US3818974A

US3818974A - Centrifugal vacuum casting apparatus

Info

Publication number: US3818974A
Application number: US00312863A
Authority: US
Inventors: O Eberle
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-06-28
Filing date: 1972-12-07
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

In combination with a centrifugal casting machine of the type described, suction cover means shaped and adapted to be fitted over the free end of the flask or cylinder containing the investment, sealing means for sealing the same to prevent entry of air between said suction cover and said flask, attachment means securing the suction cover in position and maintaining the same in position during operation of the centrifugal casting machine, and being releasable and removable therefrom subsequent to casting, flexible air hose means connectable to said suction cover, and permitting the same to swing between the vertical and horizontal position of said investment flask, fixed air conduit means positioned adjacent to said casting machine, and rotatable coupling means connecting said flexible air hose means to said fixed air conduit means, said rotatable coupling being oriented and located in alignment with the axis of rotation of said centrifugal casting machine, whereby a vacuum may be applied to the closed end of the said investment flash during operation of said centrifugal casing machine; and a method of casting precious metals by centrifugal casting including the steps of applying a vacuum to one end of the investment flask during the rotation of the investment flask and heating cylinder.

Description

United States Patent 1191 Primary ExaminerRobert D. Baldwin Eberle June 25, 1974 [54] CENTRIFUGAL VACUUM CASTING V APPARATUS 1 [57] ABSTRACT [76] Inventor; 0m Eugen Eb l 421 c ild d In combination with a centrifugal casting machine of Pk W, Hill (T t O i the type described, suction cover means shaped and Ca ada adapted to be fitted over the free end of the flask or cylinder containing the investment, sealing means for [22] Flled: 1972 sealing the same to prevent entry of air between said [21] A l N 312,363 suction cover and said flask, attachment means secur- Related U S A c ti Dal ing the suction cover in position and maintaining the pp a on a same in position during operation of the centrifugal commuatwn-m-part 0f 1 June 23, casting machine, and being releasable and removable 1971 317311725 therefrom subsequent to casting, flexible air hose means connectable to said suction cover, and permit- [52] US. Cl. 164/255, 164/289 ting the Same to Swing between the vertical and h0ri [51] Int. Cl B22d 13/06, 822d 25/02 Zonta] position of Said investment flask, fixed Com [58] Fleld of Search 164/63, 255, 289, 290, duit means positioned adjacent to Said casting 164/65; 285/276; 239/251 chine, and rotatable coupling means connecting said flexible air hose means to said fixed air conduit means, [56] References C'ted said rotatable coupling being oriented and located in UNITED STATES PATENTS alignment with the axis of rotation of said centrifugal 1,235,857 8/1917 Sweetnam 164/255 casting machine. whereby a vacuum y be pp to 2,477,092 7/1949 Rubisson 164/290 the closed end of the said investment flash during 3,05 1 9/1962 rennan 164/290 X operation of said centrifugal casing machine; and a 3,068,538 12/1962 Lindner 164/289 X method of asting Precious metals by centrifugal cast 3,117,584 1/1964 Elenbaas", 239/251 X ing including the steps of applying a vacuum to one end of the investment flask during the rotation of the 3:735:8OO 5/1973 HU RLJQIIIIIIIIIIIIIIIII 164/290 x mvestmem flask and heatmg cylmder 6 Claims, 4 Drawing Figures 1 CENTRIFUGAL VACUUM CASTINGAPPARATUS The present invention relates to apparatus for casting precious metals, by what is known as the lost-wax method, and is a continuation-in-part of application Ser. No. 157,269 entitled Method for Casting Bimetallic Jewellery, filed June 28, 1971, now US. Pat. No. 3,731,726.

BACKGROUND OF THE INVENTION Apparatus for casting by the lost wax method usually has a pair of heating chambers or cylinders for heating the precious metal which are mounted on opposite sides of a turntable. The turntable is motor driven so that it rotates to generate centrifugal force. The heating cylinders are mounted on tilting mounts so that they may be tilted from a vertical position to a horizontal position during rotation of the turntable. The moulds which are made of any suitable investment material, such as plaster of paris, are contained in cylinders known as flasks. The flasks containing the investment are firmly attached to the heating cylinders, after which the turntable is rotated and the heating cylinders are tilted into a horizontal position, and the molten metal then flows out of the cylinders into the cavities formed in the investment. Rotation is usually continued long enough for the metal to set, which takes place in a very few seconds after which the turntable is stopped and the flasks are removed, and the investment is then carefully broken so as to free the metal objects for polishing and finishing.

