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Title:
MACHINE FOR BENDING METAL BARS AND CORRESPONDING METHOD
Document Type and Number:
WIPO Patent Application WO/2013/011373
Kind Code:
A1
Abstract:
Method for bending metal bars in order to make reinforcements with a three- dimensional geometry, comprising a step of moving a metal bar (B) in a direction of feed (D) and toward a bending bench (15) provided with a contrasting surface (22), and a first step of bending a first segment of the bar (B) on a plane coplanar to the contrasting surface (22), by means of a bending device (16) associated with the bending bench (15). Said method also comprises a torsion step of the bar (B) in which a gripping device (17), disposed upstream of the bending bench (15), clamps the bar and prevents it from rotating on itself, and the bending bench (15) is rotated, in a first direction of rotation, around an axis of rotation (Z) which is substantially aligned with the direction of feed (D) so that the first bent segment of the bar (B), during the first bending step, due to contrast against the contrasting surface (22) of the bending bench (15), is inclined by a determinate angle (α).

Inventors:
DEL FABRO GIORGIO (IT)
Application Number:
PCT/IB2012/001408
Publication Date:
January 24, 2013
Filing Date:
July 20, 2012
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
PIEGATRICI MACCH ELETTR (IT)
DEL FABRO GIORGIO (IT)
International Classes:
B21D11/12; B21D7/022; B21D7/024; B21D11/06; B21F1/00
Foreign References:
EP1908537A12008-04-09
EP0419443A11991-03-27
EP0419443A11991-03-27
EP1908537A12008-04-09
Attorney, Agent or Firm:
PETRAZ, Davide, Luigi et al. (Piazzale Cavedalis 6/2, Udine, IT)
Download PDF:
Claims:
CLAIMS

1. Method for bending metal bars in order to make reinforcements with a three- dimensional geometry, comprising a step of moving at least one metal bar (B) in a direction of feed (D) and toward a bending bench (15) on which a bending device (16) is mounted, and a first step of bending at least a first segment (61) of said bar (B) on a plane coplanar to that on which said bending device (16) lies, characterized in that at least in said first bending step said first segment (61) is disposed resting on a contrasting surface (22) of a shelf (20) of the bending bench (15), said contrasting surface (22) extending externally with respect to said bending device (16), and in that it comprises a torsion step of said bar (B) during which a gripping device (17), disposed in a fixed position upstream of said bending bench (15), clamps the bar and prevents it from rotating on itself around said direction of feed (D), while said shelf (20) is rotated in a first direction of rotation around an axis of rotation (Z), which is substantially aligned with said direction of feed (D), so that the first bent segment (61) of the bar (B), remains resting on said contrasting surface (22), and due to the contrast against the latter is inclined by a determinate angle (β) around said axis of rotation (Z), longitudinally twisting said bar (B) in the segment comprised between said gripping device (17) and said bending device (16); and a second step of bending a second segment (62) of the bar (B) adjacent to the first segment (61).

2. Method as in claim 1, characterized in that said torsion step of said bar (B) is effected subsequent to said bending step of said first segment.

3. Method as in claim 1, characterized in that said torsion step of said bar (B) is effected simultaneously with said first bending step of said first segment.

4. Method as in any claim hereinbefore, characterized in that after said torsion step, said bending bench (15) is returned to its initial condition with a rotation thereof around said axis of rotation (Z) in the opposite direction to said first direction of rotation.

5. Method as in any claim hereinbefore, characterized in that said first and said second bending step each comprise at least a first sub-step of feeding said bar (B) along said direction of feed (D) and a second sub-step in which the first and the second segment are bent on a plane coplanar to said contrasting surface (22).

6. Method as in claim 5, characterized in that said bending bench (15) is returned to its initial condition during said first sub-step of said second bending step.

