U.S. patent application number 10/272210 was filed with the patent office on 2004-04-22 for head tube assembly having insulated mechanical interface with welding gun body.
Invention is credited to Altekruse, Kenneth C., Matiash, Nicholas A..
Application Number | 20040074887 10/272210 |
Document ID | / |
Family ID | 32042931 |
Filed Date | 2004-04-22 |
United States Patent
Application |
20040074887 |
Kind Code |
A1 |
Matiash, Nicholas A. ; et
al. |
April 22, 2004 |
HEAD TUBE ASSEMBLY HAVING INSULATED MECHANICAL INTERFACE WITH
WELDING GUN BODY
Abstract
A welding gun comprising: an electrically conductive gun body
having a passageway; a head tube assembly having one end inserted
in the passageway of the gun body; a rotation nut that retains the
head tube assembly in the inserted state when the rotation nut is
threadably coupled to the gun body; and an electrically insulative
ring installed between a portion of the gun body and an
electrically conductive part of the head tube assembly. The
electrically conductive gun body has a frusto-conical inner
peripheral surface that is in contact with a frusto-conical outer
peripheral surface of the electrically insulative ring. The
rotation nut comprises an electrically conductive part that is
threadably engaged to the electrically conductive gun body and that
is in electrical contact with the electrically conductive portion
of the head tube assembly. Electric current for welding is
transmitted around the electrically insulative ring, through the
electrically conductive portion of the rotation nut and into the
electrically conductive part of the head tube assembly.
Inventors: |
Matiash, Nicholas A.;
(Oshkosh, WI) ; Altekruse, Kenneth C.; (Appleton,
WI) |
Correspondence
Address: |
OSTRAGER CHONG & FLAHERTY LLP
825 THIRD AVE
30TH FLOOR
NEW YORK
NY
10022-7519
US
|
Family ID: |
32042931 |
Appl. No.: |
10/272210 |
Filed: |
October 16, 2002 |
Current U.S.
Class: |
219/137.31 |
Current CPC
Class: |
B23K 9/323 20130101 |
Class at
Publication: |
219/137.31 |
International
Class: |
B23K 009/173 |
Claims
1. A welding gun comprising an electrically conductive gun body and
a head tube assembly supported by said gun body and comprising: an
electrically conductive fitting comprising an end that is engaged
with said gun body; an electrically conductive tube comprising an
end in contact with said fitting; a retaining device comprising an
electrically conductive portion that is in contact with and coupled
to said gun body and in contact with said fitting, said retaining
device retaining said fitting in engagement with said gun body when
said retaining device is coupled to said gun body; and an
electrical insulator disposed between and in contact with
respective portions of said fitting and said gun body.
2. The welding gun as recited in claim 1, wherein said gun body
comprises a frusto-conical inner peripheral surface, said insulator
is ring-shaped and comprises a frusto-conical outer peripheral
surface in contact with said frusto-conical inner peripheral
surface of said gun body.
3. The welding gun as recited in claim 2, wherein said fitting
comprises a circular cylindrical outer peripheral surface, and said
insulator further comprises a circular cylindrical inner peripheral
surface surrounding and in contact with said circular cylindrical
outer peripheral surface of said fitting.
4. The welding gun as recited in claim 3, wherein said insulator
further comprises a chamfer at one end of said circular cylindrical
inner peripheral surface where a thickness of said insulator in a
radial direction is greatest.
5. The welding gun as recited in claim 1, wherein said fitting
comprises a collar, said insulator being disposed adjacent said
collar.
6. The welding gun as recited in claim 1, wherein said gun body
comprises a threaded portion, and said retaining device comprises a
rotation nut that threadably engages said threaded portion of said
gun body.
7. The welding gun as recited in claim 5, wherein said gun body
comprises a first frusto-conical inner peripheral surface having an
inner diameter that increases toward said retaining device, and
said electrically conductive portion of said retaining device
comprises a second frusto-conical inner peripheral surface having
an inner diameter that increases toward said gun body.
