US1544929A - Method of casting - Google Patents

Description

July 7,1925. v 1,544,929

c. PACK METHOD OF CASTING Filed Dec. 1.. 1922 2 Sheets-Sheet 1 v JG 7 6 I v u "H H l INVENTOR.

ATTORNEYS,

July 7, 1925. I 1,544,929

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TTTTTTTTTT NG Patented July 7, 1925.

UNITED STATES 4 1,544,929 PATENT OFFICE.

CHARLES PACK, OF ELMHURST, NEW YORK, ASSIGNOR TO DOEHLER DIE-CASTING COMPANY, A CORPORATION OF NEW YORK.

METHOD OF CASTING.

Application filed December 1, 1922. Serial.No. 604,122.

To all uihom it may concem.

Be it known that I, CHARLES PACK, a

citizen of the United States, residin at Elmhurst, in the county of Queens and State of New York, have invented certain new and useful Improvements in Methods of Casting, of which the following is a full, clear, and exact description.

The coring, of castings having an undercut in the cored surface presents a particular problem where the undercutting is such as to necessitate a design on the core having sharp edges, thin lips or other like characteristics, the accuracy of which must. be maintained and reproduced in the casting. This applies especially to the art of die-casting, one advantage of. which is that it practically eliminates machining of the castings, and it is therefore requisite that the sharpness of the design or configuration be produced in the casting operation. This requires a metal core and one having a sufficiently high melting point to insure that the thin projections, sharp extremities or the like in the coredesign will not break down during the casting operation.

To render possible the removal of such a core after the casting is poured, my invention contemplates making the core of a metal which will be acted upon by an acid that is inactive upon the metal of the casting, and dissolving the core out of the casting with such. an acid. A good example of a metal for the core is brass which may be dissolved in either nitric or sulphuric acid, while the casting be aluminum or one of the commercial alloys thereof, since aluminum is substantially unaffected by either of these acids in concentrated form. Unless the core is of very small cross-section, it will usually be more practical to machine out the interior of the core and dissolve out only the external shell, but where I refer herein to dissolving the core with an acid, I contemplate dissolving either the entire core or that which is left after the inside has been machined out or otherwise removed.

To illustrate my method I have selected the casting of molds for golf balls by diecasting, but it will be understood that my invention is not limited as to the particular article produced nor as to the metals employed except that they must respond to the requirements above recited.

As is well known, the surface of substantially all golf balls is characterized by a design formed of dimples or small depressions symmetrically and closely arranged. One of the last operations in the formation of the balls is the molding of this design in the surface, the mold consisting of two hemispherically recessed mold parts the molding surface of which has small rounded elevations complementary to the dimples in the surface of the ball. Heretofore these molds have been machined out at comparatively large expense, but my method provides a way to die-cast them, thereby very materially reducing their cost.

In making a golf ball mold in accordance with my invention I first make the core of the necessary size, shape and surface configuration and of a suitable metal, such as brass, and then with a proper die I make the cast about the core, the casting metal being, e. g., an aluminum-copper alloy. I then remove the casting from the die with the core locked therein and bore out the interior of the core, after which I dissolve out the rest of the core with a suitable acid, such as ordinary concentrated nitric acid. Care is preferably taken in this acid treatment not to leave any acid for an unnecessary length of time in contact with the cored surface of the casting after the core is entirely dissolved, for the reason that it will tend to attack the copper content of the alloy and make the surface more or less rough. This precaution is of course unnecessary if the casting be of pure aluminum.

I shall now describe my method with the aid of the accompanying drawings in which I show apparatus suitable for one adaptation of my invention, and shall thereafter point out my invention in claims.

Fig. 1 is an elevation of a core for use in die-casting a golf ball mold.

Fig. 2 is a cross section of the same on line 2-2 of Figure 1.

Fig. 3 is a section of an assembled die with the core in place.

Fig. 4 is an outside elevation of the half die carrying the core.

Fig. 5 is an elevation of the casting and core.

