FR2786791A1 - Precious metal article, especially a wrought gold jewelry article, is produced from a composite of precious metal and a removable copper-nickel alloy - Google Patents

Abstract

Precious metal article is produced from a composite of the precious metal and a removable copper-nickel alloy. A precious metal article is produced by shaping a composite material of one or more precious metals and a non-precious metal alloy to the desired article and then removing the non-precious metal alloy, the non-precious metal alloy consisting of copper containing 1-40% nickel. Independent claims are also included for the following: (i) a composite material for producing the above precious metal article, the composite material comprising one or more precious metals and a non-precious metal alloy of copper containing 1-40 (preferably 5-10, especially 7)% nickel; and (ii) use of the non-precious metal alloy described above for production of precious metal articles.

Description

NON-PRECIOUS ALLOY FOR THE REALIZATION OF THE SOUL OF

  SUPPORT FOR PRECIOUS METAL ARTICLES

INTERIOR HOLLOW.

  The invention relates to a non-precious alloy for producing the core for supporting articles of internally hollow precious metal, in particular in

the field of goldsmithing.

  It is known that, in order to produce light articles made of precious metal, a sheet of precious alloy is combined with a sheet of metal or metallic alloy of low value which, united by a plating process, make it possible to form a structure with two welded layers at the junction interface. This structure is transformed, by lamination and cutting processes, into a strip which, folded and then drawn, forms a rod whose interior is made of metal or a non-precious metal alloy, and whose exterior is a thin layer of precious metal alloy, with the exception of a thin groove which leaves visible the non-precious inner soul. This rod is transformed into a wire or a strap from which it is possible to make chains or other structures comprising a thin hollowed-out groove through which the inner core

of support is apparent.

  Another method consists in combining a metal bar or a non-precious metal alloy, provided with two adjacent longitudinal grooves, with a metal or precious metal alloy sheet, this sheet enveloping said bar. The lateral edges of the precious sheet are pushed into the longitudinal grooves of the non-precious bar o, after drawing, they are blocked, which makes it possible to achieve a stable junction between the precious outer sheet and the non-precious inner bar

precious.

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  The wire drawing and / or rolling processes transform the combination into a wire or a strap which comprises a very thin hollowed-out longitudinal groove through which the inner support core is visible from the outside. In these two cases, the wire, the strap or any other article is transformed into a chain or into another ornamental article constituted by a thin outer "shell" of metal or a precious metal alloy and by an inner core of metal or a metallic alloy. non-precious, the latter being able to exert a mechanical function of reinforcement of the external "shell" which would otherwise be crushed under the mechanical work which it supports during stresses

  of crushing, inflection and torsion.

  Then, the article is subjected to chemical corrosion, by which the internal support core is eliminated through the thin longitudinal groove, resulting in products comprising only the precious "shell", generally of a thickness less than the decimillimeter ; the products obtained are

therefore bulky, but light.

  The technical problem which arises for the choice of the metal or the metallic alloy of the support is the determination of a metal or a metallic alloy which is ductile and malleable, that is to say transformable into wires and blades , similar to the leaves in

  gold alloys with which it is combined.

  These metals must also be such that they have no affinity with the gold alloys so that they do not give rise to unforeseen bonds with the latter when they are subjected to strong compressions, as occurs during the drawing and rolling cycles, or during intermediate cycles for working the veneer or "stapled", especially when the wires or blades are iMil l subjected to annealing steps to eliminate work hardening

  acquired by the metal during its shaping.

  The non-precious metal or metal alloy chosen must satisfy another condition, namely that of being able to be corroded by an acid which does not attack the surface gold alloy and, at the same time, it is necessary that the process emptying is fast enough to allow prompt work, with brief

  time intervals between each work cycle.

  At the moment, we use either iron,

  or a copper-zinc alloy, called tombac.

  The use of iron is not widespread because it is more resistant than the gold alloys with which the jewelry is made: it is difficult to draw, then to bend and cut, as is required during the transformation of the wire into meshes to make chains. In addition, its corrosion by

  hydrochloric acid is long is difficult.

  On the contrary, the copper-zinc alloy (tombac) is widely used because it is very ductile and malleable, while being resistant to traction, which makes it possible to produce wires from an alloy of

  very small size without breaking.

