Welding machine for longitudinal metal objects, in particular metal blanks

Abstract

The invention relates to a welding machine of the flash welding type, intended to weld together the tail of a first longitudinal metal product and the head of a second longitudinal metal product along an advancing direction. The machine comprises:-a carriage adapted to slide along an advancing direction; the first structure is provided with a first clamping device; the second structure is supported by the bracket in a sliding manner and is provided with a second clamping device; and a power pack, which can be supplied with a power supply voltage and is provided with conductors, connected to the first and second gripping means, respectively. The power pack includes: at least one inverter; at least one transformer; at least one rectifier; and a control unit. The inverter is a single-phase or multi-phase inverter having a variable frequency. The control unit is programmed to operate the inverter at a frequency greater than 700 Hz. The transformer is dimensioned to deliver a predetermined rated power Pn at a predetermined rated supply frequency fn.

Description

Technical Field

[0001] The invention relates to a welding machine for longitudinal metal objects.

[0002] In particular, such welding machines are of the flash type and are suitable for processing longitudinal metal objects, such as metal billets, bars or blanks.

[0003] In operation, the welding machine is usually arranged upstream of the rolling mill and welds the head and tail of two continuous longitudinal products together along the conveying line, especially the rolling line. Background Art

[0004] Normally, in a rolling mill, individual metal products are welded together directly from a casting plant or a storage warehouse so that they can be rolled seamlessly.

[0005] Such metal products are usually semi-finished iron products such as metal billets, bars or billets.

[0006] Welding is performed by joining the tail of one product to the head of the next product.

[0007] Typically, welding is done according to a technique known as flash welding, ie by means of an electrical discharge generated by an electric power supply connected to the products to be welded.

[0008] In more detail, a controlled electric current is passed through the two faces of the metal product that must be welded together. This passage of the current generates energy that brings the two faces to melting temperature (the "flash" step). When the two faces are completely melted, the current is interrupted and the two surfaces are pressed together, causing them to fuse together until they are completely bonded. (the "upsetting" step).

[0009] Therefore, during welding, the products need to be firmly clamped together. For this purpose, the welding machine is provided with a clamping device suitable for holding the products in place during welding. Typically, the clamping device also acts as a conductor for the electric welding current.

[0010] Typically, such a clamping device usually includes a clamp that directly contacts the product to be welded. When welding is performed, the clamps that hold the head and tail of the product to be welded are brought close to each other by a hydraulic cylinder or an electric cylinder (called an upset cylinder). This operation requires combining the ends to be welded, eliminating any inclusions and bubbles, compensating for material loss due to melting, and allowing actual bonding between the two parts to be welded.

[0011] A known type of flash welding machine comprises a carriage movable along a track positioned on a section of a conveyor line for longitudinal metal objects. The machine also comprises two independent structures, both mounted on the carriage and each equipped with a pair of clamps. Such structures are substantially parallel to each other and inclined at an angle of about 45° relative to a plane defined by the machine carriage.

[0012] A transformer is arranged above the inclined upper surface of the two structures, the transformer being provided with conductors connected to the two structures to supply current to the tail and the head of the two products to be welded by means of corresponding clamps. As a result, access to the internal parts of the machine, maintenance and disassembly and removal of heavy parts are difficult, since these operations are performed by operators entering inside the machine itself.

[0013] Due to the nature of the operation of welding machines, the above mentioned problems are exacerbated by the fact that welding machines are in a particularly harsh environment due to the very high temperatures of the metal billets being processed, the high proportion of dust generated by the metal billets, the splashing of molten material generated by the welding process and the cooling water used to protect the machine parts being discharged onto the structure.

[0014] Furthermore, the space usually provided for the welding machine proves to be very cramped.

[0015] In this context, possible technical solutions cannot ignore the following requirements:

[0016] - The most sensitive parts must be as far away as possible from the axis where welding is performed;

[0017] - Greater accessibility must be created for conventional lifting equipment to operate inside the machine itself, thus facilitating both general and specific machine maintenance operations;

[0018] The overall size of the welding machine must be reduced or at least not increased, so that the welding machine can be used more widely in space.

[0019] In this context, it must be taken into account that the energy required for the welding process during the melting step is considerable. Therefore, the size and weight characteristics of the transformer group required to deliver this energy are as follows:

[0020] - Occupies a considerable amount of space, which limits the operator's access to the machine and the necessary passage for maintenance operations;

[0021] - No matter where it is installed, a dedicated structure is required for its support;

[0022] - In the event of a malfunction, disassembly and assembly operations prove to be complicated and time-consuming.

[0023] Another consideration is related to the fact that the transformer bank needs to be positioned as close as possible to the welding fixture. This aspect is determined by the following reasons:

[0024] - The welding machine is a mobile device, so it moves several meters in the conveying direction of the longitudinal metal product;

[0025] - This is inevitable, because the distance between the transformer group and the welding fixture increases, the electrical impedance increases, thus affecting the passage of the current required for welding.

