Technical field

This invention relates to a process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products.

Background art

Electroforming is a galvanic technique of a per se known type which, by means of an electrochemical process, allows a thin layer of metal to be deposited (for example a precious metal, such as gold) on the surface of a model previously created from low-melting metal (for example, zama). Small holes are then made on the electroformed object and the articles are then inserted in a heated centrifugal unit which makes it possible to eliminate the low-melting metal remaining inside the piece of jewellery.

In practice, the low-melting metal remaining is brought to the melting point (far from the temperature of liquefaction of the metal deposited) and escapes from the electroform by means of the holes created previously. After the centrifuging step, the electroforms are placed in baths containing acids which are able to perfectly clean the small low-melting residues still left inside, so as to obtain a piece of jewellery which is perfectly compliant with the grade of the metal, as required by the law, with large apparent surfaces and thicknesses in the order of microns.

A problem with this technology is due to the fact that electroforming cannot be used to create some types of jewellery, in particular those with the most complex shapes, due to the fact that the thin filaments which form the low- melting model would have serious problems in the hollowing.

Another well known technology in the gold and jewellery sector is electro melting.

In this case, the pieces of jewellery are made by melting directly in the precious metal selected the prototypes coming from three-dimensional printers. By means of the electro-melting it is possible to make objects with very complex designs consisting of ultra-thin filaments, which cannot be created by electroforming or other techniques such as micro-melting. However, this technology, unlike electroforming, does not allow empty spaces to be created internally and, consequently, the products are heavier and more expensive (due to the considerable incidence of the cost of the raw material on the product).

Aims and summary of the invention

The purpose of the invention is to overcome the above-mentioned drawbacks of prior art types of processes for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products which allows a piece of jewellery made of precious or non-precious metal to be obtained, which is light as if it were made by electroforming and which at the same time can be made with different and unusual shapes as if they were made by electro-melting.

In the context of the above-mentioned purpose, an aim of the invention is to make jewellery made of precious metal with a very low weight/volume ratio, so as to make the product economically competitive.

Another aim of the invention is to obtain a piece of jewellery which has a great strength and stability, allowing the creation of pieces of jewellery with designs referable to the electro-melting but with empty filaments inside, thus exploiting the principle of electroforming.

Yet another aim of the invention is to provide a process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products, which is inexpensive and industrially efficient.

Brief description of the invention

This purpose, as well as these and other aims, which are described in more detail below, are achieved by the process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products according to the invention, comprising the technical features described in one or more of the appended claims. The dependent claims correspond to possible different embodiments of the invention.

More specifically, according to a first aspect, this invention relates to a process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products, which comprises a succession of steps consisting in:

- creating at least one prototype model for the piece of jewellery to be made, designed beforehand, for example, by means of software, having a system of tubular elements internally hollow, of the filamentary type, with a maximum thickness of less than or equal to 30 pm and mechanically interconnected with each other in such a way as to form a reticular structure,

- painting the model using a metal-based solution, to obtain a painted model which is electrically conductive;

- immersing the painted model in a galvanic bath containing the metal to be deposited on its outer surface using an electrochemical process, to make a coated model;

- eliminating all the material from which the model is made from the coated model, so as to obtain the designed piece of jewellery.

The model to be coated arises during the conception and design of the piece of jewellery which takes place by means of three-dimensional graphics software. During this design stage the research and development of shapes and structures which are the best to be made is preferable. Advantageously, the tubular elements are twisted together with each other.

Equally advantageously, the tubular elements are connected to each other, without an actual twisting.

In this case, advantageously, there is a supporting element, preferably empty, positioned even more preferably in a central portion of the model, from which the tubular elements connected to it branch out.

Again advantageously, said tubular elements are twisted and also connected to each other. The need to combine an innovative design with a resistant and lightweight structure has led the Applicant to the creation of pieces of jewellery in which a system of tubular elements which are hollow and interconnected are able to give the structure of the object to be made a great stability and a high strength, despite the thicknesses of metal reduced to a minimum. After the design step there is the prototype production step, carried out by means of special three-dimensional printers which operate with the photopolymerisation of resins (DLP and SLA technologies).

