Title of Invention: METHOD AND DEVICE FOR THE PRODUCTION OF INGOTS OF

PRECIOUS METAL

TECHNICAL SECTOR

The invention relates to the technical field of precious metals, such as gold and silver, and in particular it concerns a method to melt said metals in order to obtain lingots with predetermined shape, size and weight, as well as a device that carries out this method.

BACKGROUND ART

The raw material consists of granules, flakes, chips or other fragments of the precious metal obtained from previous operations or by the destruction of old jewels and jewellery.

The prior art, in the considered field, involves the use of graphite ingot molds in which the aforesaid metal fragments, with predetermined total weight, are introduced into an imprint of the same ingot mold, destined to give the ingot the desired shape and dimensions.

Said molds are then laid on a horizontal conveyor which brings them into a tunnel furnace, inside which are heated by induction, together with the fragments contained therein, so as to cause the melting of these.

In the final section of the tunnel, before the exit, the ingot molds become colder thus allowing the solidification of the ingots.

According to the most common prior art, in the tunnel are provided flame burners whose function is to reduce as much as possible the oxygen content in the space surrounding the ingot molds to prevent their oxidation.

Because of this process, in fact, ingot molds wear out rather quickly, thereby reducing the quality of the melted items. Unfortunately, the effectiveness of the aforesaid flame burners is not optimal, therefore, not all the air around the ingot molds is burned.

Consequently, the oxidation of the ingot molds is not effectively avoided, and their frequent replacement due to wear is one of the major costs concerning the use of tunnel furnaces.

In addition to this, the intrinsic characteristics of the tunnel furnaces involve large dimensions that can be justified when the manufacturing process is continuous or at least very intense, being unfixed the above mentioned drawback concerning the wear of the molds.

A further drawback relates to the fuel consumption required to feed the burner flames, with the costs arising therefrom.

In addition, the presence of such burners involves the installation of fumes suction systems associated to the tunnel.

They are also known tunnel melting furnaces in which are adopted expedients suitable to limit the oxidation of the ingot mold without resorting to the use of burners. For example, in the international application WO 2012/130451 it is described a tunnel melting plant divided in six operational stations disposed in succession along which a train of contiguous ingot molds is fed step by step through the use of pneumatic pushers. At least the melting sections provide in the input and in the output guillotine valves arranged to selectively close the section in phase relation with the advancement of the ingot molds. During the melting phase the guillotine valves remain closed and in the melting section is an inert gas is injected which dilutes the oxygen present inside the chamber, thus limiting the oxidation of the ingot molds.

Also in the international application WO2015/083135 it is described a similar plant in which instead of the guillotine valves are used diaphragm valves.

In any case, the solutions outlined above do not allow a complete elimination of oxygen from the melting sections, but only a dilution of the same, as much greater as greater is the volume of injected inert gas. For this reason, the efficiency of the above said solutions is closely linked to the use of large quantities of inert gases.

Another problem inherent the conventional production methods is the complexity of setting the melting parameters being both the melting times and the cooling times related to the advancement speed of the ingot molds on the conveyor for which there is a necessary interdependence between the two phases.

SUMMARY OF INVENTION

Therefore, it is an object of the present invention to propose a method for the realization of precious metal ingots, and a device that carries out this method, having completely different characteristics from what in use in the prior art, designed in particular to avoid the oxidation of the ingot molds and thus their wear, thus limiting the production costs.

Another object of the invention is to propose a method designed to allow production of ingots of both small and medium-size, simply according to the needs of the moment, without space or energy waste.

A further object of the invention is to propose a device for the implementation of the method which could be simple in concept, easy to use, reliable and precise in operation.

Still another object of the invention aims to obtain an extremely compact device, in which the melting chamber is as small as possible, to minimize the heat exchange with the surrounding environment.

Another further object of the invention is to avoid the need of auxiliary plants for the supply of fuel gas, for the aspiration of combustion fumes and protective structures to prevent injuries from burns. Another object of the present invention is to propose a device in which is used an inert gas to reduce the oxidation of ingot molds in which a high oxidation reduction efficiency is obtained due to the utilization of extremely low volumes of inert gas.

Yet another object of the invention is to propose a device that thanks to the characteristics mentioned above can find easy placement even in small laboratories, also allowing an extreme ease of movement, as needed, from one place to another.

