DEVICE FOR FINAL CALIBRATION OF TAPERED TUBULAR SHAFTS

TECHNICAL FIELD The present invention relates to a device for final calibration of 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 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.

In final calibration devices of the above type, the pressure rollers define a passage through which the tapered, longitudinally open shaft for welding is fed,

and are movable radially to adapt the size of the passage to the size of the tapered shaft section currently being fed through the passage. For this purpose, the pressure rollers are connected to a radial thrust device which, in known final calibration devices, normally comprises, for each pressure roller, a respective hydraulic jack fixed, radially with respect to the axis of the passage, to an annular plate common to all the hydraulic jacks and coaxial with the passage axis. Known radial thrust devices of the above type have several drawbacks, mainly due to the presence of the hydraulic jacks, the transverse dimensions of which seriously limit the number of pressure rollers that can be accommodated about the axis of the passage, and hence the final calibration precision of the tapered, longitudinally open shaft for welding, and the hydraulic control circuits of which make for a relatively complex design of the thrust device as a whole. DISCLOSURE OF INVENTION It is an object of the present invention to provide a device for final calibration of tapered tubular shafts, in which the radial thrust device is cheap and easy to produce and, at the same time, eliminates the aforementioned drawbacks. According to the present invention, there is provided a device for final calibration of tapered tubular shafts, as claimed in Claim 1 and, preferably, in any one of the Claims depending directly or indirectly on

Claim 1.

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 front view of a preferred embodiment of the final calibration device according to the present invention;

Figure 2 shows a section along line II-II in Figure 1;

Figure 3 shows a larger-scale front view of a detail in Figure 1;

Figures 4 and 5 show a detail of Figure 3 in respective operating configurations. BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figures 1 and 2 indicates as a whole a device for final calibration of a tapered tubular shaft 2 (Figure 2) having an axis 3 and an open longitudinal join line 4. Device 1 comprises a fixed frame 5 in the form of a rectangular parallelepiped and in turn comprising a base 6, an upper cross member 7 facing base 6, and two pairs of parallel columns 8 and 9 extending upwards from base 6 to connect upper cross member 7 to base 6. Each column 8 and a respective column 9 are located specularly side by side with respect to a vertical plane P crosswise to the Figure 2 plane and to the feed direction 10 of shaft 2 through device 1.

Device 1 also comprises a carriage 11 mounted to run along columns 8 and 9, in a vertical direction 12 perpendicular to direction 10 and axis 3, under the control of an actuator assembly 13 fitted to upper cross member 7 and connected to carriage 11 by a screw-nut screw coupling 14. For each pair of columns 8, 9, carriage 11 comprises an upper cross member 15 and a lower cross member 16, each of which is horizontal, is parallel to plane P, and is fitted at each end with a bush 17 _. fitted in sliding manner to relative column 8, 9 and connected by a tubular spacer 18 to the bush 17 fitted to the same column 8, 9 and to the other cross member 16, 15. The two upper cross members 15 are connected to each other by a U-shaped bracket 19, a central plate 20 of which, extending through plane P, is fitted with the bottom end of screw 21 of coupling 14.

Carriage 11 supports a pressure device 22 movable with carriage 11 and comprising, as shown more clearly in Figure 2, a hollow, substantially cylindrical drum 23, which is located inside the space defined by columns 8 and 9, has an axis 24 perpendicular to plane P and located centrally with respect to upper cross member 15 and lower cross member 16, and has two annular end flanges 25, each lying in a respective plane parallel to plane P, and each connected integrally to a respective upper cross member 15 and a respective lower cross member 16.

Drum 23 has a circumferential rib 26 projecting

outwards from the outer surface of drum 23, and having a number of radial through holes 27, the axes of which lie in plane P. Holes 27 are substantially equally spaced about axis 24, and house, in axially sliding manner with the interposition of respective bushings, respective control rods 28 for controlling respective pressure rollers 29. More specifically, the end of each rod 28 facing axis 24 defines a respective fork which, by means of a respective pin 30 with its axis in plane P, supports for rotation relative pressure roller 29, which projects outwards of the relative fork and defines, with all the other pressure rollers 29, a circular passage 31 coaxial with axis 24.

To keep pressure rollers 29 perpendicular to plane P and in a radial position with respect to axis 24 at all times, each rod 28 has a longitudinal lateral groove, which is engaged in sliding manner by a key 32 defined by an inner tooth of a relative ring 33 fixed to rib 26 at the outer end of relative hole 27. With each flange 25, rib 26 defines an annular seat 34 which, with the interposition of a bearing coaxial with axis 24, houses in rotary manner the inner periphery of a respective face cam 35, the active surface 36 of which faces the active surface 36 of the other face cam 35, and comprises, as shown more clearly in Figure 3, a groove 37 coiling by an angle of at least 720°, and preferably of about 750°, about axis 24.

