US1727259A - Method fob - Google Patents

Description

Sept. 3, 1929. L. c. TURNOCK 1,727,259

METHOD FOR THE PRODUCTION OF PRINTING PLATES FROM ELECTROTYPES Filed March 3, 1927 INVENTOR Patented Sept. 3, 1929.

UNITED STATES LAWRENCE C. TURNOGK, OF CLEVELAND HEIGHTS, OHIO.

METHOD FOR THE PRODUCTION OF PRINTING PLATES FROM ELECTROTYIPES.

Application filed March 3, 1927. Serial No. 172,345.

The present invention relates broadly to the art of forming printing plates from electrotypes, and more particularly to a method and apparatus whereby the production there of is expedited, the quality improved and the cost materially reduced, while at the same time, establishing operating conditions such that the work is accomplished more easily by the various operatives.

At the present time, it is customary in the art to which this invention relates to place the copper or nickel electrotype, shells to be backed up with elect-rotype metal in a comparatively heavy iron pan, the copper shells having first been fluxed with a suitable material, such, for example, as zinc chloride, and then covered as to one face thereof with tin-foil. This heavy pan is then bodily lowered mechanically into contact with the surface of a bath of molten metal and permitted. to remain in contact therewith for a sutficient length of time to completely heat the iron pan and in turn have it transmit its heat to the copper shell and in turn to the tin-foil for the purpose of melting the tinfoil and causing it to firmly adhere to the surface of the copper. It is customary to retain the bath of molten metal at a temperature materially higher than its melting point in order to have sufficient heat available for heating the iron pan and transmitting this heat to the copper shell through the surface film of the iron pan which is subject to oxidation and exhibits a low degree and rate of heat transfer. This increased temperature is not only costly to maintain but results in the formation of a considerable amount of metal dross due to oxidation, the dross formation being roughly proportional to the temperature at which the bath is maintained.

After the tin-foil has become melted, the pan is bodily removed to a suitable rack, and the molten backing metal from the bath is ladled into the pan to a predetermined depth. Thereafter, the pan and its contents are artificially cooled to solidify the backing metal, and the operation is repeated with new copper shells.

Due to the relatively poor contact as between the surfaces of the iron pan and the copper shells, the rate of heat-transfer be tween the two metals is necessarily low. In order to insure a uniform temperature in each the shells within the and thereby obtain a uniform rate of melting of the tinfoil, it is necessary to raise the copper shell to a temperature higher than would be reqnired, were it possible, under such conditions, to transmit heat more uniformly thereto.

The present invention has for one of its objects the provision of an improved method and apparatus whereby the copper shells may be uniformly heated to a temperature sufliciently high to melt the tin-foil uniformly over the entire exposed surface thereof without heating the shells themselves to a temperature as high as has heretofore been required under the conditions of operation now existing.

A further object of the invention is to provide a method of heating the shells that is subject to positive control whereby the maximum temperature conditions may be predetermined and the heat held within such limits.

A still further object of the invention is to avoid the necessity of heating the bath to an excessively high temperature, the formation of dross being correspondingly decreased and the consumption of fuel likewise diminished.

Still another object of the invention is to provide an apparatus for carrying out these operations, which apparatus may be comparatively easily transported and handled,

and which may be operated in such manner that a large percentage of the heatheretofore lost during the artificial cooling re ferred to is conserved and rendered available for the subsequent heating operation.

The accompanying figure of the drawings illustrates more or less diagrammatically in cross section one form of apparatus by means of which the present invention may be carried out and the objects referred to attained, it being understood that the drawings are illustrative only and do not define the limits of my invention, as changes in the construction therein disclosed may be made without departing either from the spirit of the invention or the scope of my broader claims.

In the drawings, there is illustrated a shell-receiving, heating and casting receptacle, comprising an outer shell 2 of suitable material of such nature as to withstand the usage to which it is subjected to be. selfsupportiiigi Within the shell 2 is a bodytl of heat-insulating material limiting the transmission of heat downwardly from within the receptacle to the shell. Above the insulating material 3 is a suitable electrically heated element 4 of the resistance type receiving a; supply of electrical energy from any desired source through a suitable heatresponsive means 5 of the character shown, for example, in the patent to John A. Spencer for thermostat, No. 1,448,240, dated March 13, 1923.

The receptacle may be of any desired depth and is adapted to receive therein the copper shells 6 having suitable flux applied thereto, as referred to, and having layer of tin-foil 7 thereover.

