METHOD AND APPARATUS FOR FORMING A HIGH VELOCITY LIQUID ABRASIVE JET

METHODE ET APPAREIL DE PRODUCTION D'UN JET DE LIQUIDE ABRASIF HAUTE VELOCITE

English Abstract

ABSTRACT
A method and apparatus for producing a coherent stream of
high velocity abrasive laden liquid. The method includes allowing
the particles to assume the direction and velocity of a high
velocity jet of liquid. This method also allows concentration of
particles in the center of the flow of liquid to reduce nozzle
wear and increase cutting efficiency. The apparatus includes a
nozzle having a converging section attached to a straight section
that is sufficiently large that the abrasive particles approach
the velocity of the fluid jet before exit of the nozzle.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:

1. A method for producing an abrasive laden jet of
high velocity liquid with a pressure range of about
5000-100,000 psi at the output of a jet producing
apparatus, said method comprising the steps of:
generating a jet of high velocity liquid; and
introducing particles of abrasive into said jet;
and,
orienting said particles velocity vector to that
of said jet; and
accelerating said particles through a nozzle
arrangement having a downstream-most continuous
straight walled cylindrical passageway section which
defines an outlet end serving as said output to a speed
of at least about 80% of that of said jet as the jet
exits the apparatus output and imparting to said
particles a component of movement toward the center of
said jet sufficient to concentrate said particles at
the jet's center as the jet exits said apparatus
output, said straight walled passageway section of said
nozzle arrangement having a length which is between
about 25 and 100 times its diameter so as to impart
said speed to said particles and concentrate them in
the center of the jet.

2. A method as in Claim wherein said concentrating
is accomplished by the step of allowing said jet to
contact a wall to produce a velocity gradient providing
an area of reduced velocity in the area of said wall.




3. A method as in Claim 1 wherein said orienting is
accomplished by the steps of:
introducing said jet with abrasive particles into
a converging section of a nozzle; and
allowing said particles to assume the vector
velocity of said jet in said nozzle.

4. A method as in Claim 1, wherein said acceleration
is accomplished by the steps of:
introducing said oriented abrasive laden steam
into a straight section of a nozzle; and
allowing said particles to accelerate to a speed
approaching that of said jet before exiting said
nozzle.

5. An apparatus for producing a jet of abrasive
liquid at is output, comprising:
jet means for producing a jet of high velocity
fluid and within a pressure range of between about 5000
and 100,000 psi; and,
inlet means for introducing particles of abrasive;
and,
mixing means attached to said jet means and said
inlet means for mixing said jet of high velocity fluid
and said particle of abrasive; and,
orientation means connected to said mixing means
for orienting the velocity vectors of said particles of
abrasive; and
acceleration means including a nozzle arrangement
having a downstream-most continuous straight walled
cylindrical passageway section which defines an outlet
end serving as said output connected to said orienting
means for accelerating said particles of abrasive to a
velocity of at least about 80% of that of said jet of
high velocity fluid as the jet exits said output and
for imparting to said particles a component of movement




toward the center of said jet sufficient to concentrate
said particles at the jet's center as the jet exits
said output, said straight walled passageway section
having a length which is between about 25 and 100 times
its diameter.

6. An apparatus as in Claim 5 wherein the diameter of
said straight section is at least 1.1 times the
diameter of said jet of high velocity fluid.

7. An apparatus as in Claim 6 wherein the diameter
of said straight section is between 1.1 and 10 times
the diameter of said jet of high velocity fluid.

8. An apparatus as in Claim 5 wherein the diameter of
said straight section is at least 1.1 times the
diameter of the largest of said particles.

9. A method as in Claim 1 wherein said generating
step is further comprising the steps of;
producing a body of high pressure fluid; and,
passing said fluid through at least one orifice
less than .05 inches in diameter.

10. An apparatus as in Claim 5 wherein said jet means
includes a jewel orifice for producing a narrow jet of
high velocity fluid.

11. A nozzle as in Claim 5 wherein said straight
section is adapted for contract with a jet of fluid
directed along the center line of said straight
section.

12. A method as in Claim 1 wherein said particle
velocity is 80% of said jet's velocity.

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13. A method as in Claim 1 wherein said stream of
liquid and particles emerge as a coherent jet of small
diameter.

