U.S. patent application number 11/399565 was filed with the patent office on 2006-10-05 for high pressure abrasive-liquid jet.
This patent application is currently assigned to United Materials International, LLC. Invention is credited to Benjamin F. Dorfman, Steven A. Rohring.
Application Number | 20060223423 11/399565 |
Document ID | / |
Family ID | 37071180 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060223423 |
Kind Code |
A1 |
Dorfman; Benjamin F. ; et
al. |
October 5, 2006 |
High pressure abrasive-liquid jet
Abstract
An abrasive-liquid jet cutting head comprising at least one
mixing stage; a first mixing chamber arranged to accept a coherent
high pressure liquid from an orifice and flow of accelerated
abrasive particles from an abrasive feed tube and produce a
pressurized slurry-like flow that enters a nozzle; wherein a nozzle
to orifice ratio is in a range of about 1.2:1 to 2.49:1 wherein
nozzle opening size to orifice opening size is 1.2 to 2.49 times
larger in size.
Inventors: |
Dorfman; Benjamin F.; (San
Francisco, CA) ; Rohring; Steven A.; (Buffalo,
NY) |
Correspondence
Address: |
Vincent G. Lotempio
PO Box 820
East Amhert
NY
14051
US
|
Assignee: |
United Materials International,
LLC
|
Family ID: |
37071180 |
Appl. No.: |
11/399565 |
Filed: |
April 5, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60668453 |
Apr 5, 2005 |
|
|
|
Current U.S.
Class: |
451/38 ;
451/102 |
Current CPC
Class: |
B24C 7/0076 20130101;
B24C 1/045 20130101; B24C 5/04 20130101 |
Class at
Publication: |
451/038 ;
451/102 |
International
Class: |
B24C 1/00 20060101
B24C001/00; B24C 5/04 20060101 B24C005/04; B24B 1/00 20060101
B24B001/00 |
Claims
1. A abrasive-liquid jet cutting head comprising: an orifice
aligned to a nozzle; at least one mixing stage; a first mixing
chamber arranged to accept a coherent high pressure liquid from
said orifice and flow of accelerated abrasive particles from an
abrasive feed tube and deliver said liquid and said abrasive into
an inlet of said nozzle; an abrasive liquid jet produced by said
nozzle wherein a nozzle to orifice ratio is established in a range
of 1.2:1 to 2.49:1 wherein nozzle opening size to orifice opening
size is 1.2 to 2.49 times larger in size.
2. An abrasive-liquid jet cutting head according to claim 1 with
liquid operating parameters at 0.1 gpm to 10 gpm at high pressures
of 10,000 psi to 150,000 psi, and abrasive feed rates of 0.05
lb/min to 5 lb/min.
3. An abrasive-liquid jet cutting head according to claim 1 wherein
said abrasive particles have a specific gravity of 4.0 and
higher.
4. An abrasive-liquid jet cutting head according to claim 3 to
wherein said abrasive particles metallic elements taken from a
group consisting of metals, alloys, steel, metal oxides, and
metallic carbides.
5. An abrasive-liquid jet cutting head according to claim 1 using
an orifice with a coefficient of discharge between 85% to
99.99%.
6. An abrasive-liquid jet cutting head according to claim 1 using
an orifice with a coefficient of discharge between 60% to 85%.
7. An abrasive-liquid jet cutting head according to claim 1 having
a solid body for said cutting head is manufactured using injection
molding and sintering techniques.
8. An abrasive-liquid jet cutting head according to claim 7 where
the materials used for injection molding are hard ceramic
materials, including oxides and nitrides, or hard carbide
materials.
9. A method for producing a high velocity abrasive liquid jet
utilizing a cutting head with an orifice aligned to a nozzle with a
defined nozzle to orifice ratio of 1.2:1 to 2.49:1, being that the
nozzle is 1.2 to 2.49 times larger in size than the orifice.
Description
[0001] This application claims priority of United States
Provisional Patent Application to Benjamin F. Dorfinan and Steven
A. Rohring, Ser. No. 60/668,453 for METHODS FOR IMPROVING ABRASIVE
JET TECHNOLOGY AND APPARATUS FOR THE SAME, filed on Apr. 5,
2005.
