Note: Descriptions are shown in the official language in which they were submitted.
CA 02668794 2009-06-12
TUNGSTEN RING COMPOSITION
BACKGROUND
[0001] The present invention generally relates to the field of jewelry
articles and
specifically jewelry articles comprising tungsten.
[0002] There is a need in the jewelry industry for a durable jewelry article
that
comprises mainly of tungsten but is free of tungsten carbide. Furthermore, the
currently
available tungsten carbide articles, such as jewelry rings, typically exhibit
a dark gray
luster. For aesthetic purposes, it is advantageous to be able to offer jewelry
articles
based on tungsten with different color tints.
SUMMARY
[0003] In one embodiment, a method of forming a jewelry article comprises (a)
providing a powder mixture comprising tungsten and one or more of: titanium
carbide,
chromium carbide, nickel, molybdenum, vanadium carbide and iron, (b) placing
the
powder mixture in a mold and (c) applying sufficient pressure and temperature
to the
powder mixture to form a solid jewelry article.
[0004] In another embodiment, a jewelry article comprises less than 50% by
weight tungsten and balance titanium carbide, chromium carbide, nickel,
molybdenum,
vanadium carbide and iron.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Fig. 1 is a flow diagram illustrating the steps in the manufacture of a
jewelry article, in accordance with one embodiment.
[0006] Fig. 2A and 2B are images of jewelry article manufacture equipments, a
powder mixture and raw jewelry articles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0007] In the present embodiments, a method of forming a jewelry article
comprises (a) providing a powder mixture comprising tungsten and one or more
metallic
and/or ceramic component(s), (b) placing the powder mixture in a mold and (c)
applying
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sufficient pressure and temperature to the powder mixture to form a solid
jewelry article.
Thus, the jewelry article formed according to the present embodiments
comprises
tungsten and one or more metallic and/or ceramic components.
Powder Mixture
[0008] In one embodiment, the powder mixture comprises tungsten and one or
more of: titanium carbide (TiC), chromium carbide (Cr3C2), nickel, molybdenum,
vanadium carbide (VC) and iron. In the preferred embodiments, the powder
mixture
comprises tungsten, titanium carbide, chromium carbide, nickel, molybdenum,
vanadium carbide and iron.
[0009] The weight percentage range of each component in the mixture may vary
depending on the desired physical properties and/or aesthetic appearance of
the
jewelry article. In general, the weight percent of tungsten in the mixture is
less than
about 50%. Preferably, the tungsten weight percent is about 20 - 50%, and most
preferably about 40 -50%. The powder mixture may comprise about 15 - 25%,
preferably about 21-22% titanium carbide. The chromium carbide content may be
about
15-25%, preferably about 19-21 %. Additionally, the nickel content may be
about 15-
25%, preferably about 22-23%. Further, molybdenum and vanadium carbide
combined
amount may be about 5-10%, preferably between 7-8%. Finally, the iron content
may
be about 1-5%, preferably about 2-3%. All percent ranges described herein are
by
weight and include every individual value within each range.
[0010] In a non-limiting example, the mixture comprises about 21-22% titanium
carbide, about 20% chromium carbide, about 45% tungsten, about 22-23% nickel,
about
7-8% molybdenum and vanadium carbide combined, and about 2-3% iron.
[0011] In one embodiment, the powder mixture is prepared by milling a particle
mixture of the components for a sufficient period of time to reduce the size
of the
mixture particles. In another embodiment, the powder mixture is prepared by
combining
components that are already in powder form (fine particles). In a further
embodiment, in
addition to milling, the mixture is also subject to one or more steps of
sedimentation/separation, drying and sifting.
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[0012] In a non-limiting example, a mixture comprising tungsten and one or
more
of titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide
and iron
is milled, followed by sedimentation/separation, drying and sifting steps to
form a
powder mixture.
[0013] In another non-limiting example, a mixture of tungsten and one or more
of
titanium carbide, chromium carbide, nickel, molybdenum, vanadium carbide and
iron, is
subjected to (a) milling (b) sedimentation/separation, (c) drying, (d) sifting
and again (e)
drying to form a powder mixture.
[0014] In one embodiment, the powder mixture also comprises at least one
rubber material. In one aspect, the rubber assists in binding the powder
particles_
together. In a further aspect, the rubber assist in processing and shaping the
powder
mixture. Thus, the amount of rubber added may vary depending on the processing
and
shaping requirements. Examples of suitable rubbers include, but are not
limited to,
latex rubbers, butadiene rubbers, styrene butadiene rubbers, thermoplastic
elastomers
and melt processible rubbers. Of course, a combination of different types of
rubbers
may also be used. Preferably, the rubber material comprises styrene-butadiene-
styrne
(SBS). However, other similar polymeric materials such as styrene-isoprene-
styrene
may be equally useful. Where the mixture processing step includes milling, the
rubber
material is preferably added after the milling step.
