US2136840A - Electrotype plate and method for making the same - Google Patents

Description

NOV. 15, 1938. BUCKLER I v 2,136,840

ELECTROTYPE PLATE AND METHOD FOR MAKING THE SAME Original Filed Oct. 5, 1935 Jul/62%;": Q a/Zcmc/ 620066197? Patented Nov. 15,

a 2,136,84li

PATENT? OFFICE ELECTROTYPE P ATE ANIl METHOD FOR" MAKING THE SAME Rowland Buckler, Chicago, Ill.

Application OctolJer 5, 1935, Serial No. 43,792

Renewed April 11, 1938 12 Claims.

Myinvention relates to means and methods of producing electrotype plates and the like, and my main object is to produce aplate which is inherently firm throughout, whereby to withstand the strains of prolonged use without becoming in anyway deformed or deficient.

A further object of the inventionis to produce a plate of the abovecharacter by casting it in the curved form required for mounting it on the press cylinder, whereby to eliminate the factor of stretch'contended with in plates formed by the bending process.

A still further object of the invention is to employ a novel method for casting the plate,

l5 whereby to eliminate surface deficiency, body porosity and undue shrinkage.-

Another object of the inventionis to provide a unique mold for the casting of the plate, the mold having peculiar structural and functional values conducive to the results contemplated above. a w

A further object is to provide an improved method and mold for casting metal.

, With the above objects in view, and any others which may suggest themselves from the description to follow, a better understanding of the invention'may be had by reference to the accom'panying drawing in Which .Fig. 1 is a perspective view of a typical curved electrotype plate;

Figures 2, 3 and 4 are schematic cross-sections of the novel mold in three positions of use;

and

a Fig. 5 is a section on the line 55 of Figure 3.

5 Inthe 'production'of electrotype plates, two methods have generally been followed. By one method, the plate is cast flat and later given its curvature in a hot bender. By the other method,

, a mold of the requiredcurvature is employed to cast: the plate, this method having the advantage that stretch usually present in the plate formed by'thebending process is eliminated.

Whatever the process employed for producing the conventional electrotype plate, failure develops'during the use of the plate at one point or another, whereby to render the printing imperfect. The failure is characterized by the collapse of the plate surface in regions Where its resistance is poor by theinherent structure of the plate or as alresult of pressure encountered during the printing action. Actually, the condition just described is due to the porosity of the plate throughoxidation a'tthe time it is cast, and to irregular places in the surface of the plate as caused by uneven shrinkage as it cools. Whatever the methods may be which havebeen followed in the casting of electrotype plates, they seemto employ conventional practices already known in the casting art and unsuitable for the production of a perfect plate. a l

In contemplating the function of an electro: type plate, its main attribute is that it must be sufficiently hard to form a solid backing for the copper shell which forms its facing or printing surface. Ordinarily, a lead alloy is employed as the metal for the plate, since such metal lends itself more readily to uniting with the soldercoated inner surface of the copper shell. However, zinc or an alloy thereof is also quite suitable. Y

In my method, I prefer to cast the plate in a curved mold, whereby to eliminate at the start the stretching factor. The theory of my mold and method therefore concerns itself with overcoming or eliminating porosity and shrinkage. Thus, by determining the causes of these factors and creating a means and method wherebythese causes are diverted from the plate as it is being cast, a product having desirable qualities and no defects may be obtained. r

Porosity in the conventional electrotype plate is theresult of pouring the molten metal directly into the cavity in which the plate is to be cast or in such a manner as to reach the cavity in a turbulent or agitated state. Obviously, the molten metal absorbs a considerable'amount of oxygen by its passage intothe mold, and such absorption is increased where the metal within the mold is agitated by the incoming stream. The oxide compound formed within the mold is prevalent throughout the casting, making the plate porous. It is therefore seen that a plate socast is not actually solid,'as it contains innumerable trapped air and gas pockets, and is subject to breaking down in portions of its surface as pressure of use is applied.

Secondly, a plate made by conventional methods contends with the factor of uneven shrinkage. One reason for such shrinkageis poor conductivity of heatin the metal from which the mold is made as the plate is being cast and begins to cool. In other words, with the mold heated and of ordinary metal--such as iron more heat may occur at one point than another, such heat being unevenly transmitted to the casting, and therefore causing the plate to shrink faster in one region than in another. The result of this action is to cause low spots in the plate surfaces, so that the plate isnot only defective by porosity from the casting process but also; by the presence of irregular or uneven regions in its surfaces. To counteract uneven shrinkage, the practice has been to hammer the plate from points on its back behind the low spots, so as to raise these even with the general surface.