FIELD OF INVENTION
[0002] The invention relates to the field of high-pressure
abrasive-liquid jet (also sometimes known as `Abrasive Waterjet` or
`Abrasivejet`) technology often used in material removal, and more
specifically, improvements upon conventional abrasive-liquid jet
technology in the area of cutting head assemblies considering the
important relationship between cutting head components of Orifices
and Nozzles (also known as Focusing Tubes or Mixing Tubes).
BACKGROUND OF THE INVENTION
[0003] Conventional abrasivejet technology is used to cut a variety
of materials but is found to be highly inefficient in the use of
energy and resources mainly due to cutting head design limitations
that incorporate a 3:1 nozzle to orifice ratio. Conventional
abrasivejet is also currently limited to perform one purpose at a
time such as thru cutting of material or surface removal of
material as there are not any abrasivejet systems currently
producing useful byproducts simultaneously with the initial purpose
of material removal. This is primarily due to the widespread
acceptance of garnet as the preferred abrasive for almost all
conventional applications.
[0004] A high-pressure pump is utilized to generate fluid pressure,
usually above 30,000 psi, and preferably with water or water with
additives as the liquid medium. The pressurized liquid is then
transported at high velocities through tubing to a cutting head
that mainly consists of an orifice to deliver the liquid, an
abrasive feed tube, a mixing chamber where the liquid and abrasive
are mixed, and a nozzle (sometimes called a focusing tube or a
mixing tube) that finally directs the abrasivejet stream onto the
subject material that is to be removed.
[0005] Currently, there are not any significant differences between
any cutting heads or techniques of conventional abrasivejet
equipment manufacturers, as generally all orifice, nozzle, and
abrasive materials incorporated are the same for each manufacturer.
Orifices are usually made from hard materials such as diamond or
sapphire that generally produce a non-laminar jet. Nozzles are
mostly made from a very hard tungsten carbide. Conventional
abrasivejet equipment manufacturers also have similar cutting head
designs with non-significant variations between each design. These
cutting head designs have been widely demonstrated to cut at speeds
within 30% of each other with similar surface finishes in
comparative testing when equal parameters were used.
[0006] A more important similarity, as well as deficiency, of
conventional abrasivejet technology is the widespread use of garnet
abrasives over all other abrasives. Garnet is widely used because
of its initial low cost and ability to cut a wide range of subject
materials, however, it is widely used mainly because of its lower
overall costs when compared to other conventional abrasives.
[0007] Conventional abrasivejet technology does not effectively use
abrasives other than garnet due to numerous factors such as higher
initial costs of most other hard abrasives compared to garnet and
the inability of other hard abrasives to cut significantly faster
than garnet. These factors generally result in higher overall costs
of abrasive consumption after considering the final amount of
material cut. There is also the limitation of conventional
abrasivejet cutting head technology preventing use of harder
abrasives than garnet because of the increased costs of accelerated
nozzle wear created by these harder abrasives.
[0008] The similarities of conventional cutting head designs'
primary use of only one type of nozzle material, use of only one
abrasive medium, and use of only two types of orifice materials,
mainly produce a common limitation of an approximate 3:1 nozzle to
orifice ratio. This means the bore of the nozzle is generally three
times larger than the diameter of the orifice. The volume of the
abrasivejet stream inside the bore of the nozzle consists of an
air, high-pressure liquid and abrasive mixture, with a relatively
low amount of high-pressure liquid. The liquid is where the process
energy originates in the cutting head. Therefore, a relatively
larger volume of area in the nozzle bore compared to the smaller
area of volume of the liquid energy creates inefficiencies.
[0009] A solution to create a more efficient use of energy would
incorporate a smaller nozzle to orifice ratio such as 2:1 but this
solution is not currently viable with use of conventional cutting
heads and garnet abrasives. The best solution for conventional
technology has been use of relatively small volumes of
high-pressure liquid in the abrasivejet mixture allowing for viable
cutting, but this also reduces the effective cutting energy by
being dispersed over a greater area, hence, the effective energy is
not optimally focused.
