Note: Descriptions are shown in the official language in which they were submitted.
CA 02578656 2007-02-15
METHOD FOR COATING OF JEWELRY INCLUDING RINGS USING HIGH VELOCITY
PARTICULATE COATING SPRAYER
Field of the Invention
This invention relates generally to the field of high velocity spray coating
systems such as HVOF or Detonation Gun coating systems and techniques, and in
particular to
a method for using high velocity spray coating for coating jewelry including
rings and the like.
Background of the Invention
High velocity oxygen fuel (herein alternatively referred to as HVOF) and
detonation gun (herein alternatively referred to as D-Gun, a trademark of
Praxair S.T.
Technologies, Inc. are techniques to deposit thin films of a coating material
onto a substrate,
and can be used to deposit layers having a wear and corrosion resistant
characteristic such as
ceramic coatings applied to lightweight substrate materials. For example, the
HVOF sprayed
coatings may be chromium carbide, tungsten carbide, nickel, cobalt and blends
of other
metallic elements.
The HVOF process in the prior art may be characterized as a blend of fuel
whether gaseous or liquid and oxygen which is brought together to burn in a
gas flow which
expands and accelerates through a nozzle reaching speeds of up to for example
one thousand
five hundred meters per second. Coating material which may be powder (see for
example
United States Patent No. 4,865,252 which issued September 12, 1989 to Rotolico
et al. for a
High Velocity Powder Thermal Spray Gun and Method) or may be a wire fed into
the flame
jet (see for example United States Patent No. 6,924,007 which issued to
Browning on August
2, 2005 for a HVOF Wire Spray System), is fed either axially or radially into
the gas flow,
reaching for example a speed of up to eight hundred meters per second. The
melted coating
material in the gas flow is directed along a supersonic gas beam which is
directed from the
nozzle so as to impact the substrate to form a coating on the substrate.
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In the prior art applicant is also aware of United States Patent No. 3,958,097
which issued May 18, 1976 to Fabel et al. for a Plasma Flame-Spraying Process
Employing
Supersonic Gaseous Streams; United States Patent No. 4,540,121 which issued
September 10,
1985 to Browning for a Highly Concentrated Supersonic Material Flame Spray
Method and
Apparatus; United States Patent No. 4,788,077 which issued November 29, 1988
to Kang for a
Thermal Spray Coating Having Improved Adherence, Low Residual Stress and
Improved
Resistance to Spalling and Methods for Producing Same; United States Patent
No. 4,869,936
which issued September 26, 1989 to Moskowitz et al. for an Apparatus and
Process for
Producing High Density Thermal Spray Coatings; United States Patent No.
4,928,879 which
issued May 29, 1990 to Rotolico for a Wire and Power Thermal Spray Gun; and
United States
Patent No. 5,006,321 which issued April 9, 1991 to Dorfman et al. for a
Thermal Spray
Method for Producing Glass Mold Plungers.
Detonation Gun processes are described in the prior art such as in Praxair
Surface Technologies Publication P-9085A, G-1097 03/05, Praxair S.T.
Technology,' Inc.,
wherein it is described that a carefully measured mixture of gases, usually
oxygen and
acetylene, is fed to the barrel along with a charge of powder (usually with a
particle size less
than 100 microns). A spark is used to ignite the gas and the resulting
detonation wave heats
and accelerates the powder as it moves down the barrel. The gas is travelling
at a supersonic
velocity and the powder is entrained for a sufficient distance for it to be
accelerated to a
supersonic velocity as well, typically about 760 m/sec (2400 ft/see). A pulse
of nitrogen gas is
used to purge the barrel after each detonation. This process is repeated many
times a second.
Each individual detonation results in a deposition of a circle (disk) of
coating a
few microns thick and about one inch in diameter. The coating is made of many
overlapping
disks. Careful, fully automated, disk placement results in a very uniform
coating thickness and
a relatively smooth, planar surface.
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Summarv of the Invention
In summary, the present invention may be characterized in one aspect as a
method of coating an annular object using a high velocity particulate coating
sprayer. The
method includes the steps of:
a) providing a high velocity particulate coating sprayer;
b) providing a selectively rotatable mount having an axis of rotation which
is substantially orthogonal to a plane containing the flow path of the
high velocity spray from the sprayer;
c) mounting an annular object to be coated so as to expose an external
annular surface of an annular body of the annular object, and mounting
the object onto the rotatable mount so as to position the annular body of
the annular object to lie in the plane containing the flow path of the
spray from the sprayer and so that the plane intersects a circumference
of the annular body;
d) rotating the rotatable mount and annular object mounted thereon at a
pre-determined speed of rotation about the axis of rotation; and,
e) spraying a particulate coating from the sprayer along the flow path so as
to coat the external annular surface of the annular object while rotating
on the rotatable mount.
