Note: Descriptions are shown in the official language in which they were submitted.
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CUTTING METHOD AND APPARATUS
F IELD OF THE INVENTION
The present invention relates to a method for
cutting and an apparatus for the application thereof.
More particularly, the present invention relates to a
method for jet cutting and an apparatus for the
application thereof, which are excellent in cutting
efficiency with a uniform cut surface and permit
inhibition of production of burrs.
DESCRIPTION OF PRIOR ART
For cutting a metal object, a high temperature
gas melting-cutting method using combustion flame of
gas and a liquid jet cutting method adopted under
conditions not permitting use of flame in taking a tank
for storage of an oily material have conventionally
been known.
For example, the liquid jet cutting method is
popularly known as a water jet cutting method using
high pressure water, and widely applied for cutting a
steel sheet. This method is employed also in building
sites where powder cannot be used for cutting or
breaking rocks and concrete.
SUMMARY OF THE INVENTION
The present invention has an object to provide a
novel jet cutting method based on a jet flow which
eliminates the aforementioned defects in the
conventional method.
Furthermore, the present invention has another
object to provide a new apparatus for the application
of said jet cutting method.
The present invention provides a method for jet
cutting comprising performing cutting by ejecting a
fluid by a Coanda spiral flow generated through
introduction of a pressurized fluid.
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Furthermore, as an apparatus for the application
of the present method, the present invention provides
an apparatus for jet cutting comprising a rotatable and
movable Coanda spiral flow generating nozzle having an
annular slit for introducing a pressurized fluid
transversely to a nozzle ejecting port and a curved
wall running from said slit to said ejecting port.
According to a still further broad aspect of the
present invention, there is provided a method of jet
cutting performed by ejecting a fluid. The method
comprises transporting hard cutting particles by means
of a first pressurized fluid flowing through a conduit
having a conical nozzle at the downstream end thereof.
The diameter of the nozzle decreases in the downstream
direction and the nozzle has an axially directed
opening at its downstream end for the ejection of
cutting fluid. The method is characterized in that
pressurized fluid flowing initially towards the nozzle
axis is introduced to the nozzle around the periphery
of an upstream end of the nozzle to introduce a
tangential component to the flow of the first
pressurized fluid whereby a Coanda spiral flow of fluid
having a high velocity in the downstream direction with
the maximum downstream velocity on the axis, together
with a Coanda layer near the nozzle inner wall, is
produced.
According to a still further broad aspect of the
present invention, there is provided a jet cutting
apparatus comprising a conical nozzle having an axially
directed opening for the ejection of cutting fluid at
its downstream end through which fluid carrying cutting
particles can flow. The nozzle diameter decreases in
the downstream direction. The apparatus is
characterized in that means is provided for introducing
a pressurized fluid which flows initially towards the
axis of the nozzle into the fluid flowing in use
through the nozzle to introduce a tangential component
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to the flow of fluid flowing in use through the nozzle
provided around the periphery of an upstream end of the
nozzle, thereby to generate a Coanda spiral flow of
fluid having a high velocity in the downstream
direction with the maximum downstream velocity on the
axis in the fluid flowing through the nozzle, together
with a Coanda layer near the nozzle inner wall.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view illustrating an
embodiment of the nozzle of an apparatus of the present
invention;
Figs. 2(a) and (b) are drawings illustrating
velocity distributions of the jet flow in a method of
the present invention and the conventional method,
respectively; and
Fig. 3 is a sectional view illustrating a
conventional water jet cutting nozzle.
DESCRIPTION OF PRIOR ART
Referring to Fig. 3, there is illustrated a
typical jet nozzle used for the liquid jet cutting
method. High pressure water is introduced from a high-
pressure water inlet (B) towards a nozzle exit (A),
while introducing hard particles from a cutting
particles inlet (C) provided transversely, and cutting
is conducted by means of a jet flow ejected from the
nozzle exit (A). Hard cutting particles may be omitted
in this case.
While the jet cutting method is very useful as a
cutting method applicable under conditions making it
difficult to use fire, the conventional method and
apparatus have several points to be improved.
More specifically, in the conventional method,
the jet flow ejected from the nozzle exit (A) shown in
Fig. 3 rapidly diffuses so that it is difficult to
concentrate the jet flow onto the portion to be cut.
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Furthermore, a cut surface is apt to be uniform and
production of burrs is inevitable. When using hard
cutting particles, the nozzle inner wall suffers from
seriously being worn.
These defects are inevitable in the generation
of a jet flow based on the introduction of high-
pressure water, and this naturally limits the
applicability of the liquid jet cutting method. There
has, therefore, been a strong demand for improvement of
cutting efficiency, homogenization of a cut surface,
inhibition of occurrence of burrs, and reduction of
nozzle wear.
DETAILED DESCRIPTION OF THE INVENTION
The Coanda spiral flow used in the present
invention was discovered by the present inventor as a
state of movement different from a turbulent flow while
being under the conditions of movement of a fluid
belonging to the turbulent region, unlike the laminar
flow or a turbulent flow known as the conventional
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concept of fluid movement. A method for forming the Coanda
spiral flow has already been proposed also by the present
inventor.
More particularly, the Coanda spiral flow is a flow of a
fluid which runs at a high velocity in the pipe direction while
forming a spiral, and can be formed by adding a vector in the
pipe radial direction to the flow vector of the fluid introduced
in the pipe direction. In this case, a negative pressure having
a strong sucking force is formed on the side opposite to the
running direction of the Coanda spiral flow, and high velocity
Coanda layer based on the spiral flow near the pipe inner wallis
formed.