[0010] U.S. Pat. Nos. 3,424,386, 3,972,150, 4,080,762 and 4,125,969
all teach the abrasive (sand) stream to be in the central portion
of the nozzle while the pressurized fluid is introduced into the
peripheral area surrounding the central sand stream. A ring orifice
plate or disk such as employed in the U.S. Pat. Nos. 3,424,386,
4,080,762 and 4,125,969 to provide the fluid jets around the sand
stream has many disadvantages including: the introduction of
pressurized fluid tangentially into a nozzle a short distance above
the orifice disk is not conducive to the generation of a coherent
fluid jet due to flow disturbances upstream of the orifices; sand
in the central portion of a nozzle creates an abrasive environment
that can weaken the interior wall of the annular fluid chamber
without being detected; pressurized fluid in the outer annular
space results in a nozzle that is very large in dimensions as both
interior and exterior walls must be sized to accommodate the fluid
pressure; and sealing the annular orifice disk can be very
troublesome. The U.S. Pat. No. 3,994,097 teaches a centrally
located water jet while sand is fed into a nozzle chamber through a
single sand passageway. The sand is forced into the water jet by
passage through a conical nozzle. This patent recognizes abrasion
problems within the nozzle and the necessity of exact alignment.
These problems would be intensified at higher pressures. All of
these patents teach mixing abrasive into water by (1) intercepting
an abrasive stream with water jets, and (2) forcing abrasives,
water and air through a conical nozzle, without concern of fluid
actions.
[0011] FIG. 1 of U.S. Pat. No. 5,184,434 depicts how the majority
of abrasivejet cutting heads are currently designed. The problem
areas with the prior art cutting head shown in this patent are the
orifice, the mixing chamber and the liquid jet. The orifice is the
device where the liquid jet passes through, building up to very
high velocities. The mixing chamber is the area where abrasive
joins with the liquid jet. A problem with this design is the
separation effect of the jet as it starts to break up. The nozzle
inlet then receives the stream at various angles and straightens it
out while realizing considerable wear on its bore. FIG. 2 of U.S.
Pat. No. 5,184,434 depicts the art of Abrasive Suspension Jet
(sometimes called "Slurry Jet") cutting. This method adds abrasive
to the stream before entering the orifice. The advantage of this
method is that it produces a coherent jet, but the disadvantage is
that components such as tubing, valves and orifices wear out
quickly due to the abrasive suspension inside the system severely
eroding everything it contacts.
[0012] Another disadvantage of the orifice designs in conventional
abrasivejet is the sharp transition from the pump tubing to the
relatively small orifice. This sharp transition creates a high
resistance of the pressure flow and does not allow for properly
formed liquid optimization, resulting with jet distortion, and
decrease in overall energy efficiency of the system.
[0013] Garnet is conventionally used because it does not wear the
nozzles out significantly even with the non-laminar jet produced a
conventional orifice as shown in FIG. 1 of U.S. Pat. No. 5,184,434.
Garnet also has a low initial cost and it is effective in cutting a
wide range of materials without significantly wearing the nozzle
while using the standard 3:1 nozzle to orifice size ratio. These
factors allow for a lower overall cost compared to other abrasives
and have allowed garnet to be the primary abrasive medium used for
almost all abrasivejet applications. However, there are many
reasons why garnet is not the optimum abrasive available when
considering the complete abrasivejet system, recycling and the
ability to perform two or more processes in one operation.
[0014] One reason is that garnet is not the optimum abrasive is
because it is not effectively recyclable. It is widely accepted
that only 30% to 50% of larger garnet particles can be reclaimed
for reuse after a single cutting operation as most of the garnet
particles are reduced in size from fracturing upon impact and made
less effective for further cutting of subject materials. Current
recycling processes of garnet generally add unused larger particles
to the reclaimed particles in order to keep cutting speeds at an
acceptable level.
[0015] Another disadvantage is that very hard subject materials
such as carbides and hard ceramics are generally not cut with
abrasivejet technology because of the very low cutting speed
ability of garnet to cut these materials. Conventional abrasivejet
techniques also have problems with feeding heavier abrasives
because of the inherent design limitation of a large nozzle to
orifice ratio. A major problem with prior art is the high
concentration of air in the abrasivejet that significantly reduces
the overall energy for cutting or treating. However, the greatest
problem with prior art is the relatively slower speeds of abrasive
particles compared to the initial speed of the liquid jet. The air
and abrasive mixture introduced in the mixing chamber never
completely suspend with the liquid jet.
