GB2104429A - Grid welding machine - Google Patents

Abstract

A grid welding machine for electrical resistance welding has its welding current fed to the points of weld via busbars (1, 2) running across the welding machine from a rectifier unit (5) fed by transformers (31, 32, 33). Two beamlike busbars (1, 2) lying opposite one another on opposite sides of the plane of production of the grid carry electrodes and are movable relative to one another. The ends of the two bushbars (1, 2) which are opposite one another are connected, via leads 3, 4, respectively to opposite poles of the rectifier unit (5) so that the resistances of all of the welding current circuits are matched to one another. <IMAGE>

Description

SPECIFICATION Grid Welding Machine The invention relates to a grid welding machine for electrical resistance welding and more particularly to one in which the welding current is fed to the weld points via busbars running across the welding machine from a rectifier unit fed by transformers.

A grid welding machine of this type, which works with two active electrodes and one passive current-bridge in each welding circuit, i.e. the so-called "double spot" method, is known from the AT-A-351,904. The doublespot method certainly has the advantage that all of the active electrodes, i.e., the electrodes which are directed connected to welding current source may be arranged on the same side of the plane of production of the grid so that current feeds passing through the plane of production of the grid are avoidable. On the other hand it has the disadvantage that in the case of an alteration of the pitch of the longitudinal wires for producing grids having a different width of mesh, the current bridges must be changed, which means a considerable expenditure of time so that productivity drops.

The invention is concerned with the problem of creating a grid welding machine of the species specified initially, which in order to avoid the use of current bridges works on the single-spot welding method.

According to the invention a grid welding machine for electrical resistance welding in which the welding current is fed to the weld points via busbars running across the welding machine from a rectifier unit fed by transformers is characterized by two beam-like busbars lying opposite one another on opposite sides of the plane of production of the grid, the busbars carrying electrodes and being relatively movable towards one another, the opposite ends of the two busbars being connected respectively to opposite poles of the rectifier unit.

Such a machine has a very simple construction and by means of the method of current feed to the electrodes of each single-spot welding section ensures, as far as possible, the same length of path for the current through all of the welding sections and thereby as far as possible the same welding conditions at all of the points of weld. As is explained more fully later, in this way largely the same d.c. resistance may be ensured in all of the welding current circuits, independently of the position of the electrodes along the busbars.

Preferably, in order to enable alteration of the pitches of the longitudinal wires in the grid which is to be produced, on at least one, but preferably on both, of the surfaces of the busbars facing one another individual electrodes are provided, which can be shifted in the transverse direction along the busbar and fixed.

Advantageously on at least one, but preferably on both, of the surfaces of the busbars facing one another on the two busbars, a continuous electrode fillet is provided, which can be replaced and if necessary shifted transversely along the busbar, so that in the case of an alteration of the pitches of the longitudinal wires the work expended in the adjustment of the electrodes is reduced or even saved altogether. In the case of the employment of an electrode fillet on only one of the two busbars, there are naturally provided on the other busbar individual electrodes which can preferably be shifted in the transverse direction.In an embodiment which enables the employment of a larger number of transformers and thereby yields a better distribution of power, both the lower and the upper busbars are combined from two pairs of busbars arranged, adjacent in the transverse direction, into a continuous busbar unit, the upper busbar unit being connected at both its outer ends and the lower busbar unit at its centre, to like poles of two rectifier units.

Examples of welding machines constructed in accordance with the invention will now be described with reference to the accompanying drawing in which: Figure 1 shows a front elevation of a grid welding machine upon the busbars of which individual electrodes are arranged.

Figure 2 shows diagrammatically the busbars of the embodiment of Fig. 1, in electrical connection to a rectifier unit fed by transformers.

Figure 3 shows continuous busbar units formed of two adjacent pairs of busbars, together with their associated supply circuits.

In Fig. 1 there may be seen two busbars 1, 2, extending across the whole width of the machine. The opposite ends of the busbars 1 and 2 are connected via electrical supply leads 3, 4 to the outputs from a rectifier unit 5 and fed from the supply network by means of transformers. The lower busbar 2 is stationary and supported immovably on a machine frame 6. A lifting beam 7 is further guided in the machine frame 6 to be able to move up and down. In the embodiment illustrated the drive of the lifting beam 7 is effected by a motor-driven shaft 10 via eccentrics 11 and 12 which cause the up and downward motion of the lifting beam via connecting rods 8, 9.

In the lifting beam 7 there are arranged at equidistant intervals slidable plungerlike pressure and guide members 15 for the upper busbar 1, the supply lead 3 to which is flexible. The pressure plungers 15 are supported at their top ends from the lifting beam 7. Adjusting screws 16 are further provided, by means of which the prestressing of spiral springs 17 which surround the pressure plungers 15 may be set at option so that the total application pressure of the electrodes may be altered. The bottom ends of the spiral springs 17 bear against spring plates 18 which are connected rigidly to the pressure plungers 15, to the bottom ends of which, projecting underneath the lifting beam, is fastened the upper busbar 1.

