WO2024176041A1

WO2024176041A1 - Method for melting methods and induction furnace

Info

Publication number: WO2024176041A1
Application number: PCT/IB2024/051328
Authority: WO
Inventors: Alberto Gagliano; Tommaso ROMANELLI; Giuliano Zerbato
Original assignee: Orotig S.P.A.
Priority date: 2023-02-22
Filing date: 2024-02-13
Publication date: 2024-08-29

Abstract

A method is described for melting metals and molding objects with the molten metal thus produced, wherein a crucible containing metal to be melted is arranged integral with an electrical conductor so that the electrical conductor supports the crucible, the electrical conductor is electrically energized to generate an alternating magnetic field and by induction melt the metal inside the crucible, and the electrical conductor is rotated about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.

Description

METHOD FOR MELTING METHODS AND INDUCTION FURNACE

The present invention relates to an induction melting machine and its crucible, and a method for melting a metal.

Among the well-known precious-metal melting machines, one model involves a fixed vertical-axis coil to melt metal inside a crucible. The molten metal is transferred from the crucible to an underlying mold through a hole in the bottom of the crucible that is kept closed by a shutter (stopper) during casting and opened at the end. The molten metal drips out of the crucible very slowly, so the mold filling is slow and molding quality suffers. The stopper has a sealing limit thus creating damage to the mold and loss of metal.

Another model uses the arc developed by an electrode for the melting (see US 5685360). A cup-shaped crucible is placed in a melting chamber in contact with the electrode and melted, then the entire chamber rotates to empty the molten metal into a mold integral with the chamber. The limitation of this system is that only titanium or small amounts of chromium-cobalt and precious alloys can be melted because of the low melting power achievable with the electrode. In addition, there is little control over the temperature and composition of the molten metal, an adjustment that is much needed in the casting of precious alloys.

The object of the invention is to improve this state of the art.

In particular, it is the object of the invention to improve the quality of casting and molding by achieving a faster casting consisting of molten metal that has more uniform temperature.

In particular, it is the object of the invention to eliminate problems due to the stopper.

These and other objects, which will better appear in the following, are achieved by what is defined in the attached claims, where the dependent ones define advantageous variants of the invention.

An aspect of the invention concerns a method for melting metals and molding objects with the molten metal thus produced. A crucible containing metal to be melted is arranged integral to an electrical conductor so that the electrical conductor supports the crucible, the electrical conductor is electrically energized to generate an alternating magnetic field by which to inductively melt the metal inside the crucible, and the electrical conductor is rotated about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein (e.g. into a mold). Another aspect of the invention concerns an induction melting machine for melting metals comprising an electrical conductor configured to generate an alternating magnetic field in order to melt metal by induction and mold objects with the molten metal thus produced, and support a crucible containing the metal to be melted, wherein the electrical conductor is rotatable around an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein (into a mold).

The minimum amplitude of the rotation may be only that sufficient to achieve the pouring of the molten metal into the mold.

An advantage of the method and the melting machine is that the crucible shutter is no longer needed, thereby solving the related problems of sealing and wear; and the crucible can have a simpler structure.

Another advantage is that the rotation of the crucible allows the molten metal to fall quickly into the mold and at one time, so the metal arrives in the mold hotter and more homogeneous, and with more homogeneous temperature, which results in better casting and molding quality.

The horizontal positioning of the electrical conductor enables the horizontal positioning of the crucible, by the subsequent rotation of which the pouring is obtained of a homogeneous mass of molten metal into the mold.

The electrical conductor can be exploited to make a support for the crucible. In a variant the crucible is placed on a plane formed of a tortuous coplanar path (e.g. serpentine-shaped or spiral-shaped) of the electrical conductor, and after the melting the plane is rotated about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein into a mold. In a different variation, the electrical conductor forms a horizontal-axis coil, the crucible is placed integrally inside a tunnel formed of the turns of the coil, and after the melting, the axis of the coil is rotated about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein into a mold.