[0016] Thus it is readily apparent that there is a long felt need
for an abrasivejet cutting head that can cut subject materials more
effectively by a high-pressure liquid jet that incorporates a
nozzle to orifice ratio of less than 2.5 to 1 that can reduce
overall costs and increase process speeds and obtain faster
abrasive velocities to achieve faster cutting or treatment rates.
There is also a need to expand abrasivejet into new
applications.
SUMMARY OF THE INVENTION
[0017] The present invention is a new cutting head approach for the
effective formation of a high pressure abrasive-liquid mixture. The
mixture is made more effective over prior art by focusing of the
abrasivejet energy into a smaller area through utilizing a small
nozzle to orifice ratio less than 2.5:1. This means that the bore
of the nozzle is less than 2.5 times larger than the diameter of
the orifice in order to concentrate the abrasivejet energy into a
smaller area when compared to prior art that specifies a 2.5:1 or
greater nozzle to orifice ratio (primarily 3:1). A smaller nozzle
to orifice ratio is desired in order to create more impact energy
for faster processing of materials. Improvements are disclosed
herein describing more efficient use of energy and resources
compared to current abrasivejet technology. These improvements are
obtained by: use of specially engineered abrasive particles with
specific properties, and proper mixture of these particles in the
abrasivejet stream; optimization of individual components of the
cutting head, and optimization of their relationships to each other
as a complete system.
[0018] An abrasive-liquid jet cutting head comprising at least one
mixing stage; a first mixing chamber arranged to accept a coherent
high pressure liquid from an orifice and flow of accelerated
abrasive particles from an abrasive feed tube and produce a
pressurized slurry-like flow that enters a nozzle; wherein a nozzle
to orifice ratio is in a range of about 1.2:1 to 2.49:1 wherein
nozzle opening size to orifice opening size is 1.2 to 2.49 times
larger in size.
[0019] It is a general object of the present invention to provide
an improved cutting head with a smaller nozzle to orifice ratio in
order to create more impact energy for faster processing of
materials.
[0020] Another object of the present invention is to provide an
improved cutting head using non-conventional abrasives along with
optimized cutting head configurations to allow for improvements to
traditional abrasivejet applications along with creating new
applications currently not associated with conventional
abrasivejet.
[0021] Another object of the present invention is to provide an
improved cutting head to process subject materials more efficiently
through optimization of the abrasive mixture process into a liquid
jet stream, resulting with reduced overall costs of the abrasivejet
technique for cutting or other material removing technology, as
well as surface treatment.
[0022] Yet another object of the present invention is to provide a
cutting head that provides improvements to the abrasivejet
technique to achieve increased processing speeds, better tolerances
and better quality surface finish of subject.
[0023] Still another object of the present invention is to provide
a cutting head that fosters the creation of several novel
manufacturing.
[0024] A further object of the present invention is to provide a
cutting head that facilitates faster particle acceleration for a
more effective mixing of non-traditional heavy metallic abrasive
particles with the waterjet, resulting in lower costs, recycling of
the heavier abrasive particles and greater cutting speeds.
[0025] Yet another object of the present intention is to provide a
cutting head comprised of a solid component.
[0026] Another object of the present invention is to provide a
cutting head produced from modular components.
[0027] These and other objects, features, and advantages of the
present invention will become apparent upon a reading of the
detailed description and claims in view of the several drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1--A perspective view of a solid component abrasivejet
cutting head.
[0029] FIG. 2--A perspective view of a modular component
abrasivejet cutting head.
DETAILED DESCRIPTION OF THE INVENTION
[0030] At the outset, it should be clearly understood that like
reference numerals are intended to identify the same structural
elements, portions, or surfaces consistently throughout the several
drawing figures, as may be further described or explained by the
entire written specification of which this detailed description is
an integral part. The drawings are intended to be read together
with the specification and are to be construed as a portion of the
entire "written description" of this invention as required by 35
U.S.C. .sctn.112.
[0031] For purposes of this patent, the terms appearing below in
the description and the claims are intended to have the following
meanings:
[0032] "Abrasive" means any particulate material intentionally
introduced into a pressurized liquid jet in the form of sharp edge
particles, such as angular, cubical, or non-spherical shapes,
generally used for material removal or surface treatment upon
interaction with subject material.