In the embodiment shown in Figs. 1 and 2, individual electrodes 19, 20 are provided, which can be adjusted and fixed along the busbars 1 and 2, whereby alteration of the pitch of the longitudinal wires is possible. The pressure plungers 15 of the stiff busbar 1 remain fixed independently of the pitch of the longitudinal wires and in contrast to known grid welding machines do not need to be adjusted with the electrodes when the pitch of the longitudinal wires is altered.

As Fig. 2 shows, each welding current circuit runs from one pole of the rectifier unit 5 via the flexible supply lead 3 to the busbar 1, from the latter via an electrode 19 through a point of intersection of a longitudinal wire L with a transverse wire Q to an electrode 20 on the busbar 2 and via the latter and the supply lead 4 to the other pole of the rectifier unit 5. In the case of the same construction of the busbars 1 and 2 the total resistance of the lengths of path X and Y along which the welding current flows is independent of the position of the cooperating welding electrodes along the busbars 1 and 2, so that the d.c.

resistances of all of the welding current ciruits are matched to one another.

Since the current-carrying electrode faces coming into contact with the material to be welded, are subjected to heavy mechanical wear, the electrodes are made as easily replaceable wearing parts, the purpose of which is merely a protection of the costly copper busbars 1 and 2 against mechanical wear.

Instead of the electrode shown in Figs. 1 and 2, which can be adjusted and fixed along the busbars 1 and 2, electrode fillets 21, 22, as shown in Fig.3, may also be provided, which if necessary may be made so that they can be inserted in dovetail guides in the busbars and thereby easily exchanged and also shifted by small amounts in the direction longitudinal to the busbars, so that by slight shiftings of these electrode fillets along the busbars new regions of the surfaces can be exposed to the wear from the welding process.

In Fig. 2 there may also be seen three transformers 30, 31, 32, connected in double star connection, the central tapping from which is connected conductively to the supply lead 3, whilst their end tappings are connected conductively to the electrical supply lead 4 via rectifier diodes 33.

Finally in Fig. 3 two rectifier units 35, 36 are provided, which exhibit the same con struction as the rectifier unit 5 in Fig. 2. Each of these two rectifier units consists of a group of three transformers connected in double start connection, the central tappings 37, 38 of both transformer groups being connected together to a supply lead 39 which feeds one busbar unit 2, 2' at its centre. The end tappings 40, 41 of the transformers of both rectifier units are connected conductively inde pendently of one another, each to one end of one busbar unit 1, 1' As a comparision of Fig. 3 with Fig. 2 reveals, the busbar arrangement as Fig. 3 corresponds with the adjacent arrangement of two pairs of busbars 1, 2 and 1', 2' as in Fig.

1, where both the upper busbars 1, 1' and also the lower busbars 2, 2' of these pairs are connected to form continuous busbar units 1A and 2A respectively. The imaginery point of connected is indicated in Fig. 3 by a broken line z-z. On this line there also lies the point of connection of the current supply lead 39 for the lower busbar unit 2A.

It is clear that in the case of the embodi ment as in Fig. 3 particularly along busbar units 1A and 2A result, which in the case of the application of continuous electrode fillets 21, 22 enable relatively wide grids to be produced with pitches of the longitudinal wires which can be altered at option without adjustment of the electrodes upon transition from one pitch of the longitudinal wires to another.

Claims (10)

1. A grid welding machine for electrical resistance welding in which the welding cur rent is fed to the weld points via busbars running across the welding machine from a rectifier unit fed by transformers, characterized by two beam-like busbars lying opposite one another on opposite sides of the plane pro duction of the grid, the busbars carrying elec trodes and being relatively movable towards one another, the opposite ends of the two busbars being connected respectively to oppo site poles of the rectifier unit.

2. A grid welding machine according to claim 1, in which individual electrodes are provided on at least one of the busbars, which can be shifted along the busbar and fixed in position.

3. A grid welding machine according to claim 1 or claim 2, in which a continuous electrode fillet is provided on at least one of the busbars.

4. A grid welding machine according to claim 3, wherein the fillet can be moved along the busbar and removed.

5. A grid welding machine according to any of claims 1 to 4, in which the lower busbar is arranged stationary and the upper busbar is movable up and down.

6. A grid welding machine according to claim 5, in which the transformer-fed rectifier unit is arranged below the plane of production of the grid and one of its poles is connected via a flexible conductor to the one end of the upper busbar.

7. A grid welding machine according to claim 5 or claim 6, in which the upper busbar is supported from a lifting beam by plungerlike guide-members arranged spaced apart along the busbar, the guide-members being individually spring-loaded.

8. A grid welding machine according to claim 7, wherein the guide members are adjustably mounted on the lifting beam.

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9. A grid welding machine according to any of claims 1 to 8, which includes two pairs of busbars, the busbars of each pair having their longitudinal axes aligned so as to form a continuous busbar unit, the upper busbar unit being connected at both its outer ends and the lower busbar unit at its centre, to respective like poles of two rectifier units.

10. A grid welding machine according to claim 1, substantially as described with reference to the accompanying drawings.