[0026] The problem of machine accessibility for the operator is addressed in the international application WO2021 / 156738A1. The proposed solution is to move the transformer from the top of the clamping structure to a side position defined by a cantilevered bracket attachment extending outside the main structure of the bracket itself, on which the clamping structure is housed and which is defined by two beams parallel to the sliding direction of the longitudinal metal product to be welded. This arrangement of the transformer allows free access to the top of the clamping structure. This makes it easy to maintain the welding machine (especially the clamping structure) and to operate it with the help of auxiliary equipment for moving heavy objects, such as cranes and overhead cranes.

[0027] However, the solution described in WO 2021 / 156738 A1 has the disadvantage of increasing the plan dimensions of the welding machine and thus its overall dimensions.

[0028] Therefore, there is a need to improve the accessibility of welding machines without at the same time significantly increasing the size which has not been met to date. Summary of the invention

[0029] The main object of the present invention is therefore to eliminate all or part of the above-mentioned drawbacks of the prior art by providing a welding machine for longitudinal metal objects which exhibits increased accessibility without requiring a significant increase in size.

[0030] Another object of the present invention is to provide a welding machine for longitudinal metal objects which maintains adequate operating functionality.

[0031] Another object of the invention is to provide a welding device for longitudinal metal objects which is easy to manage and inexpensive.

[0032] Another object of the invention is to provide a welding machine for longitudinal metal objects which does not have significantly higher construction costs than similar known machines. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The technical features of the present invention according to the aforementioned objects will be clearly found in the content of the following claims, and its advantages will become more apparent from the following detailed description given with reference to the accompanying drawings, which show one or more embodiments given only by way of non-limiting examples, in which:

[0034] - Figure 1 is a top perspective view of a welding machine for longitudinal metal objects according to a preferred embodiment of the present invention;

[0035] - Figure 2 yes Figure 1 The welding machine is shown in an orthogonal front view according to the arrow II shown here;

[0036] - Figure 3 yes Figure 1 Orthogonal top view of the welding machine;

[0037] - Figure 4 yes Figure 1 A perspective view of a part of a welding machine for longitudinal metal objects, the part being associated with a moving carriage of the machine;

[0038] - Figure 5 yes Figure 1 A perspective view of a part of a welding machine for longitudinal metal objects, the part being associated with the main body of the machine;

[0039] - Figure 6 A simplified wiring diagram of a power pack of a welding machine according to a preferred embodiment of the present invention is shown, the power pack being configured with an inverter on a machine bracket;

[0040] - Figure 7 A simplified wiring diagram of a power pack of a welding machine according to a preferred embodiment of the present invention is shown, wherein the power pack is configured with an inverter arranged outside a bracket;

[0041] - Figure 8 A simplified wiring diagram of a power pack of a welding machine according to a preferred embodiment of the present invention is shown, the power pack being configured with an inverter on a machine bracket and a rectifier integrated into a transformer;

[0042] - Fig. 9 A simplified wiring diagram of a power pack of a welding machine according to a preferred embodiment of the present invention is shown, wherein the power pack is configured with two transformers connected in parallel;

[0043] - Fig.10 is a simplified schematic diagram of a transformer; and

[0044] - Fig.11 yes Figure 4 A perspective view of a variation of the center bracket. DETAILED DESCRIPTION

[0045] In the accompanying drawings, a welding machine for longitudinal metal objects according to the invention is indicated as a whole by the reference numeral 1 .

[0046] According to a general embodiment of the invention, the welding machine 1 is of the flash welding type and is suitable for processing longitudinal metal objects, such as metal billets, bars or billets.

[0047] The welding machine 1 is intended to be installed upstream of a rolling mill on a conveyance line of longitudinal metal products moving in an advancement direction X, in particular a rolling line.

[0048] Operationally, the welding machine 1 is suitable for welding the tail T of a first longitudinal metal product M1 continuously moving along said advancement direction X to the head H of a second longitudinal metal product M2.

[0049] The welding machine 1 comprises a carriage 10 which serves as a movable supporting base for the entire welding machine 1 and is adapted to slide along the advancement direction X to follow the movement of the longitudinal object.

[0050] According to a preferred embodiment of the present invention, as shown in the accompanying drawings, in particular Figure 4 As shown in FIG. 1 , the carriage 10 comprises two beams 11, 12, which are provided with wheels 17, which are suitable for enabling the carriage 10 to move parallel to the advancing direction X along the tracks B1, B2 ( Figure 4 Only a portion of the slide is shown.

[0051] In more detail, the two beams 11 , 12 are connected to each other in transverse direction by at least two connecting beams 13 and 14 so as to form a frame on which the rest of the welding machine 1 rests.

[0052] The carriage 10 is provided with a motor arrangement 16, kinematically connected to wheels 17. In particular, the motor arrangement comprises an electric gear motor with a rack-and-pinion type coupling on two tracks B1 and B2.

