US2201131A

US2201131A - Method for casting jewelry and the like

Info

Publication number: US2201131A
Application number: US139629A
Authority: US
Inventors: Thoger G Jungersen
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-04-28
Filing date: 1937-04-28
Publication date: 1940-05-14
Anticipated expiration: 1957-05-14

Description

May 14, 1940. '.l'.. .G. JUNGERSEN 2,201,131

v 7 METHOD FOR CASTING JEWELRY AND THE LIKE Filed April 28, 1937 3 She'ets-Sheet 1 fi e 1 Hi for.

Allorney -1'-. s, JUNGERSE N 2,201,131

METHOD FOR CASTING JEWELRY AND THE LIKE 3 Shuts-Sheet 2 Filed Aprii 28, 19 -1 m, mm 4 mm m 4 h flo w r WA IWM 1m W 6|. 1

y 14, 1940- 'r. s. JUNGERSENV 2,201,131

IETHOD FOR CASTING JEWELRY AND THE LIKE a Nod/um Patented May 14, 1940 UNITED STATES METHOD FOR CASTING JEWELRY AND THE LIKE Thoger G. Jungersen, Mimico, Ontario, Canada Application April 28, 1937, Serial No. 139,629

6 Claims.

The present invention relates to the art of making jewelry and other small metal articles of intricate design and fine detail, and among other objects, aims to provide an improved process or method of casting such articles.

A further object of the invention is to enable the formation of intricate castings which will so closely resemble the original and finished prodnet that the slow and tedious work of patterning and detail cutting required in connection with present casting methods is eliminated.

Other objects and features of the invention will be evident, including the various steps of the improved process, and attendant advantages over anything heretofore known, as set out in the following description of a method suitable for casting platinum, gold and other metal articles and jewelry especially of intricate designs, such as articles containing hollows, undercut portions and perforations.

This application is a continuation in part of my copending application filed September 28, 1934, Serial No. 745,893.

The manner of accomplishing the foregoing objects may be more fully comprehended by having reference to the accompanying drawings,

which are hereunto annexed and which constitute a part of this specification wherein:

Fig. l is an elevation of a model to be reproduced in accordance with the present invention;

Fig. 2 is a side elevation of the model;

Fig. 3 is a perspective view of a base with plastic material thereon, which is used to build-up or shape a flexible mold;

Fig. 4 is a plan showing the base with the model embedded in the plastic material to a predetermined depth.

Fig. 5 is a plan showing a frame enclosing the embedded model and plastic material of Fig. 4;

Fig. 6 is a perspective view showing a mass of unvulcanized rubber or the like positioned within the frame of Fig. 5;

Fig. 7 is a plan of the frame of Fig. 6 shown inverted and after vulcanization of the rubber Fig. 10 is an elevation of arpattern of readily fusible material formed in the mold and mounted on a rubber sprue holder;

Fig. 11 is an elevation partly in section, of the sprue holder and readily fusible pattern mounted thereon invested with a coating of a refractory or other suitable mold-forming material;

Fig. 12 is a view of the assembly shown in Fig. 11 mounted within the molding flask which is completely filled with a suitable investment ma- 1 terial;

Fig. 13 is a plan view of a modified form of base;

Fig. 14 is a sectional elevation taken on line l4--I4 of Fig. l3; 15

Fig. 15 is a partial sectional view illustrating the special treatment and cutting of the flexible body of the rubber mold to facilitate its removal from a deeply undercut form of pattern;

Fig. 16 is a diagrammatic view illustrating a 20 special step in the process;

Fig. 17 is an enlarged elevation of a ring made in accordance with this invention and of relatively plain design for simplicity of illustration;

Fig. 18 is a sectional view of the separable sec- 2, tions of the flexible mold in assembled relation;

Fig. 19 is a sectional view of the fusible model invested in the final mold; and

Fig. 20 is an elevation, partially in section illustrating a suitable arrangement for centrifu- 1 gally casting the fusible model as well as the final article.

