U.S. patent application number 11/468393 was filed with the patent office on 2008-11-06 for plasma torch electrode with improved insert configurations.
This patent application is currently assigned to Hypertherm, Inc.. Invention is credited to David L. Bouthillier, David J. Cook, Stephen T. Eickhoff, Jonathan P. Mather, John Sobr.
Application Number | 20080272094 11/468393 |
Document ID | / |
Family ID | 37398690 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080272094 |
Kind Code |
A9 |
Mather; Jonathan P. ; et
al. |
November 6, 2008 |
PLASMA TORCH ELECTRODE WITH IMPROVED INSERT CONFIGURATIONS
Abstract
An improved electrode for use in a plasma arc torch. The
electrode includes an electrode body, a bore defined by and
disposed in the electrode body, and an insert disposed in the bore.
The insert and/or the bore of the electrode are configured to
improve retention of the insert in the electrode, thereby extending
electrode life. The invention also includes a method for forming
the electrode. The method includes a step of positioning an insert
into a bore of an electrode such that an exterior gap is
established that is greater than a second gap.
Inventors: |
Mather; Jonathan P.;
(Cornish Flat, NH) ; Cook; David J.; (Bradford,
VT) ; Bouthillier; David L.; (Hartford, VT) ;
Sobr; John; (Lebanon, NH) ; Eickhoff; Stephen T.;
(Hanover, NH) |
Correspondence
Address: |
PROSKAUER ROSE LLP
ONE INTERNATIONAL PLACE
BOSTON
MA
02110
US
|
Assignee: |
Hypertherm, Inc.
Hanover
NH
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20070125755 A1 |
June 7, 2007 |
|
|
Family ID: |
37398690 |
Appl. No.: |
11/468393 |
Filed: |
August 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60714581 |
Sep 7, 2005 |
|
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Current U.S.
Class: |
219/121.52 |
Current CPC
Class: |
H05H 1/34 20130101; H05H
2001/3442 20130101 |
Class at
Publication: |
219/121.52 |
International
Class: |
B23K 9/00 20060101
B23K009/00 |
Claims
1. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including a closed end and an
open end, the bore defining at least a first and a second dimension
each transverse to the longitudinal axis, the second dimension
being closer to the closed end of the bore than the first
dimension; and an insert formed of a high thermionic emissivity
material disposed in the bore, the insert including an exterior end
disposed near the open end of the bore and a contact end disposed
near the closed end of the bore, the insert defining at least a
first and a second dimension each transverse to the longitudinal
axis, the second dimension being closer to the closed end of the
bore than the first dimension; wherein at least one of the second
dimension of the bore is greater than the first dimension of the
bore, or the second dimension of the insert is greater than the
first dimension of the insert.
2. The electrode of claim 1, wherein the electrode further
comprises a sleeve disposed between the insert and the bore.
3. The electrode of claim 1, wherein the second dimension
corresponds to an annular notch.
4. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including a first portion, a
second portion, and a third portion, the first portion including an
outer open end of the bore, the third portion including an inner
open end of the bore, the second portion of the bore defining at
least a first and a second dimension each transverse to the
longitudinal axis, the second dimension being closer to the third
portion of the bore than the first dimension; and an insert formed
of a high thermionic emissivity material disposed in the bore, the
insert including a first portion, a second portion, and a third
portion, the first portion including an exterior end disposed near
the outer open end of the bore, the third portion including an end
disposed near the inner open end of the bore, the insert defining
at least a first and a second dimension each transverse to the
longitudinal axis, the second dimension being closer to the third
portion of the insert than the first dimension; wherein at least
one of the second dimension of the bore is greater than the first
dimension of the bore, or the second dimension of the insert is
greater than the first dimension of the insert.
5. The electrode of claim 4, wherein the electrode further
comprises a sleeve disposed between the insert and the bore.
6. The electrode of claim 4, wherein the second dimension
corresponds to an annular notch.
7. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including a first end and a
second end, the first end of the bore including an open end of the
bore; and an insert formed of a high thermionic emissivity material
and disposed in the bore, the insert having a longitudinal length
and including: a first end portion including an exterior end
surface disposed near the open end of the bore, a longitudinal
length of the first end portion being no more than about 10% of the
longitudinal length of the insert; a second end portion, a
longitudinal length of the second end portion being no more than
about 20% of the longitudinal length of the insert; a first portion
between the first and the second end portions, the first portion
defining a first dimension transverse to the longitudinal axis, the
first portion including a first exterior surface; a second portion
between the first and the second end portions, the second portion
defining a second dimension transverse to the longitudinal axis and
including a second exterior surface, wherein the first dimension is
greater than the second dimension; and wherein a first angle of a
tangent to the first exterior surface with respect to the
longitudinal axis and a second angle of a tangent to the second
exterior surface with respect to the longitudinal axis differ by at
least 3 degrees.
8. The electrode of claim 7, wherein the longitudinal length of the
first end portion is no more than about 2% of the longitudinal
length of the insert.
9. The electrode of claim 7, wherein the longitudinal length of the
second end portion is no more than about 10% of the longitudinal
length of the insert.
10. The electrode of claim 7, wherein the high thermionic
emissivity material of the insert is hafnium or zirconium, or
tungsten, or thorium or lanthanum or strontium or alloys
thereof.
11. The electrode of claim 7, wherein the high thermal conductivity
material of the electrode body is copper or a copper alloy.
12. The electrode of claim 7, wherein a central portion of the bore
comprises at least two substantially cylindrical portions.
13. The electrode of claim 7, wherein a central body portion of the
insert comprises at least two substantially cylindrical
portions.
14. The electrode of claim 7, wherein at least one of a central
portion of the bore and a central body portion of the insert is
substantially cylindrical.
15. The electrode of claim 7, wherein the bore comprises an annular
extension.
16. The electrode of claim 7, wherein the insert comprises a flared
head.
17. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including an open end and a
closed end; and an insert formed of a high thermionic emissivity
material disposed in the bore, the insert comprising: a first
exterior surface exerting a first force against a first surface of
the bore; and a second exterior surface exerting a second force
against a second surface of the bore, the second force being
greater than the first force, and the second surface of the bore
being longitudinally closer to the closed end of the bore than the
first surface of the bore.
18. The electrode of claim 17, wherein the high thermionic
emissivity material of the insert is hafnium or zirconium.
19. The electrode of claim 17, wherein the high thermal
conductivity material of the electrode body is copper or a copper
alloy.
20. The electrode of claim 17, wherein the electrode further
comprises a sleeve disposed between the insert and the electrode
body.
21. The electrode of claim 17, wherein the sleeve is silver.
22. The electrode of claim 17, wherein a central portion of the
bore comprises at least two substantially cylindrical portions.
23. The electrode of claim 17, wherein a central body portion of
the insert comprises at least two substantially cylindrical
portions.
24. The electrode of claim 17, wherein at least one of a central
portion of the bore and a central body portion of the insert is
substantially cylindrical.
25. The electrode of claim 17, wherein the bore comprises an
annular extension.
26. The electrode of claim 17, wherein the insert comprises a
flared head.
27. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including a first portion, a
second portion, and a third portion, the first portion defining an
outer open end of the bore, the third portion defining an inner
open end of the bore; and an insert formed of a high thermionic
emissivity material disposed in the bore, the insert comprising: a
first exterior surface exerting a first force against a first
surface of the second portion of the bore; and a second exterior
surface exerting a second force against a second surface of the
second portion of the bore, the second force being greater than the
first force, and the second surface of the bore being
longitudinally closer to the third portion of the bore than the
first surface of the bore.