[0053] according to Fig.11 In the alternative embodiment shown, the carriage 10 may comprise an appendage 15 extending outside the frame in a cantilevered manner transversely to the direction of advancement X, for housing one or more components of a welding machine.

[0054] According to the aforementioned general embodiment of the invention, the welding machine 1 comprises a first structure 20 supported by said carriage 10 and defining in a portion thereof a first passage seat 20a for longitudinal metal products advancing along said transport line.

[0055] The welding machine 1 also comprises a second structure 30 slidably supported by said carriage 10 so as to slide parallel to the direction of advancement X relative to the first structure 20 and the carriage 10 itself.

[0056] This second structure 30 defines, in a portion thereof, a second passage seat 30a for longitudinal metal products advancing along said transport line. This second passage seat 30a is aligned along said direction of advancement X with said first passage seat 20a.

[0057] In more detail, Figure 5 As shown, the two structures 20 and 30 are connected to each other by two support beams 110 and 120 parallel to the advancement direction X. In turn, the two support beams 110 and 120 are fixedly anchored to the two beams 11, 12 of the carriage 10. The first structure 20 is fixedly anchored to the two support beams 110, 120, while the second structure 30 is slidably connected to the two support beams 110, 120 by means of linear guides 111, 121 to slide relative to the first structure 20 parallel to the advancement direction X. The two structures 20 and 30 are connected by means of one or more actuators 131, 132 (for example hydraulic cylinders), which are suitable for exerting a relative movement parallel to the advancement axis X between the two structures.

[0058] Especially if Figure 3 As shown, two structures 20 and 30 are positioned relative to each other with a gap 2 between them.

[0059] On the welding machine 1 , the inlet E and the outlet U of the longitudinal object can be marked. According to the embodiment shown in the figures, the first structure 20 (fixed) is arranged close to the outlet U, while the second structure 30 (movable) is arranged close to the inlet E.

[0060] The welding machine 1 also includes:

[0061] - first clamping means 21, 22, arranged on the first structure 20 at the first channel seat 20a, for clamping the tail T of the first metal product M1 or the head H of the second metal product M2;

[0062] - Second clamping means 31 , 32 arranged on the second structure 30 at the second channel seat 30a for clamping the head H of the second metal product M2 or the tail T of the first metal product M1 .

[0063] In particular, the first clamping device comprises two clamps 21, 22, which are opposite to each other relative to the first channel seat 20a and between which the longitudinal metal object slides. Figure 5As shown, a first clamp 21 (lower clamp) is arranged in the lower part of the first channel seat 20a, and a second clamp 22 (upper clamp) is arranged in the upper part of the first channel seat 20a. The two clamps 21 and 22 are movable relative to each other so as to move closer and farther apart, thereby applying a reversible clamping action to the longitudinal object. Preferably, the lower clamp 21 is fixed and the upper clamp 22 is movable along an axis Z1 intersecting the advancement axis X. For this purpose, the machine 1 is provided with a first linear actuator 26 (for example, a hydraulic, pneumatic or electric cylinder), which is supported by the first structure 20 and is suitable for moving the upper clamp 22 along said axis Z1.

[0064] Similarly, the second clamping device also includes two clamps 31, 32, which are opposite to each other relative to the second channel seat 30a, and the longitudinal metal object slides between the two clamps. Figure 5 As shown, a first clamp 31 (lower clamp) is arranged in the lower part of the second channel seat 30a, and a second clamp 32 (upper clamp) is arranged in the upper part of the second channel seat 30a. The two clamps 31 and 32 are movable relative to each other so as to move closer and farther apart, thereby applying a reversible clamping action to the longitudinal object. Preferably, the lower clamp 31 is fixed, while the upper clamp 32 is movable along an axis Z2 intersecting the advancement axis X. For this purpose, the machine 1 is provided with a second linear actuator 36 (for example, a hydraulic, pneumatic or electric cylinder), which is supported by the second structure 30 and is suitable for moving the upper clamp 32 along said axis Z2.

[0065] In particular, the first structure 20 and the second structure 30 each extend longitudinally transversely to the advancement direction X between two respective longitudinally opposite support portions 23 , 24 and 33 , 34 , where each structure 20 , 30 is connected to the carriage 10 by means of the aforementioned support beams 110 and 120 .

[0066] Preferably, each structure further comprises a frame 25 , 35 arranged between the respective support portions 23 , 24 and 33 , 34 and configured to house the actuator 26 , 36 of the respective clamping device 21 , 22 and 31 , 32 .

[0067] Advantageously, the welding machine may further comprise a first guide device 27 and a second guide device 37, which are arranged at the exit and the entrance of the welding machine, respectively, and are adapted to support and guide the longitudinal metal object near the first and second channel seats through the welding machine 1. In particular, the first guide device 27 is supported by the first structure 20, and the second guide device 37 is supported by the second structure 30.

