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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to high-velocity liquid jet cutting and, in
particular, an improved nozzle and mounting assembly.
2. Prior Art
The use of fluid jets for cutting has been the subject of continuous
experimentation and refinement. Fluid jets for cutting, drilling and the
like are well known and utilized for hydraulic mining and other rough cut
operations. Patents such as Chaney, U.S. Pat. No. 3,554,602, and Goodwin,
et al., U.S. Pat. No. 3,419,220, are typical of a host of prior art which
recognizes the use of fluid cutting as a basic technique. More recently,
with the advent of computer technology, fluid jet cutting has reached a
refined state where, by the use of collimated jet streams, cutting with a
narrower kerf is possible providing a better finish along cut surfaces.
Accordingly, fluid jet cutting has found application in such commercial
areas as high-quality mass production cutting of shoe inner liners and
soles, dress patterns and the like. A typical system is found in U.S. Pat.
No. 3,978,748 wherein a composite fluid jet computerized cutting system is
shown. In such systems, the movement of the jet is controlled by computer
such that cutting paths across the cutting table are maximized for
production output.
One area of continuing research in fluid jet cutting is the problem of
dispersion of the jet, both as it leaves the nozzle and also as it passes
through materials to be cut. Accordingly, the prior art is replete with a
number of concepts for avoiding dispersion to thereby reduce the wetting
of the material being cut and provide a better finish along the surfaces
so cut by the high-pressure nozzle.
One prior art attempt is shown in Franz, U.S. Pat. No. 3,750,961. In that
patent, a high-velocity fluid jet nozzle is shown utilizing a heavy walled
vitreous body having a jet orifice of substantially greater length than
the cross-section diameter of the orifice itself. The orifice is defined
by a smooth surface which blends into an entry chamber defined by the
vitreous body. This system attempts to reduce the problem of dispersion by
careful contouring and the reduction of upstream hydrodynamic turbulence.
Another approach is shown in Chadwick, et al., U.S. Pat. No. 3,756,106,
where a corundum crystal having an orifice of specific geometry is capable
of producing a well-defined fluid cutting jet. While all of these prior
art nozzles are directed toward the achievement of a better shaped jet by
providing carefully contoured surfaces of particular geometric
relationships, one problem which remains is that of leakage around the
nozzle elements themselves.
A recent attempt at providing a collimated jet stream which reduces kerf
widths, thereby improving the finish of the cut surfaces, is shown in
Thomas, et al., U.S. Pat. No. 3,997,111. In Thomas, et al., collimation of
the jet occurs by having a housing interconnected between the source of
fluid under pressure and the nozzle. The housing defines a flow
collimating chamber located directly upstream of the nozzle to receive the
liquid from the high-pressure generating equipment and deliver the liquid
directly to the chamber for expulsion. This flow chamber which provides
the collimation function is of a specific ratio to the discharge opening
of the nozzle. Thomas, et al. specifies the minimum ratio of the
cross-sectional area of the flow chamber to be one hundred times that of
the discharge opening of the nozzle, and preferably greater than two
hundred times that of the nozzle. An outside range is approximately 1400
times as set forth in the specification of that patent. While collimation
occurs producing very narrow diameter jets, in actual practice, the system
defined in U.S. Pat. No. 3,997,111 has been susceptible to various
mechanical breakdown phenomena. In order to improve the problems of nozzle
handling and leakage about the nozzle, Thomas, et al. utilizes a washer or
mounting ring about the sapphire nozzle such that a deformation takes
place when the system is under pressure. The sapphire nozzle in Thomas, et
al, is mounted in an elastically deformable washer or mounting ring. This
ring is to provide a seal between the nozzle element and the nozzle
housing and to exert uniform pressure radially to the sides of the nozzle
element. This elastic ring, accordingly, is designed to prevent cracking
of the sapphire nozzle element or damage to it, and to reduce the
tolerance requirements between the lateral surface of the counterbore and
the lateral surface of the nozzle element, and to provide an adequate seal
between the nozzle element and the bottom wall of the nozzle housing
against which the nozzle element rests.