Brief Description of the Drawings
Figure 1 a is a side elevation cross sectional view of a prior art HVOF
sprayer
illustrating a supersonic flow exiting from the apparatus nozzle and carrying
with it particulate
coating so as to impact a substrate to be coated.
Figure lb is a side elevation cross sectional view of a prior art D-GunTM
detonation gun.
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Figure 2 is, in side elevation view, the prior art HVOF spray apparatus of
Figure 1 spray coating a ring according to the method of the present
invention.
Detailed Description of Embodiments of the Invention
As seen in the accompanying Figures wherein similar characters of reference
denote corresponding parts in each view, Figures la and lb illustrate prior
art HVOF sprayer
gun and D-GunTM detonation gun, and Figure 2 illustrates the use of the HVOF
sprayer gun of
Figure 1 in the coating of a ring according to the method of the present
invention. The
illustration of a HVOF gun in Figure 2 and as described below, is intended to
be illustrative of
the use in the present invention of high velocity supersonic muzzle velocity
particulate
sprayers including HVOF and D-Gun processes, wherein the particulate is
heating to melting
or just below melting in the spray exiting the gun barrel.
In Figure 2 HVOF sprayer gun 10 includes a nozzle 12 cooperating with
primary and secondary combustion chambers 14a and 14b respectively. Primary
combustion
chamber 14a is contained within a base housing 16 having a fuel gas supply
port 18, an
oxygen supply port 20, a water removal valve 22a, and a powder injection tube
24. The fuel
gas is taught to be H2, C3H6, etc. The fuel gas and oxygen are mixed within
the primary
combustion chamber 14a and the results of combustion accelerate from the
secondary
combustion chamber 14b through a converging inlet 12a and through duct 12b so
as to exit
from nozzle exit 12c as a supersonic gas flow 26 in direction B. As is
characteristic of
supersonic flows exiting to typical ambient conditions, the pressure recovery
within the
supersonic flow results in shock waves forming a diamond pattern 26a within
the flow
adjacent nozzle exit 12c. Particulate powder coating material is injected in
direction A
through powder injection tube 24 so as to exit the tube at approximately the
nozzle exit 12c so
that the particulate powder coating material 24a is entrained into supersonic
flow 26 and
heated by the flow for deposition as a thin coating, in the prior art onto
substrate 28, and in the
present invention onto ring 30. Nozzle 12 is cooled by water which is injected
through water
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supply port 22b and flows through water jacket 22c along nozzle 12 ipr
removal from water
removal valve 22a. Waterjacket 22c provides for counter-flow cooling of duct
12b.
Ring 30, which advantageously is a piece of jewelry and which may be made of
lightweight material such as titanium, is releasably mounted on a rotatable
support such as
spindle 32. Spindle 32 is mounted on drive axle 34 coaxially along its
longitudinal axis of
rotation C. Drive axle 34 is rotated about axis C in direction D by, for
example, drive
transmission 36. A prime mover such as a motor (not shown) turns drive shaft
38 which
rotates drive axle 34 via transmission 36.
Rotation of spindle 32 on drive axle 34 in direction D simultaneously rotates
ring 30 also in direction D as HVOF gun 10 sprays a coating of for example
chromium
carbide, tungsten carbide, nickel, cobalt or blends of other metallic
elements, and preferably
tungsten carbide so as to coat the exterior surface 30a of ring 30.
Rotating ring 30 at a speed sufficient for uniform coverage results in a
highly
bonded evenly coated deposition of particles 24a nbtwithstanding that ring 30
is not only
curved in a plane containing the ring, that is, orthogonal to axis C, but may
be curved laterally
across its surface, that is, in a plane containing axis C, as opposed to being
a flat substrate such
as known in the prior art. The resulting coating of ring 30 provides for a
hard protective
surface which may also be used to add aesthetic appeal to the ring by various
treatments
including buffing, colorizing and the like.
As will be apparent to those skilled in the art in the light of the foregoing
disclosure, many alterations and modifications are possible in the practice of
this invention
without departing from the spirit or scope thereof.
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