METHOD AND SYSTEM FOR LONGITUDINALLY WELDING TAPERED TUBULAR SHAFTS

TECHNICAL FIELD

The present invention relates to a method and system for longitudinally welding tapered tubular shafts. BACKGROUND ART Tapered tubular shafts are known, e.g. from US- 6,629,632, to be produced by gradually folding a trapezoidal metal sheet to position two opposite lateral edges of the sheet facing each other, and to form a tapered tubular shaft with an open longitudinal join line; feeding the longitudinally open shaft, in a feed direction parallel to its longitudinal axis, through a final calibration device, in which a number of pressure rollers, substantially equally spaced about the shaft, apply radially inward pressure on the shaft to press the two lateral edges defining the join line against each other; and welding the shaft along the join line while the two lateral edges are pressed against each other by the final calibration device. Welding is performed by red-hot heating the two lateral edges immediately

upstream from the final calibration device by means of electrodes positioned substantially contacting the outer surface of the shaft.

The above known welding method has several drawbacks, mainly due to the fact that, the longitudinally open shaft being fed axially, its join line slopes with respect to the feed direction, so that, when welding the shaft, the electrodes must be moved crosswise to the shaft axis to maintain a given constant distance between the electrodes and the outer surface of the shaft .

When electrowelding a longitudinally open shaft, moving the electrodes is invariably critical on account of the fairly heavy weight of the electrodes and relative equipment (transformers, etc.) , and any vibration transmitted to the electrodes automatically affects the distance between the electrodes and the surface of the work shaft, thus possibly resulting in weld defects, which must be corrected later off-line at fairly high cost, both in terms of the manual labour involved and the space required to accommodate the shafts. DISCLOSURE OF INVENTION

It is an object. of the present invention to provide a method of longitudinally welding tapered tubular shafts, designed to eliminate the aforementioned drawbacks.

According to the present invention, there is provided a method of longitudinally welding tapered

tubular shafts, as claimed in Claim 1 and, preferably, in any one of the Claims depending directly or indirectly on Claim 1.

The present invention also relates to a system for longitudinally welding tapered tubular shafts.

According to the present invention, there is provided a system for longitudinally welding tapered tubular shafts, as claimed in Claim 11 and, preferably, in any one of the Claims depending directly or indirectly on Claim 11.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a side view of a preferred embodiment of the welding system according to the present invention; Figure 2 shows a larger-scale view, with parts removed for clarity, of a detail in Figure 1;

Figure 3 shows a schematic view in perspective of a further detail of the Figure 1 system.

BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figures 1 and 2 indicates as a whole a system for longitudinally welding a tapered tubular shaft 2 having an axis 3, and an open longitudinal join line 4 comprising two facing longitudinal edges 4a and 4b (Figure 3) .

System 1 comprises a feed line 5 for feeding shaft 2 longitudinally in a feed direction 6 - which, in the

example shown, is horizontal - so that a leading portion of shaft 2 engages an electrowelding unit 7 and then a calibration device 8; and a traction device 9 for gripping a leading end of shaft 2 immediately downstream from calibration device 8, and pulling shaft 2 in feed direction 6 through calibration device 8.

With reference to Figure 1, feed line 5 comprises a rail 10 parallel to feed direction 6 and supporting a rear carriage 11 having an adjustable supporting unit 12 for supporting a trailing portion of shaft 2; an intermediate carriage 13 having an adjustable supporting unit 14; and a fixed adjustable supporting unit 15 at the end of rail 10 facing electrowelding unit 7. Rear carriage 11 has a powered wheel 16 cooperating frictionally with rail 10; and intermediate carriage 13 is mounted idly on rail 10.

With reference to Figure 2, calibration device 8 comprises a fixed frame 17 in the form of a rectangular parallelepiped, wherein a base 18 and an upper cross member 19 are connected by four parallel columns 20 (only two shown) , which act as slideways for a carriage 21 mounts^ to s^ide §\W3 columns 20, in a vertical direction 22 perpendicular to direction 6, under control of an actuator assembly 23 fitted to upper cross member 19 and connected to carriage 21 by a screw-nut screw coupling.

Carriage 21 supports a pressure device 24 movable with carriage 21 and comprising a number of pressure

rollers 25 (only two shown) arranged radially about an axis parallel to feed direction 6 to define a passage S in a plane P perpendicular to feed direction 6. Each pressure roller 25 is connected in rotary manner to the end of a respective control rod 26, the axis of which lies in plane P together with the axes of the other rods 26, and the axial position of which, with respect to carriage 21, is adjustable, by actuating means not shown, to adjust the size and shape of passage S. More specifically, to longitudinally weld a polygonal-section or circular-section tapered shaft 2, rods 26 are designed to impart a polygonal or circular shape to passage S, and are moved axially on carriage 21, by further actuating means not shown, to gradually adjust the size of passage S.

With reference to Figure 2, electrowelding unit 7 comprises a gantry frame 27 comprising four uprights 28 (only two shown) ; four upper cross members 29 (only three shown) arranged in two parallel pairs and connecting the top ends of uprights 28; and four intermediate cross members 30 (only three shown) arranged in two parallel pairs and connecting corresponding intermediate points of uprights 28. More specifically, each upper cross member 29 is parallel to a corresponding intermediate cross member 30; and two upper cross members 29, indicated 29a, and two intermediate cross members 30, indicated 30a, extend crosswise to feed direction 6.

