US 2397731 A
Description (OCR text may contain errors)
April 2, 1946. H. a. FOWLER METHOD AND APPARATUS FOR RADIUM COATING MECHANISM Filed June 16, 1942 Y 2 Sheets-Sheet l A ril 2, 1946. H. B. FOWLER 7,
METHOD AND APPARATUS FOR RADIUM COATING MECHANISM Filed June 16, 1942 2 Sheets-Sheet 2 Patented Apr. 2, 1946 METHOD AND APPARATUS Eon RADIUM. COATING MECHANISM.
Harwood B. Fowler, Wayne, Pa.
ApplicationJune 16, 1942, Serial-N0. 441,238
My invention relates to apparatus and processes for screen printing, particularly with radium compound.
A purpose of. my invention is to mount a printing screen and screen frame on an accurate hinge, desirably a needle bearing hinge, and pref erably to provide frictional adjustment at the hinge, counterweighing to oppose the friction, and setting adjustable limit of opening of the hinge. V
A further purpose isto place-a sliding cover plate over a printing screen frame, to extend the handle of a squeegee. through the cover plate, and to move the cover plate back and forth with the squeegee;
A further purpose is to make the slidable cover plate of a printing screen frame removable from the frame.
A further purpose is to construct the sloping face of a squeegee toward the direction of printing motion so as to roll the printing ink or paste through the screen, the angle between such forward face and the screen being between 30 and 36 degrees.
A further purpose is to slope the end of a squeegee handle downwardly so as to improve the control possible over the squeegee.
A further purpose is to hold the object to be screen printed by suction, desirably supplemented by a jig having registry pins, and, preferably, eject the work mechanically against the suction.
A further purpose is to limit the copper sheet of a composite screen and sheet so that the sheet does. not touch the frame to which the screen is to be soldered and therefore does not by high heat conductivity weaken the laminating solder during soldering of the screen to the frame.
Further purposes appear in the specification and in the claims. v
Figure 1 is a perspective View of a device illustrating the present invention and the cabinet with which it will preferably be used.
Figure 2 is a perspective view of the screen printing, device itself.
Figure 3 is a fragmentary perspective of the squeegee.
Figure 4 is a perspective View of the cover plate and guard washer. I
Figure 5 is a side elevation of the device.
Figure 6 is a section of Figure '5 on the line 66.
Figure 7 is. a top plan view of the J'ig.
Figure 8 shows a typical screen-printed dial in top plan view.
Figure 9 is a fragmentary section of Figure 2 on the line. 9-9.
In. the drawings like numerals referxto like parts;
This application is. related in subject. matter to my copending' application for Metallic printing screen, Serial No., 437,543,. filed April 3; 1942,v which application is, incorporated herein by reference and made apart hereof For certain types: of printing, especially on metals or on ceramics -itg is desirable to-use a screen, oftenv a silk screen. Recently there has been considerable demand for; luminous. dials for aircraft instruments and the likes. Prior to my invention these are believed. to. have: been made entirely by hand. Such. dials present a serious problem from thestandpoint of printings, since the particles should be. relatively coarse in order to give bestv luminescence and the build-up or deposit on the work should bequi-te thick. I have succeeded in constructing. such luminous dials by screen printing.
A serious problem inv makingluminous dials is presented by the fact that radium. is very dangerous totheworkers who. handle it- I havesucceeded in rendering. the. operation quite safe if proper precautions be. observed. When I, refer herein to radium I mean any luminous dial material, whether or not. ithe actually radium.
I preferably print. througha composite metallic screen 20 (Figure 6) which consists of a screen wire 21 suitably of stain-less steel (preferably 18 percent chromium, 8 percent nickel) soldered at 22 to a sheet 23, preferably of copper. The design is etched at through the metallic sheet and solder. The making and-etching. of this composite screen is des'cribedin detail in my copending application above ref'erred'to.
The completev screen 20 is mountedv on. the bottomof a metallic frame 2-5;.prefarbly by soldering at 26.. In. order to prevent. the. soldering of the frame from melting. thev laminating solder at 22, due to the high conductivity. of copper sheet 23, the copper sheet. is terminated, at 21, beyond the edge of the design; and-not carried out as far as the substantial. rectangular frame 25. Solder masks the screen. beyond the. sheet 23.
