U.S. patent application number 09/785313 was filed with the patent office on 2001-09-06 for process and unit for plasma-arc working with a gas having controlled o2 and n2 contents.
This patent application is currently assigned to L'AIR LIQUIDE, SOCIETE ANONYME. Invention is credited to Augeraud, Regis, Delzenne, Michel, Suzon, Serge.
Application Number | 20010019041 09/785313 |
Document ID | / |
Family ID | 8847128 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019041 |
Kind Code |
A1 |
Augeraud, Regis ; et
al. |
September 6, 2001 |
Process and unit for plasma-arc working with a gas having
controlled O2 and N2 contents
Abstract
Process and unit for the arc working, particularly plasma
cutting, of a workpiece, in which a plasma torch is supplied with
an electric current and with a gas mixture containing oxygen and
nitrogen, and a plasma jet obtained by the ionization of the gas
mixture by the electric current is delivered by means of the plasma
torch. The concentration of nitrogen and oxygen in the gas mixture
is less than 50%. The gas mixture is obtained by adding a defined
amount of nitrogen or, depending on the case, oxygen immediately
before the gas mixture is introduced into the torch. The amount of
nitrogen or oxygen is defined according to the thickness of the
workpiece, to the grade of the constituent material of the
workpiece, to the desired work rate and/or to the intensity of the
electric current.
Inventors: |
Augeraud, Regis; (Pontoise,
FR) ; Suzon, Serge; (Pontoise, FR) ; Delzenne,
Michel; (Franconville, FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
L'AIR LIQUIDE, SOCIETE
ANONYME
|
Family ID: |
8847128 |
Appl. No.: |
09/785313 |
Filed: |
February 20, 2001 |
Current U.S.
Class: |
219/121.39 ;
219/121.44; 219/121.55 |
Current CPC
Class: |
B23K 2103/05 20180801;
B23K 2103/04 20180801; H05H 1/34 20130101; B23K 10/00 20130101 |
Class at
Publication: |
219/121.39 ;
219/121.55; 219/121.44 |
International
Class: |
B23K 010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2000 |
FR |
00 02022 |
Claims
1. A process for the plasma-arc working of at least one workpiece
made of structural steel, in which: (a) a plasma torch is supplied
with an electric current and with a gas mixture containing oxygen
and nitrogen, (b) a plasma jet obtained by the ionization of at
least part of said gas mixture containing oxygen and nitrogen by
said electric current is delivered by means of said plasma torch,
wherein: the concentration of nitrogen in the gas mixture
containing oxygen and nitrogen is greater than 0% by volume and
less than 50% by volume, said gas mixture is obtained by the
addition of a defined amount of nitrogen to an oxidizing gas
containing oxygen, said addition of nitrogen being carried out
immediately before the gas mixture containing oxygen and nitrogen
is introduced into said torch, and the defined amount of nitrogen
is defined according to at least one parameter chosen from the
thickness of the workpiece, the grade of the constituent structural
steel of the workpiece, the desired work rate and the intensity of
the electric current.
2. A process for the plasma-arc working of at least one workpiece
made of stainless steel, in which: (a) a plasma torch is supplied
with an electric current and with a gas mixture containing oxygen
and nitrogen, (b) a plasma jet obtained by the ionization of at
least part of said gas mixture containing oxygen and nitrogen, by
said electric current is delivered by means of said plasma torch,
wherein: the concentration of oxygen in the gas mixture containing
oxygen and nitrogen is greater than 0% by volume and less than 25%
by volume, said gas mixture is obtained by the addition of a
defined amount of oxygen or of an oxidising gas containing oxygen
in nitrogen, said addition of oxygen being carried out immediately
before the gas mixture containing oxygen and nitrogen is introduced
into said torch, and the amount of oxygen or of oxidizing gas
containing oxygen is defined according to at least one parameter
chosen from the thickness of the workpiece, the grade of the
constituent stainless steel of the workpiece, the desired work rate
and the intensity of the electric current.