Once the prototypes of resinous material have been made, the various models pass to the painting step which is fundamental for the production process, since the models are made electrically conductive and ready for the subsequent galvanic step. The painting is accomplished preferably by immersion of the models in a solution of liquid copper and solvent (for example, a generic dilutant for paints), placed inside a mixer and applied to the parts by immersion.

Advantageously, a suitable ratio between the liquid copper and the solvent allows the best conductivity of the painted model and the correct movement of the compounds.

Preferably, the metal-based solution is placed inside a mixer before being applied on the model.

The painted models are mounted in a rubber coated metal frame and inserted in a galvanic bath in which gold is deposited on the painted surface by means of an electrochemical process.

The galvanic bath has a temperature of between 60 and 85°C, inclusive, preferably between 70 and 80°C, inclusive, more preferably between 72 and 77°C, inclusive, even more preferably substantially equal to 75°C. Preferably, the parameters for setting the galvanic bath are such as to allow a maximum deposit of metallic material on the outer surface of the prototype model substantially equal to 30 pm, depending on the type of jewellery to be made.

The Applicant has noted that the majority of the resins present on the market tend to expand if subjected to high temperatures, creating breakages of the metal in the subsequent hollowing steps. On the other hand, materials which contain a high percentage of wax overcome this problem but are not able to withstand the temperatures of the galvanic baths.

For this reason, the Applicant understood that it is essential that the material from which the model is made must contain a percentage of wax inside such a way as to allow the resistance to the various production steps.

Once metal has been deposited on the model, the step of hollowing the model covered in this way is performed, thereby eliminating the resinous material of the prototype model, which has remained inside the objects. The Applicant has understood that, since the resinous materials melt at a very high temperature and before reaching the melting point they tend to undergo strong expansions, generating an increase in volume, there is the serious risk that the thin metallic outer layer (for coating the model) may break due to this increase in volume. For this reason, advantageously, the material with which the prototype production models are made must contain a suitable quantity of resin.

For this reason, it is extremely important that there is a proportion between wax and resin in the resinous material such as to make possible both the previous galvanic process and the hollowing process.

Advantageously, the material designed to be printed by means of a three- dimensional printer with photopolymer technology, comprises methacrylate oligomers, polyols and photoinitiators.

The step of hollowing the objects advantageously comprises the use of heat ovens.

In order to carry out the hollowing, the articles are placed in an oven and are brought with a heat ramp up to 350°C and the temperature is then increased by 10°C every 5 minutes until reaching 450°C. Once this temperature has been reached, it is kept stable for approximately 20 minutes and then increased directly to 470°C and then stabilised for 20 minutes.

After completion of these steps, the designed piece of jewellery is obtained, ready to be finished and completely free of any material outside the selected precious metal, therefore perfectly of the required grade. Another aspect of the invention relates to a model for making a piece of jewellery designed beforehand, for example, by means of software, particularly in the field of goldsmith's, silversmith's and costume jewellery products, comprising a system of internally hollow tubular elements, of the filamentary type, which have a maximum thickness value of less than or equal to 30 pm. The hollow tubular elements are mechanically interconnected with each other in such a way as to form a reticular structure.

Brief description of the drawings

Further features and advantages of the invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of the process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products, illustrated by way of example and without limiting the scope of the invention, with the aid of the accompanying drawings, in which:

Figure 1 is a perspective view of a first prototype model 1 with the tubular elements 2 interwoven with each other;

Figures 2A, 2B and 2C show a variant of the model of the preceding drawing, a second model 101 with the tubular elements 102 simply connected to each other in a perspective view, plan view and an elevation view, respectively;

Figure 3 shows the model 1 of Figure 1 painted: painted model 1';

Figure 4 shows the model 1 of Figures 1 and 2 coated: coated model 1". Detailed description of the actuation of invention The above-mentioned drawings show a preferred embodiment of a process for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products, according to the invention, which is identified in its entirety with the numerals 1 and 101 , which comprises the following steps in succession.