In developing the novel mold I have corrected the above deficiencies by a peculiar mold construction and a different casting method. Thus, by specific reference to the drawing it is seen that the base I and the top I I of the mold are mainly of the same and part-cylindrical form suitable for the casting of the curved plate I2 indicated in Figure 1. It is seen that the base I0 is slightly sunken to receive the copper facing shell I3. However, in the region of the mold entrance I4, it is seen that the mold base Ill first takes a slight incline Illa, and then has a considerable drop to form a trough III!) which rises along its outer side to terminate with a backward lip I00 along the entrance I4. At the opposite end, the mold also takes a slight offset Hid, terminating with an upward and dilated trough I06. It is seen that the origin points of the deflected portions I00. and Id form the terminals of the actual plate mold, such terminals later defining the lines along which the plate is cut off from the entire casting. It is seen in the section of Figure that the sides of the mold top II have flanges IIa overlapping those of the base, such flanges resting on the copper shell I3 and holding the same down. The mold top also has dowel lugs I5 depending into registering cavities in the base to keep the mold sections from shifting relative to each other. Clamps or other suitable securing means are provided, as is the usual practice in the molding art, to make the mold rigid.

The novel mold is ready, as positioned in Fig. 2, for the molten plate metal to be poured in by way of the entrance I4. It may be assumed that the metal on its way to and entering the trough Illb will draw and absorb a certain amount of air. This air, being lighter than the metal, will rise through the same as the level of the metal gains height in the trough and escapes through the entrance I 4 quite in the same manner as bubbles rise and escape from a container of water when more water is added from above. However, what air cannot escape through the entrance I4 will become lodged immediately under the top of the mold, there combining with the metal to form particles of slag or dross, which is an oxide of the metal in the trough.

In Figure 2, the body of liquid metal in the mold has reached its maximum height, and in order to permit more metal to be poured in, I cause the mold to be rocked downwardly toward the right, continuing to pour the molten metal into the entrance I4. It will now be evident that the metal in the lower part of the trough IIlb assumes a force or forms a head toward creating a fiow into the plate cavity ofthe mold. As this occurs, the slagv or floating oxide found at A in Figure 2 is caused to move forward and keep ahead of the metal flow, as indicated in Figure 3. This flow being simply a transfer from the trough IIlb into the plate cavity without any agitation or absorption of air in transit fills the mold cavity without forming the objectionable slag, so that the faces of the casting are purely of the plate metal and not converted into the oxide. The mold is further rocked to the position of Figure 4 in order to finish the process, the metal rising through the trough IOe, with the layer of slag on the surface.

Two factors contribute to the smooth fiow of the metal through the mold, one being the fact that the mold is heated and made of a metal having a rapid rate of heat conductivity, such as bronze, and the other that the rocking of the mold promotes the motion of the metal by gravity. Thus, the mold is uniformly hot before pouring begins, and the rocking action is radual, although it will be understood that the entire process is necessarily brief in order that the metal remain in the uniform fiuid state as it fills the mold. Also, the special form of the mold has an influence in this respect by the provision of the terminal troughs I01) and IlJe. It is possible that the metal in the trough IIlb' may have more or less porosity when the pouring has been finished, since no further fiow from the trough is had; also, the metal in the trough We may have absorbed some air by its contact with the outlet and also suffered a change from the slight cooling effect occasioned by such contact. However, the metal in the plate cavity is between the two troughs and therefore confined where no air contact occurs. It may consequently be assumed that the metal in the plate cavity is of uniform density and smooth texture.

Another factor taken into consideration in the design of the mold is that of shrinkage. Ordinarily, shrinkage is allowed for by dimensioning the mold cavity accordingly, and it may therefore be assumed that the plate will suffer a normal amount of shrinkage after it has cooled. However, the fact that the mold is made of bronze or other metal having a rapid rate of heat conductivity assures the uniform heating of the mold along the plate cavity and therefore the uniform shrinkage of the plate. A further characteristic of shrinkage is that its rate is proportionate to the cooling time of the casting. Therefore, it is expedient that the plate cool quickly in order to v suffer as little shrinkage as possible. By means of the novel mold, the metal in the region of the plate cools more rapidly than that of the casting in general, since the relatively larger bodies of metal in the troughs We and Illb take so much longer to cool. By this analogy it is evident that the shrinking rate of these bodies will be greater than that of the metal in the plate cavity, and that the plate will therefore have relatively less shrinkage than its terminal enlargements. Another factor helpful in cooling the metal of the casting more rapidly is that the metal of the mold is relatively cooler both at the start and afterwards than the metal of the casting, so that the mold itself is a cooling influence on the latter. Finally when the casting has cooled, it is a simple matter to saw the terminal enlargements away from the cast plate and transfer them to the melting pot.

