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Jan. 7, 1947.
Filed Nov. 26, 1942
5 Sheets-Sheet 1
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Jan. 7, 1947.
F'iled Nov. 26, 1942
5 Sheets-Sheet?
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#150 730122
Jan. 7, 1947.
Filed Nov. 26, 1942
5 Sheets-Sheet 4
Jan. 7, 1947.
Filed Nov. 26, 1942
5 Sheets-Sheet 5
Fatentecl Jan. 7, 1947
~ '
Hugo Purat, Detroit, Mich, assignor to Progres
sive Welder Company, Detroit, Mich., a corpora
tion of Michigan
Application November 26, 1942, Serial No. 466,981
6 Claims.
(Cl. 219—4)
The present invention relates to methods of
and apparatus for controlling the movements of
and pressures applied to work engaging members
Figure 1 is a view in side elevation of a resist
ance welding machine embodying the invention;
Fig. 2 is an enlarged view in side elevation of
of various types. As speci?cally disclosed herein,
the combination pneumatic-hydraulic mechanism
the invention provides improved methods of and
apparatus for controlling the movements of and
for controlling the movement of the electrodes of
the machine of Fig. 1;
Fig. 3 is a top plan view of the structure shown
in Fig. 2;
the pressures applied between the electrodes of a
resistance welding machine.
The principal objects of the invention are to
provide improved methods and apparatus, as
aforesaid, which may be economically manufac
tured and installed, and which are e?icient and
reliable in operation; to provide such arrange
Fig. 4 is a view in longitudinal section of the
dual booster unit employed in the structures of
Figs. 2 and 3;
Fig. 5 is a fragmentary view in section of an
equalizing valve which it is preferred to use with
ments utilizing combined pneumatic-hydraulic
units associated together in such a way as to en
able a desirably large range of movement of the
electrodes from a retracted position to an initial
work engaging position and to further enable the
development of desirably higher welding pres
the invention;
Figs. 6, 7, 8, 8A and 8B are views, respectively,
of solenoid operated valve mechanisms which may
be and preferably are used in connection with
the invention;
Fig. 9 is a more or less diagrammatic view of a
sures following such initial movement; to provide 20
double check valve, which may be used in con
such arrangements in which one or more of the
electrodes of the machine is provided with an
nection with the invention;
Fig. 10 is a schematic diagram of penumatic
hydraulic circuits embodying the invention;
one hydraulic circuit with a hydraulic ?uid to
Fig. 11 is a diagrammatic view of electrical con
cause the movement of the electrode from a start 25
circuits which may be utilized in the prac—
ing position to a work engaging position, and dis
tice of the invention; and,
posed to receive hydraulic pressure through an
Fig. 12 is a view showing the physical relation
other circuit to produce the actual welding pres
the relay coils and contacts shown sep
sure; to provide such arrangements in which both
arated from each other in Fig. 11.
actuating ram, disposed to be supplied through
circuits are energized by combination pneumatic
hydraulic means and wherein at least one of the
means is so arranged as to provide a succession of
diiferent pressures during the actual welding
It will be appreciated from a compelte' under
standing of the present invention that the im
provements thereof may be utilized in connection
with a wide variety of machines, intended for a
Further objects of the invention are to pro
vide a resistance welding machine having a pair
of opposed electrodes, both of which are movable
relative to the frame of the machine and both of
which are disposed to be actuated so as to apply
corresponding variety of different uses. It is now
With the above as well as other and more de
transformer 22. The electrode It is electrically
preferred to utilize the invention to control the
movements of the electrodes of resistance weld
ing machines, and in an illustrative but not in a
limiting sense, the invention is so disclosed herein.
Referring ?rst to Fig. 1, the illustrated machine
desired welding pressure to work interposed be 40
is of the vertically arranged press type and is
tween the two electrodes; to provide such ar
provided with an enclosing frame structure it},
rangements wherein the actuating means for
having forwardly projecting electrode supporting
both electrodes is common thereto and wherein
horns l2 and M, which support, respectively, the
cooperating means are provided to insure the
upper and lower electrodes 16 and IS. The main
proper relation between the distances travelled 45 body
of the frame I0 alfords space to accommo
by the respective electrodes in being brought into
date the electrode control unit designated as a
engagement with the work.
whole as 20, as well as for the usual welding
tailed objects in view, which appear in the fol
lowing description and in the appended claims, a 50 connected to one secondary terminal 24 of the
transformer through a ?exible bus bar 26, and
preferred but illustrative embodiment of the in
lower electrode i8 is similarly connected to
vention is shown in the accompanying drawings,
the other secondary terminal 28, through a flex
throughout the several views of which corre
ible bus bar 30. The holder 32 for the upper elec
sponding reference characters are used to desig
trode is suitably guided for vertical reciprocating
nate corresponding parts and in which:
movements in bearings (not shown) provided
therefor at the front’of the horn £2. The horn
12 also carries a double acting hydraulic ram 35,
the diagrammatically illustrated piston 38 where
of is connected, through its piston rod 38, to the
electrode holder 32.
The use of double acting
rams for controlling electrode movements is con
ventional, and it is believed, therefore, that no
further illustration is needed of the operative
connection between the ram 36 and the elec
trode Hi.
The lower horn is similarly arranged to pro-.
vide bearings for the holder 4!}, associated with
the lower electrode l8, and this holder is coupled
to the piston rod of a double acting hydraulic
ram G2 in a manner similar to that described
The electrodes I 6 and i8 are relatively widely
spaced when they occupy their illustrated re-v
tracted or starting positions, thus permitting the
necessary work to be readily interposed. there
inactive conditions, to equalize the levels of the
oil in the two cylinders 52 and 54.
