Classifications

• • 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
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

• the present invention relates to a gold alloy of at least 14 carats for the production of jewelry by lost wax casting.
• Investment wax casting is a method for producing complex parts with a good surface appearance and excellent dimensional accuracy.
• This technique consists first of all in making wax, by injection into tools, the replica of each of the desired parts.
• the assembly of these models on pouring channels also in wax constitutes a cluster; after having uniformly surrounded this cluster with a ceramic shell, the wax is melted, which leaves its exact imprint in the ceramic, into which the molten metal is poured. After cooling the shell is destroyed and the metal parts are separated and finished.
• This technique for melting gold jewelry dates back to the first days of metallurgy, around 4000 BC It was not until its application in dental technology at the beginning of the twentieth century that were developed mold production and melting techniques as we know them today.
• the only elements used for this purpose in practice are zinc, silicon, iridium and cobalt.
• Silicon is known to cause the formation of a stable protective oxide layer around the parts obtained by casting when it is added to 14 carat gold alloys in small quantities.
• the formation of this oxide layer makes it possible to avoid the porosities due to the reactions between the liquid metal and the coating, and to obtain a perfect surface for the alloys of 9, 14 and 18 carat gold.
• the addition of silicon leads to an increase in the grain size and a decrease in the breaking strength.
• the object or problem of the invention is to find doping elements of a gold alloy of at least 14 carats having the advantages of silicon without having the drawbacks mentioned above.
• the doping elements are Zn, Ga, Ta, Pt and Ru. Surprisingly, the presence of these elements makes it possible to avoid, during the casting by lost wax of gold alloys, the harmful interaction between the mold and the liquid metal, apparently thanks to the formation of an oxide layer. protective gas impermeable. Ruthenium is a very effective grain refiner, even at low levels.
• the invention relates to an alloy of gold of at least 14 carats, characterized in that it contains as doping elements, by weight, from 10 to 20,000, preferably from 100 to 1,000, ppm Zn, from 10 to 20,000, preferably from 100 to 1000, ppm Ga, from 10 to 20,000, preferably from 100 to 1000, ppm Ta, from 10 to 10,000, preferably from 90 to 950, ppm Pt and from 10 to 5000, preferably from 5 to 100, ppm Ru.
• doping elements by weight, from 10 to 20,000, preferably from 100 to 1,000, ppm Zn, from 10 to 20,000, preferably from 100 to 1000, ppm Ga, from 10 to 20,000, preferably from 100 to 1000, ppm Ta, from 10 to 10,000, preferably from 90 to 950, ppm Pt and from 10 to 5000, preferably from 5 to 100, ppm Ru.
• the gold alloy of at least 14 carats can be an alloy based on gold, silver and copper, in particular a 14 carat alloy such as for example a yellow gold alloy 14 comprising, expressed in weight, 58-59% Au, 24-28% Ag and 13-17% Cu or a red gold alloy comprising, expressed by weight, 58-59% Au, 7-11% Ag and 30-34% Cu, an 18-carat alloy such as for example a yellow gold alloy comprising, expressed by weight, 75-76% Au, 10-14% Ag and 10-14% Cu, a pale yellow gold alloy comprising, expressed by weight, 75-76% Au, 14-18% Ag and 7-11% Cu, a rose gold alloy comprising, expressed by weight, 75-76% Au, 7-11% Ag and 14-18% Cu, a red gold alloy comprising, expressed by weight, 75-76% Au, 2-6% Ag and 18-22% Cu, a 22-carat alloy such as for example a yellow gold alloy comprising, expressed by weight, 91-92% Au, 3-7% Ag and 1-5% Cu, or a red gold alloy compris
• the gold alloy of at least 14 carats can also be a fine gold alloy, in particular comprising, expressed by weight, 99-99.9% Au and 0-1% Cu.
• it will suitably contain from 10 to 10,000 ppm Zn, from 10 to 10,000 ppm Ga, from 10 to 10,000 ppm Ta, from 10 to 10,000 ppm Pt and from 10 to 5,000 ppm Ru.
• the gold alloy of at least 14 carats can also be a white gold alloy, for example an 18 carat white gold alloy comprising, expressed by weight, 75-76% Au, 8-12% Cu, 0 -4% In, and 11-15% Pd, or a 14-carat white gold alloy comprising, expressed by weight, 58-59% Au, 14-18% Ag, 12-16% Pd, and 6-10% Cu.
• a white gold alloy for example an 18 carat white gold alloy comprising, expressed by weight, 75-76% Au, 8-12% Cu, 0 -4% In, and 11-15% Pd, or a 14-carat white gold alloy comprising, expressed by weight, 58-59% Au, 14-18% Ag, 12-16% Pd, and 6-10% Cu.
• the same advantageous properties of the alloys are obtained by replacing the weight content of Ta specified above by an identical weight content of an element chosen from the group consisting of Ti, Zr and Nb.
