FIELD OF THE INVENTION

The present invention concerns an apparatus and a method for straightening a metal wire usable for feeding machines for working elongated metal products, for example of the type usable for realizing reinforcements for construction. In the following description, metal wire will be understood as both a rod and a pre-cut bar, as well as a real metal wire.

BACKGROUND OF THE INVENTION

Apparatus are known for straightening a metal wire in order to prepare it for use in machines for producing electro-welded mesh, in stirrup bending, or in bending/shaping machines.

The known straightening apparatuses comprise a straightening unit having one or more series of rollers between which the metal wire is passed. Downstream of the straightening unit, along the direction of advancement of the metal wire, there is a drawing unit which is configured to exert a certain pull on the metal wire.

Straightening is an operation that is necessary in order to make the wire straight through reduction of residual tensions that may be present in the metal wire for various causes, for example because they are generated during the hot production process as a result of an inhomogeneous cooling, or caused by the unwinding of the metal wire from the coil, or still generated during the rolling process.

In addition to the residual tensions, the metal wire could also have an irregular section whose shape often prevents the current straightening apparatuses from operating effectively and continuously over time without an obvious decrease in performance. The irregular shape of the section of the metal wire also causes reading errors in the wire length measuring devices that are traditionally of the contact type such as encoders.

These problems are particularly relevant in the case of metal wires for reinforcement irons, which have both discontinuous surfaces, for example ribbed, and shapes that are not always perfect.

A simple operation on the metal wire is in fact conditioned by the tensions present in it so that any geometric shapes made with the metal wire no longer maintain the desired spatial arrangement, but tend to lose it. Hence, in the case of brackets for reinforcement, whose spatial arrangement in place must be flat, it results in brackets with three-dimensional spatial shapes that are unusable or of low quality and in poor reliability once they are installed. Or, in the case of machines for the production of electro-welded mesh, the bars must be well straightened, in order to be able to be automatically loaded by the machine.

Even in cases where the mesh is produced directly from wound rolls, a correct in-line straightening operation is necessary to create regular panels consisting of straight wires.

Examples of apparatuses for straightening a mechanical wire are described in CN 213 002 131 U, CN 210 547 659 U, EP 0 362 055 Al and CH 669 128 A5.

There is therefore a need to perfect an apparatus and a related method for straightening a metal wire that can overcome at least one of the disadvantages of the state of the art.

To do this it is necessary to solve the technical problem of obtaining a uniform pull and straightening over the entire length of the metal wire without performance discontinuity.

In particular, a purpose of the present invention is to realize a machine and develop a process for straightening a metal wire in a uniform, continuous and effective manner. 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. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

In accordance with the above purposes, and to resolve the technical problem disclosed above in a new and original way, also achieving considerable advantages compared to the state of the prior art, an apparatus according to the present invention for straightening a metal wire comprises a support structure on which there are mounted in sequence at least a straightening unit, configured to reduce the tensions present in the metal wire, a main drawing unit which is configured to exert a certain pull on the metal wire for its advancement, and an outlet unit which is configured to guide the metal wire along an outlet axis.

In accordance with one aspect of the present invention, the apparatus further comprises at least one calibration unit disposed upstream of the straightening unit and provided with at least two rollers which are configured to receive said metal wire between them along an inlet axis and to exert a longitudinal flattening action on the lateral surface of said metal wire in order to regularize its cross-section.

By doing so, the metal wire can be processed continuously and uniformly by the straightening unit and the drawing unit. In addition, by regularizing the section of the metal wire, the problems of reading the length of the metal wire by means of contact-type wire length measuring devices such as encoders are reduced such that the problems of reading the length of the wire are eliminated.

In accordance with another aspect of the present invention, said calibration unit comprises at least one other roller. Furthermore, said at least two rollers and said other roller define a first group of rollers and are disposed angularly offset from each other by a same offsetting angle.