The cylinders 52 and 5t serve as a mount for
a dual booster unit ‘iii, which is shown in more
detail in Fig. 4i, as comprising a generally cyline
drical end portion ‘42, to the right-hand end
whereof a cooperating cylinder member id is
secured by means of circumferentially distrib—
uted studs '86. The right-hand end portion ll
of the interior surface of the cylinder member
‘i2 is suitably treated to slidably receive a piston
‘18. Piston i8 is provided with a piston rod 80
which projects, into and constitutes the piston
associated, with a hydraulic-cylinder ltd. The
hydraulic cylinder ltd is de?ned by a sleeve re
ceived in aneck portion 82 which projects axially
inwardly from the left-hand end of the cylinder
member l2. A spring 84, seated between the end
of the cylinder member 12 and piston 78, con
tinuously urges the latter. towards the right to
a position in which it seats against the end of
between. An important feature of the present
the cooperating cylinder member iii.
invention resides in movably mounting both the
The cooperating cylinder member ‘is slidably
upper and the lower electrodes. In thewelding
receives a piston 85,_the piston rod 88 whereof
of relatively heavy sections,_it frequently becomes
through thebase of the member ‘it into
necessary to support the work in its movement 25 projects
abutting relation with the piston 18. A suitable
into and out of the welding throat and all points
elastic fluid such as air, for actuating the piston
of the work at which welds are to be made are
18 may be introduced into the annular cylinder
not necessarily at the same elevation. By mak
space 5% between the piston ‘l8 and the end of
ing both electrodes movable, these di?erences in
the member ‘is, through a nipple 92 and a pas—
elevation do not require adjustments of the means
sage M, which opens into the space 963. Similarly,
for supporting the work, since allor any part of
a suitable elastic ?uid, such as air, for the piston
the necessary relative electrode movement can
88 may be introduced into the annular. cylinder
be imparted to either or both of the electrodes.
space 95, throughothe nipple 98. As hereinafter
As will be understood, the pneumatic-hydraulic
described, the oil cylinder Hill. communicates,
elements of the present system may be variously 35 through suitable regulator valves with the rams
constructed andmay be variously positioned rela
36 and t2, and the normal welding pressure is
tive to each other, either in the machine or in
applied to these rams by admitting air to the
part at least remotely from it. It is preferred,
cylinder space 96, thereby applying pressure to
however, to build these elements, together with
the oil, in the cylinder l?il through the piston rods
the operating valves therefor into the previously
88 and 85. The higher welding pressure is
identi?ed unitary structure, designated as a whole
aiforded by additionally admitting air to the an
as 25, and positioned, as shown in Fig. 1, within
nular space 95, thus proportionately increasing
the machine frame.
the unit pressure applied to the oil in the cyl
The unit 2%,‘ as shown in more detail in Figs.
2 and 3, comprises a base 58, upon which a pair 45 inder
On the other hand, the movements of the rams
of cylinders 52. and 54 ‘are mounted. The cyl
34 and 52, so as to. bring the electrodes l5 and
inders are disposed to be normally ?lled to sub,
I8 into engagementwith the, work, are effected
stantially three-fourths their full capacity with
by admitting air to the upper part of the cylinder
a suitable hydraulic fluid, such as oil, and, are
5a through the air inlet line 152. This action
provided with an equalizing connection 53, which
circulates oil from the cylinder 54 throughcthc
connects the two adjacent the bases thereof. The
hereinafter described control valveinto the, elec
equalizingconnection 53 includes a double checl;
trode rams 3G and 42, and in view of the mate
valve 55 of the ball type, which is shown in more
rially greater oil capacity of the cylinder 54, as
detail in Fig. 5 as comprising a tubular housing
compared to the cylinder I65, it will be appre
58 into the opposite ends of which nipples 5B are 55 ciated that a substantial amount of electrode
threaded. The nipples 55 are provided with,
movement can thus, beprovided. The return
aligned bores 52.‘ A chamber 64 is defined by
movement of the electrodes from the welding
the area between the, inner ends of the nipples
position to the position illustrated inl-i‘ig. l is
55 and the wall of the housing 58, and this cham
effected by admitting air to the cylinder 52‘,
ber receives a ball 65. It will be appreciated that
through its inlet connection I04, whichv action,
if pressure is applied to the left-hand end of
as hereinafter described; actuates the electrode
the valve 55, for example, the ball 55 is thereby
rams 3d and 42 in the opposite direction.
seated against the end of the right-hand nipple
The valving of the system is controlled by a
four-way valve E55, which controls the applica
E9 and closes off the passage therethrough. A
tion to and exhaustion of, air from the cylinders
pressure applied to the right-hand end of the
52 and 56; a three-wayvalve "18, which controls
valve, on the other hand, causes the ball 55 to
the application toand exhaustion of air from
seat against the end of the left-hand nipple til
1e welding. pressure cylinder 96; a; three-way
and close oif the passage therethrough. So long
llll'which controls the application to and.
as the pressures applied to the two ends of the 70
exhaustion of pressure from the forging pressure
valve, however, are balanced or substantially so,
cylinder 90; a threeeway valve I [2 which controls
the ball 56 occupies an intermediate position in
the inlet line associated with the'valve H36; a.
which it permits a gradual interchange of ?uid
' pair of regulator valves H4 and H6 associated,_
between the two cylinders 52 and; 55,. The valve
56 and connection 53 thus serve, under normal 75 respectively, with the electrode rams 34 and 42;
a pair of regulator valves H8 and I20 associated,
respectively, with the valves I08 and III), and
which serve, consequently, to determine the val
and the upper side of the plug. A similar tubular
member I30 is seated between the lower surface
of the plug and the lower nipple I82. The up
ues of the welding and forging pressures; a two
per tubular member I16 is provided with a ver
way hydraulic valve I22, which serves to isolate
tically slidable valve element I84 which corre
the electrode rams 32 and 132 from the cylinder
sponds to the previously described valve element
52 at the conclusion of the feed movements of the
and is similarly associated with the pivotally
electrodes; and a two-way check valve I24 as
operating arm I86. The lower tubular
sociated with the upper electrode ram 34, and
which serves to maintain suf?cient pressure in 10 element is provided with a slidable valve element
I88, which is like the valve element I84 except
this ram during inactive periods of the machine
that it does not have the annular recess for coop
to maintain upper electrode It in its elevated po
eration with the arm I86. The valve elements I82
sition. The valves I55, I38, H6, H2 and 522 may
and 388 are interconnected by a sleeve I96, and
be and preferably are located immediately ad
jacent the unit 2!}, as shown in Figs. 2 and 3, and 15 so move as a unit. These elements are continu
ously urged to their illustrated upper positions by
may, as will be understood, be supported by the
a compression spring I92.’ In the illustrated posi~
associated piping. The two regulator valves H8
tion, the upper valve element bridges the cir
and I20, which determine the welding and forg
cumferentially disposed openings I34 and I96 as
ing pressures, respectively, are preferably car
ried by‘ the upper horn. I2 of the machine and 20 sociated therewith, and thus connects the upper
nipple I'I8 to the inlet I'II]. On the other hand,
are provided with exposed operatiner handles, by
the lower valve element I83 is in its upper posi
which these pressures maybe conveniently ad
tion in which it isolates its series of openings I98
justed. Suitable gauges H9 and I2! may, as will
from the companion series 282, thus closing off
be understood, be located adjacent these valves
nipple I82 from the inlet III}. In this posi
to afford an indication of the various pressure
The regulator valves IM and IIS are 25 tion of the parts, also, the lower series of open
ings 20s is exposed so that the nipple I82 is con
nected to exhaust through the housing. If the
sociated rams 34 and 42 as is shown in Fig. 1.
electromagnet 252 is energized, on the other hand,
The check valve I24 may be and preferably is
the valve elements Ian and I38 are moved down—
located immediately adjacent the ram 34 so as to
preferably located immediately adjacent the as
enable its ready adjustment.
