Medium-frequency transformer for welding machines

Abstract

 A transformer for an electric welding machine of the type that comprises a secondary circuit composed of a center-tapped secondary winding (8) and two semiconductor diodes (18, 19) that are connected to the secondary winding so as to provide a full-wave rectifier, and further comprising two flat and parallel turns (9, 10) that form between them an interspace for accommodating the primary winding (2) of the transformer, each turn having an end that is monolithically connected to a respective laminar portion (24, 124) that is co-planar thereto and an opposite end that is connected to a common sheet-like element (29) that forms the center tap of the secondary winding and is interposed between the laminar portions (24, 124), the laminar portions having mutually opposite contact faces for diodes and the common sheet-like element being electrically insulated from the laminar portions.

Description

[0001] The present invention relates to a medium-frequency transformer for welding machines.

[0002] As is known, in current welding machines of such type the welding current is obtained by means of a circuit that is composed of a full-wave rectifier provided by means of two semiconductor diodes and by the center-tapped secondary winding of a transformer. The anodes of the diodes alternately assume a positive potential with respect to the center tap of the secondary winding, which is connected to the two cathodes across the load, so that the two diodes conduct alternately, rectifying one half-wave each.

[0003] In conventional welding machines, the connection of the secondary winding to the diodes is provided by virtue of mechanical components that are connected to each other in a very laborious manner.

[0004] This type of connection, besides being difficult to provide and therefore having a strong influence on the requirements of low commercial cost of the welding machine, is also electrically unfavorable, since it requires junctions that constitute critical points owing to the high currents that circulate in the secondary circuit in addition to causing high impedances that reduce the efficiency of the welder even significantly.

[0005] Another equally significant drawback that can be observed in known welding machines is the complexity of the cooling circuit of the secondary winding, which detracts from the efficiency and safety thereof.

[0006] The aim of the present invention is therefore to propose a transformer for welding machines that is structured so as to obviate the shortcomings of known ones, limiting the impedance by reducing the distance between the components of the secondary circuit.

[0007] Within this aim, an object of the present invention is to provide a transformer that is constructively simple, i.e., does not require complicated processes and assembly and has an effective and safe circuit for cooling the secondary winding.

[0008] This aim and this and other objects that will become better apparent hereinafter, are achieved with a transformer for an electric welding machine of the type that comprises a secondary circuit composed of a center-tapped secondary winding and two semiconductor diodes that are connected to said winding so as to provide a full-wave rectifier, characterized in that it comprises two flat and parallel turns that form between them an interspace for accommodating the primary winding of said transformer, each one of said turns having an end that is monolithically connected to a respective laminar portion that is co-planar thereto and an opposite end that is connected to a common sheet-like element that forms the center tap of said secondary winding and is interposed between said laminar portions, said laminar portions having mutually opposite contact faces for said diodes and said common sheet-like element being electrically insulated from said laminar portions.

[0009] Further features of the invention will become better apparent from the description that follows of a preferred embodiment thereof, illustrated by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a conceptual electrical diagram of a welding machine;

Figure 2 is an exploded perspective view of the transformer according to the invention;

Figure 3 is an exploded perspective view of the secondary circuit of the transformer of Figure 2;

Figure 4 is an exploded perspective view of the secondary winding of the transformer of Figures 2 and 3;

Figure 5 is a view of a component of the transformer; and

Figure 6 is a sectional view, taken along the line VI-VI of Figure 5.

[0010] With reference to Figure 1, the electrical circuit of the welding machine of which the transformer is an integral part is briefly described in order to allow better comprehension of the structure of the transformer according to the invention.

[0011] The transformer is generally designated by the reference numeral 1 and comprises a primary winding 2, composed of three partial windings 3, 4, 5 which are in series to each other and are connected to terminals 6 and 7 of an AC power supply.

[0012] As shown more clearly in Figure 2, the partial windings 3, 4, 5 each comprise a plurality of turns wound so that the windings assume a flattened shape.

[0013] The reference numeral 8 generally designates the secondary winding, which is composed of two individual turns 9 and 10 whose ends 11 and 12 are connected to a common terminal 13 that constitutes the center tap of the secondary winding.

[0014] Two respective semiconductor diodes 18 and 19 are interconnected between opposite ends 14 and 15 of the turns 9 and 10 and two connecting elements 16 and 17. The elements 16 and 17 are connected one another by an element 20, which constitutes the terminal which, together with the other terminal 13, forms the tap for supplying the welding current.

[0015] Constructively, the secondary winding 8 of the transformer 1 is as shown in Figures 2, 3 and 4.

[0016] In particular, the turn 10 is constituted by a conducting element that has a tubular rectangular cross-section and is bent in a U-shaped configuration, with two substantially parallel parts 21 and 22 connected by a curved segment 23.

