EP0638256A1 - Method for making a composite wire suitable for manufacturing hollow jewellery - Google Patents

Abstract

The subject of the present invention is a novel method for making a composite wire suitable for manufacturing hollow jewellery. According to the invention, this method is characterised in that it consists in: - introducing a cylindrical bar of approximately circular cross-section made of base metal or of an alloy of base metals into a tube made of an alloy based on a precious metal preferably obtained by continuous casting and optionally drawn to the correct dimensions, said tube having an internal diameter greater than the external diameter of said bar; - causing said tube and said bar to bond together; - wire-drawing the resulting assembly in order to give it a circular cross-section; - producing a lengthwise groove along this assembly, preferably during the last drawing pass, e.g. by scalping; and - optionally, chemically attacking said groove in order to make it more easily visible. This method produces wire of great length having a coating of precious-metal-based alloys of uniform depth. <IMAGE>

Description

The present invention relates to a new process for the production of a composite wire intended for the production of hollow jewelry.

This process makes it possible, in particular, to obtain threads of great length, of regular thickness, which can be adjusted as required by the manufacturers of articles of jewelry, such as for example rings, bracelets, hoops, chains, necklaces, etc. .

We know that the price of precious metals, and in particular gold, is high and fluctuates sharply.

This is why we have sought, in the field of jewelry, economical solutions for making jewelry from precious metal alloys.

A known and used solution for many years consists in manufacturing, not "solid" jewelry, but "hollow" jewelry.

These hollow jewels are made from a composite wire comprising a substantially cylindrical core, preferably of circular cross section, consisting of a base metal or an alloy of base metals, covered over its entire outer surface, at the with the exception of a longitudinal groove, a coating made of an alloy based on a precious metal, preferably a gold alloy.

As will be understood, since by manufacture, the core of the composite wire is not entirely covered by the alloy based on precious metal, it is possible to obtain a hollow jewel, by subjecting the formed jewel to from this composite wire to chemical attack, in particular by immersing it in a more or less dilute acid solution, capable of dissolving the core of common metal or alloy of common metals, without attacking the coating of alloy based on precious metal.

In the present description and in the claims, the term “precious metal” is intended to denote any metal generally considered as such in the field of jewelry.

A precious metal is in particular gold, silver, platinum, palladium.

The expression “precious metal alloy” designates any alloy of which at least 30% by weight and preferably at least 37.5% by weight consists of a precious metal.

Such an alloy is, for example, a 22-carat, 18-carat or 9-carat gold alloy, commonly used in jewelry.

By "base metal" is meant any metal used in jewelry that is not considered a precious metal.

A common metal is in particular copper, iron or aluminum.

Today there are two main techniques for manufacturing composite yarns.

According to a first method, hereinafter designated method A, a composite plate is prepared, in a first step, by hot or cold plating of a laminated strip made up of an alloy based on a precious metal, in particular d 'Or, on a band forming a support of the same surface made of a common metal or an alloy of common metals, the thickness ratio of the two bands being chosen according to the nature of the jewelry to be produced.

In general, in the case of gold alloys, the aforementioned support band is made of copper or copper alloy, for the manufacture of high-grade jewelry (18 carats) and of iron or alloy iron for making low-grade jewelry (9 carats).

In a second step, the composite plate thus produced is laminated until a thickness suitable for making hollow jewelry is obtained (FIG. 1A).

In a third step, this composite laminate is transformed into an unwelded rolled tube, the part made of base metal or a base metal alloy forming the internal wall. This transformation is carried out in particular by cutting, from the composite laminate obtained at the end of the above-mentioned second step, strips, the width of which is equal to the developed of the hollow wire which it is desired to obtain, and by subjecting each strip (FIG. 1B) to a rolling operation in a die, then possibly to a drawing (FIG. 1C).

The rolled tubes thus produced serve as blanks for the production of jewelry articles, such as in particular chain or curb links, or chain or necklace links.

According to a second method designated hereinafter method B, a rod of copper or of a common base metal alloy is profiled in a first step, using a laminated strip made up of an alloy based on a precious metal, in particular gold, the length of which is equal to the developed of said bar.