30 wardly to positions in which the openings I94
and IE5 are isolated from each other, the open
As will be understood, the above identi?ed
ings I94 are exposed and so connect the nipple
valves may be variously constructed, illustrative
I13 to exhaust, and the openings I28 and 2% are
constructions being shown in Figs. 6, '7, 8, 8A,
bridged so as to connect the nipple £82 to the
8B, and 9. Referring ?rst to Fig. 6, a usual 35 inlet
three-way valve construction (which may corre
two-way hydraulic valve I22 is illustrated
spond to the valves Hi8, H6 and H2) is shown as
in Figs. 8, 8A and 8B as comprising an enclosing
comprising an enclosing housing I 30, provided
housing 2H1. which receives an electromagnet 2 I 2,
with upper and lower inlet nipples I32 and I32,
armature 2M whereof is pivotally connected by
which receive threaded nipples I35 and I38. A
levers 2I6 and 2I8 to a cam shaft 220, which pro
tubular valve element Iliil is secured in place
jects into a valve body 222. The lever 2 I8 is con
between the nipples ISIS and I38, and is provided
tinuously urged to the illustrated position by a
with an intermediate dividing wall I42, which
torsion spring 224, in which position the cam
divides it into two tubular portions Hill and I46.
carried by the pin 2251 enables the spring 225 to
A series of openings M8 is positioned immediately
hold the poppet type valve 228 in the closed po
above the wall I42 and a similar series of open
sition. If the electromagnet 2I2 is energized, on
ings I50 is positioned immediately therebelow.
other hand, pin 220 is rocked in a direction to
A valve element I52 is slidably ?tted over the
force the valve 223 open against the force of the
member Hi3, and is normally held in its illus
trated upper position by a spring I54. In this up- . S‘OI'lIlg 226. It will be understood that the valve
2 I2 is so positioned in its associated line that the
per position, the valve element closes oil the
oil flows which are intended to be blocked by it
openings I48, but exposes the openings I50 to
act against the valve element 228 in a direction
exhaust, through the housing I35. The valve
to hold it closed.
element I52 is embraced by a forked operating
The remaining valve I 24 is diagrammatically
lever I56. which engages in an annular recess I58
shown in Fig. 9 as comprising a rectangular hous
in the valve element. Lever I56 is pivoted to the
ing 240, which is dri11ed and plugged to provide
housing at 569 and is disposed to be operated by
a series of four passages 242, 244, 245 and 248,
the armature I 62, associated with the electro»
which a?ord two parallel passages through the
magnet I54. It will be understood that if the
valve. The passage 242 receives a spring-pressed
lever I56 is pivoted in a counterclockwise direc
tion, it forces the valve element I52 downward‘y 60 ball valve 258, which is normally held upon its
seat 252 by a, spring 254. The passage 245 re
against the force of the spring I54 and bridges the
ceives a ball valve 256 which is normally held on
two series of openings hi3 and I50, thereby con
its seat 258 by a spring 260. The valve I24 is
necting the nipple I 36 to the nipple I38. When
interposed in the return line from the upper elec
the electromagnet I54 is de-energized, however,
trode cylinder 34 in the manner shown in Fig. 10,
the spring I54 is enabled to return the parts to
with the nipple 252 connected near the ram and
the illustrated positions in which the nipple
the other nipple 252 connected away from the
I 38 is connected to exhaust and the nipple I35
ram. The spring 254 is heavy enough to prevent
is closed oil". The four-way valve shown in Fig.
7 is similar to the above-described three-way
construction, but comprises an inlet Iii] which
communicates with the bore I72 in a stationarily
mounted plug-I14. A tubular member I15, which
may correspond to the previously described tubu
a ?ow from the ram 34 through the line 256 and -
the passage 242 when the system is inactive, at
which time the only pressure applied to this cir
cuit is represented by the weight of the upper
electrode structure, the piston ‘and piston rod
lar member MIL‘is-seated between the nipple I18 75 of the ram 34 and the weight of the oil which is
beneath the piston of the ram 34. Such flow is
entirely prevented, of course, through the passage
such as 296 and 292, into the cylinder 52. Such
246 by the valve 256. If, however, as described
below, such pressure is exceeded, the valve 256 is
removed from its seat, allowing a downwardv
side of the piston associated with the ram 42 ‘is
prevented by the weight of the moving parts asso
movement of the piston associated with the ram
ciated therewith.
A reverse or upward movement of the piston
associated with the ram 34 is readily permitted
past the valve 256, since the spring 266 associated
therewith only lightly maintains valve 256 in
a return ?ow through the line 294 to the under
Assuming it is desired to effect a welding oper
ation, the work may be positioned between the
upper and lower electrodes I6 and I8 and, as
aforesaid, the positioning of the work may be
l0 such that it'is unequally spaced from the two elec
trodes. To cause the electrodes to clamp the
The air and oil circuits of the present system
work, the valves H2, I66 and I22 may be simul
are shown diagrammatically in Fig. 10, and an
taneously energized, as described in connection
electrical control system arranged to provide the
with Fig. 11. The energization of valve I22 com
proper sequence for the system of Fig. 10 is shown
pletes the oil circuit from the cylinder 52 to the
in Fig. 11. It is believed that the remaining de 15
two' rams 64 and 42. The energization of valve
tails of the system may best be understood by a
H2 connects the air line 364 to the source 216.
description of Figs. 10 and 11. Referring ?rst
The energization of valve. I66 connects the air
to ,Fig. 10, air at a suitable pressure such, for ex
space above the oil in the cylinder 54 to exhaust
ample, as ninety pounds per square inch, is ad
mitted through a, supply line‘ 216 and through 20 and: connects the air space above the oil in cyl
inder52to line 564through line 366. The pres
suitable strainer, ?lter andoiler elements 212 and
surethus built up'in cylinder 52 forces the equal
214, to a, line 216, from which branches 218 and
izer valve 56 to the closed position and also causes
286 extend to the regulator valves H8 and I26
a flow of Oilthrollgh lines 266, 292 and 294 to the
and the three-way control valve II2. Valve I26
is connected through lines 282 and 284 and the 25 rams 34 and 42. A similar pressure is applied'to line266, but'no movement of the booster ‘I6 re
three-way control valve I I6, to thehigh pressure
sults therefrom, since the pistons thereof are at
cylinder 66 of the booster ‘I6. Similarly, valve
limit'positions. If any leakage has occurred to
H8 is connected through lines 286 and 268 and
partially empty cylinder I66 during the idle peri~
control valve I68, to the low pressure cylinder 96
odlof the machine, such leakage is, of course, im
associated with the booster.
mediately replaced by the initial ?ow from cyl
The oil cylinder I66 of the booster is connected,
inder 52. To accommodate any such leakage, a
through line 266 and branch lines 292 and 294,
drain line 25H containing a usual checkvalve 363
with the upper and lower ends, respectively, of the
may be connected between the cylinder 52 and
electrode rams 34 and 42, which branch lines in
the sump 365 of the booster unit 26.
clude the regulator valves H4 and H6.
