HK1192863B - Machine for forming metal bars - Google Patents

Description

Machine for forming metal bars

Technical Field

The present invention relates to a machine for forming metal bars, particularly suitable for melting and subsequent continuous solidification of precious metals, such as gold, silver, precious metal alloys and other pure metals or different alloys to produce ingots.

Background

As is known, the production of ingots made in particular of gold, silver, noble metal alloys, other pure metals and different alloys is generally obtained by means of two different methods.

When manufacturing light ingots of 5g to 50g, it is customary to carry out a cold moulding and die pressing process starting from a semi-finished product such as a cylindrical pre-formed pad or blank.

When producing ingots with weights varying between 50g and 50Kg, the metal is instead solidified using a melting process and subsequently in a special mould.

In practice, the metal to be melted in the form of powder, granules or loose raw materials of various sizes is placed in a ladle where it is melted. The molten metal is then poured into a single ingot mold, typically shaped to form a truncated trapezoid, where it solidifies in the shape of the ingot.

These two operations (melting operation and subsequent solidification of the material) must be carried out with particular care, considering that the final product obtained must meet strict and specific standard requirements.

In fact, commercially available ingots, except for having precise purity in the case of being made of pure metal or precise pure metal percentage in the case of being made of alloy (so-called "count"), must have extremely precise dimensions and weights, external configurations with regular surfaces, no pits or cracks, uniform coloration and above all they must have perfect internal metallographic structure, no pores, micropores and structural tensions.

In order to avoid obtaining defective ingots (which will therefore be considered as scrap) that do not allow to obtain "stamping", the whole manufacturing cycle must be carried out with great care, in particular during the steps of melting, solidifying and cooling the metal.

According to the state of the art, in addition to manual manufacturing, the manufacturing of ingots is also carried out using mechanical equipment of considerable dimensions, using a furnace provided with a melting cylinder from which the molten metal is poured into the ingot mould, wherein the main working steps are carried out by means of a continuous automatic cycle.

The most important documents of the prior art are: JP4305359A, US2001/050157A1, DE20012066U1 and US2007/289715A 1.

Disclosure of Invention

The aim of the present invention is to provide a machine for forming metal bars, in particular for making ingots made of precious and non-precious metal materials, which, despite comprising a step of melting and solidifying the material, does not have the drawbacks exhibited by mechanical devices of known type.

This object is achieved by providing a machine in which there are six operating stations arranged in succession, in which:

-in a first station, defined as "loading zone", the placing of the solid metal in the ingot mould, the addition of specific chemical additives (which react with the crystalline structure of the material to prevent the formation of inhomogeneities and internal tensions during the subsequent melting step), the placing of a lid for closing the ingot mould and in which there are pushing means for moving all ingot moulds forward during the whole operating cycle;

-in a second station, generally defined as "furnace", melting of the metal contained in the ingot mould according to predetermined temperature/time parameters is carried out;

in a third station, defined as "second addition", chemical additives are placed on the metal which is still liquid, which eliminates the unevenness which tends to form on the surface of the ingot during the subsequent solidification step.

-in a fourth station, defined as "solidification zone", carrying out the solidification of the metal in the ingot mould according to predetermined temperature/time parameters;

-cooling the solid ingot in a fifth station, defined as "cooling zone", and wherein, when rapid cooling is required, the above-mentioned ingot is unloaded into a vat containing a cooling fluid, from which it is collected when it has been completely cooled;

in a sixth station, defined as "unloading zone", the ingot moulds are unloaded, which may contain ingots in case of normal cooling or they may be empty in case of rapid cooling and separate withdrawal of cooled ingots.

Drawings

The characteristics of the invention will be made clearer by describing a possible embodiment thereof, provided by way of non-limiting example with reference to the attached drawings, wherein:

figure 1 shows a front view of a machine according to the invention;

FIG. 2 shows a detailed view of the ingot mold in the loading station;

FIG. 3 shows a T/T (time/temperature) diagram in a metal melting station;

FIGS. 4.1 and 4.2 show detailed views of the ingot mold in the solidification station in different cooling modes;

fig. 5 shows three different configurations of the slide plate of the ingot mould during the solidification step.