14. A method of producing a particle laden jet of high
velocity liquid within a pressure range of about 5000
to 100,000 psi in which the particles within the jet
are concentrated at its center, said method comprising
the steps of:
(a) providing a nozzle arrangement having a
straight passageway which is defined by an axially
extending interior wall of the arrangement and which
extends from an upstream inlet end to a downstream
outlet end, said passageway including
(i) a first, converging section which
includes said inlet end, and
(ii) a second, continuous straight walled
cylindrical section which extends from said converging
section to and includes said outlet end;
(b) at a specific point coaxial with and upstream
of the inlet end of said passageway, forming a
diverging jet of high velocity liquid having an initial
cross section which is smaller than the cross section
of said straight walled passageway section;
(c) introducing particles into said diverging jet
upstream of the inlet end of said passageway;
(d) directing said particle laden jet coaxially
into said passageway from its inlet end such that the
jet first impinges said interior wall within the
straight walled section of said passageway at a point
downstream from said converging passageway section and
thereafter fills the entire cross section of said
straight walled passageway section so as to form a
boundary layer along said wall which, in turn, forms a
cross sectional flow velocity gradient that is at a
minimum at said wall and progressively increases toward

12


the center of the passageway so as to impart to said
particles within the jet a component of movement toward
the center of the jet; and
(e) selecting the length of the straight walled
section of said passageway so that by the time the jet
exits the passageway at said outlet end, the particles
have a velocity of at least about 80% of the liquid
forming the jet and are concentrated in its center,
said straight walled section of said passageway having
a length which is between about 25 and 100 times its
diameter.

15. A method of producing a particle laden jet of high
velocity liquid within a pressure range of about 5000
and 100,000 psi, comprising the steps of:
(a) providing a nozzle arrangement having a
straight passageway which is defined by an axially
extending interior wall of the arrangement and which
extends from an upstream inlet end to a downstream
outlet end, said passageway including
(i) a first, converging section which
includes said inlet end, and
(ii) a second, continuous straight walled
cylindrical section which extends from said converging
section to and includes said outlet end;
(b) at a specific point coaxial with and upstream
of the inlet end of said passageway, forming a
diverging jet of high velocity liquid having an initial
cross section which is smaller than the cross section
of said straight walled passageway section;
(c) introducing particles into said diverging jet
upstream of the inlet end of said passageway;
(d) directing said particle laden jet coaxially
into said passageway from its inlet end such that the
jet first impinges said interior wall within the
passageway at a point downstream from said converging


13


passageway section and thereafter fills the entire
cross section of the passageway section so as to impart
to said particles a component of movement toward the
center of said jet before exiting said outlet end; and
e) selecting the length of the downstream second
section of said passageway so that by the time the jet
exits the passageway at said outlet end, the particles
within the jet are concentrated in its center, said
second section having length which is between about 25
and 100 times its diameter.

16. A method according to Claim 15 including the step
of selecting the length of the downstream section of
said passageway so that by the time the jet exits the
passageway at said outlet end, the particles have a
velocity of at least 80% of the liquid forming the jet.

17. A method of producing a particle laden jet of high
velocity liquid with a pressure range of about 5000 and
100,000 psi and in which the particles within the jet
are concentrated at its center, said method comprising
the steps of:
(a) providing a nozzle arrangement having a
straight passageway which is defined by a continuous,
axially extending, cylindrical interior wall of the
arrangement and which extends from an upstream inlet
end to a downstream outlet end
(b) at a specific point coaxial with and upstream
of the inlet end of said passageway, forming a
diverging jet of high velocity liquid;
(c) introducing particles into said diverging jet
at a point between the formation of said jet and the
inlet end of said passageway;
(d) directing said particle laden jet coaxially
into said passageway from its inlet end such that the
jet first impinges the interior wall of the passageway

14


at a predetermined point downstream from its inlet end
and thereafter fills the entire cross section of the
passageway as the jet moves through the latter to its
outlet end so as to impart to said particles a
component of movement toward the center of the jet; and
(e) selecting the length of said passageway so
that by the time the jet exits the passageway at said
outlet end, the particles therein have a velocity of at
least 80% of the liquid forming the jet and are
concentrated at its center, the length of said
passageway being between about 25 and 100 times its
diameter.