[0033] "Abrasivejet" means a mixture of a high pressure liquid jet
stream and abrasive particles focused through a nozzle to provide
for a useful tool.
[0034] "Subject material" means any material intentionally exposed
to the impact of a pressurized liquid jet carrying particles of
abrasive material.
[0035] "Waterjet" means a pressurized liquid stream generated by a
pump, distributed by high pressure tubing, and then focused through
an orifice to create a useful tool for cutting or surface
treatment.
[0036] "Nozzle" means a channel that mixes abrasive with a
pressurized liquid jet and focuses the abrasivejet in a
concentrated stream upon exit of the nozzle tip (a nozzle is also
known as a focusing tube or mixing tube). The smallest opening of
the channel is the specified size of the nozzle. The specified size
of the nozzle is important in determining the nozzle to orifice
ratio, as all of the abrasivejet is focused into the smallest
area.
[0037] "Orifice" means an opening that accepts a pressurized liquid
stream and allows it to pass thru. The opening is generally
specified as a diameter. The selection of the orifice size
generally determines the output pressure of the high pressure
system based upon the capabilities of the pump and the operating
speed of the pump.
[0038] "Cutting Head" means a device used in an abrasivejet system
that contains an orifice aligned to a nozzle, whereas the orifice
produces a jet that is directed into the central channel area of
the nozzle. The cutting head allows for the establishment of the
nozzle to orifice ratio after the nozzle and orifice are installed
into the cutting head.
[0039] "Nozzle to Orifice Ratio" means the total area of the
smallest opening of the channel in a nozzle compared to the total
area of the smallest opening of the orifice. Generally, the
openings for nozzles and orifices are cylindrical in shape. For
example, a conventional abrasivejet cutting head of prior art would
utilize a 0.030'' diameter nozzle if a 0.010'' diameter orifice
were installed, thus realizing a 3:1 nozzle to orifice ratio.
[0040] "High-Pressure" means a liquid pressure exceeding 10,000
psi.
[0041] "Surface Treatment" means intentional change of any
characteristics of materials subjected to the impact of pressurized
liquid jet carrying particles of abrasive material. Treatment may
be realized by partial removing of subject material and/or change
of its surface morphology (such as polishing or etching), and/or
superficial structure, such as size and shape of its superficial
grains, generating dislocations and/or other structural defects,
and/or superficial composition of subject material by the impact of
pressurized abrasive-liquid jet. Treatment may be resulted with
pre-designed cutting or other change of geometrical shape of
subject material or with an intentional change of its superficial
mechanical properties (such as hardness), and/or tribological,
and/or physicochemical, and/or electrochemical and corrosion
resistance properties, and/or catalytic properties, and or external
appearance, reflectivity or color.
[0042] "Coherent Jet" means a highly focused, laminar or nearly
laminar high pressure stream generated by an orifice that produces
centrally concentrated energy into the nozzle. Standard sapphire or
diamond sharp-edge orifices used in conventional art do not produce
a coherent jet without additional modifications to the jet below
the opening. It is preferred that an orifice produces a coherent
jet without any additional modifications to the jet in order to
achieve higher efficiency.
[0043] Improvements to abrasive particle selection through the
implementation of pre-engineered abrasives with high recyclability
and greater density are determined to be the optimum solution for
most abrasivejet applications. Greater amounts of cutting energy
are transmitted when a good mixture of these heavier particles are
mixed properly with a waterjet. The kinetic energy of the impact
against a subject material is improved when these particles are
accelerated to the speed of the waterjet. This can only occur with
a good suspension, or mixture, of the particles entrained into a
water jet. The present invention is a specialized cutting head with
a nozzle to orifice ratio in operatively arranged to create more
impact energy for faster processing of materials. A cutting head
with the ability to allow higher velocities and energy of the
particles. In accordance with the present invention, subject
materials may be cut more effectively by a high pressure liquid jet
mixed with abrasive particles in a concentration by utilizing
smaller nozzle to orifice ratios than proposed with prior art.
