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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/003—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using inert gases
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/38—Selection of media, e.g. special atmospheres for surrounding the working area
  • B23K35/383—Selection of media, e.g. special atmospheres for surrounding the working area mainly containing noble gases or nitrogen
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
• • 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 precious metal alloys and methods of manufacturing such.
• the present invention relates to precious metal alloy objects such as jewellery and other precious metal containing objects, for example dental implants and decorative members, that are intended to be in contact with a human body.
• precious metal objects which are worn on the human body are subjected to wear and damage.
• the ductility of precious metals is an advantage since the risk for fracture is low, but precious metals have relatively low hardness making them susceptible to wear. To make them harder, and also due to the high cost of the precious metals, precious metals used in jewellery, implants, etc. are usually alloyed with other elements.
• the precious metals may also be alloyed to improve other properties of the precious metal, such as for example to obtain a certain lustre or colour or to improve the workability.
• the allergenic potency of different elements differs and generally precious metals have the lowest potency.
• nickel has been identified as having the highest allergenic potency. Therefore the nickel release in a synthetic sweat solution has been established as a measure on the allergenicity of a nickel- containing material, and a threshold level (0.2 ⁇ g/cm 2 /week) below which an object may be considered non-allergic has been defined in the European Union "Nickel Directive" (94/27/EC).
• Similar threshold levels for other alloying elements have not been established, but it is likely that other alloying elements, even silver, copper and gold, may also cause sensitisation. Allergenic reactions or the like may also occur due to impurities in the precious metals or metal alloys.
• the impurities may appear due to impurities of the raw materials used or due to the manufacturing of the alloy.
• impurities may be added if the precious metal or metal alloy is treated with an acid in a step following a casting step to remove oxides formed on the cast object. Irrespective of the reason for the sensitisation, a precious metal object can be regarded as biocompatible if the probability of causing sensitisation is below a certain degree.
• a precious metal alloy comprising the alloying elements gold, silver and copper is usually manufactured by melting the alloying elements in a crucible and casting them in a mould to form a raw material that subsequently is subjected to further processing to form the final object.
• the prior art has drawbacks with regard to being able to provide a precious metal alloy object that is biocompatible and has the desired material properties, such as high hardness and good workability.
• the step of forming the biocompatible precious metal alloy object comprises the step of post-processing a precious metal alloy, i.e. a raw material, in the process chamber to form the biocompatible precious metal alloy object.
• a precious metal alloy i.e. a raw material
• the raw material is manufactured in accordance with the method of the present invention.
• the postprocessing may for example include soldering and/ or welding.
• a solder alloy suitable for being used in the above mentioned soldering of the precious metal alloy raw material or object, is manufactured in accordance with the method of manufacturing the biocompatible precious metal alloy object according to the first aspect.
• the content of the process gas and hence the environment in the process chamber is controlled by burning a flame that is supplied with a hydrocarbon-containing gas. Thereby oxygen present in the process chamber is combusted.
• the bulk of a biocompatible precious metal alloy object that has been manufactured according to the method of the present invention has an oxygen content of less than 5 ⁇ g/g, preferably less than 3 ⁇ g/g and more preferably less than l ⁇ g/g; and a hydrogen content of less than 0.05 ⁇ g/g, preferably less than O.Ol ⁇ g/g and more preferably less than 0.005 ⁇ g/g.
• a biocompatible precious metal alloy object according to the present invention preferably comprises 2% Ag. More preferably it is a gold alloy of more than 14 carat or a silver alloy.
• a precious metal alloy object which has tailored material properties with regards to e.g. hardness and workability.
• Such an object can be used as a raw material that is subjected to post-processing in order to form a final precious metal alloy object having adequate material properties such as high hardness and high fracture toughness.
• FIGs. 2a-b are schematic illustrations of process chambers according to the present invention.
• Fig. 3 is a schematic illustration of a crucible arranged on a mould with an intermediate pre-heater chamber according to the present invention
• Fig. 4 is a schematic diagram of a method in accordance with the present invention for manufacturing a precious metal alloy comprising the step of evacuating the mould
• the alloying elements are usually melted and subsequently cast to form a precious metal alloy object, a so- called raw material, which subsequently is subjected to post-processing, including e.g. forging, welding, soldering, casting, grinding, polishing or drawing, to form a precious metal alloy object such as a jewellery.
• One object of the present invention is to provide a method for manufacturing of precious metal objects which are biocompatible so that they do not cause sensitisation when carried in contact with the human body. Examples of such objects are jewellery (including piercing jewellery), decorative members of other kind, dental implants, etc. as well as the raw material mentioned above.
• the precious metal alloy composition according to the present invention comprise of precious metal alloys compositions commonly used for e.g.
• a gold alloy manufactured according to the present invention may be of a certain carat it may differ slightly in the content of the main alloying elements (Au, Ag, Cu) and the additional alloying elements may differ in content or composition to obtain e.g. a certain lustre.
• the term alloy is used, the present invention is not limited to alloys comprising two or more materials. Also pure precious metals may be manufactured using the method of the present invention.
• a method for manufacturing a biocompatible precious metal alloy object that is made of a precious metal alloy according to the present invention comprises the steps of: - 100 forming the biocompatible precious metal alloy object in a process chamber; and
• the step of forming further comprises the steps of: - 102 melting alloying elements together in order to form the precious metal alloy; and
• step of forming comprises the step of 1 1 1 post-processing the precious metal alloy in the process chamber 1 1 to form the biocompatible precious metal alloy object.
• the post-processing is preferably performed on a precious metal alloy raw material that has been manufactured according to the above mentioned steps of melting and casting.
• the invention is not limited to this and suitable raw materials manufactured according to other methods can be used.
• the post-processing may be made in the same process chamber 1 1 as used in the manufacturing of the raw material or in another process chamber such as a dedicated workstation chamber.
• Fig. 2a schematically illustrates a process chamber 1 1 according to one embodiment of the present invention.
• a process gas of predetermined composition is provided in the process chamber 11, preferably before and during melting and casting of alloying elements, by combusting burning a flame 19 that is supplied with a hydrocarbon- containing gas within the process chamber.
• the combustion process lowers the oxygen content of the process chamber 11 to at least less than 5%, preferably less than 2% and more preferably to less than 1%.
• dehydration means 21 may be used. This limits the water content of the process gas to at least less than 0.01 kg H2O per kg air, preferably less than 0.005 kg H2O per kg air, and most preferably less than 0.001 kg H2O per kg air.
• the process chamber 11 may further comprises a crucible 13 arranged on a mould 15, which, for example, may be a so-called flask comprising a plaster compound inside, which a skilled person is familiar with.
• the alloying elements are provided in the crucible 13 and melted.
• the mould 15 is at least partly filled by the molten alloying elements and after solidification of the molten alloying elements a precious metal alloy object is formed in the mould 15.
• Fig. 2b schematically illustrates a process chamber 11 suitable for the metling and casting according to one embodiment of the present invention.
• a process gas of predetermined composition in the process chamber 11 is accomplished by supplying a hydrocarbon-containing gas to a burning flame 19 within the process chamber 11.
• the hydrocarbon-containing gas may be a mixture of oxygen and acetylene, i.e. a welding flame, wherein the oxygen /acetylene ratio is adjusted to give a reducing flame (an over- rich mixture).
• the combustion process lowers the oxygen content of the process chamber 11 to at least less than 5%, preferably less than 2% and more preferably to less than 1%.
• dehydration means 21 are used to limit the water content of the process gas to at least less than 0.01 kg H2O per kg air, preferably less than 0.005 kg H2O per kg air, and most preferably less than 0.001 kg H2O per kg air.
• the process chamber 11 may further comprise a crucible 13 arranged on a mould 15, which may be a so-called flask comprising a plaster compound.
• the alloying elements are provided in the crucible 13.
• Inductive heating by inductive heaters 25 may be used to melt the alloying elements, which subsequently are supplied as a melt to the mould 15, for example through an openable and closable opening in the bottom of the crucible 13. After solidification of the melt a precious metal alloy object is formed in the mould 15.
• the method further comprises the step of evacuating a gas from the mould 15 prior to the casting of the molten alloying elements e.g. by connecting a vacuum pump to one end of the mould 15.
• the step of evacuating further comprises drying of an inert gas, optionally pre-heating of the inert gas, and providing a flow of the optionally pre-heated inert gas through the mould before casting.
• the inert gas may be provided from the process gas of predetermined composition.
• One alternative is to supply an inert gas of another composition.
• Inert gas is for the purpose of this application interpreted to mean a gas having a water content of less than 0.005 kg H2O per kg air and an oxygen content of less than 5% oxygen.
• the drying of the inert gas is obtained using dehydration means 21 in the form of e.g. a refrigeration drier.
• Gas from the process chamber 11 is pumped into the refrigeration drier, wherein water vapour in the gas is condensed and removed from the gas.
• the dried gas may then be fed back to the process chamber 11.
• the mould 15 is preheated, e.g. in a separate oven, to about 350-400 0 C. Thereafter, a pre-heater chamber 17, a mould 15 and a crucible 13 are assembled with the mould 15 underneath the crucible 13. Alloying elements are provided in the crucible 13.
• Heater means for example, inductive heaters 25, are used to heat the crucible 13 to a temperature which is sufficient to melt the alloying elements.
• the temperature depends on the composition of the alloying elements but may be about 900 0 C.
• the pre-heater chamber may be heated by heat transferred from the crucible 13.
• the temperature of the pre-heater chamber 17 may be about 600 0 C.
• a pressure gradient is applied over the mould 15, e.g. by applying a vacuum pump to one end, i.e. an outlet, of the mould 15, in such way that the process gas of the process chamber 11 is sucked into the pre-heater chamber 17 and gets preheated before entering the mould 15. This gives a preheating of the mould 15 which is at least sufficient for maintaining the temperature obtained after the preheating.
• the conditions for casting a biocompatible object is improved. Residual oxygen and water trapped in the mould may be forced out of it.
• the crucible may have an exit hole in the bottom, which initially is sealed using a rod. When the alloying elements have melted and reached the desired temperature the rod can be removed and the melt is poured down into the preheated mould 15.
• the method of the present invention results in precious metal objects having substantially no oxidation layer.
• One advantage with this is that no subsequent treatment in an acid bath (as is commonly used in the prior art) is required. Treatment in such acid baths is believed to be one source of impurities which may give sensitisation for a carrier of a precious metal alloy object manufactured from the acid bath-treated raw materials.
• the method comprises the steps of:
• a pre-heater chamber according to the invention may comprise a cylindrical body having holes around the perimeter to allow gas from the atmosphere of the process chamber to enter into a through bore which is open for the melted alloying elements to be supplied to the mould. Hence the gas enters the pre-heater chamber from the side and is sucked down into the mould.
• the step of casting comprises solidification of the melted alloying elements in the mould 15.
• the cooling of the solidified precious metal alloy object resulting from the solidification of the molten alloying elements is made in a controlled environment such as an atmosphere of the process gas of predetermined composition in the process chamber.
• the cooling may be performed e.g. within the process chamber or in an adjacent chamber -WhIcIi can be entered from the process chamber without exposing the mould to the ambient air.
• the mould with the solidified precious metal alloy object is quenched in an alcohol- containing water bath having a temperature of less than 5 0 C.
• the bulk of the precious metal alloy object that has been manufactured according to a method in accordance with the present invention will have an oxygen content of less than 5 ⁇ g/g, preferably less than 3 ⁇ g/g and more preferably less than l ⁇ g/g.
• the bulk of the precious metal alloy object that has been manufactured according to the method of the present invention will have a hydrogen content of less than 0.05 ⁇ g/g, preferably less than 0.0 l ⁇ g/g and more preferably less than 0.005 ⁇ g/g.
• the surface layer of the same precious metal alloy object will have an oxygen content of less than 30 ⁇ g/g, preferably less than 20 ⁇ g/g and more preferably less than lO ⁇ g/g and a hydrogen content of less than 3 ⁇ g/g, preferably less than 2 ⁇ g/g and more preferably less than l ⁇ g/g.