In accordance with another aspect of the present invention, said calibration unit may comprise a second group of rollers disposed downstream of said first group of rollers and comprising other rollers disposed angularly offset from each other by said same offsetting angle. Said second group of rollers is disposed in a rotated configuration with respect to the first group of rollers.

In accordance with another aspect of the present invention, said rollers have a cylindrical peripheral forming surface.

In accordance with another aspect of the present invention, according to further embodiments, said rollers may have a circumferentially concave peripheral forming surface toward the center of the roller.

In accordance with another aspect of the present invention, said circumferentially concave peripheral forming surface has a radius of curvature greater than the nominal radius of said metal wire.

In accordance with another aspect of the present invention, said drawing unit comprises two rollers disposed at different heights and defining between them an S-shaped path for said metal wire.

In accordance with another aspect of the present invention, said outlet axis is parallel and vertically misaligned with respect to said inlet axis by an amount equal to the sum of the distance between the centers of said drawing rollers and the radiuses of said drawing rollers themselves.

In accordance with another aspect of the present invention, each of said drawing rollers has a peripheral circumferential seat shaped as "V" for said metal wire. In accordance with another aspect of the present invention, said seat has a seat angle comprised between 50° and 100°, preferably between 60° and 90°.

In accordance with another aspect of the present invention, said seat may be provided with recesses or ribs.

In accordance with another aspect of the present invention, said drawing unit comprises one or more presser rollers disposed peripherally to said drawing rollers, for pushing the metal wire inside the seat of the drawing rollers themselves.

In accordance with another aspect of the present invention, the presser rollers have a peripheral surface that faces the seat provided on the drawing rollers. Therefore, the metal wire is sandwiched between the drawing rollers and the presser rollers. This increases the stability of the pull, prevents slippage and possible escapes of the wire and overall increases the reliability of the drawing unit.

In accordance with another aspect of the present invention, said outlet unit comprises two distinct groups of rollers. In accordance with another aspect of the present invention, said outlet unit comprises a first series of outlet rollers with a horizontal axis and a second series of outlet rollers vertical to them.

A method according to the present invention for straightening a metal wire comprises at least a step of straightening said metal wire performed by said straightening unit, a step of drawing said metal wire performed by said drawing unit, and a step of guiding said metal wire performed by said guiding unit along said outlet axis.

In accordance with one aspect of the present invention, the method further comprises a calibration step performed by a calibration unit as described above before said straightening step, wherein said at least two rollers receive said metal wire along an inlet axis and exert a longitudinal flattening action on the lateral surface of said metal wire in order to regularize its cross-section.

In accordance with another aspect of the present invention, said calibration step takes place by means of at least a first group of three rollers disposed around said metal wire, angularly offset from each other by a same offsetting angle.

In accordance with another aspect of the present invention, after said calibration step the cross-section of said metal wire has a uniform profile having at least three calibrated sides interspersed with as many sides that have not been subjected to flattening. The number of calibrated sides depends on the number of rollers acting on the metal wire. For example, in the case of two groups of three rollers the profile of the section of the metal wire has six calibrated sides and six sides that have not been subjected to flattening.

Advantageously, the slight levelling exerted on four, six or eight symmetrical sides of the metal wire, depending on the configuration of the calibration unit, prevents the metal wire from rotating around its axis in all subsequent movements determined by rollers, whether they are for drawing, guiding or straightening. This stability to rotation also benefits the machines downstream of the apparatus of the present invention, because it is possible to greatly simplify the tuning of all subsequent devices also giving greater consistency to drawing, measuring, straightening, stirrup bending and shaping operations.

In accordance with another aspect of the present invention, after said calibration step the area of the final cross-section of the metal wire is smaller than a value comprised between 0.5% and 1.5% with respect to the area of the initial crosssection of the metal wire, preferably around 1%. The calibration made is, therefore, very limited, and is such as not to significantly alter the height of the ribs previously made in order to improve the adhesion of the metal wire in place. Therefore, after calibration, the metal wire continues to meet the characteristic adhesion parameters of the metal wires for reinforced concrete applications established by the regulations of each country.