[0068] In particular, each guiding device 27, 37 defines an introducing and guiding channel 28’, 38’, and at least one sliding roller 28”, 38” is located at the bottom of the channel.

[0069] Preferably, both guiding devices are movable in height to change the height position of the longitudinal metal object supported by them passing through the welding machine 1. For this purpose, each guiding device 27, 37 is provided with a corresponding moving device 29, 39, which particularly includes a supporting guide 29’, 39’ and an actuator 29”, 39” (for example, a pneumatic cylinder or a hydraulic cylinder).

[0070] According to the foregoing general embodiment of the present invention, the welding machine 1 further includes a power supply unit 40, which can be supplied with a power supply voltage and is provided with conductors 210; 221, 222, respectively connected to the first clamping devices 21, 22 and the second clamping devices 31, 32 for supplying current to the tails and heads of the two longitudinal objects.

[0071] Advantageously, the conductors can be rigid or flexible, depending on whether they need to ensure an electrical connection with a fixed or variable distance.

[0072] The power supply unit 40 includes:

[0073] - At least one inverter 41, which can be mounted on the bracket 10 (see Figure 6 ) or outside the bracket 10 (see Figure 7 );

[0074] - At least one transformer 42, which is powered by the inverter 41 and is placed on the bracket 10;

[0075] - At least one rectifier 43, which electrically connects the transformer 42 to the first clamping devices 21, 22 and the second clamping devices 31, 32, and is placed on the bracket; and

[0076] - A control unit 50.

[0077] Preferably, as shown in Figure 8 and Fig. 9 , the rectifier 43 is integrated into the transformer 42.

[0078] The operation of the welding machine 1 according to the present invention is described below.

[0079] Two longitudinal metal objects M1 and M2 (in particular, two metal blanks) slide sequentially along the forward axis X and pass through the welding machine 1 at two channel seats 20a and 30a.

[0080] In particular, the two metal blanks M1 and M2 are slidably supported by two guide devices 27 and 37 (preferably, one arranged at the entrance of the machine and one arranged at the exit of the machine), which are in a raised position during this step of the welding process to avoid friction between the metal blanks and the lower clamps 21 and 31 of the first and second clamping devices during their transportation.

[0081] The two metal billets continue to move until the tail T of the first metal billet M1 and the head H of the second metal billet M2 approach the center of the gap 2 existing between the two structures 20 and 30. The head and tail of the metal billets are now in contact with each other.

[0082] At this time, the upper clamp 22 of the first clamping device (supported by the first (fixed) structure 20) and the upper clamp 32 of the second clamping device (supported by the second movable structure 30) slide downward along the axes Z1 and Z2 respectively by means of actuation of the corresponding linear actuators (hydraulic cylinders 26 and 36) until they clamp the two metal billets M1 and M2 against the corresponding two lower clamps 21 and 31.

[0083] Preferably, simultaneously with the movement of the upper clamp, by operation of the respective actuators 29" and 39", the guides 27 and 37 are brought to a lowered position so that they do not interfere with the clamping of the metal blank between the upper and lower clamps.

[0084] Since the welding process is carried out with the entire machine in motion, in this step the carriage 10 supporting the entire machine is moved according to a linear motion and parallel to the advancing axis X of the metal billet.

[0085] The flashing step can now begin.

[0086] During the flashing step, the current is allowed to flow between the two faces of the metal blank by means of said at least one transformer 42, which is physically connected to all four clamps 21, 22 and 31, 32 by means of secondary return conductors 210, 221, 222. The aforementioned secondary conductors are designed to separate the positive pole of the circuit on the two clamps (upper and lower) of one structure and the negative pole in the corresponding clamp belonging to the other structure.

[0087] The next step is the forging step.

[0088] When a preset melting level of both metal billet surfaces is reached, the current is stopped. The movable structure (second structure 30 ) supported by two linear guides positioned parallel to the axis X is fed by means of two hydraulic cylinders 131 and 132 fixed to the fixed structure (first structure 20 ).

[0089] Preferably, if Figure 2As shown, the axial centers of the two hydraulic cylinders 131 and 132 are aligned on the axis Y, which intersects the axis X and is particularly located at a position approximately 65° from the perpendicular to the axis X. The two hydraulic cylinders are equidistant from the axis X. The movable structure 30 is parallel to the axis X and the movement in the direction of the fixed structure 20 generates pressure between the two faces of the metal blank, ensuring their bonding.

[0090] When the upset forging is completed, the two upper clamps 22 and 32 return to their initial positions. At the same time, the two guiding devices 27 and 37 rise to support the metal blank that was previously in contact with the two lower clamps 21 and 31. The moving device 16 of the carriage 10 reverses the traveling direction and returns the welding machine to the preset starting position, waiting for a new welding cycle. During the repositioning of the carriage to its starting position, the hydraulic cylinders 131 and 132 simultaneously push the movable structure 30 back to its initial position away from the fixed structure 20.