7. Machine for bending metal bars, comprising a movement device (13) suitable to move at least a bar (B) along a direction of feed (D) and toward a bending bench (15) on which a bending device (16) is mounted suitable to bend said bar (B) on a plane coplanar and coinciding with the plane on which said bending device (16) lies, and actuation means (21) suitable to rotate said bending bench (15) around an axis of rotation (Z), characterized in that it also comprises a gripping device (17) to grip the bar (B), disposed upstream with respect to said bending bench (15), suitable to selectively clamp the bar so as to prevent it at least from rotating on itself, and suitable to be activated in a coordinated manner to the movement of the bending bench (15) determined by said actuation means (21) and in that said bending bench (15) comprises a shelf (20) provided with a contrasting surface (22) which extends externally with respect to said bending device (16) and on which, during use, the segment of bar (B), which is being bent, is disposed resting.

8. Machine as in claim 7, characterized in that said bending bench (15) is provided with said contrasting surface (22) and can be selectively rotated around at least a rotation pin (26) in order to keep the contrasting surface (22) lying on planes passing through said direction of feed (D).

9. Machine as in claim 8, characterized in that a connection element (31, 32) is solidly associated with said bending bench (15) and extends radially with respect to said rotation pin (26) and in that said actuation means (21) are associated with said connection element (31, 32) and provide to rotate said bending bench (15).

10. Machine as in claim 9, characterized in that said connection element comprises a semi-circular sector (31, 32) which extends, from the side opposite that with which said bending device (16) is associated, substantially orthogonal with respect to said contrasting surface (22).

1 1. Machine as in claim 10, characterized in that said semi-circular sector (31, 32) has at least a circular edge with which a first guide element (35) is associated, suitable to slide on a mating second semi-circular guide element (36) which is associated with a fixed bearing structure (25).

12. Machine as in claim 7, characterized in that said actuation means (21) are chosen from a group comprising hydraulic actuators, pneumatic actuators, jack screws (40), gear means or similar.

Description:
MACHINE FOR BENDING METAL BARS AND CORRESPONDING METHOD

FIELD OF THE INVENTION

The present invention concerns a machine for bending metal bars, preferably to make reinforcements for the building trade, and the corresponding bending method. In particular, the bending machine and the corresponding method allow to bend metal bars according to a three-dimensional geometry to generate a spiraliform reinforcement or similar.

BACKGROUND OF THE INVENTION

Metal reinforcement cages are known, for pillars and girders in reinforced concrete, normally with a rectangular, square or round geometry, consisting of longitudinal metal bars, or stringers, which are connected to each other by transverse stirrups at a suitable distance.

Cages are also known consisting of reinforcements with a substantially spiral development, which are made by means of successive continuous bending from a metal bar. This type of reinforcement is applied particularly in pillars and girders that are not too big, unless a plurality of reinforcements are disposed one after the other, and suitably connected to each other.

Spiraliform reinforcements can have different configurations, for example they may comprise a succession of oblique segments, or according to a substantially spring-type conformation, or a succession of oblique segments consecutive to segments perpendicular to the axis of the reinforcement.

In order to make this type of spiraliform reinforcement, however, more complex machine are required than those used to obtain traditional metal cages.

In particular, such machines normally comprise means to feed the bar to be bent toward a bending bench provided with bending devices that act by bending the bar around an axis orthogonal to the axis of feed of the bar to be bent.

One solution is known, for example from EP-A-0.419.443, in which the bending bench is associated with a rotation device that provides to make it rotate around an axis of rotation which is aligned with the axis of feed of the bar.

In particular, the bar is fed toward the bending devices which carry out a first bending thereof; afterward, if the reinforcement to be made has the spiral lying on the same plane, the subsequent bendings are also made in succession. If on the contrary the spiral consists of a plurality of oblique segments, the bending bench, after making the first bend, is rotated around its axis of rotation by an angle equal to the angle of inclination of the spiral, and subsequently the bar is fed forward and bending is done by the bending devices. In this way, the bending is carried out directly on a second plane, different from the first plane of the previous bending and coinciding with the plane of inclination of the spiral. More specifically, a plastic flexional deformation, which allows the desired geometry to be obtained, is imparted on the metal bar that progressively forms the spiraliform reinforcement.