The present invention is to perform cuttlng of a metal, an
inorganic material, cement or other solids by the use of the
features of such a Coanda spiral flow. One of the most
important things in using the present method is to concentrate
velocity distribution on the running axis relative to the
running direction of the Coanda spiral flow. This concentration
is never observed in a conventional jet flow based on a
turbulent flow. This concentration of velocity distribution
permits improvement of cutting efficiency with a uniform cut
surface and inhibition of burr occurrence.
Now, the present invention is described with reference to
following.
Fig. 1 illustrates an embodiment of the present invention
as a Coanda spiral flow generating nozzle.
The nozzle has bee developed for use in efficient mixing
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of abrasive and for improved focusing of water jet streams in
high pressure abrasive water ~et cutting applications. The
development of the nozzle was based on the spiral flow theory.
To obtain a focused jet flow, the nozzle is designed with an
annular slit connected to a conical cylinder. Pressurized fluid
is supplied through this slit and the fluid, passing through the
conical cylinder, is deformed to the spiral flow with the
maximum axial flow on the axis, caused by Coanda effect and the
instability of turbulence.
- In the embodiment shown in Fig. 1, for example, an annular
slit ~3) for pressurizing and introducing a fluid such as water
on a main cylinder (2) directed toward a nozzle exit (1), and
this slit (3) is provided with a supply pipe (7) for supplying a
pressurized fluid.
The main cylinder (2~ has a diameter becoming similarly
and gradually larger from the nozzle exit (1) toward the slit
(3) and a wall surface (5) of the main cylinder (2) is formed to
be smoothly curved. The end opposite to the nozzle exit (1) is
provided with an auxiliary cylinder (4) with an inlet (6) for a
mixed flow of a fluid, or a fluid and hard cutting particles.
At the oppoiste side of the wall surface (5) opposite to the
slit (3), a wall surface (8) of the auxiliary cylinder (4) is
bent at right angles or at an acute angle.
The interval of the slit (3) may be ad~ustable. There is
no particular limitation on the structure of the supply pipe (~)
~upplying a pressurized fluid. Furthermore, a distribution
chamber (9), for example, may be provided for the purpose of
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2~10083
ensuring uniform supply.
For the main cylinder (2), the inclination angle (~)
should preferably be such that tan ~ is about 1/3 to 1/10.
In the Coanda spiral flow generating nozzle, a typical
embodiment of which has been described above, pressurized water
as a pressurized fluid may be introduced from the slit (3) into
the main cylinder (2). This permits synthesis of the motion
vector of the pressurized water and the motion vector of the
fluid such as water and air from the inlet (6), thus forming a
spiral motion (10). This spiral motion (10) brings about
concentration of fluid velocity in the running axis direction,
forming a high velocity concentrated flow, Since a Coanda layer
is formed in the main cylinder (2), wear of the nozzle inner
wall is inhibited even when hard cutting particles are mixed in
a pressurized fluid. When mixing particles such as alumina,
SiC, Si3N4, BN, WC, etc., their dispersion is homogenized.
The nozzle has been developed for use in efficient mixing
of abrasive and for improved focusing of water jet streams in
high pressure abrasive water jet cutting applications.
The jet stream is more stable and concentrates the
particles to the axial area of the jet flow caused by the
characteristics of a spiral jet. That is the maximum axial flow
on the axis and a rotational flow around the axis.
In cutting, the pressure of the fluid such as water can be
appropriately set, and any of metals, inorganic materials as
alumina garnet, or the like may be used appropriately as hard
cutting particles. It may not always be necessary to use those
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2(~1008;~
hard cutting materials.
Pressurized fluid may be water or other fluid or a mixed
li-quid. The object to be cut may be any of metals, inorganic
materials and other solids.
Now, the present invention is described in more detail by
means of examples as follows.
EXAMPL~ 1
The nozzle shown in Fig. 1 was used. An exit diameter of
the nozzle was 19 m/m.
A distance of 50 m/m was provided between the nozzle exit
and a sample, and a concrete wall as the sample was cut. In
this case, water pressurized at 400 kgf/cm2 was ejected, without
the use of hard cutting particles.
The sample was cut to a depth of 18 cm. Cutting was
conducted by the conventional water jet method under the same
conditions. The sample was cut only to a depth of 10 cm. The
cut surface was rough and innumerous fine burrs occurring on it.
The cut width was more than twice as large as in the cutting by
the Coanda spiral flow of lthe prsent invention.
Additionaly, when mixing of alumina particles, the cut
depth increasedeven to about 26 m/m.
EXAMPLE 2
Velocity distribution of a jet flow from a nozzle of
8 mm was evaluated.
A velocity of 43 m/sec was set at a position of 4 cm from
the nozzle tip, and comparison wa~ made with the conventional
water jet.
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Velocity distributions of the Coanda jet with pressurized
water of 4.8 kgf/cm2 and the conventional water jet are shown in
Figs. 2 (a) and (b).
As is clear from the comparison of velocity distribu-tion
of 20 m/sec, i.e., expanses (~) of the velocity velocity
concentration is far higher in the Coanda jet of the present
invention than the conventional jet.
According to the present invention, as described above in
detail, the following effects are available when performing cutt-
ing with the use of a jet flow based on a Coanda spiral flow:
1) Since diffusion of the jet is smaller and the energy
exerts its effect concentrically in the running direction,
the cutting efficiency may be largely improved.
2) Wear resistance of the nozzle may be excellent.
3) Hard cutting particles may be uniformly dispersed
throughout the fluid.
For these advantages, it may be possible to achieve far
more useful method and apparatus for cutting than the
conventional ones.