Detailed Description

As can be observed from the figures, the machine according to the invention, generally indicated with reference numeral 100, comprises:

a station for loading and pushing the ingot mould 1 (indicated with reference numeral 101);

-a metal melting station (indicated with reference numeral 102) contained in the ingot mould;

-a station for "double addition" on a still liquid metal (indicated with reference numeral 103);

-a station (indicated with reference numeral 104) for solidifying the molten metal;

-a station for cooling the solid ingot (indicated with reference numeral 105);

-a station for unloading the ingot mould (indicated with reference numeral 106);

as can be seen from fig. 1, on the loading surface of the first station 101 there are placed empty ingot moulds 1, between which a spacer 2 made of graphite or any other refractory material is placed or between two or more adjacent groups of ingot moulds, said spacer having the function of maintaining a predetermined distance between the single ingot moulds or between the groups of ingot moulds, in such a way that the ingot moulds 1 forming the "ingot mould train" are always correctly placed in the working area during the forward movement; in addition, said operating surface is also provided with pushing devices 3 which can be driven in different ways, such as by worm screws, pneumatics, hydraulics or any other means which provide for pushing said queue forward and then back at a predetermined "pitch" and thus freeing up space on said loading surface in order to allow the placement of further empty ingot moulds.

From an operational point of view, in each single ingot mould 1, a precise weight of metal in the form of powders, granules or fines of various sizes is poured (pouring element "a") and chemical additives (dosing element "B") are added, which react chemically with the impurities contained in the metal and are made of boric acid, borax, potassium nitrate, ammonium, sodium, lithium and potassium and sodium chloride, used alone or mixed.

Finally, in said first station 101, the placing of a lid 4 for closing the filled ingot mould is performed.

From a constructional point of view, as can be seen in detail in fig. 2, the ingot mould 1 may have a height dimension such that when it is filled with a precise weight of metal, its cover 4 rests on the metal, but remains raised with respect to the abutment of the edge of the ingot mould, which allows the bottom of the cover to be pressed and thus regularly compact the powders, granules or swarf, so that during the subsequent melting step, when the volume occupied by the mass of metal is progressively reduced even to one third of the initial solid volume, the cover progressively lowers as the metal melts until it rests on the aforementioned abutment, thus hermetically closing the ingot mould.

Furthermore, the inner space of the ingot mould 1 consists of two different volumes: the lower volume 1.1 constitutes the actual "mould", in which the shape and dimensions of the ingot are determined according to international standards (such as, for example, the LMBA standard) or by other specific requirements of the customer; and a second upper volume 1.2 that can be configured differently, with the aim of facilitating the placement of the metal during the loading step.

Subsequently, the pushing device 3 pushes a "queue" from the station 101 for supplying ingot moulds to the melting station 102, wherein it is possible to obtain from the presence of a heating furnace 5 in which the ingot moulds and partitions slide on refractory surfaces without controlled atmospheric pressure or a tunnel 6 in which the ingot moulds and partitions slide on tunnel surfaces or on rails, heated in a different way (through resistors, by electromagnetic induction, through gas type or any other type of burner) to the operating temperature; by way of example, this temperature is about 1150 ℃ for an ingot made of silver (Ag). For ingots made of gold (Au), this temperature is about 1250 ℃, and there is a blown inert gas, such as nitrogen, a mixture of nitrogen and hydrogen, with a maximum of 4.5% hydrogen (H), in the tunnel or in the rail to create an "inert" environment, which prevents the ingot mold and lid from oxidizing and thus from wearing rapidly and keeping the molten metal free from oxygen.

In fact, the difficulty of repeatedly and constantly adjusting the melting temperature of the ingot inside the tunnel is partially overcome by using "induction" heating, in which the increase in heating temperature (thermal gradient) occurs with at least two gradients (fig. 3): a rapid slope (a) up to at least 90% of the set point to reach the melting temperature and one or more slopes (b, c) with a less sloping profile (see fig. 3).

Furthermore, for the purpose of reducing the heat and atmospheric pressure of the inert gas inside the tunnel 6, the application of moving partitions obtained by means of, for example, shearing techniques, which create a moving or flexible insulating refractory barrier, the movement of which is manual or automatic, is provided at the lateral openings of the outlet and of the inlet of the "queue".

Subsequently, still from an operational point of view, once the melting time has elapsed, the pushing device 3 is activated, which provides to move the "queue" forward; the ingot mould present on the loading surface is pushed into the furnace 5/tunnel 6 and in turn pushes the ingot mould present in the furnace 5/tunnel 6 away as well, with the aim of allowing the ingot mould containing the molten metal to subsequently enter the "secondary addition" station 103 and subsequently the solidification station 104.