• the gold alloy according to the invention is generally produced in ingots by casting under an inert atmosphere, for example nitrogen, of the constituent elements of the alloy, either in the pure state or in the state of alloy, in molds made of heat-resistant material such as for example graphite.
• the alloy can then be shaped by continuous casting in order to obtain studs.
• Continuous casting is a process where the molten alloy is fed into a graphite mold with open ends, in which the metal solidifies to produce a bar of predefined dimensions.
• the solidified form is cooled and removed from the water-cooled mold at a controlled speed using rollers, and the material is sawn to the desired length.
• the studs that can be used directly in casting are then obtained by cutting and marking in the bar from the continuous casting.
• the invention also relates to a process for manufacturing a gold alloy as defined above which comprises the casting under an inert atmosphere of the constituent elements of the alloy, either in the pure state or in the state of 'alloy.
• the preparation of objects cast by the lost wax casting technique is generally carried out as follows.
• the ingots are rolled and cut into small pieces, or if the alloy has been shaped by continuous casting, the casting studs are used as such.
• the coating used consists of gypsum and silica.
• the dewaxing is carried out without steam at a temperature of 140 to 160 ° C, then the cooking cycle is as follows: level at 200 ° C, rise by 5 ° C per minute, level at 650 ° C by 45 minutes.
• the casting is then carried out by centrifugation, after melting in a graphite crucible, under nitrogen.
• the parts are then removed from the mold and milled in order to remove the surface oxide. Correct and complete: generalize the protocol for the preparation of cast objects actually used.
• the invention also relates to the use of the alloy defined above for the manufacture of jewelry by casting with lost wax.
• the invention also relates to a cast object comprising this alloy.
• the temperature is room temperature or is expressed in degrees Celsius
• the pressure is atmospheric pressure.
• Figures 1 and 2 represent respectively the diagram of a flywheel allowing to evaluate the surface condition, the flowability, the ductility, the porosity, the oxidation as well as the grain size of the alloy after casting, and a photograph of a harp-shaped piece to assess the heat resistance of the alloy.
• Tables 1 and 2 collect respectively the compositions of the standard and doped alloys, and the main characteristics of the molded parts obtained from these alloys.
• ingots of alloys of dimensions 80 x 50 x 5 mm 3 were cast under nitrogen in graphite ingots, from shot for gold and silver, copper plates, thin pieces of zinc and gallium, and 5% gold tantalum and 5% platinum ruthenium pre-alloys in thin strips.
• the ingots were then rolled to 1 mm thick.
• a 2 cm square plate for each alloy was used (after coating and polishing) for the spectrometric color analyzes.
• the coating used consists of gypsum and silica.
• the dewaxing is carried out without steam at 150 ° C, then the cooking cycle is as follows: level at 200 ° C, rise by 5 ° C per minute, level at 650 ° C by 45 minutes.
• the casting is then carried out by centrifugation, after melting in a graphite crucible, under nitrogen. The parts are then removed from the mold and billed in order to remove the surface oxide, then analyzed according to the procedures below.
• Table 1 specifies the composition of the objects cast for four 18-karat gold alloys according to the invention, here called “doped yellow”, “pale yellow doped”, “doped pink” and “doped red”, and corresponding respectively to the alloys “standard yellow”, “standard pale yellow”, “standard pink” and “standard red” obtained in Example 2.
• Table 1 specifies the composition of the cast objects for four prior art 18-karat gold alloys, called “standard yellow”, “standard pale yellow”, “standard pink” and “standard red”, and a known silicon doped alloy with a composition close to standard yellow, called “yellow-Si”.
• the color of the alloys was measured on a square plate 2 cm side and 1 mm thick according to the 3-dimensional measurement system called CIELab, CIE being the sign of the International Lighting Commission, and Lab the three coordinate axes.
• CIELab CIE being the sign of the International Lighting Commission
• Lab the three coordinate axes.
• the human eye can distinguish a difference of 1 point on this scale.
• the properties of the alloys after casting with lost wax were evaluated for each alloy using two castings.
• the first part (Figure 1) consists of a steering wheel on which are placed a plate of 1 cm 2 of surface and 1 mm thick as well as rods of 2 cm in height and diameters 0.8, 0.6, 0.4 and 0.3 mm. On the steering wheel are placed 2 rods of each diameter, i.e. 8 rods.
• This first part makes it possible to evaluate the surface condition, the flowability, the bending, the ductility, the porosity, the oxidation as well as the grain size of the alloy after casting.
• the second part is in the shape of a harp ( Figure 2) and allows the hot resistance of the alloy to be evaluated.
• the grade given to the surface finish is calculated according to the following criteria: porosity and fine texture of the wafer. Note 10 corresponds to a perfect surface condition without defects.
• the small raised points on the surface are due to coating surface defects and are independent of the alloy, however they affect the quality of the part.