This bar has two longitudinal and parallel U-shaped grooves intended to allow a "stapling" of the strip of precious metal alloy on the bar (Figure 2A).

In a second step, the assembly thus formed is rolled into square grooves, then also drawn in a square (FIG. 2B).

Finally, in a third step, a final drawing pass is made in the round, so as to obtain a cylindrical element with a substantially circular cross section (FIG. 2C).

The element thus obtained can also serve as a blank for the production of jewelry articles, after having possibly undergone an additional drawing operation for the manufacture of meshes.

The two methods described above do not differ in their purpose, which consists in shaping a jewelry blank, the external part of which is made of a precious metal-based alloy and the internal part of which is made of base metal or a metal alloy. common.

In their use for the manufacture of jewelry, the parts prepared from such a composite wire are assembled and welded or brazed, then shaped, the core of said wire being intended to ensure rigidity and mechanical solidity for said setting. in shape.

In general, to dissolve the core in common metal or in a common metal alloy, we will choose nitric acid, for jewelry made of high-alloy gold (18 carats) and dilute sulfuric acid. for low-alloy (9 carat) gold alloy jewelry.

The gas evolution occurring during the chemical attack has the effect of evacuating the corrosion products and of renewing the solution in the hardly accessible portions.

After finishing, a hollow piece of jewelry with the desired shape is thus obtained.

The two methods described above each have advantages, but also disadvantages.

Thus, method A makes it possible to obtain the same thickness of precious metal alloy, for various diameters of wire.

However, the composite yarns thus obtained are of reduced length due to the limited lengths of the blanks usable in plating.

In addition, it is difficult to obtain a regular groove by this method, and it becomes very apparent after chemical treatment.

In contrast, method B makes it possible to manufacture wires of greater length than those produced by method A, and these wires have a rectilinear groove.

However, the thickness of the coating based on precious metal obtained according to this method is very irregular, due to the effects of "wedges" resulting from the successive use of dies with square grooves, then with circular grooves. Thus, the composite threads obtained according to this method, and the resulting jewelry, have, at the aforementioned groove, a slight internal bead.

It should also be noted that the aptitude for chemical attack on a piece of jewelry produced from a composite wire obtained according to method B is limited by the small size of the groove. Thus, the chemical attack is all the more difficult to achieve when the diameter of the composite wire is small.

In fact, method B leads to wires more suited to the manufacture of mechanical chains than to that of Creole.

Under these conditions, the present invention aims to solve the technical problem consisting in the supply of a new process for the manufacture of a composite wire intended for the production of hollow jewelry, no longer having the drawbacks of the methods discussed above.

• à introduire un barreau cylindrique de préférence à section transversale sensiblement circulaire, constitué d'un métal commun ou d'un alliage de métaux communs à l'intérieur d'un tube constitué d'un alliage à base de métal précieux, de préférence obtenu par coulée continue et éventuellement calibré par étirage, ledit tube ayant un diamètre intérieur supérieur au diamètre extérieur dudit barreau ;
• à solidariser entre eux ledit tube et ledit barreau ;
• à soumettre l'assemblage ainsi constitué à un étirage ou tréfilage ;
• à réaliser sur cet assemblage une rainure longitudinale, de préférence lors de la dernière passe d'étirage ou de tréfilage par exemple par scalpage ; et
• éventuellement à soumettre ladite rainure à une attaque chimique, afin d'en faciliter le repérage visuel.

The solution, in accordance with the present invention, for solving this problem consists of a method characterized in that it consists:

• inserting a cylindrical bar, preferably with a substantially circular cross section, made of a base metal or of a base metal alloy inside a tube made of a precious metal base alloy, preferably obtained by continuous casting and optionally calibrated by drawing, said tube having an inside diameter greater than the outside diameter of said bar;
• securing together said tube and said bar;
• subjecting the assembly thus formed to drawing or drawing;
• making a longitudinal groove on this assembly, preferably during the last drawing or drawing pass, for example by scalping; and
• possibly subjecting said groove to a chemical attack, in order to facilitate visual identification thereof.