The horizontal positioning of the electrical conductor enables the horizontal positioning of the crucible, by the subsequent rotation of which a pouring is obtained of a homogeneous mass of molten metal into the mold.

If the electrical conductor is installed inside a melting chamber, the electrical conductor is e.g. integral with the chamber and the chamber is configured to rotate. The chamber is configured to rotate e.g. by 90 degrees or approximately 90 degrees. In this variant, the crucible, mold and electrical conductor are e.g. integrally mounted together inside a melting chamber, and the rotation of the electrical conductor occurs by rotating the melting chamber. Or the electrical conductor and the melting chamber are coupled to rotate relatively to each other, and one and/or the other can be rotated to achieve a relative rotation, e.g. by 90 degrees or about 90 degrees.

In general, preferably the electrical conductor and/or the melting chamber is rotatable about said in-use horizontal axis by at least 45 degrees, more preferably by at least 75 degrees, even more preferably by at least 90 degrees.

In a preferred variation, the mold is placed under the electrical conductor and the molten metal falls by gravity into the mold after rotation of the electrical conductor. If the electrical conductor is installed inside a melting chamber, the mold is preferably mounted inside the melting chamber.

Another aspect of the invention concerns an induction melting machine for melting metals comprising an electrical conductor configured to generate an alternating magnetic field in order to melt metal by induction and mold objects with the molten metal thus produced, and support a crucible containing the metal to be melted, wherein the electrical conductor is rotatable about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein into a mold.

In a preferred variant, the electrical conductor is configured to form a horizontal-axis coil whose turns define a tunnel capable of housing the crucible, and the axis of the coil is rotatable about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein into a mold.

In a different preferred variation, the electrical conductor is configured to form a plane by means of a tortuous coplanar path thereof (e.g. serpentine or spiral-shaped), the plane being adapted to support the crucible and rotatable about an in-use horizontal axis to tilt the crucible and pour the molten metal contained therein into a mold.

Preferably, the melting machine comprises means for integrally holding the crucible within the tunnel or above said plane.

In a preferred variant, the electrical conductor is installed inside a melting chamber, and in a more preferred variant the electrical conductor is integral with the chamber and the chamber is configured to rotate in order to tilt the electrical conductor (e.g. by 90 degrees or about 90 degrees). In these variants, the crucible, mold and electrical conductor are e.g. mounted integrally with each other inside the melting chamber, and the rotation of the electrical conductor is accomplished by rotating the melting chamber.

In a variant, the electrical conductor and the melting chamber are coupled to rotate relatively to each other.

In a preferred variant, the mold is placed below the electrical conductor so that the molten metal falls by gravity into the mold after the above-mentioned relative rotation.

Below are preferred variants of crucible for the above-mentioned aspects.

In a variant, the crucible comprises a holding basin for the molten metal, the basin having a surface formed of a surface at the center of the crucible and a peripheral surface that forms a border for the surface at the center and ends in a raised edge, from which e.g. the molten metal can leave the crucible if the crucible is tilted.

To facilitate the discharge of the molten metal, the peripheral surface preferably joins said edge with the surface at the center by a gradual change of slope (different from a step). Or there is a pass-through hole on a border for the discharge of the molten metal from the basin.

Specifically, the gradual change of slope may be continuous via a curved surface or discontinuous via an inclined plane, or the combination of the two.

More specifically, the surface at the center delimits a semi-cylindrical cavity.

More specifically, the peripheral surface delimits a cavity in the shape of a spherical semi-cap.

In a more preferred variant, the crucible comprises said surface at the center and two peripheral surfaces as defined above that are located on diametrically opposite sides of the surface at the center.

In a more preferred variant, the crucible comprises a vault, e.g. a barrel vault, covering said surface at the center.

In a more preferred variant, the crucible comprises an outer profile complementary or corresponding to the inner cross-section of the coil.