Similar reference numerals refer to similar parts throughout the entire specification.

. Because of the expense attending the manufacture of platinum jewelry, many attempts have been made and large sums expended by some of the largest producers and refiners of platinum to satisfactorily cast it into jewelry and other small objects, in such condition as to require a minimum of waste of material and time in the finishing operations. However, an investigation of prior practice will undisputably reveal that all such attempts have failed, or have met with such indifferent success as to discourage the experimenters from proceeding on a commercial scale. Prior to the completion of the present invention, no platinum worker anywhere in the world had successfully cast platinum articles of intricate design.

Among the reasons for these failures were first, the difficulty of controlling molten platinum; second, the fusing of the investment material with the body of the casting causing undesirable conditions such as brittleness and porosity; third, the destruction of the mold by the molten platinum and/or the heat applied for melting the platinum; fourth the generation of gases when the platinum came in contact with the mold walls, which gases ruined the surfaces and the bodies of the castings; and finally, the pronounced tendency of platinum to absorb gases of various kinds, accompanied by blistering.

The artof casting gold articles, being attended with fewer difficulties, has progressed somewhat farther, and fairly simple gold castings, for instance of rings of plain pattern, have been produced from time to time with limited success. However, even with gold, when the castings are of intricate design, especially when provided with small hollows, perforations and/or undercuts, prior to the completion of this invention, there was no method in use which satisfactorily produced such castings, except as provided for in my copending application already referred to. The same difliculty has been present even with respect to rings, brooches and other articles of jewelry or the like of baser metals, like silver, nickel, tin, copper, etc., and their alloys, where they have been of intricate design.

The process disclosed in this application makes possible the inexpensive production of platinum, gold and other metal articles of jewelry and the like and possesses the further advantage of permitting the casting of' said articles with such fidelity to the original model as to substantially duplicate the same in any precious or base metal or in any alloy of such metals. Among other objects and advantages of this process are: a novel rubber or other plastic mold comprising a plurality of parts and method of making same; a novel mold for the direct casting of platinum or other metals and alloys of the platinum group and other high fusing metals, and intricate castings of baser metals and alloys; an article of jewelry of intricate design cast in platinum or the previously mentioned metals or alloys; a novel method of treating plastic investing material by various means comprising the use of vacuum; and investing a pattern by various means comprising the use of vacuum.

Referring particularly to the drawings, Figs. 1 and 2 show a model l5, which may be of brass, silver, wood or any other suitable material and which must be made with care, since the final casting will faithfully reproduce the same. due allowance being made for shrinkage in the casting process. undercut surfaces, hollows, and/or perforations as desired in the finished article.

The model I5 is used to make the first mold, which as here shown comprises a base 16, such as the fiat plate shown in Fig. 3, and a mass of plastic material H such as moist plaster of Paris or a similar substance, which, as shown in Fig. 3; may be placed on the plate in the form of a soft slab. Preferably the plastic material is first subjected to an appropriate treatment for the removal of air bubbles, to greatly increase its strength and to enhance its density, and accordingly produce a mold with an extremely smooth surface. A vacuum treatment has been found to serve this purpose satisfactorily.

The model l5, which may be first dipped in melted wax to fill all perforations and treated as by scraping to remove any excess wax at any desired point, is placed on the plastic material I! andmay be pressed down until it is embedded to a suitable depth therein. Then a sprue or gate former l8 may be partly embedded in the This model will contain the sameplastic material in contact with model l5, as shown in Fig. 4 and a series of holes, grooves, projections or other surface modifications, indicated in general as I9, may be arranged in the exposed plastic material either before or after it has set. These holes or the like preferably closely surround the model itself.

When the plastic material H is sufficiently hard or dry, and the wax disposed of, a frame 20, conveniently shown as rectangular, with a large central opening 20a is superimposed upon the plastic material and/or other base, as shown in Fig. 5, so that the model I5 is approximately centered in the frame, with the gate former l8 extending to one of the inner walls of the frame.