DESCRIPTION OF THE DRAWINGS

These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 is a schematic side view of an apparatus for straightening a metal wire, according to the present invention;

- fig. 2A is a view along section IIA of fig. 1; - fig. 2B is a view along section IIB of fig. 1;

- fig. 3 is a view along section III of fig. 1;

- fig. 4 is a side view of fig. 3;

- figs. 5-6 are embodiment variants of figs. 3-4; - fig. 7 is a side view of a roller of the calibration unit having a cylindrical peripheral forming surface;

- fig. 8 is an embodiment variant of fig. 7 in which the peripheral forming surface is concave;

- fig. 9 is a schematic side view showing a drawing roller coupled to a presser roller for drawing the metal wire.

We must clarify that in the present description the phraseology and terminology used, as well as the figures in the attached drawings also as described, have the sole function of better illustrating and explaining the present invention, their function being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims.

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 embodiment can be conveniently combined or incorporated into other embodiments without further clarifications. DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

With reference to fig. 1, an apparatus 10 for straightening a metal wire W, according to the present invention, is suitable for preparing the product for feeding a working machine which can be, by way of example only, a bending/shaping machine, a machine for making metal meshes for construction or other machines known and therefore not represented in the drawings.

The metal wire W may have an average diameter comprised between about 3 mm and about 20 mm, more frequently between about 3.5 mm and about 16 mm. The metal wire W may be, for example, ribbed, i.e. it may have raised surface ribs extending longitudinally, optionally with a spiral development. The apparatus 10 comprises a support structure 11 on which there are mounted, in sequence with respect to a direction of advancement of the metal wire W, at least a straightening unit 12 which is configured to reduce the tensions present in the metal wire W, a drawing unit 13 which is configured to exert a certain pull on the metal wire W, and an outlet unit 14 which is configured to guide the metal wire W along an outlet axis X.

The apparatus 10 further comprises a calibration unit 15 disposed upstream of the straightening unit 12 and provided with at least two rollers 16, 17 which are configured to receive the metal wire W between them along an inlet axis Y, which in the configuration described herein is parallel to the outlet axis X, and to exert a longitudinal flattening action on the lateral surface of the metal wire W with the aim of regularizing the geometry of its cross-section. With reference to fig. 2 A, the section of the metal wire W at the inlet may have an irregular shape while the section at the outlet represented in fig. 2B has a regularized and uniform shape.

The at least two rollers 16, 17 are operatively disposed around the metal wire W so as to press simultaneously on the same segment of the metal wire W but along different directions, for example opposite.

The calibration action on the metal wire W is preparatory so that both the straightening unit 12 and the drawing unit 13 can perform their function effectively and continuously on the metal wire W.

With reference to figures 3-4, the calibration unit 15 comprises a first group of rollers 16, 17, 18 and a second group of rollers 16’, 17’, 18’ disposed downstream of the first group of rollers 16, 17, 18 along the inlet axis Y in the direction of advancement of the metal wire W.

The number of rollers 16’, 17’, 18’ of the second group of rollers is preferably equal to the number of rollers 16, 17, 18 of the first group of rollers. However, solutions are not excluded in which the rollers of the first and second groups of rollers are in different numbers, therefore not corresponding.

Both the first and the second group of rollers comprise respectively three rollers 16, 17, 18 and 16’, 17’, 18’ which, with reference to the view of fig. 3, are preferably disposed symmetrically with respect to a central point defined by the inlet axis Y or, equivalently, defined by a longitudinal axis of extension of the metal wire W.

Said rollers 16, 17, 18 and 16’, 17’, 18’ rotate in the same direction of advancement as the metal wire W and are distinct, but equal to each other, for example having the same diameter and the same peripheral shape.

