ITVI20090202A1 - WELDING HEAD FOR LONGITUDINAL WELDING IN SUBMERGED ARCH, PARTICULARLY OF SMALL DIAMETER TUBES - Google Patents

Description

DESCRIPTION

The present invention relates to the realization of a device which allows internal longitudinal submerged arc welding of pipes, particularly of small diameter. As known, submerged arc pipe welding systems generally comprise a fixed part (the welding unit <1> with electrical and electronic control equipment, tanks, coils. Cooling points etc ...); the bundle of cables and pipes; the welding head-carriage which includes the mechanisms for feeding and releasing the flux and the wire-electrode.

The relative movement of the carriage-head with respect to the pipe to be welded allows the welding to be carried out. In the normal construction technique, the trolley-head can be both fixed and mobile and the sequence of the steps of operation, both with fixed and mobile trolley, involves first P Complete introduction of the trolley into the tube and then the welding tose that takes place while the trolley is extracted so that the head is always above the still not welded and cold part.

In the case of systems for large diameter pipes, the trolley-head has no particular encumbrance constraints; the minimum diameter that can be welded is indicatively, as an order of magnitude, 400-300 mm.

The constructive limitations and difficulties for making welding systems for small diameter pipes derive essentially from the difficulty of placing all the necessary components in the reduced space and small section of the head; furthermore by the difficulty of limiting the portion of the heat developed by the arc that is absorbed by the head and consequently limiting the temperature of its components. The above is further aggravated if the thicknesses of the material to be welded are significant.

A known solution is formed by a fixed tube which contains the bundle and at the end of which is the head; the electrode wire is pushed from the outside along a guide towards the welding point; the thrust and feeding motor of the wire-electrode is external, it is at room temperature but there are the following drawbacks:

the tube-trolley-head is long and rigid; the pipe to be welded that I contains tends to flex due to thermal deformation; consequently the height of the electrode with respect to the welding axis (stick-out) varies as the welding proceeds and the welding bead becomes irregular;

moreover, to reduce the friction inside the guide, the wire-electrode must be previously straightened and well stretched, without irregularities and roughness;

the wire must be knurled by the push wheels themselves to ensure sufficient grip; the knurling involves greater wear of the electrode-nozzle, due to the sliding of the wire in the hole;

the regularity of the wire-electrode feeding is critical and the relative control is more complex;

the last section of the wire-electrode, when the coil is exhausted, remains unusable inside the head-tube;

the hole in the nozzle must be larger than the diameter of the wire-electrode to facilitate its introduction but thus the contact surface of the wire-electrode with the hole decreases.

As an order of magnitude, with this solution it is possible to weld pipes with diameters of 2 <Q> 0'150mm,

The purpose of the present invention is to provide a device which allows longitudinal submerged arc welding in small diameter pipes, to overcome the limitations described above, and to have excellent welding qualities. This solution is obtained by adopting a particular geometry in the arrangement of the mechanical components and by exploiting the mechanical stresses induced on the wire-electrode. The wire-electrode is dragged by the end <*> of the head, by applying the necessary traction force in at least two distinct points, and this by using at least two pairs of friction wheels. A small-diameter, high-torque motor-reducer, arranged in a rearward position and parallel to the carriage axis, simultaneously drives the friction wheels, a first wheel by means of a suitable mechanical coupling along an axis and at least one other wheel. along a different axis thanks to the use of a mechanical joint. The application of the traction force of the wire-electrode in at least two distinct points allows to reduce the diameters of all the mutisms. The use of at least one mechanical joint for the transmission of the drive torque and possibly of free guide motions of the wire-electrode allows to longitudinally distribute all the mechanical components devolved to the dragging, moving away from the arc area the most critical and obtain a suitable line of dragging and bending of the wire-electrode, exploiting the tensions induced on the wire. The present invention will be better described by a preferred embodiment, provided by way of non-limiting example, with the aid of the attached drawings in which:; fig. 1) represents the operating principle of the system; fig. 2) shows the detail of the friction and dragging wheels of the wire-electrode; Fig. 3) shows the mechanism of the bending of the yarn in the final section; Fig. 4) represents an overall view of an embodiment of the invention. The operation of the invention is explained in the example of fig. 1 which represents an overall view of the carriage-head and the pipe to be welded; for simplicity and clarity of presentation, only the geometric elements that identify the device and the points that characterize its principle are highlighted. ; The relative positions of the carriage-head 20 and of the tube to be welded 10 remain identified by the axes 1, 2, 3, which are parallel to each other, by the horizontal plane 4 and by the vertical plane 5, where 1 is the main, longitudinal axis , welding. The wire-electrode 6 is pulled by two pairs of friction wheels which apply the pulling force in two distinct points B and C. The pairs of wheels are arranged on planes perpendicular to each other, preferably the first pair in a horizontal plane and the second on the vertical one 5. The wire-electrode 6 is dragged inside the head-carriage along a line parallel to the axes mentioned in the section A-B and then in the section B-C along a straight or slightly curved oblique line; the fraction C-D is a curved line lying in the vertical plane 5 so that the starting point of! arc D is located vertically above the welding point P.; The dragging of the wire-electrode made by the end of the head relaxes it, compensates for any hump, takes place in a uniform and regular way, with minimum friction and without â € “appointments” as it would happen if the thread were pushed from the opposite end. The use of two pairs of friction-dragging wheels allows to divide the total pulling force between the two and therefore to reduce the diameter of the same and of the connected gears, thus reducing the overall dimensions in section. The use of a joint allows to transmit a fraction of the drive torque to a second pair of driving wheels, offset from the first Sa; therefore a single motor can <'> operate both pairs of wheels and can be placed in a position of the head further back than the bow area. The use of the joint also allows the driving wheels to be placed in such positions as to optimize the use of the available space, which can thus be used for the remaining components; finally, it allows to obtain a suitable line for dragging and bending the electrode wire. In fact, in the last section C-D the wire electrode must be bent, passing from a horizontal to an oblique or vertical position; especially with types of rigid wire-electrode it may be convenient or necessary that the radius of curvature be as large as possible and therefore that the horizontal section of the drag takes place in the upper part of the head. ; The fìg. 2) shows the detail of the pairs of friction-dragging motions, 7 and 71, * and 81 respectively; of the wire-electrode supply line 6 through

