US2991711A

US2991711A - Fully automatic silk-screen printing machine

Info

Publication number: US2991711A
Application number: US535578A
Authority: US
Inventors: Ehrhard Georg Hermann; Ehrhard Karl Hermann; Knaus Eugen; Lorenz Fritz
Original assignee: Frank Sche Eisenwerke AG
Current assignee: Frank Sche Eisenwerke AG
Priority date: 1954-09-24
Filing date: 1955-09-21
Publication date: 1961-07-11
Anticipated expiration: 1978-07-11

Description

July 11, 1961 G. H. EHRHARD ETAL 2,991,711

FULLY AUTOMATIC SILK-SCREEN PRINTING MACHINE Filed Sept. 21, 1955 4 Sheets-Sheet l y 1951 G. H. EHRHARD ETAL 2,991,711

FULLY AUTOMATIC SILK-SCREEN PRINTING MACHINE Filed Sept. 21, 1955 4 Sheets-Sheet 2 July 11, 1961 e. H. EHRHARD EIAL FULLY AUTOMATIC SILK-SCREEN PRINTING MACHINE Filed Sept. 21, 1955 4 Sheets-Sheet 3 July 11, 1961 G. H. EHRHARD EIAL 2,991,711

FULLY AUTOMATIC SILK-SCREEN PRINTING MACHINE Filed Sept. 21, 1955 4 Sheets-Sheet 4 Fig. 7 1/5 United States Patent '0 2,991,711 FULLY AUTOMATIC SILK-SCREEN PRINTING MACHINE Georg Hermann Ehrhard and Karl Hermann Ehrhard,

Heidelberg-Handschuhsheim, Eugen Knaus, 'Mannheim-Frendenheim, and Fritz Lorenz, Mannheim, Germany, assignors to Franksche Eisenwerke Aktiengesellschaft, Adolfshntte, near 'Niederscheid, Germany Filed Sept. 21, 1955, Ser. No. 535,578 1 Claims priority, application Germany Sept. 24, 1954 '4 Claims. (Cl. 101-126) The present invention relates to a fully automatic silkscreen printing machine which makes it possible to achieve a substantial increase in printing speed as compared with known silk-screen printing machines, not only by the nature of its drive but also by the special arrangement of the printing arm carrying the screen frame and of the printing table.

As is known, the silk-screen printing process, wherein the screen and the printing table lie flat on one another during printing, is carried out substantially in three stages. These are;

(1) The material to be imprinted is placed on a fiat printing table and positioned by means of lay stops. The printing table must remain accessible to the operator.

(2) The actual printing operation, wherein the screen is made to bear against the material to be printed, and the ink is applied by means of a doctor device rubbing over the screen.

(3) Release of the printing table by lifting the screen so that the finished print may be removed.

Normally the above described stages require a comparatively great deal of time as compared with known rotary printing machines, so that the output per hour is correspondingly small. are required to attend it.

Known silk-screen printing machines are generally operated by hand. Semi-automatic machines have also been proposed wherein the screen frame is brought in contact with the material to be printed by'hand, and

the next working stage, more particularly the movement.

of the doctor and the opening of the screen frame, is carried out mechanically. All known silk-screen printing machines have a disadvantageously slow working speed. In addition, the material to 'be imprinted must be positioned on the printing table from the same side as that from which it must also be removed. The invention is intended to overcome this disadvantage.

- According to the invention the printing table and the printing arm carrying the screen frame are mounted in a pivotable manner in the machine frame, the two pivotal axes being parallel but oifset with respect to one another, so that upon pivoting in one direction the screen frame andthe printing table move towards each other, which upon pivoting in the other direction they move away from each other. The screen frame and the printing table are connected by a two-armed lever mounted in the machine frame, so that a movement of the screen frame is transmitted positively to the printing table, in an opposite direction. An .apparatus'for placing the material to be printed on the table is connected thereto and participates in its swinging movement.

According to a further feature of the invention, a pneumatic drive is provided for the machine, and electric means for assisting in the control operations and allow fully automatic operation.