This type of apparatus is very widely used in many countries for the manufacture of precious metal objects such as jewellery, rings, pendants, etc., and so long as sufficient care is taken during the various operating procedures it produces excellent results.

In some cases however where, for example it is desired to cast a particularly intricate design of precious metal, the passages in the investment are found to be extremely difficult to fill. The metal may set before the cavity is completely filled with the result that an entirely new cavity must be made in a new flask and the metal re-melted before further casting. One of the ways of overcoming this problem is to pre-heat the investment and the flask containing the investment prior to the actual casting operation. It is quite common to preheat the investment to very substantial temperatures in the region of l,000 to l,400F. This, of course, means that the metal will remain in a molten state somewhat longer, and thus the centrifugal force will have a somewhat longer period of time in which to act on the very small volumes of metal filling the finer passages in the mould. However, this excessive pre-heating involves other disadvantages. Obviously, the higher the preheating temperature of the investment, the longer it will take the investment to cool, and the longer will be the processing time involved.

In addition, however, if it is attempted to form an article or piece of jewellery of two different precious metals, by embedding a pre-formed first part in the investment, and subsequently casting the second part around the first part, excessive pre-heating is impossible. Temperatures in excess of 750F tend to tarnish and impair the finish of precious metals embedded in the investment, and consequently such a pre-heating step must be avoided.

Accordingly, it is a general objective of the invention to provide an apparatus for casting by the lost wax method in which complete fillingof the mould is insured with a greater degree of certainty, and without the requirement for pre-heating the investment to excessive temperature.

BRIEF SUMMARY OF THE INVENTION The invention therefore seeks to provide, for use in combination with a centrifugal casting machine of the type described, suction cover means shaped and adapted to be fitted over the free end of the flask or cylinder containing the investment, sealing means for sealing the same to prevent entry of air between said suction cover and said flask, attachment means securing the suction cover in position and maintaining the same in position during operation of the centrifugal casting machine, and being releasable and removable therefrom subsequent to casting, flexible air hose means connectable to said suction cover, and permitting the same to swing between the vertical and horizontal position of said investment flask, fixed air conduit means positioned adjacent to said casting machine, and rotatable coupling means connecting said flexible air hose means to said fixed air conduit means, said rotatable coupling being oriented and located in alignment with the axis of rotation of said centrifugal casting machine, whereby a vacuum may be applied to the closed end of the said investment flask during operation of said centrifugal casting machine.

The invention further seeks to provide apparatus having the foregoing advantages, and incorporating air conduit means communicating with the open end of said investment flask, and flexible air hose means connecting thereto, and connecting the same to said rotatable coupling means, whereby a vacuum may be applied to the open end of said investment flask during casting, and further incorporating valve means whereby the vacuum applied thereby may be controlled.

The invention further seeks to provide apparatus having the foregoing advantages wherein the rotatable coupling comprises a fixed conduit member depending downwardly along the axis of rotation of said centrifugal casting machine, flexible sleeve means rotatably fitting around said fixed conduit means, and there being a rotatable seal therebetween, and conduit connection means comprising a generally L-shaped conduit, one portion of which extends into said flexible sleeve means, and the other end of which extends substantially at right angles to the axis thereof for connection with said flexible hose means.

The invention further embraces a centrifugal casting machine incorporating all or part of the aforesaid apparatus, and further comprises a method of casting precious metals by centrifugal casting, including the steps of applying a vacuum to the closed end of the investment flask during the rotation of the investment flask and heating cylinder.

The foregoing and other objectives of the invention will become apparent from the following description of a preferred embodiment of the invention which is given here by way of example only with reference to the following drawings.

' BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged schematic view of a heating cylinder and investment flask, showing the general principle and purpose of the invention;

FIG. 2 is a schematic upper perspective illustration of a centrifugal casting machine, shown incorporating the invention;

FIG. 3 is a section along the line 3 3 of FIG. 2 greatly enlarged and inverted, and,

FIG. 4 is a section along the line 4 4 of FIG. 2 greatly enlarged.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT Before describing the invention in detail it will be helpful to explain the general principles and purpose, with reference to FIG. 1.

In a centrifugal casting machine of any suitable type (the details of which are shown in FIG. 2), a holder or heating cylinder is mounted so as to permit the same to be rotated at high speeds on a pivot axis 1 to create the centrifugal force required. A crucible indicated schematically as 14 is located within the holder 10 and contains the molten gold or other metal, and a closure plate 16 is associated with the crucible 14. The flask 18 containing investment 20 is arranged with its bottom end fitting within the open end of the heating cylinder 10 and the closure plate 16 closes the bottom end of the flask as shown. In order to withdraw air from the bottom end of the flask 18, a vacuum tube 22 passes through the closure plate 16, being connected with any suitable vacuum source (not shown).

Further evacuation of any residual air within the cavities in the investment 20 is achieved by placing a vacuum manifold 24 at the upper end of the flask 18, i.e., the end remote from the cavities in the investment 20. During pouring of the molten metal into the lower end of the flask 18, the manifold 24 is subjected to continuous evacuation through any suitable vacuum tube 26, and, since the investment 20 within the flask 18 is to quite a substantial extent porous to air, air contained within the cavities formed therein will tend to be evacuated, especially at the time when molten metal is entering such cavities.

In order that the

vacuum tube

22 and 26 may rotate with the holder 10 they are provided with rotatable couplings arranged on the axis of rotation 12 of the holder 10 (as shown in more detail below).

Referring now to FIG. 2, it will be seen that this drawing shows in schematic form a typical centrifugal casting machine consisting of a support frame or bench 30 which is provided with a rotatable turntable 31 which is driven in the direction of the arrow A by an electrical motor located beneath the bench 30 (not shown). Mounted on the rotatable turntable 31 are two heating cylinders 10 (only one being shown for the sake of clarity, although it will be understood that in the usual assembly there will be two such heating cylinders 10 on opposite sides of the turntable 31 for the sake of counter-balancing its operation). Each heating cylinder 10 is swingably mounted for swinging between a vertical position and a horizontal position as shown in phantom in FIG. 1, between the two upright support columns 32 fastened to the surface of the bench 30. As shown in FIG. 1, in the typical machine, the two support columns 32 will be located more or less equidistant from the periphery of the turntable 31 so as to locate the swinging axis of the heating cylinder 10 more or less along a chord of the circle defined by the periphery of the tumtable 31. In this way, when the turntable 31 is rotated in accordance with the mannerwell known in the art, the heating cylinder 10 may be tipped from its upright position to the horizontal position as shown in phantom, and the centrifugal force generated by the rotary movement of the table 31 will be directed along the longitudinal axis of the heating cylinder 10 radially outwardly with respect to the table 31.

Again, as is well known in the art, the flask 18 containing the investment 20 is releasably attachable to the upper end of the heating cylinder 10, the flask 18 being shown attached in position in FIG. 2, and thus, when the heating cylinder 10 is tipped into its horizontal position, the investment flask 18 swings with it in unison into a corresponding horizontal position as shown in phantom. In this position, the rotary motion of the turntable 31 creating a centrifugal force acting along the axis of the heating cylinder 10 and the investment flask 18 will then cause molten metal within the heating cylinder 10 to be forceably ejected therefrom and enter the investment flask 18 where, under the continued influence of the centrifugal force it will penetrate into the cavities formed therein in known manner.

As stated above, all of these features, and this mode of operation have been well known for many years and form no part of this invention.

Referring now to FIG. 3, the heating cylinder will typically be seen to enclose or contain a heating chamber or crucible l4, surrounded by one or more electrical heating elements shown in phantom as 33. These electrical heating elements may be supplied with electrical power through any suitable flexible cables, not shown, by electrical connections mounted on the turntable 31. Heating temperatures are controlled by thermocouple 34. Again, these matters are essentially well known in the art and form no part of this invention.

