frame 3 is removably secured by plates 3A to an outer frame 3B which is pivotally mounted on a shaft 5 by arms 4 connected by a rod 7, a spring 6 holding the frame in its upper position, when the squeegee mounting is in its rear, or left-hand position. Two squeegees 14 are carried on a mounting 13 at the end of arms 12 having slots 11 through which passes a rod 10 connecting posts 9 secure to chains & driven by a hand-wheel 23. The post pass through guides 15 in carriers 16 having rollers 17 and arms 20 carrying rollers 22 and pulled down by springs 21. When the squeegee assembly is at the rear, the rollers 22 rest on the ends of flanges 18 on the frame 3B, which is in raised position. When the posts 9 move forwards, on the lower run of the chains, the rollers 22 cause the screen frame to be lowered, and the rearward squeegee 14 engages the screen, the arms 12 being carried along when the rod 10 reaches the ends of the slots 11. The posts then move to the upper run thereby raising the rod 10 and swinging the forward squeegee into contact with the screen. When the rod 10 has moved a little way along the slots 11, it engages stop pins 25 pulled against it by springs 26, so that the squeegee assembly is moved rearwardly. When the squeegees are stopped in their rearward position, by the end of the frame 3, or by stops on the frame 3B which may also raise the squeegees clear of the frame, the rod 10 pushes past the pins 25 and is lowered, and as the rollers 22 reach the ends of the flanges 18, the spring 6 raises the screen frame. To prevent leakage of ink, the squeegee mounting may carry pivotal end closure members having felt bases, which remain in contact with the screen. The operating pressure of the squeegee mounting can be varied by weights, and screw adjusters vary the operation of angles of the squeegees. Inking-mechanism. An ink container located above the mounting 13 feeds a small quantity of ink continuously between the squeegees and moves across the frame during each stroke. Alternatively, ink from a container is fed to a horizontal roller having a spiral groove and rotating while the squeegees reciprocate, and a finger engaging the groove and driven laterally on a slide by rotation of the roller deflects the ink downwards from the groove. According to the Provisional Specification, two table tops are provided which are interchangeable, and when printing is finished on one table, it is moved out and replaced by the other. Two endless overlapping grooves are provided in the sides of the frame engaging lateral pins on the table tops, and a sprocket drives chains extending round each table top at each side. The sprocket is driven by a second sprocket outside the frame, there being a third freely rotatable sprocket at each side of the rear of the machine. A chain extends round each pair of sprockets and carries a heavy weight at its forward end and a lighter weight at its rearward end. Each chain carries a pin adjacent the forward sprocket and each carrier has a pawl engaging the pin at the end of the forward stroke. During the rearward stroke, each chain thus pulls rearwardly to raise the heavy weights and lower the lighter weights. At the end of the rearward stroke, the pawls release the pins and the heavy weights move the chains forward and interchange the table tops. Free-wheel devices permit rearward movement of the chains without moving the table tops. The pawls may be released by the action of the screen frame rising.