[0015] In certain cases, the weight percent of tungsten and other components
in
the powder mixture may differ from that in the raw jewelry article. For
instance, addition
of other components, such as SBS rubber, may lower the weight percent of the
powder
mixture components. Still, in some embodiments, the weight percent of the
components in the powder mixture and jewelry article maybe about the same.
[0016] In the powder mixture, the particle size range is preferably small
enough
to allow effective sintering of said powder mixture. If needed, particle size
may be
reduced by running a particle mixture through a sieve, to obtain smaller
particle sizes.
For instance in a non-limiting example, a mixture is run through one or more
sieves with
mish hole diameter(s) less than 0.40mm to obtain a powder mixture with an
average
particle size of about 1-2pm.
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[0017] The density and hardness of the formed article may vary depending on
the
type and amount of the components. In some embodiments, the formed jewelry
article
has a density between about 8-9 g/cm3 and a HRC hardness of about 74.0 or
higher.
[0018] In one embodiment, the powder mixture also comprises components
which impart color to the jewelry article. For instance an amount of a nitride
may be
added to change the color of the article.
Molding/ Melting (Sintering)
[0019] Once formed, the powder mixture is placed in the cavity of a mold and
subjected to elevated pressures to form the raw jewelry article. The mold
cavity may be
shaped according to any basic jewelry article design. In the preferred
embodiments, the
mold cavity produces an annular shaped jewelry article. The formed raw jewelry
article
may comprise one or more facets, grooves, or notches.
[0020] In a non-limiting example, the powder mixture is sintered (or melted)
in the
mold at a temperature of about 1440-1450 C. In yet another non-limiting
example, the
powder mixture is first heated to about 550 C before sintering to remove the
rubber
contents (wax).
[0021] After molding, the raw jewelry article may be then subject to further
processing steps, such as attaching precious metals pieces or gems to the
article.
[0022] The flow diagram of Fig. 1 provides a non-limiting example of
manufacturing steps 100 - 118, for forming a jewelry article in accordance
with one
embodiment. Accordingly, in step 100, a mixture comprising 21.35% TiC, 20%
chromium carbide, 45.87% W, 22.68% Ni, 7.54% Mo+VC and 2.18% Fe, is milled in
ethanol for 72 hours. In step 102, the milled mixture undergoes
sedimentation/separation followed by a drying step 104 at 90-100 C, 1 atm for
2.5
hours. Following a sifting step 106, an amount of SBS rubber is then added to
the
powder mixture in step 108. This mixture is again sifted resulting in a powder
mixture
having particles sizes in the range of about 1-2pm. The first and second
sifting steps
are carried out using a mesh with 0.19 mm and 0.38 mm diameter holes,
respectively.
The powder mixture is then dried in step 112 for about 1-1.5 hours and shaped
in
consecutive molding 114 and melting (sintering) 116 steps. The melting step is
carried
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out in a vacuum furnace by first heating the raw article (to remove the
rubber) at 550 C
for 4-5 hours, then heating at 1440-1450 C for 8-10 hours, followed by cooling
for 10-12
hours. The raw jewelry article is then obtained in step 118 for additional
processing, as
required.
[0023] Figs. 2Aand 2B depict manufacturing equipments connected with the
steps shown in Fig. 1. Specifically, Fig 2A shows a milling machine 202,
sedimentation/separation equipment 204, drying equipment 206 and 212 and
adding/sifting apparatus 208 and 210. Fig 2B shows a molding unit 216, a
vacuum
furnace 218, a powder mixture 214 as well as raw jewelry articles 220. The
density of
the jewelry article formed is about 8.81g/cm3 with an HRC hardness of about
74Ø
[0024] The manufacturing process can have a 100kg/day production capacity for
powder mixture production. Also, the molding process can have the capacity to
handle
2500 pieces/mold in one day. Finally, the production of the raw jewelry
article can be
about 5000pcs/day.
[0025] Although the foregoing refers to particular preferred embodiments, it
will
be understood that the present invention is not so limited. It will occur to
those of
ordinary skill in the art that various modifications may be made to the
disclosed
embodiments and that such modifications are intended to be within the scope of
the
present invention.