Repeated operations of this type allow to obtain a three-dimensional reinforcement of a determinate overall length.

Such machines, however, have the disadvantage that they are rather complex both to produce and to manage; moreover, the bending bench must be rotated incrementally around its axis always in the same direction of rotation without ever returning to the initial position, except after a complete rotation upon itself.

This greatly limits the sizes of the geometry of the spiraliform reinforcement which will be made, and hence the overall length obtainable. In fact, the complete rotation - or at least with a great angular amplitude - of the bending bench around the axis of feed of the bar is greatly limited by structural and constructional features of the machine and connected to the presence of the rotation devices provided to actuate the rotation of the bending bench.

Furthermore, the portion of spiraliform reinforcement made develops orthogonally to the plane of the bending bench and therefore also rotates around the axis of the metal bar being fed. This causes the disadvantage that the reinforcement portion made cannot achieve very long lengths, because the whole reinforcement that is gradually made supports itself during the bending steps. Moreover, given that also the reinforcement portion progressively made rotates around the axis of the bar, the machine needs very large working spaces so that conditions of interference with its parts are not created.

A machine is also known, from EP-A-1.908.537, for the production of spiraliform reinforcements provided with a bending mandrel disposed downstream of drawing and feed devices and of a device for cutting to size a metal bar, wherein the bending mandrel can be rotated around the axis of feed of the metal bar in the same way as described above.

The rotation of the bending mandrel allows to make bends on different lying planes determined on each occasion by the angular position assumed by the bending mandrel. The bends made by the bending mandrel occur only due to plastic deformation deriving from stress of a flexional type of the bar.

The machine is also provided with axial holding means of the bar disposed between the drawing device and the bending mandrel. The holding means comprise a fixed gripper and, immediately downstream thereof, a rotary gripper which, apart from having the function of axially holding the bar, can also rotate around the axis of feed of the bar.

In this way, by driving both the fixed gripper and the rotary gripper, and by making the latter rotate around the axis of the bar, an action of torsion of the bar is exerted on the latter on its axis. This operation allows to take the whole spiraliform reinforcement, previously bent, onto a different inclined plane from that on which the bending mandrel lies. The subsequent bending will therefore be carried out on a different plane from that of the reinforcement portion already made.

With this machine, therefore, three-dimensional reinforcements can be made in two ways. The first by rotating the bending bench so as to make the bend on the bar on different planes, the second by means of torsion of the bar to take the bent bar on a desired plane.

This machine is particularly complex since it not only requires two grippers but also respective rotation devices both for the bending mandrel and for the rotary gripper. To this must also be added the complexity of coordinating the various movements of the members of the machine.

Furthermore, the torsion of the bar is concentrated solely in the segment - somewhat limited - comprised between the two grippers. In this segment high internal tensions are induced, which reduce the overall resistance of the spiraliform reinforcement that will be made.

One purpose of the present invention is to obtain a machine for bending metal bars to form metal reinforcements of a three-dimensional type which is simple to achieve, easy to manage and which does not need big working spaces. Another purpose of the present invention is to perfect a method for bending metal bars to form reinforcements with a three-dimensional geometry which is simple and which prevents problems of interference with parts of the bending machine or with accessory equipment disposed in proximity thereto.

Another purpose of the present invention is to perfect a method to make a metal reinforcement in which the internal tensions induced by the bending operations are limited, thus increasing the overall resistance of the reinforcement.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a method for bending metal bars to form reinforcements with a three-dimensional geometry according to the present invention comprises a step of moving at least one metal bar in a direction of feed and toward a bending bench comprising a shelf on which a bending device is mounted, and a first step of bending at least a first segment of the bar on a plane coplanar to that on which the bending device lies.

According to one feature of the present invention, the shelf defines a contrasting surface that extends externally with respect to the bending device, on which, at least in the first bending step, the first segment is disposed resting.

