US3541642A

US3541642A - Casting machine

Info

Publication number: US3541642A
Application number: US716397A
Authority: US
Inventors: Eugene L Bernardi; William F Turner
Original assignee: Reichhold Chemicals Inc
Current assignee: Reichhold Chemicals Inc
Priority date: 1968-03-27
Filing date: 1968-03-27
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24
Also published as: DE1915238A1; FR2004799A1; CH494123A; GB1183807A

Description

Nov. 24, 1910 v g, BERNARD'. m. 3,541,642

CASTING MACHINE Filed March 27, 1968 2 Sheets-Sheet 1 INVENTOR WILLIAM F. TURNER EUGENE L. BERNARDI BY M, iii/a, 13%- 2 ATTORNEYS United States Patent O 3,541,642 CASTING MACHINE Eugene L. Bernardi, Oakland, Calif., and William F.

Turner, Springdale, Conn., assignors to Reichhold Chemicals, Inc., White Plains, N.Y., a corporation of Delaware Filed Mar. 27, 1968, Ser. No. 716,397 Int. Cl. B29f 5/00 US. C]. 18-17 4 Claims ABSTRACT OF THE DISCLOSURE A casting machine for casting relatively thin flat plastic articles made of a thermosetting plastic material having a flat horizontally extending lower platen, a form on the lower platen on which a liquid plastic material is poured, and a movable upper platen closing with the lower platen with a hinge-like movement and having cutting means on the rear and side edges thereof for engaging the form and cutting oif relatively thick excess plastic flashing which may extend beyond the form in order to prevent any cracks forming in the solidified flashing from extending into the cast article.

BACKGROUND OF THE INVENTION This invention relates to casting machines and more particularly to a plate casting machine used in the manufacture of plastic printing plates.

Some plastic printing plates have heretofore been made in casting machines having a horizontally extending flat platen and a moveable upper platen which closes with the lower platen with a hinge-like or clamshell movement. The lower platen is such machines carries thereon a matrix which is a reverse image of the plate to be cast and which is clamped to the lower platen by a clamping ring. A liquid resin to which a thermosetting polymer has been added is poured onto the matrix and the upper platen moved to a closure position after which the resin is allowed to set. Because the matrix usually contains raised and lowered portions corresponding to type or etched lines of a printing plate and because of the viscosity of the liquid resin, flow of the liquid resin over the complete plate can be impeded which, unless precautions are taken, can result in voids or air bubbles being contained in the cast plate. It is extremely important that the plates contain no entrapped pockets of air since this would produce a marred surface on the plate and result in faulty printing.

It is also extremely important that the plates produced be of an exact predetermined thickness to assure accurate printing since plates having printing portions which are too thin will not print clearly. This requirement further necessitates the liquid plastic completely filling the mold cavity existing between the upper platen and the matrix when in the closed position.

A difliculty existing in flat bed casting machines as explained above when used to cast printing plates is that the amount of plastic needed to produce a plate may vary considerably depending upon the amount of matter to be printed. Thus a plate representing a solid printed page on which a large amount of printed matter appears will require considerably more plastic than a plate representing a page on which little printed matter appears with the amount of plastic varying in some instances on the order of 30%. Metering of the exact amount of liquid resin onto a matrix is impractical because of the difficulty in determining changes in volume of plates having different printing portions.

In order to assure that the plate will be of suflicient thickness not withstanding the amount of printing portion on the plate and to minimize voids occurring, it has been the practice to pour an amount of liquid resin onto the matrix in exces of that required to produce a plate having a solid printing portion. Excess resin between the upper platen and matrix is then forced out the sides of the space between the two platens and out the open end between the platens as the upper platen is closed. The excess liquid resin is held in a flashing area formed between the matrix and a clamping ring clamping the outer portions of the matrix to the lower platen such that the ring acts as a coffer dam. This excess flashing is then trimmed from the plate after casting. However, this method of assuring that sui'ficient liquid resin is poured onto the matrix presents further problems in plate manufacture. Often cracking will occur in the flashing as the liquid resin solidifies due principally to the fact that the flashing is heavier and thicker than the plate being cast with the result that there is a difference in heat exotherm between the flashing and plate. These cracks have a tendency to extend into the plate thus producing a faulty printing surface.