This process makes it possible to obtain wires of very great length greater than that obtained not only by method A but also by method B.

It also makes it possible to obtain a very great regularity in the thickness of the coating of an alloy based on a precious metal, unlike method B described above.

In addition, this method makes it possible to obtain a very fine, regular groove, the width of which can be controlled and therefore adapted according to the specific requirements of the user, unlike the two methods described above.

In addition, this groove can be located, which allows it to be oriented towards the hidden face of the jewelry during the manufacture of the latter.

In addition, this groove allows in particular to take the product in half-rush.

In addition, this groove guarantees correct chemical attack whatever the diameter and thickness of the precious metal desired.

Finally, this method makes it possible to obtain a composite wire which can be used directly by the jewelry manufacturer who may, if necessary, carry out a slight recovery of the grooved wire by drawing or drawing to bring it to the desired particular ribs, and it suitable for both mechanical chain and artisanal product manufacturing.

According to a first embodiment of this method, the joining together of said tube and said bar is carried out by plating by stretching, then by diffusion annealing.

According to a second embodiment of the invention, the joining together of said tube and said bar is carried out by co-rolling, then by diffusion annealing.

This gives a doubled composite yarn.

According to a third embodiment of the method according to the invention, the joining together of said tube and said bar comprises a brazing.

To this end, a sheet or strip of solder is inserted between the precious metal-based alloy and its base in common metal and the assembly thus formed is subjected to the same treatment as those described above.

It should be noted that in this case, the liquidus temperature of the solder to be used must be absolutely higher than the temperature at which the diffusion annealing takes place.

This third embodiment of the invention makes it possible to obtain a tripled composite yarn.

According to a particular characteristic of the method of the invention, the aforementioned bar is made of copper.

In this case, the chemical attack intended to facilitate the visual identification of the groove can be carried out using a dilute solution of sulfuric acid at 20%.

According to a second aspect, the present application aims to cover the use of a composite wire obtained by the implementation of the method described above, for the manufacture of hollow jewelry.

• la figure 1A illustre une plaque composite réalisée à l'issue de la première étape de la méthode A ;
• la figure 1B illustre une bande obtenue par découpe de la plaque composite représentée à la figure 1A ;
• la figure 1C illustre le passage en filière d'une bande telle que celle représentée à la figure 1B ;
• la figure 2A illustre la première étape de la méthode B consistant à agrafer une bande sur un barreau ;
• la figure 2B en illustre la deuxième étape consistant en un laminage puis un tréfilage en gorges carrées ;
• la figure 2C illustre le fil obtenu à l'issue de la troisième étape de cette méthode ;
• la figure 3A illustre la formation de la rainure dans le procédé conforme à l'invention ; et
• la figure 3B illustre un fil composite obtenu par la mise en oeuvre du procédé de l'invention.

The appended figures schematically illustrate the methods of the state of the art and the method of the invention. More precisely :

• FIG. 1A illustrates a composite plate produced at the end of the first step of method A;
• Figure 1B illustrates a strip obtained by cutting the composite plate shown in Figure 1A;
• FIG. 1C illustrates the passage through the die of a strip such as that shown in FIG. 1B;
• FIG. 2A illustrates the first step of method B consisting of stapling a strip on a bar;
• FIG. 2B illustrates the second stage thereof consisting of rolling and then drawing in square grooves;
• FIG. 2C illustrates the wire obtained at the end of the third step of this method;
• FIG. 3A illustrates the formation of the groove in the method according to the invention; and
• FIG. 3B illustrates a composite wire obtained by implementing the method of the invention.

The following example illustrates the present invention, without however limiting its scope.