8. The welding gun as recited in claim 7, wherein said insulator
comprises a first frusto-conical outer peripheral surface in
contact with said first frusto-conical inner peripheral surface,
and said collar comprises a second frusto-conical outer peripheral
surface in contact with said second frusto-conical inner peripheral
surface.
9. The welding gun as recited in claim 1, wherein said retaining
device further comprises an electrically insulative portion
surrounding said electrically conductive portion.
10. The welding gun as recited in claim 1, wherein said head tube
assembly further comprises an electrically insulative tube
surrounding said electrically conductive tube.
11. The welding gun as recited in claim 1, wherein said
electrically conductive tube is brazed to said fitting.
12. The welding gun as recited in claim 1, further comprising a
diffuser having one end electrically coupled to said electrically
conductive tube.
13. A welding gun comprising an electrically conductive gun body
and a head tube assembly supported by said gun body, said gun body
comprising a threaded outer peripheral surface and a cavity defined
in part by a frusto-conical inner peripheral surface, and said head
tube assembly comprising: an electrically conductive fitting
comprising an end that is received in said cavity of said gun body;
an electrically conductive tube comprising an end supported by said
fitting; a rotation nut comprising an electrically conductive
portion that is in contact with said gun body and said fitting,
said electrically conductive portion comprising a threaded inner
peripheral surface that threadably engages said threaded outer
peripheral surface of said gun body, said rotation nut fastening
said fitting to said gun body when said rotation nut is threadably
engaged with said gun body; and an electrical insulator disposed
between and in contact with said fitting and said frusto-conical
inner peripheral surface of said gun body.
14. The welding gun as recited in claim 13, wherein said insulator
is ring-shaped and comprises a frusto-conical outer peripheral
surface located inside and in contact with said frusto-conical
inner peripheral surface of said gun body.
15. The welding gun as recited in claim 14, wherein said fitting
comprises a circular cylindrical outer peripheral surface, and said
insulator further comprises a circular cylindrical inner peripheral
surface surrounding and in contact with said circular cylindrical
outer peripheral surface of said fitting.
16. The welding gun as recited in claim 15, wherein said insulator
further comprises a chamfer at one end of said circular cylindrical
inner peripheral surface where a thickness of said insulator in a
radial direction is greatest.
17. The welding gun as recited in claim 13, wherein said fitting
comprises a collar, said insulator being disposed adjacent said
collar.
18. The welding gun as recited in claim 17, wherein said collar of
said fitting comprises a frusto-conical outer peripheral surface,
and said electrically conductive portion of said nut further
comprises a frusto-conical inner peripheral surface in contact with
said frusto-conical outer peripheral surface of said fitting.
19. The welding gun as recited in claim 13, wherein said rotation
nut further comprises an electrically insulative portion
surrounding said electrically conductive portion.
20. The welding gun as recited in claim 13, wherein said
electrically conductive portion of said rotation nut and said
fitting are made of brass.
21. The welding gun as recited in claim 13, wherein said insulator
is made of Delrin or an electrically insulative material having
similar rigidity, hardness and resistance to corrosion.
22. The welding gun as recited in claim 13, wherein said head tube
assembly further comprises an electrically insulative tube
surrounding said electrically conductive tube.
23. The welding gun as recited in claim 13, wherein said
electrically conductive tube is brazed to said fitting.
24. The welding gun as recited in claim 13, further comprising a
diffuser having one end electrically coupled to said electrically
conductive tube.
25. A welding gun comprising: an electrically conductive gun body
comprising a passageway, said passageway comprising a circular
cylindrical inner peripheral surface and a frusto-conical inner
peripheral surface; an electrically conductive fitting comprising a
passageway, a collar and a circular cylindrical outer peripheral
surface located inside said circular cylindrical inner peripheral
surface of said gun body; an electrically conductive tube having
one end supported in said passageway of said fitting and projecting
forward of said fitting; an electrically insulative ring comprising
a frusto-conical outer peripheral surface in contact with said
frusto-conical inner peripheral surface of said gun body and a
circular cylindrical inner peripheral surface in contact with said
circular cylindrical outer peripheral surface of said fitting; and
a retaining device comprising an electrically conductive portion
that is in contact with and coupled to said gun body and in contact
with said fitting, said retaining device retaining said fitting in
engagement with said gun body when said retaining device is coupled
to said gun body.
