U.S. patent application number 09/788039 was filed with the patent office on 2002-08-22 for mig gun nozzle with self centering, quick release screw and reduced cross-sectional area at the front.
Invention is credited to Altekruse, Kenneth C., Doherty, James E..
Application Number | 20020113046 09/788039 |
Document ID | / |
Family ID | 25143256 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020113046 |
Kind Code |
A1 |
Altekruse, Kenneth C. ; et
al. |
August 22, 2002 |
MIG GUN NOZZLE WITH SELF CENTERING, QUICK RELEASE SCREW AND REDUCED
CROSS-SECTIONAL AREA AT THE FRONT
Abstract
A MIG welding gun has a diffuser with an external thread and a
frusto-conical back ramp. A nozzle assembly includes an insert with
a back ramp and a thread that mates with the diffuser thread. The
threads of the diffuser and insert have respective ramps that mate.
A single turn of the nozzle assembly on the diffuser causes
simultaneous engagement of the insert and diffuser back ramps and
of the insert and diffuser thread ramps. Such engagement centers
the nozzle to be concentric with the diffuser and also produces a
wedging action that retains the nozzle assembly on the diffuser
until a relatively substantial reverse torque is applied to the
nozzle assembly. The nozzle front end has a narrow annulus, which
reduces the amount of radiant heat from the welding arc that
reaches the nozzle.
Inventors: |
Altekruse, Kenneth C.;
(Appleton, WI) ; Doherty, James E.; (Barrington,
IL) |
Correspondence
Address: |
Mark W. Croll
Illinois Tool Works Inc.
3600 West Lake Avenue
Glenview
IL
60025
US
|
Family ID: |
25143256 |
Appl. No.: |
09/788039 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
219/137.42 |
Current CPC
Class: |
B23K 9/173 20130101 |
Class at
Publication: |
219/137.42 |
International
Class: |
B23K 009/167 |
Claims
We claim:
1. A MIG welding gun comprising: a. a head tube; b. a conductor
having a threaded end that protrudes beyond an end of the head
tube; c. a diffuser that defines a first longitudinal axis and that
has upstream and downstream ends and a bore, the bore adjacent the
upstream end having threads that screw to the conductor threaded
end, the diffuser having a frusto-conical back ramp that makes a
first predetermined angle relative to the first longitudinal axis,
the diffuser further having an external thread of a predetermined
pitch with a flank that is formed as a diffuser thread ramp that
makes a second predetermined angle relative to the first
longitudinal axis; and d. a nozzle assembly assembled to the
diffuser comprising: i. a nozzle having front and back ends, and a
first inner diameter; and ii. means in the nozzle first inner
diameter for mating with the diffuser thread and for engaging the
diffuser back ramp when the nozzle assembly is fully assembled to
the diffuser.
2. The MIG welding gun of claim 1 wherein the means for mating with
the diffuser thread and for engaging the diffuser back ramp
comprises an electrically insulative insulator pressed in the
nozzle first inner diameter, the insulator having an internal
thread of the predetermined pitch that mates with the diffuser
thread, the insulator thread having a flank that is formed as an
insulator thread ramp that mates with the diffuser thread ramp, and
the insulator having a frusto-conical back ramp that engages the
diffuser back ramp when the nozzle assembly is fully assembled to
the diffuser.
3. The MIG welding gun of claim 1 wherein the means for mating with
the diffuser thread and for engaging the diffuser ramp comprises:
a. a tubular insulator pressed in the nozzle first inner diameter;
and b. an insert concentric with the nozzle and pressed in the
insulator, the insert defining a second longitudinal axis and
having front and back ends, and a thread of the predetermined pitch
mating with the diffuser thread, the insert thread having a flank
that is formed as an insert thread ramp that mates with the
diffuser thread ramp, and the insert having a frusto-conical back
ramp that engages the diffuser back ramp when the nozzle assembly
is fully assembled to the diffuser.
4. The MIG gun of claim 3 wherein the first and second
predetermined angles are equal.
5. The MIG gun of claim 3 wherein the diffuser back ramp diverges
toward the diffuser upstream end, and wherein the diffuser thread
ramp diverges toward the diffuser downstream end, so that a wedging
action is produced by the insert between the diffuser back and
thread ramps when the nozzle assembly is assembled on the diffuser
to thereby retain the nozzle assembly on the diffuser.
6. The MIG gun of claim 4 wherein the first and second
predetermined angles are approximately 30 degrees, and wherein the
diffuser back ramp diverges toward the diffuser upstream end and
the diffuser thread ramp diverges toward the diffuser downstream
end.
7. The MIG gun of claim 6 wherein the insert automatically centers
on the diffuser to bring the first and second longitudinal axes
concentric with each other when the nozzle assembly is fully
assembled on the diffuser.
8. The MIG gun of claim 3 wherein the diffuser thread has one turn,
so that the nozzle assembly is fully assemblable to and
disassemblable from the diffuser with a single turn of the nozzle
assembly on the diffuser.
9. The MIG gun of claim 8 wherein the pitch of the diffuser and
insert threads is approximately 0.193 inches.
10. The MIG gun of claim 3 wherein: a. the diffuser has a circular
flange at the upstream end thereof, and an outer diameter; and b.
the diffuser back ramp intersects the circular flange and the outer
diameter.
11. The MIG gun of claim 10 wherein: a. the insert has an inner
diameter; and b. the insert back ramp intersects the insert back
end and the inner diameter.
12. The MIG gun of claim 3 wherein the insert and diffuser thread
ramps, and the insert and diffuser back ramps, are so dimensioned
that the insert back ramp engages the diffuser back ramp when the
nozzle assembly has made a single turn on the diffuser, so that the
nozzle assembly is fully assembled to and disassembled from the
nozzle by a single turn of the nozzle assembly on the diffuser.
13. The MIG gun of claim 3 wherein the nozzle comprises: a. a
cylindrical section adjacent the back end and having a first outer
diameter and the first inner diameter, the cylindrical section
first outer diameter and first inner diameter defining a first wall
thickness; and b. a frusto-conical section adjacent the front end
that joins the cylindrical section at a junction, the
frusto-conical section having inner and outer surfaces that
converge toward the nozzle front end, a second inner diameter at
the junction that is equal to the first inner diameter, and a
second outer diameter at the junction that is equal to the first
outer diameter, the frusto-conical section further having a third
outer diameter and a third inner diameter at the nozzle front end
that cooperate to define a second wall thickness.
14. The MIG gun of claim 13 wherein the second wall thickness is
less than the first wall thickness.
15. The MIG gun of claim 13 wherein the frusto-conical section
outer surface converges toward the nozzle front end at a steeper
angle than the frusto-conical section inner surface.
16. A MIG gun nozzle with self centering, quick release screw and
reduced cross-sectional area at the front comprising: a. a nozzle
assembly comprising: i. a nozzle that defines a nozzle longitudinal
axis; ii. an insulator pressed in the nozzle; and iii. an insert
inside the insulator, the insert defining an insert longitudinal
axis concentric with the nozzle longitudinal axis and having a
selected surface and an internal thread of a predetermined pitch
and thread form; and b. a diffuser that defines a diffuser
longitudinal axis and that has an external thread of the
predetermined pitch and thread form and having at least one
complete turn, the diffuser having a selected diffuser surface that
is engaged by the selected insert surface when the nozzle assembly
is fully assembled to the diffuser, the selected diffuser and
insert surfaces cooperating to limit the nozzle assembly to one
complete turn on the diffuser to fully assemble the nozzle assembly
to the diffuser.
17. The MIG gun of claim 16 wherein the predetermined pitch is
approximately 0.193 inches.
18. The MIG gun of claim 16 wherein: a. the selected diffuser
surface is an exterior frusto-conical back ramp; and b. the
selected insert surface is an interior back ramp that engages the
diffuser back ramp when the nozzle assembly is fully assembled to
the diffuser.
19. The MIG gun of claim 18 wherein the diffuser back ramp makes a
first predetermined angle with the diffuser longitudinal axis, and
where the insert back ramp makes the first predetermined angle with
the insert longitudinal axis.
20. The MIG gun of claim 19 wherein the first predetermined angle
is approximately 30 degrees.
21. The MIG gun of claim 18 wherein: a. the insert thread is formed
with an insert thread ramp that makes a second predetermined angle
with the insert longitudinal axis; b. the diffuser thread is formed
with a diffuser thread ramp that makes the second predetermined
angle with the diffuser longitudinal axis and that mates with the
insert thread ramp when the nozzle assembly is assembled to the
diffuser; and c. the second predetermined angle is substantially
equal to the first predetermined angle.
22. The MIG gun of claim 21 wherein the insert thread ramp and the
insert back ramp engage the diffuser thread ramp and diffuser back
ramp, respectively, simultaneously when the nozzle assembly is
fully assembled on the diffuser, the diffuser thread and back ramps
cooperating with the insert thread and back ramps, respectively, to
produce a wedging action between the insert and the diffuser that
retains the nozzle assembly on the diffuser, so that a substantial
reverse torque is required on the nozzle assembly to disassemble
the nozzle assembly from the diffuser.
23. The MIG gun of claim 21 wherein: a. the insert thread ramp and
insert back ramp engage the diffuser thread ramp and diffuser back
ramp, respectively, simultaneously when the nozzle assembly is
fully assembled on the diffuser; and b. the diffuser thread ramp
and diffuser back ramp cooperate with the insert thread ramp and
insert back ramp, respectively, to automatically center the nozzle
longitudinal axis concentric with the diffuser longitudinal axis
when the nozzle assembly is fully assembled on the diffuser.
24. The MIG gun of claim 16 wherein the nozzle comprises: a. a
cylindrical section having a back end, and a first outer diameter
and a first inner diameter that define a first wall thickness; and
b. a frusto-conical section joined to the cylindrical section at a
junction and having a front end opposite the cylindrical section
back end, the frusto-conical section having inner and outer
surfaces that converge toward the nozzle front end, a second inner
diameter at the junction that is equal to the first inner diameter,
and a second outer diameter at the junction that is equal to the
first outer diameter, the frustoconical section further having
third inner and outer diameters at the nozzle front end that
cooperate to define a second wall thickness.
25. The MIG gun of claim 24 wherein the second wall thickness is
less than the first wall thickness.
26. The MIG gun of claim 24 wherein the frustoconical section outer
surface converges toward the nozzle front end at a steeper angle
than the frusto-conical section inner surface.
27. A method of assembling a MIG welding gun comprising the steps
of: a. providing a diffuser having a diffuser longitudinal axis, a
selected surface, and an external thread of a predetermined pitch
and thread form; b. providing a nozzle assembly having a nozzle
with a nozzle longitudinal axis, an insulator inside the nozzle,
and an insert inside the insulator, the insert having a selected
surface and an internal thread of the predetermined pitch and
thread diameter; and c. turning the insert thread a single turn on
the diffuser thread and then engaging the selected insert surface
with the selected diffuser surface and thereby fully assembling the
nozzle assembly on the diffuser with the single turn of the nozzle
assembly.
28. The method of claim 27 wherein: a. the step of providing a
diffuser having a selected surface comprises the step of providing
the diffuser with a frusto-conical diffuser back ramp; b. the step
of providing an insert having a selected surface comprises the step
of providing the insert with a frusto-conical insert back ramp; and
c. the step of engaging the selected insert surface with the
selected diffuser surface comprises the step of engaging the
diffuser back ramp with the insert back ramp when the nozzle
assembly is fully assembled on the diffuser.
29. The method of claim 28 comprising the further steps of: a.
providing the diffuser with a frustoconical diffuser thread ramp on
the external thread; b. providing the insert with a frusto-conical
insert thread ramp on the internal thread; and c. mating the
diffuser thread ramp with the insert thread ramp simultaneously
with the engagement of the insert back ramp with the diffuser back
ramp when the nozzle assembly is fully assembled on the
diffuser.
30. The method of claim 29 comprising the further step of producing
a wedging action between the insert and the diffuser and thereby
firmly retaining the nozzle assembly on the diffuser.
31. The method of claim 30 comprising the further step of applying
a substantial reverse torque on the nozzle assembly and
disassembling the nozzle assembly from the diffuser.
32. The method of claim 29 comprising the further step of centering
the insert on the diffuser and thereby bringing the nozzle
longitudinal axis to be concentric with the diffuser longitudinal
axis.
33. A method of assembling a MIG welding gun comprising the steps
of: a. providing a diffuser having a longitudinal axis, a diffuser
frusto-conical back ramp, and an external thread of a predetermined
pitch and thread form; b. providing a nozzle assembly having a
nozzle with a nozzle longitudinal axis, an insulator inside the
nozzle, and an insert inside the insulator concentric with the
nozzle, the insert having an insert frusto-conical back ramp and an
internal thread of the predetermined pitch and thread form; and c.
turning the insert thread on the diffuser thread until the insert
back ramp engages the diffuser back ramp.
34. The method of claim 33 comprising the further step of centering
the nozzle longitudinal axis to be concentric with the diffuser
longitudinal axis.
35. The method of claim 34 wherein the step of centering the nozzle
longitudinal axis comprises the steps of: a. providing the diffuser
external thread with a frusto-conical diffuser thread ramp; b.
providing the insert internal thread with a frusto-conical insert
thread ramp; and C. turning the insert thread on the diffuser
thread and simultaneously engaging the insert back ramp with the
diffuser back ramp and the insert thread ramp with the diffuser
thread ramp.
36. The method of claim 33 wherein the step of turning the insert
thread on the diffuser thread comprises the step of turning the
nozzle assembly a single turn on the diffuser thread whereupon the
insert back ramp engages the diffuser back ramp.
37. The method of claim 36 wherein the step of turning the insert
thread on the nozzle thread the single turn comprises the step of
advancing the nozzle assembly approximately 0.193 inches along the
diffuser.
38. The method of claim 35 wherein the step of simultaneously
engaging the insert back ramp with the diffuser back ramp and the
insert thread ramp with the diffuser thread ramp comprises the step
of producing a wedging action between the insert and the diffuser
and thereby retaining the nozzle assembly on the diffuser.
39. The method of claim 38 comprising the further step of applying
a reverse torque to the nozzle assembly and releasing the nozzle
assembly from the diffuser.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention pertains to welding guns, and more
particularly to the nozzles and diffusers of MIG welding guns.
[0003] 2. Description of the Prior Art
[0004] MIG welding guns are composed of several components that
must work together if successful welding is to occur. In addition,
for the gun to be acceptable to the welding industry, the various
components must be easy to assemble and disassemble.
[0005] An especially important welding gun component is the nozzle,
which directs inert gas to shield the welding arc from atmospheric
air. The nozzle is part of a nozzle assembly, which includes the
outer tubular nozzle, a tubular insulator inside the nozzle, and in
some cases, a metal insert inside the insulator. The nozzle has a
front end that is unsupported and is close to the welding arc. The
nozzle back end is retained by the insulator or insert to another
gun component, such as a diffuser. The diffuser is at the
downstream end of a head tube that extends from the gun handle. A
contact tip is connected to a downstream end of the diffuser and is
generally surrounded by the nozzle front end. The inert gas flows
through an annular passage between the nozzle front end and the
contact tip to the welding arc.
[0006] Prior nozzles assemblies can be classified in two
categories: slip-on, and screw-on. In a slip-on nozzle assembly
design, a formed retaining sleeve or retaining rings are used
between the nozzle assembly and the diffuser. The diffuser may have
grooves in an outer diameter that contain the retaining sleeve or
rings. The retaining sleeve or rings create an interference fit
between their outer diameters and the inner diameter of the nozzle
assembly. The nozzle assembly is forced over the retaining sleeve
or rings to create a frictional force that holds the nozzle
assembly to the diffuser. The retaining sleeve or rings do not
provide a solid connection between the nozzle assembly and the
diffuser so as to maintain the nozzle concentric with the diffuser
and the contact tip. Eccentricity between the nozzle and the
contact tip is detrimental, because it causes uneven flow of the
inert gas around the contact tip and welding arc. Another
disadvantage of the slip-on nozzle assembly design is that there is
no way to positively maintain the nozzle longitudinally in place on
the welding gun. Positive retention of the nozzle is especially
important during rough usage, as, for example, if an operator uses
the nozzle to knock slag from the workpiece. Maintaining proper
longitudinal relationship between the nozzle and the contact tip is
necessary for satisfactory welding. In addition, in high heat
welding conditions, the nozzle and retaining sleeve or rings get
hot, which can cause the retaining sleeve or rings to soften and
allow the nozzle assembly to fall off the gun.
[0007] A screw-on nozzle assembly utilizes several turns of threads
to retain it on the diffuser. Normal manufacturing tolerances of
the threads allow lateral movement of the nozzle from a true
concentric position relative to the diffuser and the contact tip. A
screw-on nozzle assembly normally has an insulated flat end surface
that abuts a flat surface on the diffuser when the nozzle assembly
is fully turned onto the diffuser. Retention of the nozzle assembly
on the diffuser depends on a hard stop between the abutting flat
surfaces of the nozzle assembly and diffuser. Removal of the nozzle
assembly from the diffuser requires turning it through all of the
several threads in engagement. In high heat conditions, the parts
distort, and removal of the screw-on nozzle assembly is
difficult.
[0008] The welding arc is, of course, extremely hot. Some heat from
the arc transfers by radiation to the nozzle front end. Such heat
transfer to the nozzle is detrimental, as it is a major cause of
metal distortion and softening of the nozzle material. The
annealing temperature of copper, the material from which some
nozzles are made, is approximately 800 degrees F. It is highly
desirable that the operating temperature of the nozzle assembly be
well below that temperature in order that the nozzle maintain its
strength and thus be able to withstand rough handling during
use.
[0009] The heat in the nozzle dissipates in several ways. One way
is for the heat to radiate to the atmosphere. Some of the heat is
carried away by convection of air past the nozzle. Additional
nozzle heat is transferred by conduction through the diffuser and
head tube to the gun handle.
[0010] Under some conditions, particularly when the temperature
difference is greater than approximately 300 degrees F., heat can
be transferred by radiation from the nozzle to the contact tip.
Consequently, a hot nozzle can raise the temperature of the contact
tip. A hot contact tip is undesirable, because it has a shorter
service life and reduced performance compared to a cool contact
tip. A cool contact tip also minimizes heat transfer by conduction
through the diffuser and head tube to the gun handle. Accordingly,
an important benefit of a cool nozzle is that it tends to keep the
contact tip cool and it also keeps heat distortion of the nozzle to
a minimum.
[0011] During the course of a welding operation, it is sometimes
necessary to replace the contact tip. To do so, it is first
necessary to remove the nozzle in order to gain access to the
contact tip. In a screw-on nozzle design, the operator must turn
the nozzle until it advances off the diffuser. Grabbing the hot
nozzle with a gloved hand is cumbersome and potentially
uncomfortable, so it is highly desirable that the nozzle be removed
as quickly and easily as possible. However, standard threaded
connections between the nozzle and diffuser require that the
operator turn the nozzle through all the several turns of the
mating threads before the nozzle advances off the diffuser. After
replacing the contact tip, the reverse procedure of rethreading the
hot nozzle on the diffuser must be performed.
[0012] Thus, further developments are needed in MIG welding
guns.
SUMMARY OF THE INVENTION
[0013] In accordance with the present invention, a MIG gun nozzle
with self centering, quick release screw and reduced
cross-sectional area at the front is provided that has greatly
improved thermal and mechanical characteristics compared to prior
guns. This is accomplished by designing the nozzle with a minimum
frontal area and with ramps that center and retain the nozzle on
the diffuser.
[0014] The nozzle has front and back ends. At the back end is a
cylindrical tubular section with inner and outer diameters and a
relatively thick wall. At the front end of the cylindrical section
is a hollow frusto-conical section. The frusto-conical section has
inner and outer surfaces that converge toward the nozzle front end.
At the junction of the cylindrical and frusto-conical sections, the
wall of the frusto-conical section has the same thickness as the
wall of the cylindrical section, and the frusto-conical section
inner surface is coincident with the cylindrical section inner
diameter. The wall thickness of the frusto-conical section at the
nozzle front end is less than the wall thickness at the junction of
the cylindrical and frusto-conical sections such that the nozzle
front end is a narrow annulus.
[0015] The nozzle of the invention has a screw-on design. In the
preferred embodiment, the nozzle is part of a nozzle assembly that
also includes an insulator and an insert. The nozzle assembly
insert has an internal thread with a pitch of only a few threads
per inch.
[0016] The diffuser has an external thread that mates with the
thread on the nozzle assembly insert. Preferably, the diffuser is
designed such that the nozzle assembly is fully assembled to the
diffuser by only a single turn. After the nozzle assembly has
advanced through the single turn, the insert contacts a stop on the
diffuser.
[0017] Further in accordance with the present invention, the nozzle
is centered concentrically with the diffuser when the nozzle
assembly is fully assembled to the diffuser. For that purpose, the
diffuser stop is fabricated as an exterior frusto-conical back ramp
that makes a predetermined angle with the diffuser longitudinal
axis. There is an interior back ramp on the nozzle assembly insert.
The insert back ramp is designed to engage the back ramp on the
diffuser when the nozzle is fully assembled to the diffuser. In
addition, there is a ramp on the diffuser thread that is oriented
oppositely as the diffuser back ramp. Specifically, the flank of
the diffuser thread between the thread root and tip is formed as a
thread ramp. The angle that the thread ramp makes with the diffuser
longitudinal axis is preferably equal to the angle that the
diffuser back ramp makes with the diffuser longitudinal axis. The
thread of the insert has a ramp that is complimentary to the
diffuser thread ramp.
[0018] If desired, the insulator can be manufactured with the
internal threads and ramp. In that case, a separate insert is not
needed.
[0019] As the nozzle assembly is assembled to the diffuser, the
insert thread ramp slides around the diffuser thread ramp. As the
nozzle assembly approaches its fully turned condition, the insert
back ramp approaches and then engages the diffuser back ramp. A
slight torque on the nozzle produces a wedging action of the insert
on the diffuser. The wedging action occurs because of the
simultaneous engagement of the surface areas of the insert thread
and back ramps with the surface areas of the diffuser thread and
back ramps, respectively. The wedging action performs two
simultaneous functions. First, the wedging action automatically
centers the insert and nozzle assembly to be concentric with the
diffuser. Second, the wedging action causes the insert and nozzle
assembly to become tightly retained against loosening on the
diffuser. To release the nozzle assembly, a relatively substantial
reverse torque must be applied.
[0020] During operation, the nozzle remains exceptionally cool. The
narrow annulus at the nozzle front end is practically the only
place on the nozzle that is in a direct line of sight with the
welding arc. Consequently, only a minimal amount of radiant heat
from the welding arc reaches the nozzle. At the same time, the much
larger areas of the outer surfaces of the nozzle cylindrical and
frusto-conical sections that are in the shadow of the arc allow any
heat to escape by radiation and convection. Consequently, the
nozzle operates at a relatively cool temperature, which enhances
both its performance and that of the contact tip.
[0021] Other advantages, benefits, and features of the present
invention will become apparent to those skilled in the art upon
reading the detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross-sectional view of a portion of the MIG gun
nozzle with self centering, quick release screw and reduced
cross-sectional area at the front.
[0023] FIG. 2 is a view taken along line 2-2 of FIG. 1.
[0024] FIG. 3 is a longitudinal cross-sectional view on an enlarged
scale of the insert used with the MIG gun of the present
invention.
[0025] FIG. 4 is an enlarged side view of the diffuser of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Although the disclosure hereof is detailed and exact to
enable those skilled in the art to practice the invention, the
physical embodiments herein disclosed merely exemplify the
invention, which may be embodied in other specific structure. The
scope of the invention is defined in the claims appended
hereto.
[0027] Referring first to FIGS. 1 and 2, the outlet portion 1 of a
MIG welding gun 2 is illustrated that includes the present
invention. The welding gun outlet portion 1 is located at one end 4
of a head tube 5 that is part of the welding gun 2. A second end of
the head tube 5 is secured to a handle of the gun, not shown but
well known to persons skilled in the art. Inside the head tube end
4 is a tubular conductor 7. The head tube is pressed over the
conductor 7, with an electrically insulative sleeve 9 between them.
The insulator sleeve 9 preferably has a flange portion 10 that lies
against the head tube end 4. An insulative ring 13 surrounds the
conductor adjacent the insulative sleeve flange portion 10. Inside
the conductor is a liner 15. The liner 15 has an interior 17 that
is sized to guide a weld wire 19 toward a workpiece typically
represented at reference numeral 21.
[0028] The gun portion 1 further comprises a diffuser 23. The
diffuser 23 has an upstream end 25, a downstream end 27, and a bore
29. In the diffuser bore 29 at the upstream end 25 are internal
threads 31. The diffuser screws onto the conductor 7 by means of
the threads 31, with the insulative ring 13 squeezed between the
diffuser upstream end and the insulative sleeve flange portion 10.
The diffuser bore has a locating surface 39, which, as is
illustrated in FIG. 1, may be frusto-conical in shape. The liner 15
has a downstream end 41 with a complimentary shape. Accordingly,
the liner downstream end 41 is positively located against the
diffuser locating surface 39. There are internal threads 33 in the
diffuser bore at the diffuser downstream end 27. A contact tip 35
connects to the diffuser downstream end by means of the threads 33.
The contact tip has a hole 37 through it that guides the weld wire
19 from the liner 15 to the workpiece 21. The conductor 7,
diffuser, and contact tip define a common longitudinal axis 42.
[0029] A nozzle 3 surrounds the diffuser 23 and the contact tip 35.
In the illustrated construction, the nozzle 3 is part of a nozzle
assembly 56 that also includes a tubular insert 73, and an
electrically insulative insulator 75 between the nozzle and the
insert. However, in some applications the insulator and the insert
can be combined into a single component made from an electrically
insulative material. The nozzle, insert 73, and insulator 75 are
pressed together, with the insert being at the back end 77 of the
nozzle.
[0030] During operation of the MIG gun 2, an inert gas flows in a
downstream direction 43 from a welding machine through an annular
passage 45 between the conductor inner diameter 47 and the liner
15. From the annular passage 45, the inert gas flows to the
diffuser bore 29 and out radial holes 49 into a second annular
passage 51 between the nozzle 3, the diffuser downstream end 27,
and the contact tip 35. The inert gas flows out the welding gun,
arrow 53, at the nozzle front end 54 to surround the weld wire 19
and shield the weld wire 19 from atmospheric air.
[0031] The particular nozzle 3 shown is comprised of two sections:
a tubular cylindrical back section 57, and a tubular frusto-conical
front section 59. The cylindrical back section 57 has an inner
diameter 61 and an outer diameter 62 that are substantially
parallel for the length of the cylindrical section. The
frusto-conical section 59 joins to the cylindrical section at a
junction 63. At the junction 63, the frusto-conical section has an
outer surface 65 with an outer diameter 66 that is the same as the
cylindrical section outer diameter 62. Also, the frusto-conical
section has an inner surface 67 with an inner diameter 68 at the
junction 63 that is equal to the inner diameter 61 of the
cylindrical section.
[0032] In the illustrated construction, the outer surface 65 of the
frusto-conical section 59 converges toward the nozzle front end 54
at a steeper angle than the inner surface 67. Consequently, the
thickness of the wall 69 of the nozzle frusto-conical section 59 is
not uniform between the junction 63 and the nozzle front end 54.
Rather, the wall thickness decreases in the direction of the nozzle
front end. As a result, the nozzle front end consists of a narrow
annulus 71 having an outer diameter 72 and an inner diameter
74.
[0033] The retention of the nozzle 3 on the diffuser 23 constitutes
an important feature of the present invention. Retention is
achieved by means of the nozzle assembly insert 73. Also looking at
FIG. 3, the insert 73 has an outer diameter 79 that presses against
the insulator 75, an inner diameter 81, a back end 83, and a front
end 85. There is an interior frusto-conical back ramp 87 at the
intersection of the inner diameter 81 and the back end 83. The back
ramp 87 makes an angle A with the insert longitudinal axis 89. A
preferred angle A is approximately 30 degrees.
[0034] Near the front end 85 of the insert 73 is an internal thread
91. The preferred pitch of the thread 91 is approximately 0.193
inches. The thread 91 may have a cross-sectional form generally
similar to a stub acme thread form, if desired. The flank of the
thread that is toward the insert front end 85 is tapered at an
angle B relative to the insert longitudinal axis 89, thereby
forming a thread ramp 93. It is preferred that the angles A and B
are equal. For proper assembly with the diffuser 23, the major
diameter 94 of the insert thread is slightly smaller than the inner
diameter 81. In the design in which a separate insert is not used,
the internal thread and back ramp are machined directly into the
insulator near the nozzle back end 77.
[0035] Turning to FIG. 4, the diffuser 23 has a circular flange 95
at the upstream end 25. The flange 95 intersects a frusto-conical
back ramp 97. The diffuser back ramp 97 makes an angle A1 with the
diffuser longitudinal axis 99. The angle A1 is equal to the angle A
of the nozzle assembly insert 73. The diffuser back ramp intersects
a cylindrical outer diameter 100 that is slightly smaller than the
inner diameter 81 of the insert 73. Between the diffuser upstream
end and downstream end 27 is an external thread 101. According to
one aspect of the invention, the diffuser thread 101 has but a
single turn. The external thread 101 has the same pitch and thread
form as the internal thread 91 of the insert 73. In addition, the
flank of the diffuser thread 101 that is toward the upstream end is
tapered at an angle B1 relative to the diffuser longitudinal axis
99, thereby creating a diffuser thread ramp 103. The angle B1 is
equal to the angle B of the insert. It is preferred that the angle
B1 equal the angle A1 of the diffuser back ramp 97. The major
diameter 105 of the diffuser thread is slightly less than the
insert inner diameter 81.
[0036] Returning to FIG. 1, the nozzle assembly 56 is shown
assembled to the diffuser 23. To do so, the insert 73 is slipped
over the diffuser downstream end 27. The insert back end 83 and
inner diameter 81 pass over the diffuser thread 101 until the
insert thread 91 contacts the diffuser thread. The nozzle assembly
is rotated slightly, if necessary, until the insert and diffuser
threads mate. From the point of initial mating, the nozzle assembly
is further turned. Doing so causes the insert ramp thread 93 to
bear against and follow the diffuser thread ramp 103 and advance
the nozzle assembly until the surface area of the insert back ramp
87 engages the surface area of the diffuser back ramp 97. As
mentioned, the diffuser thread may have a single turn. In that
case, the diffuser and insert are so dimensioned that the surface
area of the insert back ramp engages the surface area of the
diffuser back ramp at the completion of one turn of the nozzle
assembly on the diffuser. A slight additional torque applied to the
nozzle assembly produces a wedging action of the insert on the
diffuser. The wedging action is a result of the simultaneous
engagement of the surface area of the insert back ramp 87 with the
surface area of the diffuser back ramp 97, and the mating of the
insert thread ramp 93 with the diffuser thread ramp 103. The
wedging action of the insert and diffuser back ramp surface areas
causes the insert and thus the nozzle assembly to remain firmly
retained in place on the diffuser. The nozzle assembly remains
firmly retained on the diffuser until a relatively substantial
reverse torque is intentionally applied to the nozzle 3. When that
occurs, a single reverse turn of the nozzle assembly is sufficient
to remove it from the welding gun 2. If desired, the diffuser
thread, and the diffuser and insert back ramps, can be dimensioned
such that the insert back ramp engages the diffuser back ramp at
the completion of more or less than one turn of the nozzle
assembly.
[0037] A second major benefit of the engaged ramps 87, 97 and 93,
103 is that they cause the nozzle assembly insert 73 to
automatically center on the diffuser 23 such that their respective
longitudinal axes 89 and 99 coincide with each other and also with
the common longitudinal axis 42. The passage 51 between the nozzle
front end 54 and the contact tip 35 for the inert gas is thus
uniform around the contact tip, which is highly beneficial for both
shielding the welding arc 55 and economy of gas usage. Moreover,
the sturdy and centered retention of the nozzle assembly 56 on the
diffuser effectively eliminates the possibility that the nozzle
front end could drift toward the contact tip during use.
[0038] Thus, it is apparent that there has been provided, in
accordance with the invention, a MIG gun nozzle with self
centering, quick release screw and reduced cross-sectional area at
the front that fully satisfies the aims and advantages set forth
above. While the invention has been described in conjunction with
specific embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications, and
variations as fall within the spirit and broad scope of the
appended claims.
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