SUMMARY OF THE INVENTION
This invention is an improvement to the above-referenced prior art systems
for mounting fluid jet nozzles. It is usable in conventional fluid jet
cutting systems of the type disclosed in U.S. Pat. No. 3,978,748 wherein a
source of high-pressure fluid, such as an intensifier, is used, and the
nozzle is mounted on a movable carriage. Various high-pressure linkages
are utilized to convey fluid under pressure from the intensifier to the
nozzle for subsequent discharge as a high-velocity, extremely small
diameter jet.
The present invention eliminates the need for the elastic washer
surrounding the sapphire or jewel element nozzle. Specifically, this
invention is premised on the recognition that a mounting ring, such as
shown in Thomas, et al., is not needed and that the nozzle housing will
provide an acceptable seal without sub-surface leaks to produce an
acceptable liquid jet. The applicant has found that, in fact, a seal can
be formed between the surface of the nozzle element and the surface of the
recess in the nozzle mount against which it rests. By use of appropriate
mounting techniques, the nozzle element can be housed in a member which
extends about the nozzle element and downstream of it. Accordingly, upon
the applicaton of high-pressure fluid upstream of the surface of the
nozzle, for example, in the range of 60,000 psi, the force applied to the
upstream side of the nozzle element by this source of high-pressure liquid
is balanced by an equal and opposite force applied at the downstream side
of the nozzle by the housing. Since the surfaces of the nozzle element and
the nozzle housing are flat and are pressed together by the high-pressure
liquid, a seal is formed. The existence of any leak between the jewel
nozzle and its mount will degrade the energy distribution of the jet.
Accordingly, the elimination of such leaks--that is, sub-surface leaks--is
crucial in maintaining acceptable performance. By appropriate choice of
material, the seal is enhanced to form a coined mating surface.
Alternatively, the seal can be formed if the bearing surfaces are made
sufficiently flat by precision machining. Accordingly, the nozzle need not
be surrounded in an elastic collar.
Additionally, prior art nozzles have been found to be unsatisfactory in
actual commercial operation. This is because an elastic material changes
shape under pressure, and when relaxed, assuming its original shape may
physically move the nozzle. Accordingly, the nozzle element tends to be
displaced from its desired position--that is, in intimate contact with the
nozzle housing--thereby creating a number of undesirable effects. For
example, a leak under the nozzle element may occur, extrusion of the
washer material itself under the nozzle element may occur, or a
catastrophic upset of the entire nozzle element may result, resulting in a
loss of the fluid jet stream with resulting damage to the nozzle housing
and the possible fracturing of the nozzle element itself. These serious
problems are amplified in the realm of rapid duty cycling of the system
when on-off times are a few milliseconds, typically in the range of 30-50
milliseconds. Accordingly, the use of an elastic mounting washer has found
practical utility only in the handling of the nozzle elements in their
housing assemblies or in stable operating conditions without rapid
cycling.
This handling function is important because the nozzle element must be of a
substantial hardness to minimize erosion or wear due to liquid flow.
Generally, materials such as sapphire have been used, and the outside
diameter of this jewel element is generally only about 5-10 times that of
the orifice diameter. Accordingly, nozzle elements tend to be in the range
of approximately 0.05-0.15 inches and are not readily handled.
Accordingly, it is an object of this invention to provide a fluid jet
cutting system nozzle mount having improved characteristics in high
cycling rate environments with predictable jet stream characteristics.
It is another object of this invention to provide for a firm mounting of
the nozzle to facilitate handling of the nozzle elements.
Yet another object of this invention is to provide for a high-pressure
liquid cutting jet nozzle mount that eliminates sub-surface leaks.
A further object of this invention is to provide parameters for different
fluid jet characteristics to produce different fluid jet streams.
