US2864125A

US2864125A - Press for dental investment material

Info

Publication number: US2864125A
Application number: US442155A
Authority: US
Inventors: William D Kelley
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-07-08
Filing date: 1954-07-08
Publication date: 1958-12-16
Anticipated expiration: 1975-12-16

Description

Dec. 16, 1958 w. D. KELLEY PRESS FOR DENTAL INVESTMENT MATERIAL 2 Sheets-Sheet 1 Filed July 8. 1954 INVENTOR l l fl/l'anv 0. Kelley HIS AGENT Dec. 16, 1958 w. D. KELLEY PRESS FOR DENTAL INVESTMENT MATERIAL 2 Sheets-Sheet 2 Filed July 8. 1954 I J m y Mk N 9 1 E 0 35%; m \\\x H. W MM w Uf HIS AGENT United States Patent 2,864,125 PRESS FOR DENTAL INVESTMENT MATERIAL William D. .Kelley, Dallas, Tex. Applicati0nJuly8, 1 954, Serial No. 442,155

2 Claims. (Cl. 185.7)

This invention relatesto improvements in presses and more particularly to presses used in connection with investment molding material used in casting small metallic parts, such as dental inlays and thelike.

While the present invention is particularly adaptable for use bythe dental profession, in casting inlays and the like, it is tobe understood that it is equally adaptable for use inconnectionwith the casting of jewelry and other small metal parts, which are usually cast under pressure, as in ,a, centrifugal casting machine or the like.

The present inventionis so designed as to provide a press whereby the density of the plastic material, such as dental investment material, plaster of Paris, and the like, maybe subjected to pressure immediately after the initial mixing and such pressure will be maintained on the material until it has completely set, which relieves the material of porosity due to air bubbles, which deter fromthe molding of a smooth finished metallic piece, such as an inlay.

An object of this invention is to provide a dental press, wherein pressure may be applied to investment material so as to relieve the investment material of voids and air bubbles so as tomake the molding material more dense.

Another object of the invention is to provide a mechanically operated, hydraulically responsive dental press that may be easily manipulated by hand, yet one which will give an accurate indication of the exact amount of pressure being applied to the investment material.

Still another object of the invention is to provide a press for dental investment material that may be readily assembled and disassembled for the removal of the investment flask to enable the molding of the inlay or the like.

A further object of the invention is to provide a screw actuated, hydraulically responsive dental press that is self-contained. i

A still further object of'the invention is to provide a manually operated, hydraulically actuated press element wherein the hydraulic pump and motor are contained within a single cylinder.

Yet another object of the invention is to provide O-ring sealing elements around the plunger, which plunger extends into contact relationwith the plastic material being pressed, which sealing elements prevent passage of plastic material between the plunger and the cylinder.

Still another object of the invention is to provide a dental press wherein the pressure may be applied to freshly mixed plastic investment'material with the correct or an excess amount of water therein, so when pressure is applied the excess water may be pressed out of the investment material. thereby automatically giving an investment material the correct setting expansion.

With the foregoing objects in mind and others that will manifest themselves as the description proceeds, reference is to behad to the accompanying drawings, in which like reference characters designate like parts in the several views thereof, in which:

Fig. l is a perspective view of the manually operated,

2,864,125 Patented Dec. 1.6,

2 hydraulically responsive press taken from the top and a side thereof; v Fig. 2 is a vertical sectional view taken through the device, as shown-in Fig. 1, with parts broken awayv and shown in elevation to show the details of construction;

Fig. 3 is a sectional view taken on the line 33f of Fig. 2, looking in the direction indicated by the arrows; Fig. 4 is a cross-sectional view similar to that shown inFig. 3, but taken'on the line 4--4 of' Fig. 2, looking in the direction indicated by the arrows;

Fig. 5 is an elevational view of a modified formof invention, with parts broken away and shown in section to bring out the details of construction; i Fig. 6 is a sectional viewtaken on the line 66-of Fig. 5, looking in the direction indicated by the arrows; and t Fig. 7 is a fragmentary vertical sectional view with parts broken away and shown in section, of the .upper portion of a modified formof the invention, the lower part being substantially as shown in the form of. the invention illustrated in Fig. 2.