The method also comprises at least a torsion step of the bar during which a gripping device, disposed upstream of the bending bench, clamps the bar and prevents it from rotating on itself, while the shelf is rotated in a first direction of rotation around an axis of rotation which is substantially aligned with the direction of feed; in this way the first segment of the bar bent during the first bending step remains resting on the contrasting surface and due to contrast or interference against the latter is inclined by a determinate angle, and the bar in the segment comprised between the gripping device and the bending device is subjected to a longitudinal torsion upon itself. A second bending step is provided to bend a second segment of the bar which is adjacent to the first. In particular, the second segment of the bar corresponds to, or at least partly comprises, the segment that has been twisted during the torsion step.

By suitably coordinating the above steps it is therefore possible to achieve reinforcements shaped according to a spiral configuration, where the amplitude of the angle of inclination of the first bent segment of the bar determines the pitch between the spirals of the reinforcement.

The fact that a shelf is provided with a contrasting surface that develops outside the bending device, and on which during the torsion operations the bent segment of bar rests, allows to distribute the torsion stresses upon it, thus preventing stresses on the bending device and its supports.

Furthermore, unlike what is described in the state of the art, the torsion effect of the bar is distributed on a sufficiently long segment, such as to preserve the characteristics of overall mechanical resistance of the reinforcement that will be made.

According to another feature, the torsion of the bar is performed after the first bending step, so that the first bent segment determines a reaction arm for twisting the bar upon itself.

According to a variant, the torsion of the bar is performed at the same time as the first bending step; in this way, as soon as bending begins, this already determines in turn a reaction arm which, going in contrast against the contrasting surface, determines the torsion of the bar. This allows to considerably reduce the time required to make the spiraliform reinforcement.

In one form of embodiment, after the torsion step, the bending bench is returned to its initial condition with a rotation thereof around the axis of rotation in the direction opposite to the first direction of rotation.

According to another feature, both the first bending step of the first segment and the second bending step of the second segment comprise at least a first sub- step of feeding the bar in the direction of feed and a second sub-step of bending the segment of the bar on a plane coplanar to the contrasting surface.

The second sub-step, in the case of the second segment of the bar, can be carried out either immediately after the torsion of the bar, that is, without providing that the bending bench is returned to its initial condition, or following the positioning of the latter in its initial condition. This therefore allows to make the second bend either on the same plane on which the first side was obtained, or on a plane inclined by the above angle.

The present invention also concerns the corresponding machine for bending metal bars, able to achieve the method described above.

More specifically, the machine comprises a device for moving the bars toward a bending bench with which a bending device is associated.

Actuation means are associated to the bending bench and are suitable to rotate the latter around an axis of rotation that coincides with the axis of feed of the machine.

According to a characteristic feature, the machine according to the present invention comprises a gripping device disposed upstream of the bending bench, suitable to selectively clamp the bar so as to prevent it at least from rotating upon itself, and suitable to be activated in coordination with the movement of the bending bench determined by the actuation means.

Furthermore, the bending bench comprises a shelf on which the bending device is mounted and provided with a contrasting surface that extends externally with respect to the bending device.

In this case, by activation of the gripping device in coordination with the rotation of the bending bench we mean that the gripping device is actuated, and therefore clamps the movement of the bar, when the bending bench is rotated around its axis of rotation to determine a torsion of the bar in the segment comprised between the gripping device and the bending device.

According to one form of embodiment, the shelf is selectively rotatable around at least a rotation pin, to keep the contrasting surface lying on planes passing through the direction of feed.

In another form of embodiment, the bending bench comprises at least a connection element associated at one end to the rotation pin and which extends radially with respect to the latter. Furthermore, at the opposite end of the connection element the actuation means are associated, which act tangentially and provide to rotate the bending bench around the rotation pin.