28. The electrode of claim 27, wherein the high thermionic
emissivity material of the insert is hafnium or zirconium.
29. The electrode of claim 27, wherein the high thermal
conductivity material of the electrode body is copper or a copper
alloy.
30. The electrode of claim 27, wherein the electrode further
comprises a sleeve disposed between the insert and the electrode
body.
31. The electrode of claim 27, wherein the sleeve is silver.
32. The electrode of claim 27, wherein a central portion of the
bore comprises at least two substantially cylindrical portions.
33. The electrode of claim 27, wherein a central body portion of
the insert comprises at least two substantially cylindrical
portions.
34. The electrode of claim 27, wherein at least one of a central
portion of the bore and a central body portion of the insert is
substantially cylindrical.
35. The electrode of claim 27, wherein the bore comprises an
annular extension.
36. The electrode of claim 27, wherein the insert comprises a
flared head.
37. An electrode for a plasma arc torch, the electrode comprising:
an electrode body formed of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; a bore defined by and disposed in the first
end of the electrode body, the bore including an open end and a
closed end; a projection disposed on a surface of the bore, the
surface of the bore located away from the open end; and an insert
formed of a high thermionic emissivity material disposed in the
bore, a contact surface of the insert surrounding at least a
portion of the projection to secure the insert in the bore.
38. The electrode of claim 37, wherein the projection is disposed
at or near the closed end of the bore, the projection extending
partially towards the open end.
39. The electrode of claim 37, wherein the projection comprises
barbs, grooves, or notches.
40. The electrode of claim 37, wherein the projection is not
integrally formed with the electrode body or the insert.
41. The electrode of claim 37, wherein the projection is
substantially symmetrical about the longitudinal axis.
42. The electrode of claim 37, wherein the contact surface is a
contact end of the insert.
43. A method for fabricating an electrode having an emissive insert
for use in plasma arc torches, the method comprising the steps of:
forming an electrode body of a high thermal conductivity material,
the electrode body including a first end and a second end defining
a longitudinal axis; forming a bore in the first end, the bore
including a first portion and a second portion; positioning an
insert formed of a high thermionic emissivity material in the bore,
the insert including a contact end and an exterior end; aligning
the contact end of the insert with the second portion of the bore
and the exterior end with the first portion of the bore, such that
a first gap is established between a first exterior surface of the
insert and the first portion, and a second gap is established
between a second exterior surface of the insert and the second
portion of the bore, such that the first gap is substantially
greater than the second gap; and applying a force at the exterior
end of the insert to secure the insert in the bore.
44. The method of claim 43, wherein the bore further comprises a
third portion defining a second open end of the bore, the second
portion of the bore located between the first and third portions of
the bore.
45. The method of claim 43, wherein the second portion of the bore
defines a closed end of the bore.
46. The method of claim 43, wherein the first gap is nearer the
open end of the bore than the second gap.
47. The method of claim 43, wherein the first gap is nearer the
closed end/second portion of the bore than the second gap.
48. The method of claim 43, wherein the applied force is a
longitudinal force applied at the exterior end of the insert that
reduces the gap.
49. The method of claim 43, wherein the applied force is a
compressive force that compresses the open end of the bore about
the insert.
50. The method of claim 43, further comprising the step of
positioning a sleeve formed of a second material in the bore before
the force is applied, and the first gap is disposed between a
surface of the sleeve and the first exterior surface of the
insert.
51. A plasma arc torch comprising: a torch body; a nozzle within
the torch body; a shield disposed adjacent the nozzle, the shield
protecting the nozzle from workpiece splatter; an electrode mounted
relative to the nozzle in the torch body to define a plasma
chamber, the electrode comprising an electrode body formed of a
high thermal conductivity material, the electrode body including a
first end and a second end defining a longitudinal axis; a bore
defined by and disposed in the first end of the electrode body, the
bore including a closed end and an open end, the bore defining at
least a first and a second dimension each transverse to the
longitudinal axis, the second dimension being closer to the closed
end of the bore than the first dimension; and an insert formed of a
high thermionic emissivity material disposed in the bore, the
insert including an exterior end disposed near the open end of the
bore and a contact end disposed near the closed end of the bore,
the insert defining at least a first and a second dimension each
transverse to the longitudinal axis, the second dimension being
closer to the closed end of the bore than the first dimension;
wherein at least one of the second dimension of the bore is greater
than the first dimension of the bore, or the second dimension of
the insert is greater than the first dimension of the insert.
Description
RELATED APPLICATIONS
[0001] This application claims priority to and benefit of U.S.
provisional patent application Ser. No. 60/714,581, filed on Sep.
7, 2005, the entire contents of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The invention generally relates to the field of plasma arc
torch systems and processes. More specifically, the invention
relates to improved insert configurations in electrodes for use in
a plasma arc torch, and methods of manufacturing such
electrodes.
BACKGROUND OF THE INVENTION
[0003] Plasma arc torches are widely used in the high temperature
processing (e.g., cutting, welding, and marking) of metallic
materials. As shown in FIG. 1A, a plasma arc torch generally
includes a torch body 1, an electrode 2 mounted within the body, an
insert 3 disposed within a bore of the electrode 2, a nozzle 4 with
a central exit orifice, a shield 5, electrical connections (not
shown), passages for cooling and arc control fluids, a swirl ring
to control the fluid flow patterns, and a power supply (not shown).
The torch produces a plasma arc, which is a constricted ionized jet
of a plasma gas with high temperature and high momentum. A gas can
be non-reactive, e.g. nitrogen or argon, or reactive, e.g. oxygen
or air.
[0004] In the process of plasma arc cutting or marking a metallic
workpiece, a pilot arc is first generated between the electrode
(cathode) and the nozzle (anode). The pilot arc ionizes gas that
passes through the nozzle exit orifice. After the ionized gas
reduces the electrical resistance between the electrode and the
workpiece, the arc then transfers from the nozzle to the workpiece.
Generally the torch is operated in this transferred plasma arc
mode, which is characterized by the conductive flow of ionized gas
from the electrode to the workpiece, for the cutting, welding, or
marking the workpiece.
[0005] In a plasma arc torch using a reactive plasma gas, it is
known to use a copper electrode with an insert of high thermionic
emissivity material. FIGS. 1B-1D illustrate a known method for
inserting and securing an insert into the bore of an electrode.
FIG. 1B illustrates an insert 10 being pressed 15 into a bore in
the end of an electrode body 12. FIG. 1C illustrates the secured
insert 11 pressed 15 flush with the end surface 19 of the electrode
body 12, and presents a diagrammatic representation of the
resultant lateral forces securing the insert 11 in the electrode
body 12. These resultant forces are thought to be greater near the
exposed end of the insert due to surface friction from the
expanding insert. When assembling inserts of known configuration
into straight-walled bores, the insert tends to expand radially
more near the top of the bore than at the closed end of the bore,
tending to produce a wedge shape. A radial bulge sometimes forms
near the open end of the bore 14. This tapered bulge is not
unexpected since the insert is pressed only from the exposed end.
During pressing, once the bore is essentially filled with the
insert and can longer accept more insert material, any remaining
insert material pressed in from the open end of the bore tends to
form a bulge at the open end of the bore where the hoop strength of
the electrode body is not as great. The resulting configuration
initially secures the insert, but any movement of the insert
towards the opening of the bore significantly reduces the surface
contact and retention force of the insert. FIG. 1D illustrates a
secured insert 17 in a through-hole configuration of the bore,
where 19 is a volume defined by the inner surface of the electrode
body 16. The insert 17 is pressed from both sides in this
configuration, where the force 18 can be supplied from an anvil or
mandrel pressed into the volume 19, for installation of the insert.