26. The welding gun as recited in claim 25, wherein said
electrically conductive portion of said retaining device comprises
a frusto-conical inner peripheral surface and said collar comprises
a frusto-conical outer peripheral surface in contact with said
frusto-conical inner peripheral surface of said retaining
device.
27. The welding gun as recited in claim 26, wherein said
electrically conductive gun body, said electrically conductive
portion of said retaining device, said electrically conductive
fitting and said electrically conductive tube form a conductive
path for electric current, further comprising electrically
insulative means surrounding said conductive path.
28. A welding gun comprising: an electrically conductive gun body
comprising a passageway; an assembly comprising a sequence of
electrically conductive components connected in series to form a
conductive path for electric current and a passageway for welding
wire, one end of said assembly being inserted in said passageway of
said gun body; a rotation nut that retains said assembly in said
inserted state when said rotation nut is threadably coupled to said
gun body; and an electrically insulative ring installed between an
electrically conductive portion of said gun body and an
electrically conductive portion of said assembly, wherein said ring
comprises a frusto-conical outer peripheral surface.
29. The welding gun as recited in claim 28, wherein said
electrically conductive gun body comprises a frusto-conical inner
peripheral surface that is in contact with said frusto-conical
outer peripheral surface of said electrically insulative ring.
30. The welding gun as recited in claim 29, wherein said rotation
nut comprises an electrically conductive frusto-conical inner
peripheral surface and said comprises an electrically conductive
frusto-conical outer peripheral surface in contact with said
electrically conductive frusto-conical inner peripheral surface of
said rotation nut.
31. A method of assembling a welding gun, comprising the following
steps: sliding a ring of electrically insulative material onto an
end portion of a head tube assembly until said ring is proximal to
a first portion of said end portion of said head tube assembly
having a maximum dimension greater than an inner diameter of said
ring, said ring having a frusto-conical outer peripheral surface;
inserting a second portion of said end portion of said head tube
assembly into a cavity of a gun body until said frusto-conical
outer peripheral surface of said electrically insulative ring
engages a frusto-conical inner peripheral surface of said gun body
cavity; and fastening said head tube assembly to said gun body.
32. The method as recited in claim 31, wherein said fastening step
comprises the steps of: sliding a nut over said first portion of
said end portion of said head tube assembly; and tightening said
nut onto a threaded portion of said gun body.
33. The method as recited in claim 32, further comprising the step
of conducting electrical current through said gun body, said nut
and said head tube assembly in series.
34. A welding gun comprising: an electrically conductive gun body
comprising a passageway; an assembly comprising a sequence of
electrically conductive components connected in series to form a
conductive path for electric current and a passageway for welding
wire, one end of said assembly being inserted in said passageway of
said gun body, and a component of said assembly comprising an
electrically conductive frusto-conical outer peripheral surface;
and an electrically conductive rotation nut that retains said
assembly in said inserted state when said rotation nut is
threadably coupled to said gun body, said rotation nut comprising
an electrically conductive frusto-conical inner peripheral surface
that engages said electrically conductive frusto-conical outer
peripheral surface of said assembly component.
35. The welding gun as recited in claim 34, further comprising
electrically insulative material encasing portions of said assembly
and said rotation nut.
Description
BACKGROUND OF THE INVENTION
[0001] This invention generally relates to gas metal arc welding
(GMAW) and flux core arc welding (FCAW). In particular, the
invention relates to wire feeding guns.
[0002] Wire feeding guns must perform several different functions
in order for successful welding to occur. Those functions include
directing the weld wire to the workpiece, conducting electric power
to the weld wire, and shielding the welding arc from atmospheric
air. In addition to the foregoing basic requirements, it is highly
desirable that the weld wire be fed to the workpiece at an
adjustable rate that suits the particular welding operation at
hand. For maximum productivity, it is also necessary that the gun
be very comfortable for the operator to maneuver as he directs the
weld wire to the workpiece.