Further details of the invention will become apparent from the following description, with reference to the drawings which illustrate one. embodiment of the in-' vention. In the drawings:

' FIG. 1' is a side elevation of a fully automatic silk-- In addition, several operators 2 screen printing machine in the open positiompartly in section,

FIG. 2 is a plan view, with the screen frame removed, FIG. 3 is a sectional view taken on the line III-'III- of FIG. 1,

' FIG. 4 is a sectional view taken on of FIG. 1, and

FIG. 5 is a sectional view taken on of FIG. 1, FIG. 6 is a circuit diagram of the electro-pneumatic control means, in the laying-on position, and

FIG. 7 is a similar diagram of the control means but in the printing position.

Pivotally mounted on pins 2 in the machine frame 1 is the screen-holding frame 3, in each of whose lateral support struts 4 a cylinder 5 with a piston located there? in is arranged. The piston rods projecting out of the cylinders are connected to a tube 7 which serves as a doctor carrier. Arranged at each end of the tube 7 is a pair of scissors-action articulated arms 8 on whose free arm ends there are mounted rollers 9 subject to the action of a spring against theinside surfaces of the top and bottom walls of the support struts 4, which are' of U-shaped cross-section. This arrangement allows the constant spacing of the doctor :10 from the screen 11- lying on the underside of the holding frame 3 which is necessary for printing, without permitting any detrimental play. Mounted in the tube 7 which carries the doctor are two

rods

12 and 12 which are situated one behind the. other (FIG. 2) and which each carry a roller 13 at the end projecting from the tube 7. The rollers 13 are made to bear against the inner surfaces of the vertical walls of the struts 4 by means of a compression spring 14 arranged in the middle of the tube between the rods, which are spaced from one another.

The frame 15 carrying the screen 11 is at one sid fitted on to a clamping rail 16 fixed to a transverse support of the holding frame 3 and is held at the other side by being pressed to a clamping rail 17. Application pressure can be provided by a spindle 18 provided with right-hand and left-hand threading, on which two sets of scissors-action articulated arms 19 and -19 can'be the line Iv -rv the line V-.VI

screwed by turning the spindle at its end portions, which clamping rail, electric feelers can be provided on the.

clamping rail for controlling thereversal of the doctor at the correct time in dependence on the position of the clamping rail.

The printing table is carried on two hollow columns 21 which are provided with internal screw-thread, and

which are held at both sides by clamping sleeves 22 in' the machine frame 1. Threaded spindles 23, which engage in the internal scrcwthread of the columns, enable the columns to be adjusted vertically in dependence on' the thickness of the material being printed, after the clamping sleeves have been loosened, by a h'and-opwhich the printing table is'supported, to allow the latter" erated worm gearing 24 which acts jointly on both spin dles 23. For fine adjustment, a head 25 is adapted to be screwed into the column 21. Fineadjustment also is carried out by hand.

At the opposite side, the printing table 20 rests on a threaded spindle 26 which is arranged'in the middleof the frame and which is adjustable in a column 27 bymeans of a hand wheel 28. A chuck 27 is used to secure the threaded spindle in the desired position. 1 Articulations 29 and 30- are provided at the pointsat.

to take up various angular positions with respect to the

columns

21 and 27.

The printing table is brought from the open position as shown in FIG. 1, into the printing position by swinging the table about the articulation 29 in dependence, at the same time, on the screen-holding frame 3 which is swung downwards. For this purpose the column 27 is connected at its lower end to a transverse support 31 (FIG. 3) to each of whose ends there is connected a two armed lever '33 pivotable about bearings 32. The free arm of the two armed lever 33 is connected by a connecting rod 34 to the screw-holding frame 3. The frame can be raised and lowered by compressed air cylinders 35 which are arranged at each side of the machine frame in rotatably suspended fashion, and in which there are guided pistons whose piston rods 36 are connected to the screenholding frame 3. At the same time the connecting rod 34 connected to the two armed lever 33 moves the printing table in the opposite direction.