  However, this alloy has the drawback of requiring during annealing and / or rolling processes, frequent annealing operations on the semi-finished product, in addition to the usual welding operations during which the meshes linked together are closed. , for example for the production of

ornamental chains.

  Said operations, namely the drawing, the annealing, then the welding, involve a rise in temperature of the precious alloy and of the internal support alloy which can lead to the point where the zinc of the internal alloy spreads in the 'external gold alloy and alters its title: in this case, in the finished product, the quantity of zinc, non-precious component, is greater than the quantity initially introduced for the formation of the precious alloy sheet. This can be checked either by a chemical analysis which makes it possible to detect the increase in the percentage of non-noble metals in the final "shell", or by spectrographic analyzes making it possible to check whether the non-precious alloy has spread over the precious blade. constituting the "shell", in which case the latter presents reddish bands and halos at the level of the interior surface, which reveal the migration of the non-precious metals from the interior reinforcement core towards the precious "shell"

outside.

  For these reasons, producers, rather than using a precious alloy blade, for example of a 750/1000 grade, use a blade with a higher grade in order to obtain, in the finished product, the grade

desired from 750/1000.

  This method is however very random, since the diffusion of zinc often takes place during

  drawing and / or rolling and annealing operations.

  These operations depend on the diameter of the final wire to be produced, the final wire which will be used to make the finished product, this diameter being dependent on wishes.

of buyers.

  Another cause of diffusion of the non-precious alloy is welding which can be carried out manually or with sliding ribbons which pass through chambers heated by ovens at one

temperature of 780-800 C.

  In this case too, the result is random because the manual welding step depends on the operator who performs it, each operator performing the welding with a different speed; as for the welds with the ibIr use of tapes, they depend on the temperature in the chamber heated by the oven, usually less than 800 C, and on the speed of advance of the tape on which the

welding chain is placed.

  For all these reasons, the finished product may have a titer lower than the expected titer, since the diffusion of zinc from the reinforcing core to the outer "shell" of precious alloy occurs, by diffusion

  thermal, from a temperature of around 650 C, that is

  say at a temperature below the temperature of

  annealed (650-700 C) and at the welding temperature (780-

800 C).

  Diffusion also takes place also at very lower temperatures when the product is subjected to high mechanical stresses, as occurs during the wire drawing and / or rolling processes. If the title of the finished product ("shell") is lower than the title indicated and expected, said product cannot be marketed; it must therefore be melted down to recover its components, with the disadvantages that

this implies.

  these disadvantages are, in the field of processes for the production of precious articles in

  gold alloy, an important research subject.

  In order to overcome these drawbacks, it has been proposed to interpose between the precious outer blade and the inner non-precious bar, in the case of the "stapled", a very thin layer of oxidizing material in order to prevent migration from the interior non-precious metal to the exterior precious alloy, this solution however not making it possible to create an effective barrier. The results thus obtained, even if they are better than those obtained without the interposition of the oxidizing layer, do not make it possible to determine a priori the variation of the title of the precious alloy forming the

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  final "shell". The problem posed is therefore not resolved. The object of the present invention is therefore to provide a particular metal or a particular alloy of non-precious metals by means of which it will be possible to produce the article support core comprising an outer "shell" of gold alloy and a resistant inner core of non-precious metal which will be eliminated by chemical corrosion in order to obtain the product

final.

  The suitable metal or non-precious metal alloy must in particular meet the following criteria: - it must be ductile and malleable in a similar manner to the gold alloys which constitute the "shells" of precious ornamental articles; - It must be sufficiently resistant to traction in order to be able to obtain very thin wires and / or ribbons, without breaking during the wire drawing and / or rolling processes; - It must be, at least at annealing and welding temperatures, sufficiently incompatible with the gold alloys to prevent the migration of the non-precious inner core towards the precious outer blade or "shell"; - finally, it must be easily attackable by the acids used to hollow out the precious articles so that these articles are marketed with the intended title. The subject of the present invention is a non-precious alloy for producing the internally hollow precious metal support core, said non-precious alloy comprising a combination of copper and nickel, the latter being present in an amount between 1 and 40% relative to the precious alloy with which it is combined, the nickel preferably being present at a rate of 7%, said non-precious alloy possibly comprising traces of other binder metals retive to their diffusion in the "shell"

  precious item to make.

