U.S. patent number 3,756,511 [Application Number 05/111,867] was granted by the patent office on 1973-09-04 for nozzle and torch for plasma jet.
This patent grant is currently assigned to Kogyo Kaihatsu Kenyusho. Invention is credited to Naoki Negishi, Yukihiko Okada, Saito Shinroku.
United States Patent |
3,756,511 |
Shinroku , et al. |
September 4, 1973 |
NOZZLE AND TORCH FOR PLASMA JET
Abstract
A plasma jet nozzle is characterized by a plasma jet flame
opening mainly in the form of a slit which produces a stable and
powerful jet flame in the form of sheet-film or sector, and a long
and slender cylindrical plasma jet torch with a slit nozzle fixed
at the end is characterized by its use for boring deep into
reinforced concrete.
Inventors: |
Shinroku; Saito (Suginami-ku,
Tokyo, JA), Okada; Yukihiko (Higashicho,
Musashino-shi, Tokyo, JA), Negishi; Naoki
(Setagaya-ku, Tokyo, JA) |
Assignee: |
Kogyo Kaihatsu Kenyusho (Tokyo,
JA)
|
Family
ID: |
22340862 |
Appl.
No.: |
05/111,867 |
Filed: |
February 2, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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771496 |
Oct 29, 1968 |
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Current U.S.
Class: |
239/132.3;
239/599; 219/75 |
Current CPC
Class: |
H05H
1/34 (20130101); H05H 1/3478 (20210501) |
Current International
Class: |
H05H
1/34 (20060101); H05H 1/26 (20060101); H01j
017/26 () |
Field of
Search: |
;239/128,132,132.1,132.3,597,599,601 ;219/74,75,121,122
;137/801 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wood, Jr.; M. Henson
Assistant Examiner: Mar; Michael
Parent Case Text
This application is a continuation in part of our copending
application, Ser. No. 771,496, filed Oct. 29, 1968 now abandoned.
Claims
We claim:
1. A plasma jet nozzle for directing a flame in the form of a thin
film comprising an elongated narrow passage having a pair of smooth
generally longitudinally straight opposed side walls equidistantly
spaced from each other over their entire surfaces and a pair of
smooth generally longitudinally straight opposed end walls, said
side and end walls defining a slotted transverse inlet opening at
one end of the passage and a slotted transverse outlet opening at
the other end of the passage, one end of the nozzle being provided
with a transversely disposed concave inlet surface generally
complementary to the end surface of an electrode rod to be
positioned in axially spaced relationship to said inlet surface,
said pairs of side and end walls all intersecting said concave
inlet surface at one end of the passage and terminating at said
intersection to provide an unobstructed space completely
surrounding the tip of an electrode rod and lying between said tip
and the concave surface for gases entering the inlet opening of
said passage, the outer diameter of said concave surface being at
least equal to the transverse length of the passage at the
intersection of the passage and concave surface, whereby gases move
through the passage from inlet opening to outlet opening in
longitudinally straight directions.
2. A plasma jet nozzle as defined in claim 1, wherein the end walls
of the passage diverge in the direction toward the outlet opening
of the passage.
3. A plasma jet nozzle as defined in claim 1, wherein the side
walls of the passage are arcuate in transverse cross-section to
define a narrow curved outlet opening.
4. A plasma jet nozzle as defined in claim 1, wherein the exterior
of said nozzle includes at least one heat-conducting cooling
fin.
5. A plasma jet nozzle as defined in claim 1, wherein the ratio of
the length of the wall surrounding said passage to the
cross-sectional area of the pasasage is greater than 1.00.
6. A plasma jet nozzle as defined in claim 1, wherein the ratio of
the length of the wall surrounding said passage to the
cross-sectional area of the passage is greater than 1.20.
7. A plasma jet nozzle as defined in claim 1, wherein the
transverse width of said passage is less than 2.5 mm.