[0017] The part 22 continues, on the opposite side with respect to the curved segment 23, with a laminar portion 24 that can be likened to a quadrangular plate which, with one edge, remains spaced from the end of the part 21 so as to form a slot 25 with it. The space comprised between the parts 21 and 22, on the side toward the slot 25, is closed partially by an expansion 26 that protrudes from the part 22 toward the part 21, forming with the latter a spacing slit 27.

[0018] The slot 25 is designed to receive a lip 28 that protrudes laterally from the edge of a sheet-like element 29 whose quadrangular shape is substantially identical to the shape of the laminar portion 24 and is flat and parallel to said laminar portion.

[0019] The length of the lip 28 is equal to approximately half the length of the edge of the laminar element 29 and is welded frontally to the end of the part 21; its thickness is such that the lip 28 is not in contact with the opposite edge of the laminar portion 24.

[0020] The second turn 9 of the secondary winding 8, as shown visually in Figure 4, is constructively identical to the turn 10 and its parts, for the sake of simplicity in description, are designated by the same reference numerals increased by 100.

[0021] The turn 9 is firmly associated with the laminar element 29 in a position that is inverted by 180° with respect to the turn 10. For this purpose, the edge of the laminar element 29 that lies opposite the one from which the lip 28 protrudes has a second lip 30 that is offset with respect to the lip 28 and is welded frontally at the end of the part 121. In the same manner described above, the thickness of the lip 30 and the height of the expansion 126 are such as to avoid any contact with the laminar portion 124 and the part 121.

[0022] A rectangular flange 31 is monolithically coupled at right angles to the sheet-like element 29, on one half of the edge that lies opposite the lips 28 and 30, so as to form a sort of T-shaped element.

[0023] From what has been described above it is evident that the flange 31 and the sheet-like element 29 constitute the central terminal 13 of the electric circuit shown in Figure 1, while the lips 28 and 30 correspond to the ends 11 and 12 of the same circuit, which are connected to the same central terminal 13.

[0024] Going back to Figure 4, it is noted that the lips 28 and 30 and the flange 31 delimit, on the opposite faces of the sheet-like element 29, two respective seats which accommodate the laminar portions 24, 124 without however producing contact with the intermediate sheet-like element 29. In particular, two layers 32, 33 of material suitable to ensure electrical insulation are interposed between the sheet-like element 29 and the laminar portions 24, 124.

[0025] The laminar portions 24, 124 of the turns 9, 10 are preset for the application of two semiconductor diodes 34, 35 to their outer faces (see Figures 2 and 3). Said diodes are interposed between the portions 24, 124 and two plates 36, 37 that are connected one another by a rectangular bridge 38, which is fixed, by means of screws 39, to the plates 36 and 37 so as to form with them a sort of U-shape that straddles the laminar element 29 but is spaced due to the presence of a recess 40 on the edge of said laminar element.

[0026] The parts 29, 24, 124, 36, 37 and the diodes 34 and 35 are assembled in a pack by virtue of two external jaws 41 and 42, which are constituted by rectangular plates that are dimensionally identical to the plates 36 and 37, and by virtue of through bolts 43 driven through holes 44, 45, 46, 47, 48, 49, 50 formed at the corners of said parts. The jaws 41 and 42 are electrically insulated from the plates 36, 37 by interposing insulating sheets 51 and 52.

[0027] It is noted that by analogy with the circuit shown in Figure 1, the laminar portions 24, 124, the plates 36 and 37 and the bridge 38 correspond respectively to the ends 14 and 15, to the connecting elements 16 and 17, and to the terminal 20, while the two diodes 18 and 19 of the circuit of Figure 1 are designated by the reference numerals 34 and 35 in Figures 2 and 3.

[0028] The described secondary winding is crossed by a channel for feeding a cooling fluid, whose path is traced in Figure 4 by a dashed line. The cooling fluid is conveyed, through an inlet 53, into a part 54 of the channel that runs through the sheet-like element 29, where it divides into the two arms 28 and 30, forming two channels 55 and 56 that pass through the turns 9 and 10 and, after passing through the laminar portions 24, 124 by following respective winding paths 55a and 56a, exit through the outlets 57 and 58 that are lateral to said portions. The outlets 57 and 58 are connected, by means of connecting bushes, to respective winding channels 59 formed in the plates 36 and 37 from which they exit to merge, in a fully obvious manner, in a single outflow channel formed in the bridge 38. As shown by Figures 5 and 6, the winding channels 59 are provided by forming a slot in the bottom of a circular hollow 60 of the plates 36 and 37, which is closed hermetically by a cover 61 that is recessed therein. A similar solution can be used for the channels of the laminar portions 24 and 124. The winding channels of course lie in the regions of the laminar portions 24 and 124 and of the plates 36 and 37 in close contact with the diodes 34 and 35.