Electrode bodies of the through-hole type 19 are also known to have
linear-tapered walls, i.e., straight walls at an angle with a
central longitudinal axis, with linear-tapered inserts shaped to
match.
[0006] The insert has an exterior, or exposed, end face, which
defines an emissive surface area. The exterior surface of the
insert is generally planar, and is manufactured to be coplanar with
the end face of the electrode. The end face of the electrode is
typically planar, although it can have exterior curved surfaces,
e.g., edges. It is known to make the insert of hafnium or
zirconium. They generally have a cylindrical shape. Insert
materials (e.g., hafnium) can be expensive.
[0007] During the operation of plasma arc torch electrodes, torch
conditions such as temperature gradients and dynamics work to
reduce the retention force holding the insert in place and either
allow the insert to move in the bore or to fall completely out of
the bore, thereby reducing the service life of the electrode or
causing it to completely fail. The movement of the insert also
indicates that the insert to electrode interface has degraded,
which reduces the thermal and electrical conductivity of the
interface and thereby the service life of the electrode as well. In
addition, insert materials (e.g., hafnium) are poor thermal
conductors for the removal of heat produced by the plasma arc,
which can produce temperatures in excess of 10,000 degrees C.
Insufficient removal of heat resulting from these high temperatures
can result in a decrease in the service life of the electrode.
[0008] What is needed is an electrode with improved retention of
the insert within the bore. A first object of the invention is to
provide an electrode with improved retention of an insert,
increasing the thermal conductivity of the interface between insert
and electrode, and the efficiency and service life of the
electrode. It is another object of the invention to provide an
electrode with an insert configuration that improves the cooling,
and therefore the service life, of the insert. It is yet another
object of the invention to provide an electrode with an insert
configuration that minimizes the amount of insert material
required, thereby reducing the cost of the electrode while at the
same time not lessening the efficiency and service life of the
electrode. Yet another object of the invention is to provide an
electrode with a longer service life.
SUMMARY OF THE INVENTION
[0009] The present invention achieves these objectives by using
electrode bore and/or insert configurations to establish retention
forces located near an interior (e.g. a contact end or a central
portion) of the insert or an interior (e.g., a closed end or a
central portion) of the bore to secure the insert in the electrode.
The present invention also allows the size of the insert to be
minimized, thereby reducing insert raw material costs and improving
electrode cooling.
[0010] One aspect of the invention features an electrode for a
plasma arc torch, the electrode including an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes a closed end and an open end. The bore
defines at least a first and a second dimension each transverse to
the longitudinal axis, wherein the second dimension is closer to
the closed end of the bore than the first dimension. The electrode
also includes an insert formed of a high thermionic emissivity
material disposed in the bore. The insert includes an exterior end
disposed near the open end of the bore and a contact end disposed
near the closed end of the bore. The insert defines at least a
first and a second dimension each transverse to the longitudinal
axis, wherein the second dimension is closer to the closed end of
the bore than the first dimension. The second dimension of the bore
is greater than the first dimension of the bore, or the second
dimension of the insert is greater than the first dimension of the
insert. In some embodiments, the electrode further comprises a
sleeve disposed between the insert and the bore. The second
dimension can correspond to an annular notch.
[0011] Another aspect of the invention features an electrode for a
plasma arc torch, the electrode including an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes a first portion, a second portion, and a
third portion, wherein the first portion includes an outer open end
of the bore and the third portion includes an inner open end of the
bore. The second portion of the bore defines at least a first and a
second dimension each transverse to the longitudinal axis, wherein
the second dimension is closer to the third portion of the bore
than the first dimension. The electrode also includes an insert
formed of a high thermionic emissivity material disposed in the
bore. The insert includes a first portion, a second portion, and a
third portion. The first portion includes an exterior end disposed
near the outer open end of the bore and the third portion includes
an end disposed near the inner open end of the bore. The insert
defines at least a first and a second dimension each transverse to
the longitudinal axis, wherein the second dimension is closer to
the third portion of the insert than the first dimension. The
second dimension of the bore is greater than the first dimension of
the bore, or the second dimension of the insert is greater than the
first dimension of the insert. In some embodiments, the electrode
further comprises a sleeve disposed between the insert and the
bore. The second dimension can correspond to an annular notch.
[0012] Another aspect of the invention features an electrode for a
plasma arc torch. The electrode includes an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes a first end and a second end. The first end
of the bore includes an open end of the bore. The electrode also
includes an insert formed of a high thermionic emissivity material
disposed in the bore. The insert has a longitudinal length and
includes a first end portion, a second end portion, a first portion
between the first and the second end portions, and a second portion
between the first and the second end portions. The first end
portion includes an exterior end surface disposed near the open end
of the bore, and a longitudinal length of the first end portion
being no more than about 10% of the longitudinal length of the
insert. The second end portion includes a longitudinal length of
the second end portion being no more than about 20% of the
longitudinal length of the insert. The first portion defines a
first dimension transverse to the longitudinal axis, and includes a
first exterior surface. The second portion defines a second
dimension transverse to the longitudinal axis and includes a second
exterior surface, wherein the first dimension is greater than the
second dimension. A first angle of a tangent to the first exterior
surface with respect to the longitudinal axis and a second angle of
a tangent to the second exterior surface with respect to the
longitudinal axis differ by at least 3 degrees. In some
embodiments, the longitudinal length of the first end portion is no
more than about 2% of the longitudinal length of the insert and/or
the longitudinal length of the second end portion is no more than
about 10% of the longitudinal length of the insert. The high
thermionic emissivity material of the insert can be hafnium or
zirconium, or tungsten, or thorium or lanthanum or strontium or
alloys thereof. The high thermal conductivity material of the
electrode body can be copper or a copper alloy. A central portion
of the bore can include at least two substantially cylindrical
portions. A central body portion of the insert can include at least
two substantially cylindrical portions. At least one of a central
portion of the bore and a central body portion of the insert can be
substantially cylindrical. The bore can comprise an annular
extension. The insert can comprise a flared head.
[0013] Another aspect of the invention features an electrode for a
plasma arc torch. The electrode includes an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes an open end and a closed end. The electrode
also includes an insert formed of a high thermionic emissivity
material disposed in the bore. The insert comprises a first
exterior surface exerting a first force against a first surface of
the bore, and a second exterior surface exerting a second force
against a second surface of the bore. The second force is greater
than the first force, and the second surface of the bore is
longitudinally closer to the closed end of the bore than the first
surface of the bore. In some embodiments, the high thermionic
emissivity material of the insert can be hafnium or zirconium. The
high thermal conductivity material of the electrode body can be
copper or a copper alloy. The electrode can further comprise a
sleeve disposed between the insert and the electrode body. The
sleeve can be silver. A central portion of the bore can include at
least two substantially cylindrical portions. A central body
portion of the insert can include at least two substantially
cylindrical portions. At least one of a central portion of the bore
and a central body portion of the insert can be substantially
cylindrical. The bore can comprise an annular extension. The insert
can include a flared head.
[0014] Another aspect of the invention features an electrode for a
plasma arc torch. The electrode includes an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes a first portion, a second portion, and a
third portion. The first portion defines an outer open end of the
bore. The third portion defines an inner open end of the bore. The
electrode also includes an insert formed of a high thermionic
emissivity material disposed in the bore. The insert comprises a
first exterior surface exerting a first force against a first
surface of the second portion of the bore, and a second exterior
surface exerting a second force against a second surface of the
second portion of the bore. The second force is greater than the
first force, and the second surface of the bore is longitudinally
closer to the third portion of the bore than the first surface of
the bore. In some embodiments, the high thermionic emissivity
material of the insert can be hafnium or zirconium. The high
thermal conductivity material of the electrode body can be copper
or a copper alloy. The electrode further can comprise a sleeve
disposed between the insert and the electrode body. The sleeve can
be silver. A central portion of the bore can include at least two
substantially cylindrical portions. A central body portion of the
insert can include at least two substantially cylindrical portions.
