Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
,889~
Welding system for Yielding
The present invention concerns an electronically
operating circuit, which is meant to be mounted on
operating welding rectifiers having basic current circuits.
The known Twig welding systems can be split into two
types dependent on the way in which the welding is started.
The first system uses scrape ignition, in which the voltaic
arc is established by scraping the electrode against the
article to be welded until a spark is obtained This
method causes a 'drag' in the material upon starting and
stopping, and tungsten material is left on the welded
article, which means that the resulting weld has a poor
quality appearance. In addition, the welding electrode
must be removed and ground frequently. Another system
uses a contact free start by means of a high tension
generator, which starts the voltaic arc when a spark is
established. The drawback of this system is that the
spark moves in a circle on the article to be welded, and
the place where the welding is started cannot be precisely
controlled. Furthermore this system is very expensive.
From British patent specification no. 2,054,293 a
welding system is known which counteracts the drawbacks of
the scrape ignition system. In this system, a soft start
is obtained by coupling together a high tension via a
separate transformer winding with an existing rectifier,
which is synchronized with the main frequency. When the
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voltaic arc is established, the system electronically
changes over to a normal slope-up circuit by means of a
new rectifier. This is a rather expensive method of
advanced scrape ignition which also includes an expensive
choke coil. The user also has the possibility of getting
an electric shock if a filler metal is employed.
According to the invention there is provided a method
for the electronic control of the starting process in TWIG
welding, in which a tungsten electrode is brought into
momentary contact with the object to be welded, and then
separated from said object to initiate an arc, wherein a
low short-circuit current is led through the welding
circuit during said contact, and wherein the interruption
of said low short-circuit current is used to control the
welding power source to increase the current in the welding
circuit to a value above a preset welding current value
intended for the welding process proper, and thereupon,
after a short period of time, to decrease the current to
remain at said preset value.
The invention differs from the known systems because
high tension is not required for starting and the required
adjustment takes place as a current regulation.
The invention consists of an electronically operated
circuit which is meant to be mounted on welding rectifiers
having a basic current circuit.
The peculiar thing about the invention is that the
welding electrode can be placed directly on the article
to be welded before the welding voltaic arc has been
established, because only the basic current of 3-8 A will
pass through the electrode. When the electrode is lifted
from the article, the basic current is raised to twice the
preset welding current, and a voltaic arc is established.
The current is then immediately lowered to the value the
slope-up function has achieved. The slope-up function of
the operated circuit thereafter regulates the current up
to the preset welding current. It the article to be welded
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is touched during the welding operation, the circuit will
regulate the welding current down to the basic current
level which protects the electrode.
When the button on the welding handle is released, a
down-slope will take place, which brings about a slow
lowering of the welding current to the basic current level
and the welding stops. The slope function avoids the
formation of a 'drag' in the material.
During the welding with the preset welding current it
is possible, by trigging a burner switch to pulsate the
welding current for controlling the molten bath. The
control circuit also regulates the gas-stream in the
magnetic valve in a way that provides both for- and
after-streaming of argon. This is done to make the start
easier and to avoid oxidizing the electrode during the
cooling.
The advantages of the invention are that a 'drag' is
avoided and that the starting point of the weld can be
controlled very precisely.
The invention will be described in more detail in the
following with reference to the accompanying drawing, in
which:
Fig. 1 shows a block diagram of a circuit according to
a preferred embodiment of the present invention.
The welding system has to be connected with a thruster
operated welding rectifier with internal basic current
circuit. The welding is described with MODE switch 11 in
position for Twig welding. The tungsten electrode on the
welding handle 6 is placed on the article to be welded.
The switch on the welding handle 1 is closed and Montana-
ante circuit 2 is activated. This causes the magnetic valve 3 to open and the gas regulating circuit 4 causes
the gas streaming to start. After the gas streaming has
stopped the basic current circuit on-off 5 is activated,
which turns on the basis current to the electrode 6. When
the electrode is lifted by a small amount from the article
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to be welded, the welding voltaic arc and the idle voltage
control 7 is activated. This will activate the start
pulse circuit 8. The welding current circuit 9 shortly
lifts the welding current to establish a stable welding
voltaic arc - bigger than the value set on the control
After a stable voltaic arc has been obtained the current
falls to a value just above the basic current value. At
the same time that the voltaic arc is established the
control of the welding voltaic arc 7 will start for the
slope-up function 10. This means that the welding current
will rise for a short time to a value determined by the
preset value-control 12.
When the welding is to be stopped, the Twig burner
switch 1 is turned off, by means of which the slope-down
regulation 10 starts to regulate down through the
regulation circuit 9. When the regulation to the basic
current level is obtained the maintenance circuit 2 is
zero-set and the basic current circuit on-off 5 turns off
for the basic current in the welding rectifier. At the
same time, the gas regulating circuit 4 causes the gas
after streaming to start. After that the magnetic valve 3
has been turned off, the gas after streaming is stopped.
The time for after streaming avoids oxidizing the electrode
during the cooling.
Tack welding can be carried out by changing the MODE
switch to the tack-welding position. The welding then
works in the same way as for Twig welding, though the up
and down slope time is shortened to milliseconds.
Electrode welding can be carried out by changing the
MODE switch to the electrode welding position. This means
that the basic current circuit is constantly activated.
The slope function 10 and the gas regulating circuit 4 are
uncoupled. Normal electrode welding can then be carried
out with coupled up equipment.