In another form of embodiment, the connection element comprises a semicircular sector that extends, from the side opposite that with which the bending device is associated, substantially orthogonal with respect to the shelf. It is advantageous to provide that the semi-circular sector has at least a circular edge, with which a first guide element is associated, for example a slider, suitable to slide on a mating second guide element, semi-circular, which is associated with a fixed bearing structure of the machine.

According to another feature of the present invention, the actuation means are chosen from a group comprising hydraulic actuators, pneumatic actuators, jack- screws, gear means or suchlike.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a front view of a reinforcement obtained with the machine and method according to the present invention;

- fig. 2 is a lateral view of fig. 1 ;

- fig. 3 is a perspective view of fig. 1 ;

- fig. 4 is a plan view of a machine for bending metal bars according to the present invention;

- fig. 5 is a lateral view of fig. 4;

- figs. 6 and 7 are plan views of the machine in fig. 4 in a first and second operating configuration;

- fig. 8 is a plan view of the machine in fig. 4 in a third operating configuration;

- fig. 9 is a lateral view of fig. 8;

- fig. 10 is a plan view of the machine in fig. 4 in a fourth operating configuration;

- fig. 1 1 is a lateral view of fig. 10;

- fig. 12 is a plan view of the machine in fig. 4 in a fifth operating configuration;

- fig. 13 is a lateral view of fig. 12;

- fig. 14shows a detail of the machine in fig. 4;

- figs. 15 - 18 are schematic views of some steps in the method according to the present invention, according to a variant form of embodiment of the invention.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications.

DETAILED DESCRIPTION OF ONE FORM OF EMBODIMENT

With reference to the attached drawings, a machine for bending metal bars B is denoted in its entirety by the reference number 10 and is used for making reinforcements 1 1 with a substantially spiral development.

In particular, the reinforcement 1 1 is configured as a spiral with a polygonal shape of the spirals, in this case rectangular. The reinforcement 11 (figs. 1-3) is provided with sides 12 which, with respect to the longitudinal development, are disposed both orthogonal and inclined by a determinate angle of inclination a to define the pitch of the reinforcement 1 1.

In this specific case, the reinforcement has three consecutive sides or segments 12, bent substantially on the same bending plane, while the fourth side, consecutive to the third side, is inclined by the angle a with respect to the same plane.

It is quite obvious that with the machine 10 according to the present invention it is also possible to obtain reinforcements 1 1 bent in configurations different from those shown in figs. 1-3, for example providing one, two or more consecutive sides bent by the angle a.

The machine 10 (fig. 4) comprises a movement device 13 to move the bar B in a direction of feed D, a bending bench 15 on which a bending device 16 is mounted, and a gripping device 17 to grip and hold the bar B which is interposed between the movement device 13 and the bending device 16.

The movement device 13 in this case comprises motorized rolls 19, and is suitable to feed the bar B, for example from a loading device, not shown in the drawings, to the bending device 16. The motorized rolls 19 also have the function of preventing the bar B, during the movement steps, from rotating upon itself.

The bending bench 15 is associated with a bearing structure 25 between a first frame 28 and a second frame 29.

The first 28 and second frame 29 are provided with respective support surfaces 34.

More specifically, the bending bench 15 is selectively rotatable around rotation pins 26 mounted on the first 28 and second frame 29 and disposed coaxial to each other with respect to an axis of rotation Z. The direction of feed D of the bar and the axis of rotation Z of the bending bench 15 substantially coincide.

The bending bench 15 is provided with a shelf 20, rectangular, that lies substantially on a plane passing through the direction of feed D and through the axis of rotation Z and that defines in turn a contrasting surface 22. The contrasting surface 22 extends externally with respect to the bending device 16 so that when the bar B is bent it remains completely resting on the contrasting surface 22.

In a normal condition of the bending bench 15, the contrasting surface 22 is substantially coplanar with the support surfaces 34.

In one form of embodiment of the invention, the contrasting surface 22 has a size in plan such as to contain the segments of bar B that are bent on each occasion by the bending device 16.