At least one of a central portion of the bore and a central body
portion of the insert can be substantially cylindrical. The bore
can comprise an annular extension. The insert can include a flared
head.
[0015] Another aspect of the invention features an electrode for a
plasma arc torch. The electrode includes an electrode body formed
of a high thermal conductivity material. The electrode body
includes a first end and a second end defining a longitudinal axis.
A bore is defined by and disposed in the first end of the electrode
body. The bore includes an open end and a closed end. A projection
is disposed on a surface of the bore. The surface of the bore is
located away from the open end. The electrode also includes an
insert formed of a high thermionic emissivity material disposed in
the bore. A contact surface of the insert surrounds at least a
portion of the projection to secure the insert in the bore. In some
embodiments, the projection can be disposed at or near the closed
end of the bore, wherein the projection extends partially towards
the open end. The projection can comprise barbs, grooves, or
notches. The projection can be not integrally formed with the
electrode body or the insert. The projection can be substantially
symmetrical about the longitudinal axis. The contact surface can be
a contact end of the insert.
[0016] Another aspect of the invention features a method for
fabricating an electrode having an emissive insert for use in
plasma arc torches. The method includes the step of forming an
electrode body of a high thermal conductivity material, wherein the
electrode body includes a first end and a second end defining a
longitudinal axis. A bore is formed in the first end, wherein the
bore includes a first portion and a second portion. An insert
formed of a high thermionic emissivity material is positioned in
the bore, the insert including a contact end and an exterior end.
The contact end of the insert is aligned with the second portion of
the bore, and the exterior end is aligned with the first portion of
the bore, such that a first gap is established between a first
exterior surface of the insert and the first portion, and a second
gap is established between a second exterior surface of the insert
and the second portion of the bore. The first gap is substantially
greater than the second gap. A force is applied at the exterior end
of the insert to secure the insert in the bore. In some
embodiments, the bore can further comprise a third portion defining
a second open end of the bore, wherein the second portion of the
bore is located between the first and third portions of the bore.
The second portion of the bore can define a closed end of the bore.
The first gap can be nearer the open end of the bore than the
second gap. The first gap can be nearer the closed end/second
portion of the bore than the second gap. The applied force can be a
longitudinal force applied at the exterior end of the insert that
reduces the gap. The applied force can be a compressive force that
compresses the open end of the bore about the insert. The method
can further comprise the step of positioning a sleeve formed of a
second material in the bore before the force can be applied,
wherein the first gap can be disposed between a surface of the
sleeve and the first exterior surface of the insert.
[0017] Another aspect of the invention features a plasma arc torch
including a torch body, a nozzle within the torch body, a shield
disposed adjacent the nozzle, and an electrode mounted relative to
the nozzle in the torch body to define a plasma chamber. The shield
protects the nozzle from workpiece splatter. The electrode
comprises an electrode body formed of a high thermal conductivity
material. The electrode body includes a first end and a second end
defining a longitudinal axis. A bore is defined by and disposed in
the first end of the electrode body. The bore includes a closed end
and an open end. The bore defines at least a first and a second
dimension each transverse to the longitudinal axis, wherein the
second dimension is closer to the closed end of the bore than the
first dimension. The electrode also includes an insert formed of a
high thermionic emissivity material disposed in the bore. The
insert includes an exterior end disposed near the open end of the
bore and a contact end disposed near the closed end of the bore.
The insert defines at least a first and a second dimension each
transverse to the longitudinal axis, wherein the second dimension
is closer to the closed end of the bore than the first dimension.
The second dimension of the bore is greater than the first
dimension of the bore, or the second dimension of the insert is
greater than the first dimension of the insert.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing discussion will be understood more readily
from the following detailed description of the invention, when
taken in conjunction with the accompanying drawings, in which:
[0019] FIG. 1A is a partial cross-sectional view of a known plasma
arc torch;
[0020] FIG. 1B is a partial cross-sectional view of a plasma arc
torch electrode illustrating a known method for inserting an insert
into an electrode bore;
[0021] FIG. 1C is a partial cross-sectional view of a plasma arc
torch electrode illustrating a known method for securing an insert
into an electrode bore;
[0022] FIG. 1D is a partial cross-sectional view of a plasma arc
torch electrode illustrating a known method for securing an insert
into an electrode bore with a through-hole configuration;
[0023] FIGS. 2A-2C are partial cross-sectional views of a plasma
arc torch electrode configuration illustrating intermediate steps
of a method for securing an insert into an electrode bore
incorporating principles of the present invention;
[0024] FIGS. 2D-2F are partial cross-sectional views of a plasma
arc torch electrode configuration illustrating intermediate steps
of a method for securing an insert into an electrode bore
incorporating principles of the present invention;
[0025] FIGS. 3A-3C are partial cross-sectional views of different
plasma arc torch electrode bore configurations;
[0026] FIGS. 4A-4D are partial cross-sectional views of plasma arc
torch electrode and insert configurations;
[0027] FIGS. 5A-5F are partial cross-sectional views of plasma arc
torch insert configurations;
[0028] FIG. 6A is a partial cross-sectional view of a plasma arc
torch electrode configuration illustrating a method for securing an
insert into an electrode bore;
[0029] FIG. 6B is a partial cross-sectional view of a plasma arc
torch electrode configuration comprising an insert secured in the
electrode bore;
[0030] FIG. 6C is a partial cross-sectional view of a plasma arc
torch electrode configuration comprising an insert secured in the
electrode bore with a through-hole configuration;
[0031] FIG. 7 is another partial cross-sectional view of a plasma
arc torch electrode and insert configuration comprising a
projection in the bore of the electrode;
[0032] FIG. 8 is a partial cross-sectional view of a plasma arc
torch electrode and insert configuration comprising an insert
sleeve;
[0033] FIG. 9 is a partial cross-sectional view of plasma arc torch
electrode and insert configuration comprising an insert ball;
[0034] FIG. 10 is a partial cross-sectional view of plasma arc
torch electrode and insert configuration comprising a cross-drilled
hole;
[0035] FIGS. 11A-11B are partial cross-sectional view of a plasma
arc torch electrode and insert configurations;
[0036] FIG. 12A is a partial cross-sectional view of a plasma arc
torch electrode configuration illustrating a method for securing an
insert into an electrode bore;
[0037] FIG. 12B is a partial cross-sectional view of a plasma arc
torch electrode configuration having an insert secured in an
electrode bore according to the method of FIG. 12A;
[0038] FIG. 13 is a partial cross-sectional view of a plasma arc
torch electrode configuration comprising an annular lip and an
insert configuration comprising a flared head configuration;
[0039] FIGS. 14A-14B are partial cross-sectional views illustrating
a method of forming an electrode incorporating principles of the
present invention; and
[0040] FIGS. 15A-15B are partial cross-sectional views illustrating
central portions of inserts disposed in electrodes.
DETAILED DESCRIPTION
[0041] Reference will now be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
figures. Each embodiment described or illustrated herein is
presented for purposes of explanation of the invention, and not as
a limitation of the invention. For example, features illustrated or
described as part of one embodiment can be used with another
embodiment to yield still a further embodiment. It is intended that
the present invention include these and other modifications and
variations as further embodiments.