Face cams 35 form part of pressure device 22, and

control the axial position of rods 28 with respect to drum 23, and therefore the diameter of circular passage 31. For which purpose, as shown more clearly in Figure 2, each rod 28 is fitted, on the end outside rib 26 and opposite the end supporting relative pressure roller 29, with a cross member 38 perpendicular to active surfaces 36 and supporting, at each end, a cam follower roller 39 which rolls transversely along groove 37 of relative face cam 35. A variation, not shown, has only one cam, and each rod 28 has one cam follower.

As shown in Figure 3, being arranged along a roughly 360° arc about axis 24, and having to define, with respective pressure rollers 29, circular passage 31 coaxial with axis 24, rods 28 are of different lengths; and the length of each rod 28 differs from that of any one of the other rods 28 by an amount equal to the difference in the radius of grooves 37 between the two rods 28 considered. As shown in Figure 3, the rod 28 whose pressure roller 29 would be located, in use, at longitudinal join line 4 of shaft 2 is missing.

As shown in Figure 2, face cams 35 are rotated about axis 24 by an actuator assembly 40 fitted to carriage 11, and which comprises two ring gears 41, each of which is integral with relative face cam 35, is coaxial with axis 24, and is connected in rotary manner to the outer periphery of relative annular flange 25; a drive shaft

42, which is parallel to axis 24, is supported for rotation by two brackets projecting downwards from lower cross members 16, and is fitted with two pinions 43, each meshing with respective ring gear 41; and a reversible motor reducer 44, which is controlled by a central control unit not shown, is supported by one of lower cross members 16, and powers drive shaft 42.

In actual use, device 1 can be operated in two modes . In a first mode, to which the accompanying drawings refer, shaft 2 is fed to device 1, by a feed device not shown, with axis 3 parallel to feed direction 10, and so that one end of the shaft engages circular passage 31 defined by pressure rollers 29. As shown in Figure 2, shaft 2 is positioned with its longitudinal join line 4 facing upwards and beneath two electrowelding electrodes 45 located immediately upstream from circular passage 31 and between passage 31 and a spacer 46, which is inserted between the edges of longitudinal join line 4 to keep the edges a given distance apart.

Before inserting the end of shaft 2 through circular passage 31 to reach the initial position shown in Figure 2, actuator assembly 40 is operated to rotate face cams 35 (anticlockwise in Figure 3) to the maximum diameter of circular passage 31; electrodes 45 are raised; and actuator assembly 13 is operated to lock axis 24 at a given level. Said feed device (not shown), which a known type, also comprises level adjusting devices, which are

operated to position axis 3 of shaft 2 coaxial with axis 24. Alternatively, shaft 2 is made coaxial with axis 24 by moving carriage 11.

Face cams 35 are rotated (clockwise in Figure 3) to bring pressure rollers 29 into contact with, and to press on, the outer surface of shaft 2, so as to press the edges of longitudinal join line 4 against one another with a given pressure; and electrodes 45 are lowered substantially into contact with the outer surface of shaft 2.

At this point, carriage 11 - which is not needed in the first operating mode - is locked in position; electrodes 45 are activated to heat the edges of longitudinal join line 4 to close to melting temperature; shaft 2 is pulled in direction 10 through circular passage 31 at a given travelling speed, normally by means of a traction device (not shown) connected to the leading end of shaft 2; and actuator assembly 40 is synchronized with the traction device (not shown) to adapt, instant by instant, the diameter of passage 31 to the diameter of the section of shaft 2 travelling through plane P, to press the edges of longitudinal join line 4 against each other and weld the edges to each other.

Since longitudinal join line 4 slopes with respect to direction 10 as shaft 2 is fed in direction 10 parallel to axis 24, the level of electrodes 45 is adjusted gradually to adapt to the varying level of the portion of longitudinal join line 4 beneath electrodes 45

(in the example shown, in which shaft 2 is advanced narrow-end first, the join line slopes upwards, though shaft 2 may equally well be advanced wide-end first) .

In the second operating mode, shaft 2 is fed to device 1 with longitudinal join line 4 parallel to direction 10.

Electrodes 45 may therefore be maintained at a fixed level. In this case, however, since it is axis 3 that slopes with respect to direction 10, and the point of intersection of axis 3 with plane P moves (downwards, in the example shown) as shaft 2 travels through passage 31, but must always coincide with the centre of passage 31, actuator assembly 13 is also synchronized with the traction device (not shown) to shift carriage 11 gradually and keep the centre of passage 31 along axis 3 at all times .

As will be clear from the foregoing description, pressure rollers 29 being activated, not by respective actuating devices, but by a single pressure device 22 acting simultaneously from the outside on rods 28 of all the pressure rollers 29, pressure rollers 29 can be spaced close enough apart to define, for the section of shaft 2 currently be fed through passage 31, a substantially continuous retaining surface preventing deformation of shaft 2 in the area close to longitudinal join line 4, as normally occurs when using hydraulically controlled pressure rollers.