US2842818A - Apparatus for pressure casting of printing plates - Google Patents

Description

July 15, 1958 w. B. cocKs ETAL 9 3 APPARATUS FOR PRESSURE CASTING 0F PRINTING PLATES 2 Sheets-Sheet 1 Filed Aug. 25. 1954 IN V EN TOR.

" Wei/2 8b- 5 Cocks Warren fiqgjon July 15, 1958 w. B. cocKs ETAL ,3

APPARATUS FOR PRESSURE CASTING OF PRINTING PLATES 2 Sheets-Sheet 2 Filed Aug. 23, 1954 m2 m Vcu mo 9 39 m 6 x WW far-e3 APPARATUS FGR PREEsSURE CASiTENG GF PRENTHNG PLATES Walter B. Cocks and Warren A. Button, Des Moines, Iowa, assrgnors to Meredith lrublishing \Coinpany, Des Moines, liowa, a corporation of liowa Application August 23, 1954, Serial No. 453,541

5 Claims. (Cl..22-===58) This invention relates to the manufacture of printing plates, and more particularly, to' a method and apparatus for casting reinforcing metal integrally with a flexible electro-formed shell bearing the subject matter to be printed. Such plates, referred to as electrotypes, are usually arcuate in shape and adapted to fit around cylinder of a printing press, although the invention is also suitable for making flat plates for use in fiat-bed type presses.

At the present time arcuate printing plates are cast in the fiat against the thin flexible shell and then bent to the proper curvature. This process results in inaccurate curvature and irregularities and ripples in the face surface of the plates, which defects must be compensated for by placing shims between the relatively soft curved plate and the printing roll. This operation is knovinas make ready on the presses, and demands considerable time.

The object of the present invention is to provide a simple and elficient method and apparatus for producing dense, high quality, accurately-shaped electrotype printing plates faced with the standard thin shell, bearing the subject matter to be printed. The plates made in accordance with our invention are characterized by a high degree of finish on the inner concave surface upon removal from the mold, thus minimizing machine or hand finishing which tends to distort the plates and adversely afiect color register. Because the plates of the present invention are cast to accurate curvature and to uniform thickness, they conform to the printing plate cylinder and, consequently, the necessity for make ready on the presses is reduced to-a minimum. Also, the printing plates of the present invention have been found to have a longer life, which further increases the savings efiected by their use.

The invention consists in casting the standard base alloy used for printing plates between complementary curved male and female mold halves confined in a platen press, the female half carrying the electrotype shell to become an integral part of the printing plate, and applying fluid pressure to the molten metal while simultaneously cooling the casting. Further, the invention contemplates a novel press and mold construction forcarrying on the process.

In the drawings:

Figure 1 is a side elevational view, partly in section, of the apparatus of the invention.

Figure 2 is a perspective view of the sandwich-type mold used in the apparatus shown in Figure l, with the electrotype shell in place.

Figure 3 is a top'view of the central portion of the apparatus of Figure 1, the platens being'shown in open position.

Figure 4 is a similar View after theplatens have been closed, showing means for supplying casting metal and for application of fluid pressure to the metal in the mold.

Figure 5 is a sectional view taken along the line 5-5 of Figure 4.

Referring to Figure 1, the basic element of the apparatus is a platen press of conventional construction indicated generally by the numeral 10. Such a press is normally mounted in vertical position, but for purposes of this invention we mount the press horizontally on frame 28 supported by upright members l2, 14 which rest on the floor 16. The press illustrated has a movable platen 20 and a fixed platen or strain head 22. It will be understood, however, that a multiple platen press may be used. The movable platen 20 is advanced and retracted by an air cylinder 24 through a toggle mechanism 26 of conventional construction which multiplies the force applied to the movable platen 2d. The raising and lowering mechanism for the platen may be hydraulic in nature, or it may be purely mechanical rather than pneumatic. Plane platen 26 is converted to an'arcuate supporting surface by a series of vertically-spaced arcuate or curved ribs 32 secured to vertical supporting rods The assembled arcuate ribs 32 are secured to the plane platen of the press by means of a pair of vertical channel members 29 which have longitudinal T-shaped strips 27 formed integrally with the bottoms thereof adapted to fit into corresponding T-shaped slots in the platen 2%, as best shown in Figure 3. The rib assembly described provides a convex supporting surface for the male portion of the mold as will be described hereinafter.

In like manner, the upper plane platen or strain l' 22 is supplemented with a concave supporting surrace comprising parallel spaced ribs as of arcuate configuration, secured to vertical rods 34, and fixed to plates. 22 similarly to assembled ribs 32. The concave arcuate ribs 36 are preferably opposed to the ribs 32 in the complementary male assembly secured to the platen 26,

so as to exert substantially uniform pressure on the curved sandwich mold placed between the platens. The curvature defined by the outer complementary edges of ribs 32 and opposed ribs 36 corresponds to the curvature of the mold. The reinforcing ribs 35 are completely enclosed by sheet metal facing Bil and similar cover'ag on the sides, bottom and ends, to form a leak-tight cc tainer 38 which is connected to a source of cooling fluid entering through pipes 4t), joining the bottom thereof. The cooling fluid rises and is discharged the drain through a pair of pipes 4-2 joining container 30 ..t the top. Suitable valvestnot shown) are provided in pipes 40 and 32 to permit adjustment of the flow of cooling fluid through the container 38 at any de d rate. This construction is best shown in Figure 5 an adapted to conduct heat through the face of the mold adjacent to covering 30, progressively from the bottom up. Openings 37 are provided through the ribs to permit complete circulation of cooling fluid throu h the container 38.