[0091] According to a first aspect of the invention, the inverter 41 is a single-phase or polyphase inverter with a variable frequency, and the control unit 50 is programmed to operate the inverter 41 at a frequency higher than 700 Hz.

[0092] The at least one transformer 42 is dimensioned to deliver a predetermined rated power Pn at a predetermined rated supply frequency fn.

[0093] According to another aspect of the invention, an operating power Pex to be generated during welding has been defined, and two alternative solutions are possible with respect to the dimensional characteristics of the transformer 42.

[0094] According to the first alternative, the predetermined rated power Pn of the transformer 42 is lower than the predetermined operating power Pex, and the rated supply frequency fn is lower than 700 Hz. The at least one transformer 42 is dimensioned to deliver an actual power Pe equal to or greater than the predetermined operating power Pex at a frequency higher than 700 Hz.

[0095] According to the second alternative, the predetermined rated power Pn of the transformer 42 is at least equal to the predetermined operating power Pex, and the rated supply frequency fn is higher than 700 Hz. The at least one transformer 42 is dimensioned to deliver an actual power Pe greater than the predetermined operating power Pex at a frequency higher than 700 Hz.

[0096] In both cases, compared to the systems known so far suitable for flash welding longitudinal metal products, using a frequency above 700 Hz allows meeting the energy requirements necessary for welding with a transformer 42 of small size and low weight, while the operating electric power Pex to be delivered for welding is the same.

[0097] According to the invention, the operating power Pex has been defined, so that the welding machine 1 can be operated using a transformer of small size and low weight. In particular, the small size of the transformer reduces the space occupied by such a transformer and thus the accessibility of free space is greater to ensure that the operator can access the welding machine.

[0098] According to the invention, the welding machine 1 thus exhibits increased accessibility, but without requiring a significant increase in size.

[0099] The welding machine for longitudinal metal objects according to the invention also does not have significantly higher construction costs than similar known machines.

[0100] According to the aforementioned first alternative, the transformer 42 (which is sized to deliver a rated power Pn less than Pex at a rated frequency fn less than 700 Hz) is forced to deliver a power equal to or greater than Pex by operating at a frequency higher than the rated frequency fn. Thus, the power demand for welding is met by using a smaller transformer. However, this mode has the disadvantage of increasing transformer losses and is therefore inefficient.

[0101] According to the aforementioned second alternative, the transformer 42 (which is sized to deliver a rated power Pn at least equal to Pex at a rated frequency fn greater than 700 Hz) can be operated at the rated frequency fn by delivering the required power, or forced to deliver a power greater than Pex by operating at a frequency greater than the rated frequency fn. Thus, the power demand for welding is met by using a smaller transformer. When this mode involves operating the transformer at the rated frequency, it also has the advantage of minimizing transformer losses and is therefore more efficient.

[0102] In more detail, refer to Fig.10 , the transformer consists of a ring (core) made of ferromagnetic material (usually thin silicon steel sheets) around which are wound two windings: a "primary" consisting of n1 turns and a "secondary" consisting of n2 turns. It is therefore a double dipole. If the primary is supplied by a voltage generator v1 ("primary voltage") so that a current i1 ("primary current") flows through it, and the secondary is open circuited so that the current i2 ("secondary current") is zero, a magnetic induction field will be established in the ring (corresponding to Fig.10The "primary" flux φ is shown. The induced field lines also connect to the secondary winding, so if i1 varies with time, according to Faraday's law (or the law of electromagnetic induction), a voltage v2 (the "secondary voltage") will be induced at the secondary terminals. If the secondary is connected to a load (such as a resistor), current will circulate through it. Therefore, with the help of a transformer, power can be transferred from the primary winding to the secondary winding without any electrical connection between the two windings; instead, the power transfer occurs through the magnetic field, which is mainly present in the iron core of the transformer and is able to exchange energy with both loops.

[0103] If the magnetic flux in the core is sinusoidal, for the two windings, the relationship between the effective voltage E, the supply frequency f, the number of turns N, the cross-sectional area a of the core and the peak magnetic flux density B is given by the following FEM equation:

[0104]

[0105] Assuming a constant flux density B, for the same effective voltage E, higher frequencies significantly reduce the core cross-section and the number of winding turns.

[0106] Similarly, assuming constant flux density B, core cross-section, and number of winding turns, higher frequencies significantly increase the effective voltage E

[0107] Therefore, at a given flux density, the fem of a transformer increases with frequency. Operating at higher frequencies, the transformer can be physically more compact because a given core can transfer more power without saturating, and fewer turns are required to obtain the same impedance.

[0108] According to the present invention, the problem of ensuring adequate proximity to the welding machine is substantially solved by reducing the size and weight of the transformer, rather than (or not necessarily) by changing the placement of the transformer itself on the welding machine.

[0109] Preferably, the control unit 50 is programmed to operate said inverter 41 at a frequency between 700 and 2000 Hz.