As shown by way of alternative, particularly in Figs. 13 and 14, the base may comprise a substantially fiat master plate 5' of metal or other suitable material having its surface permanently impressed or provided with suitable holes, grooves, projections or the like such as indicated at IS). A cavity or perforation is provided in the base for the reception of a quantity of plastic material H, such as moist plaster of Paris or similar substance in or on which the model l5 may be embedded so as to leave a suitable portion thereof exposed. In the making of ring molds the cavity may conveniently include a more shallowrecess or groove 2 connecting with the main cavity I and encircling a hub portion 2 of the base, on which a removable core piece 4 is adapted to be positioned as by interfitting projections or dowels. This hub portion may be shaped to snugly fit against the inner periphery of the head of the model ring, and if desired the hollow interior of the model may first be filled to a suitable or predetermined depth with a quantity of the plastic base material, as shown in i1", which depth may be accurately determined by the temporary presence of a quantity of wax in the perforations or piercings as shown at 5 (Fig. 14).

After the base has been completed and suitably parted about the model, it may be heated sufficiently to remove or disperse the wax from the perforations or piercings of the model.

A groove 2' may be formed in the plate I leading from the cavity 2 to receive and position a sprue former I8. As shown, this sprue former has its inner end widened where it abuts the model and is embedded in the plastic H. A semi-spherical or other enlarged shape sprue throat former l8" cooperates with the sprue former l8 and may be a part thereof. This throat former flatly abuts the inner face of the retaining form 20', which is shown in this case interfitting directly with the permanent or master base plate l6.

, Either form of base plate may be employed without affecting the subsequent steps of the process. Unvulcanized rubber, which may be in the form of a block 2| cut to fit the opening 20a of either base plate, is laid inside the frame (Fig. 6) in contact with the model l5 and the now hardened plastic material l1, and the whole assembly comprising the base, model, frame and rubber is heated to a vulcanizing temperature while subjecting the exposed rubber surface to an applied pressure for a period necessary to insure the flowing of the rubber around the model. The rubber, which is preferably of a soft gum type,

must be of a character which will not injure the model, if of metal, and it must also separate cleanly from the model.

Instead of employing rubber or other similar or senate material for the initial mold, 1 may use other materials such for instance as Bakelite, plaster of Paris or certain metals, for ex ample, type metal, Wood's metal, or even a pluof rubber, it has been found that rubber gives smoother results andis generally preferable.

After vulcanizing of the rubber, or completing the first part of the mold, whatever the molding material may be, the base-plate 16 or l6 and the plastic material I] or ll are removed to expose the model and the mold section 22 is inverted, as shown in Fig. 7. The mold section 22 is then cleaned, to remove all traces of the plastic bedding material I! or H and a parting composition such as an oil or a powder which will not injure the rubber, is spread over the parting surface ,of the clean rubber mold. In the next step,

'a frame 23 which is similar to and matches frame 20, is placed over the latter and preferably interlocked therewith as by suitable pins entering predisposed openings 2%.. Then a second mass of unvulcanized rubber 24 in block or slab form is placed in the opening 23a of the matching frame, and is vulcanized while pressed into close contact with the exposed portion of the model and the treated parting surface of the previously vulcanized mold section of Fig. 7.

The product of this second vulcanizing process is a second mold section 25 (Fig. 9) which may or may not be a substantial duplicate of the first depending upon whether or not the model itself is symmetrical. In any event, the second mold section fits the other first invested or embedded side of the model (which may not be symmetrical with respect to the parting plane) and has dowel holes 25a or the equivalent so arranged as to' register with the dowels which were formed in the first mold section as result of the holes or equivalent surface modifications I9 in the plastic material.

, The two registering rubber mold sections thus formed about the model are depicted in Fig. 18

of the drawings. According to the preferred embodiment of the invention; these two sections are intended to be used in casting a wax or other relatively readily fusible pattern preparatory to the production of the ultimate mold.

