US2660768A - Means for forming molds - Google Patents

Description

Dec. 1, 1953 R. E. BARR 2,660,768

MEANS FOR FORMING MOLDS Filed Dec. 2, 1949 3 Sheets-Sheet l 36 Roy E. Barr IN V EN TOR.

Dec. 1, 1953 R. E. BARR MEANS FOR FORMING MOLDS 3 Sheets-Sheet 2 Filed Dec. 2, 1949 Roy EBarr V INVENTOR.

'Dec. 1, 1953 R. E. BARR 7 8 MEANS FOR FORMING MOLDS Filed Dec. 2, 1949 3 Sheets-Sheet 5 Roy E Barr IN VEN TOR.

Patented Dec. 1, 1953 UNITED STATES FATENT OFFICE MEANS FOR FORMING MOLDS Roy E. Barr, Childress, Tex.

Application December 2, 1949, Serial -No. 130,721

7 Claims.

This invention relates to new and useful improvements in means io'r forming molds, and in particular to means for forming molds .for making extremely accurate casting of articles of very close dimensions and tolerances.

Although the invention is applicable in a great number of instances such as the forming of items of jewelry or portions of precision instruments and-other similar devices, it is particularly applicable to the casting of dental inlays and certain types of dental restorative castings. For the purposes of clarity the invention will be described largely with respect to use in the dental profession. However, it is to be noted that the invention is not limited to such use, but may be advantageously applied in a number of entirely dissimilar arts.

The problems of accurate and satisfactory casting of small and extremely accurately dimen sioned elementsare substantially the same in all instances in which such casting necessarily is employed whether the same be a filling for a tooth or an item of jewelry or-an important element of a precision instrument. Therefore, it is further to be noted that the various problems and obstacles to accurate casting which will be set out hereinafter with regard to casting applications in the dental field, exist in other arts or applications where accurate casting is desirable, and that themeans contemplated by this invention finds equal advantages and applicability in all such instances where accurate casting is desired as well as with particular respect to the formation of various dental devices or prosthetic elements.

In casting procedures, the existence of a master form or pattern is necessary and for the purposes 'of'this applicationmay be assumed to be in existence. For instance, in the utilization of this invention for the formation of a dental device, such as an inlay, the existence of a model or pattern may be assumed. Such a mo'delnormally consists of a wax form 'or pattern of the size and shape of the article to-be cast and amounting to an exact duplicate of such article. Although such impressions are "normally formed of wax, the invention is obviously applicable with the utilization of patterns or modelsformed of other materials. The customary procedure is to form or obtain such apattern ormodel through usual and well-known procedures, and .then to duplicate such pattern-iormodel in goldpor-gold alloy, or other suitable material ;r alloy suchras ris customarily employed for the constitution of such devices. This invention deals particularly with such duplication.

In the past, in duplicating of a wax form or pattern for the creation of a gold inlay =for instance, it has been customary to mount the pattern upon a suitable sprue-forming wire and to paint or coat the pattern carefully with a creamy mixture of an investment compound, similar in nature :to plaster of Paris. Great care has been necessary in such a coating operation to prevent the occlusion of air bubbles between the investment compound-and the wax pattern since such bubbles will obviouslycause imperfections in the article cast from the mold which is eventually produced around the pat tern. Following this'painting or coating operation, the waxpatternis 'sui-tablypositioned within the usual casting ring, and the latter filled with an investment compound mixture which is allowed to harden around the pattern and the investment compound previously applied to said pattern or form. In this manner, a plaster-like mold is formed around the pattern. This mold, after removal of the wax therefrom, may be employed for the casting of a duplicate of the wax pattern in metal or other suitable material.

After the mold so formed has hardened, it is customarily heated to cause the meltingor burning of the Wax impression therefrom whereby a cavity in the shape of the desired article remains within said mold with a passage created by the sprue-forming wire leading from the exterior of the mold to said cavity. Following this step, the normal procedure is to remove themold from the place of heating and to fill or cast the same with molten metal or other suitablematerial.