18. A method according to Claim 17 wherein said jet,
upon impingement with the interior wall of said
passageway and filing its entire cross section, forms a
boundary layer along said wall which, in turn forms a
cross-sectional flow velocity gradient that is at a
minimum at said wall and that progressively increases
toward the center of the passageway so as to impart to
the particles a component of movement toward the center
of the jet.

19. A method according to Claim 17 wherein said
passageway at least includes a straight walled section
and wherein said jet first impinges said interior wall
within said straight walled section.

20. A method according to Claim 19 wherein said
passageway includes a converging section upstream of
said straight walled section.

21. An apparatus for producing at its output end a
particle laden jet of high velocity liquid within a
pressure range of between about 5000 and 100,000 psi
and in which the particles within the jet are




concentrated at its center as the jet exits said output
end, said apparatus comprising:
(a) a nozzle arrangement having a straight
passageway which is defined by an axially extending
interior wall of the arrangement and which extends from
an upstream inlet end to said outlet end downstream
from said inlet end, said passageway including
(i) a first, converging section which
includes said inlet end, and
(ii) a second, continuous straight walled
cylindrical section which extends from said converging
section to and includes said outlet end;
(b) means located at a specific point upstream of
the inlet end of said passageway for forming a
diverging jet of high velocity liquid having an initial
cross section which is smaller than the cross section
of said straight walled passageway section;
(c) means for introducing particles into said
diverging jet upstream of the inlet end of said
passageway;
(d) said jet forming means being positioned such
that said particle laden jet enters coaxially into said
passageway from its inlet end such that the jet first
impinges said interior wall within the straight walled
section of said passageway at a point downstream from
said converging passageway section and thereafter fills
the entire cross section of said straight walled
passageway section so as to form a boundary layer along
said walled passageway section so as to form a boundary
layer along said wall which, in turn, forms a cross
sectional flow velocity gradient that is at a minimum
at said wall and progressively increases toward the
center of the passageway so as to impart to said
particles within the jet a component of movement toward
the center of the jet; and


16


e) the length of the straight walled section of
said passageway being such that, by the time the jet
exits the passageway at said outlet end, the particles
have a velocity of at least about 80% of the liquid
forming the jet and are concentrated in its center,
said length of said straight walled section being
between about 25 and 100 times its diameter.

22. An apparatus for producing a particle laden jet of
high velocity liquid within a pressure range of about
5000 and 100,000 psi and in which the particles within
the jet are concentrated at its center, said apparatus
comprising:
a) a nozzle arrangement having a continuous
straight cylindrical passageway which is defined by an
axially extending interior wall of the arrangement and
which extends from an upstream inlet end to a
downstream outlet end;
(b) means positioned at a specific point coaxial
with and upstream of the inlet end of said passageway
for forming a diverging jet of high velocity liquid;
(c) means for introducing particles into said
diverging jet at a point between the formation of said
jet and the inlet end of said passageway;
(d) said jet forming means being positioned such
that said particle laden jet is directed coaxially into
said passageway from its inlet end so that the jet
first impinges the interior wall of the passageway at a
predetermined point downstream from its inlet end and
thereafter fills the entire cross section of the
passageway as the jet moves through the latter to is
outlet end so as to impart to said particles a
component of movement toward the center of the jet; and
(e) the length of said passageway being such
that, by the time the jet exits the passageway at said
output end, the particles therein have a velocity of at

17


least 80% of the liquid forming the jet and are
concentrated at its center, said length of said
passageway being between about 25 and 100 times its
diameter.

23. An apparatus according to Claim 22 wherein said
passageway at least includes a straight walled section
and wherein said jet first impinges said interior wall
within said straight walled section.

24. An apparatus according to Claim 22 wherein said
passageway includes a converging section upstream of
said straight walled section.