• a perfect surface from the point of view of porosity and fineness of texture but having raised points will obtain a score of 9.5 or 9 depending on the size or frequency of these points in order to distinguish it from a perfect surface and without raised points.
• the alloys doped according to the invention have better flowability than the corresponding standard alloys (14.12 / 9.40, 14.50 / 9.25, 16.90 / 9.40, 18.5 / 12.6) and the alloy doped with silicon
• the bending test is used to simulate the crimping step at the jeweler. It is important that the crimping rods can be bent several times in order to allow the jeweler several tests without the entire piece having to be rolled up.
• the bent rods have a diameter of 0.8 mm in this test.
• the bend test consists of a first twist at an angle of 90 ° and the following are alternately opposed at 180 ° of an angle. A value of 1 corresponds to a 90 ° angle break, a value of 2 corresponds to a 90 ° break + 180 ° angle. The higher values correspond to an additional torsion opposite to the previous one and of 180 ° of angle.
• Table 1 shows that the objects cast in doped alloys according to the invention have better bending than those in corresponding standard alloys (4/3, 4.5 / 3.5, 3/2, 2/1) or in silicon doped alloy (4 / 2).
• the so-called ring enlargement test showed that the doped alloys according to the invention are more ductile than the corresponding standard alloys and can withstand up to 24% elongation before rupture.
• the cast rings had a diameter of 15.9 mm (number 10) and a section of 2 mm 2 .
• the standard alloy without refiner supports an enlargement of 2 numbers, and the doped alloy supports an enlargement of 1
• the hot rupture resistance test is carried out by pouring a harp-shaped piece ( Figure 2).
• Figure 2 The difference in the coefficient of expansion of the mold and of the metal generates a tension capable of causing the metal to break depending on its fragility. This test makes it possible to discriminate fragile structures as well as possible harmful pollution of the metal.
• the score is awarded by subtracting 20, 1 point per broken stem. Only the alloys having obtained the note 20/20 were retained.
• Table 1 shows that the doped alloys according to the invention have excellent resistance to hot rupture, unlike the alloy doped with silicon.
• the state of porosity is noted by observing the wafer on the wafer under an optical microscope.
• the score out of 10 is given according to the number of pores and their size and the regularity of the surface: - if large pores are observable, the score 0 is automatically assigned.
• the minimum acceptable score is 9/10. Parts with surface porosity are automatically rejected. The less porous the alloy, the better its mechanical properties and the easier the polishing.
• Table 1 shows that the doped alloy according to the invention has a porosity state identical to that of the silicon doped alloy (10/10) and much better than each of the standard alloys (10/8, 10/6, 9/0 and 9/7).
• the oxidation state is noted according to the appearance of the part just after demolding. The more the part will present a uniform aspect close to the color of the alloy without black traces due to copper oxide, the more the note obtained will tend towards 10/10. Copper oxide is to be avoided in the field of the possible because it does not protect the part against gases and it is suspected of favoring the reactions of degradation of the mold leading to the release of sulfur dioxide gas.
• the parts from doped alloys according to the invention have a uniform surface close to the color of the alloy without traces of copper oxide and therefore have an excellent oxidation state, much better than that of parts from standard alloys ( Table 1: 10/0, 10/0, 10/5, 10/10).
• ASTM grain size is given by the superimposition of an ASTM grid on the photo of a metallographic grid of a part cast after chemical attack to reveal the grain boundaries.
• ASTM conversion table a size of 7 corresponds to an average grain diameter of 32 microns.
• ASTM 3 corresponds to an average diameter of 125 microns. The higher the ASTM value, the smaller the grains, the better the mechanical properties of the alloy and the easier the polishing.
• Table 1 shows that the parts from doped alloys according to the invention therefore have a grain size identical to or finer than that of parts from standard alloys (7/7, 7/7, 6 / 3-4, 6 / 6) or of the alloy doped with silicon (7 / 2-3).
• Table 1 Compositions of standard and doped alloys, in mass percentages.
• Table 2 Comparison table of 18 carat gold alloys of standard color and doped with the different characteristics of the castings. The casting conditions are strictly the same for all the tests. The results for the alloy doped with silicon (yellow-Si) are given by way of example.

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• 2003
  • 2003-02-11 EP EP03405074A patent/EP1447456A1/de not_active Withdrawn
• 2004
  • 2004-02-10 ES ES04709565T patent/ES2305723T3/es not_active Expired - Lifetime
  • 2004-02-10 WO PCT/CH2004/000076 patent/WO2004072310A2/fr not_active Ceased
  • 2004-02-10 EP EP04709565A patent/EP1594995B1/de not_active Expired - Lifetime
  • 2004-02-10 JP JP2006501446A patent/JP4879729B2/ja not_active Expired - Fee Related
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• 2005
  • 2005-07-29 US US11/193,921 patent/US20060029513A1/en not_active Abandoned

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