TECHNICAL FIELD The present invention relates - to a method of profiling a tube of given length, in particular a metal tube obtained by cutting a tube of indefinite length transversely at the end of a continuous production process. BACKGROUND ART

To profile metal tubes of given length and cross section, various methods are used to convert the original cro'ss section of the tube to a different, e.g. circular, square, rectangular, lobed, star- shaped, cross section etc.

One of the commonest methods is to feed the tube through a number of forming dies aligned in a given travelling direction of the tube and each comprising a number of rolls arranged to define a passage for the tube.

The cross sections of the successive passages differ from one another, and increasingly approximate, in the travelling direction of the tube, the final cross section of the tube, so that the tube, as it proceeds in the travelling direction, is gradually deformed from its original to the desired final cross section. The above method produces profiles of fairly- good quality, but has several drawbacks which seriously impair output.

A first of these lies in anomalous deformation of the leading end portion of the tube when the tube is inserted between the rolls of the dies. As a result, the end portion must be removed at the end of the profiling process, thus resulting in additional cost in terms of both equipment and waste.

Another drawback of the above method derives from the fact that the forming dies are normally designed for a given tube size and a given final cross section, so that, for each different starting size of the ' tube and/or each different final cross section, all or some of the dies must be changed, thus -incurring additional cost in terms of production holdups and the high cost of the equipment required.

To eliminate the latter drawback, which obviously gets worse as the tube gets bigger, a different method has been proposed whereby all the dies, or at least all those interposed between an initial rough . die and a final finish die, are replaced by a number of pairs of opposite rolls movable, with respect to each other and within a given range, in a radial direction with respect to the tube axis.

Though more flexible, by being fairly adaptable to the size and shape of the tubes, this solution fails to solve the first of the drawbacks described above, relative to anomalous deformation of the leading end of the tube.

Moreover, the systems used to implement this method have the drawback of being relatively bulky, on account of requiring a large number of pairs of rolls to achieve gradual, geometrically accurate deformation of the tube.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a method of profiling a tube of given length, which is cheap and easy to implement and, at the same time, provides for eliminating the aforementioned drawbacks .

According to the present invention, there is provided a method of profiling a tube of given length, as claimed in the accompanying Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a schematic view in perspective of operation of a preferred embodiment of a unit for profiling a tube of given length and implementing the method according to the present invention;

Figures 2 to 6 show schematic views in perspective of operation of respective variations of the Figure 1 unit;

Figure 7 shows a larger-scale cross section of the Figure 6 unit;

Figures 8 and 9 are similar to Figure 7 and show cross sections of respective variations of Figure 1. PREFERRED EMBODIMENTS OF THE INVENTION

Number 1 in Figure 1 indicates as a whole a unit for profiling a tube 2 of given length L.

By way of example, the tube 2 in Figure 1 has an original circular cross section coaxial with a longitudinal axis 3 and to be converted by the profiling method into a substantially square cross section.

Unit 1 comprises a number of pairs 4 of opposite rolls 5 equally spaced along axis 3 and on a portion of tube 2 shorter in length than length L.

Rolls 5 in each pair 4 are identical, are located on opposite sides of axis 3, rotate about respective parallel, coplanar axes 6 crosswise to axis 3, each have a cylindrical work surface, and are each of a length at least equal to the side of the desired _. final square cross section.

Pairs 4 of rolls 5 are arranged in alternate positions offset angularly by 90 degrees about axis 3. That is to say, the work surfaces of rolls 5 in each pair 4 face respective portions of tube 2 at 90 degrees to the portions facing the work surfaces of each of the adjacent pairs 4. Rolls 5 in each pair 4 are fitted adjustably to respective supports (not shown) so as to move gradually, with respect to each other and radially with respect to axis 3, between an open position, in which the respective work surfaces are spaced apart by a distance d, measured along the centre distance, equal to or greater than the initial diameter of tube 2, and a closed position, in which distance d between the respective work surfaces of rolls 5 equals the length of the side of the desired square cross section.

Rolls 5 are moved radially by actuating devices (not shown) controlled by an electronic central control unit" (not shown) , and which may be defined, for example, by known mechanical jacks, known hydraulic cylinders, or other similar actuating systems of known design and operation and therefore not described in detail.

Rolls 5 in pairs 4 are powered by reversible electric or hydraulic motors (not shown) to rotate in both directions about respective axes 6. In a variation, some rolls 5 are powered, and some idle.