In an advantageous form of embodiment, it is provided that the bending bench 15 is mounted on the first 28 and second frame 29 so that its contrasting surface 22 is facing downward. This allows the reinforcement 1 1 which is made due to the effect of gravity to always have its axis of longitudinal development vertical or sub- vertical.

The shelf 20 is provided with a first side 30 and a second side 31, opposite each other, which rotate, when the shelf 20 is made to rotate around the axis of rotation Z, lying always on the same plane.

In proximity to the first side 30 and the second side 31 connection elements are associated, in this case respectively a first sector 32 and a second sector 33, which extend substantially orthogonal with respect to the shelf 20 and in this case are substantially semi-circular in shape.

Each sector 32, 33, is provided on its circumferential edge with a semi-circular slider 35 suitable to slide along respective guides 36 provided on the first frame 28 and the second frame 29.

At least one of the two sectors, in this case the first sector 32, is associated to actuation means 21 suitable to rotate the bending bench 15 around the axis of rotation Z of the shelf 20.

The actuation means 21 in this case comprise a hydraulic actuator 40 which is connected at one end to a plate 41, in turn associated with the first frame 28, and at the other end to the first sector 32 in an offset position with respect to the axis of rotation Z.

With reference to fig. 5, by commanding the rod to exit from the actuator 40, the bending bench 15 rotates around the axis of rotation Z in a clockwise direction, whereas by retracting the rod of the actuator 40 the bending bench 15 is made to rotate around the axis of rotation Z in an anti-clockwise direction.

In other forms of embodiment, the actuation means 21 can comprise a jack screw, a worm screw mechanism, or other suitable system.

In still other forms of embodiment, it is possible to provide that the actuation means 21 comprise at least a toothed crown, which develops at least for a determinate circular sector and is keyed to the bending bench 15, and a drive toothed wheel which engages on the toothed crown and is associated to drive members, for example an electric or hydraulic motor which, making the drive toothed wheel rotate, makes the toothed crown rotate and also in turn also the bending bench 15.

Between the movement devices 13 and the bending device 16 a closed pipe 68 is provided (fig. 14), through which the bar B is fed.

The bending device 16 (figs. 4 and 5) is associated with the bending bench 15 and comprises a rotary mandrel 42 conformed substantially as a disc and provided on its periphery, solid thereto, with a bending pin 43 with a substantially cylindrical shape which extends orthogonal with respect to the rotary mandrel 42.

The rotary mandrel 42 is associated with a drive member 69 (fig. 14) and a transmission unit 70 which provide to make the rotary mandrel 42 rotate around an axis of rotation thereof.

In advantageous forms of embodiment, it is possible to provide that the bending pin 43 is associated to translation means which provide to take it under the plane of the rotary mandrel 42, so that it can be used both to make right-hand bends and also left-hand bends of the bar B, without the disadvantage of interfering with the latter.

The bending device 16 (figs. 4, 5 and 14) also comprises two contrasting elements 44, substantially hoe-shaped and defining between them a channel 45 for the passage of the bar B, aligned with the axis of rotation Z and with the direction of feed D of the bar B.

The passage channel 45 is substantially aligned with the pipe 68 that feeds the bar B.

The two contrasting elements 44 each comprise a contrasting portion 47, at least partly circular, around which the bar B is bent, and a lead-in portion 48 which facilitates the insertion and the passage of the bar B through the passage channel 45.

The two contrasting portions 47, in use, are disposed substantially in proximity to the center of the rotary mandrel 42, while the lead-in portions 48 extend substantially radial toward the periphery of the latter.

In particular, the bar B fed by the movement device 13 is inserted through the passage channel 45 protruding from the contrasting portions 47 by a determinate length. The rotary mandrel 42 is made to rotate so that the bending pin 43 bends the bar B around one of the contrasting portions 47. The bending pin 43 is disposed on a first semi-plane 42a or a second semi-plane 42b of the rotary mandrel 42, respectively above or below the direction of feed D of the bar B, in order to carry out respectively bends in a clockwise or anti-clockwise direction, that is, right-hand or left-hand.