[0110] More preferably, the control unit 50 is programmed so as to cause said inverter 41 to operate at a frequency between 900 and 1100 Hz, even more frequently at a frequency equal to approximately 1000 Hz.

[0111] By utilizing the above mentioned frequencies, a very small size and low weight of the transformer is achieved compared to known systems applied to metal billet welding.

[0112] The small size of the power pack (one or more transformers) allows its placement inside the welding machine without restrictions on the occupied space. This facilitates freedom in positioning the transformer, increasing accessibility and ease of machine maintenance.

[0113] Since the size and weight of the transformer are no longer limiting factors, the location of the transformer can be chosen to be as far away as possible from the axis where welding is performed. This choice can be made by simultaneously creating space for greater accessibility for traditional lifting devices operated inside the machine itself to facilitate both ordinary and special machine maintenance operations.

[0114] All of this can be accomplished without increasing the overall size of the welding machine.

[0115] Advantageously, according to the invention, the power pack (one or more transformers) can also be arranged inside the machine, as close as possible to the welding fixtures, in order to minimize the length of the conductors connecting them to the fixtures, thereby reducing the electrical impedance generated by the conductors.

[0116] Advantageously, the welding machine is powered by a power distribution network or a battery system.

[0117] The power pack 40 may include a single transformer 42 (eg Figure 6 , Figure 7 and Figure 8 ) or multiple transformers (42a, ... 42n) connected in parallel (as shown) Fig. 9 shown).

[0118] Each transformer 42a, ... 42n is powered by a dedicated variable frequency inverter 41a ... 41n and is preferably electrically connected to the clamping devices 21, 22 and 31, 32 by means of a dedicated rectifier 43a ... 43n.

[0119] Each of the transformers is dimensioned to deliver a predetermined rated power Pna, ... Pnn at a predetermined rated supply frequency fn.

[0120] The transformer is sized according to two possible alternatives, similar to the case of a single transformer.

[0121] According to a first alternative, the sum of the rated powers Pna, ... Pnn of the plurality of transformers is less than the predetermined operating power Pex to be generated during welding, and the predetermined rated supply frequency fn is less than 700 Hz. The plurality of transformers are dimensioned to deliver a real power Pe, as a whole, equal to or greater than the predetermined operating power Pex at a frequency higher than 700 Hz.

[0122] According to a second alternative, the sum of the rated powers Pna, ... Pnn of the plurality of transformers is at least equal to the predetermined operating power Pex to be generated during welding, and the predetermined rated supply frequency fn is greater than 700 Hz. The plurality of transformers are dimensioned to deliver as a whole an actual power Pe greater than the predetermined operating power Pex at a frequency greater than the rated supply frequency fn.

[0123] Preferably, said predetermined operating power Pex has a value between 200 and 2000 kVA.

[0124] Advantageously, each of the one or more transformers 42, 42a, ... 42n weighs between 150 and 700 kg, depending on the power rating.

[0125] Advantageously, each of the one or more transformers 42, 42a, ... 42n has, depending on the rated power:

[0126] - height between 450 and 650 mm;

[0127] - a length between 400 and 450 mm; and

[0128] - Depth between 300 and 350 mm.

[0129] Operationally, during the welding of metal billets, it may be necessary to perform a voltage boost in the first step of welding to strike the arc and generate plasma. Once the arc is struck, the voltage must be reduced and reach a steady-state value, which must be maintained during the second step of welding until the weld is complete.

[0130] Preferably, the power pack 40 may include a system adapted to provide a voltage boost during welding.

[0131] In more detail, such a system can be obtained by means of a device in the primary circuit of the transformer adapted to select a preset number of turns, called the effective number of turns. Specifically, such a device must reduce the effective number of turns of the primary circuit in order to perform a voltage boost at the output of the transformer.

[0132] In fact, it is well known that the ratio of the secondary circuit voltage (Vs) to the primary circuit voltage (Vp) is given by the turns ratio of the secondary winding (ns) to the primary winding (Np):

[0133]

[0134] Therefore, in order to increase the voltage, it is necessary that Ns>Np occurs. This occurs when the device selects a smaller number of effective turns in the primary.

[0135] Alternatively, a system suitable for providing a voltage boost can be implemented with the aid of a circuit element capable of varying the voltage of the primary circuit of the transformer. In particular, such an element (boost converter) is capable of increasing the voltage of the inverter upstream of the transformer, so that the voltage on the primary Vp increases. By keeping the ratio of the number of turns constant, the increase in the voltage on the primary in turn causes an increase in the voltage on the secondary.

[0136] The system provides a voltage boost of 1 to 1.8 times the rated welding voltage.

[0137] The system provides a voltage boost preferably equal to 1.4 times the rated welding voltage value.

[0138] Preferably, during the welding step, the power factor on the grid will have a value between 0.92 and 1.

[0139] As described above, according to the present invention, the problem of ensuring and adequate proximity to the welding machine is substantially solved by reducing the size and weight of the transformer, rather than (or not necessarily) by changing the arrangement of the transformer itself on the welding machine. In other words, due to the fact that one or more transformers have very small size and very light weight, they can be arranged in the welding machine without substantial restrictions.