The work table dd supported by the, press and; thereover is provided for work being placed :1 moved from the press. An oven 46, heated by r ventional source of heat, may be mounted corn on frame members 12 and 15 to heat molds prior L sorting in the press. Any suitable source of h be used, for example, direct gas flames or high fr electricity. A melting pot 48, equipped with an ele heating means or other suitable heater (not shown), is used as a reservoir for the molten metal from which the plates are cast. The metal may be a standard alloy having a relatively low melting point commonly used in manufacturing printing plates, which consists essentially of lead. An electrically-heated isolated line 5 3 is employed to conductmolten metal from the pot id to the mold in the press. When the pot is located as shown in Figure l, with the level of the molten liquid below the discharge nozzle 52 on the end of the line 50, a pump must be provided in the line 56 to force the metal through the line. W

The novel mold construction in which the actual casting takes place is shown in Figure 2 and consists of a sandwich designated generally by the numeral 60. The sandwich mold 66 is shown in Figures 3, 4 and 5 in assembled position in the press. The mold comprises a first curved plate or mold half 62 made of rather heavy metal such as sheet steel which lies adjacent the convex ribs 32, in the press, a second similar curved plate or female half 64 which lies next to the concave facing 36, and an electro-deposited copper shell 66 which carries the embossing or impression of the subject matter that will be printed. The subject matter may be half tone, type, solid, reverse printing or any combination thereof.

he shell 66 is generally formed in the fiat and then curved by reforming against the heavy plate 64 to which it is secured by any suitable means, for example, the shell may be notched to fit between pins 67 projecting from the face of the female mold half 64. The shell should be trimmed so that the subject matter is centered with respect to the edges of the mold. The inner surface 661: is coated with tin to obtain adhesion between the shell and the cast metal backing.

The plate 62 has a block '76 fixed to the backside thereof flush with the top edge to facilitate introducing molten metal into the space 65 between the plates 62 and 64. An opening 72, which is threaded near the upper end, leads through the block and the plate 62 into the space 65, as best shown in Figure 5. The thickness of the plate being cast in the mold is determined by spacers or metal bearers 68, which consist of strips of metal, or other suitable hard material, fixed to the convex face of the plate 62 opposite the margins of the shell 66, and forming part of the male member of the mold. The strips may be welded, bolted, or otherwise secured to the plate. The vertical spacers 63 are notched at 67a to fit pins 6'7 for holding the sandwich in assembled relation. The pins 67 are shorter than the thickness of the spacers 68, so that the spacers determine the thickness of the casting. The surfaces of the spacers 68 facing the shell 66 have a plurality of rather sharp longitudinal ridges 6? projecting therefrom, which are adapted to embed in the surface 66a of the shell when the press is closed. The metal from which the spacer 68 is made must be considerably harder than the shell 66 so that it will cut into the surface of the shell to define a leak-tight cavity 65 between the inside surface of the plate 62 and the shell 66. Any number of ridges 69 may be used, three having been found to work out satisfactorily.

To facilitate pouring molten metal into the cavity 65 a cup or funnel 74 terminating in an externally threaded tube 75 (see Figure 5) is adapted to screw into the threads in the upper end of the sprue opening 72 in block 70 which leads to the cavity 65. The cup is also externally threaded at the top and has a cap 76 which may be screwed over the top. Cap 76 has a short nipple 78 extending therethrough and adapted to be connected to an air line 80 through a union 79. The line 86 contains a pressure gauge and the necessary valves, and leads to a source of compressed air.

In casting a printing plate using the apparatus described, the first step is to prepare the sandwich 60. The standard electro-deposited shell 66 is flat, and therefore, must be curved to fit accurately the inside surface of the female mold half or plate 64. The shell is then secured to the plate 64 by compressing between the pins 67, with the printing surface facing the plate, and the tinned surface 66a facing outwardly. The shell should have sufficient good metal around the margins to permit the ridges 69 of the spacers 68 to make a leak-tight seal that will withstand considerable pressure. The male mold half comprising the plate 62 and the spacer 68 1s assembled with the female half by engaging slots 67a in frame 68 with pins 67, and the resulting sandwich is placed in the oven 46 or subjected to other suitable heating means. Preferably, the assembly should be heated rather quickly so that the tin on the back 66a of the copper shell 66 will be oxidized as little as possible. The ribs 32 and 36 in the press may be preheated so that they do not conduct heat away from the sandwich when it is placed therebctween. The temperature to which the sandwich is heated should be e ual to or higher than the melting point of the metal being cast. The heated and assembled sandwich is then placed between the rib assemblies and the platens are closed. The sandwich is supported by a platform 17 secured to the lower portion of the platen 20, as indicated in Figure l. The uppermost and lowermost ribs are aligned with the horizontal spacer members 68 to insure adequate pressure thereon to effect a seal of the cavity 65. Cup 74 is screwed into the sprue opening 72 and the molten metal is then pumped from the tank 48 through the line 56 into the cup from which it flows into the cavity 65 of the mold. Air in the cavity is permitted to vent through the same sprue opening 72. A screen disc may be held over the sprue to reduce turbulence.

