D E S C R I P T I O N

The present invention relates to a device for the adjustment of the electric current, adapted to be used in association with an arc welder with perishable coated electrode.

The finding therefore falls within the field of welding machines, namely of the arc welders using perishable coated electrodes.

The operation of a welder of such type is widely known to the man skilled in the art. A standard welder shall be briefly described hereinafter, by limiting the description only to the components aimed at understanding the present finding. As known, the arc welding technology with coated electrode (commonly defined with the acronym MMA, "manual metal arc", or SMAW, "shielded metal arc welding", in the US AWS terminology) is a manual process wherein the thermal source consists of the electric arc which sparks off between said electrode and the piece to be welded, the arc being powered by the electric power generated by the welding machine.

Said technology contrasts with the equally widespread methodology of welding, such as:

the continuous wire welding MIG/MAG ("metal-arc inert gas" or "metal-arc active gas") with gas-protected electrode, both indicated in the AWS terminology as GMAW ("gas metal arc welding", arc metal welding under gas protection), wherein the weld puddle is protected by a blanket gas (which may be inert or active),

- the welding TIG ("tungsten inert gas") or GTAW ("gas tungsten arc welding"), wherein the arc welding utilizes a tungsten infusible electrode, under inert gas protection.

Such methodologies require the use of various electrodes (fusible and infusible), having a gas protection, and implies different components for the electric circuit of the welder, starting from the current generator, which must be suitably adapted to the use of gas-protected and non-perishable electrodes.

The present invention, instead, relates exclusively to the field of arc welders using coated electrodes, without gas protection, perishable following use.

The typical electric circuit of a welder with coated electrode comprises at least the following components:

- the current generator, consisting of the welding machine, having:

- an electric power converter, adapted to draw supply energy from the mains, provided with a power switch and a power selector knob,

- two outputs wherefrom the positive and negative polarities of the generated current may be collected,

- the gripper cable, usually connecting the electrode-holder gripper to such negative polarity output,

- the ground cable, usually connecting the clamp associated with the piece to be welded to such positive polarity output, so as to close the electric circuit.

Such electrode consists of a metal core, covered by a coating of deoxidizing materials of various types, according to the result to be obtained and the material of the piece to be welded (for more information on this regard, please refer to the electrode unification standards, according to EN 499 classification of CEN or the AWS classification of the American Welding Society).

When the welder is switched on and the electric power is suitably adjusted, the electric arc sparks off when the operator approaches the electrode to the piece to be welded; by moving the gripper, the operator is able to manage the weld puddle and complete the process.

Such ease of use has produced the success of welders with coated electrode over time, also thanks to the fact that these are compact machines and can be transported both indoor (such as workshops) and outdoor (such as worksites). However, the arc welders with coated electrode currently known show a series of drawbacks that limit the use thereof to predetermined types of target materials and use categories.

The first limit inherent in such type of welders is related to the same nature of the coated electrodes used: in fact, considering that even the smallest of the electrodes on the market still has a diameter of about 1.6 - 2 mm (the dimensions of such electrodes is conventionally defined by the section of the metal core alone, irrespective of the thickness of the coating), it is necessary that the piece to be welded has a thickness of at least 2 - 2.5 mm, in order to avoid breakings of the piece or burns.

Therefore, the arc welders that use coated electrodes have difficulties in successfully operating on target pieces with a thickness that is thin, or in any case lesser then the diameter of the same electrode, such that they are currently used mainly in the shipbuilding and oil sectors, where the sheets to be welded are of sufficiently high thickness.

A further drawback of the welders examined lies in the rigid operating methodology, related to the almost absent possibility of modulating the electric power generating the arc: in fact, once the quantity of energy needed to spark off the arc is selected, it often shows to be in excess relative to the process to be carried out, forcing the operator to subsequent adjustments of power and consequent interruptions in welding.

At the same time, the uninterrupted power supply of the welder is a source of significant and useless waste of electric current caused by an excessive heat input when the arc is inserted, cause of the known phenomena of distortion and deformation of the material subject to welding. Another drawback, related to the previous ones, consists in the fact that the welding machine is usually located in a place relatively far from the place where the welding process is being performed; therefore, the subsequent operations of power adjustment or a delayed restart of the processing, may result in unintentional ignitions of the electric arc (which may cause arc strokes on the object), with the risk of flare-ups to the limbs and eyes.

The main object of the present invention is to obviate the drawbacks described above by providing an additional device to be connected to or incorporated into an arc welder with coated electrode of the prior art, capable of extending the field of application thereof.