- It is therefore an object of our invention to provide a positive means whereby any cracks which may form in the flashing comprising the excess liquid resin may be prevented from extending into the printing plate. Broadly this is accomplished by having a first cutting bar positioned on the rear of the platen which will engage the matrix as the platen is lowered. Second and third cutting bars extend along the side edges of the upper platen to adjoin the rear cutting bar so that as the upper platen is lowered, these cutting bars will also engage the matrix and sever the excess flashing from the plate portion. The bars thus provide a positive stop means for preventing any cracks that may form in the excess flash portion upon solidification thereof from extending into the plate portion. The cutting bars are provided with a knife edge in order to facilitate passing through the liquid resin to engage the matrix and further are provided with a smooth surface such as by chrome plating to assure that solidified plastic may be easily stripped therefrom. The knife edge of each bar extends below the engaging surface of the upper platen by at least an amount equal to the thickness of the non-printing areas of the plate. Preferably the bars extend down a small additional amount to assure their contacting a matrix of less than usual thickness with the bars cutting a small amount into matrices of normal thickness. The open or front end of the upper platen does not have a cutting bar thereon as this would prevent escape of air from the mold cavity during the last few degrees of closure of the upper platen. Instead, the front end of the upper platen is provided with a bar that extends slightly below the platen and which has a hook portion proturding therefrom about which plastic flashing may solidify in order that the plate may be stripped from the matrix when the upper platen is raised.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a casting machine made according to the invention illustrating the upper platen in the open position and placement of the cutting bars on the upper platen;

FIG. 2 is an enlarged cross-sectional view of FIG. 1 taken along lines 11-11 but with the upper platen in the closed position; and

FIG. 3 is an enlarged cross-sectional view of portions of FIG. 1 taken along lines HIIII but with the upper platen in the closed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there is illustrated a casting machine 1 having a movable flat upper platen 2 and a flat horizontal platen 3. The upper platen 2 is mounted by means of frame 2' and arm 4 to a shaft 5 which corresponds to a hinge line such that the upper platen may close with respect to the lower platen with a hinge-like or clamshell motion wherein the rear end of the platen adjacent the shaft 5 closes before the front or open end of the platen. Power closure means, not shown, are provided for rotating the shaft 5 to raise and lower the platen.

A matrix M is positioned and held onto the lower platen by a clamp ring 6 as more fully explained hereafter. The matrix area defined by the ring 6 is greater than the area of the upper platen 2 such that the flat engaging surface 7 of the platen will be contained within the ring 6 when the upper platen is in the fully closed position.

A first cutting bar 8 extends along the rear end of the upper platen as shown in FIG. 1 and is adjoined by second and

third cutting bars

9 and 10 which extend along the sides of the upper platen. As shown in FIGS. 2 and 3,

cutting bars

9 and 10 are mounted to the block by means of bolts 11 with precise and exact setting of the bars being achieved by stop screws 12 contained in the upper platen frame 21. Bar 8 is mounted on the platen in the same manner as

bars

9 and 10.

The cutting bars each have a knife edge 16 which extends below the engaging surface 7 of the upper platen an amount equal to at least the thickness of the nonprinting area N of the plate P and preferably a slightly additional amount to assure engagement with a mat of less than normal thickness.

Adjustable stops, not shown, limit the downward movement of the upper platen with respect to the lower platen in order that the thickness of the printed plate (i.e. distance from the backside of the plate to the top of the printing portion P of the plate) may be precisely con trolled.

The bottom platen 3 is mounted to the machine frame 20 by bolts 22. Both the upper platen and lower platen have

passages

23 and 24 respectively through which a heating medium may flow in order that the temperature of the platens may be brought up to a predetermined temperature prior to the resin being poured onto the low er platen. The bottom platen in addition is provided with passages 25 connecting the subpassages 26 in turn joining with grooves 27 on the upper surface of the platen 3. Passages 25 are connected to a source of vacuum in order to initially position and hold the matrix M on the surface of the lower platen prior to the locking of the matrix on the platen by the clamping ring 6.