Still another object of the present invention is to propose a method and a device in which the melting and cooling steps can be completely independent one from the other so that they can both be automated and optimized without having to find a compromise between the respective different needs.

These and other objects are fully achieved by a method for the realization of precious metal ingots, which includes:

- the introduction of granules, chips and/or pre-weighed fragments of said precious metal in a graphite ingot mold;

- the positioning of said ingot mold, loaded with the grains and/or the precious metal fragments, over a liquid cooling plate provided in a loading/cooling chamber;

- the vacuum-proof coupling between said loading/cooling chamber and a melting chamber;

- the transfer of the loaded ingot mold from said cooling plate to the melting chamber; - the suction of the air present in said melting chamber and loading/cooling chamber up to create a vacuum condition;

- the activation of induction heating means, present in said melting chamber, according to predetermined parameters, for the heating up to the melting temperature of the aforementioned precious metal granules, until their complete melting in liquid form inside the relative ingot mold;

- the deactivation of the abovementioned induction heating means;

- the transfer of the said ingot mold with the respective liquid ingot on said cooling plate; - the detachment of said loading/cooling chamber from the melting chamber;

- the extraction of the cited ingot mold from said loading/cooling chamber, with the relative solidified ingot;

- the extraction of the precious metal ingot obtained from said ingot mold.

The above objects are also achieved by means of a device for the realization of precious metal ingots, comprising:

- a melting chamber having an open side and bearing in its interior induction heating means;

- air suction means, disposed in said melting chamber and intended to remove the air present in the latter;

- at least one loading/cooling chamber, arranged to be selectively sealingly connectable, in correspondence of an open side, with said open side of the melting chamber so as to form therewith a hermetically sealed volume;

- a liquid cooling plate, provided in said loading/cooling chamber;

- at least a graphite ingot mold in the shape of a tray with a lid, intended to be removably housed in said cooling plate, said ingot mold being provided to contain granules and/or pre-weighed fragments of said precious metal or an ingot obtained with said granules and/or fragments; - first actuating organs, provided for transferring said ingot mold from said cooling plate to said melting chamber in correspondence of said induction heating means, and vice versa;

- power and control means of said device, adapted to actuate in a suitable sequence, subsequently to the positioning of said ingot mold on said cooling plate and to the aforementioned relative movement for which said loading/cooling chamber sealingly engage the melting chamber, said first actuator means for the transfer of said ingot mold in the above mentioned melting chamber, said air suction means for creating a vacuum condition in said melting chamber, said induction heating means for the melting of the aforementioned granules and the obtaining of a corresponding precious material ingot, said first actuator means for returning said ingot mold to rest on the cooling plate, collant circulation means for the circulation, in the latter, of coolant liquid, in order to determine a heat exchange with said ingot mold and the consequent solidification of the relative ingot, with the latter destined to be manually extracted from the cited ingot mold subsequently to the decoupling of said loading/cooling chamber with respect to the melting chamber.

BRIEF DESCRIPTION OF DRAWINGS

The above-mentioned features of the present invention and still others will become apparent from the following description of a preferred embodiment of the method for the realization of precious metal ingots, and of the device that carries out this method, in accordance with what is proposed in the claims and with the aid of the accompanying drawings, in which:

- Fig. 1 illustrates an axonometric overall view of a device for the realization of precious metal ingots, able to implement the method of the invention;

- Fig. 2A illustrates, in an exploded axonometric view, a cooling plate of the device of Fig.

1 and an ingot mold to be associated with it; - Fig. 2B illustrates, in plan view, the cooling plate of Fig. 2A, with highlighted in transparency the internal channels for the circulation of coolant liquid;

- Fig. 3 illustrates a front sectional view of the melting and loading/cooling chambers provided in the device of Fig. 1 ;

- Fig. 4 illustrates the device of Fig. 1 in a different operative configuration.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the above listed figures, it has been indicated as a whole with reference 1 a preferred embodiment of a device for the implementation of the method of the invention, which includes, in order:

- the introduction of pre-weighed granules and/or fragments of said precious metal (not shown) in a graphite ingot mold, 2;

- the positioning of said ingot mold 2, loaded with precious metal grains and/or fragments, over a liquid cooling plate, 3, provided in a loading/cooling chamber, 10;