A further object of the present invention is to provide means for a convenient use, from the ease of use and cost efficiency point of view, of the arc welders with coated electrode, provided with the present finding.

Further features of the present invention shall be better highlighted by the following description of a preferred embodiment, in accordance with the patent claims and illustrated in the enclosed figures. Such figures should be considered as having an illustrative and non-limiting purpose, in which:

- Fig. 1 schematically shows an arc welder with coated electrode, provided with the additional device according to the invention;

- Fig. 2 illustrates the flame protection mask of the operator, provided with means for remotely actuating the additional device according to the invention;

- Figs 3. A to 3.C show different types of time pulses of the electric wave producing the arc, that may be generated by the welder through the additional device according to the invention.

The features of the finding shall now be described using the reference numerals contained in the figures and with particular relevance to the variant represented therein.

Reference numeral 1 globally indicates the additional device object of the invention, hereinafter called "power modulator 1" and adapted, as it shall be seen, to modulate the welding power of a standard arc welder with coated electrode, generally identified with reference numeral 2.

Said welder 2 performs in a known manner the role of current generator suitable for arc welding with coated electrode and comprises:

- a connection cable 3.1 between a pole of the welder 2 and the electrode-holder gripper 3, supporting a coated electrode 4, capable of generating an electric arc 6, and

- a link cable 5.1 between the other pole of the welder 2 and the clamp 5 associated with the piece 7 to be welded,

- a secondary winding whereon current "I" is induced from a primary winding.

The power modulator 1 , which shall be described in detail hereinafter according to a preferred variant, is inserted in the electrical supply line 1.1-1.2, upstream of the welder 2.

Reference numeral 2.1 indicates the power switch of the welder 2, while 2.2 indicates the power selector knob, having the function of adjusting, in a known manner, the value of the current intensity delivered by said welder 2 (or better, by the current generator 2.0 incorporated in said welder 2).

The power modulator 1 , object of the present invention, is powered by the mains voltage through cable 1.2.

It substantially consists of an electronic control unit, which, according to a preferred variant, comprises a containment box 1.0 wherein two servo-controls are seated, each of which is piloted by a receiver radio control.

The control panel of said power modulator 1 (hereinafter shortened to "power modulator 1") comprises the following components:

two potentiometers 1.5 and 1.6, activated and adjusted by two switches (not shown in figure),

- two receiver radio controls (not shown in figure), adapted to receive remote signals from special radio controls for the activation of said servo- controls, - two luminous visual control LEDs 1.3 and 1.4, identifying respectively the power supply of the welder 2 and the activation of the function which such power modulator 1 is intended for, according to the various methods which shall be explained hereinafter.

Fig. 2 shows a typical shielded mask 8, that the operator usually uses in order to avoid flare-ups and burns during the welding operations.

It comprises a screen 8.1 with actinic protection glass and a handle 8.2: two radio controls 8.3 and 8.4 (self-powered by batteries or similar means), adapted to communicate remotely with the respective receiver radio controls of the power modulator 1 are arranged on said mask 8, preferably on said handle 8.2 or in any case in a position that is easily accessible to the operator.

As an alternative to the placement on the mask 8, such radio controls 8.3 and 8.4 may be arranged at the electrode-holder gripper 3, always in a position readily accessible by the operator.

Typically, said radio controls 8.3 and 8.4 may consist of buttons (provided with luminous LEDs, preferably of the same colour as the corresponding LEDs 1.3 and 1.4 of the power modulator 1 , so as to enable a correct an unique identification of the operational function by the operator), the pressure thereof remotely activates or deactivates the receiver radio controls of the power modulator 1 ; more precisely:

- the radio control 8.3 communicates with the receiver radio control of the power modulator 1 which is responsible for supplying and removing power to the welder 2,

- whereas the radio control 8.4 communicates with the receiver radio control of the power modulator 1 which is responsible for activating or deactivating the modulating function, described hereinafter.

In fact, the function of such power modulator 1 consists in modulating the power of the electric energy generating the arc 6; more in detail, said power modulation is carried out by an adjustment of interposed powering or unpowering intervals of the welder 2, selectable by suitably acting on the two potentiometers 1.5 and 1.6.

According to the embodiments of the prior art, the operator, by the knob 2.2, selects the power suitable for the activation of the electric arc 6, according to the type of welding required, the coated electrode 4 used and the material of the piece 7 to be welded: such initial selection is typically made on the basis of past experience and/or with the aid of known comparative tables, written according to the CEN or AWS standards mentioned above.