The next step therefore, is to cut the two separated rubber mold sections at various selected points, so that they may be easily removed from .the wax or other readily fusible pattern P, which is to be cast therein. If the pattern is to be quite plain in design, cutting may not be necessary, as the flexibility of the mold sections may be suflicient to permit their manual separation from the pattern. If the pattern is intricate however, such cutting becomes necessary. The location and direction of the cuts, and their number, will be dictated by the particular design, the object being to insure separation of the rubber mold from the pattern, which may be of wax, without any distortion or other injury whatsoever to the latter, and without detrimentally affecting the accuracy or detail of the mold. As an example, there is shown in Fig. 15, a rubber mold portion 1 within a deeply undercut or hollowed pattern P, the actual volume of which may be reduced as by the insertion of a heated pointed instrument to form a cavity 8. Moreover, a plurality of slits 9 are cut into the opposite sides to extend part way across the mold body, so that the respective portions will befree to flex easily in withdrawn through the opening il ofthe pattern.

Prior tocasting the wax or other pattern, the

registering surface of the two mold sections may be covered with a fluid or other suitable substance or lubricant for facilitating their separation. Such a substance is preferably an oil which will not injure the rubber, such for example, as castor oil. If the pattern is to be formed from a readily fusible metal, such as Woods" metal, the sepa-' machine, the pattern may be cast by centrifugal force exerted manually, as by whirling the mold on the end of a sling or cord. Then patternforming material in liquid form is poured into the gate of the mold and the latter is immediately rotated as stated above. The mold is removed from the machine after the pattern has been formed and the sections are carefully separated from'the pattern such as by flexing them on the lines of the cuts mentioned above (where such cuts have been deemed desirable or necessary), so that the mold is separated without injury to itself or to the pattern.

Experience has proved the great importance of employing centrifugal force when casting a wax or other readily fusible pattern in a rubber mold,

for the reason that centrifugal force acts in a peculiar way to cause the molten'wax or other pattern-forming material to completely fill the mold space and yet permit escape of all the air through the center of the pattern while the wax or the like is still liquid, with the result that the pattern is a perfect reproduction of the cavity in the mold. Thus any air which may be trapped in a recess of the mold will be crowded larly waxwhich is light in weight, especially where the patterns are of small dimension and/or of intricate design.

As stated above, instead of wax, fusible alloys, such as Woods metal may be used, and indeed may be preferred when the pattern is relatively large and hence likely to shrink too much if cast in wax. When the pattern is made of readily fusible alloys, it may be dipped in a solution of wax'to fill any-very fine pores or imperfections occurring in the metal. This results in a superior final product because in this manner the formation of an oxide coating on the metal is practically obviated the reason being that the wax acts as a separating agent upon the application of heat to remove the readily fusible pattern from the mold, and thus causes the pattern to flow or separate away from the mold with a minimum disturbance or deposit of slag on the surfaces of the cavity of the finished mold.

The sprue stem for the pattern is inserted in a sprue holder 26 (Fig. 10) and assembled with the pattern. Preferably the sprue holder is made of rubber and has an annular flange 26a which frictionally grips a flask 21 (preferably a metal cylinder) adapted to surround the pattern and hold a mass of investment material. The sprue holder 26 has an integral central boss 261), with one or more perforations 260, for receiving one or more of the fusible patterns as shown.

If the final product is to be of platinum, the wax or fusible metal pattern, held by the sprue holder 26, Fig. 10, is preferably treated with a liqiud such as sodium silicate to remove any trace of oil from the surface, to make the investment material adhere better, and also to exclude air from small holes, corners or piercings so the investment material may completely occupy all spaces. Then the pattern is dipped, preferably, into a silica mix, which may comprise silica flour with a binder, for instance sodium silicate, which will generate a minimum of gases when exposed to the very high heat of fused platinum; and glycerine or caustic soda, for example, to prevent the formation of a hard skin, to enhance elasticity and to retard distortion during drying. In other cases magnesium oxide or other suitable materials may be used to hasten the setting.

