US1238183A - Method or art of making molds. - Google Patents

Description

UNITED STATES PA ENT orrron.

LEO FRANK NOGK, OF BROOKLYN, NEW YORK, ASSIGNOR. TO DOEHLER DIE CASTING COMPANY, OF BROOKLYN, NEW YORK, A CORPORATION OF NEW YORK.

METHOD on ART or MAKING Moms.

He Drawing.

To all whom it may concern:

Be it known that I, LEO FRANK NooK, a citizen of the United States, residing in the borough of Brooklyn, in the city of New York, county of Kings, and State of New York, have invented certain new and useful Improvements in the Method 0r Art of Making Molds, of which the following is a specification.

My invention relates to the method or art of making molds and more particularly to themaking of molds of plastic material to be used in making metal castings of mechanical parts wherein it is not only necessary to preserve accuracy in the contour and smooth-- ness of finish of the castings, but exactitude in the dimensions thereof.

Plastic molds have heretofore been used in the art for making castings of yarious kinds, such as works of art, dental inlays and other articles, a common practice being to embed a wax pattern in the plastic material of which the mold is formed, and subject the mold With the wax pattern therein to the action of heat, thus reducing the pattern to a molten state and causing it to be absorbed by the plastic material of the mold. Under conditions where exactitude of dimensions is not essential or where the nature of the work is such that re-finishing of the casting is not prohibitive, this method of making molds has proven satisfactory. In the production of commercial castings, however, where uniformity of finish and of dimensions in a large number of similar parts is essential, and where one of the objects of producing the castings is to avoid the necessity for machine finishing, or for any substantial quantity of machine-finishing, the methods above describedare not suitable.

I have determined in actual practice that the absorption of the wax, or other material of the pattern, by the plastic material of the mold has the effect of closing the pores of the mold in a manner to interfere with the free venting of the mold cavity during the pouring of the molten metal therein. A further condition resulting from the use of moldsmade in this manner, is the presence of surface imperfections in the casting in addition to those resulting from the imper- Specification of Letters Patent.

feet venting, due to the burning of the wax by the inflowing metal and resultant surface flaws due to the disintegration of the mold surface and the formation of gases within the mold cavity and the minute voids in the walls thereof. There is also a further dis-' advantage that the presence of the wax has a tendency toward the formation of open cells in the wall of the mold cavity, into which cells the metal flows with a resultant surface finish which is undesirable in mechanical parts, the presence of the wax preventing the solidification of the material of the mold while it is setting and drying.

By the method or art of my invention, I produce a mold of suitable plastic composition utilizing a wax or other similar pattern and removing the pattern from the mold by the application of heat thereto to reduce the pattern to a molten state while at the same time preventing the material of the pattern being absorbed by the material of the mold. By the method or art of my invention, I retain in the mold that porosity inherent to the constituents of the composition from which it is made, thus facilitating the venting of the mold during the pouring of the.

Patented Aug. 28, 1917.

Application filed January 5, 1917. Serial No. 140,712.

molten metal thereinto, securing a smooth surface to the mold cavity, and avoiding the formation of gases Within the mold while pouring. Furthermore, a mold made in accordance with my invention may be thoroughly and uniformly dried.

The invention consists primarily in the method or art of making molds consisting in embedding a pattern formed of wax in plastic material, saturating said mold after the material thereof has set, with a fluid medium, repellant to wax and at a temperature which will melt said wax whereby said pattern will be reduced [0 a fluid state and rial of the mold will be prevented, flowing said fluid wax through an opening in the mold and finally drying the mold; and in such other novel steps and practices as are hereinafter set forth and described and more particularly pointed out in the claims hereto appended.

