Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
  • C22C30/06—Alloys containing less than 50% by weight of each constituent containing zinc
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
  • C22C30/02—Alloys containing less than 50% by weight of each constituent containing copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/02—Alloys based on gold
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/06—Alloys based on silver

Definitions

• the present invention is generally applicable to the technical field of jewelery, and particularly relates to master alloys usable with gold, in particular to obtain a gold alloy or a jewelry item having a 9 to 18 carat finess, for manufacturing white gold alloys.
• the invention relates to a method for manufacturing such master alloys, thanks to which the same are manufactured in the form of a tablet.
• the term "finess" or derivatives thereof of a gold alloy or jewelry item is intended to indicate, unless otherwise specified, the minimum concentration of gold in the alloy or the jewelry item. Typically, the finess of gold is expressed in thousandths of a mass/mass or in carats.
• the term "carat” or derivatives thereof referred to the finess of an alloy or a jewellery item is intended to indicate, unless otherwise specified, the twenty-fourth part of the total mass of a gold alloy or jewelry item. Therefore, for example, a gold alloy or jewelry item having finess of 18 carats contains minimum 75% of gold.
• the term "consists essentially of” or derivatives thereof associated with a composition or product of interest which comprises two or more components is intended to indicate, unless otherwise specified, that the product or composition consists of the listed components (i.e. that the components listed amount to 100% of the composition or the product), apart the impurities.
• grain refiner or derivatives thereof is intended to indicate, unless otherwise specified, a compound or element poorly soluble in the alloy or master alloy and capable of promoting the formation of a high number of little grains, rather than a few grains of large dimensions.
• a fine grain alloy has generally better mechanical performances and often a higher resistance to corrosion.
• deoxidizer agent or derivatives thereof is intended to indicate, unless otherwise specified, a compound or element capable of removing the oxygen present in the alloy or the master alloy in the molten state to prevent it combining with its functional elements thus modifying the composition, purity and/or optomechanical properties thereof.
• the term "master alloy” or derivatives thereof is intended to indicate, unless otherwise specified, a semi-finished product susceptible to be combined, i.e. alloied, with gold for manufacturing gold alloys.
• alloy or derivatives thereof is intended to indicate, unless otherwise specified, a product derived the combination of a master alloy and gold, in the raw state, i.e. at the end of the process of alloying gold and master alloy.
• jewelry item or derivatives thereof is intended to indicate, unless otherwise specified, a finished product, of any shape and size, resulting the working of an alloy in the raw state, i.e. at the end of the process of alloying gold and master alloy.
• percentage by weight or “% by weight” or derivatives thereof is intended to indicate, unless otherwise specified, the weight percentage of a component of interest with respect to the total weight of the composition wherein the same component of interest is included.
• the term "providing" or derivatives thereof is intended to indicate, unless otherwise specified, the preparation of a component of interest to a process step of interest, thus including any preventive treatment adapted to the optimum exploiting of the same process step of interest, such as the simple pick up a storage site or the purification, the addition of other materials, or heat and/or chemical and/or physical pre-treatments or the like.
• a white gold alloy, a white gold jewelry item or a master alloy that when combined with gold is susceptible to make a white gold alloy or jewelry item with a value of yellow index YID1925 calculated according to the formula 1 below more than 32 (not included) should not be regarded as falling within the scope of the present invention.
• the index value of yellow YID1925 is calculated using the following formula: lOOx ((X x 1,275) - (1,057 x Z))
• a white gold alloy, a white gold jewelry item or a master alloy that when combined with gold is susceptible to make a white gold alloy or jewelry item with a value of of Chroma C* index calculated according to the formula 2 below more than 18 (not included) should not be regarded as falling within the scope of the present invention.
• indices a* and b* must be within the white gold domain proposed in the article: S. Henderson, D. Manchanda, "Report on Measurements and Classification of white gold", 2003 of the Birmingham Assay Office.
• a white gold alloy, a white gold jewelry item or a master alloy that when combined with gold is susceptible to make a white gold alloy or jewelry item having a value of Vickers hardness (HV) more than 100 (not included) should not be regarded as falling within the scope of the present invention.
• the Vickers hardness HV is calculated according to ASTM E92-82, which in paragraph 2 refers to ASTM E384-99.
• Silver is a highly bleanching and very easily alloyable metal, but when added to form alloys having a finess of more than 10 carats, tends to have a greenish color.
• nickel also has a high bleaching power, and allows to form master alloys for obtaining white gold items.
• nickel is highly toxic and causes allergies and dermatitis in sensitive peoples, which represent a significant proportion of population (approximately 10%).
• the release of nickel the alloy is mainly due to the incomplete miscibility of this metal in the precious matrix and to the formation of a nickel-rich phase, which is easily dissolved and absorbed by biological fluids.