The silica mixture is preferably treated to remove any air or other internally contained gases by subjecting the same to a vacuum, preferably, in the manner illustrated in Fig. 16. The container a, which holds the mix, is placed upon a plate I) mounted on springs 0 above a rotatable cam or other vibrator member (1, so that by depressing the plate, it is moved into engagement with the said vibrator member. A bell jar e connected by a diagrammatically shown tube j with a suitable vacuum pump 9 is placed over the container 0. and 'as the vibrations are produced, the vacuum pump withdraws the air or other gases from the mix. Investing of platinum may also be effected in the manner to be described for the casting of gold, silver, etc., wherein the pattern is surrounded with the platinum investing material and then subjected to vacuum with or without attendant vibrations.

This silica mix coats'the pattern with atenaciously adherent primary investment 28, which covers all surfaces of the pattern, so that the latter will appear after this step, substantially as shown in the irregular profile in Fig. 11. Following this treatment, the invested pattern may be dried either in the open or in an oven, sufliciently moderately heated so as not to fuse the pattern. The coated pattern may also be treated with an oil, wax or acid solution to render the investment less subject to attack by water, so that the steam from a secondary investment during drying will not attack the binder of the silica coating. The pattern in this condition is now ready for its final investment for which purpose the flask 21 is placed on the sprue holder and the investment material or other filler is packed into the space between the pattern and the wall or walls of the flask so as completely to fill said space. I

If desired, a coated wax pattern may be heated to a temperature sufficiently elevated to cause the wax to penetrate the minute pores of the coating to further'preserve the coating against the effects of moisture and steam arising from the subsequent drying. The coating may then be a hollow shell or Wax-treated silica or the like, with practically no wax in the interior, and if desired the heat may be raised sufficiently high, so that the coating becomes a shell of hard burned silica, similar to a porcelain shell.

The final mold 40 thus formed about the wax or other relatively readily fusible pattern is shown in Fig. 19. This mold will be an exact negative of the wax pattern, which is itself a counterpart of the original model.

In preparing the casting mold for reception of the molten platinum or other high [using metal or alloy, it is important to completely remove or destroy all traces of the wax pattern and any carbon deposits that may be left in the mold as residue. This may be accomplished by maintaining the investment or casting mold at a red heat for a suflicient period, which temperature may range above 1200 degrees F. Theplatinum is preferably cast in the thus prepared mold after the investment has cooled somewhat, say to about 800 F.

The heat treatment of the investment in this way alters its characteristics, so that it is capable of contact with the molten platinum without gas formation or eruption and accordingly, softer castings of smoother grain are produced, devoid of the porosity and brittleness, which heretofore have attended any attempt to cast platinum.

A contributing factor in the successful castingof platinum and kindred or high melting point metals and alloys also resides in the choice of a suitable refractory as well as binder therefor, which forms a coating capable of receiving molten platinum with the minimum formation of gases and minimum detrimental effect on the resultant casting.

While silica is preferred, because it can be easily removed from undercuts, perforations and hollow spaces by using acids, other suitable refractory substances such as alumina, zirconium, silicate and the like with a suitable binder can be used, although they introduce different problemsin removal from the casting.

The actual casting of the platinum is accomplished in much the same manner as was employed for the wax pattern, namely by centrifugal force at a relatively high rotational speed and at the vastly higher temperature required for melting platinum. In this manner the platinum is rapidly cast before it can possibly cool, and the entrapped air or gas is forced from the mold by virtue of the relatively higher density of the platinum. In view of the pronounced tendency of platinum to absorb gases, this elimination of air and gases accounts in a large measure for the successful application'of the present invention to the casting of platinum and its alloys, free from blisters and surface voids.

When desiring a gold or gold alloy casting, or a casting of any metal having a fusing point considerably below that of platinum, where a simple plaster investment may be employed, the fusible pattern may be treated with a liquid (for example, an alcohol) to remove any oil and permit the investment to adhere and fill all fine cavities, piercings, corners or hollows with a minimum of entrapped air, thus insuring a more perfect casting. Such a pattern is then coated or covered with an investment material, preferably a silica and plaster of Paris mixture which may have been treated by vacuum, vibration, or a vacuum vibratory mechanism such as that already alluded to, to remove any air bubbles. These treatments may be effected either prior to appli- .sprue holder 26, surrounding the coated pattern.

