US20030121304A1

US20030121304A1 - Apparatus for the production of stretched wire

Info

Publication number: US20030121304A1
Application number: US10/310,934
Authority: US
Inventors: Carsten Schauhoff; Rene Aschwanden
Original assignee: HA Schlatter AG
Current assignee: HA Schlatter AG
Priority date: 2001-12-07
Filing date: 2002-12-06
Publication date: 2003-07-03
Also published as: CA2411623A1; JP2003236609A; EP1317975A1

Abstract

A stretching machine (21) for the production of discontinuously stretched wire (31) comprises a rolltype straightening mill (22), a first roll-type advancing unit (23), a first clamping device (24), which is capable of being moved on a hydraulic linear booster (25), and a second clamping device (28), to which a cutting device (29) is attached. A pushed-in rolled wire (31) to be stretched is prestraightened by the roll-type straightening mill (22) and is advanced to the second clamping device (28) by the first rolltype advancing unit (23). Subsequently, the wire (31) is held by the two clamping devices (24 and 28), the first clamping device (24) being moved opposite to the push-in direction by the amount of a degree of stretching and correspondingly cold-forming the rolled wire. By means of the apparatus, a favourable yield-point ratio is achieved, the strain properties being maintained. By means of a sensor, the final values of, for example, the steel stress are detected, stored and used for the further production of the stretched wires.

Description

TECHNICAL FIELD

The invention relates to an apparatus for the production of discontinuously stretched wire, with two spaced-apart clamping devices, at least one of which is capable of being moved by the amount of a stretching length. Further, a plant with such an apparatus preceding it is claimed. In addition, the invention relates to methods for the industrial production of discontinuously stretched wire.

PRIOR ART

For structural-steel mats—what are known as reinforcing meshes—cold-rolled steel wire (KR) is mainly used, which is rolled in the incandescent state in the steel mill and is subsequently cold-formed to the desired nominal dimension and ribbed in two stages on a cold-rolling plant. For embossing the ribs, the wire is formed by the amount of 15% to 25%. Cold-formed wires have increased strength, as compared with a rolled wire, but at the same time the material becomes more brittle and the elasticity falls.

The most important characteristic quantities for structural steel and, in particular, for wires in structural-steel mats are predetermined, for example, by the German DIN standard 488. The present-day steel qualities for structural steel consist 100% of scrap, primarily of scrap from motor vehicles, and contain sometimes high alloying fractions of various foreign metals. As a result, the minimum values, required in the standards, for the yield point (R _e) and the tensile strength (R_m) are achieved without any particular outlay. Cold-forming for producing the ribs is no longer required in order to achieve the prescribed strengths. However, it becomes increasingly more difficult to meet the requirements as to the yield-point ratio (R_m/R_e) and the elasticity properties.

Hot-rolled and ribbed steel wire (WR) is rolled in the incandescent state to the nominal dimension. In the last rolled stand, a ribbing is applied to the rolled wire. So that the yield point (R _e) reaches a higher value than is normally afforded in the case of a WR, the WR may be cold-formed in an additional work step. For example, the WR is cold-formed by stretching.

At the present time, three basic types of stretching are employed in practice and can be divided into two main groups. The first main group constitutes continuous stretching, in this case a multiaxial or uniaxial stress being exerted on the wire. Continuous stretching with multiaxial stress is the method adopted most frequently for the production of stretched wire. The wire is drawn through upper and lower rolls which are displaced relative to one another in their axial orientation in such a way that the wire is drawn through these rolls in a serpentine manner. Combination plants, which combine the cold-rolling and stretching operations, are often used for this purpose. In the other method of continuous stretching, a uniaxial stress is applied to the wire. The wire is led around a first roll in the opposite direction and again in the drawing direction over a second roll which is arranged in the opposite direction to the tensile force with respect to the first roll. In the view of the rolls, the wire is led in the form of a horizontal 8. This method for the production of stretched wire is hardly used nowadays because of the high outlay in mechanical terms and the lack of flexibility.

A further possibility for discontinuous stretching with uniaxial stress belongs to the second main group. In this method, the wire is stretched, straightened and cut in a combined manner. Due to what may be referred to as the start/stop mode of operation, this method is appreciably slower than continuous methods.

PRESENTATION OF THE INVENTION

The object of the invention is to provide an apparatus and the associated method which allows a discontinuous stretching of wire at high speeds and with high production reliability.