A shears 18 is also integrated with the bending device 16 (fig. 14), and provides to shear the bar B to size once the bending operations are finished.

More specifically, the shears 18 comprises a linear actuator 65, in this case hydraulic, suitable to slide in a transverse direction with respect to the direction of feed D of the bar B.

The linear actuator 65 has one end 66 with which a cutting blade 67 is associated and which is suitable to act substantially in correspondence with the pipe 68 that feeds the bar B.

In proximity to its end open toward the bending device 16, the pipe 68 that feeds the bar B comprises a counter-blade 71 which, cooperating with the cutting blade 67, provides to cut the bar B.

In other forms of embodiment, instead of being provided with the hoe-shaped contrasting elements 44, the bending device 16 can comprise only one contrasting element, central with respect to the rotary mandrel, and a bending pin disposed on its periphery.

In this case the rotary mandrel 42 is disposed axially offset with respect to the direction of feed D so that when the bar B is fed to the bending device 16 it is substantially tangent with respect to the contrasting element. By making the rotary mandrel 42 rotate, the bending pin 43, solidly associated therewith, provides to make the bend on the bar B around the contrasting element.

The gripping and holding device 17 is mounted in a fixed position with respect to the first frame 28 and comprises a contrasting element 50 and a gripping element 51 which is selectively actuated by an actuation mean 52 in a direction orthogonal to the direction of feed D, to be thrust against the contrasting element 50, so that the bar B, which is made to pass between both, is securely clamped between them, both with respect to a translation in direction D, and also with respect to a rotation on itself. The gripping and holding device 17 is disposed immediately upstream with respect to the rotatable shelf 20. The fact that a fixed gripping and holding device 17 is provided allows to limit, unlike in the state of the art, the bulk in a direction orthogonal to the supporting surfaces 34. This feature is advantageous because it not only reduces the interference that could occur during the bending of the bar, but also prevents any possible plastic deformation of the bent bar when it is obliged, during the bending operation, to pass over the gripping and holding device 17. The positioning of the gripping and holding device 17 in proximity to the rotatable shelf 20 also allows to control with greater precision the holding of the bar B, both longitudinally and also with respect to its rotation around its axis.

The surfaces of the contrasting element 50 and the gripping element 51 which, during use, come into contact with the bar B, can be suitably shaped so as to increase the usable gripping surface with the bar B, or in other forms of embodiment can be provided with knurls or grooves which increase the gripping capacity.

The bending method according to the present invention with the bending machine 10 as described above, provides the following steps.

The bending machine 10 is put in a condition where the contrasting surface 22 is coplanar with the supporting surfaces 34, and the bending pin 43 is disposed in the first semi-plane 42a of the rotary mandrel 42. The method provides a first step of feeding the bar B to the bending device 16 (fig. 4) by the movement means 13, making it pass through the passage channel 45 of the rotary mandrel 42, and making a segment thereof protrude from the contrasting portions 47 by a determinate distance such as to allow the bending pin 43, which is disposed in the first semi-plane 42a, to bend it around the contrasting portion 47.

Once this first bend has been made, the bending pin 43 is returned to the first semi-plane 42a and the bar B is made to advance by a determinate length, substantially equal to the length of one of the sides of the reinforcement 1 1 to be obtained.

By making the rotary mandrel 42 rotate in a clockwise direction (fig. 7), a second bend is made on the bar B to achieve a first segment 61 of the reinforcement 1 1.

In this condition the gripping and holding device 17 is actuated, so that the bar B is clamped in its rotation upon itself and in its translation, between the contrasting element 50 and the gripping element 51.

Subsequently, a torsion is made on the bar B in the segment comprised between the gripping and holding device 17 and the rotary mandrel 42, in this case in an anti-clockwise direction, commanding the actuator 40 to retract.