Now more investment material (which may or may not be of a different quality or character than the coating investment) is poured into the flask and allowed to set, or suitable investment material such as clay or damp sand may be gently packed into place to support the investment coating. The sprue former is removed and the flask is ready for bakin to remove the fusible pattern.

With certain types of patterns having small cavities or piercings, it is very difficult to invest them without entrapping air, in spite of the precautions described above. However. this can be accomplished by coating the pattern with a more or less liquid investment material and then subjecting it to a vacuum, with or without accmpanying vibration, which will exhaust all air entrapped under atmospheric pressure. The investment material will then be forced into the finest cavities or piercings completely to fill them without trapping air. When performing the very finest work, the investment material, before being placed about the pattern. may be vacuum treated to remove air bubbles and the vacuum process just described may then be carried out, or the pattern and investment material may first be separately treated in a vacuum chamber, then the pattern submerged in the vacuum treated investment before the vacuum is removed, with or without vibration. It is to be understood that where the term vibration is used it is meant to include the step of agitating.

Whether the final casting is of platinum or some other metal, the flask is heated to a temperature which will melt the pattern, which temperature may create a slight pressure due to the moisture vaporized from the investment mate rial. This pressure will tend to force the pattern away from the surfaces of the cavity and out through the sprue hole, leaving said surface absolutely clean. Optionally the wax may, as already stated. be driven by the heat into the investment material to be absorbed thereby after the investment has been thoroughly dried at lower temperatures. This latter method is not the preferred one however, as there is always the possibility that some depo'it of dirt or scum or foreign matter (from the face or body of the wax) will accumulate or the cavity wall, which mi ht result in an impe l'ect casting.

The mold in condition for the final casting, is preferably placed in a centrifugal casting machine for casting in the prescribed manner. Instead of centrifugal force, applied pressure or vacuum may be used, where the nature of the metal or alloy will permit such a variation. After the casting step has been completed. the flask maybe dropped into water and allowed to remain for a time sufficient'to facilitate removal of the investment material from the casting. In the case of platinum, the casting may be pickled in acid. such as hydrofluoric, to remove all of the investment, prior to the final finishing operations.

The silica and sodium silicate and plaster of Paris mixture mentioned above as the pre ferred investment material for platinum casting, may be replaced by a plastic mixture of silica or alumina and silica gel, or materials of a similar character, with a small quantity of a suitable accelerating agent, such as magnesium oxide, to hasten the initial setting.

For example, liquid tetra-ethyl silicate may 'be mixed with a small quantity of water to which have been added a few drops of an acid, such as hydrochloric, to induce partial hydrolysis, together with a little alcohol to promote mixing. This mixture, when heated and stirred, provides a binder, which may be mixed in suitable proportion with a suitable refractory material such as silica. Instead of employing magnesium oxide, initial setting may be promoted by heat, and I may optionally select any suitable binder such for instance as silica gels, phosphoric acid cements, magnesium oxide cements and various oxide salt cements.

While platinum is referred to above as the metal most likely to cause trouble when casting, it will be understood that commercial platinum, and commercial platinum alloys, especially platinum-iridium, are equally included since pure platinum is seldom used in the jewelry trade, and the term platinum is to be construed as including such kindred alloys or metals offering similar problems. the casting of which will be facilitated by my process in whole or in part.

The present invention provides a mode of producing castings of intricate design from metals whose fusing temperatures may range from quite low values to a point even considerably higher than the melting points of platinum or platinumiridium. Hence the method is not to be construed as solely applicable to a jewelry producing process. but is rather a process of making castings of intricate design from nearly all known metals and most alloys.