The flow to rams 64 and 42 occurs at relative
The branch line 294 is also connected to line
rates determined by the adjustments of the regu
266 which is connected in turn to the cylinder 52
lator valves I I4 and I I6 audit will be appreciated
and includes the two-way valve I22.
that these rates may be adjusted not only to com
The remaining cylinder 54 is connected through
oil line 298 and branch lines 366 and 362 into the 40 pensate for the normal tendency, due to gravity,
of ram 42 to stay in its lower position and for
rams 34 and 42 at points below and above the pis
ram 34- to move to its lower position, but may also
tons thereof, respectively. The branch line 366
be adjusted to provide any desired ratio between
includes the previously mentioned double check
the rates of travel of the rams toward the work
valve I24.
In the normal or inactive position of the ma as ,) engaging position. In most cases it is preferred
to use an adjustment which causes the rams 34
chine, the piston of the ram 34 is elevated and the
and 42 to move at approximately the same rate.
piston of the ram 42 is at its lower position.
Assuming the spacing‘ between the work and the
Under these conditions, check valve I24 prevents
respective electrodes is unequal, one or the other
a flow out of the ram 34 through the line 266, and
ram 34 and its associated electrode I6 are, conse 50. of the electrodes engages the work prior to its
quently, maintained in their upper positions.
The weight. of the lower electrode structure and
the movable parts of ram 42, on the other hand,
maintain these members in their lower positions.
Cylinders 52 and 54 are normally ?lled, as afore
said, with oil to approximately the levelv of the
usual ?oats 55 and 51 therein, which levels are‘
maintained equalized by the previously described
equalizing valve 56. The oil lines extending be
tween the cylinders 52 and54, the booster ‘I6 and
the rams 34 and 42 are, of course, ?lled with oil.
Under the conditions stated, further, valves
H2 and W6 are d‘e-energized so that, conse
quently, the air spaces above the oil in the cyl
inders 52 and 54 are connected to exhaust. The
exhaust connection for the‘ cylinder‘ 52 is made
directly through the housing of the‘ valve I66, as
described above, whereas the exhaust connection
for the cylinder 54 is made through the valve I66
vand the housing of the valve H2, Further, the
engagement by the other electrode. When such
engagement occurs, a resistive pressure is applied
to such engaging electrode which interrupts its
further movement. The movement of the other
electrode, however, continues until it engages the
55 work and it will be understood that the initial
engaging pressure of the electrodes against the
work‘ is determined by the unit pressure applied
to the cylinder 52 through the line 366. During
such downward and upward movements of the
60 rams 34 and 42, respectively, oil is discharged
from the under and upper sides of the pistcns
thereof through lines 366, 362 and 268 into‘ cylin
der' 54. It will be understood that the pressure
applied to ram 34 through the line 262 is effective,
as aforesaid, to overcome the resistance of the
valve I24 to such ?ow.
After the electrodes have engaged the work,
the hydraulic valve I22 is de-energized, which ac
tion interrupts the hydraulic circuit between the
valves I68 and H6 are in the d'e-energized condi 70 cylinder 52 and the rams 34 and 42, thereby pre
tion, so that the cylinder spaces 66'and'96- of the
venting an escape of oil from these rams and
ram ‘I6, associated therewith, are connected to‘
exhaust. At the same time, the hydraulic valve
I22 is~ in its closedv position, in which it is effective
to prevent a return ?ow of ?uid from the lines,
serving to maintain the electrodes in‘ engagement
with the work.
At the same time, or‘ shortly after the valve I22
is ole-energized, the low pressure booster valve
I08 is energized, connecting the low pressure cyl
returned to its normal condition in readiness for
another cycle.
In certain cases it is desirable to employ the
inder 95 of the booster ‘Hi to the source of air sup
ply through the regulator valve H8. As soon as
this action occurs, pressure is applied to the oil
in the booster cylinder Hi0 through the pistons
86 and '58, which pressure is transmitted to the
rams 34 and 42 through the lines 290, 292 and
294. This action immediately increases the pres
present system withsone or the other of the
electrodes retained in a stationary position. As
shown in Fig. 10, a shut-off valve 3 l B is associated
with the lower ram 42 and it will be understood
that if this valve is closed, ram 42 remains con
application of Leathers and Benkert, Serial No.
447,006, ?led June 15, 1942, as a continuation of
afford an understanding of such operation.
sure applied between the electrodes by an amount 10 tinuously in its lower position, the only movable
electrode being the upper electrode associated
‘ determinedby the boosting ratio of the booster ‘ill.
with ram 34.
The high pressure booster valve may be actu
t will be appreciated that in the broader as
ated at a desired stage of the welding operation,
pects of the invention various dilferent control
depending upon the character of the welding proc
systems may be associated with the above de
ess employed. The electrical control system of
scribed machine, it being preferred, as aforesaid,
Fig. 11 is one which is adapted to practice the
to use the machine to practice the process of
process disclosed and claimed in the copending
the aforesaid copending application. Fig. 11 il
lustrates diagrammatically su?icient circuits to
their earlier application, Serial No. 422,036, ?led 20 Fig. 11 the electrodes 16 and I8 are shown as
December 8, 1941. In this process, the welding
connected to the welding transformer 22 in the
cycle includes one or more successive stages, each
previously described manner and current flow
stage being made up by a controlled heating e
to the electrodes is controlled by a pair of electric
riod and. a controlled cooling period. With this
discharge devices RI and R2, which may be and
process, it is preferred ‘to employ the aforesaid 25 preferably are of the type sold commercially un
lower welding pressure, as determined by valve
der the trade-name “Ignitrons,” the operation
Hi8, throughout the heating part of each stage,
whereof is well understood. The discharge de
and to employ a higher or forging pressure,
vices-Pei and :R2 are provided with a conven
throughout the cooling part cfeach stage. Ac
tional excitation circuit comprising auxiliary rec
cordingly, with such process the energization of 30 ti?ers 322 and 322 and the normally open con
valve Hil is delayed for a suitable period after
tact CRila of a usual electromagnetic control re
the energization of valve I 08. The energization
lay. It will be understood that so long as contact
of valve Hll connects the forging pressure cyl
Child is open, the devices RI and R2 are non
inder space Sll of the ram l!) to the source of air
conductive and that, consequently, no current is
supply through the regulator valve E23 and, con
sequently, increases the pressure applied between
the electrodes by an amount determined by the
supplied to the welding transformer 22.