Fixed to the free end of the two armed lever 33 is a roller 37 which when the lever moves upwards and downwards, operates

electric switches

38, 39 and 40, arranged in the machine frame. When the printing table is in the open position the switch 38 switches over valves for the movement of the pistons in the cylinders 35 by means of which the screen-holding frame is lowered and the printing table raised. In the printing position the lowest switch 40 operates valves for changing over the movements of the doctor in the cylinders 5. The middle switch 39 operates the valves to provide a vacuum in the printing plate, further details of which will be explained in another part of the specification. The printing plate 20 is provided with small holes 41 for suction or compressed air which are distributed over the surface of the said plate and open into a chamber 42 provided below the plate. An electric motor 44, by means of a compressor 43, mounted below the table in the frame, produces a vacuum in an air vessel 45 which communicates with the chamber 42 through

conduits

52, 53 and 54. By means of the vacuum a sheet of paper lying on the printing plate is held fast during the printing operation. The suction air control means provided for this purpose will be explained in a later part of the specification.

Besides producing a vacuum, the compressor also produces the compressed air necessary for lifting and lowering the screen frame and the printing plate, said compressed air being stored in an air vessel 46. Also coupled to the electric motor 44 is a generator 47 which supplies the current for operating the valve controls.

Front lay stops 48 and side lay stops 49 are also pivotally mounted in the printing plate 20 outside the region of the chamber 42, and the said stops project, in the erect position, through slots provided in the printing plate. The stops 48 are actuated on a common shaft by the piston of a compressed air cylinder 50 and the stops 49 by a compressed air cylinder 51. All of the stops can have their angular position relatively to the printing plate surface adjusted independently of one another, so that the material to be printed is positioned as accurately as possible. The height of the so-called top stops which are provided on the aforesaid stops can also be adjusted in accordance with the height of the material to be printed. *For positioning the material to be printed in the correct manner, it is sufficient to have two front stops and one side stop, against which the material to be printed comes to bear, whilst the other lay stops can be withdrawn so that they do not come into operation, depending on the size of the format to be printed.

The automatic positioning apparatus is arranged on a special frame 55 which is carried on rollers 56a. It is positioned at the end face of the machine and connected thereto by screws.

Mounted in the frame 55 are two

shafts

56, 56 on each of which two chain wheels 57, 57' are fixed. Over these wheels run chains 58 to one end of which a weight 59 is suspended, whilst the other end is connected to a table 60 carried in the frame and receiving the material 63 which is to be printed. The shafts 56, 56' can be rotated by a transverse shaft 61 by way of worm gearing 62. Drive is effected through a ratchet arrangement 64 provided on the transverse shaft 61 and pivotally connected by means of a connecting rod 65 to the printing table 20, and whose pivotal movement actuates the ratchet.

Electrical control means make the engagement of the ratchet independent of the particular height of the stack of material to be printed 63. By means of a feeler switch 67 arranged above the pile of material to be printed, an electric magnet 68 is energised and the latter brings the toothing of the ratchet into or out of engagement with the associated ratchet wheel.

Arranged on the frame 55 at that side of the table 60 adjacent the printing table 20 is an abutment plate 70 which is carried by columns 69 and against which there bears the pile of material 63 which is to be printed. Threaded spindles 71 which are located in the said columns and can be turned by hand enable the abutment plate to be very accurately adjusted in the vertical sense with respect to the edge of the printing table. Arranged on the upper part of the plate is a transverse blower arrangement 72 which blows a current of air between the upper layers of the material to be printed and whose method of operation will be explained in more detail with reference to the circuit diagram in FIGS. 6 and 7.

The pile 63 of material to be printed is laid on the table 60 and caused to bear against the abutment plate 70 by means of an adjustable setting plate 73, whilst two other setting plates 74 and 74' act as side limits by way of advance guides for the side laly stops 49' situated on the p'nnting table.

The laying-on apparatus is carried by a frame 75 which forms an extension of the printing table plate 20, is screwed thereto and participates in its swinging movement. -Arranged in the middle of the frame is a compressed air cylinder 76 whose piston rod 77 is connected to a tubular support member 79 which extends transversely over the width of the pile of material to be printed and is provided with suction cups 78. Mounted at each end of the suction means support member is a roller 80 for the travel of the support member to and fro over the printing table plate.

The suction means 78 are connected to a vacuum pipe 83 by means of two pipes 81, 81' which are inserted in one another, and which are sealed from one another by stuffing boxes 82, and of which the one pipe 81 is displaceable.

Provided under the frame is a transversely disposed feeler arm 84 which blocks the topmost sheet of printing material lifted by the current of air of the transverse blower arrangement 72 and makes it easier for the suction means 78 to grip the sheet.