The solution for achieving the object is defined by the features of claim 1. According to the invention, an apparatus for the industrial production of discontinuously stretched wire has two spaced-apart clamping devices, at least one of which is capable of being moved by the amount of a return stroke and at least one of which is equipped with a sensor for determining the wire stress.

By industrial production is meant production in quantities. This is in contrast to test arrangements, in which individual wires are machined and processed in order to arrive at test results, for example in a destructive test for checking the maximum tensile strength.

The wire is delivered as a rolled-wire bundle in the form of a coil. By means of the one clamping device capable of being moved by the amount of the stretching length, during stretching the wire is simultaneously straightened by virtue of plastic deformation. There is no need for any additional setting work, as in the case of straightening blades or roll-type straightening mills. Further, the wire stress is detected continuously by means of the sensor. The detected values may be stored, assigned to a wire portion. Wire portions produced thereafter are checked merely with regard to their final values. Stretching can automatically be adapted continuously on the basis of statistic evaluations of the measured values. In addition, a stress threshold value may be predetermined, at which the wire portion to be stretched is oriented absolutely straight.

The degree of stretching can thus be programmed continuously. Adaptations on the apparatus when different production lengths are to be produced may therefore be dispensed with. Further, in the event of a change in the diameter of the wire, the apparatus does not have to be converted.

Each wire portion is checked continuously by means of the values detected by the sensor and stored. Material strength fluctuations are detected during production, and the apparatus can be adapted continuously, according to the detected values, to the material to be processed. At the same time, any material faults or rejects are detected by the apparatus during production, and wires of lower quality can be separated out or be removed from the further process for the production of finished products. This prevents the situation where wire portions of lower quality are welded together with wire portions conforming to the standards in order to form structural-steel mats. Any rejects which there may be are merely individual wire portions, not entire structural-steel mats. This leads not only to a material saving, but also to an appreciable time saving in the production of structural-steel mats.

Preferably, means for introducing or advancing the wire in the wire longitudinal direction are provided. As is typical of industrial production, the rolled wire is introduced directly from the rolled-wire bundle into the apparatus according to the invention. In this case, the rolled wire may be shot into the apparatus. The means for introducing or advancing the wire ensures the feed during production, even when a change of the rolled-wire bundle takes place.

In a variant of this, cut-to-length and preferably prestraightened wire portions can preferably be fed from a magazine or storage unit of the apparatus according to the invention transversely to the stretching direction. The wire portions fed in this way are stretched to the apparatus and are subsequently further processed.

On the entry side, the apparatus is preferably provided with a roll-type straightening mill. The latter prestraightens the wire to an extent such that it can be pushed through the apparatus more easily. Preferably, the rolls of the roll-type straightening mill are mounted displaceably, so that the distance between the rolls arranged above and below is adapted to the diameter of the wire preferably by automatic control. For an automatic control of the rolls of the roll-type straightening mill, for example, the first mutually opposite rolls in the push-in direction can be mounted so as to be freely moveable. When the wire is introduced, the rolls are displaced out of their neutral position respectively upwards and downwards according to the diameter of the wire. By means of a separate sensor, the distance between the first two rolls can be detected and the following rolls can be positioned by mechanical control according to this distance. Further, a spring force can act on the displaceable rolls, which exerts on the wire a sufficiently high pressure force for the satisfactory guidance of the wire.

Instead of a roll-type straightening mill, the wire may be bent straight, for example by straightening pressing. Another possibility for prestraightening the wire is a straightening rotor with straightening blocks. Further, the apparatus according to the invention may be preceded by a flat-straightening machine which orients the wire, straight, prior to the stretching. Furthermore, the roll-type straightening mill may be replaced essentially by any apparatus which, for example, at least prestraightens the wire by rolling, drawing or pressing.

Preferably, in the apparatus, a first roll-type advancing unit, a first clamping device, a straightening section and a second clamping device are arranged downstream of the roll-type straightening mill in the direction of advance of the wire. The approximately prestraightened wire is led, by means of the first roll-type advancing unit, out of the roll-type straightening mill and through the first clamping device, the straightening section and the second clamping device. After the two clamping devices retain the wire, the wire is stretched by the at least one moveable clamping device, preferably the first clamping device. By means of the roll-type advancing unit, the wire is transported further on, so that the operation can be repeated for the next wire portion.