- the vacuum-proof coupling between said loading/cooling chamber 10 and a melting chamber, 20;

- the transfer of the loaded ingot mold 2 from said cooling plate 3 to the melting chamber 20;

- the suction of the air present in said communicating melting chamber 20 and loading/cooling chamber 10 up to create a vacuum condition;

- the activation of induction heating means, 21 , present in said melting chamber 20, according to predetermined parameters, for the heating up to the melting temperature of the aforementioned precious metal granules, until their complete melting inside the relative ingot mold 2;

- the deactivation of said induction heating means 21 ; - the transfer of said ingot mold 2 with the respective liquid ingot on said cooling plate 3;

- the detachment of said loading/cooling chamber 10 from the melting chamber 20;

- the extraction of said ingot mold 2 from said loading/cooling chamber 10, with its solidified ingot;

- the extraction of the precious metal ingot obtained from the ingot mold 2.

In one optional and advantageous embodiment of the method described above, it is provided to insert inert gas heavier than air, such as argon, into the melting chamber 20 and loading/cooling chamber 10, made communicating as result of their cited coupling, subsequently to the suction of the air.

In functional combination with the just described phase, in order to contain the leakage of the inert gas heavier than air from the loading/cooling chamber and avoid any risk of oxidation of the ingot mold also during the cooling phase, the method provides the sealing of the loading/cooling chamber 10 by means of a lid, 1 1 , after the mentioned detachment of the same from the melting chamber 20 and up to the aforementioned extraction phase from said loading/cooling chamber 10 of the ingot mold 2 with its solidified ingot.

The method provides, with reference to the previous step, to limit the time lag between the detachment of the loading/cooling chambers 10 and melting chamber 20 and the tight coupling between the aforementioned loading/cooling chamber 10 and the related lid 1 1 , so that it is less than the time needed for the inert gas, still present in the same loading/cooling chamber 10, to disperse into the environment. To achieve the above, the aforementioned time is preferably about two seconds, and in any case less than ten seconds.

The vacuum-proof coupling between the loading/cooling chamber 10 and melting chamber 20, provided by the method is preferably obtained with a shift of the same loading/cooling chamber 10, together with said cooling plate 3 and the loaded ingot mold 2, from a position at the side of the melting chamber 20 to one below this, followed by the lifting of the same loading/cooling chamber 10.

Accordingly, the above mentioned detachment between the same loading/cooling chamber 10 and melting chamber 20 is followed by a reverse movement of the same loading/cooling chamber 10 in the aforementioned position at the side of the melting chamber 20.

The displacement procedure described above, makes it possible to implement the method according to an interesting variant aimed to increase the production speed; indeed, the arrangement of the loading/cooling chamber 10 at the side of the melting chamber 20, makes it possible to use two loading/cooling chambers 10, alternatively switching them in the coupling with the melting chamber 20, so that when the first of them is joined to the latter for a corresponding melting phase, the second is positioned to the side for the aforesaid ingot cooling cycle and for a new introduction of pre-weighed granules and/or fragments into said ingot mold 2, and vice versa.

The device 1 , according to the invention, comprises a box structure 4 for the containment of power supply and control organs, not shown in detail since substantially known and whose functions will be better described below.

Outside of the box structure 4, in the upper part thereof, is cantilevered said melting chamber 20, having its lower side 20B open and bearing inside said means for induction heating 21 , connected to the aforementioned power and control organs.

In the melting chamber 20 there are provided air suction means (not visible in the figures), of a substantially known type, intended to remove the air present therein.

In the melting chamber 20 are also provided injection organs (also not visible in the figures), of a substantially known type, for the adduction of the aforementioned inert gas heavier than air (argon) to be inserted in the same melting chamber 20 to replace air. In addition, the melting chamber is provided with water cooling means (not shown), which allow to keep sufficiently low the temperature of the outer surface limiting the heat exchange with the outside.

In Figs. 3 and 4 is illustrated a melting chamber 20 whose upper portion 20A is hinged and is openable with respect to the underlying body; this constructive arrangement allows an easier inspection and cleaning of the melting chamber 20 itself.