Cooperating with relay CR9 is a similar series
of usual electromagnetic relays CRI through CR8,
the contacts whereof bear similar designations
with the postscripts a, 1), etc. The system further
pressure built up in such cylinder space.
In case the cycle includes a succession of stages,
the valve llll may be energized and lie-energized
a plurality of times, being energized at the be~
ginning of the cooling part of each stage and
being de-energized again at the beginning of the
heating part of the following stage.
At the conclusion of the weld, the valves IE8
and I iii are de-energized. which relieves the forg
ing and welding pressures on the electrodes and
initiates a reduction in the pressure between them
to the value initially determined by cylinder 52.
At the same time, or very shortly thereafter, the
four-way valve I26 is ole-energized and the hy
draulic valve 122 is ice-energized, valve 322 being
retained for the time being in the energized con
dition. The de-energization of valve Hi6 connects
the air space in cylinder 52 to exhaust, and con
40 includes a series of usual three-element elec
tronic valves VI, V2, V3 and V4, all of which
may be and preferably are of the high vacuum
or continuous control type. The system further
includes a pyrometer unit which is described in
detail in the aforesaid copending application and
is shown diagrammatically only in Fig. 11. The
unit is designated PY and is provided with a sin
gle contact PYa, which is open so long as the
thermoelectric potential applied between the in_
50 put leads 324 and 326 is below a predetermined
value.v These contacts close when, and remain
closed so long as, this potential exceeds the just
mentioned value. The thermoelectric potential
is developed between the leads 324 and 326 by
55 forming a thermocouple between the electrode l6
nects the air space in cylinder 54 to the source
and a suitable element 328 embedded therein, all
through valve H2. The consequent air pressure
as described in said copending application. Co
in cylinder 54 closes valve 55 in its opposite po
operating with the pyrometer is a ratcheting unit
sition and causes a return ?ow of oil therefrom
336, which may be of a conventional type and
to the rams 34 and 22, causing these rams to re 60 is diagrammatically shown. This ratcheting unit
assume their normal positions in which the elec
is provided with a series of movable arms 332,
trodes are separated from the work. This return
‘534 and 336, which cooperate with series of asso
?ow is accompanied by a return flow through lines
292 and 294, the now open valve 122 and line 295
to cylinder 52.
At the conclusion of the just-mentioned return
movement ofv the electrodes, valves H2 and I22
are ole-energized. These actions again close off
the line 295 and prevent a circulation of oil from
the lines 2% and 292 into the cylinder 52 and also
connect the air space in cylinder 54 to exhaust,
thereby relieving the air pressure therein and en
~abling the equalizer valve 56 to equalize the oil
ciated contacts to adjust the heat setting of the
pyrometer, to control the application to and re
" moval of the forging pressure and to e?ect the
resetting of the system at the conclusion of a
welding operation. The initiation of a Welding
operation is under the control of a two-stage
switch, shown as made up of two separately op
erable push buttons Pl and P2.
It is believed the remaining details of the sys
tern may best be understood by a description of
the operation‘thereof.
levels in the two cylinders. The system is thus 75 To place the system in condition for operation,
the illustrative disconnect switches LS! and LS2
conductors Li and L2 to a suitable source of al
ternating current. Energization of the line con
ductors Ll and L2 is without immediate effect
other than to complete circuits for transformers
T3, T5 and Ti i, associated with the grid circuits
of valves Vl, V2 and V4. Upon being energized,
these transformers apply blocking vpotentials to
the grids of these valves, thereby'preventing cur
rent ?ow therethrough, and also charge up the
grid control condensers Cl, C2 and C5, associated
To initiate a welding operation, the first-stage
complete, since the second-stage starting switch
P2 is still open. So long, therefore, as switch Pi
is retained closed, the electrodes Hi and ‘it re
main in-engagement with the work with the pre
liminary contact pressure. Closure of contact
C3311 is without effect other than to further con
dition the circuit for control relay CR1.
To actually initiate the weld. the second-stage
switch Pl may be closed, which action eifects the
switch P2 may be closed and this action may be
I caused to take place substantially simultaneously
previously desoribedoperations of bringing the
electrodes into engagement with the work ‘at a
pressure determined by the pressurein the cylin
der 52 (Fig. 10). ‘More particularly, closure of
switch Pl completes obvious energizing circuits
in parallel for valves H2, 122 and IE5, and for
transformers Tl and'TLassociated'with the an
ode and ‘grid circuits of valve VI‘. The .circuit
for transformer Tl includes the now closed back
contacts CRla of control relay CR1, the ‘circuit
’ with the closure of switch Pl or after an interval
thereafter. If the closure of switch P2 takes place
substantially simultaneously with the closure or
switch Pl, the actuation of the welding pressure
for ‘valve H2 includes the now closed back con
tacts CRQIJ of control relay'CRS, and the circuit
vfor valve ‘r22 ‘includes the last mentioned con
tacts and also theinow closed back contacts CR2?)
of control'relay‘ CR2.
tacts ‘Cl-‘c311 and (IBM complete parallel circuits
which retain the valve l 12 energized. The closure
of contact CR’o‘c prepares circuits for the welding
pressure control valve l?l? and for the plate trans
former Tl, associated with valve V3 and control
relay CR6, ‘which circuits, however, remain in
may be closed, thereby connecting ‘the supply
The energization of ‘the vthree valves H2, I22
and i616 e?ects the operations previously de
scribed, namely, to bring the electrodes into en
. easement with'the work.
‘ The energization :of transformer T2 opposes
relay i538 and the just-mentioned transformer Tl
is, nevertheless, delayed long enough to allow for
the movement of the electrodes into engagement
with the work, which time interval is afforded by
the delay in the closing movement of the last
rnentioned relay contact CR'Bc, This latter delay,
as aforesaid, is controlled by condenser C2.