[0044] Adverting now to the drawings, FIG. 1 is a perspective view
of the present invention showing a solid component cutting head 10,
which, in one embodiment, comprises solid member 30 which is the
main body of the cutting head and has at least one abrasive feed
tube 16; wherein the mixing chamber 24 is arranged to accept a flow
of accelerated abrasive particles from at least one abrasive feed
tube 16 (also referred to as an abrasive inlet) and a pressurized
liquid flow from orifice 20 wherein a pressurized slurry-like flow
is generated. The mixing chamber 24 associated with one or more
feed tubes is arranged to introduce the slurry-like flow and focus
that flow through nozzle 12 for the purpose of cutting or treating.
The type of materials used to make solid member 30 may vary
depending on the abrasive used and the desired output. Orifice 20
may be polished to achieve higher surface finished quality if the
manufacturing process, such as injection molding/sintering, does
not yield suitable water jet quality.
[0045] Nozzle 12 has a cylindrical opening the size of which is
preferably at a ratio less than 2.5 times smaller in size than
orifice 20. In the mixing chamber the pressurized slurry-like flow
mixes the liquid energy and abrasive mass to allow for greater
effective transfer of energy, thus providing the higher energy
efficiency of the entire cutting process. The density of water is
far less than the desired abrasives, thus making the mixture of
abrasives into the liquid jet stream difficult. The speed of water
is also orders of magnitude higher than the speed of the abrasive
particles introduced into the stream. The abrasive does not
naturally enter the stream in these difficult cases, thus a nozzle
is used to mix and focus the liquid jet with the abrasives in order
to create a good abrasive suspension in the jet. It is preferable
that the nozzle is less than 2.5 times smaller in size than the
orifice in order to allow for a more effective mixture of abrasives
with the liquid jet.
[0046] The purpose of this design is to reduce costs through the
utilization of injection molding. Various hard materials such as
ceramics, nitrides and carbides can be injection molded in order to
reduce costs. Suitable hard materials may include, but are not
limited to, tungsten carbide, silicon carbide, alumina, or
zirconia.
[0047] Although the solid component cutting head 10 of the
embodiment, as shown in FIG. 1, is formed in a unitary construction
as a single molded unit wherein solid member 30 cutting head must
be attached to a sleeve or a suitable body it should be understood,
that other constructions may be used without departing from the
invention. For example, the modular component cutting head 10
having an interchangeable cutting head body 22 as is shown in FIG.
2. The supporting sleeve or body for either embodiment must then be
connected to a high pressure system via any suitable method to seal
in the pressurized liquid in order that the liquid may only pass
through the orifice. High pressure tubing, fittings, valves or
adaptors can be connected to a multi-stage cutting head 10 by
various sealing methods to accomplish this requirement. Nozzle nut
28 of FIG. 2 holds the interchangeable components in place and also
may allow for sealing to take place.
[0048] Both the single component unit, and the interchangeable
modular component unit, cutting heads 10, utilize a nozzle to
orifice ratio of less than 2.5:1. Although different configurations
or designs for the instant intervention can be utilized, the
significant feature of the invention is the nozzle to orifice
ratio.
[0049] Different styles of cutting head 10 may utilize similar
orifice 20 geometries or different geometries of conventional or
non-conventional design. However, an orifice with an efficient
coefficient of discharge of at least 85% is preferred over
industrial standard orifices that have sharp-edges producing lower
efficiency discharge coefficients. Although it is preferred to
utilize higher efficiency orifices, any reasonable orifice design
can be utilized in order to achieve the desired nozzle to orifice
ratios. In some cases, modifications to the orifice or liquid jet
can be made in order to produce a more coherent stream. For
example, an industry standard orifice that produces a non-laminar
jet can be used if the jet is redirected into a more coherent flow
to be utilized in small nozzle to orifice ratios.
[0050] The modular component multi-stage cutting head 10 having an
interchangeable cutting head body 22 as shown in FIG. 2 offers
greater flexibility of use than the solid member style cutting
head. First, a modular component is not limited to materials that
can only be used for injection molded units. Second, it offers the
ability to interchange orifice 20 or nozzle 12 components for
various applications that may require certain abrasive materials,
or different results. Third, it offers modularity by providing for
more orifice and nozzle combinations and ratios without the need
for as extensive inventory.
[0051] Also in accordance with the present invention, two or more
different abrasive materials may be combined in one abrasive jet.
The abrasive materials may differentiate in size of particles,
and/or in density (specific gravity) of particles, and/or other
physical properties of particles, such ductility vs.
brittleness.