First form of 'invention With more detailed reference to the drawing, asehpwn in Figs. 1 through 4, the numeral. 11. designates a tubular base which. is. internally threaded at the. respective upper and lower ends, as indicated'at 12 and 1,4, as is bes t seen in Fig. 2. The hydraulic assembly -unit, generally designated by thenumeral 16, has external screw threads :1 the lower. end, which are adapted to interfitgwith screw threads 14. A plate 20 is secured to the lowe r end of the hydraulic member 16 by means of screws 22 and has a spring 2 interposed between theplate ZO-and the lower face of a shouldered piston 26, which is fitted within cylinder 28. A sealing element, such as a rubber cup member 30, is fitted above shouldered piston 2 6Qso as to form a fluid tight seal with the cylinder 28. to prevent leakage of hydraulicfluid outward thereby. The lower end of shouldered piston, 26 has a plunger 32 thereon which is adapted to extend through an aperture formed within partition plate 34, when the plunger is in extended position. The plunger has annular grooves formed therearound, which are preferably square in cross section, and which annular grooves receive Ov-rings 3 6.

A molding flask, which comprises an upper rubber portion 38 which has a hole 40 formed thereth rough, which hole is tapered at the upper end thereof, but which is'in tight fitting relation with the plunger 32 for the greater part of its length, which enables the plunger 32 to form a tight seal within the hole 4t! while the press is being used. The rubber portion 38 has an annular groove around the under side thereof to complementarily receive the upper end of cylindrical ring 42, the inner portion of which form the mold cavity. The lower end, rubber cap portion 44 forms a seal for the lower end of the ring 42, which cap portion has an upwardly extending conical portion 46 which serves to form a funnel or neck to provide for the introduction of material into the mold cavity when an inlay or the like is being molded. A pin 48 is centrally mounted within the upwardly extending neck portion 46 and is adapted to receive a wax model on the upper end thereof, which wax model is designated at 50. 'When plastic material is poured into the m old cavity formed in the ring 42, the plastic investment material will surround the wax model. However, under normal conditions, the investment material will be laden with minute to large air bubbles, but, with a molding flask comprising the upper rubber portion 38, the ring portion 42, and the lower cap portion 44, the flask may be placed in the lower end of the tubular base member 11 so it will abut with the partition 3.4. With the device in this position, a screw-threaded plug 52 is screwed into screw threads 12 until the flask is in secure relation with respect to the tubular base. It is preferable to have the plunger 32 arranged so that it will extend substantially flush with the lower end of plug 38 when in pressing posit on, so as to present the investment block with a substantially smooth upper end. With the device arranged in this manner, it is ready to invest a model of a dental inlay or the like.

The upper portion of the cylinder 28 has cupped piston member 54, which piston is attached to a screw-threaded bolt 56 by means of a hollow bolt 58, which hollow bolt 58 interconnects with a passage 60 within screw-threaded bolt 56. The bolt 56 threadably engages a shouldered portion 62 of the piston 54, so upon rotation of the head of bolt 64, the piston 54 is forced downward. It is preferable to have the head portion 64 of the bolt knurled or otherwise roughened or irregular in shape, so as to enable the gripping thereof by hand. It is also preferable to have the cylindrical portion designated at 16 adjacent the head portion 64 roughened or knurled so as to enable it also to be gripped by hand, to enable the operation of the bolt 56.

A pressure gauge 66 threadably engages the upper end of bolt 56 and connects with passage 60 so that the pressure of fluid entrapped between

piston cups

30 and 54 may be read on the gauge 66.

A dowel pin 68 interconnects bolt 56 and piston 54 to prevent relative rotation therebetween to prevent rotation of the head 64.

Operation of first form of invention The flask F, which comprises the upper rubber portion 38, the cylindrical ring 42, and the lower cap portion 44, is inserted within tubular base member 11 and with the wax model 50 in place on the sprue pin 48, investment material is poured through opening 40 until the cavity within the ring 42 is filled with the material extending up into hole 40, and with the plunger 32 in retracted position, the cylinder portion 16 is screwed into place in the upper portion of tubular base member 11 and without any pressure within cylinder 28, the spring 24 will hold the piston 26 in raised position, and the screw threaded bolt 56 will be in upward position with the piston 54 a spaced distance from piston 30, and with the chamber between the

