Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to arc welding generally,
and more particularly to a portable wirefeed arc welding
system.
Conventional portable arc welding systems include
a welding machine or power source (preferably a DoCo constant
voltage type), a portable wire feeding unit with controls, and
a welding gun or torch, with electrode power cables rom the
power source to the wire feeding and control unit and to the
gun, a ground ca~le between the power source and the work,
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and contactor control and llO or 115 volt AoCo supply cables
between the power source and the portable control unlt. The ~:
latter cables are hazardous and their maintenance is an : :~
important factor in efficiency, productivity and costs,
especially in welding on bridges, ships, tan~s, pipe lines,
or other large structuresO Consequently, elimina~ion of t.hose
contactor control and 115 volt AoCo supply cables is very
: desirable. :~
That has been accomplished with the so-called arc :-
voltage system by using a DoC, motor for the wirefeeder which
: 20 operates from the low voltage in the welding current cable,
but that requires the main contactor to be closed at all times
which maintains the welding cables and welding wire "hot"O
That is a very dangerouæ condition, and an accidental touching -~
of the wire or gun t p to the work sr surrounding grounded
structure will cause instantaneous arcing and probable serious
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damage to the wirefeed system, such as a "burnback" o the
wire into the gun tip, and possible burning of the operator's
eyes if his protective helmet is not in place. Further,
arcing on critical weldments not only leaves a cosmetic
blemish, but also is metallurgically undesirable.
According, the invention provides in a portable
wirefeed arc welding system for depositing metal on a selected
piece of work and having a power source including a normally
open contactor, a portable wirefeed unit, a welding gun in-
cluding a normally open gun switch, a ground cable inter-
connecting said power source and said work, an electrode power
cable interconnecting said contactor with said wirefeed unit
and said gun, and control,leads interconnecting said wirefeed --~
unit with said work and said gun: a remote control unit in-
cluding a normally inoperative sensing means, a capacitor
connected in series with said gun switch across said power
cables and said gun switch and capacitor in serles being ~ ;~
connected in parallel with said sensing`means, a voltage ,~
source, means for charging ~said capacitor from said voltage
source in response to closing of the switch to render said
sensing means operative to close said contactor for energizing
said cables from said power source, and means responsive to
closure of the contactor to disconnect the capacitor and
sense relay from the power cables.
This invention eliminates the conventional
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contactor control and 115 volt A.C. supply cables between
the portable wirefeed and thé power source of an arc welding
~- system without requiring the welding cables and wire to be
~; "hot" at all times. This is accomplished by providing a
control unit at the power source including a capacitor
operable in response to closing of the gun switch to place
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an override current on the welding cables, and sensing
means operable in response to such override current to
effect closing of the power source contactor to supply
welding current to the electrode and ground welding cables.
In the preferred embodiment of the invention, that sensing
means comprises a control sensor employing the Hall effect,
and a sense relay which is operable in response to a
predetermined override current on the welding cables to
close a normally open cycle hold delay relay and the power
source contactor to supply wPlding current to the gun.
Closing of the cycle hold delay relay, in turn, closes a
rearming delay relay which opens the circuit to the sense
relay. If the cycle hold delay relay times out after a
predetermined time, preferably two seconds, the circuit to
the rearming delay relay is opened and the welding c~ntactor
is opened~ Until the rearming delay relay thereafter times
out (one-half second), the welding cable capacitor cannot
re-energize the system which gives an~ other capacitors
tim~ to discharge before rearming the sense relay.
~hen the power source contactor is closed in
response to closing of the gun switch, as above described,
and welding current is being drawn, the control sensor
effects closing of a control relay which remains closed and
holds the cycle hold delay relay closed as long as welding
current is drawn. Brief interruptions in the welding,
preferably of up to two seconds, can occur, however, with-
out the contactor being opened. But if the welding current
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is lost for more than two seconds, a rearming sequence must
be followedO This provides an inherent and very desirable
burnback controlO
This control system thus eliminates the use of the
conventional contactor control and A~Co supply cables
between the power source or welding machine and the portable
wirefeed control unit in an arc welding system, while the
contactor normally is open, by applying a control current
override to the welding electrodes and ground cables, in
response to initial closing of the gun switch, which is
sensed remotely at the welding machine to close the contactor.
~he gun switch therefore serves the two functi~ns of
initially causing closing of the normally open welding
contactor and, thereafter, controlling the start-stop
wirefeeder motor after welding voltage has been established.
In the drawings: ~
FIGURE 1 is a schematic view of a portable wirefeed ~ .
arc welding system embodying this invention; and
FIG. 2 is a wiring diagram of the preferred remote
control unit employed therein.