[0052] The cutting head may be fed with abrasive particles from any
abrasive material selected from, but not limited to, the following
groups of abrasive materials: the first abrasive group comprising
glass, obsidian, quartz, aluminum oxide, boron carbide and silicon
carbide; the second abrasive group comprising: garnet, olivine,
chromite, ilmenite, rutile, pyrite, zircon, hematite, magnetite;
the third abrasive group comprising: cassiterite, metals, steel,
alloys; the fourth abrasive group comprising: hard melting heavy
metals including but not limited to: tungsten, molybdenum, tantalum
and/or respective carbides.
[0053] The use of heavier abrasive particles, such as stainless
steel material, with higher fracture toughness compared to garnet,
allow for lower overall costs through optimization of the entire
abrasive jet process that garnet or other conventional abrasives
cannot achieve. Through the effective mixture of select abrasive
particles with a small nozzle to orifice ratio approach,
improvements to the abrasive jet cutting process can be achieved
allowing for abrasive jet to become a highly productive and
efficient technology.
[0054] The ultimate goal of abrasivejet cutting technology is to
provide a satisfactory quality surface finish onto the subject
material at the lowest possible cost. Thru cutting of the subject
material in length of travel is the predominant use of the cutting
tool; typically, removing of a wider channel of material is not
required or desired. By focusing of the abrasivejet particle energy
into a smaller diameter nozzle, less width of cutting is produced
but longer lengths of travel are experienced with the same amount
of possible liquid energy from the pump. The output pressure and
flow rate of the pump is limited at the maximum capability of the
pump but the cutting head is the apparatus that efficiently or
inefficiently utilizes the same amount of fixed liquid energy to
produce abrasivejet cutting energy.
[0055] Still another feature of the invention is the specifically
designed orifice 20 that increases effective cutting energy,
efficiency, and life of the nozzle by minimizing wear in comparison
to conventional orifices. The angle of jet impact inside the bore
of the nozzle is minimized through the utilization of an orifice
that produces a coherent jet stream. The concentration of the
coherent stream combined with a small nozzle to orifice ratio
allows for a higher vacuum to mix particles in the liquid jet
stream, and allows for reduced negative effects of air mixed into
the abrasivejet. These improvements allow for greater energy when a
more concentrated mixture of abrasive and liquid is achieved, and
less air volume is obtained. The coherent stream also allows for
less wear of the nozzle, faster process speeds, and use of harder
abrasive materials than garnet.
[0056] Empirical evidence demonstrates that an increase in cutting
speeds can be achieved while using the proposed smaller nozzle to
orifice ratio. For example, garnet 80 mesh abrasive was used at a
rate of 1 lb/min to cut a 0.50'' thick 4140 annealed steel plate at
8 ipm (inches per minute). The orifice used was 0.013'' diameter
with a 52,000 psi waterjet generated. The nozzle used was 0.040''
diameter, thus an approximate 3:1 nozzle to orifice ratio was used.
Using the exact same conditions, the abrasive was switched to HG80
steel grit at the same rate of 1 lb/min. A slightly improved
cutting speed was achieved at 8.5 ipm, probably because of the
increased density of the steel over garnet. However, when the
conditions changed to a use a smaller nozzle of 0.030'' and only a
half pound of steel grit per minute instead of one, the cutting
speed increased to 10 ipm of the same 4140 steel plate with the
same jet conditions. The effect of using a cutting head with a
2.3:1 nozzle to orifice ratio is an increase in focus, mixture and
acceleration of the steel particles and thus increased efficiency,
lower costs, and improved process speed.
[0057] When any hard abrasives such as garnet are used in a cutting
head, smaller nozzle restriction is detrimental to nozzle wear.
Thus a cutting head of the preferred invention, with smaller nozzle
to orifice ratios configurations, can be used with abrasives that
are softer than garnet, such as steel, and do not wear the nozzle
as quickly.
[0058] It will thus be seen that the objects set forth above, among
those made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
construction without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings, shall be
interpreted as illustrative and not in a limiting sense. It is also
to be understood that the following claims are intended to cover
all the generic and specific features of the invention herein
described, and all statements of the scope of the invention which,
as a matter of language, might be said to fall therebetween.
* * * * *