It will be'evident from the above description that I have provided a novel mold and process which make it possible to produce a firm, solid and smooth electrotype plate. Not only is the peculiar design of the mold essential to procure a desirable plate as an intermediate element formed by the uniform action of the molten metal in a confined state, but the end portions of the mold also serve as guards to retain such influences as would change the balance or prejudice the uniformity of the process. The latter is, at the same time, of extreme importance since it procures the shifting of the undesirable slag or dross in a forward direction to met the air in the unfilled portion of the mold and gather even more, to be removed finally to a zone distant from the plate cavity and where quality of the metal is of no concern. Moreover, the process is significant by the gradual fall or rocking movement of the mold whereby to create a pressure or head for the metal going into the plate cavity without agitation or air contact, such flow coming from the bottom of the reservoir in which the metal initially accumulates. Finally, it will be evident that the novel mold is built along lines of extreme simplicity, making it inexpensive to produce and operate.

While the novel means and method have been described as applied to electrotype plates, the same are equally applicable to stereotype plates and any other articles. for which the novel casting process and equipment are suitable, and it is understood that I am including all such articles as coming within the scope of the appended claims.

I claim:

1. A mold comprising a base formed with upwardly extended end portions, one of such end portions having a return bend formed thereon to overlie a portion of said base, and a top for said mold adapted to be supported on said base and spaced centrally therefrom, the ends of said top terminating short of said end portions to provide at one end a space between the same and the free edge of said return bend to form an. entrance to the mold and to provide at the other end a space adjacent the opposite end of the mold as a final gate cavity therefor.

2. A mold for casting molten metal, said mold being closed at the top and sides and open at both ends, one'end being normally positioned on a lower plane than the other end, said molds being adapted to be tilted gradually to position both ends on the same horizontal plane, means for continuously supplying molten metal to said lower end during the entire tilting operation to cause said metal to rise progressively in said mold to fill the same, and an open extension on said second named end of said mold, said extension being positioned above the plane of said mold.

3. A mold for casting molten metal, said mold being closed at the top and sides and open at both ends, one end being normally positioned on a lower plane than the other end, said mold being adapted to be tilted gradually to position both ends on the same horizontal plane, and means for continuously supplying molten metal to said lower end during the entire tilting operation to cause said metal to rise progressively in said mold to fill the same, said mold being arcuate in section.

4. The structure of claim 3, and an open extension on said second named end of said mold, said extension being positioned above the plane of said mold.

5. The structure of claim 2, and said means for supplying molten metal to said mold comprising a trough having an open communication with said first named end of said mold.

6. The structure of claim 3, and said means for supplying molten metal to said mold comprising a trough having an open communication with said first named end of said mold.

7. The structure of claim 3, and said means for supplying molten metal to said mold comprising a trough having an open communication with said first named end of said mold, and an open extension on said second named end of said mold, said extension being positioned above the plane of said mold.

8. The method of casting metal into an upwardly inclined mold cavity comprising the pouring of the molten metal into a trough having an open communication with the lowest point of said mold cavity, tilting said trough and mold jointly while continuing to pour metal into said trough to cause said metal to rise in said cavity up the incline towards the highest point thereof until said cavity is filled and stopping said pouring and tilting when said highest point and said lowest point are on substantially the same horizontal plane.

9. The method of casting metal into an elongated and arcute mold cavity which is arranged to have one end thereof higher than the other, comprising the introduction of the molten metal into substantially the lowest point thereof, tilting said mold continuously as said metal is introduced to cause said metal to rise in said cavity up the incline thereof towards the highest point of said cavity until said cavity is filled, and stopping said tilting and the introduction of said metal when said highest point and said lowest point are on substantially the same horizontal plane.

10. The method of casting metal into an elongated and upwardly inclined mold cavity, comprising introducing said molten metal into substantially the lowest point of said mold, tilting said mold continuously while continuing to introduce metal to said lowest point to cause said metal to rise in said cavity towards the highest point of said mold until said cavity is filled, and stopping the introduction of metal and said tilting when said highest point and said lowest point of said mold are on substantially the same horizontal plane.

11. The method of casting arcuate metal plates with a minimum shrinkage factor, comprising the forming of the actual casting as a medial unit, forming terminal units of considerably greater cross section than said medial unit on either end of said medial unit, and positioning both of said terminal units on a plane above that of said medial unit.

12. A mold comprising an initial portion into which the metal is poured, a medial portion for the actual casting, said medial portion being of arcuate section, a final chamber for an extra casting portion, said initial portion and final chamber being of considerably greater cross section than said medial portion, and both said initial portion and final chamber being positioned on a plane above that of said medial portion.

ROWLAND BUCKLER.

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