[0042] FIGS. 2A-2B illustrate an exemplary method for securing an
insert into an electrode bore and the resulting electrode
configuration incorporating principles of the present invention.
The electrode body 22 comprises a bore in which an insert is to be
secured. The bore can include two substantially cylindrical
portions, wherein a portion defining the closed end has a diameter
smaller than the portion defining the open end of the bore. This
discontinuity in diameters can define a step surface 26, which can
be located anywhere along the length of the bore. A substantially
cylindrical insert 20 with a diameter slightly less than the
diameter of the closed end portion of the bore is illustrated. FIG.
2A illustrates an initial configuration of the electrode after a
substantially cylindrical insert 200 has been placed in the bore of
electrode body 22. The diameter of the insert can be smaller than
both diameters of the bore to provide a gap such that the insert
200 can easily fit in the bore. In the situation illustrated, the
gap between the insert 200 and the electrode 22 is greater for the
open-end cylindrical portion than the gap for the closed-end
cylindrical portion. In situations wherein the diameter of the
insert is formed to be virtually indistinguishable from the
diameter of the closed-end cylindrical portion of the bore, a gap
between the insert and the bore around this portion can be small or
nonexistent. FIG. 2B illustrates an intermediate configuration of
the electrode after the insert 20 has been pressed 15 into the
closed end portion of the bore and presents a diagrammatic
representation of the initial resultant lateral forces present
between the sidewalls of the insert 20 and the electrode body 22.
The greater clearance at the top allows the insert to expand more
in the bottom of the bore before wall friction from the upper
expanding insert material restricts movement near the bottom. As a
result, the forces are greater near the step surface 26 due to
surface friction from the expanding insert. The applied pressure 15
eventually forces the insert 20 to expand into the open end portion
of the bore. FIG. 2C illustrates a final configuration of the
secured insert 21 and presents a diagrammatic representation of the
resultant lateral retention forces between the sidewalls of the
insert 21 and the electrode body 22. The initial clearance between
the open end portion of the bore and the insert results in the
formation of a radial bulge deeper in the bore than in the prior
art case illustrated in FIG. 1C, because of the absence of surface
friction at said open end. As a consequence, the retention forces
are greatest near the step surface 26, which are advantageously
located away from the exposed portion 24 of the insert 21 to which
the plasma arc attaches during torch operation. Thus, this portion
of greatest retention strength is kept cooler and is less prone to
erosion.
[0043] FIGS. 2D-2F illustrate another embodiment of the invention,
somewhat similar to those illustrated in FIGS. 2A-2C, except that
the closed end surface 23 of the bore can include a tapered
depression, e.g., formed by a drill point, with which the contact
end of the insert 27 can be configured to mate. The end surface 23
of the bore can have other configurations as well, which mate with
a contact end of an insert in accordance with principles of the
present invention. Similar principles can also be used with a
through-hole configuration, in which case an inner open end would
replace the closed end surface 23 in the representation in FIGS.
2D-2F.
[0044] FIGS. 3A-3C are partial cross-sectional illustrations of
embodiments of a plasma arc torch electrode bore configuration.
More specifically, FIG. 3A illustrates an electrode body 32
comprising a bore with two substantially cylindrical portions,
wherein the portion defining the closed end has a smaller diameter
than the portion defining the open end of the electrode body 32. A
frustoconical surface step 36 is illustrated between the two
cylindrical portions and can be located anywhere along the length
of the bore. FIG. 3B illustrates an electrode body 33 comprising a
bore with two substantially cylindrical portions, wherein the
portion defining the closed end has a smaller diameter than the
portion defining the open end of the electrode body 33. A surface
projection 37 can be located between the two cylindrical portions,
and can be located anywhere along the length of the bore. The
surface projection can be one or more barbs, possibly at different
longitudinal depths, or an annular projection. FIG. 3C illustrates
an electrode body 34 comprising a bore with a substantially
cylindrical portion 36 defining a closed end and a frustoconical
portion 38 defining the open end. A bore with the opposite
configuration, i.e., a frustoconical portion defining a closed end
and a cylindrical portion defining an open end, can be provided as
another embodiment or configuration. The electrode embodiments
illustrated in FIGS. 3A-3C can each have a gap, as illustrated in
FIG. 2A, with respect to an insert when the insert is initially
pressed into the bore. Thus, a radial bulge can be formed away from
the open end of the bore, resulting in the retention forces being
greatest around this bulge and the insert being secured in the
electrode body. The end surfaces 39 of the bore can be planar
surfaces, but they can have other configurations as well, e.g., a
tapered depression, which can mate with a contact end of an insert.
Similar principles can also be used in a through-hole
configuration, in which case an inner open end would be replace the
closed end surface 39 in the representation in FIGS. 3A-3C.
[0045] FIGS. 4A-4D are partial cross-sectional illustrations of
intermediate plasma arc torch electrode and insert configurations.
FIG. 4A illustrates an electrode body 42 comprising a substantially
cylindrical bore. The insert can include a substantially
cylindrical contact end 49 and an elongated frustoconical exposed
end 41. FIG. 4B illustrates an electrode body 44 comprising a
substantially cylindrical bore. The insert 43 can include two
substantially cylindrical portions and a frustoconical portion
located between the two other portions, wherein the contact end
portion of the insert 43 has a larger diameter than the exterior
end portion of the insert 43. FIG. 4C illustrates another
embodiment including an electrode body 46 comprising a
substantially cylindrical bore. The insert can include an elongated
frustoconical body, wherein a contact end 49 has a larger diameter
than an exterior end 45. FIG. 4D illustrates an electrode body 48
comprising a bore, which can include two substantially cylindrical
portions similar to electrode 22 of FIG. 2A. The insert 47 can
include two substantially cylindrical portions with an annular
notch located between the two portions. The notch can be formed
around the insert to align with a step in the bore of the electrode
body 48. The electrode and insert embodiments illustrated in FIGS.
4A-4D each have a gap 40 when the insert is initially pressed into
the bore. Thus, a radial bulge can form away from an open end of
the bore, causing the retention force to be greatest around this
bulge, thereby securing the insert in the electrode body. The end
surfaces 49 of the bore can be planar surfaces, but they can have
other configurations as well, e.g., a tapered depression, which
mate with a contact end of an insert. Similar principles can also
be used in a through-hole configuration, in which case an inner
open end would replace the closed end surface 49 in the
representation in FIGS. 4A-4D. The electrodes 42, 44, 46, and 48
comprise cylindrical bores, but they can have other configurations
as well, e.g., the electrode configurations 22, 32, 33, and 34, in
accordance with principles of the present invention.
[0046] The bore and insert diameters, lengths, and tapers
illustrated in FIGS. 3A-3C and 4A-4D can all be modified, e.g., the
tapers could be straight, convex or concave, and they can have
multiple steps or tapers in combination, all in accordance with
principles of the present invention.
[0047] FIGS. 5A-5F are partial cross-sectional illustrations of
embodiments of a plasma arc torch insert configuration in
accordance with embodiments of the invention. FIG. 5A illustrates
an insert with a notched head and an elongated taper lead out. FIG.
5B illustrates an insert with a notched or grooved 51 head. FIG. 5C
illustrates an insert with a notched or grooved 51 head and a
spherical end surface. FIG. 5D illustrates an insert with a notched
head and with a smaller diameter lower cylindrical portion. FIG. 5E
illustrates an insert with multiple notches or grooves. FIG. 5F
illustrates an insert with an external projection 52 that can mate
with a surface of an electrode bore, e.g., step surface 26. Each of
these insert configurations can be used with, e.g., the various
bore configurations of the invention. Although FIGS. 5A-5E
illustrate annular notches or grooves on an insert, they can also
have notches or grooves that are not annular, e.g., one or more
barbs, which can be located at different longitudinal positions.