The closure of switch P2 completes an obvious
energizing circuit for the winding of control relay
CRi, which thereupon closes its normally open
contacts CRia, CPA!) and CRlc. Closure of con
, tacts CRM and CRlb completes self-holding cirr
cuits in parallel with the switches Pi and P2,
which may thereupon be released to the open po
sition without interrupting the welding cycle.
the originally energized transformer T3 and en- ;
ables the energy originally stored in the grid con
The closure of switch P2 and of contact CRib
trol condenser Cl to discharge through the indi
cated local circuit, including resistor 340. At the
expiration of a discharge period determined by
the characteristics of this circuit, valve VI be
comes conductive and enables the now energized
transformer TI' to passcurrent‘therethrough and
energize controlrelayCRZ. This action causes
this relay to close ‘its normally open contacts
CR‘rla,1CR2c, and CRZcZ and to-open its back con
tact 0321). The latter action tie-energizes the
two-way hydraulic valve 122, thereby, as afore
SalQ,'l7IT3¢ppiIl_-g su?ieient oil in the electrode rams
es and J32 to ‘maintain the electrodes in engage
merit with-the work with the desired preliminary
is, consequently,
valve V3 isenabled
to ener
gize controlrelay Cll. Upon being energized, con
trol relay C4 closes its normally open contact
. pressure. It will be understood, accordinglsh'that
the-timinga?orded by condenser Cl is sufficient
to allow for the full travel of the electrodes from
their retracted positionsvto their work engaging
positions. The closure ofcontact CRZa is without
effect in the operation now being described, since
it is assumed that the switch Pi ‘is ‘still closed.
Closure of contact CR-2dserves only to prepare a
also completes the previously traced circuit for
the welding pressure valve lllil, which thereupon
operates, as described with reference to Fig. 15,
to apply the normal or welding pressure to the
electrodes ill and it. The effect of contact CRic
is described below.
The circuit for transformer T1 is completed
simultaneously with the completion of the cir
cuit for valve lat. 'Upon'being energized, trans
former Tl applies potential to valve V55. Under
CRl‘la, thereby energizing the welding controlre
lay CR8. Upon being energized, relay‘ CR9 closes
its sole contact Chats and aotuates the power con
tactor represented by the reversely connected
main recti?ers R5 and R2. This action, as will
be understood, initiates the ?ow of welding cur
rent to the work.
Closure of contact CRéa also energizes the grid
transformer T8, associated with valve V3, and en
ables it to apply a blocking potential to valve
V3, This action interrupts the supply or" ener
circuit for control relay CR1.
Closure of contact CRZc completes obvious en
ergizing circuits for transformers T4 and T5, as
gizing current to control relay CRil, whereupon
sociated-with the anode and grid circuits of valve
the energy stored in the winding thereof starts
V2. Upon being energized, transformer T5 op
to discharge through the associated condenser
poses the originally energized transformer T6 and
enables the energy originally stored in the asso 65 CG. At the expiration of a so-called “heat” period
following this action control relay CRQ resumes
ciated condenser C2‘ to discharge through the
its original tie-energized position and opens con
local circuit including resistor 3&2. At the com
tact'CRiic. This action ole-energizes the welding
clusion of a relatively short discharge period de
relay CR3, which thereupon interrupts further
termined by the characteristics of this circuit,
valve V2 becomes conductive and enables the now 70 fiow of welding current. to’ the work. The open
ing of contact CRila also enables the energy stored
energized'transformer T4 to energize control re-.
in condenser C3 to start discharging through the
. lay CB3. This action causes this relay to close
associated local circuit including-resistor ass, and
its normally open contacts CRSa, CRSc and CHM
at the expiration of a “cool” period, valve V3
and to .open' its back contact 03131).‘ The latter
action ‘is without veffect since the now closed con 75 again becomes conductive, enabling transformer
T1 to re-energize relay CR4. This re-energiza
tion again initiates the ?ow of welding current,
as before, and also applies a blocking potential to
valve V3. Control relay CR6 therefore nulsates
between the energized and de-energized condi
tions, current being supplied to the Welding circuit
so long as relay CR4i is energized, and being in»
terrupted so long as relay CR4 is ole-energized. It
will be understood that the heat and cool inter~
vals are adjustable in length and are propor
tioned to suit the Work being vwelded.
Reverting to the energization of control relay
.CRl, closure of contact CRlc thereof completes
_ a circuit through the now closed back contacts
CREZ) and CRiib of relays CR5 and CR3, respec
tively, to thereby connect the operating winding
366 of the ratchet unit sec to a. suitable source of
direct current illustrated as a battery 343. Upon
being energized, winding 346 operates its arma- '
ture and causes the ratchet unit to advance one
notch from its initial or starting position to its
?rst operating position in which the arms 33 .
334 and 335 are in engagement, respectively, with.
terminals at, hi and cl. In the sequence now
being described, terminals bi and cl are idle, but
transition movement of the arm 332 from ter
minal al to terminal a2. As soon, of course,
as terminal a2 is engaged the pyrometer re
adjustment takes place and the pyrometer is
thus effective to maintain the contact PYa closed
until the temperature of the work falls to the
aforesaid relatively low value.
The movement of arm 334 into engagement
with terminal b2 completes an obvious energiz
ing circuit for the winding of control winding
CR8, which thereupon closes its sole contact
CRta and completes an energizing circuit for
the high pressure or forging valve i It. Upon be
ing energized, as described in connection with
Fig. 10, valve I it] increases the electrode pressure
to the maximum or forging value.
The above-mentioned energization of control
relay CR5 also causes its contact CRiic to open,
which action immediately de-energizes trans
former T1 and the welding current relay CR8.
The ‘de-energization of the welding current relay
CR9 interrupts further flow of welding current
to the work and it will be understood, therefore,
that the attainment of the welding temperature
in the work results in the interruption of the
flow of welding current and further results in
terminal al adjusts the pyrometer PY to respond
to a temperature corresponding to the critical
the application to the work of the higher or forg
welding temperature of the work.
ing pressure.
The current supplied to the work during the
The de-energization of transformer T1 also
successive “heat” periods gradually elevates the 30 causes relay CR4 to resume the de-energized
temperature of the work, and when
condition after the timing out of condenser C6, as
temperature is reached, a weld nugget is formed
aforesaid. This action is without effect in the
between the two workpieces. When this tempera
sequence being described in view of the fact that
ture is attained, the thermoelectric potential be
control relay CR9 is now in the de-energized
tween the pyrometer leads 321i and 323 is suf?cient hCo Cr condition. It will be noted that if the energiza
to cause this element to close its sole contact
tion of control relay CR5 takes place during a
PYa. Closure of contact PYa completes obvious
“cool” period between successive pulsating flows
energizing circuits in parallel with each other for
of welding current, such action serves merely to
‘control relay CR6 and for transformers T9 and
prevent the re-energization of relay CR4 and
Tit, associated with the anode and grid circuits
CR9 at the expiration of the “cool” period in
of valve VG. Upon being energized, relay CRii
closes its contact CR?a and opens its contact
When the work temperature falls to the afore
CRBb. The latter action interrupts the previously
said relatively low value, at which temperature
traced circuit for the operating winding 3156 of
the weld may be expected to have solidly set,
the ratchet unit, ‘which action does not advance a.) so that the electrode pressure may be relieved,
the ratchet unit but does allow a return move
the pyrometer PY releases its contacts PYa to
.ment of the armature to a position in which it
the open position. This action immediately de
engages the next successive tooth of the ratchet
energizes control relay CR5 and transformers
member. Upon being energized, transformer Tit’!