Preferably, the heating cylinder 10 is mounted be tween the columns 32 by means of the two mounting rods 35 attached on either side of the heating cylinder 10. The mounting rods 35 themselves carry sliding T- shaped sleeve members 36 which are connected to cross-shafts 37 mounted in upright columns 32. The open end of the cylinder 10 is provided with a neck or collar 37 adapted to fit snugly around the investment flask 18 as shown in FIGS. 1 and 3. The investment flask 18 is of cylindrical construction open at both ends, and containing the investment material 20. The investment material is essentially similar to plaster of paris, although commercially available investment materials incorporate various additives and conditioners which improve the end result obtained. Within the investment 20 there are formed a series of cavities 38 in the shape of rings or like articles of jewellery, which are connected by passageways 39 to an open well 40 formed essentially by a depression in the investment material. Preferably, a groove 41 generally of a circular shape as shown connects all of the passageways 39. The

formation of the investment 20 with the various cavities, passageways and grooves as shown is very well known in the art and the process does not require further description except to say that it is usually made by the so-called lost-wax method. The investment throughout the remainder of the flask 18 is free of any cavities but is porous to air.

According to the invention, a vacuum may be applied to the upper or free end of the investment flask 18, and according to a further optional feature of the invention,

may also in certain circumstances be applied to the opening or well 40 of the lower end of the investment flask 18.

In order to achieve this result, an end closure cap or cover 24 of generally cylindrical shape is provided, having a collar portion 41 adapted to fit snugly around the exterior of the investment flask 18 as shown, and having an interior ledge 42. A vacuum pipe 26 connects with the interior of the cover 24, and is connected to a suitable vacuum conduit by means of a flexible hose connection 43. Preferably, heat resistant sealing means 44 are provided on the ledge 42 for engaging the investment flask 18 as shown and making a good airtight seal therewith.

Preferably, the cover 24 also serves to retain and fasten the investment flask 18 in position in the collar 37 of the heating cylinder 10. For this purpose, it is provided with flanges 45, for receiving any suitable fastening means such as rods 46 which may be fastened thereon by fastening devices such as nuts 47.

Clearly, such fastening means as shown here is purely exemplary. In practice, the cover 24 may be made separately from the fastening means, and the fastening means itself may take a variety of forms.

In order to apply a vacuum to the other end of the investment flask 18 namely to the well 40, vacuum conduit 22 is arranged to extend through a portion of the heating cylinder as shown so that the inner end thereof communicates with the well 40 and the open end of the investment flask 18. The conduit 22 extends through the exterior of the heating cylinder 10 and is preferably connected to any suitable vacuum supply through a flexible hose 48. Preferably, a heat resistant sealing means 49 will be provided between the open end of the investment flask 18, and plate 16 of the heating cylinder 10 as shown so as to provide a good airtight seal therewith, at least in cases where the additional vacuum conduit 22 is in use.

As shown in FIG. 2, the hose 43 is connected to one side of a T-shaped connecting member 50. The stem portion of the T-shaped connecting member 50, shows as 51, is connected to a flexible coupling sleeve 52, and the upper end of the flexible coupling sleeve 52 is connected to a further T-shaped connecting member 53. The upper T-shaped connecting member 53 is fastened to a fixed conduit 54 which is supported transversely of the rotary table 31, by means of the two upright conduit portions 55. The T-shaped connecting member 53 is preferably aligned with its stem portion 56 extending perpendicularly downwardly and aligned with the axis of rotation of the table 11.

The other flexible hose 48 is connected to the other side of the lower T-shaped member 50, and in this case is preferably provided with a control valve 57. If desired, a pressure gauge 58 and a further control valve 59 may be provided in the transverse conduit 51. Preferably, one of the upright conduits 52 is sealed, and the other of the upright conduits 52 is connected to a suitable vacuum pump which may or may not incorporate a vacuum tank, according to the well known practice whereby to apply a vacuum to the interior of the transverse conduit 54.

The lower rotary connecting T member 50 is preferably fastened in some way to the table 31, such as by cross-member 60 fastened across the centre of the table 31 as shown. The T-member 50 is fastened at the mid-point of cross-member 60 so as to rotate in unison with the table 31.