The surface roughness of the insert and/or the bore can also be
configured to provide a roughness to enhance insert retention. For
example, small grooves in the surfaces of the bore and/or insert,
or even threadlike patterns, can be used to enhance surface
retention. In addition, all insert contact surface geometries,
e.g., planar, spherical, conical end surfaces, can be used with any
of the insert configurations illustrated in FIGS. 5A-5F, or their
respective through-hole configurations, in accordance with
principles of the present invention.
[0048] FIGS. 6A-6B illustrate another embodiment of a method and
apparatus for securing an insert into an electrode bore, and the
resulting electrode configuration. The electrode body 62 comprises
a bore in which an insert is to be secured. The bore can include
two portions, wherein the portion defining a closed end 66 has a
diameter greater than a portion defining an open end of the bore. A
substantially cylindrical insert 60 with a diameter slightly less
than the diameter of the open end portion of the bore is
illustrated. FIG. 6A illustrates an intermediate configuration of
the electrode after the insert 60 has been pressed 15 into the
closed end portion of the bore and presents a diagrammatic
representation of the initial resultant lateral forces present in
the insert 60. Before insertion of the insert, the gap 67 between
the insert 60 and the electrode body 62 is greater for the
closed-end portion than the gap 69 for the open-end portion. In
situations where the diameter of the insert is formed to be
virtually indistinguishable from the diameter of the open-end
portion of the bore, a gap between the insert and the bore around
this portion can be small or nonexistent. The applied pressure 15
can force the insert 60 to expand, where it is unrestrained, into
the larger diameter closed end portion 66 of the bore. FIG. 6B
illustrates a final configuration of a secured insert 61 and
presents a diagrammatic representation of the resultant lateral
retention forces between the sidewalls of the insert 61 and the
electrode body 62. The absence of a side surface in the closed end
portion 66 allows the insert to expand into this space, resulting,
even when the insert expands only partially, in the retention
forces being greatest in this portion of the electrode body 62. The
location of these forces at this position in the electrode are
advantageously located away from the exposed portion of the insert
21 to which the plasma arc attaches during torch operation. Thus,
this portion of greatest retention strength is less affected by the
plasma arc and is cooler and less prone to erosion. As described
below, the end surface of the bore can be a tapered depression, but
other configurations can also be used, e.g., a planar surface,
which can mate with a contact end of an insert. FIG. 6C illustrates
another configuration of a secured insert 63 in an electrode with a
through-hole configuration, inserted and secured in a similar
fashion as illustrated in FIGS. 6A-6B. The absence of a side
surface in the central portion 64 allows the insert to expand at
this depth, resulting in increased retention forces at this portion
of the electrode body 68.
[0049] FIG. 7 is a partial cross-sectional view of another
embodiment of an intermediate plasma arc torch electrode and insert
configuration. The electrode body 72 comprises a bore in which an
insert is to be secured. The bore can include a cylindrical portion
and a projection 73, e.g., disposed on the closed end surface of
the bore. A cylindrical insert 71 with a diameter slightly less
than the diameter of the bore is provided. A contact end of the
insert 71 comprises a bore 74. The bore 74 of the insert 71 can be
configured to mate with a projection 73 of the electrode bore such
that before the insert 71 can be completely pressed flush with the
bore of the electrode body 72, a surface 75 of the projection can
contact the insert 71. Upon an applied pressure, the imperfect
matching of the insert 71 and the electrode body 72 configurations
can force the insert 71 to expand outwardly into the electrode body
72, resulting in increased retention forces at this portion of the
electrode body 72. The location of these forces at this position in
the electrode are advantageously located away from the exposed
portion of the insert 71 to which the plasma arc attaches during
torch operation. Thus, this portion of the insert experiences
increased retention strength, is kept cooler, and is less prone to
erosion. The projection in this embodiment can be centered and
symmetric about a center axis of the electrode body, but other
configurations can also be used, e.g., a tapered wall aligned along
a diameter of the bore, or one or more tapered projections
emanating from the walls of the bore, in accordance with principles
of the present invention.
[0050] FIG. 8 is a partial cross-sectional view of an intermediate
plasma arc torch electrode and insert configuration. The electrode
body 82 comprises a cylindrical bore in which an insert is to be
secured. The insert 81 can include two substantially cylindrical
portions and a frustoconical portion 83 illustrated between the two
other portions, similar to insert 43, wherein a contact end portion
of the insert 81 has a larger diameter than an exterior end portion
of the insert 81. A sleeve 84 is provided and can be configured for
insertion between the insert 81 and the bore of the electrode body
82. The sleeve 84 can include a contact end 85 configured to mate
with the frustoconical portion 83 such that as the sleeve 84 is
pressed into the insert 81, the surface 83 of the insert 81
contacts the contact end 85. Upon an applied pressure, the
imperfect matching of the insert 81 and the sleeve 84
configurations force the sleeve 84 to expand outwardly into the
electrode body 82, resulting in an increase in the retention forces
at this portion of the electrode body 82 and, in effect, "crimping"
or securing the insert 81 into the bore of the electrode body 82.
The location of these forces at this depth are advantageously
located away from the exposed portion of the insert 81 to which the
plasma arc is attaches during torch operation. Thus, this portion
of increased retention force is kept cooler and is less prone to
erosion. The sleeve can be formed of a high emissivity material,
e.g., hafnium or zirconium, or of a high thermal conductivity
material, e.g., copper, a copper alloy, or silver. The sleeve and
the insert can be of different materials. For example, the insert
can be hafnium and the sleeve can be silver, or the insert can be
silver and the sleeve can be hafnium. The end surface of the bore
can be a planar surface, but can have other configurations as well,
e.g., a tapered depression, which mate with a contact end of an
insert. Similar principles can also be used with a through-hole
electrode configuration, in which case the closed end surface
represented in FIG. 8 would be replaced with an inner open end.
Preferably, before a sleeve is used to secure the insert in the
bore, the insert can be supported by an anvil or mandrel at the
inner open end of the electrode body.
[0051] FIG. 9 is a partial cross-sectional view of an embodiment of
an intermediate plasma arc torch electrode and insert configuration
comprising an insert object, e.g., a spherical object. The
electrode body 92 comprises a cylindrical bore. A substantially
cylindrical insert 91 with a diameter slightly less than the
diameter of the bore is provided. A ball 95 can be placed into the
bore of the electrode body 92 prior to the insertion of the insert
91. The ball 95 can be formed of a material, e.g., steel, which is
harder than the material of the insert. Upon insertion of the
insert 91 into the bore, the hard surface of the ball 95 can cause
a contact end of the insert 91 to expand outwardly, thereby
securing the insert in the bore of the electrode body 92. The ball
95 thus can perform a function similar to the projection 73
illustrated in FIG. 7. Of course, other configurations can be used,
e.g., a preformed indentation can be formed at the bottom of the
insert, square shavings can be placed in the bore, and/or one or
more other shapes/objects in place of the ball 95.
[0052] FIG. 10 is a partial cross-sectional view of plasma arc
torch electrode and insert configuration comprising a cross-drilled
hole. The electrode body 102 can include a cross-drilled hole 105,
which can cross paths with a cylindrical bore. In some embodiments,
the cross-drilled hole is formed by drilling a hole from outside of
the electrode into at least a portion of the bore. The drilling
operation can be terminated after the bore is reached, i.e.,
without extending the hole to the far side of the electrode. Of
course, other configurations can be used. A substantially
cylindrical insert 101 with a diameter slightly less than the
diameter of the bore is provided. The cross-drilled hole 105 can
provide two areas of unrestricted expansions for the insert 101,
such that upon insertion of the insert 101 into the bore, the
insert 101 can expand 106 into the cross-drilled hole 105. Said
expansion thus can secure the insert 101 in the bore of the
electrode body 102. Multiple cross-drilled holes can also be used
in accordance with principles of the present invention, and these
multiple holes can be at different points at different points along
the longitudinal axis of the electrode, i.e., at different
elevations.