In particular, the bending bench 15 is rotated around the axis of rotation Z by a determinate angle β or, in other words, the contrasting surface 22 and the supporting surface 34 are put at angles to each other by the angle β.

The amplitude of the angle β is substantially greater than the amplitude of the angle of inclination of the spiral a. Indeed, during the rotation of the bending bench 15 the bar B is plastically deformed under torsion, and it is advantageous to provide that the amplitude of the angle β is greater than that of angle a in order to compensate for possible elastic returns of the bar B.

During this step, the first segment 61 of the bar B acts as a reaction arm to twist the bar B on itself in the segment comprised between the gripping and holding device 17 and the point of bending of the first segment 61.

The first segment 61 of the bar B, remaining resting against the shelf 20, interferes at the same time with it, and is inclined by angle β. The presence of the shelf 20 prevents the rotary mandrel 42 from being stressed under flexion, and prevents damage to the supports and interference with the functioning of the transmission unit 70.

The gripping and holding device 17 is driven in coordination with the rotation of the bending bench 15; in other words, before rotating the latter to effect the torsion on the segment of the bar B, the gripping and holding device 17 must be activated to keep the bar B clamped in its rotation upon itself.

In some forms of embodiment, it is possible to provide that the rotation of the bending bench 15 to twist the bar B is carried out at the same time as the bending step of the first side 61, that is, as soon as the first segment 61 being bent defines a reaction arm sufficient to allow the bending thereof.

Subsequently, in this position of the bending bench 15, the gripping and holding device 17 releases the bar B and the movement device 13 feeds it forward in direction D, by a determinate length. The motorized rolls 19 prevent the bar B just bent from rotating upon itself, due to its own weight, around the axis of rotation Z.

During or after this operation, the bending bench 15 is returned to its initial condition, that is, with the contrasting surface 22 coplanar with the supporting surface 34.

In this condition the rotary mandrel 42 is made to rotate so that the bending pin 43 bends a second segment 62 of the reinforcement 1 1.

Given that the bending bench 15 has been returned to its initial condition, that is, with the contrasting surface 22 coplanar with the supporting surface 34, the bending of the second segment 62 is made on an angled plane with respect to the plane on which the first segment 61 is disposed.

Therefore, the second segment 62 is angled with respect to the first segment 61 by the established angle a, so as to determine the pitch between the spirals.

In general, therefore, with a combined action of feeding the bar B, holding it by the gripping and holding device 17, bending it by means of the bending device 16, and bending/twisting it by rotating the bending bench 15 around the axis Z, it is possible to obtain reinforcements 1 1 configured as a spiral as shown in figs. 12 - 13, or also according to other configurations.

It is obvious that the bending bench 15 can be rotated around the axis of rotation Z also in the opposite direction to that shown in figs. 8 and 9. For example (fig. 15), it is possible to make the bend on the first segment 61 in the opposite direction to that previously described. In this case the shelf 20 (figs. 16 and 17) is rotated in a clockwise direction so that the first segment 61 contrasts against the contrasting surface 22. Once the torsion has been made on the bar B, the bending bench 15 is returned to its starting condition leaving the first segment 61 (fig. 18) inclined by the angle ά, the angle of inclination of the spiral.

It is clear that modifications and/or additions of parts may be made to the machine and method for bending a metal bar as described heretofore, without departing from the field and scope of the present invention.

For example it is possible to provide that support means are associated to the bending bench 15, which are conformed and suitable to support the reinforcement 1 1 when the spirals are being made.

The support means can be provided with bearing elements of the adjustable type, conformed so as to support at least some of the spirals that are made.

Rolls can also be associated with the bearing elements, with the function of allowing the spirals to slide along the bearing elements, and hence to reduce the friction between them.

The support means can also be associated with actuators and position detection means, which allow the selective reciprocal positioning of the support elements both when the spirals of the reinforcement 11 are being made, and also when the machine 10 is being prepared for the specific form of embodiment of the reinforcement 1 1.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of machine and method for bending a metal bar, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.