  Such an alloy, which can be used in particular in goldsmithing, is particularly advantageous because it is very ductile and malleable; as a result, it is easily subjected to traction, thus making it possible to produce very thin wires and ribbons which do not

  not break during the wire drawing processes.

  Finally, the alloy according to the present invention has few migratory capacities: it has indeed been experimentally noted that, on the one hand, it is not an eutectic alloy with low melting temperature, and that on the other hand nickel is reluctant to migrate to the precious "shell" and contributes to the maintenance of a

  very high melting point, well above 800-

  820 C, i.e. at the melting temperature of the

precious outer shell.

  In this case, no diffusion into the precious alloy constituting the external "shell" of the article to be produced takes place, neither during the drawing and / or rolling processes, nor during the annealing or welding, as has been verified not only by chemical analysis of the finished "shell", but also by spectrographic examinations which have revealed the absence of diffusion of the non-precious alloy in the external "shell", of which the interior surface remains uniform in color, signifying that the migration of non-precious metals into this "shell" has not taken place. The characteristics of the non-precious alloy according to the present invention are highlighted in the table below, in which appear: the compositions of two alloys according to the present invention, one comprising 7% nickel and the other 10 % of

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  nickel; the compositions of the precious alloys conventionally used for the production of articles ("shells") in gold; the temperatures at the start of the diffusion; the annealing temperatures of wires or bars with two layers, core and "shell", during the drawing; and the temperatures at which the ribbon oven welding is performed. The results presented in this table demonstrate the advantages indicated above, namely the absence of variation of the titre in the products emptied and produced by means of a reinforcing core produced with

  the alloy according to the present invention.

BOARD

  NON ALLOY ALLOY TEMPERATURE WELDING TEMPERATURE

  PRECIOUS PRECIOUS BEGINNING OF ANNUIT ARUBAN OVEN

DIFFUSION

  Cu (93%) Au (75%) Ni (7%) Ag (11.5%)> 850 C 700 C 780 - 800 C Cu (13.5%) Cu (90%) Au (75%) Ni ( 10%) Ag (11.5%)> 850 C 700 C 780 - 800 C Cu (13.5%) Cu (90%) Au (75%) Zn (10%) Ag (11.5%) 650 C 680 - 700 C 780 - 800 C Cu (13.5%) It appears from this table that the alloys according to the invention are such that the temperature of the start of the diffusion of Nickel in the exterior gold alloy ("shell" ") is much higher either at the annealing temperature, to bring the wire or bar back to its normal plastic state and to remove surface cracks from metal and metal alloys, or to the temperature at which the sheet begins to melt

  exterior ("shell") during welding processes.

  The absence of this diffusion during the annealing processes, which are often very long, and during the final welding phase, eliminates the risk of the variation of the title of the precious alloy, making it possible to obtain a finished product. with the desired title, without variations due to changes either in the dimensions of the wire or ribbon from which the finished articles are made, or in the operators who perform the welding, or in the temperature and duration of the annealing phases.

2786791

Claims (3)

  1) Non-precious alloy for producing the core for supporting articles of internally hollow precious metal, having ductility and malleability characteristics compatible with those of the gold alloys which constitute the shells of precious articles, of tensile strength for   obtain very thin threads and / or ribbons, from   compatibility, at least at annealing and welding temperatures, with gold alloys to prevent the migration of said non-precious inner core towards the precious outer shell, as well as the characteristic of being easily attackable by the acids used to hollow out precious articles , characterized in that it comprises a combination of copper and nickel, the latter being present in said combination in an amount between 1% and% relative to the precious alloy of the outer shell of which the non-precious alloy constitutes soul of interior support.   2) Non-precious alloy according to claim 1, for the production of the inner support core of articles of precious alloy internally comprising 75% gold, 11.5% silver and 13.5% copper, characterized in   what nickel is present in the copper-   nickel at a rate of 7% compared to the precious alloy of the outer shell including the non-precious alloy   constitutes the inner support core.   3) Non-precious alloy according to claim 1, characterized in that it comprises traces of binder metals which are resistant to their diffusion in the "shell"   precious of said article to be made.