The said upper portion 20A of the melting chamber 20 is advantageously provided with at least one glazed surface 120 in correspondence of which is associated, externally of said melting chamber 20, at least one optical temperature sensor, for example an optical pyrometer, arranged to monitor, through the glazed surface 120, the temperature of the ingot mold 2 and then the process of heating and melting of the precious metal. The aforementioned solution which provides to use an optical pyrometer externally associated to the melting chamber to measure the temperature of the ingot mold when it is inside the melting chamber 20 is particularly advantageous since it has extremely low manufacturing and maintenance costs and allows a very accurate temperature measurement. However, alternatively the means for measuring the temperature of the ingot mold in the melting chamber 20 are constituted by a contact thermocouple installed inside the melting chamber 20.

The device 1 includes at least one loading/cooling chamber 10, already previously mentioned, arranged to be selectively sealingly connectable, in correspondence of an open upper side 10A, with said open lower side 20B of the melting chamber 20, so as to form therewith a hermetically sealed volume.

In the preferred embodiment referred of Figs. 1 and 4, are advantageously provided two loading/cooling chambers 10, arranged symmetrically with respect to said melting chamber 20 and intended to be in turn coupled to the latter, according to what has already been explained in the above method.

Each loading/cooling chamber 10 is fixed to relative supporting organs, 12, bound to a corresponding vertical rod, 14, rigidly coupled to said box structure 4.

Therefore, each loading/cooling chamber 10 with its supporting organs 12 is adapted to oscillate on a horizontal plane and to axially slide with respect to the respective rod 14, so as to define, respectively, for the same loading/cooling chamber 10, three positions, respectively the first L1 , in which is disposed adjacent to said melting chamber 20, the second L2, in which is arranged coaxially below the latter and the third L3, in which it is raised so that the edge of its aforementioned open upper side 10A sealingly abuts the edge of said open lower side 20B of the melting chamber 20.

In each loading/cooling chamber 10 is disposed a liquid cooling plate 3, already mentioned in the method, on which is removably housed the graphite ingot mold 2, shaped as a tray (Fig. 2A) with its lid (not shown in Fig. 2), intended to contain the pre-weighed granules and/or fragments of said precious metal or the ingot which will be obtained (granules and ingot not illustrated).

The cooling plate 3 is made of copper and provided on the inside with ducts 31 (see in particular Fig. 2B), which are placed in communication with coolant circulation means, not shown.

To each loading/cooling chamber 10 are associated first actuating organs, 13, constituted for example by a pneumatic jack, provided for transferring said ingot mold 2 from the cooling plate 3 to the melting chamber 20 in correspondence with the induction heating means 21 , and vice versa.

To this purpose, in the preferred constructive solution referred to the figures, the cooling plate 3 is affected by three vertical passing holes 30, arranged substantially in a triangle, in which three corresponding movable rods 130, freely slide activated synchronously by the jack 13 and intended to intercept from below the ingot mold 2 and then to lift it in the melting chamber 20 and, vice versa, to bring it back to rest on the cooling plate 3. The aforesaid three movable rods 130 have their respective contact ends with the ingot mold 2 of pointed shape and are horizontally aligned so as to define three substantially punctiform contact zones located in the vicinity of the peripheral areas of the lower surface of said ingot mold 2. The presence of three rods 130 who insist on separate peripheral points of the ingot mold and the pointed shape of the relative ends allow to alter as little as possible the homogeneity of the lower surface of the same and then its thermal profile in the melting and solidification phase.

In the device 1 illustrated are advantageously provided also second actuating organs, 15, for example a pneumatic jack, which are associated with the loading/cooling chamber 10 from time to time under the melting chamber 20, in order to move it vertically upwards and dowards and define said positions L3, L2 of coupling and decoupling with the same melting chamber 20. The jack 15 is supported under a plate, 16, which connects the rod 14, and its stem 15S is able to protrude upward through an opening made for this purpose in said plate 16, to intercept the bottom of the other jack 13 which is located above it and push it upwards together with the relative loading/cooling chamber 10.

The operation of the device 1 , already understandable from the previous description, is activated by appropriate control means present on a panel, 17, incorporated in the box structure 4, and makes use of said power and control means of the device 1 , which actuate the various organs in a suitable sequence and in accordance with the provisions of the method, subsequently to the positioning of an ingot mold 2 on a cooling plate 3.