[0140] According to a preferred embodiment shown in the drawings, the at least one transformer 42 or the plurality of transformers 42a, ... 42n can be arranged behind the frames 25, 35 of the two structures 20, 30 relative to the two channel seats 20a, 30a. Preferably, the at least one transformer 42 or the plurality of transformers 42a, ... 42n are arranged on the support parts 24, 34 of the structures 20, 30. In particular, the at least one transformer 42 or the plurality of transformers 42a, ... 42n are arranged on the support part 24 of the fixed structure 20.

[0141] According to an alternative embodiment not shown in the drawings, said at least one transformer 42 or said plurality of transformers 42a, ... 42n are arranged on top of the frame 25, 35 of said first structure 20 or said second structure 30. Preferably, they are arranged on top of the frame 25 of the fixed structure 20.

[0142] According to an alternative embodiment not shown in the drawings, said at least one transformer 42 or said plurality of transformers 42a, ... 42n can be arranged in front of the frames 25, 35 of said two structures 20, 30 relative to said two channel seats 20a, 30a. Preferably, said at least one transformer 42 or said plurality of transformers 42a, ... 42n are arranged on the support parts 23, 33 of said structures 20, 30. In particular, said at least one transformer 42 or said plurality of transformers 42a, ... 42n are arranged on the support part 23 of the fixed structure 20.

[0143] According to another optional embodiment not shown in the accompanying drawings, the at least one transformer 42 or the multiple transformers 42a,...42n can be arranged on the outside of the frame 25, 35 of one of the two structures 20, 30, wherein the outside of the structure refers to the wall of the frame of the structure opposite to the wall facing the gap 2 between the two structures 20, 30.

[0144] As mentioned above, the carriage 10 comprises in particular a framework delimited transversely to the direction of advancement X by two beams 11 , 12 .

[0145] Preferably, the frame is dimensioned to support the two structures 20 and 30 within its plan dimensions.

[0146] according to Fig.11 In the alternative embodiment shown, the carriage may include an attachment 15 extending outside the framework in a cantilevered manner transversely to the direction of advancement X, preferably behind the two frames 25, 35. The at least one transformer 42 or the plurality of transformers 42a, ... 42n may be arranged on the attachment 15.

[0147] Advantageously, due to the small size and weight of the transformer, the size of the accessory 15 can also be minimized.

[0148] The present invention provides several advantages, some of which have already been described.

[0149] The welding machine 1 for longitudinal metal objects according to the invention exhibits increased accessibility without requiring a significant increase in size.

[0150] The welding machine 1 for longitudinal metal objects according to the invention retains adequate operating functionality.

[0151] The welding machine 1 for longitudinal metal objects according to the invention is easy and convenient to manage.

[0152] The welding machine 1 for longitudinal metal objects according to the invention does not have significantly higher construction costs than similar known machines.

[0153] Therefore, the present invention thus designed achieves the preset objectives.

[0154] Obviously, in its actual implementation, it may also adopt shapes and configurations other than those disclosed above without departing from the scope of protection.

[0155] Moreover, all the details may be replaced by technically equivalent elements and any dimensions, shapes and materials may be used as desired.

Claims

1. A welding machine (1) of the flash welding type, intended to be installed on a conveying line of longitudinal metal products moving along an advancing direction (X), for welding the tail of a first longitudinal metal product to the head of a second longitudinal metal product along said advancing direction (X), said welding machine (1) comprising: - a carriage (10) adapted to slide along said direction of advancement (X), - a first structure (20) supported by said carriage (10) and defining in a portion thereof a first passage seat for longitudinal metal products advancing along said transport line; - a first clamping device (21, 22) arranged on the first structure (20) at the first channel seat for clamping the tail of the first metal product or the head of the second metal product; - a second structure (30) slidably supported by the carriage (10), intended to slide relative to the first structure (20) and the carriage (10) itself parallel to the direction of advancement (X), and defining in a portion thereof a second passage seat for longitudinal metal products advancing along the transport line, the second passage seat being aligned with the first passage seat along the direction of advancement (X); - a second clamping device (31, 32) arranged on the second structure (30) at the second channel seat for clamping the head of the second metal product or the tail of the first metal product; a power pack (40) capable of being supplied with a power supply voltage and provided with conductors (210; 121, 122), connected to the first clamping means (21, 22) and the second clamping means (31, 32), respectively, for supplying current to the tail and the head; Wherein, the power supply group (40) comprises: - at least one inverter (41) which can be mounted on the bracket or outside the bracket; - at least one transformer (42) supplied with power by means of said inverter (41) and placed on said support; - at least one rectifier (43) electrically connecting said transformer (42) to said first and second holding means (21, 22) and located on said bracket; - a control unit (50); Characterized in that the inverter (41) is a single-phase or multi-phase inverter with variable frequency, the control unit (50) is programmed to operate the inverter (41) at a frequency greater than 700 Hz, and the at least one transformer is dimensioned to deliver a predetermined rated power Pn at a predetermined rated supply frequency fn, where the operating power Pex to be generated during welding is defined, alternatively: - said predetermined rated power Pn of the transformer is less than said predetermined operating power Pex, and said rated supply frequency fn is less than 700 Hz, said at least one transformer (42) being dimensioned to deliver an effective power Pe equal to or greater than said predetermined operating power Pex at a frequency greater than 700 Hz; or - the predetermined rated power Pn of the transformer is at least equal to the predetermined operating power Pex, and the rated supply frequency fn is greater than 700 Hz, and the at least one transformer (42) is dimensioned to deliver an effective power Pe greater than the predetermined operating power Pex at a frequency greater than the rated supply frequency fn.