A considerable number of problems and disadvantages arise in-the course of forming a suit able cast article with this herebefore employed means. To begin with, a considerable degree of skill is required to paint or coat the wax-pattern properly with the creamy investment mixture. Quite-often, air bubbles are trapped between the investment mixture and the wax pattern regardless of the care 'andskill displayedby the technician. Also, the investment mixture itself, which consists :of :a plaster'-zlike-material mixed with water, contains 7 large numbers of gaseous bubbles which are not always obvious "to the eye but which cause imperfections in the mold produced and consequently in the article cast therein. These gaseous bubbles may be formed of air or other gaseousm'aterials which were originally ,present in the .water or' trapped in the investment powder or which were generated or freed in some manner bythe mixture fthe investment powder with the water.

Methods have been developed for partially avoiding this problem, such methods involving the placing of the investment mixture, after it has been stirred or spatulated to the proper consistency, under vacuum conditions so as to exhaust gaseous bubbles therefrom. However, the actual investing of the wax pattern with the investment mixture is carried out in open air with ample opportunity for aeration or the occlusion of the bubbles during such procedure. These methods also contemplate the evacuating of the investment compound after it has been poured into the casting ring around the pattern. Obviously, evacuating the investment compound at any point is of some advantage. However, the removal of anything but relatively large bubbles from points adjacent the surfaces of the investment compound either before pouring or after its introduction into the casting ring, is questionable.

It is, therefore, one object of this invention to provide improved means for forming casting molds wherein the investment compound mixture is evacuated before, during, and/ or after mixing, and while the same is being introduced or poured into a form around the article which is to be duplicated.

An important object of the invention is to provide an improved mold-forming device wherein the component parts of an investment compound mixture may be evacuated before mixture, then thoroughly admixed and spatulated while under partial high vacuum, and subsequently introduced into a casting form while being maintained under partial high vacuum so as to preclude the presence of any gaseous bubbles or voids in the completed mold.

Yet another object of the invention is to provide an improved molding device having provision for receiving the component parts of a molding compound while retaining the same in separation and placing the same under partial high vacuum, and having means for admixing and thoroughly spatulating and combining said ingredients without an interruption of the vacuum being applied thereto; and wherein, in addition, the device may include means for pouring the molding mixture so compounded into a suitable form in the shape desired for casting, while maintaining the vacuum pull upon the mixture without interruption.

A pertinent object of the invention is to provide an improved mold-forming device for producing very accurate castings having intricate shapes and very close dimensions or tolerances, and which are substantially exact and absolute duplicates of the original pattern or form which it is desired to copy.

A construction designed to carry out the invention will be hereinafter described together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings, wherein examples of a means for carrying out the method of the invention is shown, and where- Fig. 1 is a side elevation of a molding device constructed in accordance with this invention,

Fig. 2 is a vertical, sectional view of the device shown in Fig. 1, with the same being upended,

Fig. 3 is a side elevation of the insert for the molding device, Y

Fig. 4 is a plan view of the insert shown in Fig.

Fig. 5 is a vertical, sectional view of the insert shown in Fig. 3,

Fig. 6 is an exploded view of the entire assembly showing the relation of the various parts,

Fig. 7 is a vertical, sectional view of a modified form of the invention showing the investment compound ingredients unmixed,

Fig. 8 is a view similar to Fig. 7 showing the ingredients mixed,

Fig. 9 is a view similar to Fig. 8 showing the ap paratus inverted into a pouring position, and.

Fig. 10 is a fragmentary, isometric view of the investment ring retaining means.

This application is a continuation in part of my 'co-pending application, Serial 768,874, now Patent 2,490,193 issued December 6, 1949, filed August 15, 1947, and also of my co-pending application, Serial No. 117,379, filed September 23, 1949, now abandoned.