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Description

METHOD AND APPARATUS FOR FORMING A HIGH
VELOCITY LIQUID ABRASIVE JET
FIELD OF THE INVENTION
This invention relates to liquid jets, particularly to
abràsive loaded liquid jets, and more particularly to high
velocity abrasive liquid cutting jet.
DESCRIPTION OF THE FIELD OF ART
It has long been proposed to accelerate abrasive particles
with a jet of high velocity fluid Such jets may be used for
cleaning and surface finishing applications. Dry and wet sand
blatting are examples ox such applications. In all such methods
only the surface of the target material is removed and there is no
deep psnetration. The fluid used in such applications is commonly
air or gas.
It has been proposed that a jet of a liquid could be created
havinq entraped abrasive particles that could be used to cut hard
i materialsO Through proper choice of materials and careful design,
it has been found possible to produce jets of liquid havinq
velocities as high as 3000 ft/sec. Such jet may be used to cut a
wide variety of relatively soft materials. of such a jet could be
charged with abrasive particles, it could jut even very hard
materials such as steel or glass at a rapid rate. Attempts to
produce such a stream have not met with success for several
reasons. First, the high velocity abrasive stream is extremely
erosive and has caused destruction of nozzles a a rate sufficient
to render the process impractical. Second, existing nozzle
designs do not allow the particles of abrasive to reach jet speed,
or a substantial fraction thereof, resulting in far less than
theoretical cutting capacity. Finally, existing nozzles do not
produce a coherent stream of abrasive charged particle resulting
in insufficient cutting power and a large kerf.


"

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~3~L2~i

It has been determined that to produce a useful nozzle for
abrasive liquid jet cutting, it is necessary to ir~t produce a
coherent stream of abrasive loaded liquid, secondly to maximize
the velocity of the particles on the stream, and, finally,
accomplish the first two requirement with minimal nozzle wear.
SUMMARY OF THE INVENTION
The invention provides a method and apparatus for producing
high velocity, abrasive loaded, coherent streams of liquid. The
invention maximizes abrasive particle exit velocity and reduces
nozzle wear to provide a long service life.
The method of the invention first forms a stream of high
velocity liquid. The stream is directed through a chamber where
abrasive particles of low velocity and random direction are added.
Air flow in the chamber directs the particles into the entry of
the mixing tube where they randomly impact the high velocity water
jet. The result is a mixture of high velocity liquid and
particles of abrasive having random direction and velocity. This
mixture then continues into a reorientation zone where the
particles o abrasive are allowed to orient their direction to
that of the liquid. This results in a stream of liquid having
abrasive particles entraped at its core region. This stream is
allowed to continue motion in a nozzle until the particles are
accelerated to a velocity approaching that of 'the liquid.
Finally, the stream of liquid and rapidly moving particles exit
the nozzle
The apparatus of the invention includes a nozzle having zones
of curvature and profile necessary to accomplish the method. The
entry zone i5 a converging conical section that may be produced by
the action of the particles themselves. A change in outline forms
the beginning of the reorientation zone. An accelerator zone


~3~ 5

follows which may be a straight section.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a section elevation view ox a converging -
diverging nozæle.
Figure 2 is a section elevation view of a converging nozzle.
Figure 3 is a schematic section elevation view of a high
velocity water jet jutting system incorporating the invention
Figure 4 i9 a schematic section elevation ViQW of a high
velocity water jet cuttiny system incorporating the invention.
Figure 5 is a section elevation view of a nozzle assembly
incorporating the inventionO
Figure 6 is a block diagram of the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In sand blasting or abrasiye jet machining two types of
nozzles are in general use. Figure 1 illustrates the first type
of nozzle, a eonverging - diverging or venturi type nozzle. This
type ox nozzle hàs been found unsuitable for use in high velocity
abrasive water jet cutting due to extreme nozzle erosion problems.
A second type of nozzle illustrated in~Figure 2 has shown somewhat
more promise. This nozzle called a straight nozzle including a
converging sectlon 1 and a straight section 2 having a length (a)
and a diameter (d3~ The sum of the length of straight section 2
and converging section 1 is the total length (L) of the nozzle.
In present nozzles, the ratio of (a)/(d) is less than 20 and is
much less for those nozzles where it is between 0.060 and 0.125
inches r
Figure 3 shows a typical arrangement of components used in
abrasive water jet cutting. The drawing is broken or clarity. A
high pressure water jet nozzle having an orifice 7 of diameter
~dn) receives high pressure liquid having a pressure (P) from a