2. The welding machine (1) according to claim 1, wherein: The control unit (50) is programmed to operate the inverter (41) at a frequency between 700 and 2000 Hz.

3. The welding machine (1) according to claim 1 or 2, wherein: The control unit (50) is programmed to operate the inverter (41) at a frequency comprised between 900 and 1100 Hz and preferably equal to approximately 1000 Hz.

4. The welding machine (1) according to any one of the preceding claims, wherein: The power pack (40) comprises a plurality of transformers (42a, 42b, ... 42n) connected in parallel to each other, each of the transformers being sized to deliver a predetermined rated power Pna, Pnb ... Pnn at the predetermined rated supply frequency fn, and wherein the sum of the rated powers Pna, Pnb ... Pnn of the plurality of transformers is alternatively: - if said predetermined nominal supply frequency fn is less than 700 Hz, less than said predetermined operating power Pex to be generated during welding, said plurality of transformers are dimensioned to deliver as a whole an effective power Pe equal to or greater than said predetermined operating power Pex at a frequency greater than 700 Hz, or - if the predetermined rated supply frequency fn is greater than 700 Hz, at least equal to the predetermined operating power Pex to be generated during welding, the plurality of transformers are sized to deliver as a whole an effective power Pe greater than the predetermined operating power Pex at a frequency greater than the rated supply frequency fn.

5. The welding machine (1) according to any one of the preceding claims, wherein: Said predetermined operating power Pex has a value comprised between 200 and 2000 kVA.

6. A welding machine (1) according to any one of the preceding claims, wherein: Each of the one or more transformers (42; 42a, 42b, ... 42n) has a weight comprised between 150 and 700 kg.

7. A welding machine (1) according to any one of the preceding claims, wherein: Each of the one or more transformers (42; 42a, 42b, ... 42n) has: - a height h comprised between 450 and 650 mm; - a length L comprised between 400 and 450 mm; and - A depth p comprised between 300 and 350 mm.

8. The welding machine (1) according to any one of the preceding claims, wherein: The power pack (40) includes a system adapted to provide a voltage boost.

9. The welding machine (1) according to any one of the preceding claims, wherein: The first structure (20) and the second structure (30) each extend longitudinally transversely relative to the advancement direction (X) between two longitudinally opposite support parts (23, 24; 33, 34), at which the structures (20, 30) are connected to the bracket (10), and wherein, between the corresponding support parts, each structure includes a frame (25, 35) configured to accommodate an actuator of a corresponding clamping device (21, 22; 31, 32).

10. The welding machine (1) according to claim 9, wherein: The at least one transformer (42) or the plurality of transformers (42a, 42b, ... 42n) are arranged on top of a frame (25, 35) of the first structure (20) or the second structure (30).

11. The welding machine (1) according to claim 9, wherein: The at least one transformer (42) or the plurality of transformers (42a, 42b, ... 42n) are arranged behind the frames (25, 35) of the two structures (20; 30) relative to the two channel seats, preferably at the supporting parts of the structures.

12. The welding machine (1) according to claim 9, wherein: The at least one transformer (42) or the plurality of transformers (42a, 42b, ... 42n) are arranged in front of the frames (25, 35) of the two structures (20; 30) relative to the two channel seats, at the support portion.

13. The welding machine (1) according to claim 9, wherein: The at least one transformer (42) or the plurality of transformers (42a, 42b, ... 42n) are arranged outside a frame (25, 35) of one of the two structures (20; 30).

14. The welding machine (1) according to claim 9, wherein: The carriage (10) comprises two beams (11, 12), the beams being provided with wheels (17) suitable for enabling the carriage (10) to slide along tracks parallel to the direction of advance (X), and the beams being transversely connected to each other to form a frame, the frame being dimensioned to support the two structures within the limits of its plane, and wherein the carriage comprises an attachment (15) extending cantilevered out of the frame transversely to the direction of advance (X) behind the frame (25, 35), and wherein the at least one transformer (42) or the plurality of transformers (42a, 42b, ... 42n) are arranged on the attachment (15).

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