Firstly, the item of jewellery to be made is designed using three- dimensional modelling software (3D CAD) which creates a prototype model 1 or 101 using a three-dimensional printing process which uses a DLP or SLA technology.

The model 1 or 101 has a structure formed by interconnected hollow tubes 2 or 102, interlaced and/or connected to each other, which give the structure a great stability and an excellent strength despite the thicknesses of metal reduced to a minimum with a thickness SMAX equal to or less than 30 pm.

In a first embodiment, the model 1 for the piece of jewellery to be made designed beforehand, has a twist of internally hollow tubular elements 2, of the filamentary type, mechanically interconnected with each other in such a way as to form a twisted reticular structure (Figure 1 ).

According to an alternative embodiment, the model 101 for the piece of jewellery to be made designed beforehand, has on the other hand, a connection of internally hollow tubular elements 102, of the filamentary type, mechanically interconnected with each other in such a way as to form a reticular structure of empty threads which are mutually connected (Figures 2A-2C).

In this case, the filamentary tubular elements 102 which act in conjunction to form the model extend from the supporting element 103.

Alternatively, it is also possible to consider a model (not illustrated) in which the tubular elements are partly interwoven and partly simply connected to each other.

In any case, the material chosen for the prototype model 1 or 101 is designed to be printed using three-dimensional printers with photopolymerisation technology and has a quantity substantially between 10 and 70% by weight, inclusive, of methacrylate oligomers; a quantity substantially between 10 and 70% by weight, inclusive, of polyols (or poly alcohols) and a quantity of between 0.1 and 5% of photoinitiators.

Once the model 1 or 101 has been made, it is immersed in a solution of liquid copper and solvent wherein, preferably, the quantity of copper varies in a range of from 20 to 40% depending on the type of part treated; the solution is contained in a mixer.

For this reason, the painted model 1' is in this way electrically conductive and ready for the galvanic step (Figure 3). For that purpose, it is mounted in a frame made of metal coated with rubber and then inserted in a galvanic bath at 75°C, in which gold is deposited above the painted surface by means of an electrochemical process. The thickness of metal deposited varies up to a maximum of 30 pm, so as to make a coated model 1" from a thin gold film (Figure 4).

After the gold is deposited, the hollowing is carried out in heat ovens which allow the almost finished product to be obtained, eliminating the prototype production material still remaining inside the model 1.

In order to carry out the hollowing, the coated model 1" is inserted inside the oven and it is initially brought up to 350°C, with a heat ramp.

At this point, the temperature of the oven increases by 10°C every 5 minutes to 450°C. Once this temperature has been reached, it is kept stable for approximately 20 minutes and then increased directly to 470°C and then stabilised for 20 minutes.

The piece of jewellery made in this way, emptied of every material apart from the gold, is ready for prior art finishing processes.

From the above description it may be seen how the invention achieves the preset purpose and aims and in particular the fact that a process is implemented for making pieces of jewellery, particularly for goldsmith's, silversmith's and costume jewellery products, which makes it possible to obtain a piece of jewellery made of precious or non-precise metal, which can be made in the most diverse and complex shapes and as if it were made by electro-melting, but which is - at the same time - sufficiently light as if it were made by electroforming.

More specifically, the making of the prototype model using a system of thin hollow tubular elements with a maximum thickness of 30 pm makes the piece of jewellery even lighter and more delicate, almost gaseous. Another advantage of the invention is due to the fact that the very low weight/volume ratio makes the piece of jewellery obtained in this way extremely competitive from an economic point of view.

Another advantage of the invention is that the extraordinary weave of the structure provides the piece of jewellery with great strength and stability, thus allowing the creation of pieces of jewellery with complex design even though they consist of a system of filaments which are empty, interwoven and/or connected to each other.

The production method is also extremely economical and industrially efficient. The invention can be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

Moreover, all the details of the invention may be substituted by other technically equivalent elements.

In practice, the materials used, as well as the dimensions, may be of any type, depending on requirements, provided that they are consistent with their production purposes.