3S

source (not shown) of high pressure liquid which may be a
hydraulic intensifier or equivalent. A jet 8 emerges from orifice
7 and enters the convergent section 9 of a nozzle 11. Convergent
section 9 of nozzle 11 is also connected to a source (not shown)
of abrasive particles 10 having a predetermined size (dp~ and a
flow rate (m). The entrance of jet 8 into converting section 9 of
nozzle 11 creates an area of low pressure 12 at the entrance to
nozzle ll. The mate~ial~ used and the geometry of the apparatus
must be adapted to the parameters defined above to produce a
satisfactory nozzle.
Figure 4 illustrate the characteristics of fluid flow in a
high pressure fluid jet nozzle 21. The drawing is broken for
clarity. A jet 22 of high pressure fluid exit from an orifice
23. Typical orifice diameters are from 0.001 to 0.050 of an inch
with operating pressures from 5,000 to lOO,OOOpsi or above. This
is a jet similar to that used in water jet cutting and orifice 23
is typically synthetic sapphire. It will be noted that jet 22 is
slightly divergent when lt issues from orifice 23. Abrasive
particles are introduced into the entry 26 of nozzle 21. The
abrasive particles will typically have a random distribution of
direction and velocity, but it is desirable to minimize the
turbulence and try to direct toward exit point 29. As jet 22
enters nozzle 21 an area of low pressure will be created in the
convergent area o nozzle 21 between points 2~ and 27. The
reduced pressure in this area causes abrasive particles to be
entrained into jet 22. The direction and velocity of the abrasive
particles between points 27 and 28 in nozzle 21 still retains a
random component and if jet 22 were allowed to exit at point 27
the cutting efficiency would be low. Between points 27 and 28 in
nozzle 21 the direction of the abrasive particles is oriented by



jet 22 to assure a predominant axial velocity, to toward point
29 and the randomness of direction it removed. The abrasive
particles are still moving much slower than jet 22, however, as
time is required to transfer momentum from the relatively light
liquid to the denser particles of abrasive. Accordingly, a
section of nozzle 21 from point 28 to point 29 must be provided.
The length of the section between point 28 and 29 must be
sufficient so that the velocity of the particles entrained
approaches that oE jet 22 by polnt 29. I nozzle 21 is lengthened
beyond point 29~ frictional losses will occur resulting in
deceleration of abrasive particle velocity and loss of cutting
power. Prior nozzle designs have attempted to mix and accelerate
the particles with the water in the region between 23 and 26 and
have allowed exit of the jet either before axial orientation has
occured or before the abrasive particles have reached the
approximate velocity of the liquid jet. It will be noted that at
polnt 28 jet 22 contact the wall of nozzle 21. Once contact
occurs, jet 22 will assume the flow characteristics of a fluid
flowing down a tube at high velocity. The fluid will,
accordingly, have a relatively low velocity in that area which is
in contact with the wall of nozzle due to formation of a boundary
layer. Flow velocity will be much higher as it progresses toward
the center of the nozzles diameter. This gradient of velocity
will cause the abrasive particles to concentrate at the center of
jet 22. The formation of a boundary layer of relatively low
velocity and lowered abrasive particle population allows a greatly
extended nozzle life and can allow fabrication of the area of
nozzle 21 between points 2~ and 29 of relatively inexpensive
material. Prior designs have allowed the jet to exit before
concentration of particles in the center of the jet and have