• the manufacturing of master alloys usually comprises three subsequent steps.
• a first step is to load the raw material in a melting crucible, wherein each element is solubilized in the other by an electromagnetic induction heating, said homogenizing.
• a second step involves the pouring of the melt at a certain temperature in a cooling vessel filled with water and surfactant additives or in a cast iron flask.
• the molten material passes through a spinneret having thin holes that allow the ginning of the master alloy, namely the decomposition of the melt in tiny spheres or more irregular particles of few millimeters in diameter, while the pouring in the flask produces a solid ingot which is then sliced into small plates, after lamination.
• a third step consists of the tumbling of the particles, a process that transforms the matt and partially oxidized surface of the various particles in a bright and shiny surface, which eventually makes the master alloy ready for packaging and sale.
• the crucibles used can be contaminated, with a consequent increase in terms of costs and timing of processing.
• the basic components of the master alloy can react or solubilize the graphite crucibles, vaporize, oxidize, forming intermetallic compounds, incorporate water moisture off and, therefore, in general, introduce deleterious alterations to the nominal composition of the product.
• Another object of the present invention is to provide a master alloy that allows to obtain white gold jewelry items having low surface defects.
• Another object of the invention is to provide a method which allows manufacturing in a quick and easy way a master alloy for obtaining white gold alloys.
• the master alloy according to the invention can be used with gold to obtain a 18 carats, 14 carats, 10 carats or 9 carats alloy.
• the master alloy according to the invention may comprise, respectively may essentially consist of:
• the bleaching action of the above master alloy is due to manganese, which allows to avoid the allergenic action of nickel and the high cost of palladium. Therefore, the master alloy according to the invention is free of nickel and palladium.
• manganese has a very strong affinity for boron and tends to alloy therewith in the form of manganese boride (Mn2B), which is very hard. Therefore, the master alloy of the present invention may be free of boron.
• the master alloy according to the invention has good melting, workability, hardness and color properties, so as to be suitable to be used in the jewelery industry.
• manganese is a metal difficult to alloy in the appropriate proportions to the master alloy because of its susceptibility to thermal oxidation and its limited solubility into silver.
• the main problem in the use of manganese is its high sensitivity to oxidation, which causes the formation of significant amounts of metal oxides upon its melting together with the other elements of the master alloy, despite the use of a gas protection.
• the master alloy of the present invention solves the above problems by providing a high- bleanching composition which is low cost and non-toxic.
• the grain refiner (E) may be present in the master alloy in a percentage by weight of 0,01% to 0,25% by weight with respect to the total weight of the master alloy.
• the at least one grain refiner (E) may be present in all the master alloys susceptible to be combined with gold to obtain a 18 or 14 carats alloy, as well as in all the master alloys for plastic deformation suscetible to be combined with gold to obtain a 9 or 10 carats alloy.
• the master alloys for investment casting susceptible to be combined with gold to obtain a 9 or 10 carats alloy may be free of grain refiner (E).
• the grain refiner (E), when present, may consis of one or more elements selected from: iridium, ruthenium, rhenium, cobalt or rhodium.
• the grain refiner (E), when present, may consist of iridium only.
• the deoxidizing agent (F) may be present in master alloy in a percentage by weight of 0,01% to 0,5% by weight with respect to the total weight of the master alloy.
• the deoxidizing agent (F) may be present in all the master alloys for investment casting susceptible to be combined with gold to obtain a 18, 14, 10 or 9 carats alloy.
• the master alloys for plastic deformation susceptible to be combined with gold to obtain a 18, 14, 10 or 9 carats alloy may be free of deoxidizing agent (F).
• the deoxidizing agent (F), when present, may consist of one or more elements selected from: silicon, lithium or phosphorus. Further, in a preferred but not exclusive embodiment of the invention, the deoxidizing agent (F), when present, may consist of silicon only.
• the master alloy according to the invention may comprise, respectively may essentially consist of:
• gallium (G) may be 0,1% to 3% by weight. More generally, gallium (G) may be present if and only if the master alloy is free of deoxidizing agent and has a percentage by weight of (D) Manganese equal to or greater than 30% by weight with respect to the total weight of the master alloy. Preferably, the gallium (G) may be present exclusively in master alloy for plastic deformation is intended to be combined with gold to obtain a 18 carats alloy.
• the master alloy according to the invention is also extremely simple and quick to use.
• the master alloy of the present invention may preferably be in the form of tablet, so as to be very simple and quick to manipulate for the user.
• the method may include the steps of providing a mixture of the above components (A) to (G) and of tableting this mixture.
• This method allows to cold alloy the manganese to the other metals of the master alloy in a uniform way and without the necessity of having to melt.