3. The process as claimed in either of claims 1 and 2, wherein the
plasma-arc work process is a plasma cutting or plasma marking,
preferably plasma cutting, process.
4. The process as claimed in one of claims 1 to 3, wherein the
concentration of nitrogen in the gas mixture containing oxygen and
nitrogen is between 10% by volume and 40% by volume, preferably
between 20% by volume and 40% by volume.
5. The process as claimed in either of claims 2 and 3, wherein the
concentration of oxygen in the gas mixture containing oxygen and
nitrogen is between 1% by volume and 22% by volume, preferably
between 5% by volume and 20% by volume.
6. The process as claimed in one of claims 1 to 5, wherein the
oxidizing gas is oxygen or compressed air, possibly dried and
stripped of oil droplets likely to be generated by compression,
preferably oxygen.
7. The process as claimed in one of claims 1 to 6, wherein the
addition of gas is carried out in at least one gas mixer,
preferably said gas mixer including means for controlling or
adjusting the content of the gas to be added.
8. The process as claimed in one of claims 1 to 7, wherein the
defined amount of gas to be added is defined according to the
thickness of the workpiece and to at least one parameter chosen
from the grade of the material, the desired work rate and the
intensity of the electric current.
9. The process as claimed in one of claims 1 to 8, wherein the
thickness of the workpiece is between 0.4 mm and 20 mm, the desired
work rate is between 0.5 m/min and 10 m/min, the intensity of the
current is between 10 A and 150 A and/or the grade of the
constituent material of the workpiece is chosen from 304 L or 316 L
stainless steels.
10. A unit for the plasma-arc working of at least one workpiece,
particularly one capable of implementing a process as claimed in
one of claims 1 to 9, which comprises: at least one plasma torch
(21) fastened to a support frame and able to move along at least
one axis of movement, at least one current generator (24) connected
to said torch (21), at least one source (25, 26) of oxidizing gas
containing oxygen, at least one nitrogen source (27), and at least
one gas mixer (28) supplied with oxidizing gas containing oxygen by
said at least one source (25, 26) of oxidizing gas and with
nitrogen by said at least one nitrogen source (27), said gas mixer
(28) including means for controlling or adjusting the concentration
of nitrogen and/or of oxidizing gas containing oxygen, so as to
obtain a gas mixture containing oxygen and nitrogen with a nitrogen
concentration in said gas mixture of greater than 0% by volume and
less than 50% by volume, or an oxygen concentration in said gas
mixture greater than 0% by volume and less than 25% by volume, the
amount of nitrogen or oxygen being defined according to at least
one parameter chosen from the thickness of the workpiece, the grade
of the constituent material of the workpiece, the desired work rate
and the intensity of the electric current.
Description
[0001] The present invention relates to a plasma-arc work process
using a plasma torch supplied with a gas mixture of an oxidizing
gas and nitrogen, the amount of one gas in the mixture with respect
to the other being defined according to one or more parameters
chosen from the thickness and/or the grade of the constituent
material of the workpiece, the desired work rate and the intensity
of the electric current.
[0002] A plasma-arc torch that can be used in a cutting, welding,
marking or spraying operation, or in any other heat-treatment
operation, on a metallic or nonmetallic material usually comprises
an electrode made of copper or of a copper alloy carrying a
cylindrical insert generally made of hafnium, tungsten or
zirconium, on which the electric arc serving to ionize the gas
feeding the torch takes root, that is to say the defined flow rate
of pressurized gas, called plasma gas, which is delivered between
the electrode and the nozzle and which flows out via an orifice of
said nozzle toward the workpiece.
[0003] The electrode is generally centered above this orifice for
ejecting the plasma jet, which is placed axially in the nozzle -and
which forms a constriction diaphragm.