- In the drawings, the numeral 2i] designates a molding device or receptacle following the teach-- ing of this invention. The device includes an upper molding container or shell 2! having a general hemi-ovoid shape or outline. The shell 2| is hollow, having a molding chamber 22 therein, and carries a suitable valve or petcock 23 extending laterally from one side wall near the lower edge thereof. The petcock 23 is provided with the usual type of nozzle or hose fitting 24 to which a suitable rubber hose (not shown) may be attached. The upper and opposite wall of the shell is flattened to form a rest or support 25 upon which the shell 21 may be disposed. As will be noted from Fig. 2 of the drawings, when the shell is placed upon the rest 25, its longitudinal axis extends upwardly at an angle of between and The open lower end of the shell 2l, as viewed in Fig. 1, carries an annular seating surface 26 in which an annular, internal shoulder 21 is machined or otherwise formed.

A mixing or spatulating cup 28 forms the lower portion of the molding device as viewed in Fig. 1. The cup 28 has the general outline of an ellipsoid out along its minor axis, although any suitable or desirable shape or configuration may be employed for this cup. The cup is hollow and contains a mixing chamber 29 of conical or hemiellipsoid shape in which the ingredients of the molding compound are mixed and spatulated. The side wall of the cup 28 is thickened at 33 around the upper edge of the cup as viewed in Fig. 1. A seating groove 3! is formed in the edge of the cup and carries a suitable packing ring or gasket 32. The seating face or edge 26 of the shell 2| is adapted to enter the groove 3| and seat against the packing ring 32. The casting ring insert includes a circular, disk-like spider or diaphragm 33 of such thickness and diameter as to permit seating upon the shoulder 21 of the shell 2| and engagement by the edge of the mixing cup 28. A crescent shaped container 34 having an open top 35 and a closed bottom 36 extends through the diaphragm 33 so as to have its open upper end projecting a short distance thereabove, while its closed bottom is positioned a considerable distance below said diaphragm. The dimensions of the container 34 are such as will permit its insertion into the chamber 22 when the diaphragm is seated upon the shoulder 21. An offset, vertical partition 37 divides the container 34 into a small or water-containing chamber 38 and a, large or investment compound-containing chamber 39.

As will be noted in Fig. 4 of the drawings, the

. to taih r 3*4 1's offset with respect t6 the center of the diaphragm 33,- a'r'i'd a circular opening E0" is provided in the opposite half ofthe' diaphragm more or'less adjacent orco'n'ti'gu'ous" to the curved ir iner wall ofs'ai'd container; The opening 40 is traversed by a morality of' bars s1 which may b formed integrally of the" diaphragm 33 or con sist of suitable elements secured thereto so" as to' overlie said opening; I

1he bot"to'm 3'6 of the chamber 31%" is" extended laterally so as to underlie the opening ill. A suitable wing bolt 42 is threaded through the extended portion of the bottom 36 and extends vertically in vertical alignment with the center of the opening 40'. A follower disk 43 is carried by the upper end of the bolt 52 above the extended portion of the bottom 3t, s'aid' disk being adapted to be moved upwardly and downwardly by mea'ns of the bolt 42'.

The usual small casting ring ie, comprising an open-ended cylinder as is customarily employed for' ca's't'ing dental inlays and other similar small articles, is positioned between the underside of the diaphragm 33 and the upper side of the disk 43 The opening is slightly less in diameter than the casting ring 34 so that the latter" does not pass therethroug'h, although the bars ill may be used for such retaining purpose if so desired. As is customary, the" open lower end of the ring 44 is closed by the usual sprue-forrner in the shape of a hemispherical plug or cap is formed of rubber or some other suitable material. A sprue-fo'rmer wire 46 extends axially upwardly of the casting ring from the sprue-former l5 and carries upon its upper end the model or pattern 4! which it is desired to duplicate. Normally, in the dental profession, this will consist of a wax pattern of the cavity to be filled or a wax fn'odel of the item it is desired to duplicate in a casting. Obviously, by tightening of the wing bolt 42, the casting ring along with the sprueformer are urged upwardly into snug engagement with the underside of the diaphragm 33 and held securely in such position. To aid in positioning the casting ring beneath the diaphragm, a short depending skirt 48 may be provided about the opening 49 on the underside of said dia-' phragm and extending annularly in close relation to the edge of said opening. For spatulating purposes, a ball or spatulator 69, formed prefeiably of some relatively heavy and corrosion resisting material such as brass or bronze, is secured by a chain 5b to the central portion of the dia hragm as, the chain being attached to the upper side of said diaphragm and being or such length as to allow the ball as a considerable de- 'gree of movement within the mixing chamber 29 when this latter described insert is positioned within the molding chamber 22 and the molding device is assembled.

