METHOD FOR THE REALIZATION OF A TWO LAYER METAL WIRE, IN PARTICULAR MADE OF GOLD-BASED ALLOY AND OF SILVER, AND A SEMI-FINISHED TUBULAR ELEMENT

Abstract

A method of manufacturing a two-layer metal wire, in particular in a gold-based alloy and of silver, which comprises a succession of steps which consist in coupling an outer metal tube (2) to an inner metal tube (4) interposing a first binding thickness (3) in low-melting metal material, welding the inner surface (12) of the outer metal tube (2) to the outer surface (13) of the first binding thickness (3) and the inner surface (13″) of the same first binding thickness (3) to the outer surface (141) of the inner metal tube (4), to firmly associate the outer tube (2) with the inner tube (4) together, so as to form a tubular element (7, 107) which has at least three metal layers, and then draw, by final drawing, the tubular element (7, 107) to obtain a compound metal wire (9) from at least three metal layers. The object of the present invention is also a semi-finished tubular element (7, 107), having at least three metal layers, which comprises an outer metal tube (2), an Inner metal tube (4) and a first binding thickness (3) interposed between the outer metal tube (2) and the inner metal tube (4).

Claims

1. Method for the manufacturing of a two-layer metal wire (1), in particular made of a gold-based alloy and of silver, comprising a succession of steps comprising: coupling an outer metal tube (2) to an inner metal tube (4) by interposing a first binding thickness (3) made of a low-melting metal material, welding the inner surface (12) of said outer metal tube (2) to the outer surface (13′) of said first binding thickness (3) and the inner surface (13″) of said first binding thickness (3) to the outer surface (14′) of said inner metal tube (4) in order to firmly associate said outer tube (2) and said inner tube (4) together, so as to form a tubular element (7, 107) having at least three metal layers, and drawing, by means of a final drawing process, said tubular element (7, 107) to obtain a compound metal wire (9) made of at least three metal layers.

2. Method according to claim 1, comprising the step of elimination of the low-melting metal material from said compound metal wire (9) to obtain a two-layer metal wire (1).

3. Method according to claim 1 wherein said low-melting metal material is eliminated from view so that said first binding thickness (3) is removed.

4. Method according to claim 1, wherein the size of said first binding thickness (3) is comprised between 0.6 and 0.9 mm, including the ends, preferably between 0.7 and 0.8 mm, including the ends, even more preferably substantially equal to 0.75 mm.

5. Method according to claim 3, wherein the welding of said first binding thickness (3) to said outer tube (2) and to said inner tube (4) takes place in a furnace equipped with belt conveyors defining a movement direction, said furnace having a first combustion chamber and a second combustion chamber at different temperatures.

6. Method according to claim 1, wherein a support thickness (5) is coupled internally to said inner tube (4).

7. Method according to claim 6, wherein the outer surface (15) of said support thickness (5) is welded to the inner face (14″) of said inner metal tube (4) so as to form a tubular element (107) consisting of four metal layers.

8. Method according to claim 7, wherein the welding of said support thickness (5) to said inner tube (4) takes place after the welding of said first binding thickness (3) to said outer tube (2) and to said inner tube (4).

9. Method according to claim 7, wherein said tubular element (7) with at least three layers undergoes a first drawing before being coupled with said support thickness (5), said first drawing consisting in the forced passage of said tubular element (7) inside at least one hole (6) along said drawing direction (8).

10. Method according to claim 6, wherein said support thickness (5) is a wax or a metal, preferably a copper- or aluminium-based alloy, or salts.

11. Semi-finished tubular element (7, 107), having at least three metal layers, comprising an outer metal tube (2), an inner metal tube (4) and a first binding thickness (3) interposed between the outer metal tube (2) and the inner metal tube (4).

12. Element (107) according to claim 11, comprising a support thickness (5) within said inner metal tube (4).

13. Element according to claim 12, wherein said support thickness (5) is a wax or a metal, preferably a copper- or aluminium-based alloy, or salts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further features and advantages of the invention will be more apparent from the description of a preferred but not exclusive embodiment of the method for manufacturing a two-layer metal wire, in particular of a gold-based alloy and of silver, illustrated by way of non-limiting illustration with the aid of the accompanying drawings, wherein:

[0040] FIG. 1 shows the tubular element 7 with three metal layers, in a perspective view with a sectioned portion;

[0041] FIG. 2 shows the tubular element 107 with four metal layers, in a perspective view with a sectioned part;

[0042] FIG. 3 shows the drawing of the tubular element 9 in FIG. 1, with a dashed section in the wire 5;

[0043] FIG. 4 shows the two-stage metal wire produced with the manufacturing method according to the invention.