pistons

30 and 54 filled with suitable fluid, such as hydraulic fluid, the head 64 is rotated so as to screw bolt 56 downward to urge piston cup 54 toward the piston cup 30. The pressure will cause the piston 26 to move downward to compress spring 24 to urge plunger 32 downward into hole 40, which is in tight fitting relation with respect to the plunger and with plastic investment material extending into the opening 40, the pressure of the screw bolt member 56 will be transmitted through hydraulic fluid to cupped piston member 30 which will urge the plunger 32 downward into contact relation with the plastic material, which is made chiefly of a chalky solid and water, such as plaster of Paris, dental investment stone and the like. As the pressure is increased on the plastic material within the cavity of the flask F, the air bubbles within the material will be compressed until they are practically non-existant, and the voids made thereby will be filled with solid material. The pressure can be minutely controlled and gauged by the pressure gauge 66 so that the wax model 50 will not be damaged. The flask containing the plastic material may be left under pressure until the material is completely set. In this manner a dense block of investment material may be formed with the wax model therein, so upon removal of the investment block from the press, the rubber portion 38 and cap portion 44 may be removed from the cylinder ring 42, and after removing the rubber portion 38 and the lower cap portion 44, the cylindrical ring may be reinserted within the lower portion of the tubular base 11,

so the lower edge thereof will rest on the upper face of screw-threaded plug 52, then upon applying pressure again to the plunger 32 and to the upper end of the investment block, the investment block will be moved downward along the inner taper of the cylindrical ring 42 a sufficient distance to loosen the block from the cylindrical ring which will permit ready removal thereof and with the investment block now being removed from the forming flask, it may be heated in the usual manner, to remove the wax, and placed in a pressure molding machine for molding the inlay in the usual manner.

An alternate method of introducing plastic material into the cylindrical flask F, is to assemble the parts together with the wax model 50, of the object to be cast, in place on sprue pin 48, then plastic investment material is poured into opening 40 until the investment material is substantially level with the top of the rubber portion 38, and while the material is still plastic, the entire flask assembly, comprising the rubber portion 38, cylindrical ring 42 and cap portion 44, is inserted through the open end of tubular base member 11, then the screw threaded thumb nut 52 is screw threaded into the lower end of tubular base member 11 until it is in binding engagement with the lower end of the flask, whereupon, hydraulic fluid pressure is ready to be applied in the manner hereinbefore set out.

Second form of invention The form of invention, as disclosed in Figs. 5 and 6, shows a device, the operating mechanism of which, including the tubular base 11, is substantially the same as the form of the invention illustrated in Figs. 1 through 4, and described above. However, this form of the invention utilizes a base 71 in which a rubber bottom cap 72 is fitted, which cap has an annular groove 74 formed therein, which groove is spaced radiallyinward from the outer periphery of the cap to receive the lower end of a cylindrical ring member 76. A cap portion 78 has a screw threaded neck portion 80 thereon which threadably engages screw threads 12 that are formed within the cylindrical base portion 11. A rubber cap portion 79, having a hole 81 formed therein, is fitted within the cap portion 78. The inner cylindrical bore of the neck portion 80 has fitted therein an enlarged piston element 82, with O-ring elements 84 thereon, to form a sealing engagement between the piston and the bore of the neck. The upper end of the piston 82 has a connecting rod 86 thereon, the upper end of which is reduced and threaded, as indicated at 88, to threadably engage a threaded hole 31 in the lower end of plunger 32. By removing a blind screw 33 from the lower end of plunger 32, the connecting rod 86 may be connected thereto, so the flask member, designated at 90, and comprising a base plate 71, bottom cap 72, cylindrical ring 76, cap portion 78, and upper rubber cap portion 79, may be connected thereto. The flask is held together by means of posts 92 which threadably engage the base 71 and extend upward. The upper ends of the respective posts 92 are reduced, as indicated at 94, to telescope into the respective holes 96 formed in the upper cap 78. A thumb screw 98 passes through the respective holes within cap plate 78 and threadably engage ascrew-threaded hole which is formed within the respective ends of the posts 92.

The respective lower and

upper caps

72 and 79 have

annular grooves

100 and 102 respectively formed therein, which are spaced radially inward from the outer periphery thereof to receive the respective lower and upper ends of cylindrical ring member 76. The hole 81 is in register with the cylindrical bore formed in upstanding threaded neck 80 so that the piston 92 will travel free from the neck into the cap portion 79, so when the cylindrical cup piston 30 is in its lower-most position, the lower end of the piston 82 will be flush with the lower edge of the cap portion 79. In this manner a lar e m d web s ndicated at 50a, may be mounted on the sprite pin 4811, than could be mounted in the type of flask shown at F, in the form. of invention described above.