Fig. 6 is a section of the same after the casting has been machined.

Fig. 7 is a section after the core has been reduced to a shell.

Fig. 8 is a section of the mold similar to Figure 7 but showing its appearance after the core is removed.

While the core element shown in detail in Figures 1 and 2 may be formed in any-suitable way, I prefer to turn it from bar stock for reasons which will hereinafter appear, and then machine the dimples in the molding surface. As an example, the bar stock may be brass, since this is soluble in nitric acid or sulphuric acid, and also because it machines easily and yet has a sufficiently high melting point to enable it to retain its surface design at the temperature to which it is subjected during the casting'upon it of a metal suitable for the purpose, such as aluminum-copper alloy.

The core, as shown, has ahemispherical end .1 in which the depressions or dimples 2 are formed in any suitable way, as by ma-' chining, the diameter and surface configuration of the portion 1 being a replica of one half of a golf ball. This hemispherical end merges into a plain, cylindrical zone or bend 3 of proper width, the forward limitation of which is indicated by the dotted diametral line in Figure 1. The purpose of this band is to provide material to allow the face of the mold to be machined off, as will presently appear. Back of the zone 3 the diameter is reduced to form a shank or stem- 4 for anchoring in the die.

The two halves of the die are shown in Figure 3, the one half 5 containing the mold cavity 6 and carrying the core, and the other half 7 containing the gate or sprue opening 8. The mold cavity 6 is shown as undercut, being of substantially frusto-conical shape. Therefore,'the mold 9, as'shown in Figures 5 to 8, has its side Walls thicker at the top than would be the case if the topdiameter were the same as the bottom diameter. Due to the pressure to which these molds are subjected in the molding of golf balls, it is desirable to provide this substantial thickness of wall throughout.

To enable-the removal of the mold 9 from the die, the half 5 of the die is made in tWo parts, dividing on the central transverse line 5, as shown in Figures 3 and 4;

As above suggested a suitable metal for the casting is an aluminum-copper alloy since under ordinary conditions aluminum is not affected by nitric or sulphuric acid in concentrated form, and also because this alloy die-castsvery easily and has considerable strength.

Following the casting operation, the core and casting are removed from the die, ap pearing at that point as shown in Figure 5. The round bosses or elevations on the upper part of the surface of the concavity of the mold 9 interlock with the corresponding dimples in the core face so as to prevent the withdrawal of the core. The mold may now be mounted for machining with respect to the shank or stem 4, and since the core was originally turned, it follows that the mold may be accurataely machined aboutthe axis of the core as a center. In this operation the face of the mold surrounding the core is machined down to-the diametral line of the core, which is the dotted line indicated in Figure 1, thereby reducing the mold cavity to'a-n exact hemisphere while leaving the zone 3 of the core protruding beyond the face of the mold. This condition is shown in Figure 6.

With a core of the size here illustrated it is more economical to cut ofi the stem 4 and grind out the interior of the core, as shown in Figure 7, rather than employ acid to dissolve all the metal of the core. When this has been done ordinary concentrated sulphuric or nitric acid is applied to the remaining shell which is thus dissolved leaving the mold surface as shown in Figure 8.

It is obvious that my invention is in no wise confined to the particular details of the steps as explained above, but that the details may be variously modified by those skilled in theart to adapt the method to particular conditions without departing from the spirit and scope of my invention as pointed out in l the appended claims.

I claim: i a

1. The method of making castings having an internal undercut consisting in forming a core of a metal soluble'in an acid, casting about the core a metal insoluble in the acid, and then dissolving the core in said acid.

2. The method of making castings having an internal undercut consisting in forming a core of a metal soluble in an acid, casting about the core a metal insoluble in the acid, removing the interior of the core, and then 1 dissolving the remaining shell in said acid.

3. The method of making castings having an internal undercut consisting in forming a core of metal composed at least mostly of copper, casting about the core a metal com- 110 in signature. 7 y CHARLES PACK.

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