The flexible coupling 52 is shown in detail in FIG. 4 and comprises a length of flexible plastic tube 61 fastened by a clamp 62 to the stem 56 of the upper T- member 53. The lower end of the tube 61 fits over the stem 51 of the lower T-member 50. At this lower end, there is no clamping means as such, and a rotary seal is achieved by means of the O-ring 63.

The procedure prior to actual casting will be in essence the same as the procedure in conventional casting practice. Thus pieces of the gold metal will be placed in the heating chamber or crucible 14, and heated until they are in a molten state. During this stage the heating cylinder 10 will of course be in its upright position with the investment flask 18 removed. At this stage, the investment flask 18 will already have been filed with investment material, and the cavities have already been formed therein according to known practice. Usually, during the melting of the gold in the chamber or crucible 14, the investment flask 18 will actually be in a pre-heating oven.

In accordance with conventional practice, where molding a very intricate object, the pre-heating step would often be carried out up to high temperatures.

According to the invention, the use of such excessive pre-heating is unnecessary as will appear below. Accordingly, such pre-heating step will only, in the majority of cases, be carried out up to temperatures in the range from about 400 to 700F.

Once the gold has been completely melted, and the investment flask 18 pre-heated to the correct temperature the flask 18 is then placed in position with its open end, i.e., the end containing the well 40 and the groove 41, will be directed downwardly, and the flask 18 will be received within the collar 37. The cover 24 will then be fastened to the upper or closed end of the flask 18, and the fastening means 46 and 47 will then be secured in position so that the cover 24 is pressed firmly onto the investment flask 18 which in turn is pressed firmly between the

seals

44 and 49 thereby rendering both ends air-tight.

The valve 59 is then opened so as to apply a vacuum to the flexible hose 43 and conduit 26. In this way, air within the cover 24 is exhausted. As the air within the cover 24 is Withdrawn, it will apply a vacuum to the investment 20 within the investment flask 18. As mentioned above, the investment 20 in its dried and finished state is in fact porous to air and air within the cavities 38 andthe well 40 will also be at least partially, if not substantially completely evacuated, at least to the extent of the reduced pressure applied by the vacuum conduit 26.

Just before the turntable 31 is set in motion, the valve 57 may optionally be opened so as to apply the vacuum briefly to the flexible hose 48 and the conduit 22 to thereby still further evacuate the well 40 and the cavities 38 and passageways 39. In many cases, this additional step can be omitted, but in cases of extremely intricate work, or where for example the pre-heating of the investment 20 is restricted to a lower range of temperatures the additional evacuation step is found to be effective.

The valve 57 is the shut off so as to discontinue the application of the vacuum to the conduit 22. Immediately afterwards, the turntable 31 is set in motion by operating a suitable electric switch (not shown) and at 7 the same time, by the operation of another control (not shown) the heating cylinder 10, and the investment flask 18 attached thereto are tilted from the vertical into the horizontal position as shown in phantom in FIG. 1 while the turntable 31 is actually in motion. The application of centrifugal force by the rotation of the turntable 31 ejects the molten gold from the crucible 14, and it flows directly into the well 40 of the investment flask l8 and then into the groove 41, passageways 39 and cavities 38. The flow of the gold in this direction is considerably increased and accelerated by the continued application'of the vacuum to the closed end of the investment flask 18 by means of the cover 24. In addition, any resistance to such gold flow which might otherwise occur by reason of the presence of air within the cavities 38 will be substantially reduced if not completely eliminated. As a result, the gold will be found to completely fill the cavities 38 even when it is quite an intricate detailed design, and without the use of excessive pre-heating temperatures in connection with the heating of the investment 20.

It will of course be appreciated that in FIG. 1 the axis of rotation shown schematically as 12 in fact corresponds to the axis of rotation of the turntable 31, the tilting mechanism having been omitted from FIG. 1 for the sake of clarity.

The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only, The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the appended claims.