After the plates have been placed in position within the receptacle, the current may be manually turned on, whereby the heating element becomes effective for heating the plates. This heatis preferably transmitted to the plates through a layer 8 of heat-transmitting material having a high coefficient of heat transfer, and preferably having an extremely smooth and highly polished surface 9 in contact with the plates. Such a surface may be obtained, for example, by the use of a chromium coating on a suitable steel or alloy backing. By reason of the intimate contact thus permitted be tween the plates 6 and the surface 9, heat is uniformly transmitted to the shells for effecting the melting of the, tin-foil 7 The thermostat or heat-responsive means 5 will. be so set as to limit-the maximum temperature to which the casting pan may be raised, thereby preventing any unnecessary expenditure of electrical energy. When this temperature has been attained, the heat-responsive means will automatically function to break the circuit. The plates 6 at this time will be in condition to receive backing metal 10, which may be supplied to the receptacle in any desired manner and to the depth de sired.

The thermostat will preferably be so set that after it has functioned to cut-oil the supply of current" to the heating element, it will not again function to establish the circuit until the ten'iperature conditions within. the receptacle have dropped to a point snflic-iently low'to permit solidification of the metal 10. At this time, it will be removed bodily with the plates 6 and fresh shells will be placed in position within the receptacle ready for a succeeding operation.

It will be apparent that the heat-responsive means thus controls the maximum temperature, thereby being effective automatically for reducing current consumption. and that it likewise controls the low limit of temperature, whereby the heat within the receptacle is conserved to as great an enter t as is consistent with the proper solidification of the material 10. Under such conditions, the

bath from which the material 10 is supplied may be kept at any desired temperature, irrespective of the necessity for utilizing the same as a heating medium for the plates. Also, the shells themselves do not have to be raised to as high a ten'iperature, due to the uniform transfer of heat thereto, and their likelihood to Warping and buckling is correspondingly lessened. These results are accomplished, together with a uniform melting of the tin-foil 7, such that when the molten metal 10 is supplied to the casting pan an extremely tight bond is established between the same and the copper shells, which bond is uniform throughoutthe entire area of the shells. The operation, therefore, results in a better electrotype than has heretofore been obtained with the ten'iperature conditions controlled automatically.

)ther advantages of the invention arise from the provision of an electrically heated casting pan, and also from the provision of ieatnfesponsive means for automaticall controllin the upper and lower temperature conditions therein.

Still other advantages arise from the provision of the use of a heat-transfer material having a surface of such nature that heat is uniformly transmitted therefrom to the electrotype shells and oxidation of its surface eliminated, thereby maintaining a maximum rate of heat-transfer as between the surface of theta-sting pan and the copper shells.

I claim:

1. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat-conductingand supporting contact bet-ween the entire surface area of one side of a copper shell and a preformed heating surface, adding flux to a portion of said shell, placing tin-foil thereon, applying controlled heat to said heating surface to effectuni form melting of the tinfoil, and then adding the backing material to the shell.

2. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat-conducting and supporting contact between the entire surface area of one side of a copper shell and a preformed heating surface, adding a flux to a portion of said shell, vlacinp; tin-foil thereon, electrically heating said heating surface to effect a uniform melting of said tin-foil, and then adding the backing mate rial to the shell.

3. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat-conducting and supporting contact between the entire surface area of one side of a copper shell and a preformed heating surface, adding a fin): to a portion of said shell, placing tin-foil. therein, heating said heating surface, controlling the maximum amount of heat available for heating duty, and then adding the backing material to the shell.

4C. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat-conducting and supporting contact between one entire surface of a copper shell and a preformed heating surface, insulating said heating surface in one direction, applying flux to said shell, adding tin foil thereto, heating said surface from a point intermediate said shell and the insulation for said surface, and then adding the backing material to the shell.

5. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat-conducting contact between one entire surface of a copper shell and a heating surface, insulating said heating surface in one direction, applying flux to said shell, adding tin-foil thereto, heating said surface from a point intermediate said shell and the insulation for said surface, controlling the heating of said. sur face to maintain the temperature thereof within definite limits, and then adding the backing material to the shell.

6. In the method of producing printing plates, the steps comprising establishing an intimate and uniform heat conducting and supporting contact between the entire surface area of one side of a copper shell and a preformed heating surface, adding a flux to the back portion of the shell so supported, placing tin foil thereon, applying heat to said heating surface to effect uniform melting of the tin foil, controlling the application of said heat to maintain it Within a definite temperature range, and adding a backing material to the shell after the shell, flux and tin foil have been heated to the desired temperature.

7. In the method of producing printing plates, the steps comprising uniformly supporting a copper shell, uniformly heating the shell While so supported, and controlling the heating of said shell to maintain it Within a definite temperature range.

8. In the method of producing printing plates, the steps comprising uniformly supporting a copper shell, and heating the shell uniformly throughout its entire area while so supported.

In testimony whereof I have hereunto set my hand.

LAWRENCE C. TURNOCK.

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