As said, the welding carried out with these standard methods undergoes a series of problems, mainly due to the excessive electric power which is constantly released by the current generator 2.0 of the welder 2, which originates an arc 6 of power exceeding the actual needs.

With the power modulator 1 examined, instead, the operator who is preparing for the welding may proceed as follows:

A) turns on the welder 2 and selects, always by the knob 2.2, the sufficient power for triggering the electric arc 6 (the welder, however, remains not operational because it is not yet powered);

B) chooses the powering and unpowering intervals of the welder 2, by acting respectively on the potentiometer 1.5 and the potentiometer 1.6 of the power modulator 1, according to the type of welding to be performed, the practice inferred from past processes and/or the comparative tables mentioned above;

C) having moved to the place where he must perform the welding, presses the radio control 8.3 (located on the mask 8 or electrode-holder gripper 3) that activates the power supply of the welder 2 through the power modulator 1, so that the electric arc 6 is triggered;

D) presses the radio control 8.4 (always located on the mask 8 or electrode-holder gripper 3) that determines the activation of the modulating function carried out by said power modulator 1 , so as to power or unpower the welder 2 according to the intervals selected at step B with the two potentiometers 1.5 and 1.6; E) completes the welding, until he presses again the radio control 8.3 to turn off the welder 2 through the power modulator 1.

As an alternative to the sequence mentioned above, it may be necessary a further step of adjusting the powering and unpowering intervals of the welder 2 by means of said potentiometers 1.5 and 1.6, to be carried out subsequent to the step D in case the operator verifies that the arc 6 has a power not suitable for the welding in progress (it is clear that this additional step may be easily avoided with experience, being generally sufficient the only step B of initial adjustment). At the same time, in case the type of processing requires it (i.e. it is not necessary to activate the power modulating function), the operator may limit to the steps A, C and E only (or also perform the adjustment of step B without then switching it on with step D): in such a case the welding takes place in the same way as that carried out by the current welders of the prior art, with the power modulator 1 that acts only as a transit unit for the powering and unpowering signal of the welder 2.

Therefore, the modulating function of the power, which may be activated with the power modulator 1 of the present invention, is based on the succession of powering and unpowering periods of the welder 2, described at step D and illustrated in Figs. 3. A, 3.B and 3.C, wherein exemplary charts of the behaviour of the electric arc 6 are shown.

With particular reference to Fig. 3. A, the initial stretch of the chart shows the electric arc 6 at full power, which sparks off between the end of the coated electrode 4 and the piece 7 to be welded when power is supplied to the welder 2. The next stretch of the chart, however, shows such electric arc 6 at reduced power, resulting from the unpowering of the welder 2 following the activation of the modulating function performed by the power modulator 1 : specifically, this second stretch of the chart means that this is the time interval adjusted by the potentiometer 1.6 that is responsible for removing power to said welder 2. This time interval at reduced power is identified with reference TBP.

Figs. 3.B and 3.C show two further examples of adjustment of such operation time intervals of the arc 6, depending on the choices made by the operator on the potentiometers 1.5 and 1.6 and the activation of the modulating function carried out by the power modulator 1.

In Fig. 3.B a regular succession of times with the same duration between high power periods (identified with reference TAP and managed by the potentiometer 1.5, which allows the welder to be powered) and low power periods TBP (managed by potentiometer 1.6, which removes power to the welder 2) is noted. In Fig. 3.C, instead, the high power periods TAP are of longer duration than those at low power TBP, the operator having selected a greater value on the potentiometer 1.5 than the value chosen on the potentiometer 1.6, clearly because needing an electric arc of higher power than the example of Fig. 3.B. As mentioned above, the intermittence between those times at high power TAP and low power TBP of the arc 6 (resulting from the succession of powering and unpowering periods of the welder 2), is made by means of the switches underlying said potentiometers 1.5 and 1.6.

As mentioned above, said switches, irrespective of their nature (contactors, triac solid-state switches, motorized rotary switches or piloted dynamic switches), act on the primary winding of the current generator 2.0 of the welder 2, interrupting or restoring the power supply thereof.

As a result of its inductance, however, even when the primary is unpowered, the electric current "i" continues to flow for a certain time in the circuit comprising the secondary winding, the electrode, the electric arc and the metal mass being welded.