~2~ 3~-~
experienced high wear rates
Due to the complications of mixed phase high veloclty flow in
and outside of walls, it has not yet been found possible to
determine a general equation that allows deslgn of a nozzle that
fits the above requirements. Ranges can be defined however for
the above parameters which will produce satsifactory nozzles.
Fir3t, nozzle 22 must be sufficiently long for the abrasives to
accelerate to at least 80~ of the speed of jet 22 and to have a
direction nearly parallel to the tube wall in order to provide a
coherent and nearly parallel, cohesive, abrasive jet at point 29.
Second, the diameter of the section between points 27 and 29
should be sufficiently small so that the abrasive particles are
forced to remain in contact with the liquid, but large enough to
pass the abrasives and the liquid. Tubes as small as 0.06 inches
have been made to run on 0.03 inch jets and 16 mesh abrasives.
This bore should be straight and the material o the tube should
have a knoop hardness over 1000 to reduce wear. To fulfill the
above requirements, it has been found that the length of nozzle 22
between point 27 and 2g should be between 25 to 100 times its
diameter. The diameter of this section should be at least 1.1
times the diameter of the abrasive particles ( Do l.ldp). Finally,
the diameter of this section should be between 1.1 and 10 times
the diameter of orifice ~3 (lOdj~ do l.ldj). This requires, for
example, a nozzle length between point 27 and 29 of at least 4
inches for an orifice 23 of diameter more than or equal to 35
mils. Similarly, a 2 inch, or larger, tube is needed for a 20 mil
or larger oriice 23. For an orifice diameter of 1 mil, the
length of the nozzle between points 27 and 29 must be at least 0.5
inches. As stated earlier, the section of nozzle l between
points 28 and 29 may be made of the material having a knoop


~;~3~;~3~

hardness over 1000 which includes carbides, ceramics, and similar
materials.
The upper section of nozzle 21 between points 26 and 28
should be thick walled Jo that the abrasive particles can erode
the inlet section between points 26 and 27 into a nozzle inlet
shape.
Fiyure 5 it a section elevation view of a nozzle
incorporating the invention. High pressure liquid enters via a
supply tube 31 from a high pressure intensifier or equivalent (not
shown). Supply tube 31 is attached to the nozzle body 32 by means
of a gland 33 and collar 34, although any other connector
appropriate for the pressure used could be substituted. The high
pressure fluid then flows down the interior of nozzle body 32
which is closed at the end opposite supply tube 31 by a jewel
holder 36. Jewel holder 36 seals to nozzle body 32 and includes a
recess containing a jewel orifice 37. Jewel orifice 37 is
constructed of a hard material such as synthetic sapphire having
an orifice diameter of 0.001 to 0.05 inches and it similar Jo
those jewels used in high pressure water jet cutting. The feed
water emerges from jewel orifice 37 as a high pressure jet 38 into
the interior of the nozzle holder 39. Nozzle holder 39 includes a
threaded attachment point 41 Eor nozzle body 32 and an
introduction port 42 for particles of abrasive. The particles of
abrasive flow down a line tnot shown) attached to port 42 from a
storage tank (not shown). Jet 38 and the abrasive particles then
pass a collar 43 in the interior of nozzle holder 39. Collar 43
prevents erosive wear of nozzle holder 39. The particles of
abrasive and jet 38 then enter a tapered sleeve 44 before entering
a nozzle 46. Nozzle 46 it constructed of carbide, or hard
material, and is 2 to 8 inches long with a 0.03 to 0.150 inner





diameter and 0.363 outer diameter. Nozzle 46 is attached to a
steel adapter 47 by a compression fittlng nut 48 and compression
fitting sleeve 49, adapter 47 is threadably connected to nozzle
holder 39, although equivalent attachment means could be used.
Collar 43, tapered sleeve 44 and the upper portion of nozzle 46
form the mixing chamber of the device. The abrasive loaded stream
50 of liquid finally emerges at the end 51 of nozzle 46 and may be
used for cutting such hard materials a steel or glass.
Figure 6 is a block diagram of the method of the invention.
First a high velocity water jet is generated 61. This Jay be done
much as is presently done in water jet cutting. Abrasive
particles are then introduced with the stream 62 into an orienting
tube. The particles are then orientated ~3 into the direction of
the stream. Time is next allowed for acceleration of the
particles 64 to a sizeable fraction of stream velocity. The
acceleration is accomplished by forcing the stream into an
additional lensth to assume a pipe flow where a boundary layer of
fluid having reduced velocity causes concentration of particles in
the center of the jet. Finally, the jet charged with particles
exits 65 to do work9
Although the present invention has been described with
reference to the particular embodiments thereof, it will be
understood by those skilled in the art that modifications may be
made without departing from the scope of the inventionO
Accordingly, all modifications and equivalents which are properly
within the scope of the appended claims are included in the
present invention.




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