[0053] FIGS. 11A-11B are partial cross-sectional views of other
embodiments of intermediate plasma arc torch electrode and insert
configurations. The electrode body 112 comprises a cylindrical bore
in which an insert is to be secured. A substantially cylindrical
insert 111 with a diameter slightly less than the diameter of the
bore is provided. The contact end of the insert 111 can include a
countersunk surface 115. FIG. 11A illustrates an intermediate
configuration of the electrode as the insert 111 is being pressed
into the bore. FIG. 11B illustrates a second intermediate
configuration of the electrode as the insert 111 is pressed against
the end surface of the bore and presents a diagrammatic
representation of the initial resultant lateral forces present
between the sidewalls of the insert 111 and the electrode body 112.
The contact end of the insert, as a result, expands radially
outwardly into the bore, securing the insert. As a consequence, the
retention forces can be increased near the end surface of the bore,
which is advantageously located away from the exposed portion of
the insert 111 to which the plasma arc attaches during torch
operation. Thus, this portion of increased retention strength is
kept cooler and is less prone to erosion.
[0054] FIGS. 12A-12B illustrate a method for securing an insert
into an electrode bore, and the resulting electrode configuration.
The electrode body 122 comprises a cylindrical bore in which an
insert is to be secured. An elongated tapered insert 120 is
provided, wherein a contact end 128 can have a larger diameter than
the exterior end 129. FIG. 12A illustrates an intermediate
configuration of the electrode after the insert 120 has been
pressed into the closed end portion of the bore. It also presents a
diagrammatic representation of lateral forces 120 applied on and
around an end portion of the electrode body to secure the insert.
These forces can be applied to an external surface of the electrode
body. The resulting forces 120 are directed radially inwards and
can force the electrode body 122 to at least partially conform to
the insert 121. FIG. 12B illustrates a final configuration of the
secured insert 121 in the electrode body 123. In this manner, the
hoop strength at the compressed end of the electrode body 123
secures the insert 121.
[0055] FIG. 13 is a partial cross-sectional view of an intermediate
plasma arc torch electrode and insert configuration. The electrode
body 132 comprises a cylindrical bore. The bore can include an
annular extension 133 around the open end of the bore. A
cylindrical insert 130 with a flared head 131 is provided. Inserts
can be sized to allow the insert to fit into the bore leaving
enough insert material extending out of the bore to overfill the
hole when pressed. The flared head 131 of the insert 130 can be a
different configuration for providing additional insert material.
The flared head 131 can also ensure that after the insert 130 has
been press fit into the bore of the electrode body 132 no air gap
exists around the exposed end of the insert 130 between the insert
and the side walls of the bore, which can degrade the thermal
cooling of the electrode insert. The annular extension 133 in this
embodiment can be uniformly symmetric about a center axis of the
electrode body, but other configurations can also be used, e.g., a
non-uniform extension, or series of extensions surrounding the open
end of the bore, in accordance with principles of the present
invention. While the electrode illustrated in FIG. 13 is one
particular embodiment, the extension 133 can be used with other
electrode embodiments, e.g., electrodes 22, 29, 32, 33, 34, 42, 44,
46, 48, 62, 68, 72, 92, and 112 of FIGS. 2A, 2D, 3A-3C, 4A-4D, 6A,
6C, 7, 9, and 11A, in accordance with principles of the present
invention. The extension 133 can be used with inserts that do or do
not include a flared head 131.
[0056] FIGS. 14A-14B are partial cross-sectional views illustrating
a method of forming an electrode incorporating principles of the
present invention. A first portion 141 of the electrode body can be
provided with a closed-ended cylindrical bore having a first
diameter D1. A second portion 142 of the electrode body can be
provided with an open-ended cylindrical bore having a second
diameter D2 greater than the first diameter. FIG. 14A illustrates a
method of solid state welding, e.g., friction welding 140 the
second portion 142 to the first portion 141. In another embodiment,
the diameter D1 of the first portion 141 is greater than the
diameter D2 of the second portion 142. FIG. 14B illustrates a final
configuration of the electrode body of FIG. 14A wherein the
surfaces 143 can secure the first portion 141 to the second portion
142 as a result of solid state welding (e.g., friction welding) the
surfaces of the two portions 141 and 142. The first and second
portions can be formed of a high thermal conductivity material,
such as copper, copper alloy, or silver. The second portion can be
formed from the same or different material from that of the first
portion. While the electrode illustrated in FIG. 14B is one
particular embodiment, the same method can be used to form other
electrode embodiments, e.g., electrodes 29, 32, 33, 34, 62, and 72
of FIGS. 2D, 3A-3C, 6A, and 7, in accordance with principles of the
present invention. Similar principles as those illustrated in FIGS.
12A-12B, 13, and 14A-14B can also be used in respective or combined
through-hole configurations, in which case an open end surface
would be replace the closed end surface of the electrode body
illustrated.
[0057] FIGS. 15A-15B are partial cross-sectional views illustrating
central portions of inserts disposed in electrodes. FIG. 15A
illustrates a final configuration of a central portion of an insert
151 secured in an electrode body (not shown). The central portion
of the insert 151 can have a longitudinal length of no less than
about 70% of the longitudinal length of the insert. The central
portion of the insert 151 can include a first portion 152, a second
portion 153, and a third portion 154. The first portion 152, second
portion 153, and third portion 154 can each define an angle
relative to the longitudinal axis 150 of the insert and a tangent
to their respective exterior surfaces. For example, as illustrated
in FIG. 15A, the angle 155 defined between the longitudinal axis
150 and a tangent to an exterior surface of the second portion 153
is greater than 0 degrees. Likewise, the angle defined between the
longitudinal axis 150 and a tangent to an exterior surface of
either the first portion 152 or the third portion 154 is zero,
because the first portion 152 and the third portion 154 are
cylindrical.
[0058] FIG. 15B illustrates a different final configuration of a
central portion of an insert 156 secured in an electrode body (not
shown). The central portion of the insert 156 can include a first
portion 157, and a second portion 158. The first portion 157, and
second portion 158 can each define an angle relative to the
longitudinal axis 150 of the insert and a tangent to their
respective exterior surfaces. For example, as illustrated in FIG.
15B, the angle 159 defined between the longitudinal axis 150 and a
tangent to an exterior surface of the first portion 157 is greater
than 0 degrees. Likewise, the angle defined between the
longitudinal axis 150 and a tangent to an exterior surface of the
second portion 158 is zero, because the second portion 158 is
cylindrical.
[0059] In one embodiment, the angles defined by the tangents to the
exterior surfaces of the insert and the longitudinal axis of the
insert differ by at least 1 degree. In another embodiment, the
angles defined by the tangents to the exterior surfaces of the
insert and the longitudinal axis of the insert differ by at least 3
degrees. While the secured central portions of inserts 151 and 156
illustrated in FIGS. 15A and 15B are two particular embodiments,
the same minimum angle differentiation between different central
portions of an insert can be used with other insert embodiments,
e.g., inserts 21, 28, 41, 43, 45, 47, 61, 62, 63,71, 81, 91, 101,
111, 121, and 130, of FIGS. 2C, 2F, 4A-4D, 5A-5F, 6B, 6C, 7-11,
12B, and 13 in accordance with principles of the present invention.