The resultant casting, whether of platinum, gold, silver or other metal, requires nothing but extremely simple finishing operations to be ready for the market. The only part of the casting requiring any rough finishing work at all is the part II (Fig. 17) where the sprue joins the casting, which may be smoothed by filing, grinding, cutting or otherwise. The final bufiing and polishing operations may thus be performed directly on the article as removed from the casting mold. Thus the process effects very large savings, especially in the manufacture of fine jewelry.

With known processes of casting rings, it may take an expert jewelry worker several hours to finish a ring to a certain standard after casting, while with the present process, only fifteen to thirty minutes may be required to finish a ring to the same standard. These figures are for ordinary rings. With finer work in platinum, several days may be required for making a ring by hand in accordance with known methods, while as little as ten minutes would suffice for casting the same ring by the present process, and the time necessary for finishing it might require as little time as a fractionof an hour.

The process of the present invention will produce rings on a quantity basis without the necessity for making dies, a huge saving in itself, since a properly constructed set of dies in the jewelry trade costs from $100.00 to perhaps $1,000.00 or even more. As compared with this excessive investment required by the use of dies, the present process permits the production of rings and other articles of jewelry at a total cost of from $2.00 to $3.50 for the first mold. Thus a manufacturer employing this process may effect a large savings in capital investment in dies and in precious metals inasmuch as a large number of rings, etc, must be initially produced froma die in order to justify the expense while only a few rings need be made from a mold constructed in accordance with the present invention to pay adequately for the cost of the mold. Hence it will be evident that the process of the present invention may effect savings up to in the cost of production, especially where the production contemplates relatively small quantities.

I claim:

1. The method of making molds which comprises: subjecting a quantity of mold material disposed in a liquid or viscous condition in a container to a vacuum process to remove substantially all of the occluded air therefrom; after the air has been removed, subjecting said quantity of mold material to atmospheric pressure; carefully introducing a pattern into said quantity of mold material while said mold material is under atmospheric pressure; permitting the mold material to harden; and finally removing the pattern to form a mold cavity.

2. The method of making molds which comprises: subjecting a quantity of plastic mold material to a vacuum process to remove substantially all of the occluded air therefrom; after the air has been removed, subjecting said quantity of mold material to atmospheric pressure; carefully introducing a pattern into said quantity of mold material while said mold material is under atmospheric pressure; permitting the mold material to harden; and finally removing the pattern to form a mold cavity.

3. The method of making molds which comprises: subjecting a quantity of mold material disposed in a liquid or viscous condition to a vacuum process to remove substantially all of the occluded air therefrom; after the air has been removed, subjecting said quantity of mold material to atmospheric pressure; investing a pattern directly into said quantity of mold material while the same is under atmospheric pres sure; subjecting the invested pattern to a vacuum process for a time sufficient to remove any air which may have been entrapped; permitting the mold material to harden and finally removing the pattern to form a mold cavity.

4. The process of preparing an investment material for the casting therein of molten material including precious metals, such as platinum, gold or silver, comprising investing a pattern in liquid or viscous. investment material and subjecting the pattern and investment to a negative pressure, then vibrating the pattern and the investment material and raising the pressure, whereby the investment material will be packed to form an accurate mold corresponding to the pattern.

5. The method of preparing a mold for the casting therein of articles intricate to the extent of having one or more small projections or depressions comprising preparing a liquid or viscous refractory investment compound, subjecting the same to a negative pressure to remove air trapped therein, vibrating same and admitting air, investing a pattern in the thus treatedinvestment material and then subjecting the investment and pattern to negative pressure, vibrating the investment and pattern to pack the investment into close conformity with the contours of the pattern and admitting air.

6. The method of preparing a mold for the casting therein of an article intricate to the extent of having one or more projections or depressions comprising preparing a liquid or viscous investment compound, subjecting it to a negative pressure, investing a pattern therein, again subjecting the investment to a negative pressure, vibrating the investment and pattern to cause the investment material to conform mitting air to the investment.

THOGER G. JUNGERSEN.