MACHINE FOR FORMING METAL BARS

Abstract

A machine for forming metal bars, in particular for producing ingots made of precious metal such as gold, silver, precious alloys, as well as other pure metals or different alloys, including a melting station for melting the metal contained in an ingot mould, wherein the ingot mould contains an accurate amount of metal, in the form of powder, grits or swarf of various sizes and a chemical additive, which creates a chemical reaction with the impurities contained in the metal. The chemical additive may be any of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides.

Description

The present invention regards a machine for forming metal bars, in particular for producing ingots made of precious metal such as gold, silver, precious alloys, as well as other pure metals or different alloys.

As known, producing ingots, in particular made of gold, silver, precious alloys, other pure metals and different alloys, is usually obtained by means of two different methods.

When producing light ingots, from 5 g up to 50 g, there is used a cold moulding and coining process, starting from semi-finished products, such as cylindrical-shaped preformed pads or billets.

When producing ingots with weight varying between 50 g and 50 Kg there is instead used the melting method and subsequent solidification of the metal in the special moulds. In practice, the metal to be melted is placed within ladles, in form of powders, granules or loose raw materials of various sizes, wherein it is brought to melting. Then the molten metal is poured in single ingot moulds, generally shaped to form a truncated-trapezoid wherein, solidifying, it takes the form of an ingot.

Such two operations, the melting one and the subsequent one for solidifying the material, must be carried out with special care, given that the obtained end-product must meet strict and specific standard requirements.

Actually the ingots available in the market, besides having an exact purity if made of pure metal, or an exact percentage of pure metal if made of an alloy (the so-called “count”), must have extremely precise dimensions and weight, an external configuration with regular surfaces, without depressions or cracks, a uniform coloration and, above all, they must have a perfect internal metal-graphic structure, without blowholes, microporosities and structural tensions.

In order to avoid obtaining faulty ingots not capable of allowing obtaining “punching”, which would thus be considered as waste material, it is necessary that the entire production cycle be carried out with much care, in particular during the steps of melting, solidifying and cooling the metal.

An object of the present invention is to provide a machine for forming metal bars, in particular for producing ingots, made of precious and non-precious material and, which does not have the drawbacks revealed by the plants of the known type.

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

FIG. 1 represents an elevational view of the machine according to the invention.

As observable from the drawing, the machine according to the invention, generally indicated with reference 100, comprises a melting station, indicated with reference 102, for melting the metal contained in the ingot moulds, indicated with reference 1.

As can be seen in FIG. 1, on a loading surface of the first operating station 101 there are positioned the empty ingot moulds 1, interposing between an ingot mould and the subsequent one or between groups of two or more mutually adjacent ingot moulds, spacers 2, made of graphite or any other refractory material. Spacers 2 serve the function of maintaining a predefined distance between the single ingot moulds or between the groups of ingot moulds, in a manner such that the ingot moulds 1, forming a “train of ingot moulds” are positioned, during the forward movement, always correctly within the work area. Furthermore, said operating surface is also provided with a pushing device 3, driven variously, such as by a worm screw, a pneumatic means, hydraulic means or any other means, which provides for pushing, with a predefined “pitch”, the aforementioned train forward, and then returning and thus freeing space on the aforementioned loading surface, to allow depositing further empty ingot moulds.

According to the invention, in each single ingot mould 1 there is poured an exact weight of metal, in form of powder, grits or swarf of various sizes and there is added a chemical additive, which creates a chemical reaction with the impurities contained in the metal and which is made up of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides, used separately or mixed. Lastly, in said first station 101 there occurs the positioning of the cover 4 for closing the filled ingot mould.

