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Method for adding boron to metal alloys

a metal alloy and boron technology, applied in the field of adding boron to metal alloys, can solve the problems of frequent introduction of hard spots into products, needless expense in the processing of ultimately unsatisfactory products, and frequent contamination of 2% boron master alloys with silicon

Inactive Publication Date: 2006-10-19
STERN LEACH CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0014] It is another feature of the invention that more than 20 ppm of boron can be incorporated into a silver-base, or other precious metal, alloy without the development of hard spots.

Problems solved by technology

However, the use of such a master alloy frequently introduces hard spots into the products.
The hard spots are frequently not detected until after the precious metal jewelry alloy is polished and inspected resulting in needless expense for the processing of ultimately unsatisfactory product.
Copper—2% boron master alloys are frequently contaminated with silicon.
The silicon contamination may lead to brittleness, as a result of the formation of brittle intermetallic compounds, oxides and low melting eutectics.
A further disadvantage with the use of a copper—2% boron master alloy is that the high mass percent of copper may not be desired for the alloy product.
Excess copper may cause a silver-base alloy to be subject to tarnish and / or firestain.

Method used

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  • Method for adding boron to metal alloys
  • Method for adding boron to metal alloys
  • Method for adding boron to metal alloys

Examples

Experimental program
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Effect test

example 1

(Prophetic)—Ag—Cu—Ge—Si Alloy

[0061] A silver alloy is made by melting together 93.2 weight percent fine silver casting grains, 1.3 weight percent germanium in the form of small broken pieces, 0.2 weight percent silicon (added as a Cu / Si master alloy containing 10 weight percent silicon) and the balance being copper granules. Melting is by means of a gas-fired furnace heated to a pour temperature of about 2000° F. The melt is covered with graphite to protect against atmospheric oxidation. In addition, a hydrogen gas protective flame is provided. Stirring is by hand using a graphite stirring rod.

[0062] When the alloy constituents liquefy, 20.2 grams (0.65 troy ounce) of sodium borohydride per 46.7 kilogram (1500 oz.) melt are wrapped in a pure silver foil, about 0.15 mm thick. The foil wrapper holds the sodium borohydride to prevent it from floating to the surface of the melt. The wrapped sodium borohydride is placed into a hollow cup-shaped end of a graphite stirring rod and plunge...

example 2

(Working)—Manufacture of Sterling Silver Casting Grain

[0065] Two hundred troy ounces of a sterling silver precursor melt were melted in a clay-graphite crucible. The precursor melt had a nominal composition, by weight, of 93% silver, 5.7% copper and 1.3% germanium. The precursor melt constituents were mixed together and heated under a carbon monoxide flame and covered with a one inch thick layer of borax salt. When the precursor melt temperature reached the flow temperature, 0.0125% boron was added as NaBH4. The boron compound was wrapped in 0.15 mm silver foil for introduction to the master melt. Sufficient power was provided to maintain the temperature of the molten precious metal alloy at the flow temperature. The molten precious metal alloy was then stirred with a graphite stirring rod for 3.7 minutes and poured into a grain box. The molten precious metal alloy was protected by a reducing atmosphere during pouring at the flow temperature. After about 0.25 minutes, the entire mo...

example 3

(Working)—Manufacture of Sterling Silver Grains by Batch Process

[0067] Table 1 illustrates that the process of the invention is effective to add boron to a sterling silver precursor alloy and that the melt cover appears to have more of an effect on the boron content in the precious metal alloy than does the pour gas. In no instance were hard spots detected on the cast grains.

TABLE 1BoronTimeContentBetweenBoronAmountinBoronContentMeltNaBH4PourPrecursorAdditionin CastMeltSizeAddedPourMeltTemp.Alloyand PourGrainsNumber(troyoz)(grams)GasCover(° F.)(ppm)(minutes)(ppm)02812002.78N2 / H2Borax21501253.713.8032215003.33N2 / H2Borax2150204.09.503262003.04COBorax21501374.2523.503272003.04COBorax21501376.56.10338 / 34002.02COBorax215045.55.023.9035315005.05N2 / H2Borax215030.35.2512.20339728.09COBorax215010113.09.0081006 3003.03COBorax2150914.011.4B0120017.77COGraphite20008005.00.6B022008.89COGraphite20004005.00.6B032005.55COGraphite20002505.01.3BS420035.53COGraphite220016006.42.4BS052008.89COGraphi...

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Abstract

A method to grain refine and deoxidize a precious metal alloy or a master alloy includes the steps of (a) forming a precursor melt consisting essentially of constituents of the precious metal alloy or master alloy and inevitable impurities; (b) dispersing a compound selected from the group consisting of boron containing metal hydrides, boron containing metal fluorides and mixtures thereof throughout the precursor melt; and (c) solidifying the boron containing precious melt alloy or master alloy. One suitable compound is solid sodium borohydride (sodium tetrahydroborate). To minimize evaporation of the boron on contact with the precursor alloy melt, the sodium borohydride may be wrapped in a metal foil formed from constituents of the precious metal alloy or master alloy. The cast precious metal alloy or master alloy has been found to have a reduced number of hard spots and reduced silicon contamination when compared to conventional casting methods.

Description

CROSS REFERENCE TO RELATED APPLICATION(S) [0001] This patent application claims priority to U.S. provisional patent application Ser. No. 60 / 672,566 by P. G. Johns and S. A. Davis that was filed on Apr. 19, 2005; United States non-provisional patent application Ser. No. 11 / 132,621 by S. A. Davis, N. D. Baker, J. J. Riskalla and R. V. Carrano that was filed on May 19, 2005; and U.S. provisional patent application Ser. No. 60 / 732,784 by P. G. Johns and S. A. Davis that was filed on Nov. 2, 2005. The subject matters of all three U.S. patent application Ser. Nos. 60 / 672,566; 11 / 132,621 and 60 / 732,784 are incorporated by reference herein in their entireties.U.S. GOVERNMENT RIGHTS [0002] Not Applicable. BACKGROUND OF THE INVENTION [0003] 1. Field of the Invention [0004] This invention relates to a process to manufacture boron containing precious metal alloys and master alloys. More particularly a solid compound that is either a boron containing metal hydride, and preferably a solid tetrahy...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C9/04C22C5/08C22C5/02B22D17/00
CPCC22B9/103C22B9/106C22B11/02C22C9/00C22C5/02C22C5/08C22C1/06
Inventor DAVIS, SAMUEL A.JOHNS, PETER G.BAKER, NEIL D.RISKALLA, JOHN J.CARRANO, RICHARD V.
Owner STERN LEACH CO
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