[0003] To satisfy the foregoing requirements, the wire feeding gun
is connected by a long flexible cable to a wire feeder, which is
wired to a welding machine. The wire feeder supplies the weld wire,
electric power, cooling fluid, and shielding gas through the cable
to the gun. In some instances, the cable may be as long as 50
feet.
[0004] In a typical wire feeding gun arrangement, there is a head
tube on the end of the handle opposite the flexible cable. A
diffuser is joined to the free end of the head tube. A contact tip
is connected to the diffuser. The weld wire is guided by a liner,
placed inside the head tube, that extends from the handle to the
diffuser. From the diffuser, the weld wire passes through the
contact tip, from which it emerges under the impetus of the feed
mechanism.
[0005] In gas-shielded applications, it is vital that the gas
adequately shield the welding arc from the ambient atmosphere. For
that purpose, gas is supplied to the wire feeding gun from the wire
feeder through the flexible cable. The gas is directed through the
head tube to the interior of the diffuser. The gas flows from the
diffuser to a nozzle that surrounds the contact tip. The gas then
flows out the nozzle and surrounds the contact tip and the weld
wire emerging from the contact tip. The gas thus shields the weld
wire and the welding arc from the ambient atmosphere.
[0006] In known MIG welding guns of the type disclosed in U.S. Pat.
No. 6,225,599, the nozzle assembly is insulated by a tubular
insulator from an electrically hot conductor that conducts welding
power from the gun handle to the diffuser. Accordingly, the
diffuser is electrically hot. Another insulator is supported by the
diffuser to separate the electrically hot conductor and diffuser
from the electrically cold head tube exterior, locking nut, and
nozzle. The contact tip can be connected to the diffuser by a nut,
in which case, both the contact tip and nut are electrically hot.
The contact tip transmits the welding electrical power from the
diffuser and the conductor to the weld wire. The contact tip may be
screwed into the diffuser.
[0007] In a known MIG welding gun, the welding electrical power is
transmitted from the gun body to a brass fitting, which in turn
transmits the welding electrical power to the aforementioned
conductor. That brass fitting was designed with a frusto-conical
surface that seats inside and against a frusto-conical surface
formed in the distal end of the gun body. These engaging
frusto-conical surfaces provide a self-centering of the brass
fitting relative to the distal end of the gun body. The brass
fitting is captured between a rotation nut and the distal end of
the gun body, the latter having a threaded outer periphery that is
threadably engaged by a threaded bore inside the rotation nut. The
known rotation nut comprises a threaded brass nut encased in a
shroud of molded nylon.
[0008] In this known MIG gun arrangement, current is carried from
the gun body to the brass fitting across the aforementioned
frusto-conical interface. This caused problems because the fit
between the two frusto-conical surfaces was not always tight due to
manufacturing tolerances and the current passing between them
caused pitting and corrosion. Once pitting and corrosion started,
the fit would deteriorate further, giving rise to a compounding
problem. Furthermore, the brass fitting and gun body distal portion
also had a non-frusto-conical interface where water was present,
which could sometimes compound the problem if the head tube were
mishandled. Corrosion at the frusto-conical interface could
ultimately cause binding of the head tube assembly to the gun
body.
[0009] There is a need for an improved mechanical interface between
the head tube assembly and the welding gun body that will not be
afflicted by pitting and corrosion, and that will not cause the
binding of the head tube to the gun body.
BRIEF DESCRIPTION OF THE INVENTION
[0010] The invention is directed to a welding gun in which a
mechanical interface between the gun body and the head tube
assembly is electrically insulated, and electric current is
transferred through a rotation nut or other fastener that holds the
head tube assembly and the gun body together.
[0011] One aspect of the invention is a welding gun comprising an
electrically conductive gun body and a head tube assembly supported
by the gun body, the head tube assembly comprising: an electrically
conductive fitting comprising an end that is engaged with the gun
body; an electrically conductive tube comprising an end in contact
with the fitting; a retaining device comprising an electrically
conductive portion that is in contact with and coupled to the gun
body and in contact with the fitting, the retaining device
retaining the fitting in engagement with the gun body when the
retaining device is coupled to the gun body; and an electrical
insulator disposed between and in contact with respective portions
of the fitting and the gun body.