8. A plasma jet torch comprising an elongated housing having a
nozzle at one end and inlet means at the other end for gases and
cooling fluid, the interior of the housing being provided with a
first cylindrical conduit in communication with the nozzle at one
end and with the inlet means at the other end for conducting gases
to said nozzle, a second cylindrical conduit surrounding said first
conduit in concentric relationship thereto and in communication
with said inlet means, said second conduit forming with said first
conduit a passage for circulating cooling fluid in heat-exchanging
relationship with said first conduit, said nozzle being provided
with an interior longitudinally extending passage having a narrow
slotted inlet opening at one end and a narrow slotted outlet
opening at the other end generally similar to and in axial
alignment with said inlet opening, an elongated electrode rod
concentrically positioned in said first conduit having an exposed
tip spaced from and in axial alignment with the slotted inlet
opening of the nozzle, the interior walls of said first conduit and
said passage in the nozzle being smooth and defined by
longitudinally extending straight lines whereby gases moving from
said inlet means of the torch to the outlet opening of the nozzle
do not acquire any spiral motion.
9. A plasma jet torch as defined in claim 8, wherein the outlet
opening of the nozzle has a deflected configuration.
10. A plasma jet torch as defined in claim 8, wherein said nozzle
is provided with at least two slotted outlet openings in
communication with the internal passage.
11. A plasma jet torch as defined in claim 8, wherein at least a
portion of the outlet opening of the nozzle has an L-shaped
configuration in transverse cross-section.
12. A plasma jet torch as defined in claim 8, wherein the outlet
opening of the nozzle has an arcuate configuration in transverse
cross-section.
13. A plasma jet torch as defined in claim 8, wherein the outlet
opening of the nozzle has an X-shaped configuration in transverse
cross-section.
14. A plasma jet torch as defined in claim 8, wherein said nozzle
is also provided with at least one discharge orifice for a fluid
under pressure adjacent said outlet opening.
Description
The present invention relates to a nozzle and a torch for the
plasma jet.
In recent years the plasma jet has begun to find a wide application
because of its capability to give a very high temperature. For
example, it is used not only for cutting metals and refractory
materials but also for producing a static super-high temperature by
an arc image furnace, and its unique performance is evaluated to be
quite excellent.
On the other hand, however, this plasma jet has some difficult
problems still to be solved such as instability of flame, no
variety of the form of flame and complicated structure of torch
required for giving spiral motion of gas within the plasma torch.
To solve these difficulties, various attempts have been made, but
no striding growth has been made.
The object of the present invention is to provide a new plasma jet
flame characterized by stability, powerfulness, low cost, unique
shape and a very wide field of application.
The inventors of the present invention have been conducting
researches over many years to apply the plasma jet to the cutting
and boring of reinforced concrete and as a result have made an
invention of a nozzle and a torch capable of producing quite a new
plasma jet flame.
In the attached drawings,
FIG. 1a is a fragmentary cross-section of a conventional
nozzle;
FIG. 1b is an end view looking upwardly at the nozzle of FIG.
1a;
FIG. 2a is a fragmentary cross-section of a preferred form of
nozzle having a slit opening in accordance with the present
invention;
FIG. 2b is an end view of the nozzle of FIG. 2b;
FIG. 3 illustrates the plasma jet flame issuing in the form of a
film;
FIG. 4a shows a cross-section taken at right angles to FIG. 2a;
FIG. 4b is the end view of the nozzle of FIG. 4a;
FIG. 5a illustrates the formation of a conical surface at the end
of the nozzle adjacent the electrode; in FIG. 5b the space is
generally ellipsoidal, while in FIG. 5c the conical surface is
shown extending through the length of the nozzle;
FIG. 6a illustrates the formation of a slit surface by a tool which
enters from the face of the nozzle, as shown in FIG. 6b;
FIG. 7a illustrates the resulting combination of interior surfaces
resulting from the operations of FIGS. 5 and 6;
FIG. 7b is a view of the face of the nozzle of FIG. 7a;
FIGS. 8a and 8b are corresponding views, but taken at right angles
to FIGS. 7a and 7b;
FIG. 9 is a perspective view of a nozzle indicating the various
dimensions which influence the jet flame;
FIG. 10a is a cross-section of a modified form of nozzle in which
the slit tapers outwardly toward the outlet;
FIG. 10b is a view of the end surface of the nozzle of FIG.