In the practice of the method or art of my invention, I provide a plurality of patthe absorption of the fluid wax by the mate terns in wax or other similar material fusing at a low temperature. ,These patterns preferably are produced in metal dies by what is known as the pressure die casting process in order to insure uniformity in different patterns, these wax patterns when thoroughly hardened are embedded in a plastic composition which may consist of plaster of Paris alone; plaster of Paris mixed with asbestos; or any other desired composition, the ingredients of which possess' the characteristic of readily absorbing water, or any other suitable fluid medium which may be brought to a temperature above that at which the material of the pattern will fuse or melt. When the plastic material has been properly formed about the pattern, I allow the material thereof to set with the pattern therein. When the mold in this condition is sufficiently firm to permit it to be readily handled, I saturate the material of the mold with a fluid medium maintained at a temperature sufficiently high-to melt or fuse the material of the pattern. By reason of the low conductivity of the material of the mold, the pattern will not begin to melt until the fluid medium has penetrated to that portion of the mold which when the pattern has been removed, will form a wall of the mold cavity; so that as the pattern .melts, or fuses, the presence of this fluid at the said surface, will prevent the absorption of the wax by the material of the mold, the fluid being repellant tothe wax.

In actual practice, I have secured highly satisfactory results by merely immersing the mold in a bath of ordinary water maintained at a temperature of approximately 210 to 212 F. or at about boiling point, although the same result can be attained by the application of a saturated steam to the mold. When the pattern is reduced to a fluid state, it will readily flow from the mold; and, if desired, after all the wax has left the mold, the mold may be subjected to the continued action of the fluid medium until the mold cavity itself, has been completely filled with this medium so as to avoid any possibility of any wax remaining in or, about the mold cavity.

The adaptability of a plastic composition .such as I have described, to absorb water far in excess of that quantity which is combined with the ingredients thereof, permits the utilization of a suflicient volume of the. fluid in and about the mold to prevent any portion of the wax adhering to the wall of the mold cavity or being absorbed thereby.

After the removal of the wax, or other material of the pattern, and of any liquid contained in the mold cavity, I beat dry the mold, thus removing the fluid medium and conditioning the mold for the pouring operation. By reason of the complete saturation of the material of the mold withthis fluid, likelihood of the premature drying of any portion of the mold isavoided.

The method herein described is particularly adapted for the production of inside unitary molds, asdistinguished from sectional or split molds, although if desired it may be used with the latter type of mold. This type of mold is used ordinarily where the intricate nature of the design of the machine part is such as to prevent the drawing of a pattern. In split molds metal patterns are ordinarily used, however. The wax composition used forms no part of my pres-- ent invention, as any wax or composition may be'used, the fusing point of 'which is sufliciently high to permit the handling of the pattern. While in practice, I have found that water alone gives entirely satisfactory results, it is not my intention to limit the invention to the use of water as various solutions might be used, the sole function of which would be to fill the pores of the mold and combine with the material thereof in a manner to prevent the absorption of the wax by the mold, without departing from the spirit and scope of the invention;

Having described the invention, what I claim as new and desire to have'protected by Letters Patent is: 1. The method or art of making molds consisting in embedding a pattern formed of wax in plastic material, saturating said mold after the material thereof has set with a fluid medium repellant to wax and at a temperature which will melt said wax whereby said pattern will be reduced to a fluid state and the absorption of the fluid wax by the material of the mold will be pre-' vented, flowing said fluid material through an opening in the mold and finally drying the mold.

2. The method or art of making molds consisting in embedding a pattern formed of, wax in plastic material, immersing said mold after the material thereof has set in a liquid bath repellant to wax and maintained at a .temperature which will melt said wax whereby the material of the mold will be saturated with said liquid, said pattern will be reduced to a fluid state and the absorption of the fluid wax by the material of the mold will be prevented, flowing said fluid wax through an opening in the mold and finally drying the mold.

3. The method or art of making molds consisting in embedding -a pattern formed of .wax in plastic material, immersing said mold after the material thereof has set in a liquid bath repellant to wax and main- Sorption of the fluid wax by the material signature in the presenoe of two subscribof the mold will be prevented, flowing said ing witnesses, this 28th day of December, fluid wax through an opening in the mold, 1916.

causing the mold cavity to fill with the liq- LEO FRANK NOOK. 5 uid of the bath as the wax is flowing there- Witnesses:

from and finally drying the mold. C. Tm. FETT,

In witness whereof, I hereunto afiix my WM. G. GUTMUELLER.