When the mold has been completely filled the cap 76 is screwed onto the cup 74 and the air inc is con nected to the nipple 73 extending from the cap. The valve in line 86 is opened and air of the desired pressure is permitted to fiow into the cup, thus applying pressure to the molten metal within the cavity to compact it. Tic pressure may be varied to accommodate casting treat in the plate and allow variation dependent upon subject matter on the shell. The application of pressure causes the shell 66 to be formed to prefectly arcuate curvature insured by the accurately-shaped complementary ribs 32 and 36. While the pressure is maintained on the metal, cooling fluid such as ordinary tap water is introduced into the tubes 40 connecting to the bottom of the cooling liquid container 33 and the heat in the molten metal is couducted away rapidly through the shell 66, plate 64, and sheet metal covering 34). The cooling takes place progressivcly from the bottom up, the water being discharged through pipes 42 to drain. Some cooling occurs due to conduction through the male half 62 into the ribs but the amount of heat transfer in this way is relatively small due to the small contact area through the rib edges. The pressure is maintained while the cooling is taking place and until the casting has completely solidified. The Cup 74 is removed from the sprue opening 72 by twisting and thus shearing the metal in the sprue. Then the press is opened and the mold halves are stripped away from the casting. It is important that cooling take piacc progressively from the bottom up. This procedure insures and adequate supply of molten metal to 'all sections of the mold, the metal flowing under tl e force of gravity, applied external pressure and the natural drawing ac ion that occurs due to dendritic formation of capillary spaces Within the crystalline structure of 1c metal. Ar; metal shrinks during cooling, molten metal from the cu 74 flows into the voids under the action of the forces mentioned.

Furthermore, it is necessary to cool from the shell or female side of the mold sandwich to insure dense metal structure. Impurities, voids or starved areas within molten metal are always present in the portion of the casting which is last to solidify. By cooling the side adjacent the shell, the impurities, voids and starved areas are confined to the opposite side, which will be shaved off after removal from the mold in the shaving operation.

From the foregoing description it is apparent that we have provided a process and apparatus which results in a printing plate having a dense, uniform structure, which is uniform in thickness and accurately curved. Because the plates are accurately formed, they are particularly suitable for color printing because proper register can be maintained. Excessive finishing required after casting and the necessity for shirnming the plate when it is applied to the cylinder is a source of poor registry and, of course, this is substantially eliminated by our method and apparatus for producing the plate.

It will be appreciated that various modifications of our invention, as illustrated herein, may be made without departing from the scope and spirit thereof. It is, therefore, our intention not to limit the invention other than as necessitated by the appended claims.

We claim as our invention:

1. In an apparatus for pressure casting printing plates, a platen press having complementary convex and concave supporting surfaces, a male mold half comprising a curved plate having a marginal frame-like spacer, a female mold half comprising a complementary curved plate and adapted to carry a thin electrotype shell, said plates being separate from said supporting surfaces, said supporting surfaces comprising opposed parallel spaced ribs, the edges of which are accurately curved to insure the formation of an accurately curved mold cavity marginally enclosed by said spacer between said halves when said platens are closed and said edges are engaged with said plates, said spacer having a plurality of sharp parallel edges adapted to become embedded in the surface of said shell to seal said cavity, cooling means associated with said concave supporting surface for conducting heat from said cavity through the female mold half, a filler conduit communicating with said cavity, and means for applying fluid pressure on a casting in said cavity.

2. The apparatus of claim 1 in which said cooling means comprises an enclosed container about said concave supporting surface having conduits connecting thereto for circulation of cooling fluid to cool progressively from the bottom up.

3. The apparatus of claim 1 in which said means for applying fluid pressure connects to said filler conduit.

4. The apparatus of claim 1 including means for detachably securing said male and female mold halves together.

5. The apparatus of claim 1 wherein said filler conduit connects to said male mold half.

References Cited in the file of this patent UNITED STATES PATENTS 672,859 Ringler Apr. 23, 1901 915,021 Dunton Mar. 9, 1909 1,286,323 Hopkins Dec. 3, 1918 1,314,275 LeCrone Aug. 26, 1919 1,614,479 Leinweber Jan. 18, 1927 1,922,514 Wilson Aug. 15, 1933 2,016,283 Huck Oct. 8, 1935 2,109,207 Bungay Feb. 22, 1938 2,131,062 McBride Sept. 27, 1938 2,236,212 Huck Mar. 25, 1941 2,344,363 McWane Mar. 14, 1944 2,679,079 Lyons May 25, 1954 2,748,433 Preston et a1. June 5, 1956

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