[0004] In the particular case of a plasma cutting operation, the
plasma cutting device or system usually comprises a plasma torch, a
source of electric current, an electric-arc ignition system and one
or more sources of fluids, particularly of plasma gas, possibly of
shielding gas or of post-injected fluid, and of fluid for cooling
the torch, generally distilled water.
[0005] Such torches or units are well known to those skilled in the
art, since they have already been described in many documents to
which reference may be made for further details, especially
EP-A-599709, EP-A-872300, EP-A-801882, EP-A-941018, EP-A-144267,
EP-A-410875, EP-A-772957, EP-A-902606, EP-A-810052, EP-A-845929,
EP-A-790756, EP-A-196612, WO-A-89/11941, U.S. Pat. No. 4,521,666,
U.S. Pat. No. 4,059,743, U.S. Pat. No. 4,163,891 and U.S. Pat. No.
5,591,357.
[0006] In a known manner, plasma-arc cutting uses the thermal and
kinetic effects of a plasma jet to melt the material to be cut and
to expel the molten material from the kerf formed after the torch
has moved relative to the workpiece.
[0007] Moreover, it is also known that, in plasma cutting, the
plasma gas or gas mixture used is not the same depending on the
nature of the material to be cut.
[0008] Thus, a nonoxidizing gas, for example nitrogen, is generally
used for stainless steels or for light alloys, whereas it is
preferred to use an oxidizing gas, such as oxygen or air, for
cutting structural steels. However, in the case of structural
steels, even though compressed air has the advantage of being
simpler to use than oxygen, since a simple air compressor is
sufficient to supply the torch and there is therefore no need to
supply gas bottles, it is found that the air used as cutting gas
results in cut faces which are of inferior quality to those
obtained using oxygen, that is to say it results in the presence of
flash and of striations. Oxygen is therefore usually preferred for
this reason.
[0009] Moreover, the use of mixtures of nitrogen and oxygen in
proportions of about 30% nitrogen, as plasma gas, make it possible
to increase the cutting speed by about 20% with respect to pure
oxygen.
[0010] In addition, this same type of nitrogen/oxygen mixture used
as a dual flow enables, in some cases, the roughness of the cut
faces to be reduced.
[0011] However, this nitrogen/oxygen mixture is usually premixed,
that is to say manufactured according to the chosen contents,
before being used to fill suitable containers, such as gas bottles,
which are then taken to the operating site, that is to say the
point where the cutting has to be carried out.
[0012] Now, the fact that this type of nitrogen/oxygen mixture must
be premixed and contained in gas bottles poses a problem.
[0013] Thus, it will be understood that, when a nitrogen/oxygen
mixture has to be used with different nitrogen contents in the
oxygen in order to comply with several different cutting
applications or situations, it is necessary to store as many gas
bottles as desired contents, that is to say nitrogen/oxygen
mixtures having different nitrogen contents.
[0014] This therefore requires the use of a large stock of gas
bottles of different compositions suitable for the various
situations that might arise and also requires many bottle movements
and handling operations.
[0015] Under these conditions, it is essential to put into place
strict procedures for storing and handling each bottle, as well as
precise monitoring of the stocks in order to prevent any shortage
in terms of a particular gas mixture, something which is difficult
to manage and involves relatively large financial investment and
operating costs.
[0016] The object of the present invention is therefore to solve
these problems of bottle storage and movement while making it
easier to use mixtures of nitrogen and oxygen of different
contents.
[0017] In other words, the aim of the present invention is to
provide a plasma-arc work process using nitrogen/oxygen mixtures of
variable contents compatible with various arc-work situations,
particularly various material-cutting situations, while at the same
time maintaining or improving the cutting performance in terms of
rate, flash and/or roughness of the cut faces, and, more generally,
a plasma-arc work process using nitrogen/oxygen-containing gas
mixtures.