In other embodiments, one or more exterior surfaces of the insert
can be disposed at a constant or continuously varying tangential
angle relative to the longitudinal axis. The exterior surfaces can
also be non-uniform, e.g., about a perimeter of a cross section of
the insert.
[0060] Experimental testing during development of the present
invention was undertaken using a MAX100 torch with a 100 A
electrode (part number 120433), both manufactured by Hypertherm,
Inc. of Hanover, N.H. All testing was done using a test stand that
included a rotating copper anode as a substitute workpiece, at 100
amps of transferred current. The benchmarking of five electrodes of
the known configuration produced the following results: [0061]
Average number of 20 second starts: 134.4 [0062] Standard
deviation: 68.7
[0063] Two of the parts tested failed around 60 starts, e.g., from
the insert falling out. The insert bore depth of these electrodes
was about 0.100 inches. Parts having a new design were then tested
that had a stepped hole design, similar to FIG. 2D, made by adding
an outer 0.052'' diameter hole to the previous 0.0449'' diameter
hole. Three configurations were made with these 0.052''
counter-bores drilled to depths of 0.030'', 0.040'' and 0.050''.
The emissive insert used was Hypertherm part number 120437, having
a 0.0445'' diameter. Three parts each were tested for different
counter-bores, with the results listed below: [0064] 0.030'' depth
[0065] Average 20 second starts: 254.7 [0066] Standard deviation:
15.9 [0067] 0.040'' depth [0068] Average 20 second starts: 213.7
[0069] Standard deviation: 37.1 [0070] 0.050'' depth [0071] Average
20 second starts: 249.0 [0072] Standard deviation: 63.4
[0073] Despite the somewhat lower average number of starts for the
middle test (having a counter-bore depth of 0.040''), the results
of all three tests are statistically similar. All three
counter-bore tests show statistically higher starts than the stock
results, and each had no extremely early failures. The higher than
average start counts, with one part lasting over 300 starts,
indicates improved performance.
[0074] The next parts tested used the same 0.052'' counter-bore,
but the deeper hole (e.g., the inner hole that extended to
.about.0.100'' in overall depth) was increased to a 0.0465''
diameter. One set of parts that was tested had the 0.052'' diameter
counter-bore drilled to a depth of 0.030'', with the smaller
diameter hole drilled to a depth of 0.090''. The next set of parts
tested were drilled to 0.050'' (larger diameter) and 0.095''
(smaller diameter). The same 120437 insert described above was
used, producing the following results based on three samples each.
[0075] 0.030'' depth [0076] Average 20 second starts: 181.7 [0077]
Standard deviation: 12.2 [0078] 0.050'' depth [0079] Average 20
second starts: 240.3 [0080] Standard deviation: 37.1
[0081] Next, more parts were fabricated with the same smaller hole
size (0.0445'') but with a counter-bore having a depth of 0.060''.
In these embodiments, an insert of the same size was used. Ten
samples were tested under similar conditions, producing the
following results: [0082] 0.060'' depth [0083] Average 20 second
starts: 300.0 [0084] Standard deviation: 24.8
[0085] These parts produced over twice as many total starts as the
stock configuration, and with a much lower standard deviation. The
lowest number of starts achieved was 270.
[0086] Experimental results were also obtained that measured the
force required to remove the insert from the electrode. These tests
were first performed on new, unused parts. Measurements were then
taken on electrodes that had been used for a controlled period of
time. Tests were performed on stock electrodes, and electrodes
having counter-bored hole depths 0.03'', 0.05'', and 0.06''. The
results of these measurements are listed below in units of pounds
force.
[0087] To obtain the removal force measurement, the inside (upper)
portion of the electrode was removed using a lathe and a cutting
tool to expose an interior cross-sectional surface of the emissive
material. A plunger/mandrel type device was then used to press the
emissive material out of the surrounding copper material, in a
direction towards the emissive working surface of the emissive
material. The tables below indicate the amount of force exerted by
the plunger to dislodge the emissive insert, in a longitudinal
direction of the electrode. TABLE-US-00001 TABLE 1 Stock New Stock
Used Average 102.9 51.3 Std. Dev. 9.2 35.6 Minimum 93 6 Samples 7
4
[0088] TABLE-US-00002 TABLE 2 0.03'' 0.03'' Step Step 0.05'' Step
0.05'' Step 0.06'' Step 0.06'' Step New Used New Used New Used
Average 85 29.5 105 65 90.3 62 Std. Dev. 1.4 2.1 22.8 15.6 25.1 17
Minimum 84 28 79 54 62 45 Samples 2 2 4 2 3 3
[0089] The used parts indicated in Table 1 were run for 50, twenty
second starts. These parts were not modified in accordance with
principles of the invention. In every case tested, the used parts
required a lower force to remove the insert. The used stock parts
produced the highest standard deviation and the lowest push out
force, sometimes requiring only 6 pounds of force to dislodge the
emissive insert. As indicated in Table 2, the two best stepped hole
designs required a minimum of 45 and 54 pounds to remove the
insert. These results for the used parts were also more consistent,
as indicated by the reduced standard deviation of the sample
results.
[0090] Embodiments of the invention also include a method for
forming an electrode body of a high thermal conductivity material.
Steps of the method, as partially described above in FIGS. 2A-2F
and 6A-6C, include forming the electrode body to include a first
end and a second end defining a longitudinal axis. A bore is formed
in the first end, such that the bore includes a first portion and a
second portion. An insert formed of a high thermionic emissivity
material is positioned in the bore, wherein the insert includes a
contact end and an exterior end. The contact end of the insert is
aligned with the second portion of the bore, and the exterior end
is aligned with the first portion of the bore, such that a first
gap is established between a first exterior surface of the insert
and the first portion, and a second gap is established between a
second exterior surface of the insert and the second portion of the
bore. The first gap is substantially greater than the second gap. A
force is applied at the exterior end of the insert to secure the
insert in the bore.
[0091] Embodiments of the invention also include a method for
optimizing the combination of insert emissive area and insert
volume, thereby reducing the cost of the insert material while
maintaining a high quality emissive area.
[0092] The electrode body in each embodiment described or
illustrated herein can be formed from a high thermal conductivity
material, e.g., copper, a copper alloy, or silver. It is also to be
understood that each electrode body embodiment also represents the
situation in which the bore illustrated is formed in a sleeve,
either before or after the sleeve can be inserted into a larger
bore in the electrode body. The sleeve can be formed from a high
thermal conductivity material, e.g., copper, a copper alloy, or
silver, or from a high thermionic emissivity material, e.g.,
hafnium or any material the insert can be formed of. The insert in
each embodiment described or illustrated herein can be formed from
a high thermionic emissivity material, e.g., hafnium, zirconium,
tungsten, thorium, lanthanum, strontium, or alloys thereof.
[0093] As seen from above, the invention provides an electrode with
improved retention of an insert, thereby increasing the thermal
conductivity of the interface between insert and electrode, and the
efficiency and service life of the electrode. The invention also
provides an electrode with an insert configuration that improves
the cooling, and therefore the service life, of the insert. The
invention also provides an electrode with an insert configuration
that minimizes the amount of insert material required, thereby
reducing the cost of the electrode while at the same time not
lessening the efficiency and service life of the electrode. The
invention also provides an electrode with a longer service
life.
[0094] While the invention has been particularly shown and
described with reference to specific preferred embodiments, it
should be understood by those skilled in the art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention as defined by the
appended claims.
* * * * *