In printing position the metallic sheet 23- is down against the work 28, and the screen is above it and spaced-by it from the. work. As also ex- .plained in my copending application, the thickness of the sheet 23 determines the thickness of build-up when radium is forced through the screen in the design areas bye, squeegee 29 moving. longitudinally in the'space. inside the frame 25. This will be understood when it is considered that the screen. in the design areas can get no (Figure 9).
closer to the work than the thickness of sheet 23 permits.
The frame 25 is supported by beams 39 and 3| which have bearing openings 32 engaging conical 1 ends 33 of a needle 34. The needle is rigidly sup- 1 ported by brackets 35 mounted on a base 36 hav- Beam 3| is also provided with an adjustable stop 42 which engages an anvil 43 .on the base to prevent too wide opening of the screen. Frictionat the. needle hinge bearing is adjusted by tightening bolt 44 which'extends between beams 30 and 3|.
It is necessary to lift the screen frame far enough to give clearance for removal of the fin: ished work. theangle to which the screen frame is lifted for (See Figure 5.) At'the same time clearance must not. be so great as to cause the a 3 radium compound to shift unduly to the left end i of the screen frame. Both of these conditions are met by placing the needle bearing well to the 1 rear (left) of the screen frame giving the low angle of lift shown in dot and dash.
The work is positioned beneath the screen in jig 45'mounted on'the base-and having a suitable (here a circular) depression 46 provided with suction 52 with the bottom of the work so as to hold the work down when the screen is raised after each printing. The source of suctionis conradium, and not'a forcing or packing action as in previous screen printing.
registry pins 41 and- 48 toengage with the holes 49 and 50 in the work. 7 I V 1 An opening 5| in the jig connects a source of nected with the opening 5| by a tube 53, and it discharges through a tube into an exhaust fan 55. The fan is located within a discharge opening 55 ofa hood 5'! having a transparent cover 58 and aside working opening BEN Figure 1).
When the screen has been opened, the work is l raised'from the jig by an ejector E0 operated manually in an opening 6| of the jig by a lever 62 pivoted at 63 on the bottom of the base.
Above eachbeam 3|1.or 3| is an angle bar 64 7 nor as, hinged to the beam at 66 or e1. They are united together at 68 and 69, and latched in closed position' at 10, by spring latches 1| The spring latches are pivoted at 12 and enter openings 13 Between'the beam 30 or 3| and the angle bar I 64 or 65 is a space 14 in which a cover 15, suitably of transparent plastic, is free to move backward 1 or forward while fully covering the frame 25 in all positions of movement. The length of the cover'fl5 is great enough to cover the frame 25 in both extreme positions, but is less than the dis- The rear face 80 of the squeegee will preferably be vertical with respect to the screen in operation, as will be the upper forward face 8|. But the forward sloping edge 19 should maintain an angle of approximately 33 with the screen when the squeegee is making its printing stroke in order to get best results on radium printing. Good results will be assured if this angle is between 30 and 36. V
The squeegee'blade is held between two metallic plates 32 and 83, the plate 83 forming part of an angle 84 secured to the end of the handle 11.
V The handle extends through the cover plate and is then bent at about right angles, (practically horizontal), at 85. Near the grip 86 the handle is bent down at 81, and this latter bend is found to assure'better control of the squeegee.
v In operation, the screen is raised, a piece of workis placed in the jig, registered by the pins,
contact with the scieemthe operation being repeated, forward and back until a uniform printing distribution has been obtained over the dc sign. Then the screen is raised and the work is lifted by the ejector and manually removed. A new work piece can then be substituted and the cycle repeated.
In all these operations, a strong exhaust should be maintained in the'hood to Withdraw dangerous radium emanation and keep it away from the operator. The cover plate prevents too rapid escape of emanation from the radium and also protects the lacquer contained in the radium paste from drying too rapidly. V
The radium paste is quite viscous, and must be kept so in order to be screen printed. It probably has a viscosity about like S. A. E. 120 oil, very similar to "molasses in January? ations and modifications to meet individual whim tance between crossmembers 68 and 69 so that i it can move the distance oftravelof the squeegee.