Mat clamping ring 6 is movable up and down in a vertical direction and has thereon a knife edge 30 which may firmly engage the outer portions of the mat. As shown in FIG. 3, the ring-6 also also serves as a coffer dam to contain a flashing 31 formed from excess liquid resin squeezed from the space between the engaging surface 7 and the matrix when the upper platen is closed. The size of the flashing 31 varies with the plate to be cast. As the same amount of liquid resin is poured onto the matrix each time a plate is made, there will be a greater excess of unused resin when a plate having a small amount of printing portion P is cast than when a plate having a greater amount of printing portion is cast. Since the thickness of flashing 31 is greater than that of the cast plate P, it has a much higher exotherm, which, when the resin solidifies, results in small cracks being formed in the flashing, which have a tendency to extend into the printing area of the plate. The cutting bars provide a positive mean for preventing extension of any cracks from the flashing into the printing area as they sever the flashing from the printing plate.

The front side of the upper platen has a stripper bar 35 thereon having a hook portion 36 about which the liquid flashing may solidify in order that a cast plate may be stripped from the matrix as the upper platen is raised. The bottom end of the stripper bar extends down beyond the engaging surface 7 of the upper platen but not as far down as the cutting bars nor so far as to engage a matrix. This is to assure that an opening remains between the upper platen and matrix through which air may escape as the upper platen closes.

While we have described a preferred embodiment of our invention as applied to printing plate casting machines, it is apparent our invention would have utility with other flat bed casting machines used for casting thin articles. Further, it is apparent that slight structural changes could be made to the machine described and still come within the scope of the invention which is described in the claims hereto.

We claim:

1. A plate casting machine for casting a plastic printing plate made of a thermosetting liquid plastic material, said machine having a heated lower platen, a matrix clamping ring for clamping a matrix to said lower platen and for providing a coffer dam for containing liquid plastic flowed onto said matrix, a heated upper platen mounted for closing engagement with said lower platen with a hinge-like movement along a hinge line adjacent the rear end of said upper and lower platens, and closure means for moving said upper platen about said hinge line; the improvement which comprises having a first cutting bar positioned on the lower surface of the upper platen at the rear thereof adjacent and parallel to the hinge line and second and third cutting bars adjoining said first cutting bar and extending along the sides of said upper platen whereby when the upper platen closes with respect to the lower platen, said bars will engage a matrix within a matrix area bounded by said clamping ring such that excess plastic flashing between said cutting bars and said matrix clamping ring will be sheared off to prevent any cracks that may occur in said flashing upon solidification thereof from extending into a cast plate.

2. A plate casting machine according to claim 1 wherein the portion of each cutting bar contacting a matrix comprises a knife edge.

3. A plate casting machine according to claim 2 wherein the improvement comprises in addition having the cutting bars chrome-plated to facilitate release of solidified plastic from the surfaces of said bars.

4. A casting machine for casting thin flat articles made of a thermosetting plastic material wherein said machine has a heated flat horizontally extending lower platen for receiving a form thereon, a heated flat upper platen, means movably supporting said upper platen for pivotable movement about a rear end thereof and about a rear end of said lower platen to open and close the upper platen with respect to said lower platen, closure means for moving said upper platen to open and close positions with respect to said lower platen, and a form holder for clamping the peripheral edges of a form into said lower platen wherein the area bounded by said form holder is greater than the area bounded by said upper platen and whereby said form acts as a coffer dam to contain liquid plastic on said matrix; the improvement which comprises having cutting bars extend along the rear and side edges of said 6 upper platen to engage said form near said form holder 2,718,029 9/1955 Collins 18-17 when said upper platen is in the closed position to cut 2,734,227 2/1956 Costick et a1 18- 39 off excess plastic flashing extending between the form and 2,929,104 3/ 1960 Hutton 1839 the sides of the upper platen in order to prevent any cracks 3,161,911 12/ 1964 Mathews 1817 X formed in said excess flashing upon solidification thereof 5 3,264,382 8/1966 Angeli et al. from extending into the cast article. 3,408,695 11/1968 Scott 18-39 References Cited J. HOWARD FLINT, JR., Primary Examiner UNITED STATES PATENTS US. Cl XIR. 1,908,681 5/1933 Bronson 1817 10 1g 5 39 42 2,071,646 2/1937 Melind 18-44