What I claim is:

1. Apparatus for centrifugal casting of metallic objects such as precious metal objects, in mould cavities formed by the lost wax method, in investment material porous to air, said investment material being contained in flask means open at both ends, said apparatus comprising;

crucible means for melting said metal and having an outlet;

rotatable carriage means carrying said crucible means, and rotatable whereby to expel said melted metal therefrom out of said outlet under centrifugal force;

attachment means for fastening said flask means to said crucible means, with one end in registration with said outlet, oriented to receive said melted metal therefrom when the same is expelled by centrifugal force as aforesaid;

end closure means attachable to the other end of said flask means;

sealing means locatable between said crucible means and said flask means, and sealing means locatable between said flask means and said end cover means whereby to seal the same against entry of air therein from either end of said flask;

vacuum hose means connecting with the interior of said end cover means whereby to apply a vacuum to said other end of said flask means;

stationary vacuum pipe means located adjacent to said rotatable carriage means, and connectable to any suitable vacuum source, and,

rotatable connection means extending between said vacuum pipe means and said vacuum hose means, whereby to permit rotation of said vacuum hose means relative to said vacuum pipe means while maintaining said vacuum in said end cover means, during ejection of said melted metal from said crucible means.

2. Apparatus for centrifugal casting of metallic objects as claimed in claim 1 including swingable mounting means for said crucible means, said mounting means being carried on said rotatable carriage means, with the swing axis of said crucible means located whereby to permit said crucible means to swing between a vertical position and a horizontal position, said horizontal position directing said crucible outlet outwardly with respect to the centre of rotation of said carriage means.

3. Apparatus for centrifugal casting of metallic objects as claimed in claim 2 including means-for tipping said crucible means from said vertical position into said horizontal position during rotational movement of said carriage means.

4. Apparatus for centrifugal casting of metallic objects as claimed in claim 1 including hose attachment means on said rotatable carriage means supporting and locating one end of said rotatable connection means along the axis of rotation of said carriage means.

5. Apparatus for centrifugal casting of metallic ob jects as claimed in claim 1 including second vacuum hose means connectable with said one end of said flask means, and connecting .with said rotatable connection means, whereby to apply a vacuum to said one end of said flask means.

6. Apparatus for centrifugal casting of metallic objects as claimed in claim 1 including swingable mounting means for said crucible means, said mounting means being carried on said rotatable carriage means, with the swing axis of said crucible means located whereby to permit said crucible means to swing between a vertical position and a horizontal position, said horizontal position directing said crucible outlet outwardly with respect to the centre of rotation of said carriage means, and including hose attachment means mounted on said rotatable carriage means supporting and locating one end of said rotatable connection means along the axis of rotation of said carriage means, said vacuum hose means being at least partially flexible, and extending between said hose attachment means and said end closure means, whereby to avoid restriction on the tipping of said crucible means, whereby said vacuum can be applied to said end closure means prior to rotation of said rotatable carriage means, and said vacuum can be maintained in said end closure means during said rotation.

Claims

1. Apparatus for centrifugal casting of metallic objects such as precious metal objects, in mould cavities formed by the lost wax method, in investment material porous to air, said investment material being contained in flask means open at both ends, said apparatus comprising; crucible means for melting said metal and having an outlet; rotatable carriage means carrying said crucible means, and rotatable whereby to expel said melted metal therefrom out of said outlet under centrifugal force; attachment means for fastening said flask means to said crucible means, with one end in registration with said outlet, oriented to receive said melted metal therefrom when the same is expelled by centrifugal force as aforesaid; end closure means attachable to the other end of said flask means; sealing means locatable between said crucible means and said flask means, and sealing means locatable between said flask means and said end cover means whereby to seal the same against entry of air therein from either end of said flask; vacuum hose means connecting with the interior of said end cover means whereby to apply a vacuum to said other end of said flask means; stationary vacuum pipe means located adjacent to said rotatable carriage means, and connectable to any suitable vacuum source, and, rotatable connection means extending between said vacuum pipe means and said vacuum hose means, whereby to permit rotation of said vacuum hose means relative to said vacuum pipe means while maintaining said vacuum in said end cover means, during ejection of said melted metal from said crucible means.

3. Apparatus for centrifugal casting of metallic objects as claimed in claim 2 including means for tipping said crucible means from said vertical position into said horizontal position during rotational movement of said carriage means.

5. Apparatus for centrifugal casting of metallic objects as claimed in claim 1 including second vacuum hose means connectable with said one end of said flask means, and connecting with said rotatable connection means, whereby to apply a vacuum to said one end of said flask means.