Said rollers 16, 17, 18 and 16’, 17’, 18’ are disposed in such a way as to define between them a passage channel for the metal wire W. The passage channel has a smaller section than the section of the metal wire W which therefore undergoes a flattening action.

Said rollers 16, 17, 18 and 16’, 17’, 18’ are disposed angularly offset from each other by a same offsetting angle a which, in the case of three rollers can be favourably equal to about 120°. The rotation axes of the rollers 16, 17, 18 are therefore incident between them by an angle equal to the offsetting angle a.

The offsetting angle a may also be different in the case where the number of rollers 16’, 17’, 18’ of the second group of rollers is different from the number of rollers 16, 17, 18 of the first group of rollers.

With particular reference to fig. 3, the second group of rollers 16’, 17’, 18’ is disposed in a rotated configuration with respect to the first group of rollers 16, 17, 18, for example rotated by a rotation angle |3 equal to 60°. By way of explanation only, the rotated configuration is understood taking into consideration as the center of rotation the inlet axis Y or, equivalently, the longitudinal axis of extension of the metal wire W.

Therefore, the rollers 16, 17, 18 and 16’, 17’, 18’ cause a flattening on the metal wire W along six different directions which are opposite in pairs.

The section of the metal wire W, after passing through the calibration unit 15, therefore has six calibrated sides interspersed with as many sides that have not been subjected to flattening, fig. 2B. Overall, the section of the metal wire W is made more regular and the nominal section of the metal wire W is reduced by about 1%. This value guarantees, however, that a minimum height of the ribs present superficially on the metal wire W is maintained within the parameters established by the standards.

In this way, any initial geometry of the cross-section of the metal wire W is made overall symmetrical so that the metal wire W is ready to be processed uniformly and continuously by the straightening unit 12 and by the drawing unit 13. According to embodiments the rollers 16, 17, 18 and 16’, 17’, 18’ have a respective cylindrical peripheral forming surface 16a, 17a, 18a and 16a’, 17a’, 18a’, fig. 7, whereby they are adapted to determine six spaced flat faces with angular pitch equal to the offsetting angle a. According to further embodiments, the peripheral forming surface 16a, 17a, 18a and 16a’, 17a’, 18a’ of the rollers 16, 17, 18 and 16’, 17’, 18’ may be circumferentially concave toward the center of the roller, fig. 8. The radius of curvature of the concavity of the peripheral forming surface 16a, 17a, 18a and 16a’, 17 a’, 18a’ is preferably greater than the average radius of the metal wire W.

According to possible embodiments, the rollers 16, 17, 18 of the first group may differ from the rollers 16’, 17’, 18’ of the second group. For example, the rollers 16, 17, 18 of the first group may have the cylindrical peripheral forming surface 16a, 17a, 18a while the rollers 16’, 17’, 18’ of the second group may have the concave peripheral forming surface 16a’, 17a’, 18a’ or vice versa.

According to possible embodiment variant, the calibration unit 15 may comprise a single group of rollers having more than three rollers, for example four or more rollers, or more distinct groups made up of two or more rollers. For example, in figs. 5-6 the calibration unit 15 comprises two groups of rollers made up of two rollers 16, 17 and 16’, 17’ which are offset from each other by an offsetting angle a equal to 180° while the rotation angle P between the two groups of rollers is equal to 90°.

With reference to fig. 1, the drawing unit 13 comprises two coplanar drawing rollers 13 a, 13 b. The drawing rollers comprise an upper drawing roller 13a and a lower drawing roller 13b which are disposed at different heights and defining between them an S- shaped path for the metal wire W. This path develops vertically. Therefore, the outlet axis X is vertically misaligned with respect to the inlet axis Y. The vertical misalignment is equal to the sum of the distance between the centers of the drawing rollers 13a, 13b and the radiuses of the drawing rollers 13a, 13b themselves.

The drawing rollers 13a, 13b have respective horizontal rotation axes.