• the mixture will in fact be in powder form, which may preferably have an average diameter between 10 ⁇ and 150 ⁇ .
• the tableting step may be accomplished by compacting the powder in a die for tablet with a compression strength of 20 kN to lOOkN, preferably of 50 kN to lOOkN.
• the master alloy according to the invention in the form of a tablet, preferably with a porosity of 5% to 20% by volume.
• At least a part of the particles of the powder may have a not spherical, irregular shape.
• the powder to be inserted in the die for tablet may be prepared in any way.
• one or more of the components (A) to (G) may be mixed together and atomized to obtain a powder to be mixed with the other components.
• the manganese (D) may be introduced into the mixture as pure component and/or using a copper/manganese 50:50 prealloy.
• the iridium (E) may be added to the mixture through a prealloy with copper (Cu/lr) in a 98:2 ratio.
• the silicon (F) may advantageously be added to the mixture through a prealloy with Copper (Cu/Si) in a 90:10 ratio. Thanks to the method according to the invention, the correct mixture of the components of the master alloy is made available to users who, otherwise, would be required to alloy to the gold, in a separate way and with all the consequent problems, the various components of the master alloy.
• the powder containing the components (A) to (G) may be added, in a per se known manner, small amounts of priming powders. The latter occludes the air -filled porosity of the tablets and drags off the accidental formation of oxides in the molten alloy.
• the master alloy according to the invention may comprise, respectively may essentially consist of:
• the master alloy according to the invention may comprise, respectively may essentially consist of:
• gallium (G) may be 0,1% to 3% by weight.
• the master alloy according to the invention may have a different composition depending on the intended use, and in particular depending on the finess of the gold with which it is susceptible to be combined and the method by which the white gold alloy thus obitained is susceptible to be worked to obtain a jewelry item, whether by investment casting or plastic deformation.
• the master alloy according to the invention susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• the master alloy according to the invention susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• This master alloy has a high bleaching power.
• the master alloy susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• the master alloy susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• a master alloy for investment casting susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) Gallium.
• the master alloy for investment casting susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) gallium.
• This master alloy has a high bleaching power.
• the master alloy for plastic deformation susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• master alloy is free of (F) deoxidizing agent and free of (G) gallium.
• the master alloy for plastic deformation susceptible to be used with gold to obtain a 18 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (F) deoxidizing agent.
• This master alloy has a high bleaching power.
• the master alloy susceptible to be used with gold to obtain a 14 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) gallium.
• the master alloy for investment casting susceptible to be used with gold to obtain a 14 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) Gallium.
• the master alloy for plastic deformation susceptible to be used with gold to obtain a 14 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (F) deoxidizing agent and (G) gallium.
• the master alloy susceptible to be used with gold to obtain a 10 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) gallium.
• the master alloy for investment casting susceptible to be used with gold to obtain a 10 carats alloy may include, respectively may essentially consist of:
• master alloy is free of (E) of grain refiner and (G) gallium.
• the master alloy for plastic deformation susceptible to be used with gold to obtain a 10 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (F) deoxidizing agent and (G) gallium.
• the master alloy susceptible to be used with gold to obtain a 9 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (G) gallium.
• the master alloy for investment casting susceptible to be used with gold to obtain a 9 carats alloy may include, respectively may essentially consist of:
• master alloy is free of (E) grain refiner and free of (G) gallium.
• the master alloy for plastic deformation susceptible to be used with gold to obtain a 9 carats alloy may include, respectively may essentially consist of:
• the master alloy is free of (F) agent and flux -free (G) Gallium.
• the white gold alloys may consist of a master alloy according to the present invention combined with gold to obtain a 18 carats, 14 carats, 10 carats or 9 carats alloy.
• a 18 carats white gold alloy may essentially consist of at least 75,00% by weight, and preferably 75,00% to 76,00% by weight, of gold and the remaining part (balance to 100%) of one of the master alloys usable with gold to obtain a 18 carats alloy as described above.
• a 14 carats white gold alloy may essentially consist of at least 58,50% by weight, and preferably 58,50% to 59,50% by weight, of gold and the remaining part (balance to 100%) of one of the master alloys usable with gold to obtain a 14 carats alloy as described above.
• a 10 carats white gold alloy of 10 carat white gold title may essentially consist of at least 41,70% by weight, and preferably 41,70% to 42,70% by weight, of gold and the remaining part (balance to 100%) of one of the master alloys usable with gold to obtain a 10 carats alloy as described above.
• a 9 carats white gold alloy may essentially consist of at least 37,50% by weight, and preferably 37,50% to 38,50% by weight, of gold and the remaining part (balance to 100%) of one of the master alloys usable with gold to obtain a 9 carats alloy as described above.