FIGS. 6 and 7 show two different control positions of the electroepneumatic control means which are used in the present automatic machine. It should be noted that for the sake of greater clarity, the particular pressure obtaining in the pipe lines inthe drawings is characterised by different kinds of lines. Conduits which are drawn in ful lines have compressed air (approx. 6 atmospheres absolute), conduits shown in chain-dotted lines a vacuum, and conduits drawn in chain lines atmospheric pressure.

The compressor 43 driven by the electric motor 44 draws in air from a. vacuum air vessel 45. After a specific vacuum has been produced, a change-over valve 85 automatically interrupts the connection and changes over the suction conduit of the compressor to communicate with the ambient air. The compressor 43' forces the aspirated into an air vessel 46 after it has passed through an oil purifier 86, and after a specific working pressure (for example 6 atmospheres absolute) has been reached, .a relief pressure valve 87 allows the surplus air to escape.

The diagram shown in FIG. 6 illustrates the position of the machine when a sheet 88 is being delivered by the suction means 78 to the printing table 20, which takes up an angular position of approx. in the opened position. The front -lay stops 48 for positioning the sheet are swung upwards and have reached their end position, whilst the side lay stop 49 has not yet reached its end position since it is delayed by a' hand-adjusted valve 89 which throttles the conduit supplying compressed air to the compressed air cylinder actuating the said stop.

The laying-on apparatus whose suction means 78 communicate through the

slide tubes

81, 81 and by way of an electrically controlled valve 89 with the vacuum conduit 5-2, has, in the end position, freed an opening 90 which is provided in the tube 81 and which eliminates the vacuum at the suction means and frees the sheet. Owing to the inclined position of the printing table, the sheet drops down to the front stops 48 which arrest the said sheet. The side lay stop 49 whose erection was delayed, has now also reached its end position, so that the sheet is held in the correct position.

In the end position, the piston which erects the stop 49 operates a switch 91 which switches oif a relay 92 from the circuit and thereby changes over an associated relay switch 93. This has the result of closing a valve 95 which connects the chamber 42 in the printing table to the pressure conduit 94, and thus eliminates the air cushion flowing between the table plate and the sheet 88 through the small openings. At the same time another valve 96 is opened which causes the chamber to communicate with the vacuum conduit 52. Consequently the sheet lying on the plate is aspirated by the vacuum and held fast.

The changing-over of the relay switch 93 also closes a valve 9'7 which interrupts the supply of compressed air to the feed cylinder 76, and opens a second valve 98 which allows the pressure conduit 94 to communicate with that part of the cylinder 76 lying on the other side of the piston, and thereby returns the suction means into their initial position. Before the machine is closed, the lay stops 48 and 49 are swung back again into the retracted position in the printing table. Provided for this purpose on the tube 81, with which the suction means support member is connected, is a control rail 100 which operates a switch 99 as it passes to and fro, and the said switch opens or closes a valve 101 which establishes a connection between the compressed air conduit 94 and the

cylinders

50 and 51 actuating the lay stops 48 and 49. The valve 101 standing in the open position is therefore closed by a switch 99 withdrawing from the rail, at the time of the return movement of the tube 81, so that the pistons operating the lay stops return to their initial position under the pressure of springs.

When the side lay stop 49, which is erected with some delay, reaches its final position, the laying-on operation is completed. The switch 91 which is actuated during this operation is a double-throw switch which on the one hand switches oif the relay 92 and on the other hand switches on a relay 102. Current is supplied to the latter by way of a switch 38 which is held in the switched position by the two-armed lever 33. The relay 102 changes over a relay switch 103 and thereby closes a valve 104 which has brought about the upward movement of the piston in the compressed air cylinder 35 in order to open the machine, whilst another valve 105 is opened so that the compressed air can pass to the other side of the piston into the cylinder. This initiates the downward movement of the screen-holding frame 3, which, by means of the connecting rod 34 and by way of the two-armed lever 33 and the column 27, also swings the printing table 20 into the horizontal position.