[0012] Another aspect of the invention is a welding gun comprising
an electrically conductive gun body and a head tube assembly
supported by the gun body, the gun body comprising a threaded outer
peripheral surface and a cavity defined in part by a frusto-conical
inner peripheral surface, and the head tube assembly comprising: an
electrically conductive fitting comprising an end that is received
in the cavity of the gun body; an electrically conductive tube
comprising an end supported by the fitting; a rotation nut
comprising an electrically conductive portion that is in contact
with the gun body and the fitting, the electrically conductive
portion comprising a threaded inner peripheral surface that
threadably engages the threaded outer peripheral surface of the gun
body; and an electrical insulator disposed between and in contact
with the fitting and the frusto-conical inner peripheral surface of
the gun body. The rotation nut fastens the fitting to the gun body
when the rotation nut is threadably engaged with the gun body.
[0013] A further aspect of the invention is a welding gun
comprising: an electrically conductive gun body comprising a
passageway, the passageway comprising a circular cylindrical inner
peripheral surface and a frusto-conical inner peripheral surface;
an electrically conductive fitting comprising a passageway, a
collar and a circular cylindrical outer peripheral surface located
inside the circular cylindrical inner peripheral surface of the gun
body; an electrically conductive tube having one end supported in
the passageway of the fitting and projecting forward of the
fitting; an electrically insulative ring comprising a
frusto-conical outer peripheral surface in contact with the
frusto-conical inner peripheral surface of the gun body and a
circular cylindrical inner peripheral surface in contact with the
circular cylindrical outer peripheral surface of the fitting; and a
retaining device comprising an electrically conductive portion that
is in contact with and coupled to the gun body and in contact with
the fitting. The retaining device retains the fitting in engagement
with the gun body when the retaining device is coupled to the gun
body.
[0014] Yet another aspect of the invention is a welding gun
comprising: an electrically conductive gun body comprising a
passageway; an assembly comprising a sequence of electrically
conductive components connected in series to form a conductive path
for electric current and a passageway for welding wire, one that
retains the assembly in the inserted state when the rotation nut is
threadably coupled to the gun body; and an electrically insulative
ring installed between an electrically conductive portion of the
gun body and an electrically conductive portion of the assembly.
The ring comprises a frusto-conical outer peripheral surface.
[0015] A further aspect of the invention is a method of assembling
a welding gun, comprising the following steps: sliding a ring of
electrically insulative material onto an end portion of a head tube
assembly until the ring is proximal to a first portion of the end
portion of the head tube assembly having a maximum dimension
greater than an inner diameter of the ring, the ring having a
frusto-conical outer peripheral surface; inserting a second portion
of the end portion of the head tube assembly into a cavity of a gun
body until the frusto-conical outer peripheral surface of the
electrically insulative ring engages a frusto-conical inner
peripheral surface of the gun body cavity; and fastening the head
tube assembly to the gun body
[0016] Other aspects of the invention are disclosed and claimed
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a drawing showing a sectional view of a head tube
assembly fastened to a welding gun body in accordance with one
embodiment of the present invention.
[0018] FIG. 2 is a drawing showing an exploded view of the head
tube assembly depicted in FIG. 1.
[0019] FIG. 3 is a drawing showing a magnified sectional view of
the mechanical interface between the head tube assembly and the
welding gun body depicted in FIG. 1.
[0020] FIG. 4 is a drawing showing a sectional view of an
electrically conductive fitting incorporated in the head tube
assembly depicted in FIGS. 1-3.
[0021] FIG. 5 is a drawing showing a sectional view of a rotation
nut incorporated in the head tube assembly depicted in FIGS.
1-3.
[0022] FIGS. 6 and 7 are drawings showing side and isometric views
respectively of an electrical insulator incorporated in the head
tube assembly depicted in FIGS. 1-3.