From an operational point of view, in the station 103, the raising of the lids of the ingot moulds by means of mechanical, pneumatic or any other type of gripper is carried out, while in each single ingot mould 1 a mechanical, pneumatic or any other type of dosing system adds on the molten metal a precise quantity of chemical additives (dosing elements "C") which react with the impurities contained in the molten metal, made of boric acid, borax, potassium nitrate, ammonium, sodium, lithium and potassium and sodium chloride, used alone or mixed; subsequently, the lid is replaced on the ingot mold.

In addition, during the "second addition", a "sexual" environment should be created for which a flow of inert gas, such as nitrogen, argon or a mixture of nitrogen and hydrogen, is introduced, which prevents oxidation of the ingot mould and the lid and protects the metal, which is still in liquid form, from oxygen. Subsequently, in the solidification station 104, the ingot moulds containing molten metal and hot temperatures closed by the caps are slid until they stop on the cooling plate 10, which cooling plate 10 is cooled by water by means of the through holes present therein and is made using copper, aluminum or alloys thereof or using other materials suitable for controlled heat dissipation, wherein they are kept for a predetermined period of time (on average 1 to 5 minutes) depending on the quantity of material to be solidified until complete solidification of the entire mass.

In addition, during the curing process, an "inert" environment should be created, so a flow of inert gas such as nitrogen, argon or a mixture of nitrogen and hydrogen is introduced, which prevents oxidation of the ingot mold and lid and protects the solidified metal from oxygen.

In particular, depending on the internal metallic structure (which should have large, medium or small crystals and a more or less significant solidification shrinkage) that the ingot needs to obtain, the solidification stage 104 may be provided with: a further insulating or refractory cooling plate 11 for slowing down heat dissipation; such plates may be able to be provided with grooves for defining local hot areas, which plates are placed near or in contact with one or more sides of the ingot mould and the lid (see fig. 4.1); and/or further heating plates 21 for slowing down the cooling, made of graphite, metal or refractory or insulating material, smooth or provided with raised or recessed suitable toothed rims, which can be placed between the cooling plate 10 and the ingot mould 1 (see fig. 4.2).

Alternatively, when precise control of the thermal solidification gradient is required, the solidification station 104 may be provided with a heating panel 12, for example heated using resistors, gas or using any other means, also positioned around the ingot mould and on the cover, for the purpose of obtaining an ingot with the most suitable solidified metal structure.

Furthermore, for the purpose of having a further possibility of accurately determining the thermal gradient, the cooling plate 10 may have a sliding surface (on which the ingot mould rests in the solidification step), with a flat and smooth surface or with convex or concave rolling edges, depending on the internal metal structure that the ingot needs to adopt; in addition, the passage of the cooling fluid may be effected longitudinally and/or transversely with respect to the direction of movement of the "file" of ingot molds (see fig. 5).

For construction reasons, in some cases, the "double addition" station 103 and the curing station 104 may be combined in a single station 103/104, with the addition and curing steps performed sequentially.

Subsequently, the ingot mould passes in the cooling station 105 and this operation can be performed by two different operating modes, according to the set manufacturing time and according to the type of material and the "size" of the ingot manufactured.

Specifically, the two cooling methods are:

normal cooling: the ingot molds with still very hot ingots are subjected to controlled cooling in a free environment and they are then sent to the unloading station 106.

Rapid cooling of the ingot: when the ingot molds with the still very hot solid ingots are brought to the cooling zone, they are emptied and the ingots are thrown into the cooling water tub 13, while the empty ingot molds are sent to the unloading station 106.

From an operational point of view, the rapid cooling provides for raising the cover of the ingot mould by means of a clamp of the mechanical type, of the pneumatic type or of any other type, while an actuator of the mechanical type, of the pneumatic type or of any other type locks the ingot mould on the base.

The aforesaid actuators then rotate and tilt the ingot mould and, by gravity, the hot ingot falls into a basket 14 immersed in a cooling vat 13, which after a suitable cooling time is moved away from the aforesaid vat by a translational movement to allow the collection of the cooled ingot 20.

Subsequently, conversely, after the empty basket 14 has been returned, the empty ingot mould is repositioned and the cover is lowered, and the head pushing device 3 moves the "queue" forward, thus causing the empty ingot mould to slide, finally being positioned in the unloading station 106, from where it is collected together with the ingot 20.

In particular, the unloading station 106 may be suitably extended so as to allow the "queue" of ingot molds to remain exposed on the cooling plate for a long period of time, so as to be able to gradually reach a temperature suitable for allowing easy handling by the operator who should collect those empty molds (in the case of rapid cooling) or should remove the cover and collect the cooled ingot from the ingot mold (in the case of normal cooling).