An adjustable supporting unit 31 is connected to an

intermediate point of each intermediate cross member 30a, and comprises a lever 32 sloping upwards and outwards of frame 27, hinged at its bottom end to relative intermediate cross member 30a to rotate, with respect to intermediate cross member 30a, about an axis crosswise to feed direction 6, and fitted on its top end with a roller 33 for supporting shaft 2. The level of roller 33 is adjusted by adjusting the slope of lever 32 by means of a hydraulic jack 34 fixed to relative intermediate cross member 30a and having an output rod connected elastically to an intermediate point of lever 32.

The two adjustable supporting units 31 are associated with respective counterpressure units 35, 36 supported by upper cross members 29a; the upstream counterpressure unit 35 is adjustable hydraulically; and the downstream counterpressure unit 36 comprises a vertically adjustable carriage 37 having two rollers 38 arranged in series in feed direction 6.

The upper cross member 29a supporting carriage 37 is fitted, by means of a hinge 39 with a vertical axis 40, with a fork 41 supporting a spacer wheel 42, which rotates about a pin fitted to fork 41 and substantially crosswise to feed direction 6.

Electrowelding unit 7 also comprises a number of guide units 43 fitted to uprights 28 and having rollers 44 cooperating laterally with shaft 2.

Finally, electrowelding unit 7 also comprises a transformer 45 located over frame 27 and movable with

respect to frame 27 in a downward-sloping direction 46 towards calibration device 8 by known actuating means not shown. An arm 47 is connected to transformer 45, is substantially coplanar with spacer wheel 42, extends downwards in a direction parallel to direction 46, and is fitted on its bottom end with electrodes 48.

As shown in Figure 1, traction device 9 comprises a guide 49, parallel to feed direction 6, for a traction head 50, which is drawn together with shaft 2 along guide 49 by a known traction device not shown, and comprises, as shown in Figure 2, a hydraulic gripper 51 for gripping the end of shaft 2 immediately downstream from plane P in feed direction 6.

In actual use, shaft 2, by now formed but still open along longitudinal join line 4, is placed on adjustable supporting units 12, 14, 15, which are adjusted to position longitudinal join line 4 parallel to feed direction 6. In the example shown, feed direction 6 being horizontal, shaft 2 is positioned on adjustable supporting units 12, 14, 15 so that longitudinal join line 4 is horizontal and facing upwards, and axis 3 slopes downwards. In the attached drawings, the work shaft 2 is shown positioned with its narrow end or section forwards; it should be stressed, however, that shaft 2 may equally well be fed wide-end-first with no complications .

Next, drive wheel 16 of rear carriage 11 of feed line 5 is operated to feed shaft 2 through electrowelding

unit 7 and calibration device 8. During this feed stage, adjustable supporting units 31 are kept lowered _/ counterpressure units 35, 36 are kept raised; transformer 45 is raised in direction 46 to lift electrodes 48 outwards of frame 17 into a raised rest position; pressure rollers 25 are parted to maximize the section of passage S; carriage 21 is moved to align passage S with shaft 2; and spacer wheel 42 is inserted between the edges (4a, 4b) of open longitudinal join line 4 of shaft 2.

Once the leading end of shaft 2 passes plane P by a given relatively small distance, normally about 10 cm, drive wheel 16 of rear carriage 11 is stopped to arrest shaft 2 in its current position, and adjustable supporting units 31 and counterpressure units 35, 36 are positioned to support shaft 2 with longitudinal join line 4 facing upwards and parallel to feed direction 6. Finally, pressure rollers 25 are moved to adapt the size of passage S to the size of the section of shaft 2 currently located at plane P. Once this is done, by adjusting both the position of pressure rollers 25 with respect to carriage 21, and the position of carriage 21 with respect to frame 7, the centre C of passage P is located at the intersection of axis 3 and plane P, and pressure rollers 25 press shaft 2 radially at plane P to press edges 4a and 4b of longitudinal join 4 against each other .

In connection with the above, it should be pointed

out that, whereas counterpressure units 35, 36 are substantially rigid, adjustable supporting units 31 are elastically deformable to allow gradual movement of rollers 33 as shaft 2 advances. At this point, as shown in Figure 2, a jaw of hydraulic gripper 51 is inserted inside the leading end of shaft 2, and hydraulic gripper 51 is closed to grip shaft 2; at the same time, transformer 45 and arm 47 are lowered in direction 46 to move electrodes 48 into a lowered work position, in which, electrodes 48 are located inside frame 17, substantially contacting the outer surface of shaft 2 at longitudinal join line 4, and at a fairly small distance, of about 10 cm, from plane P.

Next, head 50 is moved in feed direction 6, and, at the same time, electrodes 48 are activated to heat edges

4a and 4b of longitudinal join line 4 to close to melting temperature; shaft 2 is pulled in feed direction 6 through passage S; and pressure rollers 25 press edges 4a and 4b against each other to weld edges 4a and 4b to each other.

Given the axial travel of longitudinal join line 4 parallel to feed direction 6, electrodes 48 can be locked in position and maintained stationary throughout the welding process, with obvious advantages in terms of both weld quality and the working life of electrodes 48.

Conversely, precisely because longitudinal join line 4 travels axially parallel to feed direction 6, axis 3 of shaft 2 slopes with respect to feed line 5, and the

intersection of axis 3 and plane P, which must coincide with centre C of passage S at all times, moves down or up, depending on whether shaft 2 advances narrow-end or wide-end first. Consequently, as shaft 2 travels through plane P, carriage 21 must be moved gradually in direction 22 synchronously with the travel of shaft 2 through plane P to keep centre C of passage S along the sloping axis 3 of shaft 2 at all times.