DETAILED DESCRIPTION OF ONE OR MORE PREFERRED EMBODIMENTS OF THE INVENTION

[0044] With reference to the mentioned figures, a preferred embodiment of the method for manufacturing a two-layer metal wire, in particular made of a gold-based alloy and of silver, is shown, comprising a succession of steps consisting in: [0045] coupling an outer metal tube 2 to an inner metal tube 4 by interposing a first binding thickness 3 made of a low-melting metal material, [0046] welding the inner surface 12 of said outer metal tube 2 to the outer surface 13′ of said first binding thickness 3 and the inner surface 13″ of said first binding thickness 3 to the outer surface 14′ of the inner metal tube 4 in order to firmly associate the outer tube 2 and said inner tube 4 together, so as to form a tubular element 7 or 107 containing at least three separate metal layers, and [0047] drawing, by means of a final drawing, the tubular element 7 or 107 to obtain a compound metal wire 9 made of at least three metal layers.

[0048] Subsequently, the low-melting metal material is eliminated from view by the compound metal wire 9, so as to obtain a two-layer metal wire 1.

[0049] In our manufacturing solutions, the outer metal tube is always a gold-based alloy having a fineness of 750/1000 (Au-14 kt), with a thickness substantially in the range of mm. 0.10-0.20.

[0050] The inner metal tube is instead a silver 725 (Ag725) alloy of variable thickness ranging from about 1.00 to 2.80 millimetres.

[0051] The binding thickness 3 of both of the implementing examples presented herein is made of copper (Cu) and has a thickness 3 preferably in the range of 0.6 to 0.9 mm, including the ends, even more preferably in the range of 0.7 to 0.8 mm, including the ends, in our case it is substantially equal to 0.75 mm.

[0052] Following the welding, the thickness 3 is eliminated from view.

[0053] In the embodiment of FIG. 2, there is the support thickness 5, also made of copper (Cu), which has a minimum size of about 1.5 mm, since during the intermediate operations it acts as a support core for the four-layer metal wire 9 obtained from drawing.

[0054] Following the design of the metal alloy which forms the outer and inner tubular elements, as well as the fineness of the base alloying material and the thicknesses, the alloy metals are placed in the casting machine and then in the moulding machine which produces the metal plate of Au-14 kt or Au-18 kt and Ag725.

[0055] In lathe machining, the plate takes on the desired thickness and then is passed to the profiling machine which, by means of an argon welding, allows to obtain the desired tube.

[0056] This series of operations for forming the outer 2 and inner 4 tubes are known per se.

[0057] Before coupling the outer tube 2, made of an Au-14 kt gold-based alloy, to the inner tube 4 made of Ag725, it is preferable to proceed with a cleaning of the outer surface of the inner tube 4, for example by milling, so as to eliminate the oxides formed on the surface and/or the residues of previous processes.

[0058] The coupling of the outer 2, inner 4 tubes and with the binding thickness 3 is achieved by the passage of the two tubes one within the other, for example through a widia draw plate having a hole with a diameter equal to the outer diameter of the outer tube.

[0059] Advantageously, the welding of the first binding thickness 3 to the outer tube 2 and to the inner tube 4 takes place in a furnace provided with belt conveyors defining a movement direction, which, for example, can coincide with the direction defined by the axis of symmetry 10 (or 110) of the tubular element 7 (or 107).

[0060] The furnace also has a first combustion chamber and a second combustion chamber, having different temperatures: the first chamber has a temperature of about 770° C., the temperature of the chamber is substantially 775° C.

[0061] By changing the speed of the belts, the time spent in the furnace varies, and, in this way, it is possible to optimize the welding so that the metal layers 2, 3 and 4 are steadily associated, while avoiding overheating the material too much. After many attempts, it was calculated that the optimum rotational speed of the belt is 150 rpm, equal to a residence time in a furnace along outer meters, of about 10 minutes.

[0062] In the case wherein the gold-based alloy is of the Au-18 kt type, the temperatures of the first and second combustion chambers would be respectively about 780 and 770° C., while the rotational speed of the belt would consequently increase so as to have a residence time in a furnace for example of 2 meters, of about 13 minutes.

[0063] In the case wherein it is decided to resort to the support thickness 5, to be internally coupled to the inner tube 4, the outer surface 15 of the support thickness 5 is welded to the inner surface 14″of the inner metal tube 4 so as to form a tubular element 107 composed of four metal layers (FIG. 2). The process proceeds as follows.

[0064] After the outer tube 2 in Au-14 kt (or Au-18 kt), the binding thickness 3 in copper (Cu) and the inner tube 4 in Ag725 have been coupled and welded together to form the three-layer tubular element 7 (in Au-14 kt+Cu+Ag725 or Au-18 kt+Cu+Ag725), the latter undergoes a first drawing, before being coupled with the low melting point material, so as to be compacted and work hardened. This first drawing can consist of the forced passage, normally cold, of the two-layer tube inside a hole along the drawing direction (FIG. 3).