According to possible embodiments, the drawing rollers 13a, 13b of the drawing unit 13 may have respective vertical rotation axes. In this case, the S-shaped path for the metal wire W develops horizontally and the inlet Y and outlet X axes are always parallel, but horizontally misaligned.

Such a configuration of the drawing unit 13 serves to increase the drawing force of the metal wire W since the latter must also pass through the calibration unit 15.

According to embodiments, the drawing rollers 13a, 13b have a peripheral circumferential seat 19 shaped as "V". Said seat 19 is configured to receive the metal wire W in order to realize an interlocking effect thereof so that it can be dragged more effectively.

The "V" shape of the seat 19 is characterized by a seat angle y varying from a minimum of about 50° to a maximum of about 100°, preferably between about 60° and about 90°.

According to a variant, the seat 19 may have recesses or ribs to improve the adhesion effect on the metal wire W.

The drawing unit 13 may also comprise one or more presser rollers 13c disposed to cooperate with the drawing rollers 13a, 13b to push the metal wire W inside the seat 19 of the two drawing rollers 13 a, 13 b, always in order to improve the dragging effect exerted by each drawing roller 13a, 13b.

The presser rollers 13c have rotation axis parallel to the rotation axis of the drawing rollers 13a, 13b. The presser rollers 13c are movable toward/away from the drawing rollers 13a, 13b. In other words, the position of the presser rollers 13c is adjustable with respect to that of the drawing rollers 13a, 13b. Therefore, the presser rollers 13c are advantageously able to deliver an adjustable pressure on the metal wire W and to allow the flattening of metal wires W having different diameter. Further configurations of the drawing unit 13 are however possible, and may comprise by way of example even a single drawing roller, for example the upper one, preceded by a return roller or pulley.

In any case, all these configurations must be suitable to guarantee the correct drawing force on the metal wire W. In further embodiment solutions, for example, the drawing unit 13 can comprise a winch or one or more pairs of suitably grooved and shaped, partly motorized, rollers and coupled in contact to allow the metal wire W to advance in the desired way.

The straightening unit 12 comprises a plurality of straightening wheels, which in the example described herein are seven, of which some are fixed straightening wheels 12a, integral with the support structure 11, while the others are movable straightening wheels 12b, fixed to a vertically movable carriage, in order to vary the passage gap and therefore the pressure exerted on the metal wire W.

The fixed straightening wheels 12a and the movable straightening wheels 12b define between them a straightening axis which in the illustrated case coincides with the inlet axis Y.

In the example of fig. 1, the straightening wheels 12a, 12b have horizontal rotation axis. According to a possible embodiment, the straightening unit 12 could also be preceded by a further similar straightening unit, but having straightening wheels with axis placed at 90 degrees, i.e. with vertical rotation axis. This further straightening unit is then interposed between the calibration unit 15 and the straightening unit 12. The outlet unit 14, or guiding unit, allows to guide the metal wire, and to perform any further straightening on the metal wire W exiting the drawing unit 14 toward the operating stations of the working machine placed downstream and not illustrated.

The outlet unit 14 comprises a first series of outlet rollers 14a with a horizontal axis and a second series of outlet rollers 14b vertical to them.

The operation of the apparatus 10 described so far, which corresponds to the method according to the present invention comprises at least the following steps: a step of straightening the metal wire W, performed by the straightening unit 12, a step of drawing the metal wire W, performed by the drawing unit 13, and a step of guiding the metal wire W performed by the guiding unit 14 along an outlet axis X.

The method further comprises a calibration step performed by the calibration unit 15 before the straightening step and in which at least two rollers 16, 17 receive the metal wire W between them along the inlet axis Y and exert a longitudinal flattening action on the lateral surface of the metal wire W in order to regularize its cross-section.

It is clear that modifications and/or additions of parts can be made to the apparatus 10 and to the method described above, without departing from the field and scope of the present invention, as defined by the claims.

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 other equivalent forms of an apparatus and a method for straightening a metal wire, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby. In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.