the utilization of this device, the pattern 4? is positioned within the casting ring es in the usual manner to constitute a mold flask and the latter is mounted within the insert device shown in Fig. 3- of the drawings. Measured quantities of water and investment compound are placed in the chambers 38 and 39 and the insert structure introduced into the chamber 22 with the diaphragm 33 resting upon the shoulder 2i. rhe shell 2i may be held in a semi-vertical or vertical position during such procedure with its open end directed upwardly so that the investment ingredien'ts remain at rest with the container 34. The ball as may be rested upon the diaphragm as,

and the mixing cup 28 placed in "position by e'iigaging the groove 31" over the seating rate 2'6 of said shell". A suitable source of vacuum or partial high vacuum is then attached through a flexible conductor to the nozzle 2 of the petcock 23; The petcock is openedand thevacuum pump is" started.

Once any reasonable degree of vacuum established within themolding device, the atmos' pheric pressure exerted upon the outer surfaces. of the shell 21 and the cup 28 is su-flicient to hold the same in engagement, the packing ring 32 serving to prevent the entry of air between said elements into the interior of thedevice. It

. is pointed out that there is nosealing between the mixing chamber ZSand the molding 22, so that the vacuum exerted through the pet cook 23' iscommunicated to both chambers.- To insure" this communicationcf the applied vacu' the diaphragm may be provided with the vent tubes 5!. I

It is preferable, although not necessary;- that the device remain in' the aforementioned position for a short period after the vacuum within the device has been created. It is wellknownthat nearly all water contains a considerable roper; tion of gas, both dissolved and otherwise held,- and it is desirable to eliminatesuch gas before the mixing procedure" is instituted. At-the same time, air and other gases trapped iri the dry investment compound powder are also evacuated and removed. After a suitable period of evacuation, the device is inverted into the position shown in Fig. l of the drawings. in version causes the ingredients of the investment compound to fall intothe mixing chamber 29 along with the ball 4'9; The device may be. shaken and agitated, either manually" or means of a mechanical agitator or mixer) causing the ball to move about rapidly with the chamber in the manner of a; spatulato'r of a pestle, to mix and combine the water and the dry investment compound into a. smooth, homogeneous', thoroughly stirred investment mixture. It will be noted, the application of vacuum isco'z'i tinu'e'd during this mixing process so that any gas which may be evolved or released 1 in.- Ined'ia'tely removed. Because of the agitation of the mixture, different portions of the ingredients are constantly being brought to the surface for evacuation of any gas which may be entrapped.

The mixing is continued for a suitable time,- or until the technician is certain that a smooth, uniform mixture has been obtained. The molding device is then again inverted and placed in the position shown in Fig. 2 of the drawings. It' is desirable that in passing from the position of the molding device shown' in Fig. 1 to the position shown in Fig. 2, that the" device be turned a clockwise direction so that the investment mix ture will flow down the left-hand side of the cup 28, as viewed in Fig. 2, into contact with the diaphragm 4| and through the opening 40 into the casting ring 44- of the mold flask. The upstanding portion of the side wall of the container 34 which projects above the diaphragm acts as 'a baflie to prevent the investment mixture from being trapped or collected within said container.