• the white gold alloys according to the present invention it is possible to obtain jewelry items, for example necklaces, pendants, earrings, bracelets or rings.
• the white gold jewelry items may be rhodium plated to obtain a particularly brilliant jewelry itrems.
• the jewelry items made by the white gold alloys manufactured by the above high bleaching power master alloys may be worked without rhodium plating.
• Au 18-14-10-9 Kt Master alloy susceptibl to be alloyied with gold to obtain a 18, 14, 10 or 9 carats white gold alloy;
• the master alloys of the samples 1-10 shown in Table 1 were prepared by cold tableting from two different powders, compacted together by means of an uniaxial press of 25 kN type.
• the final product is a tablet about 1,5 gr.
• a first type of powder consists of only (D) pure manganese, while the other type consists of an alloy of all the other elements (A) - (C) and (E) - (G) (when present) that forming the composition of the master alloy.
• the second powder is first made by prealloying the various components to obtain a prealloy, and then atomizing the prealloy in order to obtain a powder having an average diameter of less than 150 ⁇ (microns). After the atomization step, the second powder is then sieved to obtain an optimal particle size distribution.
• the iridium (E) and silicon (F) were inserted into the mixture through a prealloy with copper, respectively Cu/lr in a 98:2 ratio and Cu/Si in a 90:10 ratio.
• the two types of powders were then mixed using a planetary mixer and introduced into the die of the press, where they were pressed to obtain the above tablet, which porosity is about 10%.
• weight ratios between the two powders and between the components of the second powder vary according to the provisions in the above table 1.
• a lubricant is used mixed with the two above powders in a ratio of about 0,2% by weight of the total weight of the composition.
• the lubricant consists essentially of kenolube or graphite.
• the master alloys of the examples 1-10 shown in Table 1 were employed to achieve white gold alloys, as shown below.
• the alloys of the samples 11-15 were prepared starting respectively from the master alloys of samples 1, 2, 5, 7 and 9.
• the alloys of the samples 16-20 shown in Table 2 were prepared starting respectively from the master alloys of the samples 3, 4, 6, 8 and 10.
• Each master alloy was combined with gold in a weight ratio according to the shiwn finess.
• the weight ratio between gold and master alloy is 75:25 (75% gold, 25% master alloy)
• the weight ratio is 58,5: 41,5
• the weight ratio is 41,7: 58,3
• the weight ratio is 37,5: 62,5
• each alloy had a form of an ingot.
• master alloy and gold in the appropriate weight ratios were introduced into a crucible protected by argon gas or reducing gas, and thereafter a temperature of 1100 ° C, i.e. a temperature of 100-150 °C greater than the liquidus temperature, were reached.
• the metal had been then poured into a flask, wherein the alloy was cooled.
• Each of the alloys was analyzed to determine the color and the mechanical properties.
• a gold alloy in the jewelery field can be defined as white gold if the color has a yellow index (YID1925), defined by the formula 1 below, equal to or less than 32.
• YIDl925 100x((X xl,275) - (l,057xZ))
• the parameters X, Y and Z are tristimulus values calculated according to ASTM E308-99, In particular, paragraph 7.1.1 of this standard concerns the calculation of these parameters.
• white gold alloys which have a value of yellow index YID1925 less than 19 are generally considered particularly valuable in the jewelery field.
• Chroma index C* is calculated using the formula 2 below:
• indices a* and b* must also be within the scope of definition of the white gold proposed in the article: S. Henderson, D. Manchanda, "Report on Measurements and Classification of white gold", 2003 of the Birmingham Assay Office.
• the white gold alloys are considered to have good mechanical properties if they have a value of Vickers hardness (HV) equal to or greater than 100.
• the Vickers hardness HV is calculated according to ASTM E92 -82.
• the alloy has been introduced into a crucible protected by argon gas or reducing gas, and a temperature of 1100 °C, i.e. a temperature of 100-150 °C higher than the liquidus temperature, were reached.
• the molten alloy was then poured into refractory molds, which were then rested for 5 minutes and then immersed in water.
• the shaft has been cleaned from the refractory mold with a high pressure water jet and then it is left in an amidosulfuric acid solution to remove residual of surface oxides and mold.
• the wedding rings were finished and polished to obtain finished wedding rings.
• the alloy in the form of a bar was worked by laminations and subsequent annealing.
• the laminations were performed with a thickness reduction of at least 50% and the annealing carried out at a temperature of about 75-80% of the solidus temperature of the alloy for about twenty minutes in a protected atmosphere.
• the same laminate is cut to obtain the wedding rings.
• the cut wedding rings were then finished and polished to obtain finished wedding rings.

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