Operation of second form' of invention When it is desired to mold a larger object than may be received within the flask F, of the form of invention as shown in Figs. 1 through 4, the screw 33 maybe removed from the end of the plunger 32 and the upstanding connecting rod 86 screw-threaded into the lower end of the plunger 32, then, with the flask 90 clamped together by thumb screws 98, and with the model 50a in place on sprue pin 48a, and with the flask 90' separated from the tubular member 11, plastic investment material is introduced into flask 90 until the screw threaded neck portion 80 is substantially filled. Whereupon, the neck portion 80 is screw threaded into the lower end of tubular base memberll so that the piston 82 will register with the cylindrical bore of neck 80', whereupon the method of applying pressure to the plastic material isthe same as set out for the form of the invention as illustrated in Figs. 1 through 4, and described above.

After the piston 82 has applied pressure to the plastic material to compress the air bubbles therefrom, so as to render the investment block more dense, a predetermined amount of pressure is maintained thereon until the plastic investment material is thoroughly set, whereupon, the thumb screw 98 is loosened to enable the removal of the flask 99 from between the base plate 71 and the upper cap portion 78, then by removing the upper and

lower cap members

72 and 79, the cylindrical. ring 76 may be reinserted between base plate 71 and upper cap 78, and the thumb screw 98 tightened, and with the cylindrical member 76 resting on the base plate member 71, and with the lower face of the investment block being a spaced distance upward from the lower end of the cylindrical ring 76, and with the piston 82 either in contact relation with the upper face of investment block within cylindrical ring 76 or resting on proper spacer elements which are interposed between piston 82 and the upper face of the investment block, pressure may be applied to the piston 82 by the rotation of upper knurled portion 64 of screwthreaded bolt 56, whereupon, the piston 82 will move the investment block downward along. the inner tapered surface of the cylindrical ring 76 to break the bond therebetween to permit the ready removal of the block.

It is to be pointed out that this arrangement allows different sizeflasksto be used with. the same pressure generating elements, and if desired, the pressure gauge may be arranged to carry dual calibrations, in event the pistons acting upon the plastic investment material have different cross-sectional areas. However, it is to be understood that while piston 82 is shown to be of larger crosssectional area than plunger 32, it is within the scope of the present invention, to use a plunger of a size to fill the needs of the particular job at hand.

By utilizing a flask or ring, as indicated in Figs. and 6, two or more small rings similar to the ring 42 and lower cap portion 44, respectively, with wax models, such as indicated at 50, the cap portion may be seated on the upper face of the lower cap portion 72, and with the rings 42 open at the top, the ring 76 and rings 42 may be filled with plastic investment material so when pressure is applied by plunger 82, equal pressure will be applied to investment material within each of the rings 42, and since the pressure is equal in all directions on the wax model 50, production molding may be easily performed in this manner.

Third farm of invention The form of the invention, as shown in Fig. 7, has a tubular body member 111 that has the lower portion thereof of substantially the same construction as the tubular base 11, and which is adaptable for use with either form of flask F or 92. The upper portion of the tubular body 111 is screw threaded, as indicated at 112 to threadably" receive a hollow screw-threads.d" bolt; 1 14, which hasthreads 116.- The hollowportion of the-bolt isw a cylindrical bore 118 that is adapted tolreceive a piston cup 120 therein, which cup is'fitted on theupper end of piston member 122, in substantially the same manner as the form of the-invention asdescribed above. How, ever, the upper end of the cylindrical bore 118 is closed and a pressure gauge 66, which has a threaded connection thereon, threadably engages a screw-threaded hole 124 which interconnects with cylindrical bore 118; The pressure gauge 66 sealsthe upper end of cylindrical bore 11% in fluid tight relation. A spring 126 is. interposed between the shouldered upper endof cylindrical bore 118 and the cylindrical cup member 120, so as to normally urge plunger 132 downward. The-plunger 132 has a threaded hole 131 in the lowenend thereoflwhich normally receives a blind screw 133. The plunger-132 is maintained in place by an. annular screw'threaded ring 134 that is screw threaded into the lower end of screwthreaded bolt 114. However, it is in loose fitting relation with the plunger 132 so as to enable; the relative turning, and the sliding of the plunger 132 with respect to the annular ring 134.

It will be seen that this form of invention eliminates the upper cup member and the mechanism incident thereto, and it is to be pointed out that this form of pressure applying arrangement can be used either with the flask F, asshown in Figs. 1 and 2, or with flask asshown in Figs. 5 and 6. The results and operation with respect to the insertion and removal of the flask is the same as for the aforementioned forms of invention.