10a;
FIG. 11 illustrates the sector-shaped flame produced by the nozzle
of FIGS. 10a and 10b;
FIG. 12a illustrates a form of nozzle having radial cooling
fins;
FIG. 12b is an end view of the nozzle of FIG. 12a;
FIG. 13a is a longitudinal cross-section of a rod-type plasma torch
provided with a nozzle according to the present invention;
FIG. 13b is a view of the lower end face of the torch of FIG.
13a;
FIGS. 14a, b and c respectively illustrate diagrammatically various
configurations of narrow slit openings in a nozzle;
FIG. 15a shows a nozzle with longitudinal cooling fins taken on the
cross-section E--E' of FIG. 15b which is an end view of this
nozzle;
FIG. 16 is a cross-section taken on the line A--A' of FIG. 13a;
FIGS. 17 - 23 illustrate diagrammatically various other
configurations for a nozzle outlet opening;
FIG. 24a is a cross-section of a nozzle having an angularly
directed slit opening;
FIG. 24b is an end view of the nozzle of FIG. 24a;
FIG. 24c illustrates the shape of the flame produced by the nozzle
of FIGS. 24a and b;
FIG. 25a is a cross-section of another form of angled slit;
FIG. 25b is an end view of the nozzle of FIG. 25a;
FIG. 25c illustrates the shape of the flame produced by the nozzle
of FIGS. 25a and b, and;
FIG. 26 is a cross-section of a typical nozzle indicating the
rounded edge which may be used along the intersection of the slit
with the end face.
As shown in FIG. 1, the conventional nozzle has a circular opening
3 for jetting the plasma flame in the plasma flame jet face 2 at
the bottom of the nozzle 1. The upper part of the nozzle has also
an opening for example in the form of a cone according to the shape
of the tungsten electrode rod 4, and the gas passes through the
nozzle with a spiral motion and its thermal pinch effect is given
at the jet opening 3.
We found out that this thermal pinch effect is dependent on the
ratio of the sectional area of the jet opening 3 to the length of
the surrounding wall of the jet opening 3, and after many trial
manufactures and tests of nozzles, we have found that with the same
sectional area, the thermal pinch effect increases with larger
ratio of the length of surrounding wall B to the sectional area A:
B/A. This shows that with the same sectional area, a rectangular
shape or further a slit-like shape of the jet opening 3 is more
desirable than a circular opening. This finding has led the
inventors to the invention of quite a new nozzle shape, namely, a
slit-like nozzle, and surprisingly enough, it has been found out
that the use of such a slit-nozzle makes it unnecessary to provide
the spiral motion of gas which has been thus far regarded as
indispensible for the plasma jet torch and a mere turbulent flow of
gas itself determined by the Reynolds number at the nozzle is
sufficient. These will be explained in more detail in the following
with reference to the drawings.
FIGS. 2a and 2b show a slit-nozzle of the present invention. As is
obvious from these Figures, the plasma flame jet opening 5 in the
plasma flame jet face 2 at the bottom of the nozzle 1 is designed
with a slit form. The plasma jet flame emitted through such a
nozzle has a shape of a thin film as shown in FIG. 3. This is a
shape of a plasma jet flame that has never been available.
FIG. 4a shows a side view of the nozzle of FIG. 2a. Irrespective of
the shape of the upper opening 7, it is possible to produce a flame
of such a form by designing the jet port 5 as a slit opening.
As regards the space in the nozzle between the slit at the plasma
jet face and the part near the tungsten electrode rod, i.e., the
opening 7 of the electrode surface 6 of the nozzle 1, it is
designed as a combination of a variously shaped space 8 such as a
cone, a pyramid, a hemisphere and an ellipsoid of revolution made
at the opening part 7 of the electrode surface 6 as shown in FIGS.
5 a, b and c and a slit structure space 9 formed from the plasma
flame jet face 2 as shown in FIG. 6. For example, if 8 is a
conically formed space, such a conical space 8 made downward from
the upper opening part 7 is combined as an overlapping form with
the slit-like space 9 formed upward from the plasma flame jet face
2 as shown in FIG. 7 and in FIG. 8 which is a side view of the
structure shown in FIG. 7.
The form of the space 8 varies chiefly according to the form of the
electrode rod and an adequate form must be selected. In addition,
the form of the space 8 is supposed to be dependent on such factors
as the flow rate of gas used for plasma jet, voltage, electric
current, gas composition (argon, hydrogen, nitrogen, air,
combustion gas or misture thereof), required for the power of the
jet plasma flame in the form of a flame, etc.