the electrode-plate 9, up to the arc striking point D.

In each pair a mota and "master (7, 8), has a rotation step in one position

fixed and is mechanically coupled to the motor shaft or joint; the other (71, 81) and '

slave, has the axis of rotation on a hinged and pivoting arm. In

working position the slave wheel is approached and mechanically coupled to the corresponding master, pressed against it by an adjustable force which is discharged on the

wire-electrode at the contact point, B and C respectively. The pressure on the wire ne

allows dragging.

The pressure on the wire is obtained from the compression of a spring, 72 and 82 respectively, and is adjustable; it is therefore possible to divide the total pulling force among the

two pairs of wheels. The first couple, 7 and 71, do some mechanical work only due

to the dragging of the wire-electrode and proportional to the pulling force applied at the point

B. The second pair 8 and 81 do mechanical work which is the sum of that

due to its own drag contribution, that due to the friction of the wire electrode 6 against the hole 91 of the plate-electrode 9 and of the work spent in

deformation of the wire. Based on the mechanical characteristics of the wire-electrode la

deformation can be (mainly) of the elastic type or (mainly)

plastic type. In both cases, however, a correct adjustment of the spring 82

guarantees the electrical contact of wire 6 with plate 9, the collector electrode.

Fig. 3) shows how the position of the pair of wheels 8 and 81 with respect to the direction of the wire 6 and how the different mechanical characteristics of the different types of wire can affect its curvature. The connecting O-Oâ € ™ the rotation axes 8 and 81 can be chosen in an intermediate position, between the vertical (figJa) and the horizontal (fig.3c), yes with a fixed and definitive arrangement that adjustable, in this case by means of a suitable mechanism, fn general the plastic deformation (dashed) involves a greater curvature than that of the elastic deformation (solid line); a further contribution is given by the pressure exerted by the spring 82. The electrode wire of the rigid type passes through the hole 91 of the plate 9, sliding along the line 92, pressed against it by an elastic force; the soft type wire crawls along line 93, pressed against it due to the greater curvature and plastic deformation. The diameter of the hole 91 is <1> slightly greater than that of the wire-electrode (a few tenths of a mm) so that in both cases the surface and the pressure of the contact are optimized.

The regularity of the dragging of the wire-electrode up to the point D of the arc striking and the constant contact of the wire plate 9 (collector electrode) guarantee a high quality of welding.

Claims (1)

CLAIMS 1 Exhibition called welding head, for submerged longitudinal internal welding of small diameter pipes, having a cylindrical geometry, characterized by the fact that the wire-electrode is dragged by pulling from the front end of the head, near the Of the arch. 2) Device according to the previous claim, characterized by the fact that the dragging force of the wire is distributed and applied in at least two distinct points, along a mixed longitudinal line partly parallel to the axes and partly oblique, by means of the use of at least two pairs of friction-drag wheels, 3} Device according to the preceding claims, characterized by! the fact that the drive of at least one of the said pairs of wheels takes place via a corresponding mechanical joint, so that â € ™ a single motor-reducer can drive all the pairs of wheels, however arranged along a longitudinal axis. 4) Device according to the preceding claims, characterized by the fact that the friction wheels, all the components collected and the motor-reducer have small diameters and that their arrangement, longitudinally distributed in the volume of the head, allows to place the motor. gearbox in a rear position. They imitate from the Fareo area, and to reduce the encumbrance in the diametrical section of the head. 5) Device characterized by the fact that the arrangement of the components allows to carry out the dragging of the wire-electrode along a longitudinal line in the upper part of the head, so as to be able to bend the final section with the largest radius possible. ¬bile, resulting in a very regular and uniform drag. 6) Device characterized by the fact that the adjustable pressure exerted by the friction wheels on the wire-electrode allows to adapt the operation of the system to the characteristics of the different types of wire-electrode, thus ensuring a high quality of welding.