In a more preferred variant, the crucible comprises a longitudinal axis along which it has major dimension, said surface at the center and the or each peripheral surface extending parallel to said axis. In an even more preferred variant, the crucible comprises a longitudinal axis along which it has major dimension, and the basin is formed of the juxtaposition of a first peripheral surface as defined above, said surface at the center and a second peripheral surface as defined above, wherein said surfaces extend parallel to said axis to join two opposite edges of the basin.

Another aspect of the invention relates to a crucible for induction metal-melting machine as characterized here, in one or each of the variants.

Another aspect of the invention concerns an assembly comprising an induction metal melting machine and a crucible as characterized here, in one or each of the variants.

Preferably the crucible is made of ceramic or graphite.

Preferably, the melting machine comprises an electrical circuit configured to electrically power the electrical conductor so that the conductor emits a magnetic field to inductively melt the metal in the crucible. The electrical circuit is for example mounted on the melting chamber or is remotely located.

The term horizontal should be understood here to preferably also comprise an inclination between ± 25 degrees.

Further aspects and advantages of the present invention will best appear from the following detailed description of a preferred practical embodiment illustrated by way of example and not limitation with reference to the attached drawings, in which:

Fig. 1 shows a front view of a melting machine;

Fig. 2 shows a front view of a melting machine in a different operating configuration;

Fig. 3 shows a side view of a crucible;

Fig. 4 shows a view from above of the crucible in Fig. 3;

Fig. 5 shows a three-dimensional view of the crucible in Fig. 3;

Fig. 6 shows a front view of a second melting machine;

Fig. 7 shows a plan view of a coil.

In the drawings, same or similar parts or components have been marked with the same reference numbers. To avoid crowding the drawings some repeated elements are not indicated by a number.

With reference to Fig. 1 , is illustrated a preferred induction melting machine comprising a melting chamber 12 bounded by a boxy housing 14. Preferably, the housing 14 is equipped with a transparent window 16 to observe its interior. Inside the chamber 12 is mounted an electrical conductor wound as a coil 20 formed of a plurality of turns 22 which develop along and around an X axis. The coil 20 has terminals 26 fixed to a wall of the chamber 12 via feed-through connectors 18, to which an external circuit 24 is connected that is able to electrically power the coil 20 in a manner known in the field of melting machines. In the example shown, the coil 20 is integral with the chamber 12.

The housing 14 comprises a door 98 that can be opened to give access to the chamber 12.

The turns 22 delimit and constitute a tunnel within which a crucible 50 can be stably housed (see also fig. 3). E.g. the turns 22 are sufficiently rigid to stably support the crucible 50 in a position integral with the coil 20.

Various arrangements can be used to prevent the crucible from falling out of the coil 20 when the former is rotated. E.g., the relative dimensions of the tunnel formed by the coil 20 and the crucible 50 are such that the two match and a shape-coupled mutual interlocking is created. Or during rotation the crucible 50 can rest against the underlying mold 80 or against a bulkhead between the mold and crucible (not shown). Otherwise, connecting means (not shown) can be used for attaching the crucible 50 to the coil 20 or to the back of the coil 20. Or the crucible 50 may have an element to attach to the coil 20 or the back of the coil 20.

In proximity of the coil 20 there is a fixed wall 70 having a pass-through opening 72 coaxial to the X axis. A mold 80 with an inlet 82 is installed in the chamber 12 so that the inlet 82 and the pass-through opening 72 collimate. Specifically, the mold 80 is held abutting against the wall 70 by a pusher 92 movable linearly back and forth in a direction parallel to the X axis (see arrow F). The pusher 92 may be a, e.g. pneumatic, piston or a motorized actuator, or a worm gear system, or even a manual drive.

A bracket 74 supports one side of the mold 80 and centers it with respect to the pass- through opening 72.

The coil 20 is preferably circular in cross-section to better concentrate the generated magnetic flux, but it could also be square, elliptical, or polygonal in cross-section. Preferably the mold 80 is made of refractory material with disposable wax for mold cavity 84. In the example shown, the mold 80 is used for casting rings.