These and other objects of this invention will be described with relation
to the drawings and the preferred embodiments thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a prior art nozzle housing assembly as shown in
U.S. Pat. No. 3,997,111.
FIG. 2 is a perspective side view of the nozzle housing assembly made in
accordance with this invention.
FIG. 3 is a side view of a second preferred embodiment of the nozzle
housing assembly of the present invention.
FIG. 4 is yet another preferred embodiment of the nozzle housing assembly
of this invention.
FIG. 5 is a fourth preferred embodiment of a nozzle housing assembly made
in accordance with the teachings of this invention.
FIGS. 6A-8B show alternate embodiments of different nozzle configurations
and related energy density plots as a function of stream cross-sections.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, this invention is a direct development of the
prior art taught in Thomas, et al. FIG. 1 is a simplified side view of the
nozzle housing assembly shown in FIG. 3 of U.S. Pat. No. 3,997,111.
Accordingly, the teachings of Thomas, et al. show a nozzle housing 10
holding a mounting ring 12 and a nozzle element 14. High-pressure fluid
enters the system in the direction shown by the arrow in FIG. 1 and is
collimated upstream of the arrow to form a high-pressure jet. Nozzle 14
has an opening 16 to receive the high-pressure fluid. The nozzle is
conventionally fashioned from sapphire and is held in place by a mounting
ring 12 formed of an elastically deformable material. This mounting ring
is set in the nozzle housing 10 to define seal areas between the
corresponding elements Accordingly, a first seal area 18 is defined
annularly between the elastic ring and the nozzle 14. A second concentric
seal area 20 is defined between the mounting ring 12 and nozzle housing
10, and a third transversely extending seal area 22 is defined
perpendicular to the nozzle opening 16. An exit port 24 is utilized to
discharge the thusly formed high-pressure stream.
As previously indicated, the nozzle mount shown in the prior art FIG. 1 has
shown a propensity to leak under the nozzle area--that is, in the area of
seal 22. Additionally, the deformable mounting ring 12 has tended to,
under pressure, extrude into the seal area 20 thereby reducing the area of
seal between the nozzle element 14 shown as seal 18. Moreover, deformation
of elastic material has caused displacement of the nozzle element 14
relative to the discharge opening 24.
Turning now to FIG. 2, a first preferred embodiment of this invention is
shown which eliminates the deformable mounting ring 12. As shown in FIG.
2, the nozzle housing 26 is secured in a support 28. The support has a
threaded portion 30 for threading of the support and allied internal
structure into an upstream pipe not shown. The housing 26 can be fashioned
of a steel material, such as 300 series CRES. A first high-pressure seal
is formed between the nozzle housing and the threaded support element 26
along surface 32. This seal is applied by the use of a mounting nut, not
shown, which is threaded onto an upstream pipe 34 which contains the
nozzle housing. The nozzle element itself, 36, fashioned typically from
sapphire, is a disc of approximately 0.090 inches. It may typically range
from 0.050-0.150 inches and has an internal bore constituting a jet
shaping port 38. The diameter of that shaping port is in the range of
approximately 0.003-0.015 inches.
A nozzle mount 40 is used to position and seat the nozzle 36 in the housing
26. The nozzle mount is formed from a material which, although relatively
hard, tends to yield slightly under the influence of high pressure.
Accordingly, with the application of fluid pressure in the range of 60,000
psi, the nozzle 36 tends to be impressed upon the mount 40 creating a seal
about the surface 42.