The molding device is now transferred to a suitable vibratory table of the usual and ordinary type, and rested thereon upon th flattened face 25 whereby the device is supported at an angle as shown in Fig. 2. In this position, with the application of vibration or tapping by manual or mechanical means, the majorrportion of the investmeht mixture overlies the opening 46 and may pass downwardly therethrough into the casttern 41 and insures the obtaining of a satisfac-' tory and accurate reproduction of said pattern in the investment. Again it is to be noted that the application of vacuum is continued through the mixing, the pouring, and the vibrating steps. Thus, at all times the mixture is protected against contact or exposure to the atmosphere so that gaseous bubbles cannot be trapped within the finished mold and thus cause imperfections of the cast object.

After a suitable vibration period, atmospheric pressure may be allowed to enter the molding device by opening petcock 23 thereby breaking the vacuum seal, and the mixing cup 28 is removed from engagement with the molding shell 2|. Since the casting ring 44 is filled with a compacted fluid mass, there is no tendency for air to re-enter the investment mixture, and in any event such re-entry would only be into a relatively thin portion adjacent the exposed upper surface of said mixture immediately below the opening 40. As a supplemental compacting force, the inrushing air serves to compact further the investment compound around the wax pattern in the ring. The mold flask is now removed and allowed to stand until the investment mixture has set to the desired degree, after which the casting procedure may be continued.

A modification of the invention is shown in Figs. 7 through 10. In the modified form, larger sizes of investment rings may be handled and larger molds made. The modification includes a locking collar 52 which is of such diameter as to enter into the open end of the chamber 22 and carries a peripheral external flange 53 having a snug fit within the seating face 25 so as to rest upon the shoulder 21. side diameter somewhat less than the inside diameter of the shell 22 and carries a plurality of radially extending wedge-like lugs 54 upon its outer surface spaced below the flange 53. The lugs 54 engage beneath similar lugs 55 which project radially inwardly from the inner wall of the shell 2| at a point slightly below the shoulder 21. Thus, by rotating the collar 52, the lugs 54 and 55 engage and coact to lock the collar in position within the shell 2| by urging the flange 53 into snug engagement with the shoulder 21.

A cylindrical, open-ended, casting ring 56, of the usual construction, is carried within the collar 52. An annular flange 51 projects inwardly from the upper end of the collar so as to abut the upper end of the ring 56, and lugs 58 and 59, similar to the lugs 54 and 55, and carried by the ring 55 and the collar 52, respectively, are adapted to engage one another, so that upon rotation, the ring 56 is urged into snug engagement with the underside of the flange 51 and thus securely positioned within the shell 2|. Obviously, the various sets of lugs may be arranged in any desired fashion, or other suitable means may be employed for securing the casting ring in position within the molding chamber 22. In addition, provision may be made, if desired, for alining the ring within the chamber in any one particular position which may appear desirable, such as causing any particular portion of the ring always to be adjacent the higher or lower side of the chamber 22, as viewed in Fig. 9 of the drawings. A spatulating ball 60, similar to the ball 49, is carried method as previously The collar 52 has an outdescribed for the smaller investment ring may be followed in making molds for larger castings by employing the large size casting ring 56. A relatively large pattern or Wax impression 6| with suitable sprue-formers 62, consisting of wax rods or other material, is positioned within the lower portion of the casting ring 56 and the latter filled with an open-air mixed investment mixture to a point immediately below the critical portions of the pattern. In this manner, the lower end of the casting ring is closed to permit additional pouring operations in the upper portion thereof.

The ring is then locked into position within the collar 52 and the latter locked in position within the open end of the shell 2|. Now, the proper proportions of the investment mixture ingredients including water and investment compound are placed in the mixing chamber 28 and the mixing ball (50 is dropped therein. The shell 2| is inverted over the mixing cup and placed thereon as shown in Fig. 7 of the drawings. While vacuum is being established, as described hereinbefore, the water and unmixed investment compound are thoroughly evacuated. This is important in obtainin a smooth bubble-free mixture. Because of the low viscosity of the water and the substantially unwet condition of the investment compound, evacuation takes place much morerapidly and completely than would be the case if the vacuum was applied after mixing of the ingredients.