The invention conceived is thus susceptible of numerous variations and modifications, and its construction details may be substituted by technically equivalent elements, all of which are within the inventive concept defined by the following claims.

Claims (16)

1. Machine for forming metal bars, suitable for melting and subsequent continuous solidification of precious metals, precious metal alloys, including gold, silver, and other pure metals or different alloys, in the form of powders, granules or fines of various sizes, to produce ingots with masses varying from 50g to 50kg, said machine (100) being characterized in that it has six stations arranged in succession, wherein:

-in a first station (101) defined as "loading zone", there are a pouring element "a" to place solid metal in the ingot mould (1) and a feeding element "B" adapted to allow the addition of specific chemical additives reacting with the crystalline structure of the material, there being a pushing device (3) for moving all ingot moulds forward throughout the operating cycle, there also being provided a lid (4) for closing the filled ingot moulds and a partition (2) made of refractory material having the function of maintaining a predetermined distance between the individual ingot moulds or groups of ingot moulds;

-in a second station (102), defined as "melting station", carrying out the melting of the metal contained in the ingot mould according to predetermined temperature/time parameters;

-in a third station (103), defined as "second addition", there is a feed element "C" that provides to place the chemical additive on the still liquid metal;

-in a fourth station (104), also called solidification station, defined as "solidification zone", there are channels or cooling baths, whereby solidification of the metal in the ingot mould according to predetermined temperature/time parameters is carried out;

-in a fifth station (105), also called cooling station, defined as "cooling zone", there are further means adapted to determine the cooling of the solid ingot and when rapid cooling is required there is a vat containing a cooling fluid, further means are provided adapted to collect the ingot when it is completely cooled;

-in a sixth station (106), also called unloading station, defined as "unloading zone", there are means allowing unloading of said ingot moulds, which are adapted to contain the ingots in case of normal cooling or they are empty in case of rapid cooling and separate withdrawal of the cooled ingots.

2. The machine for forming metal bars according to claim 1, characterized in that in said first station (101), on a loading surface, empty ingot moulds (1) are placed, a spacer (2) made of graphite or any other refractory material being interposed between an ingot mould and the next ingot mould or between a group of two or more adjacent ingot moulds, said spacer having the function of maintaining a predetermined distance between the single ingot moulds or between the groups of ingot moulds, so that the ingot moulds (1) forming a "train of ingot moulds" are always correctly placed in the subsequent station during the forward movement, said loading surface being further provided with pushing means (3) driven in a different way, selected from worm screws, pneumatic means, hydraulic means or any other means, which provide to push the train forward and then back at a predetermined "pitch", and thus free space above the loading surface to allow placement of additional empty ingot molds.

3. Machine for forming metal bars, according to claim 2, characterised in that in said first station (101) there are means able to pour in each single ingot mould (1) precise quantities of metal in the form of powders, granules or fines of various sizes, with the addition of chemical additives, chemically reacting with the impurities contained in the metal and made of boric acid, borax, potassium nitrate, ammonium, sodium, lithium and potassium and sodium chloride, used individually or mixed, and then a lid (4) is placed for closing the filled ingot mould.

4. The machine for forming metal bars according to claim 2, characterised in that the ingot mould (1) has a height dimension such that when it is filled with a precise weight of metal, its cover (4) can rest on the metal, but remains raised with respect to the abutment of the edge of the ingot mould, which allows the bottom of the cover to press and thus regularly compact the powders, the granules or the fines, so that during the subsequent melting step, when the volume occupied by the mass of metal is progressively reduced even to one third of the initial solid volume, the cover is progressively lowered as the metal melts until it rests on the aforementioned abutment, thus hermetically closing the ingot mould, the ingot mould (1) having an internal space consisting of two different volumes and precisely the lower volume (1.1) constituting the actual "mould", wherein the shape and size of the ingot is determined according to international LMBA standards or other specific requirements of the customer; and a second upper volume (1.2) that can be configured differently, with the aim of facilitating the placement of the metal during the loading step.

5. The machine for forming metal bars according to claim 2, characterized in that in the melting station (102) there is a heating furnace (5) wherein the ingot mould (1) and the partitions (2) slide on refractory surfaces without controlled atmospheric pressure.