Now explanation will be made about the variety of the form of the
slit nozzle. First a model of slit is assumed as shown in FIG. 9.
This is a slit as shown in Figures up to FIG. 8. To indicate the
dimensions of the plasma flame jet opening 5, symbols W, H and L
are used, denoting the width 10, height 11 and length 12 of the
slit respectively.
FIG. 10 shows a variety of this slit form, in which the electrode
surface 6, its opening part 7 and the conical space form 8 are the
same as before, but the slit-like space 13 from the plasma flame
jet face 2 is different from the above-mentioned regular slit form.
As can be seen from the Figure, the slit beginning from the jet
face 2 extends upwards to a suitable height H of the nozzle 1,
namely up to 14 in this Figure. The length 1 of the slit becomes
gradually shorter as it rises, thus a slit space is made in the
form of a sector. In other words, the length of the slit becomes
larger as the jet gas proceeds. In this case, the width of the slit
remains unchanged. The spaces of 8 and 13 are formed in this way,
the two spaces overlapping each other to form a passage
characterized by a modified slit form.
With the standard form of a slit-nozzle as shown in Figures up to
FIG. 8, the plasma jet flame has a form of a film (14 in FIG. 3),
but with the modified slit-nozzle of FIG. 10, the plasma jet flame
is characterized by a form of a thin sector (15 of FIG. 11). The
plasma jet flame formed by the slit nozzle according to the present
invention has many new applications. For example, in case of
cutting a metal plate or refractory material, a very thin cutting
is possible if the nozzle is moved in the direction of the slit
length, while a cutting with a large width is possible if the
nozzle is moved in the direction of the slit width. If the nozzle
is rotated around its axis, a circular boring will be effected, and
if the nozzle is moved forward while rotating, cutting and boring
will be effected in a variety of forms. The greatest advantages of
this slit nozzle, however, are large thermal pinch effect and high
and uniform density of the flame, which produces a stable flame and
large heat output. The jet flame emitted from this slit nozzle is
so powerful that it can give a cutting speed 1.5 times as high as
that of the previous plasma jet flame, or with the same cutting
speed, the power consumption by the new slit nozzle is far smaller
than that in the case of the conventional nozzle and the cut
surface is much neater. With the modified form of the slit nozzle,
the flame is produced in the form of a sector having a much larger
length than the diameter of the nozzle itself. When such a variety
of the slit nozzle is used for cutting work, another effect will be
added to those mentioned above, namely, such a sector flame will
make it possible to cut with a larger width than the standard slit
nozzle, and if rotation of the nozzle is combined with such sector
flame, a boring will be made with a larger diameter than that of
the nozzle itself, the hole being so large that the complete torch
is allowed to be inserted into the hole. Therefore, such a sector
slit nozzle will find applications, for example in making deep
holes by boring.
The effects of the slit nozzle for the plasma jet according to the
present invention may be summarized as follows:
1. Thermal pinch effect is large and the flame density is high and
uniform.
2. Since the flame can be produced with a very small width, the
slit nozzle is most suitable also for making a plasma jet flame for
the arc image furnace.
3. Plasma jet flame is very stable.
4. Thermal output is large and the jet flame is powerful and
economical.
5. When it is applied to cutting and boring, the speed of cutting
or boring is very high.
6. It is possible to cut with a small cutting width.
7. It is possible to cut with a large cutting width.
8. By changing the direction of the slit-formed flame from the
advancing direction of the torch, it is made possible to cut with a
freely adjustable width. This width is adjustable at any desired
time.
9. The cut surface is very neat.
10. Rotation of the modified slit nozzle produces easily a hole
having a diameter larger than that of the nozzle itself, so that
such a nozzle is suitable also for boring of a deep hole.
Thus it is obvious that the slit nozzle has truly great effects. As
mentioned above, the nozzle of the present invention increases the
thermal pinch effect substantially, but still there are methods to
further increase the thermal pinch effect as illustrated in FIG. 12
or FIG. 15. The 17 of FIG. 10 indicates an external water cooling
wall surface. If this wall surface is provided with one or more
fins 16 or ribs which will serve for heat conduction as shown in
FIG. 12 or FIG. 15, the heat conductive surface area will be
greatly increased. This will result in greater cooling effect,
which will increase the thermal pinch effect. As a result, a more
powerful plasma jet flame in the form of a film or a sector will be
produced.