• * Réalisation des ébauches :
  • coulée continue d'un tube en alliage à base d'or, ∅ 30 x 40 x L 500 mm avec une épaisseur de paroi en alliage d'or égale à 5 mm ;
  • laminage d'un barreau de cuivre ∅ 30 x L 500 mm jusqu'à ∅ 28 mm.
• * Préparation des surfaces :
  • brossage intérieur du tube en alliage à base d'or ;
  • brossage extérieur du barreau de cuivre.
• * Sertissage par colaminage ;
     - l'assemblage tube en alliage d'or sur barreau de cuivre est laminé, avec un laminoir gorges circulaires, de ∅ 40 à ∅ 20 mm en 19 passes.
• * Recuit de diffusion :
     - effectué à 740°C pendant 2 h, sous atmosphère d'ammoniac craqué, dans un four à passage.
• * Tréfilage :
     - effectué en filières circulaires de ∅ 20 à ∅ 1,1 mm. Au cours de la dernière passe de tréfilage, une rainure mettant à jour l'âme en cuivre a été réalisée par scalpage.
• * Recuits de recristallisation intermédiaires ou final :
     - réalisés à 650°C pendant 0,5 h, sous atmosphère d'ammoniac craqué, dans un four à passage.
• * Repérage de la rainure :
     - effectué par attaque chimique, par exemple, à l'aide d'une solution diluée d'acide sulfurique à 20 %.

We manufacture a lined and machined composite wire made of an alloy based on 18 carat gold, on a copper core, by proceeding as follows:

• * Drafting:
  • continuous casting of a gold-based alloy tube, ∅ 30 x 40 x W 500 mm with a wall thickness of gold alloy equal to 5 mm;
  • rolling of a copper rod ∅ 30 x L 500 mm up to ∅ 28 mm.
• * Surface preparation:
  • internal brushing of the gold-based alloy tube;
  • external brushing of the copper bar.
• * Crimping by colaminating;
  - the assembly of a gold alloy tube on a copper bar is laminated, with a rolling mill with circular grooves, from ∅ 40 to ∅ 20 mm in 19 passes.
• * Diffusion annealing:
  - carried out at 740 ° C for 2 h, under a cracked ammonia atmosphere, in a passing oven.
• * Wire drawing:
  - made in circular dies from ∅ 20 to ∅ 1.1 mm. During the last drawing pass, a groove updating the copper core was made by scalping.
• * Intermediate or final recrystallization annealing:
  - performed at 650 ° C for 0.5 h, under a cracked ammonia atmosphere, in a pass-through oven.
• * Location of the groove:
  - carried out by chemical attack, for example, using a dilute 20% sulfuric acid solution.

At the end of these manufacturing operations, a doubled composite wire is obtained, wound in a crown and measuring approximately 600 m, with an external diameter equal to 1.1 mm and with a final wall thickness of gold alloy equal to 0 , 22 mm, having the advantageous properties stated above.

Claims (7)

Process for the manufacture of a composite wire intended for the production of hollow jewelry, of the type comprising a substantially cylindrical core made of a base metal or of a base metal alloy covered over its entire outer surface, with the exception of 'a longitudinal groove, of a coating consisting of an alloy based on a precious metal, preferably a gold alloy, said core; characterized in that it consists: - to introduce a cylindrical bar preferably with a substantially circular cross section made of a common metal or an alloy of common metals inside a tube made of an alloy based on precious metal preferably obtained by casting continuous and optionally calibrated by drawing, said tube having an inside diameter greater than the outside diameter of said bar; - Securing together said tube and said bar; - subjecting the assembly thus formed to drawing or drawing; to make a longitudinal groove on this assembly, preferably during the last drawing or drawing pass, for example by scalping; and - Possibly subjecting said groove to a chemical attack, in order to facilitate visual identification. Method according to claim 1, characterized in that the joining together of said tube and said bar is carried out by plating by stretching, then by diffusion annealing. Method according to claim 1, characterized in that the joining together of said tube and said bar is carried out by co-rolling, then by diffusion annealing. Method according to one of claims 1 to 3, characterized in that the joining together of said tube and said bar comprises a brazing. Method according to one of the preceding claims, characterized in that the aforementioned bar is made of copper. Method according to claim 5, characterized in that the above-mentioned chemical attack is carried out using a dilute solution of 20% sulfuric acid. Use of a composite wire obtained by the implementation of the method according to any one of claims 1 to 6, for the manufacture of hollow jewelry.

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