T9 and Till. The deenergization of control relay
opposes transformer Til and enables the energy . CR6 causes its contact CRBa to reopen and its
stored in condenser Ct to start discharging
contact CR6b to reclose. The latter action is
through the local circuit including resistor
without effect, since contact CR5b is still open,
- At the expiration of a short discharge period just
but the former action again interrupts the cir»
su?lciently long to allow. the above mentioned re“
cuit for the ratchet operating winding 345. This
turn movement of the armature associated with
action does not cause an advancing movement
the ratchet operating Winding 3%, valve V-‘i be’
of the ratchet unit, but it does allow the arma
comes conductive and enables transformer T9 to
ture of winding 346 to be withdrawn to a posi
energize control relay CR5.
tion in which it engages the next successive
Upon being energized, relay CR5 closes its con
ratchet tooth.
tact CRlia and opens its contact CRSb. The for 60
The de-energization of transformer TH} en
mer action completes a circuit through the now
ables transformer Tll to again apply a blocking
closed contacts CRlc and C‘Riia for the operat~
potential to the grid of valve Vt. This action
ing winding 346, which thereupon moves the
coupled with the de-energization of transformer
.ratchet unit 330 to its second operating position
T5; interrupts the supply of energizing current
in which the arms 332, 33¢ and 336 are in en
for the winding of relay CR5 and enables the
gagement with terminals a2, b2 and c2, respec
energy stored in the winding thereof to start
tlvely.‘ Terminal 02 is an idle terminal in the
discharging through the associated condenser
sequence now being described, but the movement
(3?. After a short period of the order, for ex
of arm 332 onto terminal a2 readjusts the pye
ample, of several cycles of the source, relay CR5
rometersetting to a relatively low temperature
the deencrgized position. This interval
corresponding, for example, to a temperature well
is long enough, as will be understood, to enable
below the annealing temperature of the work.
the just-mentioned return movement of the
As described in the aforesaid copending applica
armature associatedv with they ratchet operating
tion, the'pyrometer is sluggish enough in its 'ac
winding 34B.
tion to retain the contact PYa closed during the 75 Upon being ole-energized, relay CR5 opens its
contact CREa, without eiiect, and also recloses its
contact CREb. This action re-energizes the
ratchet operating winding 346 and enables it to
advance the ratchet unit to its. third position in
which the arm 336 engages the terminal 03. This
action also moves the arms 332 and 3% out of
engagement with their terminals a2 and‘ b2. The
former action is without effect, since the pyrom
eter contact PYa is already open, ‘but the latter
action interrupts the circuit for the .high pres 10
sure control relay-CR8. Upon being so de-ener
gized, control relay CR8 interrupts the circuit for
the high pressure valve 1 Ill which, as describedin
connection with Fig. 10, thereupon acts to relieve.
the high or forging pressure'from the electrodes.
The engagement of arm 33% with terminal c3
completes a circuit for the winding of control
relay CR1, (through now closed contacts CRM
and CRM) which thereupon opens its contact
CHM and closes its contacts CR'lb and CRlc.. ‘
Contact CRlb completes a circuit for the reset
winding 352, associated with the ratchet unit
are, which thereupon withdraws its armature
from engagement with the ratchet teeth and
enables 'the return spring 355 to restore the,
ratchet unit to its initial or starting position in
which arms 332, 334i and 336 occupy their illus
trated inactive positions. When the ratchet unit
reaches its starting position, the limit switch 358
is opened thereby, which action interrupts the ‘
circuit for the reset winding 352.
During the return movement of the ratchet
unit, the arm 332 sweeps over the terminals a2 ,
and al, which action is, however, without effect,
since the work is now at a temperature below
the temperatures at which these terminals re
ratchet unit. Contact CHM and contact GR“),
in opening, further interrupt the circuit for
transformer Ti and also interrupt the previously
traced holding circuit in parallel with the pilot
switches Pi and P2. In addition, the opening
of contact CRih interrupts the circuit for the
welding vpressure valve Hi8, which thereupon, as
described in connection with Fig. 10, relieves the
welding pressure from the work and restores this
pressure to the initial low value.
The opening of contacts CRIa and CRlb also
interrupts the remaining energizing circuit for
the winding of the four-way valve its, associated
with the two cylinders 52 and 54, thereby con- _
necting cylinder 52 to exhaust and connecting
the return cylinder 5% to the source of air Pres
sure. This action is preparatory to the return
or separating movements of'the electrodes.
The de-energization of transformer TI de-en
ergizes control relay CR2, which thereupon re
sumes the de-energized condition, opening its
contacts CR2a, CRZc and CRZd and closing its
contact CRZb. The opening of contacts CHM
and CRZd is without immediate e?ect, but the clo
sure of contact CR2!) recompletes a circuit for the
two-way hydraulic valve i222, which thereupon
functions, as described in connection with Fig.
10, to enable the separating movements of the
electrodes under the influence of the air pres
sure now applied to cylinder 54.
The opening of contact CRZc interrupts the
circuits for transformers T6 and T5, associated
with valve V2, and control relay CR3. These
actions cooperate to interrupt the further How of
energizing current to control relay CR3, where
upon the energy stored in the coil thereof starts
to discharge through the associated condenser
05. At the expiration of a relatively short period,
arm 3% sweeps over the terminal b2, but the
long to enable the full separating
period of this energization is too short to enable
the electrodes to take place, relay
relay CR8 to become re-energized. If desired
CR3 resumes the ale-energized position, opening
and as shown, a delaying condenser 356 may be
its contacts CRZ-la, CR3c and CR3d, and reclos
connected in parallel with the winding of relay
‘ ing its Contact cast. The opening of contact
C330 and the closure or contacts CR3b are with
The return movementof the arm 33% inter-v
out e?ect, since the associated circuits areopen
rupts the original circuit for relay CR1. Closure
at other points. The opening of'contact CR3a
spond. During this return movement, also, the
of contact CRlc, however, completes a self-hold
ing circuitlfor relay CR1, so that such movement
interrupts the only remaining energizing circuits
for valves H2 and [22. Upon being de-ener
gized, valve 522 closes= off the line 296, as afore
As to resetting actions,-the opening of contact
said, and valve H2 relieves the air pressure ‘ap
CR'la directly interrupts the energizing circuits 50 plied
‘to cylinder '54 through the now tie-ener
for control relay CR5, transformer Tl, trans
gized valve lilii. The opening of contact CR3d
former T‘? and control relay CR9. It is noted
interrupts the previously traced holding circuit
that the de-energization of relay CR5 at the con
for relay CR‘E, which thereupon resumes the de
clusion of the cooling down of the work also
energized position without e?'ect. These reset
caused its contact C1250 to reclose, which action 55 ting operations, therefore, serve to restore the
tends to recomplete the circuit for transformer
system to its normal condition, in readiness for
Tl’ and for control relay CR9. The de-energi
the next welding operation.
