Note: Descriptions are shown in the official language in which they were submitted.
~ guide tube for a filler metal wire, particularly for use in an arc
welding machine.
This invention relates to welding and particularly to machines and
devices used to establish an electric arc between an electrode and a region
of a part to be welded, in such a manner as to heat said zone to a high
enough temperature for filler metal to flow thereon.
Several welding processes fall into this category. In some of them the
filler metal is supplied in the form of wire which is unwound from a reel as
fast as it is ued up. In -this type of method the wire is sometimes used as
an arc-forming electrode and sometimes not.
For accurate welding the end of the filler wire must be suitably guided
relative to the zone to be welded. Further, the wire must be moved along a
weld line smoothly and without jerking.
Tradi-tionally the wire of filler metal is guided by a tube having a bore
with a rear opening through which the wire enters the tube and a front open-
ing through which a short length of wire projects, to be presented in a
suitable position next to a weld zone. The bore of -the tube is subjected to
rapid wear and numerous play take up means have been proposed to maintain a
good sliding contact between the wire and the inside wall of the tube.
Play take up means are particularly useful in the common case of the
filler metal guide tube also serving to supply electric curren-t to the wire,
in which case the tube may be called a contact tube~ Conventional tubes give
rise to numerous difficulties in operation. In particular, they give rise to
arcing inside the guide tube bore, thereby pitting i-ts inside surface and
deteriorating the quality of the electrical contact. However, known play
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take up means are often ex-tremely complicated and consequently too expensive
for practical use. They are also often excessively bulky and are therefore
difficult to use i.nside a nozzle which is also intended to blow gas over the
weld melt zone.
Further, such known guide -tubes suffer from accumulations o matter
projected from the weld melt in molten form because of the turbulent s-tate of
the melt which is accentuated by the gas je-t. The projected matter tends to
cause harmful sticking between the tube and the end of the filler metal.
Further as i-t solidifies the mat-ter -tends to create accumulations of metal
which in turn tend to block the outlet from the gas nozzle and, in contact
tubes, encourages the formaion of unwanted arcs, particularly be-tween the
surface of the tube and the nozzle. Such arcs give rise to all sorts of
faults in operation, par-ticularly in machines having au-tomatic arc current
regulation.
Preferred embodimen-ts of the present invention eliminate -these difficult-
ies, providing guide tubes of greatly increased lifetime, while s~stantialiy
improving welding quality.
In a first aspect the presen-t inve:ntion provides a guide tube for
guiding filler metal wire in welding apparatus, particularly electric arc
welding apparatus, the tube comprising a tubular body having a wire-guiding
bore and play take up means comprising at least one thrust membar movably
mounted in a passage located in the guide tube wall, which passage is trans-
verse to said bore and opens our therein, said thrust member being urged by
resilien-t means to project into said bore whereby a wire passing along -the
bore is resiliently urged against the opposite wall of the bore by said play
~ 2~ b
take up means. The improvement wherein said resilient means is a conical
compression spring having turns that compress into a spiral, said spring
being entirely lodged in said passage in the -thickness of t'ne guide tube
wall.
Unlike a compression spring which is cylindrical, with helical turns
that stack on top of each other when the spring is compressed giving a
minimum compressed spring length equal to the sum of the thicknesses of the
-turns, a conical spring with sprial turns can be compressed, in theory, down
to the thickness of a single -turn, by vir-tue of the smaller turns being
10' received inside the larger turns~ This conical feature makes it possible -tomount a thrust member, preferably a ball, -together wi-t.h its thrust-providing
spring, in a passage whose length in limited to the thickness of the guide
tube wall, in such a manner that -there are no projections from the outside
surface of -the tube. The degree of ball penetration into the bore o:E -the
tube should be limited by a ball-retaining seat.
In preferred embodiments of the invention, the -thrust members are made
of electrically insulated material, or are a-t least coated with such a
material and the springs are likewise coated with insulating material. This
prevents any danger of the moving parts of -the play take up means triggering
parasitic arcs.
In one preferred embodiment the passage in which the spring is housed
opens out in the outside surface of the guide tube wall, and the passage is
closed by a sheath which surrounds the guide tube~ The largest turn of the
conical spring then abuts against the sheath. The sheath is preferably
~5 designed to protect the outside surface of at least the front end of the
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(1nide L~lbe ac~airlst metal sputtered up from the weld melt and adhering thereto,
arld it also provldes an electrical insulation for the guide tube. Thus
arasitic arc are E~revented from Eorming and solidiEied weld melt is prevented
trom ac:cumulatillcl and blocking the outlet of a gas outlet nozzle, or causing
the riller wire to stick t~o the tube.
~ second aspec~ of the invention provides a guide tube for guiding
{iller metal wire in weldinq apparatus~ particularly electric arc welding
apparatus, the tube comprising a tubular body having a wire-guiding bore
and e~tended at its front end by an end piece which is not adhesive with
LO respect to ~no]ten metal and which is provided with a hole extending the
guide bore, the improvement wherein said end piece comprises a rear portion
which is moun~ed on the front of the tubular body and is held inside a pro-
tectLve sheath ~itted over said body, said sheath having an inwardly directed
end piece retaining neck, and a front poition proiecting beyond the front end
of the sheath towards the welding zone.
The end piece serves to prevent the end of the filler wire being
accidelltally jal~ed, by weld melt entering the bore of the guide tube and
deterioratillg it. The end piece is advantageously tapered towards its tip
which has the effect of making it easier to weld in rece~ses in the surface
~() of the parts being welded.
In one embodimellt, the rear portion of the end piece is larger than
its front portion and there is h step between the two portions providing
a shoulder, that can be retained by a neck in the form of an inwardly direct-
ed rim at the end oE the sheath.
Advantageously a degree of transversal play iq left for the rear portion
~6~
of -the end piece held by the end of the sheath. This enables the end piece
to centre itself on the bore of the guide tube to match wear -therein~ W~len
play take up means are provided in the guide tube, the filler wire progress-
ively wears itself a groove in the wall of the bore. It thus moves off-
centre in the course of time. I.eaving the end piece free to move means that
it can follow the wear withou-t hindering the passage of filler wire.
In a preferred embodiment the cross section of the hole through the
end piece varies along the leng-th of the end piece. This arrangement serves
to prevent the fil]er metal wire from deposi1:ing a continuous layer of metal
particles a]ong the wall of the hole as it: passes therethrough. In a hole of
uniform section, such a deposit builds up to create a conductlve lining
along -the length of the end piece. Such a conductive lining encourages the
formation of electric arcs inside the hole through tha end piece. In a hole
of varying cross section, particles are only deposited on the narrowest
portions oE the hole. Thus a tapering bore is advantageous regardless of
whether it tapers towards the front or towards the rear.
Embodimen-ts of the invention are described by way of example, with
reference to the accompanying drawings, in which:
Figure l is a diagram showing welding apparatus fitted with a guide
tube and a reel of filler metal wire.
Figure 2 is a side view in partial section of apparatus using a
different technique for feeding the filler metal wire, from that shown in
Figure l.
Figure 3 is an exploded longitudinal section through a guida tube for
filler metal wire
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Figure 4 is a longitudinal section through the front end of a variant
of the guide tube shown in Figure 3.
Figure 5 is a longitudinal section through a refractory end piece.
Figures 6 and 7 are longitudinal sections through another form of
guide tube for filler meta:L wire.
Figure 8 shows a detail of Figure 3 on a larger scale.
In a more detailed description of the preferred embodiment, Figure 1
shows on electric arc welding machine which can operate ei-ther according
to -the metal active gas (~G) process or else according to the metal inert
gas (MIG) process. It comprises a metal head 12 whose bottom end terminates
in the form of a nozzle 13, having a nozzle charrlber 14 through which gas can
Elow in the direction of an arrow 15. The gas is active or passive relative
to the weld melt depending on the welding technique being used. The bottom
16 of the nozzle 13 opens out over a work piece 17 on which a weld fillet
18 is being made. An electric arc 20 is maintained between the work piece
17 and one end 22 of a wire 23 of filler metal. The arc serves to keep the
weld zone 18 at a very high temperature and causes the end 22 vf the filler
metal wire to melt away progressively.
Near to its end 22 the filler metal wire 23 is held in place by a tube
25, known as a contact tube. This tube is vertically rnounted along the
axis of the noæzle chamber 14. The upper end of the tube 25 is threaded
and is screwed into a cylindrical conductive support 30 which has a long-
itudinal passage 32. The wire 23 is pushed Eorward to compensate for its
being consumed at the end 22 by two wheels 33 which unwind it from a reel
35 and push it down the longitudinal passage 32 into the bore of the con-tact
:~2~
tube 25 from whose front the end 22 projec-ts. Tne cylindrical support 30
is supplied wi-th electricity by a cable 38 connected to one terminal of a
source of electricity, whose other terminal is connected to -the work piece
17 by a conductor 39. The bore along the con-tact tube 25 is calibrated to
match the filler metal wire 23. It serves both to guide the wire and to
supply it with electricity by contact between the bore and the wirel as is
explained below.
~round the support 30 the body of the head 12 defines an annular
chamber 40 having an inlet 42 passing through the wall of -the head 12. A
gas supply conduit 44 is connected -thereto for supplying a gas suitable
for the welding techni~ue being used. The annular chamber 40 is connected
to the nozzle chamber 14 via longitudinally ex-tending channels 46 passing
through insula-ting material 48 which electrically separates the support
30 frorn the body of the head 12.
The bottom of the nozzle 13 tapers slightly -towards its axis, with
its circular opening 16 surrounding a neutralizing ceramic end piece 50
(described in greater de-tail below) fixeci to the front end of the tube 25
through which the end 22 of the filler metal wire 23 projects. The electric
arc 20 and the weld zone 18 are bathed in the gas blown out from the nozzle
in the direction of the arrows 15.
~igure 2 shows electric arc welding apparatus 60 for use in the tungsten
inert gas (TIG) process. An electrode 62 is disposed axially along the
inside of the a nozzle 64 via which gas is blown in the direction of an
arrow 65 towards the part 70 to be welded. The and 71 of the tungsten
electrode 62 is located in the opening of the nozzle 64. The electrode
~a~
62 and the part 70 are supplied with electricity in such a manner as to
maintain an arc between the end 71 of the electrode 62 and the weld ~one
72 on the part 70. Filler metal is added in -the form of a wire 75 whose
end 76 advances across the arc near the point where it leaves the electrode
62 at the outlet from the nozzle 64. The wire filler metal 75 is guided
by a guide tube 78 whose front end is terminated by a ceramic neutralizing
end piece 79.
The contact tube 25 (Figure 31 comprises a t~ular body 80 made of
an electrically conductive me-tal such as copper. It has a longitudinally
extending bore 82 which inter-connects its front end with its rear end 83.
The diameter of the bore is uniform except near the rear end of -the tube
where it is first enlarged at 86 and counter-sunk at the end 83 to facilitate
inserting -the filler metal wire 23 therein. Going along the tube from i-ts
rear end 83 to its front end 85, its outside surface comprises the following
regions: the thread 26; a cylindrical portion 88 having two diametrically
opposed flats to give a spanner a purchase on the tube; and then a shoulder
92 leading to a front cylindrical portion 90. A circumferentially extending
groove 93 is cut into the front cylindrical portion near to the shoulder 920
Two tapering passages 95 are made through the wall of the tube per-
pendicularly to its axis. The srnall ends of the tapering passages 95 open
out into the bore 82. The large ends of the passages 95 open out in the front
portion 90 roughly half way between the shoulder 92 and the front end 85. The
passages 95 both lie on the same generator line of the tube. They receive
respective balls 96 with a diameter which is slightly larger than the diameter
of the small ends of the tapering passages 95. Each ball 96 is urged to
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project into the bore 82 by a respective compression spring 97 having
conical turns with the smaller of the end turns pressing against the ball.
The larger of the end turns is located in the opening at -the larger end of
the tapering passage 95 is is held therein by a cylindrical sheath 100
having an inside diameter that is substantially equal to the outside dia-
meter of the cylindrical portion 90. The sheath 100 is fitted over the
por-tion 90 by putting the front end 85 of the tubular body 80 into the
rear end 102 of -the sheath 10. The shea-th is long enough for its rear end
to abut against -the shoulder 92 when fi-tted in position. The sheath 100
is of such a thickness that when in position the outside surEace of the
shea-th 100 constitutes an extension of the cylindrical portion 88 of the
tube 80.
The neutrali~ing end piece 50 is a single ceramic block comprising
two ju~taposed coaxial cylindrical portions, namely a Eront portion 120
and a rear portion 110, together wi-th an axial bore 115 of the same diameter
as the bore 82. In the assembled tube 25 the end piece 50 has a rear face
112 which is applied agains-t the front face 85 o-E the body of the tube 80.
The rear cylindrical portion 110 of the end piece 50 is of substantially
the same diameter as the inside diameter of the sheath 100 and is lodged
therein. The front portion 120 is of smaller diameter than the rear portion
112 and is joined thereto via a shoulder 118. The front end of the shea-th
100 is partially closed by an inwardly turned rim 104 which bears against
the shoulder 118 of the end piece 50, leaving an opening 105 via which the
fron-t portion 120 of the end piece 50 projects for about 5 mm.
Thus, once the contact tube 25 is assembled, the sheath 100 abuts
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L
against the shoulder 92 and serves to retain bo-th the neutralizing end
piece 50 on the front end of the tube 80 and also the compression springs
97 in their respective passages 95.
In operation of apparatus of the -type shown in Figure l, the tube 25
serves to guide the filler metal wire 23, letting i~ run smoothly without
jerking, inside the bore 82. The wire is helcl in good electrical contact
wi-th -the inside wall 99 of -the bore opposite to the passages 95, by the
thrust from the balls 96. The spring force ac-ting on the balls 96 is chosen
so that when the balls are lifted off -their respective seats by a wire
passing through the bore 82 the balls press the wire firmly against the
opposite side 99 of -the bore 82. The wire then passes through the ceramic
end piece 50 to present a perfectly straight length of wire at its leading
end 22, opposite to the weld melt at the ou-tlet from the nozzle 13.
Figure 8 is an enlarged view of the play take up means constituted
by -the balls 96. It shows one ball 96-1 pressed against its seat 130-1
projecting out from the passage 95-1 into the bore 82. In this position the
ball projects far enough into the bore to engage a wire 23 of a diameter
chosen for its fit inside the bore. As shown, the wire 23 lifts the ball
96-2 off its seat 130-2, pushing it towards the larger opening 131-2 of the
conical passage 95-2 at the outer surface 90 of the tube. The motion of
the play take up balls between the position shown for the ball 96-l and the
ball 96-2 is absorbed by their respective conical compression springs 97.
This compression spring effect is made possible in the very thin space
available in the thickness of the wall of the tube 25, by virtue of the
conical shape of the turns of the spring, which enables them to s-tack
2~.
inside one another, rather than on top of one another. The springs 97 are
no-t shown per se in Figure ~3, but -their compressed lenyth C and iheir
extended length C' are shown. It can be seen that -the absolute lengths
are relatively s~lall, as is the difference between them. Thus, in a tube
25 with an outside diameter ~ of 6 mm, for guiding a wire that is 1.6 mm
in diameter (F) the diameter of the bore 82 is 2 mm. Th~e wall thickness
through which the passages 95 are pierced is thus 2 mm. The balls 96 are
also 2 mm in diameter, res-ting on sea-ts 130 that are 1.8 m~ in diameter.
C and C' are then 0.4 and 0.6 mm respectively~
The following table summaries various examples of suitable dimensions for
the play take up means shown in Figure 8. In all cases the balls are 2 mm
in diameter and -their seats 130 are 1.8 mm in diame-ter. ~1 is the uncompress-
ed height of the springs 97 and a is the angle of -their conicity.
A ~ C Cl E F a H
_
~ 2.6 0.75 0.95 1.3 0.9 20 3
6 2.5 0.4 0.6 2 1.6 20 3
7.2 3 0.8 1 2.4 2 28 4
9.7 3.5 1.6 1.8 3.2 2.~ 26 4.5
All lengths are in millimeters.
By using conical springs 97 it is possible to obtain s~lfficient thrust
on the wire to ensure good electrical contact between the wire and the tube,
together with sufficient travel for the ball to accommodate the wear and
irregularities to be expected in the wire and the tube, even after long use.
Thus, for example, a conica] spring having a relaxed length of 3 mm is used
compressed in the range 0.4 to 0.6 mm. In such and arran~ement the compressed
~12
spring is virtually flat i.e., each turn is practically entirely received
inside -the nex-t larger turn. In this example the spring has -three turns,
using wire 25 hundreclths of a millimeter in diameter, a smalles-t turn of
1 mm inside diameter and a largest turn of 2.3 mm outside cliameter.
S This arrangement makes it possible to house the entire play take upassembly i.e., the balls 96 and the spring 97, inside the wall of the tube 80
underneath the surrounding sheath 100, without any projections requiring slots
in -the sheath, or hindering the flow o~ gas -through the nozzle 13. The
passages 95 are simple to produce using a conical drill bit. Minimal machin-
ing is thus required to produce play take up means that do not project beyond
the thickness of the tu'oe wall, even if it is as little as 1.8 mm in thickness.Depending on the nature of -the metals used and on the size of -the
Eiller metal wire, a single ball may be adequate -to take up any play. This
is particularly the case for soft metals i.e. aluminum and its alloys. Other-
wise it is bet-ter to provide two balls, as shown in Figure 3~ or even more
balls.
One of the main advantages of play take up means is maintaining good
electrical contact between the filler metal wire 23 and the bore 82 of
the tube 25 in spite of the tube wearing during use. This serves in particu-
2~ lar pitting and to burned zones which have the effect of deteriorating
electrical contact and hence make further arcing all the more likely. Using
two balls as shown, serves to spread out the zone of contact between the wire
and the tube, along a generator line of the tube and thereby reduces friction
and hence wear.
The balls 96 are advantageously made oE electrically insula-ting
material and preferably from a hard material. Balls made of quenched
glass, ceramics, ruby or synthetic sapphire may be used. The use of an
insulating material further reduces the chances of arcing inside -the
contact tube 25. In spite of being relatively expensive, ruby balls have
the advantage of being very hard, which increases the tube lifetime.
The springs 97 may be made of refractory stainless steel or of Incone:L
or of a ni-mon-ick alloy that ~dithstands high temperatures. Further it is
advantageous to cover the sur~ace wlth a covering such as chromium dioxide
e.g. using a pistol device or heat treatment in order to make thern electric-
ally insulating. This further reduces the dangers of arcing inside the tube,
thereby increasing its operating qualities and its leng-th of life. In
addition -to their corrosive effects, parasitic electric arcs striking inside
prior art -tubes also tend to in-terfere with the smooth mo-tion of -the wire,
thereby causing non-uniformities in the welding.
The sheath 100 is made of refractory steel capable of withstanding
tempera~ures of up to 1100 C for example. It is completely covered both
inside and outside, with an electrically insulating material such as chromium
doixide in the present example, applied in the same manner as to the springs.
This ensures t'hat drops of metal spattered up from the weld melt 18 (Figure
1) during welding, do not adhere to the sheath l00 even if they do enter
the nozzle 13. This avoids solid material from accumulating on the tube 25
which could partially block the path of gas being blown out through the
nozzle. Parasitic arcs are therefore avoided between the contact tube 25
and the nozzle 13. ~'inally, the sheath 100 provides thermal insulation for
the body of the tube 80 and in particular for the play ta~e up means.
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~he nozzle 13 itself is preferably covered with a ceramic covering. If
the nozzle is made of metal, such as copper or brass, i-t is advantageously
covered by projecting a ceramic powder thereon, e.g. using a pistol of the
type marke-ted by CHPOLANSKY. The covering should be on the inside, on the
ou-tside and on the lip at the mouth of -the nozzle. The ceramic covering
provides bo-th eiectrical insulation and protection against splashes of
molten metal Erom the weld melt, in that -the splashes do not adhere to the
covered surface of the nozzle.
In an embodiment not shown, the sheath 100 may cover the front face
85 of the tube body 80 with the front face being covered by a wall having a
hole therethrough to pass the end of the filler metal wire 26. The sheath
could be made of a single block oE ceramic material. The presently pre-
ferred embodiment shown in Figures 1 to 3 with its end piece 50 has the
advantage that, in the event of an accident jamming the end 22 of the filler
wire, molten metal tending to rise up along the contact tube 25 has no chance
of adhering thereto because of the impossibility of welding the metal to the
ceramic of the end piece 50. The end of the sheath 100, which is relatively
thin, is -thus protected against the very high temperatures to which it would
otherwise be subjected, in the absence of a neutralizing end piece 50.
In an advantageous embodiment of the invention the end piece 150 is
long and tapering as shown in Figure 4. It is mounted at the front end of
the tube body 80 by the sheath 100 as before. It has a cylindrical rear
end portion 152 leading via a shoulder 153 to the larger or rear end of a
tapering front portion 154, which front portion may be 10 mm long. The
shoulder 153 abuts against the inwardly turned rim 104 of -the sheath 100
and the filler me-tal wire 23 passes through a bore 156 which extends the
bore 82. The leading end 22 of the wire 23 projects frorn-the stnall front
end of -the tapering portion 154. This shape of end piece 150 is particularly
useful when welding a-t the bottom of a hollow such as 160 in the parts 162
to be welded. The end piece 150 prevents weld melt from accumulating at
the bottom of hollows 160 and melting the bottom of the filler metal wire
-to the end of the contact tube itself. The tapered shape also helps promote
gas flow from the nozzle into -the bottom of the hollow 160 where the welding
is being done.
In the example shown in Figure 3 the sheath 100 is held to the body of
the tube 80 by three point crimping at the circumferential groove 93 in the
surface 90. It thus serves both to hold the springs 97 in place in their
passages 95 and to hold the end piece 50 on the front end of the tube body
80, while protecting the sides of the tube.
In Figure 5 such an end piece 190 comprises a cylindrical rear portion
192 suitable for being received in an end recess such as -the recess 172 in
the tube body 144 shown in Figure 6. The end plece then has a girth portion
194 which is cylindrical bu-t of greater diameter than the rear portion 192.
The girth portion fits over the end of the tube body but is small enough to
fit inside a sheath such as the sheath 100 described with reference to
Figure 3. Thereafter there is a forwardly tapering front portion 196 which
has a large base of smaller diameter than -the girth portion, so that it can
project through the front opening 105 of the sheath, wi-th the inwardly
turned lip 104 abutting against the front shoulder 197 on the girth portion
194.
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~62~
Fi.gures 6 and 7 use the same reference numerals for par-ts as shown in
Figure 3.
A neutralizing end piece 200 (see Figure 6) is mounted on the front of
a metal tube 85. It comprises a rear portion 202 and a front por-ti.on 204
with a step or shoulder 205 at the join between said portions. The shoulder
abu-ts against the inwardly directed rim 104 at the front end of the sheath
100 in order to keep the rear face of -the end piese i.n contact with the front
85 o~ the tube body 80. The diameter of the rear portion 202 i.s slightly
less -than the inside diameter of the sheath 100 thereby leaving a small
amount of transversal play 208. Likewise, the outside diameter of the front
portion 204 of the end piece is slightly smaller than the inside diameter
of the opening 105 in the end of the sheath 100. Thus the end piece 200 is
capable of moving transversely inside the sheath 100 which nevertheless
keeps the plane of the end piece fixed. This arrangement enables the end
piece to keep i.n alignment with the filler metal wire passing therethrough,
in spite of any wear that may eventually occur in the guide tube bore.
The end piece 200 has a hole 210 through which the filler metal wire
passes as it leaves the guide bore 82. The hole 210 is of non-uniform
cross section. In the embodiment shown in Figure 6 i-t is flared in the
direction of wire movement, having a rela-tively small diameter at its rear
end 21~ and a relatively large diameter at its front end 212A. The rear
end diameter is substantially the same as the diameter of the guide tube
bore. The hole is in the shape of a truncated cone.
In Figure 7 the hole 210 is again in the shape of a trunca-ted cone
but this time it is the other way round, it is funnel shaped from a relatively
large rear end 211B leading to a relatively small front end diameter 212B.
The non-uniform diameter prevents the Eiller metal wire from depositing
a continuous conductive lining along the length of the walls of the hole 210.
Filler metal wire guide -tubes such as have been described above can
advantageously be used in welding machines of types other than that shown
in Figure 1. For e~ample, the machi.ne shown in Figure 2 does not use the
guide tube to supply arc current. The tube serves to guide the filler
wire 75 so that its leading end is accurately placed in the arc and so -that
it advances smoothly without jerking. It is provided with a ceramic end
piece 79 to avoid the filler wire becoming welded to the end of the guide
tube in the event of the leading end 76 stopping accidentally. Its sides
are advantageously covered with a protective sheath such as the shea-th
].00, to help avoid any drops of molten metal spattering up from the weld
melt 72 and sticking to -the tube 78. Play -take up means may be fitted
optionally.
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