Because the nozzle mount 40 is set in the housing 26 and this element is of
a harder material than the mount 40, a support is formed for the mount by
the harder material which will withstand the sliding contact forces
applied during installation. A suitable material for the mount is one
which has a yield strength in proportion to the working pressure of the
fluid. Such an element allows firm placement of the nozzle element in the
mount, yet provides for a good sealing surface. In view of the relatively
small size of the nozzle element, the increased size of the mount provides
an adequate technique for handling of those elements when not in the mount
itself. Additionally, because the nozzle mount has a section 44 disposed
immediately downstream of the nozzle element 36, a sealing surface of
compatible yielding material is provided along surface 42 backed up by
nozzle housing 26 without the problems of deformation and elastic recovery
in the prior art. This section eliminates the problem of the washer
extruding into the seal area. Also, the use of the harder steel material
in the nozzle mount 26 provides a third sealing area 44 between the
housing mount 26 and the nozzle housing 40. A small radial clearance shown
as surface 39 in FIG. 2, typically of the order of 0.001-0.003 inch, is
provided between the nozzle element 36 and the nozzle mount 40 to prevent
cracking or other structural damage to the nozzle element due to radial
yielding deformation of the nozzle mount when subjected to the
high-pressure fluid.
In operation, high-pressure fluid in the realm of 40,000-60,000 psi is fed
to the nozzle element via upstream pipe 34. The nozzle element 36, having
a flat surface to contact its housing, is forced down by liquid pressure
providing an adequate high-pressure seal such that no liquid will flow
around the nozzle element. In this example, a material such as
free-machining brass, having a yield strength of about 50,000 psi, can be
used for the housing 40. This minimizing of leakage reduces wetting of the
material being cut. Additionally, because the housing not only surrounds
at surface 39 but additionally provides a yielding bearing surface 42,
firm placement of the nozzle element against lateral shifting or
displacement is facilitated.
The nozzle element 36 in intimate contact with the nozzle mount 40 prevents
leaks which would tend to form in the prior art, for example, between the
nozzle element 14 and the housing 10 along the common surface wall 22 as
shown in FIG. 1. In this invention, the elimination of contact between the
nozzle and the nozzle housing improves control of the liquid jet by
eliminating all leaks along that surface. Hence, as shown in FIG. 2, the
surface 46 between the nozzle mount and its housing 26 does not in any way
involve contact of the nozzle element 36. Additionally, repeated and rapid
duty cycling by means of an upstream valve resulting in the cycling of
high-pressure liquid through the orifice 38 will not dislodge the nozzle
element 36 as is a tendency in prior art designs.
Referring now to FIG. 3, another preferred embodiment is shown wherein the
same basic concept--namely, of having the nozzle element bear against a
mount for it as opposed to direct contact with the nozzle housing--is
shown. In FIG. 3, as in other designs, a support 28 is screwed into a pipe
section 50 by means of thread elements 30. The nozzle element 36 has an
axial bore 38 aligned with a complementary bore 52 in the mounting plate
40. This alignment is self-centering during operation. A high-pressure
seal is formed along surface 32 between the support 28 and the pipe 50.
High-pressure cutting fluid in source 34 tends to press the nozzle element
36 into contact along surface 42 with the mounting plate 40. A small
amount of grease on surface 42 will hold element 36 in position during
assembly. Accordingly, a high-pressure seal is formed between the nozzle
element 36 and the support 40 during cutting.
As in the prior examples, the nozzle support plate 40 shown in FIG. 3 is
fashioned from a material which will withstand sliding forces applied to
it, but will yield slightly under the influence of the fluid pressure.
FIG. 4 shows a variation of the FIG. 2 embodiment wherein the nozzle
element 36 is disposed in the housing 40 in the same manner as shown in
FIG. 2. Additionally, however, a mounting plate 54 is utilized and
interposed between the nozzle housing and the housing mount 28. This plate
54 extends the full circumferential width of the chamber 34 to provide, in
a manner shown in FIG. 3, adequate seating for the nozzle housing against
the support 28. As in prior examples, the nozzle element 36 has a surface
42 bearing against its mount 40 to provide sealing contact, thereby
preventing leakage.