I Operarionof third form. of invention With the screw threaded bolt 114 screwed to the uppermost position, and with the flask F or 90 filled, in" the manner hereinbefore set out, and in place, the knurled head of bolt 114 is turned to screw the bolt downward into the tubular body 111 as the spring compresses, and with the hydraulic fluid within cylindrical bore 118, the plunger 132 is forced downward into opening 40 of flask F to apply pressure. to the plastic investment material therein to compress the air bubbles therefrom, in the manner described for the forms above. In this manner the fluid pressure is applied to the pressure gauge 66 directly through threaded connection 67, when the maximum pressure to be applied is attained, theplastic material may be allowed to remain. in the flask until completely set, whereupon, it is removed therefrom in the manner set out above.

It is to be pointed out that the form of the invention as shown in Fig. 7 may be constructed of fewer parts than the previously described forms of the invention, thereby reducing the cost thereof. By having a single piston cup positioned within cylindrical bore 118, the possibility of leakage of the hydraulic fluid is minimized.

By the use of a relatively thin mixture of investment material, the material will flow around the body of the wax model so more minute detail may be obtained and the possibility of thick material abridging interstices, which would result in an imperfect casting, is eliminated.

By having the setting expansion of the dental material and the thermo-expansion of the gold equal, a high degree of accuracy is obtained in the casting. By the application of the pressure to the plastic investment material, the air bubbles within this material are reduced to approximately one-ninth their size under forty-five pounds pressure.

It is to be further pointed out that the shrinkage of gold is approximately 2.5% when cooled from the molten state to normal temperature, and since the accuracy with which dental inlays must be very exact, it was necessary heretofore to adhere to a very strict water-powder ratio to give the correct setting expansion of the investment material, which is approximately 2.5%, therefore ifthe water-powder ratio varied, the accuracy of the finished casting was impaired. However, with the present arrangement, the excess water is pressed out of the mixture until the mixture contains the correct propor tions of water-powder to give the correct setting expansion ratio. In this manner, it is not necessary to adhere to the exact water-powder ratio in mixing the investment material, in fact better results may be obtained by the use of a relatively thin investment mixture, as long as sufficient water is added, or any excess, the pressure of the plunger forces the excess water out of the investment ring, giving the correct water-powder ratio.

While the invention has been described and illustrated in some detail so to the forms shown, it is to be understood that changes may be made in the minor details of construction, and adaptations made in particular applications, without departing from the spirit of the invention or the scope of the appended claims.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. In an investment molding press for applying pressure to plastic dental investment casting material, at least two elongated tubular shell members screw threaded together in end to end relation, one of said shell members having a cylindrical bore formed axially therein, a pair of opposed pistons within said bore, hydraulic fluid between said pistons, one of said pistons being attached to a hydraulic pressure applying plunger, which plunger is apertured longitudinally and carries a pressure gauge thereon which is in communication with said cylindrical bore through said aperture in said plunger, said second piston being attached to a shouldered, fluid responsive plunger fitted in the other end of said cylindrical bore, the reduced portion of which plunger extends outward therefrom, a retaining ring surrounding the reduced portion of said shouldered plunger and being secured to the end of said shell member having a cylindrical bore, a spring interposed between said retaining ring and said shouldered portion of said last mentioned plunger, said second mentioned elongated, tubular shell member having an abutment intermediate the length thereof, which abutment is centrally apertured, said reduced end portion of said fluid responsive plunger being adapted to extend through said apertured abutment into said last mentioned tubular shell member, said last named tubular hell member being adapted to receive a molding flask having an axial hole formed therein, and screw means in said second mentioned tubular member at the end remote from said cylindrical bore, for retaining said molding flask within said tubular member.

2. In an investment molding press for applying pressure to plastic dental investment casting material, at least two elongated tubular shell members screw threaded together in end to end relation, one of said shell members having a cylindrical bore formed axially therein, a pair of opposed pistons within said bore, hydraulic fluid between said pistons, one of said pistons being attached to a hydraulic pressure applying plunger, which plunger is apertured longitudinally and carries a pressure gauge thereon which is in communication with said cylindrical bore through said aperture in said plunger, said second piston being attached to a fluid responsive plunger fitted in the other end of said cylindrical bore, which plunger extends outwardly therefrom, means retaining said plunger within said cylinder, a spring interposed between said cylinder and said plunger to urge said plunger into said cylinder, said second mentioned elongated, tubular shell memberhaving an abutment intermediate the length thereof, which abutment is centrally apertured, said outwardly extending end portion of said fluid responsive plunger being adapted to extend through said apertured abutment into said last mentioned tubular shell member, said last named tubular shell member being adapted to receive a molding flask having an axial hole formed therein, and screw means in said second mentioned tubular member at the end remote from said cylindrical bore, for retaining said molding flask within said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS