Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2001-09-10
2003-05-13
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S538000, C148S430000, C148S405000
Reexamination Certificate
active
06562158
ABSTRACT:
TECHNICAL FIELD
The present invention relates to platinum-gallium-palladium alloys which are heat-treatable to high strength and hardness for use in jewelry, art objects and related articles.
BACKGROUND ART
It is known in the jewelry-making art that the hardness and strength of alloys can be increased by cold deformation. That is, it is known how to work gold and platinum alloys by various forging processes to harden and increase yield strength to create stronger components, and for the use of exerting spring pressure. Increased strength is necessary for many types of durable structural parts such as lighter chains, pin stems, and thinner stampings. Spring pressure can be applied to form spring components for clasps, closures, wires, and springs. Even rings, pendants, bracelets, can mount center gemstones by compression spring power. The necessary pressure, in the latter examples, is supplied by the springiness inherent in the structure of the worked precious metal mounting itself.
It is also known to those interested in the metallurgy of precious metals that many gold alloys and certain platinum alloys can be hardened by heat-treatments to increase their hardness and yield strengths, sometimes even more than is possible through cold working. In this regard, U.S. Pat. No. 5,084,108 discloses a heat-treatment process for increasing the strength of certain alloys specifically for use as compression-spring gemstone mountings.
Platinum is a precious metal and is relatively expensive. Platinum for fine jewelry is sold in high concentrations of over 90% and, by law, must be hallmarked accordingly. Platinum alloys are desirable for their neutral color when combined with gems, they are hypo-allergenic, they have high tensile strength, and a pleasurable heft due to its high-density. In America, platinum alloys for jewelry manufacturing traditionally have concentrations of over 90 percent platinum and contain small amounts of iridium or ruthenium. There has been a recent introduction of platinum-cobalt alloys for casting alloys that are somewhat harder than the traditional iridium or ruthenium platinum alloys. Although work-hardenable, they are permanently softened by heat when soldering or using other metalworking techniques in jewelry manufacturing. Platinum-cobalt alloys do not respond to heat-treatments.
U.S. Pat. No. 5,084,108 discloses certain heat treatable alloys of platinum containing 5 to 25% copper, 5 to 50% gold, 10 to 40% indium, 10 to 70% iron or 7 to 35% silver. None of these alloys contain gallium or palladium, nor is there any specific disclosure of hardness for these platinum alloys. Instead, that patent is primarily concerned with the strengthening of certain alloys to provide compression spring mountings for gemstones.
Various gallium containing platinum alloys are known in the field of metallurgy. These alloys include 89-98.9% Pt, 1.1-11% Ga; 85-95% Pt, 2-4% Ga, 3-12% Cu; 95% Pt, 2-2.5% Ga, 2.5-3% Au; and 95% Pt, 2-3% Ga, 1-3% Au, 0-2.5 In. To the present inventor's knowledge, however, none of these alloys have been heat-treated to increase strength and hardness for use as jewelry components.
U.S. Pat. No. 4,165,983 discloses a number of different alloying elements including palladium that can be used with platinum-gallium alloys, but is silent as to whether any heat treatments should be conducted on these alloys, despite a recognition that for many platinum jewelry applications, much harder metals (i.e., harder than 200 Vickers) are needed for use in the manufacture of springs and clasps. The solution to the problem of low hardness taught in this patent relates to a modification of the type and amount of alloying elements. Again, heat treatments are not used to increase hardness.
There are known heat-treatable platinum alloys such as 90% platinum-10% gold, but these alloys have undesirable characteristics for jewelry work. A 90% Pt, 10% Au alloy tends to crack, is extremely difficult to draw into wire or roll, and does not cast well by known jewelry-making techniques. Platinum (90%+)/copper, used in Europe, does not significantly respond to heat-treatments, and only can be strengthened by a few percent.
Due to the potential improvements in properties and performance of such heat-treated alloys, there is a need for additional alloys that are heat-treatable for use in jewelry and art applications. The present invention provides one alloy family for this purpose.
SUMMARY OF THE INVENTION
The present invention relates to a method for making jewelry, which comprises formulating a platinum alloy of at least about 95 weight percent platinum, about 1 to 5 weight percent gallium and an additional alloying element of palladium in an amount effective as a property enhancing agent but in a total amount of less than about 3 weight percent. This alloy is heat-treated to increase its initial Vickers hardness by at least about 20% but to not greater than a Vickers hardness of 350. Preferably, the alloy has an initial hardness of about 150 to 200 and this is increased to about 250 to 325 after heat treatment. More preferably, the initial hardness is at least about 160 and is increased to at least about 275. The heat-treated alloy has particular properties that render it useful as in general purpose jewelry applications.
In this method, the two stage heat-treating operation may include solution-treating the alloy at a temperature of at least about 1700 F., quenching the solution-treated alloy to a temperature of below about 200 F., and then, hardening the quenched alloy at at least 900 F. for a sufficient time to achieve the desired hardness. Preferably, the solution-treating temperature is at least 1800 F., the alloy is held at that temperature for at least 10 minutes, and the solution-treating step is conducted in an inert, non-oxidizing or anti-oxidizing environment. The solution-treated alloy is then quenched in water that is at room temperature or colder. Also, the hardening treatment is preferably conducted by heating the alloy in an inert, non-oxidizing or anti-oxidizing gas atmosphere for at least 30 minutes at 1100 to 1200 F. The hardened alloy is then cooled to room temperature.
The alloy may be formed into a desired shape prior to the two-stage heat-treating operation. Such operations are many and include casting or fabricating. Some examples of fabrication can be by rolling of the alloy into a sheet, drawing a wire, molding, casting, forging, stamping or constructing the object or shape useful as a jewelry component. It is also useful to process the hardened alloy to remove or prevent surface oxidation. One method to remove surface oxidation is by abrasion, although as previously mentioned, the alloy may be shielded during the heat-treating operations to prevent surface oxidation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention of this particular high-concentration platinum alloy hardened significantly by heat-treatment is extremely appropriate for the manufacturing of jewelry, allowing for many advantages to the jewelry manufacturer over presently utilized alloys, such as:
1) Thinner, lighter constructions and castings, possessing significantly lowered weight and costs.
2) Springier clasps and mechanisms, not previously possible to construct.
3) Strengthening of delicate fabrications such as prong setting after construction.
4) Higher polish, much easier to achieve, due to increased hardness.
5) Lower casting temperatures than previously known.
6) Lower costs with alloy additions other than traditional iridium or ruthenium.
7) Expanded jewelry design possibilities.
The invention is preferably directed to platinum-gallium-palladium alloys that can be cast to a desired form or worked by traditional fabrication methods in an annealed state, then heat-treated and age-hardened to significantly increase their yield strengths so that they become hardened and spring-like. The alloys can be used for a wide variety of jewelry components, such as rings, clasps, spring parts, even compression-spring settings for gemstones, and the like. These alloys can be repeate
Sheehan John
Winston & Strawn
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