In the meantime, it was also found out by further researches that
with the above-mentioned slit nozzle, the spiral motion of the gas
which has thus far been considered to be indispensable for the
plasma jet torch becomes almost unnecessary and that the turbulent
flow of gas itself specified merely by the Reynolds number at the
nozzle is sufficient.
This may be attributable to the fact that in the previous plasma
jet torch a nozzle form having a relatively small thermal pinch
effect was used and this insufficient pinch effect had to be made
up by a powerful spiral motion of gas. Therefore, with the use of
the slit nozzle of the present invention, it is possible to produce
a sufficiently powerful plasma jet flame in the form of a film or a
sector without using a specially generated spiral motion of the
gas. This elimination of the spiral motion makes it possible to
design the gas piping of the torch as a straight pipe, making the
torch itself slender, more simplified and less costly.
FIG. 13(a) and FIG. 16 show a rod-type plasma jet torch of the
present invention, in which a slit nozzle of a modified form 1 is
used. FIG. 13b shows a nozzle viewed from the plasma flame jet
face. In the Figure, 4 is a water-cooled tungsten electrode rod
disposed at the central axis of the torch. Around this electrode
rod there is a concentric hollow cylinder 18 to provide the passage
of gas, which is further surrounded by another concentric hollow
cylinder 28 to provide the passage for cooling water 27. The
direction of the flow of the cooling water is indicated by 19. 21
and 22 are electric wires connected respectively to the electrode
rod 4 and the nozzle 1. The cooling water cools also these wires.
The plasma jet gas enters the torch through 23 as indicated by an
arrow and flows in the torch in the direction of the arrow 20
without making any specially designed spiral motion. The gas flows
thus to the nozzle having an outlet of the plasma jet flame 5 in
the form of a slit as already explained above. The torch itself has
a slender rod-like form. In this FIG. 13, the form of the slit
nozzle is that shown in FIG. 10, but it is of course possible to
use the standard slit nozzle form as shown in the Figures up to
FIG. 8 and the modified form shown in FIG. 12 and thereafter.
The torch according to this invention has a simple structure and
accordingly can be manufactured at low cost. Therefore, a stable,
powerful and unique plasma jet flame can be produced at low cost
and in a very thin form. This makes the torch suitable also as a
plasma jet torch for boring work. The slender rod-like for of torch
mentioned above does not mean only a straight rod form. It may be a
suitably curved form according to the desired boring shape. Thus
the "rod-like" in this invention includes a curved rod.
The slit-like structure of the slit-like nozzle of the present
invention means a generally narrow opening. This may be in a
variety of form, i.e., it may be a long rectangular form as shown
by FIG. 14a or a similar shape with rounded corners as shown by b
or a convex as shown by c of FIG. 14. In any case the form must
have a considerably larger length (L in FIG. 9) than the width (W
in FIG. 9) in the plasma jet face 2.
The nozzle of this invention can be designed so as to have a
deflected slit. In this case, the plasma flame will be produced in
a direction somewhat inclined against the axial direction of the
torch (FIG. 24c and FIG. 25). If a torch having such a deflected
slit is rotated around its axis, the boring will have a further
greater diameter. This deflection can be made chiefly at the slit,
for example, at 24 of FIG. 4 or at 24 of FIG. 2 in the direction of
the slit width or length respectively (24 of FIG. 25 and FIG. 24).
The nozzle may also be deflected at 14 of FIG. 10.
In case of using this nozzle for boring, it may be provided with an
orifice or a port for jetting water or gas (e.g., air) through the
plasma flame jet face. This will serve for discharging the melt out
of the bored hole. An example of such a jet orifice for jetting
water or gas is shown by 25 in FIG. 8a and b. The nozzle may be
provided with one or more of such orifice. If water or air is
jetted in case of boring reinforced concrete, melted concrete will
be cooled rapidly and become fine powder, which is very easy to
discharge from the bored hole.