[0065] The coupling of the low-melting element 5 with the inner cavity of the tubular element 7 is also carried out by passing them one inside the other through another widia draw, which this time has a hole with a diameter equal to the outer diameter of the three-layer tube 7.

[0066] The welding of the three-layer tubular element 7 and of the low-melting element 5 is also carried out in a second furnace completely similar to the aforementioned oven, again by means of belt conveyors. The reference temperatures for the combustion chambers of the second furnace may vary in this case between 780 and 850° C.

[0067] It can obviously be provided that the welding of the three-layer tube 7 with the low-melting one 5 takes place precisely in the same furnace used for welding the outer and inner tubes, with the precaution of increasing the temperatures of the combustion chambers.

[0068] With reference to FIG. 3, the final drawing consists in passing the tubular element 7 or 107 through a series of holes 6, defined in the draw 16, along the final drawing direction 8. Each of these holes 6 has a diameter which is gradually lower than the diameter of the next hole.

[0069] The metal wire 9 thus obtained with three or four layers (depending on whether it starts from tube 7 or 107) is passed to the machine tools so as to obtain a machined wire of the desired aesthetic shape.

[0070] In the variant embodiment which provides the four-layer wire 9, it will be necessary to eliminate the low-melting metal material (copper or alloys thereof) from the wire 9 by immersing the machined wire in a emptying bath, where the copper, liquefying, goes into solution and subsequently the machined wire already emptied is passed to the finishing operations so as to obtain the two-layer metal wire 1.

[0071] For example, if machining of the wire 1 is performed to manufacture a chain, the three- or four-layer wire 9 is cut so as to obtain small meshes which, once emptied and cleaned, can be connected together to form a chain.

[0072] As said, if the support thickness is a salt, it can be eliminated by means of a mixture of salts diluted in water containing iron polyamide in a concentration varying substantially from 30 to 50% and a mixture of corrosion inhibitors in a maximum concentration of 5%. For example, the solution used may be the one commercially known as ADIX118.

[0073] Dilution in water allows silver to form the surface oxide which prevents acid corrosion.

[0074] Preferably, the dilution in water provides an amount of distilled water, on the total volume, of not less than 15% and not more than 30%.

[0075] In particular, in the examples proposed here, the dilution in water in the case wherein the wire to be machined contains the 14 carat gold alloy (Au-14 kt+Cu+Ag725(+Cu)) varies from 25% to 30%, while for 18 carat gold alloys (Au-18 kt+Cu+Ag725(+Cu)), the percentage of distilled water will decrease up to a range comprised between 18% and 25%.

[0076] The dissolution temperature varies between 80 and 70° C., the minimum time taken to eliminate the thickness is about 24 hours and the maximum time does not exceed 40 hours.

[0077] Finally, it is important to note that, by increasing the fineness of the gold-based alloy, or its thickness, the furnace welding temperatures will increase, while the residence time and the dilution in water in the furnace of the solution to form the dissolution bath will decrease.

[0078] The tubular element (with three layers) 7 and (with four layers) 107 is a semi-finished which has at least three metal layers and comprises a outer metal tube 2, an inner metal tube 4 and a first binding thickness 3 interposed between the outer metal tube 2 and the inner metal tube 4 (FIG. 1).

[0079] An embodiment variant (FIG. 2) is to have a support thickness 5 inside the inner metal tube 4.

[0080] From what has been described above, it can therefore be seen that the invention achieves the intended aim and objects, and in particular it is underlined that a method for manufacturing a two-layer metal wire, in particular made of a gold-based alloy and of silver, which allows to manufacture a two-stage metal wire, with a gold-based alloy coating on a silver matrix resistant to the wearing effect of time and oxidation, is provided.

[0081] In particular, having thought of a copper thickness as a binder between the upper metal layer in gold alloy and lower, in silver alloy, allows to obtain an extremely stable binding between the two steps, reducing the machining waste products.

[0082] Another advantage of the invention is that since the two-stage metal wire is obtained from a metal wire with three or more layers, it is possible to think of any type of possible machining, avoiding the risk of separation of the gold-based alloy interface and silver inner part, avoiding flaking problems, scratches, bubbles or other surface imperfections.

[0083] Another advantage of the method for manufacturing a metal wire according to the invention is to be easy and cost-effective.

[0084] Moreover, the low-melting layer(s) of the tubular element can be easily eliminated after the desired machinings. This allows to obtain a gold-plated silver chain of any shape and consistency, resistant over time and to any type of environment.

[0085] Not a least advantage of the invention is that the method for manufacturing the two-stage metal wire is carried out with means that are readily available on the market and with the use of common machinery and standard materials; in this way the final product is economically competitive.

[0086] The so-designed invention is susceptible of numerous modifications and variations, all of which fall within the scope of the inventive concept.

[0087] Further, all the details will be replaced by other technically equivalent elements.

[0088] In practice, the materials employed, as well as the dimensions, may be different according to requirements, provided they are consistent with the realization purpose.