With manual action, the respective loading/cooling chamber 10 is placed below the melting chamber 20 (position L2) and by the second actuating organs 15 it is lifted (position L3) to achieve the vacuum-proof coupling with the latter. The first actuating organs 13 implement the transfer of the ingot mold 2 (with its load of granules and fragments) within the melting chamber 20, while the air suction means create a vacuum condition in the latter.

Then, said injection organs enter the above mentioned inert gas, and the induction heating means 21 are activated to determine the melting of the aforementioned granules and to obtain a corresponding precious material ingot.

By means of the optical temperature sensor 121 the heating cycle of the ingot mold 2 and of the valuable material granules is continuously monitored, until reaching a predetermined temperature, at which are deactivated the induction heating means 21 and are operated in the reverse direction the first actuating organs 13 to bring back the ingot mold 2 to rest on the cooling plate 3, where a coolant liquid starts to circulate to cool the ingot mold 2 and to solidify its ingot. In an alternative embodiment, the optical temperature sensor may not be present and the activation period of the induction heating means in this case would be automated by means of timing. However, the presence of the temperature sensor allows to significantly reduce the setting times of the process and also to obtain a quality of ingots much more homogeneous, as it is not influenced by small size variations of the ingot mold 2 that you have both during the use due to the wear and between one ingot mold and another.

The loading/cooling chamber 10 is decoupled from the melting chamber 20 and moved to one side (position L1) and then, as required by the method, the same loading/cooling chamber 10 is selaingly closed by means of a lid 1 1 , before the inert gas there present can disperse in the environment, negating its protective action against the oxidation of the ingot mold 2. The use of a protective inert gas heavier than air such as argon ensures a dispersion of the same negligible in the normal lid handling times. After the ingot has solidified and the ingot mold sufficiently cooled, the ingot mold 2 is manually extracted from the loading/cooling chamber 10 and subsequently the ingot itself is extracted. Meanwhile, in a suitable operational timing, it may have already been put into work the remaining loading/cooling chamber 10 with a relative ingot mold 2 loaded with granules and/or fragments of precious metal to be melted.

From what above said they are quite evident the peculiar characteristics of the method and of the device object of the present invention, which are completely different from what is in use in the prior art and are extremely advantageous compared with these.

The small sizes of the melting chamber allow to easily create a vacuum in its interior and to insert inert gas heavier than air, so as to realize the best conditions in order to avoid the oxidation of the ingot molds and thus their wear, thus limiting the production costs.

For the same purpose it is useful the application of a lid during the solidification phase of the ingot.

From the description and from the attached figures it is easy to understand how both the method and the device make it possible to vary the production of ingots within a sufficiently large "range", according to the needs of the moment, without this entailing difficulties, with dimensions and energy consumption limited.

The device presents simple constructive solutions and all the organs of the machinery as well as the accessory elements that guarantee its functionality are widely tested, so it follows high ease of use, long-term reliability and precision in the results.

The compactness and the water cooling of the melting chamber allow, advantageously, to limit at maximum the heat exchange with the surrounding environment, also thanks to the fact that the body of the chamber itself is suitably distant from the induction heating means; consequently, there is no risk of burns for operators. The cooling plate made of copper, a very high thermal conductivity material, allows to reduce the cooling times to improve the productivity of the device and to obtain a better quality of the produced ingots.

It is to highlight, moreover, how the proposed device is devoid of auxiliary systems for the fuel gas supply and for the aspiration of combustion fumes.

The conformation of the device that results, allows to easily find a place for it even in small laboratories, also allowing the possibility to easily move it, as needed, from one place to another. Variant embodiments of the device of the invention require the presence of more melting chambers 20 and more of the respective loading/cooling chambers 10 supplied from the electrical and hydraulic point of view and controlled in the relative work phases by power supply and control organs contained in a single box structure 4. For example, the melting chambers and the loading /cooling chambers could be organized in a carousel chambers, with a plurality of loading/cooling chambers arranged angularly equidistant along a circumferential path and movable jointly along the aforesaid path to align with one or more melting chambers arranged in specific angular positions of the aforementioned virtual circumference. A solution as outlined above allows to considerably increase the productivity of the device without significantly increasing the overall dimensions.

It is understood however that what above said has value of example and not limiting, therefore any modifications of detail that may be necessary to be taken for technical and/or functional reasons, are considered from now as remaining within the protective scope defined by the claims below . 