In actual use, at the start of the profiling process, rolls 5 in each pair 4 are set to the open position to define, as a whole, a through channel wider than the original circular cross section of tube 2.

Tube 2 is then positioned between rolls 5, with axis 3 of the tube substantially crosswise to axes 6, and with the cylindrical lateral wall 8 of the tube substantially equidistant from the work surfaces of rolls 5.

Once tube 2 is positioned, rolls 5 in each pair 4 are moved, radially with respect to axis 3, up to tube 2 and are rotated in opposite directions about respective axes 6.

On reaching lateral wall 8, rolls 5 begin compressing and deforming lateral wall 8 and, at the same time, push tube 2 axially in the same direction as the rotation direction of rolls 5 at the point of tangency. When the trailing end of tube 2, in the travelling direction of tube 2, reaches the rear pair

4, rotation of rolls 5 is inverted so tube 2 moves axially in the opposite direction.

As tube 2 moves back and forth as described above, rolls 5 in all of pairs 4 are gradually

^" pressed simultaneously against lateral wall 8, so the combined action of the pressure of rolls 5 and the axial movement of the tube produces gradual, even deformation of lateral wall 8.

Profiling terminates as rolls 5 reach the closed position, in which the cross section of the passage defined by pairs 4 as a whole matches the desired final cross section of tube 2 and the whole of tube 2 is equally deformed.

At this point, tube 2 can be removed from rolls 5, which are then reset to the open position to receive the next tube 2. Alternatively, rolls 5 may be reset to the open position before tube 2 is removed, in this case manually.

In connection with the above, it should be pointed out that the initial position of tube 2 is in no way compulsory, and tube 2 need not be positioned with its central portion at pairs 4, as in the example described. For example, if tube 2 is positioned initially with an end portion facing pairs 4, the first axial movement of tube 2 need simply be modified so that deformation by rolls 5 is "distributed" along the whole length of tube 2.

In this connection, it should be pointed out that, unlike conventional profiling methods, the method described also has the advantage of enabling profiling of a portion of tube 2 of any length, equal to or less than length L, or of two or more noncontiguous portions of tube 2, by programming the ^" central control unit (not shown) to appropriately control rotation of rolls 5 and the radial opening and closing movement of pairs 4. In which case, rolls 5 must be. restored to the open position before tube 2 is removed from rolls 5 at the end of the profiling process .

It should be pointed out that the method described above relative to unit 1 in Figure 1 applies regardless of the number and arrangement of rolls 5.

For example, in the Figure 2 variation, unit 1 comprises, in addition to pairs 4 as in Figure 1, two forming dies 7 located at respective ends of pairs 4 and each comprising four identical coplanar rolls 5 arranged in two opposite pairs to form a passage A coaxial with axis 3.

In the Figure 3 and 4 variations, unit 1 comprises a number of dies 7 aligned along axis 3, and one die 7, respectively. For maximum versatility of unit 1, dies 7 are preferably so-called "all-purpose" dies, i.e. in which rolls 5 can assume various closed positions, each corresponding to a given size of the desired final cross section. Like pairs 4, .rolls 5 of each die 7 are fitted to a support (not shown) and are radially adjustable with respect to axis 3.

In the Figure 5 variation, unit 1 comprises one pair 4 of rolls 5. This solution has the major advantage of being simple, compact, and cheap, but, to work the whole outer surface of tube 2, calls for profiling in stages, and rotating tube 2 about axis 3 between one stage and the next to selectively position contiguous portions of lateral wall 8 facing the work surfaces of rolls 5.

It should also be stressed that the method described relative to unit 1 in Figure 1 also applies regardless of the shape of rolls 5 and/or of dies 7, i.e. regardless of the shape of the desired final cross section.

For example, as shown in Figures 7 and 9, final lobed cross sections of various types can be obtained using appropriately shaped rolls 5 offset appropriately about axis 3.

Finally, Figure 6 shows a variation of the method described above, by which to obtain a tube 2 with a helical lobed cross section which is impossible using known conventional methods. In this case, rolls 5 have respective axes 6 sloping with respect to axis 3 of tube 2, so that tube 2 is rotated back and forth simultaneously and in time with' its back and forth axial movement.

In this connection, it is important to note that, in a variation, rolls 5 may all be idle, and tube 2 may be moved axialIy and rotated back and forth by means of one or more external actuating devices (not shown) controlled by the electronic central control unit (not shown) .