. The cover 15 can be removed readily by releasing 1 the latch 10, and moving the angle bars away from 1 the beams at the free ends of the angle bars. Arielongated opening l6, suitably centrally 10- j cated, extends through the cover 16, and the handle" of squeegee 29 is carried through this opening. A guard washer 18 suitably of transparent plastic; closely fits the handle and covers the elongated opening 16.
or particular need will doubtless become evident claim as new and desire, to secure by Letters'Patent is: I
1. In apparatus for screen-printing, a screen, a frame supporting the screen and hinge means supporting the frame upon a horizontal axis'to shift in vertical planes, a squeegee on the screen, adapted to print through the screen in one position thereof and having a handle, and means sign, or slightly more, with a forward sloping op-. erating edge -'|9 whose angle is rather important.
This edge must produce a rolling action on the for closing the top of the frame'during move ment of the squeegee to. print through the screen.
2. In apparatus for screen printing,.a screen, a frame supporting the screen, a cover over the frame having a cover opening, a squeegee having a handle extending through theopeningand means for guiding the cover to permit it to move with the squeegee.
3. In apparatus for screen painting, a screen, a frame for the screen, a squeegee on the'screen adapted to print through the screen and having a handle, and mean for closing the top of the frame during movement of the squeegee to print through the screen. i
4. In screen printing apparatus, a screen, a frame positioning the screen, a squeegee in contact with the upper surface of the screen and having a handle, a transparent cover for the frame having an opening through which the handle passes, and releasable guides for the cover permitting it to move with the squeegee.
5. In a screen printing apparatus, a screen, a frame for the screen, a needle bearing pivotally supporting the frame adjacent to but inwardly of the ends of the frame, a counter weight secured to the frame on the opposite side of the needle bearing from the screen and means for adjusting the friction in the needle bearing comprising means for adjusting the ends of the frame relative to said needle bearing.
6. In a screen printing apparatus, a screen, a frame for the screen adapted to open and close the screen, a needle bearing pivotally supporting the frame, adjacent to but inwardly of the ends of the frame, a rod secured to the frame on the opposite side of the needle bearing from the screen, a counterweight on the rod and adjustable means mounted on the rod for limiting the opening movement of the screen to a point at which the counterweight holds the frame and screen in a raised position enough to enable the operator to use both hands for removing and replacing articles to be stencilled through the screen.
'7. A screen printing squeegee of resiliently deformable material having a sloping forward face and making an angle with the screen during printing which is between 30 and 36 degrees.
8. A screen printing squeegee of resiliently deformable material having a sloping forward face and making an angle with the screen during printing which is about 33 degrees.
9. In a screen printing apparatus, a composite screen having a metallic screen wire and a copper sheet laminated by'solder to the screen wire, in combination with a metallic fram and solder uniting the screen wire to the frame, the copper being restricted in area and not reaching as far as the frame.
10. The process of radium printing, which comprises rolling radium paste through a screen by a sloping resiliently deformable surface making an angle of between 30 and 36 with the screen.
11. An apparatus as recited in claim 2, in which the cover opening is an elongated slot in which the handle has limited motion relative to the cover, and a device overlying and contacting said cover and movable with said handle to cover said slot in different positions of relative adjustment of the handle and cover.
12. In radium printing, a hood for printing with radium through a stencil screen, said hood comprising a supporting plate, a rear wall, a cover in part at least transparent and engaging the rear wall, end walls supporting the cover relative to the plate, means disposed in the space defined by the forward edges of the end walls, cover and plate to reduce the open area thereof to form a restricted opening through which the operators hands and an intake air supply can enter the hood, a radium stencilling device disposed inwardly of the hood in the path of air entering said restricted opening, an exhaust channel communicating with the hood toward the rear thereof, and means for generating suction in-said exhaust channel to draw air over said stencilling device and into said exhaust channel.
HARWOOD B. FOWLER.