Then, the pushing device 3 pushes the “train” from the station 101 for supplying the ingot moulds to the melting station 102, wherein there may be a heating furnace 5, in which the ingot moulds and the spacers slide on a refractory surface in absence of controlled atmosphere, or a tunnel 6, in which the ingot moulds and the spacers slide on the surface of the tunnel or on guides, variously heated, through electrical resistors, by electromagnetic induction, through burners of the gas type or of any other type, up to the operating temperature. By way of example, regarding the ingots made of silver (Ag) such temperature is of about 1150° C. While for the ingots made of gold (Au) it is of about 1250° C. and in the tunnel or in the guides there is insufflated inert gas, such as nitrogen, nitrogen-hydrogen mixture with maximum 4.5% of hydrogen (H), to create an “inert” environment, which prevents the ingot moulds and the covers from being subjected to oxidation and thus prevents quick wearing and keeps the molten metal protected from oxygen.

Furthermore, with the aim of reducing the heat and the atmosphere of the inert gas, within the tunnel 6 there is provided for, at the lateral openings for the inlet and outlet of the “train”, the application of mobile partitions 7 obtained, for example, with the guillotine technique, which create a mobile or flexible insulating refractory barrier, the movement thereof being manual or automatic.

Then, still from an operational point of view, once the melting time elapses there is activated the pushing device 3, which provides for moving the “train” forward. The ingot moulds present on the loading surface are pushed into the furnace/tunnel 5/6 and the same, in turn, push the ingot moulds present in the tunnel/furnace 5/6 to exit, with the aim of allowing the latter, containing the molten metal, then to pass in the station of “secondary addition” 103 and, subsequently, in the solidification station 104.

From an operational point of view, in the station 103 there occurs the raising of the cover of the ingot mould, by means of grippers of the mechanical type, pneumatic type or any other type, while dosing systems of the mechanical type, pneumatic type or any other type, add in each single ingot mould 1, on the molten metal, an accurate amount of chemical additive (dosing element “C”), which creates a chemical reaction with the impurities contained in the molten metal. The additive being made up of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides, used separately or mixed. Subsequently, the cover is repositioned on the ingot mould.

Also in the process of “secondary addition” there should be created an “inert” environment, regarding which there is introduced a flow of inert gas such as nitrogen, argon or nitrogen-hydrogen mixture, which prevents oxidation of the ingot moulds and the covers and protects the metal still in liquid form against oxygen.

Due to construction reasons, in some cases the “secondary addition” station 103 and the solidification station 104 may be incorporated in a single station 103/104, where the addition and solidification steps are performed sequentially.

The invention thus conceived can be subjected to numerous variants and modifications and the construction details thereof can be replaced by technically equivalent elements, all falling within the inventive concept defined by the following claims.

Claims

1. A machine for forming metal bars, in particular for producing ingots made of precious metal such as gold, silver, precious alloys, as well as other pure metals or different alloys, comprising a melting station for melting the metal contained in at least one ingot mould which includes a cover, wherein said at least one ingot mould comprises an accurate amount of metal, in the form of powder, grits or swarf of various sizes and a chemical additive, which creates a chemical reaction with impurities contained in the metal wherein said chemical additive is selected from the group consisting of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides, and combinations thereof.

2. The machine according to claim 1, wherein said melting station comprises at least one melting furnace in which one or more ingot moulds containing said metal and said chemical additive are pushed.

3. The machine according to claim 1, comprising a station of secondary addition said station of secondary addition adding an accurate amount of a second chemical additive in each ingot mould, on the molten metal, said accurate amount of said second chemical additive creating a chemical reaction with the impurities contained in said molten metal, said second chemical additive being selected from the group consisting of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides, and combinations thereof.

4. The machine according to claim 3, wherein said station of secondary addition comprises dosing systems that add said second chemical additive on the still liquid metal contained in each ingot mold.

5. The machine according to claim 3, wherein said station of secondary addition comprises grippers that raise the cover of each ingot mould.

6. The machine according to claim 3, wherein said station of secondary addition is incorporated in a single station which also comprises a solidification station.

7. The machine according to claim 3, wherein said station of secondary addition comprises an inert environment which comprises inert gas which prevents the oxidation of said ingot moulds and said covers and protects the metal still in liquid form against oxygen.

8. The machine according to claim 7, wherein said inert gas is nitrogen, argon, or nitrogen-hydrogen mixture.