zation of relay CR5, however, and as aforesaid,
In certain cases it is found necessary, after
also causes the energization of relay CR1, which,
at contact CRla, prevents recompletion of these 60 initially moving the electrodes into engagement
with the work, to again separate them'beiore ini
circuits. In practice, it is found that, in view of
tiating the actual welding operation. 'Such an
the relatively heavier character of at least con
action can readily be accomplished by closing
trol relay CR9, contact CR‘ia takes e?ect before
pilot switch Pl, without closing pilot switch P2,
relay CBS is re-energized. ' Thus, contact CREic,
and by thereafter releasing pilot switch Pl. It
in reclosing, is ineiiective to re-initiate a ?ow
will be recalled from previous description that
of welding cur-rent to the work. If desired, of
closure of pilot sWitch'Pl ?rst energizes valves
course, such proper sequencing can be further in
H2, 522 and N36 to thereby cause the electrodes
v sured by interposing a slight delay in the closing
of arm 33% is without effect.
movement of contact .CR?c, so as to cause the
' to start towards the work engaging positions.
70 Also, by causing the‘ energization of relays CR2
and CR3, pilot switch Pl causes the two-way
sure of contact CREE).
hydraulic valve I22 to be tie-energized after the
Continuing with the resetting action, the deen
electrodes engage, the work. It will further be
ergization of relay CRl causes its contacts ‘CRla,
recalled that so long asswitch PI is held closed
CRlb and CRlc to reopen. The latter contact
lie-energizes the operating, winding, 3416, of the 75 (assuming switch P2, is maintained in the open
closing of this contact to lag behind the reclo
position), valves H2 and H36 and relays CR2 and
CR3 remain energized, and the electrodes engage
for moving them between said positions, a source
of power common to said motive means for ef
fecting a said movement to the work engaging
the work with the relatively light preliminary
If, under these conditions, switch Pi is re
opened, such action immediately de~energizes the
four-way valve I06 and also immediately de-en
ergizes transformers TI and T2. The de-ener
gization of the four-way valve Hit applies air to
the cylinder 54, preparatory to the return move 10
ment of the electrodes, as aforesaid. The de
energization of transformers Ti and T2 causes
relay CR2 to be de-energized. This action
continued movement of the other electrode, and
means for actuating said motive means to re
tract the electrodes to the retracted positions
2. A welding machine having an electrode mov
able between a retracted position and a work en
gaging position, a hydraulically operated motor
for effecting a said movement of said electrode,
a reservoir disposed to be in communication with
said motor, means for applying an elastic ?uid
pressure to ?uid contained in said reservoir to
cause a delivery of such ?uid from the reservoir
to the motor, and supplemental means operative
to increase the hydraulic pressure in said motor
after said electrode has reached the work en
gaging position, said supplemental means includ
ing a conduit communicating with the motor and
containing hydraulic ?uid, piston means for
transmitting pressure through the conduit to the
motor, and control means for applying an elas
tic ?uid pressure to the piston.
3. In a welding machine, the combination of
causes contact CRZa to reopen and contact CRZb
to reclose. The former action is without e?ect,
since contact CR3a is still closed, but the latter
action recompletes the circuit for the two-way
hydraulic valve I22, which thereupon reopens and
enables the return movements of the electrodes,
as previously described.
The de-energizaticn of relay CR2 also opens
its contact CRZc which, as described in connec
tion with the usual resetting operation, results
in the de-energization of relay CR3. This latter
de-energization occurs at the end of a period
su?ic-ient to allow the full separating movement
of the electrodes. When relay CR3 resumes the
de-energized position, it completes the reset
ting action, in the previously described manner,
by de-energizing the remaining valves 1 l2 and
As described above, the control system of Fig.
position, said source of power including means
constructed and arranged to enable the source to
continue to move one electrode independently of
a work engaging part movable between a re
30 tracted position and a work engaging position, a
11 provides only a single heating stage and a
single cooling stage. It will be understood that,
if desired, the indexing unit may be provided with ;
additional terminals, as indicated, so that as
described in the aforesaid Leathers and Benkert
application, a succession of heating and cooling
?rst motive means for eilecting a said movement,
a second motive means for applying a working
pressure to said part while in the work engaging
position, and control means for said motive means
selectively operable to either actuate only said
?rst-mentioned motive means or to operate both
said ?rst and second motive means in sequential
relation, and timing means responsive to said
stages are provided. In such case, it will be un
control means for interposing a predetermined
derstood that the high pressure relay CR8 may
40 time delay between the operation of said ?rst and
be energized during each cooling stage and it will
second means.
also be understood that the actuation of the re
4. The structure of claim 3 wherein said part
setting relay CRT is delayed until the end of the
provided with a ?uid motor, and said ?rst and
?nal cooling stage. It is thought, however, that
second motive means comprise means for supply
the single stage system speci?cally described
ing said motor with fluid pressure.
above serves to illustrate the operation of the
5. The structure of claim 3 wherein said part
present invention.
provided with a ?uid motor, wherein said ?rst
Although only a single speci?c embodiment of
and second motive means comprise means for
the invention has been described in detail, it will
supplying said motor with ?uid pressure, and
be appreciated that various modi?cations in the
wherein means are provided to render the ?rst
form, number and arrangement of the parts
motive means ine?ective while the second motive
may be made without departing from the spirit
means is e?ective.
and scope of the present invention.
6. The structure of claim 2 including means
What is claimed is:
operative to prevent a ?ow of ?uid from said mo
1. A welding machine having a pair of opposed
tor to said reservoir when said control means is
electrodes, each movable between a retracted po 55 actuated.
sition and a work engaging position, means in
cluding motive means individual to each electrode
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