The following nozzle forms are also included in the scope of the
present invention: Two or more slits conforming to the present
invention are made in the plasma flame jet face as shown in FIG. 17
and FIG. 18; the slit is bent or curved at one or more positions as
illustrated in FIG. 19 and FIG. 20; various cross slits are
illustrated in FIG. 21, FIG. 22 and FIG. 23.
Further,the jet slit of all the nozzle according to this invention
may have a rounded edge instead of a sharp edge at the plasma flame
jet face as shown by 26 of FIG. 26. Such a rounded edge has an
effect of making the jet flame a little longer than usual.
Thus, according to this invention, it is possible to obtain easily
a new plasma jet flame which is stable, powerful and of low cost
and has a unique shape and a very wide scope of application.
The following examples will further illustrate the nature of this
invention but the invention is not restricted to these
examples.
EXAMPLE 1
By using a spiral-gas plasma jet torch for laboratory
use(commercially available), comparison was made between the
standard slit nozzle according to this invention as shown in FIG. 8
and a generally used nozzle as illustrated in FIG. 1. The result
was as follows:
---------------------------------------------------------------------------
Nozzle of this invention Conventional nozzle
__________________________________________________________________________
Shape of plasma Width of slit 1.2mm circle of 4mm dia. flame jet
opening Length of slit 10mm Height of slit 9mm Gas composition Ar
95% Ar 95% H.sub.2 5% H.sub.2 5% Voltage 90 V 80 V Electric current
300 A 300 A Shape of plasma Thickness of flame ca. 2 mm Diameter of
flame jet flame Width of flame ca. 10mm ca. 5mm Length of flame ca.
30mm Length of flame Flame in the form of thin film Flame in the
form of a slender cone Speed of cutting 200-300 mm per minute 150
mm per minute iron sheet (20 mm thick) Width of cut in 10 mm in
case of moving the same case as the nozzle in width above direction
of slit 6 mm 4 mm in case of moving the nozzle in length direction
of slit
__________________________________________________________________________
EXAMPLE 2
When the modified slit nozzle of this invention as shown in FIG. 10
was used instead of the standard slit nozzle used in Example 1, the
result was as follows:
---------------------------------------------------------------------------
Nozzle of this invention
__________________________________________________________________________
Shape of plasma flame Width of slit 1.2 mm jet opening Length of
slit 15 mm Height of slit 9 mm Length of slit at a height of 9 mm;
10 mm Slit in the form of a sector Gas composition Ar 95% H.sub.2
5% Voltage 95 V Electric current 300 A Shape of plasma jet Flame in
the form of a thin sector flame Thickness of flame ca. 2 mm Width
of flame near the plasma flame jet face: ca. 13 mm Width of flame
at a flame length of about 30 mm: 25 mm Speed of cutting iron sheet
(20 mm thick) 200-350 mm/min Width of cut in the 15 mm in case of
moving the nozzle same case as above in width direction of slit 4
mm in case of moving the nozzle in length direction of slit
__________________________________________________________________________
EXAMPLE3
The experiment was conducted by using a torch in the form of a
straight rod (as shoen in FIG. 13) with the following
specification:
The torch is provided with a thin steel electrode rod (5 mm .phi.)
having a tungsten electrode at its top; at its outside, a first
concentric cylinder for passage of gas with an inside diameter of
10 mm; a second concentric hollow cylinder for passage of cooling
water with an inside diameter of 15 mm; diameter of torch 17mm;
length of torch about 1 m. At the top of the torch was connected a
slit nozzle having a modified slit form of this invention as shown
in FIG. 10 (the nozzle being provided with a water jet orifice 25
as shown in FIG. 8). Argon gas was fed at a rate of 5 kg/cm.sup.3,
30 lit./min. and a voltage of 30 V as applied. Under these
conditions, electric current was passed and the torch was put into
operation, by which almost the same plasma jet flame as in Example
2 was produced and maintained. Under the influence of water jet,
this plasma flame was a little inclined to the opposite side of
water. During about one hour, the flow rate and voltage were
changed in a wide range, and the torch was swayed to various
directions and further subjected to vibration, but the flame was
kept in stable condition all the time.