In fact, such circuit consists of an inductive-resistive circuit (said circuit RL) in "free evolution", where there is a resistance R (in this case substantially concentrated in the electric arc) and an inductance L (in this case substantially concentrated in the secondary winding).

"Free evolution" means that the circuit has no external sources of voltage or current, and thus the current "i" that travels through it continues to circulate until the complete dissipation, by the resistance R, of the inductive energy stored. The electric arc 6, then, while not getting more energy from the primary circuit, is still triggered by the inductive current "i": it does not turn off abruptly, but fades gradually before turning off.

The unpowering intervals are arranged short enough to ensure that, before the complete turn off of the arc 6, the power modulator 1 again provides power to the primary winding in order to bring power back to the arc 6.

Preferably, their duration is comprised between 0.01 and 2 seconds; even more preferably between 0.1 and 0.8 seconds, but it depends, of course, from the set of means and materials involved (e.g. type of welder, inductance of the secondary winding, type of coated electrode, etc.).

As it is clear from the above description, the power modulator 1 object of the present finding allows to achieve the above mentioned objects and to obtain advantages not easily achievable with the current arc welders with coated electrode.

A first order of advantages relates to the extension of the fields of application of the welder 2, which, thanks to the power modulation of the arc 6 carried out by the power modulator 1, may also be used on thin materials, that is, with a thickness lesser than the diameter of the coated electrode 4 used for the welding. Practical tests have in fact shown that, with the addition of this power modulator 1, it is possible to operate easily even on sheets having a thickness of up to 0.5 mm, without the risk of breakings or burns: this is just thanks to the power modulation of the arc 6, calibrated on the specific piece 7 to be welded, according to the real needs of the operator.

The activation of the modulating function of the power modulator 1 also allows to perform the welds even in difficult positions, for example overhead or vertical down: in fact such modulation, by intermittently providing less heat to the arc 6, allows the molten bath to be more viscous and to be more supported from the end of the electrode 4, not casting on the molten zone of metal.

A second order of advantages is economic: with such modulation a consumption of electrical energy of about 35 - 45% less compared to a welder without the power modulator 1 is achieved, obtaining also a decrease of the deformation and distortion of the piece 4 to be welded of about 30-35%, thanks to the reduction of the otherwise excessive heat input provided by the arc 6.

It is clear that several variants of the power modulator 1 described hereinabove are possible to the man skilled in the art, without departing from the novelty scopes of the inventive idea, as well as it is clear that in the practical embodiment of the invention the various components described above may be replaced with technically equivalent ones.

In fact, the power modulator 1 according to the invention has been described so far in a variant having at least two advantages:

- allowing the construction thereof without particular investments in specific equipment by substantially providing only components that are already available on the market;

- allowing the installation thereof upstream of a welder 2 without interfering at all with its construction and functionality.

However, other versions are also possible, both simpler and more sophisticated. What in fact is essential for the purposes of the invention is that the power modulator 1 is capable of activating and deactivating, upon operator command, the power modulating function by powering and unpowering the primary circuit of the welder 2, and that therefore includes, for this purpose, activation and deactivation means 8.4 actuable by the same operator.

Very advantageously such activation/deactivation means 8.4 are remote controls capable of acting remotely on the power modulator 1 when the operator is at his workstation, even away from the welder 2, and are therefore adapted to communicate with the corresponding receiver means of the power modulator 1 that are responsible for such activation/deactivation.

Only preferably, that remote control takes place via radio, being also possible via cables preferably constrained to the power cable of the electrode 4.

Only preferably, for greater convenience, the power modulator 1 also has means 8.3 adapted to the activation of the welder 2. Again only preferably the luminous LEDs 1.3 and 1.4 are provided for visual control.

Moreover, instead of separately selecting the powering and unpowering intervals of the welder 2, by acting respectively on the two potentiometers 1.5 and 1.6, it is possible to provide a single potentiometer 1.5-1.6 to adjust the reduced power to be delivered to the arc, which in turn automatically adjusts, as a consequence, the ratio between the durations of said time intervals at high power TAP and low power TBP.

Finally, instead of setting the reduced power to a fixed value by said two potentiometers 1.5 and 1.6 or single potentiometer 1.5-1.6 arranged on the power modulator 1 , it is possible to provide the adjustment thereof through remote control by the operator, so that he may not interrupt the welding operation if he set a value not suitable for the reduced power.

Finally it may also be envisaged that the power modulator 1 object of the present invention is incorporated within the same welder 2, i.e. it does not consist of an external device to be connected upstream of the same, but its components find allocation within the structure of the welder 2.