• the oxygen and hydrogen content of the precious metal alloy object are important for their mechanical properties, in particular if the cast precious metal alloy object is a raw material that is going to be worked by a goldsmith to form for example jewellery.
• High hydrogen content may, for example, give a hard and brittle alloy which is not easily post- processed by a goldsmith. This phenomenon is known in the field of metallurgy as hydrogen embrittlement.
• a method for testing the hydrogen and oxygen content in the surface layer comprises heating of the precious metal alloy object to a temperature close to, but below, the melting temperature of the alloy and then measuring the residual gases. At this temperature only gases originally trapped in the surface of the alloy object are released.
• the bulk values have been obtained in a similar way but by heating the alloy object to a temperature well above the melting temperature so that gases originally trapped in the bulk of the alloy object are released.
• the precious metal alloy object comprises at least 2% Ag.
• examples of such precious metal alloys are 18 carat gold, 14 carat gold, Sterling silver etc.
• the advantageous properties of the precious metal alloy object of the present invention may be ruined by improper treatment of e.g. a goldsmith in his post-processing to form e.g. jewellery of the precious metal alloy object, i.e. a raw material, which has been manufactured in accordance with the method of the present invention.
• a process chamber that is a dedicated workstation chamber for post-processing of a precious metal alloy in accordance with the method of the present invention is provided.
• the precious metal alloy is preferably manufactured according to the method of the present invention, but this embodiment is not limited to this.
• the workstation chamber is a glove box, i.e. a closed chamber having two gloves extending into the chamber.
• machining Any kind of machining that normally is performed on precious metal alloys objects can benefit from being performed within the workstation chamber.
• biocompatible precious metal alloy has been formed e.g. using the method of the present invention, the properties of that alloy can be maintained using this workstation.
• machining there is an overwhelming risk that the advantageous properties are ruined. Examples of machining that can be performed are cold working, hot working, soldering, drawing, forging, polishing, etc.
• the method further comprises the step of soldering and/or welding of a precious metal alloy object, which preferably has been melted and cast according to the method of the present invention, in the process gas of the process chamber or the dedicated workstation chamber.
• a typical solder for soldering precious metal alloy objects of the present invention is a precious metal alloy itself.
• the solder is fabricated in the same way as the precious metal alloy object of the present invention in a process chamber having a process gas of predetermined composition, i.e. having a water content of less than 0.005kg H2O per kg process gas and an oxygen content of less than 5%.
• a method for manufacturing a solder according to the present invention comprises the steps of providing a process gas of predetermined composition in a process chamber, the process gas having a water content of less than 0.005 kg H2O per kg air and an oxygen content less than 5% oxygen; melting solder elements; and casting the molten solder elements to form the solder, by way of example in the form of a rod or a block, wherein the steps of melting and casting are carried out within the process chamber.
• the step of providing further comprises the step of combusting oxygen of the process chamber using a flame that is supplied with a hydrocarbon-containing gas.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Adornments (AREA)
• Materials For Medical Uses (AREA)

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• 2009
  • 2009-03-26 EP EP09731318.3A patent/EP2265737A4/en not_active Withdrawn
  • 2009-03-26 JP JP2011503937A patent/JP2011516734A/ja active Pending
  • 2009-03-26 CN CN200980121747XA patent/CN102057067A/zh active Pending
  • 2009-03-26 WO PCT/SE2009/050317 patent/WO2009126095A1/en active Application Filing
  • 2009-03-26 CA CA2719536A patent/CA2719536A1/en not_active Abandoned
  • 2009-03-26 MX MX2010010972A patent/MX2010010972A/es unknown
  • 2009-03-26 US US12/936,967 patent/US20110030853A1/en not_active Abandoned
  • 2009-03-26 RU RU2010145401/02A patent/RU2010145401A/ru not_active Application Discontinuation
  • 2009-03-26 AU AU2009234487A patent/AU2009234487A1/en not_active Abandoned

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