This torch was also used for boring reinforced concrete having a
thickness of about 300 mm. During this use, the torch was turned
around its axis, and by the effect of water jet, the melt gushed in
the form of fine powder together with the water from the upper
opening of the hole. In two and a half minutes, a hole was
completely bored into a depth of 300 mm. Nearly the same results
were obtained by using air jet instead of water jet. Needless to
say, the torch itself was brought into the hole as it was bored
deeper.
EXAMPLE 4
Various cutting experiments were conducted under the same
conditions as in Example 1 to measure cutting speeds and the
following results were obtained:
450 mm/min. with aluminum sheet having a thickness of 12 mm, and
250 mm/min. with 30 mm thick concrete slab. In case of cutting in
water, 220 mm/min. with 12 mm thick aluminum sheet, 90 mm/min. with
9 mm thick iron sheet and 80 mm/min. with 40 mm thick concrete
slab. Since the conditions of experiments were not optimum, it has
been ascertained that the cutting speed will be further increased
through future reasearches. It has also been ascertained that it is
possible to generate and maintain safely air plasma and nitrogen
plasma as well.
EXAMPLE 5
As mentioned above, it is desirable that the ratio of the length of
the surrounding wall B to the sectional area A, i.e., B/A, of a
slit-like nozzle should be large. The results of an experiment
conducted with varying ratios are as follows. For the experiment
mixed gas of Ar (95percent) and H.sub.2 (5 percent), 280-320 amps
of the electric current and 80-95 volts of the voltage were used.
The evaluation of the results was divided into the following four
grades depending on the amount of gas, voltage and vibration. The
highly stable grade is indicated by the symbol : the stable grade
by O; the slightly stable grade by .DELTA.; and the utterly
unstable grade by X.
type of nozzle A(mm.sup.2) B B/A Evalu (mm.sup.2) ation width(mm)
length(mm) 1.2 10.0 (slit) 12.0 22.4 1.87 0.6 12.0 (slit) 7.2 25.2
3.50 2.0 8.0 (slit) 16.0 20.0 1.25 O 1.6 10.0 (slit) 16.0 23.2 1.45
1.2 15.0 (slit) 18.0 32.4 1.80 2.5 8.0 (slit) 20.0 21.0 1.05
.DELTA. 2.0 10.0 (slit) 20.0 24.0 1.20 O 1.0 10.0 (slit) 10.0 22.0
2.20 2.3 10.0 (slit) 23.0 24.6 1.07 .DELTA. 3.0 10.0 (slit) 30.0
26.0 0.87 X 1.65 12.0 (sectorial) 19.8 27.3 1.38 1.35 12.0
(sectorial) 16.2 26.7 1.65 1.2 22.0 (cross) 49.4 84.8 1.72 4 .phi.
(circular) 12.5 12.5 1.00 O 5 .phi. (circular 19.6 15.7 0.80
.DELTA. 6 .phi. (circular) 28.3 18.8 0.67 X
according to the above-mentioned equipment, each of the slit-like
nozzles, sectorial nozzles, and cross nozzles of our invention
showed a remarkable result when B/A was over 1.00 and preferably
over 1.20, and particularly when B/A was over 1.4 the result was
highly stable. The width of the slits was found to be limiting, and
widths over 2.5 mm were found to be undesirable while widths under
2.0 mm were found to be preferable. On the other hand, in the case
of a conventional circular opening, the result of an experiment
showed that 4 mm (B/A 1.00) was stable and over 5 mm was unstable.
Consequently, a slit-like shape of a jet opening of our invention
is to be evaluated on a different basis from that of the B/A of a
conventional opening.
Thus it is desirable to make the ratio B/A larger, and as is clear
in Example 5 a good result is obtained when B/A is over 1.00,
preferably over 1.20 and particularly over 1.4. As far as the
results of the experiment are concerned further limitation may be
provided by the selection of the width of the slit under 2.5 mm,
preferably under 2.0 mm. This basis is quite different from that of
a circular nozzle under 5 mm and with the B/A over 0.80. Our
invention is remarkably characterized by an adequate sectional area
A even when B/A is large, thus providing the great advantage of
being able to increase the power. A circular type has no such
advantage.
It is noted that the slits illustrated in the drawings have been
simplified to facilitate understanding of the present invention and
do not represent the correct width and length dimensions, as
specifically recited in the examples.
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