The schematic drawing of FIG. 1 illustrates an arc
welding system having a conventional power source P;
preferably a DoC~ constant voltage type, with a normally
open contactor C controlling the usual welding cables
comprising a ground cable G from the power source to the
wor~ ~ and an electrode power cable E from the power source
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to a portable wirefeeder F which includes a wire speed
control S, a wire drive motor D and a supply of weld wire :-
on reel R. The weld wire extends with the power cable E
through a suitable conduit from the wirefeeder to the welding
gun A. The gun switch T is connected in the usual manner with
the wire speed control S by a lead U, and a lead V inter-
connects the control S and the work ~O The use of a shielding
gas is optional and is illustrated in FIG. 1 as passing ~;
through the wirefeeder under the control of a solenoid valve
therein in well known manner. ::
From the preceding it will be noted that the
contactor control and 115 volt AoC~ supply cables extending
between the portablewirefeeder and the power source in the
conventional arc welding system are not employed in the :~
present system. Instead, the system of this invention pro- :
vides a remote control unit, indicated generally by X, which
is located at the welding machine or power source P to effect
closing of the normally open power source contactor C to : :
supply welding current to the gun A~
~ FIG. 2 comprises a wiring diagram of a preferred ~;
; 20 embodiment of that control unit X which includes two ~:
: transformers Tl and T2 connected across 115 volt AoC~ supply
lines Ll and L2. A sense relay Rl is connected across the
secondary of transformer Tl with diodes H and J and a 150 ohm
resistor K, as illustrated, so that a one-half wave pulsating
D~Co voltage is placed across relay Rl, but such voltage is -~
not of sufficient magnitude to close that sense relayO The
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relay Rl also i9 connected to the welding cable E through a
10 ohm resistor M and normally closed sampling contacts R4.
The normally open gun switch T is connected to a 1500 MFD
capacitor Cl across the welding cables E, G through normally
closed contacts CR2 of a relay CR2. Consequently, when the
gun switch T is closed, the 1500 MFD capacitor Cl is placed
across the welding ca~les and the voltage across the sense
relay Rl increases sufficiently to close the c~ntacts Rl of
that relayO
A full-wave bridge rectifier N is connected across
the secondary of transformer Tl and at its positive terminal
to a line 01 and at its negative terminal to a line 02. The
normally open contacts Rl of the sense relay Rl are connected
with a cycle hold delay relay R2 across the lines 01 and 02, ~-
as are the normally open contacts R2 of the cycle hold delay
: relay and a rearming delay relay R4. The normally open `
contacts R3 of a weld current override relay R3 are connected
in parallel with the sense relay contacts Rl; and a 3000 MFD
capacitor C2 and a 1000 MFD capacitor C3 are connected in
parallel, respectively, with the cycle hold delay relay R2,
and the rearming delay relay R40
; Therefore, when the contacts Rl of the sense relay Rl
are closed in response to closing of gun switch T as previous-
;: ly described, the cycle hold delay relay R2 is actuated to
close its contacts R2, which also are in a welder control
circuit WC, to effect closing ofthe contactor C. Such
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operation of the cycle hold delay relay R2 also actuates
rearming delay relay R4 to open its normally closed contacts
R4 and the circuit to sense relay Rl. When cycle hold delay
relay R2 times out, preferably in two seconds, the contactor
C is opened and the circuit to rearming delay relay R4 is opened
to start its timing out. When relay R4 times out, preferably
in one-half second, the capacitor Cl is re-energized and the
control circuit is back to normal, the delay occasioned by
relay R4 enables any capacitors in the welding machine to
discharge before the sense relay Rl can be rearmed. ;
A brief sequence of ~he above-described operation
is as follows:
1. Gun switch T closing places capacitor Cl across ~ ;
welding cables E, G to provide override current to close
sense relay Rl. ~;
2. Closing of Rl closes cycle hold delay relay R2
which~
A. Closes main contactor C.
B. Closes rearming delay relay R4 which opens
circuit to sense relay Rl.
3. Opening of Rl contacts starts cycle hold delay
; relay R2 timing out.
4~ If R2 time8 out:
A. Contactor C is opened. `
B. The circuit to rearming delay relay R4 is i~
opened to start R4 timing out. -
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A second portion of the sensing means of the remote
control unit X at the welding machine or power source P is a
current sensor Sl for sensing the current passing through
the welding or electric power cable E. In the preferred
embodiment, Sl is a Hall effect sensor which is illustrated .
in FIG. 1 as surrounding the welding cable E. As shown in
FIG. 2 sensor Sl is connected across the secondary of trans-
former T2 and its output is connected to a conventional
operational amplifier OA. A normally non-conductive 2N2905
transistor indicated generally by reference character NT
has its emitter lead EL connected to the positive line 01,
its base lead BL to the amplifier OA, and its collector lead
CL to one side of a relay R3, the other side of which is
connected to the negative line 02, in turn connected to the
amplifier OA.
Any time a welding current of 50 amperes or more
is drawn through the power cable E and, therefore, through
~ the Hall effect sensor Sl, sufficient voltage is available
:~ on the output o the operational amplifier OA to make trans-
;~ 20 istor~NT conductive which cIoses relay R3. The contacts R3
of the latter are connected in series with the cycle hold
delay relay R2 between line 01 and 02, so that their cIo~ing
by such closing of reIay R3 holds relay R2 to prevent its
timing out. Brief welding interruptions or extinguishments
of the arc for periods of up to two seconds will not result
in opening of the contactor C~ However~ if welding current
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is lost for two or more seconds, the contactor C will
open and the rearming sequence previously set forth herein
will follow closing of gun switch T.
As soon as welding voltage is applied to power
cable E, relay CR2 is energized to open its normally closed
contacts CR2. This transfers control of the gun switch rom
the capacitor Cl to the usual wirefeeder start-stop circuit
through the gun control lead U tFIGo 1), and allows the ~-
gun control switch to serve two functions:
A. Initially effect closing of the normally open .
main contactor.
B. Start-stop wirefeeder motor after welding
voltage has been established.
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