[0029] Once assembly has been completed, the laminar portions 24 and 124 and the intermediate sheet-like element 29 form a very compact structure in which the flat and parallel turns 9 and 10 delimit an interspace 59a which accommodates the central part 4 of the primary winding of the transformer, while the other two parts 3 and 5 of said winding are laterally adjacent to the outer sides of the turns 9 and 10.

[0030] As can be seen, a substantial advantage of the described transformer is the reduced number of parts that compose the secondary circuit and accordingly of junctions required to assemble them, which are notoriously critical points of the transformer due to the high currents that cross them.

[0031] Another important advantage of the invention consists of the limited impedance, due to the fact that the two branches of the secondary circuit are perfectly identical, said branches extending from the plate-like element 29 through the turns 9 and 10 and the diodes 34 and 35 to the bridge 38, and of the constructive compactness, which by containing the distance between the turns of the secondary winding allows to reduce their impedance to values that are significantly lower than those of conventional transformers, this being very important for medium frequencies from 1000 to 5000 Hz.

[0032] In the practical embodiment of the invention, numerous modifications and variations are possible, and all are within the scope of the appended claims. For example, the channel for conveying the cooling fluid through the plates 36 and 37 and the laminar portions 24 and 124 can be obtained, instead of by forming a slot directly in the bottom of the hollow as in the example shown in Figures 5 and 6, by inserting in said hollow a disk in which a slot has been formed which duplicates the shape of the channel. The slot, once the disk has been recessed in the hollow, is closed on one side by the bottom of the hollow and on the other side by the cover, so as to form a channel that connects the inlet to the outlet of the cooling fluid.

[0033] In practice, the materials used, as well as the shapes and dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

[0034] The disclosures in Italian Patent Application no. BO2002A000173 from which this application claims priority are incorporated herein by reference.

[0035] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A transformer for an electric welding machine of the type that comprises a secondary circuit composed of a center-tapped secondary winding and two semiconductor diodes that are connected to said winding so as to provide a full-wave rectifier, characterized in that it comprises two flat and parallel turns that form between them an interspace for accommodating the primary winding of said transformer, each one of said turns having an end that is monolithically connected to a respective laminar portion that is co-planar thereto and an opposite end that is connected to a common sheet-like element that forms the center tap of said secondary winding and is interposed between said laminar portions, said laminar portions having mutually opposite contact faces for said diodes and said common sheet-like element being electrically insulated from said laminar portions.

2. The transformer according to claim 1, characterized in that each one of said turns is constituted by a U-shaped conductor that has a tubular rectangular cross-section, a substantially quadrangular laminar portion being monolithically coupled to one end of said conductor and co-planar thereto and remaining spaced, with one edge, from the other end of said conductor so as to form a slot that is suitable to receive a lip that protrudes laterally from said sheet-like element and is monolithically coupled to said other end, said sheet-like element having a quadrangular shape that is substantially identical to the shape of said laminar portions and being interposed between said laminar portions with the interposition of electrically insulating layers.

3. The transformer according to claim 2, characterized in that said turns and said laminar portions are associated with said sheet-like element in inverted position and in that said lips protrude in staggered positions from opposite sides of said sheet-like element in order to engage in the respective slots formed between said turns and said laminar elements.

4. The transformer according to claim 3, characterized in that said two semiconductor diodes are interposed between said laminar portions and two plates that are mutually connected by a bridge that is fixed to said plates so as to form with said plates a sort of U-shaped element that straddles without contact said plate-like element.

5. The transformer according to claim 3, characterized in that said sheet-like element, said laminar portions, said plates and said diodes are assembled in a pack by means of two external jaws that are dimensionally identical to said plates and by means of through bolts that are driven through holes formed at the corners of said parts, said jaws being insulated electrically from said plates by interposing electrically insulating layers.

6. The transformer according to one of the preceding claims, characterized in that said secondary winding is crossed by channels for feeding a cooling fluid which run through said laminar element, said turns, said plates and said bridge.

7. The transformer according to claim 6, characterized in that the channels that pass through said plates and said laminar portions trace a winding path at the regions meant to make contact with the semiconductor diodes.

8. The transformer according to claim 7, characterized in that said winding channels are provided by forming a slot in the bottom of a circular recess of said plates and/or of said laminar portions, said slot being closed hermetically by a cover that is recessed therein so as to form a channel that connects the inlet to the outlet of the cooling fluid.

9. The transformer according to claim 7, characterized in that said winding channels are obtained by inserting in a hollow of said plates and/or laminar portions a disk in which a slot has been formed beforehand, said slot duplicating the shape of the channel and, once the disk has been recessed in the hollow, being closed on one side by the bottom of the hollow and on the other side by the cover, so as to form a channel that connects the inlet to the outlet of the cooling fluid.

Drawing