The switch 39 actuated by the lever 33 during the swinging movement has no effect since the associated circuit has been interrupted by the preceding change-over of the relay switch 103. on the other hand,the switch-40 which has been operated'by the lever 33 in the endposi-' tion of the said lever releases a relay 105. The released associated relay switch closes a valve107, which connects the pressure conduit 94 to the front end of the cylinder 5 which brings about the movement of the doctor. At the same time the relay switch 106 opens a valve 108, which allows compressed air to be supplied to the part of the cylinder located behind the piston. The doctor bridge 7 held by the forwardly moving piston rod 6 rubs over the screen 15, and thus the sheet under the said screen is printed.

A rod 109 connected to the doctor bridge carries at'its 112 which is situated behind said cam and which switcheson the relay 105. The associated relay switch 106 causes the valve 107 to open and at the same time closes the valve 108, thereby stopping the movement of the doctor and obliging the doctor to reverse and rub over the screen, which has now been relieved of load. When the machine is opened the lever 33 connected to the connecting rod strikes up against the switch 39, which closes a circuit by means of a so-called vacuum supervising device 115 for actuating the relay 92. By means of the relay switch 93 the circuit is maintained through the switch 91. Moreover, by closing the valve 96, the vacuum in the chamber 42 located under the printing plate is shut oil and a valve is opened, which causes the chamber 42 to communicate with the compressed air conduit 94. The surge of air caused by this operation lifts the material 88 to be printed away from the printing plate, and the sheet slides from the sloping plate on to a drying conveyor belt.

The switching-on of the relay 92 also closes the valve 98 and opens the valve 97, so that compressed air can flow into the cylinder 76, and displaces the suction means support, which is connected to the piston rod 77, over the printing plate 20. During the feed movement, the switch 99 travels with its roller up against the control rail 100. The switch 99 on the one hand interrupts a circuit by means of which the valve 89 is closed and the vacuum conduit to the suction means shut off, whilst on the other hand a circuit is closed which opens the valve 101 and thereby opens the way for the compressed air to pass to the

compressed air cylinders

50 and 51 which drive the lay stops.

During the following closing operation of the machine, the supply conduit to the piston of the closing cylinder 35, which conduit has been subjected to pressure by the opening of the valve 105, conveys compressed air through a conduit 113 branching from said supply conduit towards the transverse blower arrangement 72, which loosens-up the upper layers of the pile 63 of material to be printed. A hand-operated valve 114 arranged in the supply conduit serves for adjusting the strength of the blast of air.

After the front and side lay stops have been erected, the switch 91 initiates the closing movement of the machine, and the cycle of operations is repeated as already described.

For laying-on by hand the material to be printed, a special switch 117 is provided on the printing table plate. A further switch 118, which controls the valve 108 for the doctor movement, can be used in the case of a direct copying process wherein the screen and table plates lie horizontally.

If the row of suction means 78 has not seized the material to be printed, then the machine remains stopped, since the vacuum supervising device 115 is adapted to interrupt, by its position, the circuit for closing the relay 92.

1. A screen printing machine comprising a machine frame, a printing table, a screen frame contacting said table during printing, said screen :frame and said printing table being pivotably mounted parallel but offset with respect to one another, a lever pivotably mounted in the machine frame for connecting said table and said screen frame, connecting rods pivotable at each end of the lever and to said table and screen frame respectively for transferring the pivoting motion of the screen frame to the printing table whereby the screen frame pivots in one direction, said frame and the printing table move towards one another maintaining parallelism of their position throughout their entire movements by corresponding dimensions of their respective operating lever linkage but 15 move away from one another when the pivotal movement is in the other direction so that the removal of the printed material is made possible.

2. A machine according to claim 1 and a pneumatic drive associated with the screen frame and the printing table for pivoting same, said drive comprising a cylinder secured to said frame, means operatively connecting said cylinder to said screen frame, and an airy compressor to ling same.

4. The machine according to claim 2, wherein said compressor is provided with air suction means, a vacuum vessel with which said air suction means is connected.

and a suction chamber disposed below said printing table 10 and connected with said vessel, whereby paper to be imprinted is held fast during the printing operation.

References Cited in the file of this patent UNITED STATES PATENTS 148,049 Gordon Mar. 3, 1874 483,564 Korsmeyer Oct. 4, 1892 1,188,993 Rathbum June 27, 1916 2,230,633 Williams Feb. 4, 1941 0 2,246,000 Pollard June 17, 1941 2,497,798 Root Feb. 14, 1950