Although the crucible 50 may be constructed with any tray shape, a preferred construction embodiment is shown in Fig. 3 et seq. The crucible 50 extends longitudinally along a central axis W and comprises a central part 52 and two end parts 54 that preferably are equal to give geometric and use symmetry to the crucible 50.

Both the central part 52 and the end parts 54 preferably have a respective outer surface 60, 62 that fits the cross-section of the coil 20.

The central part 52 has a tubular structure defined by the composition of a bottom 56 and a top 58 (optional). The bottom 56 preferably has as its outer surface 60 a portion of a cylindrical surface and has as its profile, viewed in a plane orthogonal to the W axis, a semi-circumference. The top 58 preferably has a barrel-vault shape, and has an outer surface 88 that is a portion of a cylindrical surface and has as its outline, viewed in a plane orthogonal to the W axis, a semi-circumference.

The central part 52 has an inner surface 64, on which the material to be melted rests, which has a concave shape, and in particular is a semi-cylindrical channel and has as its profile, viewed in a plane orthogonal to the W axis, a semi-circumference.

The end portions 54 have as their outer surface 62 a rounded portion that has as its outline, seen in a plane orthogonal to the W axis, a semi-circumference.

The end parts 54 have an inner surface 66 that joins with the inner surface 64. The union of the inner surface 64 and the two inner surfaces 66 together form a basin to contain the molten metal.

Preferably, at least one of the two inner surfaces 66 has a curved development that curves from the edge of the inner surface 64 toward the W axis (and toward the center of the crucible 50). Specifically, at least one of the two inner surfaces 66 joins with the inner surface 64 by an initial segment 80 that is contained in a plane parallel to the W axis and then develops with a curved portion 82 whose tangent gradually veers toward the W axis, specifically ending with a terminal section 84 lying in a plane orthogonal to the W axis.

More preferably, one or each inner surface 66 is essentially a quarter of spherical surface (half the outer surface of a hemisphere). Or one or each inner surface 66 is substantially a straight ramp joining the surface 64 to the rim of the crucible 50.

The melting machine 10 works according to the following preferred processing steps (not all necessary):

1 . the crucible 50 is loaded with metal to be melted, e.g. gold or titanium;

2. the crucible 50 is inserted into the chamber 12 inside the coil 20 (see Fig. 1 ). The W axis of the crucible 50 is parallel to the X axis of the coil 20; 3. the mold 80 is inserted into the chamber 12, then the piston 92 is activated to push the mold 80 against the wall 70 aligning the inlet 82 of the mold 80 with the pass- through opening 72 and blocking the mold 80 in place;

4. the door is closed and vacuum is created inside the chamber 12;

5. the circuit 24 energizes the coil 20 and the metal inside the crucible 50 is melted. The molten metal spreads over the inner surface 64 and the inner surfaces 66;

6. the housing 14 is rotated 90 degrees (see arrow Q in Fig. 1 ), so that the X-axis and W-axis rotate together by 90 degrees, becoming vertical. The rotation results in the molten metal sliding over an inner surface 66 from the rim of which the molten metal detaches to fall by gravity into the pass-through opening 72 toward the mold 80;

7. the whole system is rotated to the horizontal position, the door 98 is opened and the mold 80 is removed;

8. the molten metal in the mold 80 is awaited to solidify, and the mold 80 is broken to take out the molded objects.

The described shape for the basin is optimal for quickly discharging all the molten metal from the crucible 50 while still containing an adequate amount of molten metal. The inner surface 64 may be designed sufficiently extended to provide the desired flow rate of the crucible 50, while the curved inner surfaces 66 - or inclined with respect to the W axis - guarantee the sliding of the molten metal and its fast ejection from the crucible 50 when the crucible 50 is rotated.