[0018] The present invention therefore relates to a process for the
plasma-arc working of at least one workpiece made of structural
steel, in which:
[0019] (a) a plasma torch is supplied with an electric current and
with a gas mixture containing oxygen and nitrogen,
[0020] (b) a plasma jet obtained by the ionization of at least part
of said gas mixture containing oxygen and nitrogen by said electric
current is delivered by means of said plasma torch, wherein:
[0021] the concentration of nitrogen in the gas mixture containing
oxygen and nitrogen is greater than 0% by volume and less than 50%
by volume,
[0022] said gas mixture is obtained by the addition of a defined
amount of nitrogen to an oxidizing gas containing oxygen, said
addition of nitrogen being carried out immediately before the gas
mixture containing oxygen and nitrogen is introduced into said
torch, and
[0023] the defined amount of nitrogen is defined according to at
least one parameter chosen from the thickness of the workpiece, the
grade of the constituent structural steel of the workpiece, the
desired work rate and the intensity of the electric current.
[0024] So-called "structural" steels are defined by the Comit
Europen de Normalisation [European Standardization Committee] as
belonging to the families of nonalloy steels, low-alloy steels or
high-alloy steels satisfying the EN 10025, EN 10113-2, EN 10113-3,
EN 10137-3 et seq. standards.
[0025] According to another aspect, the invention also relates to a
process for the plasma-arc working of at least one workpiece made
of stainless steel, in which:
[0026] (a) a plasma torch is supplied with an electric current and
with a gas mixture containing oxygen and nitrogen,
[0027] (b) a plasma jet obtained by the ionization of at least part
of said gas mixture containing oxygen and nitrogen by said electric
current is delivered by means of said plasma torch,
[0028] wherein:
[0029] the concentration of oxygen in the gas mixture containing
oxygen and nitrogen is greater than 0% by volume and less than 25%
by volume,
[0030] said gas mixture is obtained by the addition of a defined
amount of oxygen or of a gas containing oxygen in nitrogen, said
addition of oxygen being carried out immediately before the gas
mixture containing oxygen and nitrogen is introduced into said
torch, and
[0031] the amount of oxygen or of oxidizing gas containing oxygen
is defined according to at least one parameter chosen from the
thickness of the workpiece, the grade of the constituent stainless
steel of the workpiece, the desired work rate and the intensity of
the electric current.
[0032] Steels-called "stainless" steels belong, according to the
Comit Europen de Normalisation [European Standardization Committee]
to the family of alloy steels containing at least 11% chromium.
[0033] Depending on the case, the process of the invention may
include one or more of the following characteristics:
[0034] the plasma-arc work process is a plasma cutting or plasma
marking, preferably plasma cutting, process;
[0035] the grade of the constituent material of the workpiece is
chosen from structural steels and stainless steels;
[0036] the material making up the workpiece may or may not include
a surface coating such as of paint, zinc, aluminum or another
protective coating;
[0037] the process uses a plasma gas mixture adapted or adaptable
to the work to be carried out;
[0038] the concentration of nitrogen in the gas mixture containing
oxygen and nitrogen is between 10% by volume and 40% by volume,
preferably between 20% by volume and 40% by volume, for work on
structural steel;
[0039] the concentration of oxygen in the gas mixture containing
oxygen and nitrogen is between 1% by volume and 22% by volume,
preferably between 5% by volume and 20% by volume, for working on
stainless steels;
[0040] the oxidizing gas is oxygen or compressed air, which is
possibly dried and stripped of dust and of oil droplets liable to
be generated by compression, and preferably oxygen;
[0041] the addition of gas is carried out in at least one gas
mixer, preferably said gas mixer includes means for controlling or
adjusting the content of the gas to be added;
[0042] the amount of gas to be added is defined according to the
thickness of the workpiece and to at least one parameter chosen