After a period of evacuation, the device is shaken and agitated to mix and blend the investment mixture as shown in Fig. 8, and to remove any gases evolved in the mixing process before the mixture is introduced into the casting ring.

Some suitable means may be employed for preventing the ball 5!} from entering the ring 56 as by providing a spider (not shown) over the open upper end of the ring 55, or by attaching the ball to the cup 28 by a suitable length of small chain (not shown) An alternate mode of operation is to mix the investment compound ingredients in the open air and then to blend and agitate them additionally after they have been placed under a vacuum in the chamber 28. In most cases, however, the evacuation of the ingredients before mixing is preferable.

After the investment ingredients have been properly evacuated and thoroughly mixed, the molding device is inverted to allow said mixture to flow downwardly into the casting ring and thereby form a mold of the pattern 6|. The molding device is vibrated in the same manner as before and substantially the same procedure followed throughout after said inversion of the molding device. The shell 2| may be supported upon the flattened base 25 or may be suitably held in an upright position, as shown in Fig. 9, during the vibration and subsequent operation depending upon the nature and size of the pattern 6|. Obviously, in many instances it Will be preferable if not essential that the molding shell be supported in a substantially upright position to insure proper filling of the casting ring 56. Following the vibration step, the casting ring 56 is removed and allowed to stand in the same manner as the ring 44 until the investment mixture has hardened to a proper degree therein.

The foregoing description of the invention is explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made,

within the scope of the appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is:

l. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a plurality of receptacles in one section of the housing for receiving separately the ingredients of a molding composition and for maintaining said ingredients isolated from one another, and a molding flask secured in said one section of the housing, the second section of the housing constituting an ingredient mixing space, and the housing having a valve controlled opening therein, and an agitating ball secured within the housing in the mixing space thereof.

2. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a partition between the sections, a plurality of receptacles carried by the partition for receiving the ingredients of a molding composition, and means for securing a molding flask to the partition in open communication with said receptacles.

3. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a partition between the sections, a plurality of receptacles carried by the partition for receiving the ingredients of a molding composition, the interiors of the receptacles being exposed on one side of the partition, said partition having an opening, and means for securing a molding flask to the partition in alinement with the opening therein in open communication with that side of the partition to which the interiors of the receptacles are exposed,

4. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a web between the sections, an open-ended multi-compartment container carried by the web having its closed end projecting into one of the housing sections and its open end extending through the web, said web having an opening laterally spaced from the container, and means for securing a molding flask to the web in alinement with the latter opening.

5. A molding device for forming a mold of an article including, a housing formed of a pair of open-ended shells having their open ends adjoining one another, a supporting partition member removably carried in the open end of one of said shells so as to be adjacent the point of adjoining of the shells and to be readily removable from the shell in which it is carried, a molding flask in said one shell carried by the supporting member, means in said one shell for receiving the ingredients to be mixed, means in the other shell for mixing ingredients placed therein, and means adapted to connect the housing with a vacuum.

6. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a partition between the sections, at least one receptacle carried by the partition for receiving the ingredients of a molding composition, and means for securing a molding flask to the partition in open communication with said receptacle.

7. A molding device for forming a mold of an article including, a housing formed of a pair of sections joined in pressure tight relation, a web between the sections, an open-ended container carried by the web having its closed end projecting into one of the housing sections and its open end extending through the web, said web having an opening laterally spaced from the container, and a molding flask secured to the web having an open end in communication with the other housing section in alignment with the latter opening.

ROY E. BARR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,325,004 Davidson Dec, 16, 1919 1,703,739 Klepsch Feb. 26, 1929 2,144,636 Piper Jan. 24, 1939 2,416,506 Vest Feb. 25, 1947

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