[0023] Reference will now be made to the drawings in which similar
elements in different drawings bear the same reference
numerals.
DETAILED DESCRIPTION OF THE INVENTION
[0024] A welding gun in accordance with one embodiment of the
invention is shown in FIGS. 1-3. Referring to FIG. 1, the welding
gun comprises a head tube assembly 2 mechanically and electrically
coupled to an electrically conductive welding gun body 4. The
welding gun body 4 has a threaded outer peripheral surface and a
cavity defined in part by a frusto-conical inner peripheral surface
6. The head tube assembly 2 comprises respective fittings 8 and 10
brazed to the opposing ends of a tubular structure consisting of an
inner copper tube 12, an outer copper sleeve 13, a steel tube 14
surrounding copper sleeve 13, a Teflon casing 16 encasing steel
tube 14, a steel tube 18 surrounding Teflon casing 16, and an outer
Teflon casing 20 encasing steel tube 18. The end of the copper tube
12 is inserted in and brazed to brass fitting 8. Middle and end
sections of the fitting 8, having different diameters, fit inside
respective sections of the aforementioned cavity of the gun body 4.
Thus, the head tube assembly 2 is supported at one end by the gun
body 4.
[0025] At the other end of the head tube assembly, a head tube
outer jacket fitting 10 is brazed to the distal end of steel tube
18 and in turn supports the nozzle 22. The nozzle 22 is fastened in
place by a nozzle adapter locking nut 24. A diffuser 26, disposed
inside the nozzle, is threaded into copper piece 30, which is
brazed to the end of the copper tube 12. Copper piece 30 is
surrounded by a ceramic insulator ring 32. Item 28 in FIG. 1 is a
diffuser insulator. The copper tube 12 conducts electric current
from the fitting 8 to the diffuser 26, which in turn transmits the
electric current to the contact tip. Accordingly, the diffuser 26
is electrically hot. The ceramic insulator 32 is supported by the
copper piece 30 to separate the electrically hot copper tube 12 and
diffuser 26 from the electrically cold steel tube 18, fitting 10,
and nozzle 22. The contact tip (not shown) transmits the electrical
current from the diffuser 26 to the welding wire (not shown). The
welding wire is fed to a bore in the diffuser 26 via a liner (not
shown) that lies inside the copper tube 12.
[0026] Referring to FIG. 3, the fitting 8 is coupled to the gun
body 4 by means of a molded rotation nut 34. As best seen in FIG.
5, the rotation nut 34 comprises a threaded brass nut 38 encased in
molded nylon 36. In the assembly view of FIG. 3, the brass nut 38
is in contact with the gun body 4 and the fitting 8. As will be
explained in more detail below, electric current is transmitted
from the gun body 4 to the fitting 8 via the brass nut 38. The
brass nut 38 has a threaded inner peripheral surface 40 that
threadably engages a threaded outer peripheral surface 42 of the
gun body 4. The rotation nut 34 retains the fitting 8 in a coupled
state with the gun body 4 when the rotation nut 34 is fully
threadably engaged with the gun body 4.
[0027] In accordance with a known welding gun having a fitting for
electrically coupling the head tube assembly to the gun body, the
fitting has a frusto-conical outer peripheral surface in contact
with a frusto-conical inner peripheral surface of the gun body
similar to surface 6 shown in FIG. 3. As explained in the
Background of the Invention section, such an arrangement has been
known to give rise to pitting and corrosion due to arcing. In
accordance with one embodiment of the invention, this problem is
solved by redesigning the fitting to eliminate the frusto-conical
outer peripheral surface and substitute a tapered electrically
insulative insert 60 having an outer peripheral surface with the
same frusto-conical geometry. As best seen in FIG. 3, the
electrical insulator 60 is disposed between and in contact with a
circular cylindrical outer peripheral surface 48 of the fitting 8
and the frusto-conical inner peripheral surface 6 of the gun body
4. The insulator 60 may be made of Delrin. The electrical insulator
60 acts as a shield to prevent current from being transmitted
directly from the frusto-conical inner peripheral surface 6 of the
gun body 4 to the fitting 8.
[0028] The electrical insulator 60 is shown in more detail in FIGS.
6 and 7. The insulator 60 is ring-shaped and comprises a
frusto-conical outer peripheral surface 64 that will be located
inside and in contact with the frusto-conical inner peripheral
surface 6 of the gun body. The insulator 60 further comprises a
circular cylindrical inner peripheral surface 66 surrounding and in
contact with the outer peripheral surface 48 of the fitting 8. The
insulator 60 has a chamfer 68 at the end of the inner peripheral
surface 66 where the insulator thickness (measured in a radial
direction) is greatest. The chamfer facilitates insertion of the
insulator onto the fitting. The opposing frusto-conical surfaces 6
and 64 have the same slope, so that the interaction of these mating
surfaces during insertion of the insulator 60 into the cavity of
the gun body 4 causes self-centering of the insulator (and
consequently, centering of the fitting) relative to the gun body
cavity.
[0029] Referring now to FIG. 4, the brass fitting 8 that couples
the head tube assembly to the gun body is a machined part
comprising a generally circular cylindrical middle section having a
first outer diameter, a collar 44 on one side of the middle
section, and a generally circular cylindrical end section having a
second diameter on the other side of the middle section, the second
diameter being smaller than the first diameter. The gun body has
respective bore sections sized to receive the circular cylindrical
middle and end sections of the fitting. As best seen in FIG. 3,
respective surfaces on the fitting 8 and the gun body 4 define a
volume occupied by the electrical insulator 60. A side wall 46 of
the collar 44 of the fitting abuts a proximal end face of the
insulator 60; the inner peripheral surface 66 (see FIG. 6) of the
insulator 60 sits on the circular cylindrical outer peripheral
surface 48 of the middle section of the fitting; and the
frusto-conical outer peripheral surface 64 of the insulator 60
bears against the frusto-conical inner peripheral surface 6 of the
gun body 4, as previously described.
[0030] The collar 44 of the fitting further comprises a
frusto-conical outer peripheral surface 45 (see FIG. 4) that
engages a frusto-conical inner peripheral surface 41 (see FIG. 5)
of the brass nut 38 during tightening of the molded nut 34 onto the
threaded end 42 (see FIG. 3) of the gun body 4. The frusto-conical
surface 6 of the gun body has an inner diameter that increases
toward the rotation nut 34, whereas the frusto-conical surface 41
has an inner diameter that increases toward the gun body. Thus,
when the nut is tightened onto the gun body, these tapered surfaces
6 and 41 hold the fitting 8 and electrical insulator 60 in the
positions seen in FIG. 3.
[0031] Referring again to FIG. 4, the fitting 8 has a passageway
comprising a circular cylindrical first bore section 50 of a first
diameter and a circular cylindrical second bore section 52 of a
second diameter less than the first diameter. As seen in FIG. 3,
the ends of tube 12 and sleeve 13 fit inside the bore section 50,
but cannot be inserted into bore section 52. A liner (not shown)
that guides the welding wire to the diffuser will be inserted in
the passageway formed by the tube 12 and bore section 52 of the
fitting 8.
[0032] As best seen in FIG. 4, the bore section 52 of the fitting 8
is provided with a plurality of radial holes 56 spaced at equal
angular intervals about the circumference, which holes allow
communication between the bore section 52 inside the filling and an
annular groove 80 formed on the outer periphery of the filling. The
annular groove 80 in turn communicates with a channel in the gun
body that supplies shielding gas. The gas flows from the holes 56
to the gas diffuser 26 along the outside of the liner (not shown)
and inside the copper tube 12. As best seen in FIG. 3, a pair of
O-ring seals 82 are seated in respective annular grooves 74 that
flank the annular groove 80. Seals 82 press against the opposing
inner peripheral surface of the gun body and effectively seal the
inert gas channel formed by the annular groove 80 and the opposing
inner peripheral surface of the gun body. The gap between the end
section of the fitting and the liner (not shown) is sealed at one
end by another O-ring seal 88, which is seated in an annular groove
76 (see FIG. 4) formed on the inner peripheral surface of the
fitting end section and presses against the outer peripheral
surface of the liner.
[0033] Referring again to FIG. 4, the middle section of the fitting
8 is provided with a first pair of slots 54 and a second pair of
slots 55 displaced longitudinally relatively to the first pair of
slots 54. These slots allow communication between the second bore
section 50 and a respective pair of annular grooves 71 and 73
formed on the outer periphery of the fitting. One of annular
grooves 71 and 73 communicates with a channel in the gun body that
supplies cooling water, while the other annular groove communicates
with a channel in the gun body that removes cooling water. The
water enters via one pair of slots, travels toward the diffuser in
channels between longitudinal lobes formed on the one side of the
outer periphery of copper tube 12, encapsulated by copper sleeve
13, reverses direction in an annular groove at the end of the
copper tube, travels back toward the fitting in channels between
longitudinal lobes formed on the other side of the outer periphery
of copper tube 12, and then exits via the other pair of slots.
[0034] As best seen in FIG. 3, an O-ring seal 86 is seated in an
annular groove 72 that lies between the annular grooves 71 and 73.
In addition, a trio of O-ring seals 84 are seated in respective
annular grooves 70 that flank the annular grooves 71 and 73. Seals
84 and 86 press against the opposing inner peripheral surface of
the gun body and effectively seal the cooling water channels formed
by the annular grooves 71 and 73 and the opposing inner peripheral
surface of the gun body.
[0035] The above-described mechanical interface design solves the
problem of corrosion and binding between the head tube assembly and
the gun body. The solution is accomplished by passing the welding
current through the brass nut 38 that holds the head tube assembly
in place, instead of through the tapered surface 6 in the gun body
that locates the head tube assembly in a centered position. As a
result, no arcing occurs across the mechanical interface between
the head tube assembly 2 and the gun body 4.
[0036] Referring again to FIG. 3, the current path in the disclosed
embodiment can be traced. In a prior art design, current was
carried from the gun body 4 to the head tube assembly 2 through the
area labeled as "A". This caused problems because the fit between
the two frusto-conical surfaces in area "A" was not always tight
and the current passing between them would cause pitting and
corrosion. Furthermore, water (for cooling) is present in the area
labeled "D" that could sometimes compound the problem if the head
tube were mishandled. The tapered insulator 60 provides a
nonconductive interface in area "A" on the head tube assembly 2.
Consequently, the current (seeking a path of least resistance) is
carried through the threaded area "B", through the brass nut 38 and
then through the interface (of frusto-conical surfaces 41 and 45)
in area "C" into the fitting 8. The surfaces 41 and 45 have a tight
fit and do not give rise to the same problem. The taper of the
frusto-conical inner peripheral surface 41 (see FIG. 5) of the nut
38 matches a taper of the frusto-conical outer peripheral surface
45 (see FIG. 4) of the fitting 8, providing enough surface contact
for current conduction to occur.
[0037] Current could be conducted through area "D" because of the
cooling water present there. However, due to the readily available
current path through areas "B" and "C", most of the current will
travel through areas "B" and "C" because it will take the path of
least resistance. Furthermore, there is no chance that the current
will arc across area "D" because of the path that is available
through areas "B" and "C". Also, the fact that water is the
connection between the two metal parts 4 and 8 means that these
metal parts cannot bind or arc together.
[0038] The specific materials cited above are disclosed for
illustrative purposes only. It should be appreciated that the
invention is not limited to the use of the specific materials
disclosed herein. For example, the electrically insulative insert
need not be made of Delrin, but instead could be made of other
electrically insulative materials having sufficient rigidity,
hardness and resistance to corrosion. Furthermore, the wire feeding
gun may be an air-cooled system instead of a water-cooled
system.
[0039] While the invention has been described with reference to
preferred embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for members thereof without departing from the scope of
the invention. In addition, many modifications may be made to adapt
a particular situation to the teachings of the invention without
departing from the essential scope thereof. Therefore it is
intended that the invention not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this invention, but that the invention will include all embodiments
failing within the scope of the appended claims.
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