The crucible 50 is open to variants, e.g.: it may have only one surface 66 and the molten metal is always poured on the same single side of the crucible; it may also have only one surface 66 (for loading of the metal) and the molten metal is poured from the opposite side through a hole of various shapes; it may be of closed cylindrical shape with a slit in the upper part (for loading the metal) and the molten metal is poured from the opposite side through a hole of various shapes.

All of the above-mentioned variants can be implemented in another preferred embodiment of melting machine, visible in fig. 6 and denoted by 100. Here, inside the chamber 12 is integrally mounted an electrical conductor 102, powered as the coil 20, which develops planarly with tortuosities 110 (see fig. 7) to form a flat supporting surface 104 for a crucible 120 or 50. To prevent the crucible 50 or 120 from falling off the surface 104 the expedients mentioned for the coil 20 can be used.

The melting machine 100 works similarly to the melting machine 10:

1 . the crucible 50 or 120 is loaded with metal to be melt; 2. the crucible 50 or 120 is placed on the surface 104. The W axis of the crucible 50,

120 is now horizontal;

3. the mold 80 is inserted into the chamber 12, then the piston 92 is activated to push the mold 80 against the wall 70 aligning the inlet 82 of the mold 80 with the pass- through opening 72 and blocking the mold 80 in place; 4. the door is closed and vacuum inside the chamber 12 is created;

5. the circuit 24 energizes the conductor 102 and the metal inside the crucible 50, 120 is melted as before;

6. the housing 14 is rotated by 90 degrees (see arrow Q in Fig. 6), so that the chamber 12 and the W axis rotate together by 90 degrees (the W axis thus becomes vertical). The rotation results in the pouring of the molten metal inside the mold 80.

The conductor 102 may also be rotatable with respect to the chamber 12.

The crucible 120 also illustrates the variant of crucible 50 without the top 58.

Claims

1. Method for melting metals and molding objects with the molten metal thus produced, wherein a crucible containing metal to be melted is arranged integral with an electrical conductor so that the electrical conductor supports the crucible, the electrical conductor is electrically energized to generate an alternating magnetic field and by induction melt the metal inside the crucible, and the electrical conductor is rotated about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.

2. Method according to claim 1 , wherein the electrical conductor forms a coil with a horizontal axis, the crucible is placed inside a tunnel, formed of turns of the coils, integrally with the tunnel, and after melting the metal, the axis of the coil is rotated about an - in use - horizontal axis use to tilt the crucible and pour the molten metal contained therein.

3. Method according to claim 1 , wherein the crucible is placed on a plane formed by a tortuous coplanar path of the electrical conductor, and after melting the metal the plane is rotated about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.

4. Method according to any preceding claim, wherein the electrical conductor is installed inside a melting chamber and is integral with the melting chamber, and the melting chamber is rotated to pour the molten metal.

5. Method according to any preceding claim 1 to 3, wherein the electrical conductor is installed inside a melting chamber and the electrical conductor is rotated relative to the chamber.

6. Method according to any preceding claim, wherein a mold is placed below the electrical conductor and molten metal falls by gravity into the mold.

7. Induction melting machine for melting metals comprising: an electrical conductor configured to generate an alternating magnetic field in order to melt metal by induction and mold objects with the molten metal thus produced, and support a crucible containing the metal to be melted, wherein the electrical conductor is rotatable about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.

8. Melting machine according to claim 7, further comprising a horizontal-axis coil formed of turns of the electrical conductor, wherein the turns form a tunnel capable of housing the crucible, and the axis of the coil is rotatable about an - in use - horizontal axis for tilting the crucible and pouring the molten metal contained therein.

9. Melting machine according to claim 7 or 8, comprising a plane formed by a tortuous coplanar path of the electrical conductor, wherein the plane is adapted to support the crucible and is rotatable about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.

10. Melting machine according to claim 7 or 8 or 9, comprising a melting chamber, and the electrical conductor is installed within the melting chamber integral with the chamber, and the chamber is rotatable about an - in use - horizontal axis to tilt the crucible and pour the molten metal contained therein.