Referring now to FIG. 5, yet another preferred embodiment is shown. In this
embodiment, the support pipe element 50 is threaded by internally
extending threads 56 to couple the support housing 26 directly to the
pipe. The threads 56 extend to the upper surface where the housing joins
in forming a common surface with the nozzle element mount 40. A
high-pressure seal 32 is formed between the pipe 50 and the support
housing 26 in a manner described hereinabove. The nozzle element 36 has a
portion raised above the surface 56 defined by the top walls of the
support housing 26 and the nozzle mount 40. In this embodiment, the use of
a lower support plate 28 is eliminated and the nozzle housing extends
contiguous to the outer pipe 50 and is threaded into it by threads 56. As
in the prior embodiments, the nozzle element itself, 36 having orifice 38,
is disposed in a pressure transfer relationship with the mount 40.
Referring now to FIG. 6A, there is shown a first preferred fluid jet
nozzle configuration, and in FIG. 6B a plot of energy density for the
nozzle of FIG. 6A as a function of cross-section. The nozzle 36 has an
orifice 38 with a bevel section either radiused or conical in shape. The
angle of the taper is generally in the range of 10-20.degree.. The nozzle,
typically fashioned from sapphire, has a height T in the range of
0.030-0.040 inches and the radius of the taper 60 is approximately 0.5 T
to a depth of 0.005 inches. The ratio of length/diameter (L/D) for the
orifice 38 is in the range of 1.5-2.5.
As shown in FIG. 6B, the energy density (ED) is plotted as a function of
cross-section of the nozzle. The nozzle of FIG. 6a will produce a
well-collimated beam having a dispersion rate of 1.0-1.2 diameters at 100
diameters nozzle length. At a working pressure of 40,000-60,000 psi, an
optimum cutting speed is about 13 inches per second. Because the beam is
well shaped, it is suited for low-ply fabrics, homogeneous solids and hard
materials.
FIG. 7A shows a second preferred embodiment of the nozzle element 36. The
nozzle of this configuration will produce a more dispersed beam having
areas of spray as shown in the shaded portions of the energy density plot
shown in FIG. 7B. Such a nozzle will be usable for fibrous goods,
loose-woven materials and low-density laminates. The jet produced has a
high energy density during the center portion of the beam with residual
areas at the outside of the jet to sever threads or fibers that are not
rigidly held in place by the interior properties of the material.
Such a jet can be accomplished by using the taper configuration of FIG. 6a
with an L/D ratio reduced to 0.7-1.0. The taper 60 is primarily for
purposes of reducing nozzle wear at the upstream section but plays a role
in jet shaping. Accordingly, the depth of the taper T.sub.1 can be
increased from 0.005 to approximately 0.010-0.015. In such a
configuration, the L/D ratio is in the range of 1.5-1.8. A nozzle fasioned
in accordance with the above-referenced parameters will also produce the
beam having the energy density shown in FIG. 7B.
FIG. 8A shows a third nozzle configuration having a broad energy density
configuration shown in FIG. 8B. As in the case of FIG. 7B, the area of
spray is shown as the shaded portion of FIG. 8B. Such a jet is suitable
for very loose-weave materials, multiple ply cutting and elements that
tend to move on the cutting table. Although a large degree of dispersion
occurs, so long as the jet strength is greater than four times the tensile
strength of the material to be cut, adequate cutting will take place. The
depth of the taper T.sub.1 is approximately 0.015 inches and the L/D ratio
is in the range of 0.2-1.5.
As shown in FIG. 8A, the depth of taper is deep relative to the orifice 38.
A wide beam of relatively uniform energy density in the cutting region is
produced. Since cutting occurs at the edge of the stream as it moves
across the material, the jet produced by the nozzle of FIG. 8b will having
a relatively longer duration of cutting time per cut to insure complete
severing of the goods.
It is readily apparent that other configurations and embodiments are
present without departing from the essential aspects of this invention. So
long as the nozzle element bears directly against a mounting element to
provide sealing contact under pressure between those elements, a
well-collimated beam will result without the attendant problems of leakage
around the nozzle.
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