from the grade of the material, the desired work rate and the
intensity of the electric current;
[0043] the thickness of the workpiece is between 0.4 mm and 20 mm,
preferably between 0.5 mm and 12 mm;
[0044] the desired work rate is between 0.5 and 10 m/min,
preferably between 1 and 5 m/min;
[0045] the intensity of the current is between 10 A and 150 A,
preferably between 15 and 120 A;
[0046] The invention also relates to a unit for the plasma-arc
working of at least one workpiece, particularly one capable of
implementing a process as mentioned above, which comprises:
[0047] at least one plasma torch fastened to a support frame and
able to move along at least one axis of movement,
[0048] at least one current generator connected to said torch,
[0049] at least one source of an oxidizing gas containing
oxygen,
[0050] at least one nitrogen source,
[0051] at least one gas mixer supplied with the oxidizing gas
containing oxygen by said at least one source of oxidizing gas and
with nitrogen by said at least one nitrogen source, said gas mixer
including means for controlling or adjusting the concentration of
nitrogen and/or of oxidizing gas containing oxygen, so as to obtain
a gas mixture containing oxygen and nitrogen with a nitrogen
concentration in said gas mixture greater than 0% by volume and
less than 50% by volume, or an oxygen concentration in said gas
mixture greater than 0% by volume and less than 25% by volume, the
amount of nitrogen or oxygen being defined according to at least
one parameter chosen from the thickness of the workpiece, the grade
of the constituent material of the workpiece, the desired work rate
and the intensity of the electric current,
[0052] the gas mixer is placed between said source of oxidizing gas
containing oxygen, said nitrogen source, and said torch,
[0053] means for controlling the flow rate and/or the pressure of
the gas mixture are placed between the outlet of the mixer and the
inlet of the torch.
[0054] By virtue of the present invention, it is possible, from
pure or substantially pure gases and because of the use of a means
of adding and controlling either the amount of nitrogen mixed into
the oxidizing gas, such as oxygen or compressed air, or the amount
of oxidizing gas, such as oxygen or compressed air, mixed into the
nitrogen to guarantee, in a plasma cutting machine, a controlled
content of each constituent of the nitrogen/oxygen mixture which is
adapted to each particular use or operation that has to be carried
out.
[0055] Precise control of the content of each constituent depending
on the type of application makes it possible to increase the plasma
cutting performance according to productivity and/or quality
criteria.
[0056] The nitrogen content in the oxygen or the oxygen content in
the nitrogen is controlled automatically by an external control
depending on several parameters, such as the thickness of the
sheet, the intensity of the current, the grade of material to be
cut, the cutting rate, etc.
[0057] FIG. 1 appended hereto shows schematically the operation of
the active part of a plasma torch of the dual-flow type, shown
during an operation of cutting a sheet 11.
[0058] The plasma torch includes an electrode 1 where the electric
arc serving to ionize the gas feeding the torch, that is to say the
defined flow of pressurized plasma gas, which is delivered and
flows into the plasma chamber 3 located between the electrode 1 and
the nozzle 2, takes root. The plasma jet 10 is expelled from the
plasma chamber 3 via an orifice made in the nozzle 2 toward the
sheet 11 to be cut. The electrode 1 is centered above the
plasma-jet ejection orifice made axially in the nozzle 2 and
forming a constriction orifice.
[0059] The plasma torch is supplied with electric current by an
electric current source 5 connected to an electric arc ignition
system 6 allowing a leading arc to be struck between the nozzle 2
and the electrode 1.
[0060] FIG. 1 also shows that the torch is of the dual-flow type,
that is to say it has a peripheral second nozzle 4 forming a sleeve
around the nozzle 2 and that a shielding gas flows through the
inter-nozzle space 7 until it reaches the region of space lying
between the end of the nozzle 2 and the upper surface of the sheet
11. The nozzle 2 is cooled by a coolant, such as distilled water,
circulating in a cooling chamber 8.