6. Machine for forming metal bars, according to claim 2, characterized in that in said melting station (102) there are tunnels (6) heated in different ways, the increase of the heating temperature being carried out with at least two slopes, a rapid slope (a) up to at least 90% of the set value of the melting temperature and one or more slopes (b, c) with a less sloping profile, in which there is a blown inert gas, including nitrogen or a mixture of nitrogen and hydrogen with a maximum of 4.5% of hydrogen (H), in order to create an "inert" environment, providing a partition wall movement at the lateral openings of the inlet and outlet of said "train".

7. Machine for forming metal bars according to claim 1, characterised in that in the solidification station (104) the cooling plate (10) has sliding surfaces on which the ingot mould rests during the solidification step, the passage of the cooling fluid being effected longitudinally and/or transversely with respect to the direction of movement of the "file" of the ingot mould.

8. Machine for forming metal bars according to claim 7, characterised in that in the solidification station (104) between the cooling plate (10) and the ingot mould (1) there are placed further heating plates (21) for slowing down the cooling, made of graphite, metal or other refractory or insulating material, provided with suitable toothed rims, convex or concave.

9. Machine for forming metal bars, according to claim 8, characterised in that in the solidification station (104) there are cooling or thermal insulation plates (11) provided with grooves for defining localized hot areas, placed near or in contact with one or more sides of the ingot mould and the lid, when a precise control of the thermal solidification gradient is required, in order to obtain an ingot with the most suitable solidified metal structure, the addition of heating panels (12) of the resistor type, gas type or heated by other means, also positioned around the ingot mould and on the lid, is further provided.

10. Operation of the machine for forming metal bars according to claim 6, characterised in that once the melting time has elapsed, the pushing device (3) moves the "queue" forward, so that the ingot moulds present on the loading surface are pushed into the furnace/tunnel (5/6) and they in turn push away the ingot moulds present in the furnace/tunnel (5/6), subsequently passing through the "double addition" station (103), where in each single ingot mould (1) a chemical additive is added, which reacts chemically with the impurities contained in the molten metal and which is made of boric acid, borax, potassium nitrate, ammonium, sodium, lithium and potassium and sodium chloride, used alone or mixed.

11. The operation of the machine for forming metal bars according to claim 2 or 6, characterised in that in the solidification station (104), ingot moulds containing molten metal and hot temperature closed by the lids slide until they stop on a cooling plate (10), the cooling surfaces are cooled by water by means of through holes present therein and made using copper, aluminium or alloys thereof or using other materials suitable for controlled heat dissipation, wherein they are kept for a predetermined period of time, on average 1 to 5 minutes, depending on the quantity of material to be solidified, until the whole mass is completely solidified, and wherein an "inert" environment is created by introducing a flow of inert gas comprising nitrogen, argon or a mixture of nitrogen and hydrogen, which prevents the oxidation of the ingot moulds and the lids and protects the solidified metal from oxygen.

12. Operation of the machine for forming metal bars according to any one of claims 1 to 6, characterised in that the operations carried out in the third and fourth stations (103/104) are carried out in a single station.

13. Operation of the machine for forming metal bars according to any one of claims 2 to 6, characterised in that in the cooling station (105) the ingot moulds with the still very hot ingots are subjected to controlled cooling and they are subsequently conveyed to the unloading station (106).

14. Operation of the machine for forming metal bars according to any one of claims 2 to 6, characterised in that in the cooling station (105) a rapid cooling is obtained, which provides that when the ingot moulds with the still very hot solid ingots are in the cooling zone, they are emptied and the ingots fall into a cooling water tank (13), while the empty ingot moulds are transported to the unloading station (106).

15. Operation of the machine for forming metal bars according to claim 11, characterised in that rapid cooling provides for raising the lid (4) of the ingot mould (1) by means of a clamp of the mechanical type, of the pneumatic type or of any other type, while an actuator of the mechanical type, of the pneumatic type or of any other type holds the ingot mould; the aforementioned actuators then rotate and tilt the ingot mould and, by gravity, the hot ingot falls into a basket (14) submerged in a cooling vat (13).

16. Operation of the machine for forming metal bars according to claim 15, characterised in that after a suitable cooling time, the basket (14) is moved away from the tub (13) by a translation movement to allow the collection of the cooled ingot (20), and subsequently, the repositioning of the empty basket (14), the repositioning of the empty ingot mould and the lowering of the lid are carried out, and subsequently the pushing device moves the "queue" forward, thus causing the empty ingot mould to slide, finally being positioned in the unloading station (106), from where it is collected together with the ingot (20).