[0061] As regards FIG. 2, this shows schematically a plasma cutting
unit, seen from the front, comprising schematically at least one
plasma cutting torch 21, operating as explained above and
illustrated in FIG. 1, fixed to at least one motorized shaft 22 for
relative movement of said torch 21 with respect to the workpiece
11, that is to say the sheet to be cut.
[0062] As may be seen in FIG. 3, which is a top view of the unit in
FIG. 2, the plasma cutting torch 21 is connected to a current
generator 24.
[0063] The unit also includes means of connection, of distribution
and of information exchange between said current generator 24, the
torch 21 and said movement shaft.
[0064] A supply source 25 of oxidizing gas, such as oxygen, or a
compressed-air compressor 26 and a nitrogen supply source 27 allow
the torch 21 to be supplied with the cutting gas.
[0065] Between said gas sources 25, 26, 27 and the plasma cutting
torch, there is a gas mixer 28 which receives, on the one hand, the
oxidizing gas and the nitrogen and delivers, on the other hand, the
plasma gas mixture to said torch 21 in the required mixture
proportions, that is to say having a nitrogen and oxygen content
controlled according to the present invention.
[0066] The mixer 28 is provided with means for controlling the
content of one gas in the other, for example by controlling or
adjusting the nitrogen content.
[0067] Additional means 29 for controlling the flow rate and/or
pressure, for example an expansion valve or a mass flow rate
regulator, are preferably inserted between the outlet of the mixer
28 and the torch 21.
[0068] Such a unit may furthermore include means 30 for cooling the
torch 21, means for managing the work cycles and means 31 for
programming and managing the movements of said at least one
movement shaft.
[0069] By using such a unit, the content of one gas in the other,
for example nitrogen in oxygen, is controlled so as to optimize the
cutting performance in terms of productivity (increase in cutting
speed) and/or in terms of quality (decrease in flash, roughness or
taper) of the cut faces.
[0070] Thus, depending on the grade of steel or of the material
that has to be cut, and/or on its thickness, oxygen having a
controlled nitrogen content of strictly between 0 and 50% or,
depending on the use, nitrogen having a nonzero and controlled
oxygen content of between 0 and 20%, will be used.
[0071] In order to verify the effectiveness of the process of the
invention, measurements were made according to the DIN 2310
standard and the results are given in FIG. 4.
[0072] A comparison was made regarding the cutting speed, the
roughness and the maximum deviation of the cut face from the
vertical, according to various nitrogen/oxygen mixture
concentrations.
[0073] By way of example, according to the present invention, a
mixture containing 30% nitrogen in oxygen makes it possible either
to increase the cutting speed without increasing the taper or to
decrease the taper for a constant speed.
[0074] Likewise, depending on the thickness of the sheet, the
presence of the nitrogen in the oxygen makes it possible to reduce
the flash or the roughness of the cut faces
1TABLE Ni- Thick- Sheet trogen Oxygen Current ness Speed made of
(%) (%) (A) (mm) Grade (m/min) Stain- 100 to 0 to 20 15 to 120 0 to
20 304 L 1 to 5 less 80 316 L steel Carbon 0 to 50 100 to 50 15 to
120 0 to 15 E24 1 to 5 steel
[0075] The plasma cutting process according to the invention, in
which a mixer allows various types of gas mixtures with controlled
contents to be produced from pure gases or from compressed air, can
be used by any type of plasma cutting unit, whether manual or
automatic, so as to optimize the cutting performance in terms of
productivity and/or quality according to the grade of the
material.
[0076] The invention has been described above in relation to a
plasma cutting torch, but, of course, the application of this
invention is not limited to only cutting torches and relates,
entirely or partly, to marking, welding and spraying torches and,
in general, to any torch for the heat treatment of metallic or
non-metallic materials.
[0077] Furthermore, the invention has the advantages of resulting
in a higher speed and a higher productivity when cutting structural
steels and in a higher quality of the cut for stainless steels,
that is to say of obtaining cut edges with substantially no flash
or taper.
* * * * *