In a variant of this, the first roll-type advancing unit may be arranged downstream of the first clamping device in the direction of advance of the wire, the roll-type advancing unit coming to rest within the straightening section. Further, only the second clamping device may be capable of being moved. Further, both, the first and the second, clamping devices may be designed to be moveable.

The straightening section preferably has an adaptable length. For this purpose, for example, the roll-type straightening mill, the first roll-type advancing unit and the first clamping device are combined to form a unit of the apparatus, and the second clamping device is designed as a further unit of the apparatus which is displaceable relative to the first unit. The second unit may be shortened, for example by means of a worm drive, from a predetermined maximum length of the straightening section to any desired dimension. The maximum length of the straightening section is in interrelation with the length of travel of the moveable clamping device, the said travel resulting from the degree of stretching.

In order to simplify the wire transport during the entire production, a second roll-type advancing unit, which assists the wire transport, may be arranged upstream of the second clamping device between the straightening section and the second clamping device. The arrangement of the second roll-type advancing unit may be advantageous particularly in the case of high numbers of cycles of the apparatus. As regards the arrangement of two roll-type advancing units, these are preferably operated synchronously. In a variant, for example, only one of the roll-type advancing units is actively operated and the other roll-type advancing unit corotates passively. The wire can be maintained under prestress by means of the second roll-type advancing unit.

The first clamping device, which is arranged on the entry side and is capable of being moved by the amount of the stretching length, is preferably arranged on a linear hydraulic power booster which can execute freely programmable travels. A rolled wire is stretched preferably by the amount of 3% to 5% in the apparatus according to the invention. The necessary stroke or the executable travel of the first clamping device thus amounts to somewhat more than 5% of the length of the maximum straightening section. Instead of the moveable clamping device on a hydraulic power booster, another tensioning device may also be provided.

Alternatively to this, the second clamping device may be arranged on a linear hydraulic power booster, in this variant the first clamping device arranged on the entry side being arranged fixedly. Further, both clamping devices may be arranged on linear hydraulic power boosters. In such an arrangement, the clamping devices are moved preferably simultaneously away from one another or alternately in opposite directions until the rolled wire has been lengthened by the amount of the desired stretching dimension.

Preferably, a pressure cell is arranged as a sensor on the fixed clamping device. By means of the pressure cell, the stress in the wire during the entire stretching operation and, in particular, the final value for each stretched wire portion is detected. The pressure cell may operate, for example, on the basis of a spring (spring principle) or on the basis of hydraulic pressure (hydraulic principle). The data from the pressure cell are stored in a control unit and are made available for the further production of stretched wire. Discontinuous stretching with simultaneous (online) quality control is made possible by means of the measured and stored values.

The stored final values may be used further for statistic evaluation for the individual stretched wire portions. A stress threshold value may also be defined, which lies unquestionably on the elastic straight line of the stress/strain diagram of the rolled wire, thus ensuring that the wire is oriented absolutely straight and that stretching has commenced.

Further, the apparatus preferably has a cutting unit arranged on the exit side, in order to cut the stretched wire to length. Preferably, the stretched wire is cut to the desired length by means of a cutting device, for example a shear arrangement. As a variant of this, the stretched wire may also be cut to length by means of a cutting torch.

For receiving the cut-to-length wires, a receptacle is preferably arranged at the exit of the apparatus according to the invention, the said receptacle preventing the cut-to-length wires from falling to the ground and making the wires available for further processing. If the apparatus is preceded by a wire-mesh welding machine, the receptacle serves as a material repository or storage region, from which the wires required are extracted by a feed device of the wire-mesh welding machine.

Preferably, the apparatus comprises a control device which sets the stretching length on the basis of the wire stress measured by the sensor. If the total length of the wire portion to be stretched amounts to more than the length of the straightening section, which is determined by the distance between the first and the second clamping device, in a first step the wire portion is lengthened by the amount of the maximum possible stretching length which is in a percentage relation to the straightening section. Subsequently, the wire is advanced by the missing amount of the desired total length and is stretched once again, in the same percentage relation, by an amount which results from the amount of the advance. Preferably, the stretching length is automatically adapted, by means of the control, to the length of the straightening section or of the advance.

The control is typically designed as a module and is not installed permanently in the apparatus. It is thereby possible for the control to be employed, adapted according to the user's requirements or to the local conditions.

Advantageously, a plant with a wire-mesh welding machine is preceded by an apparatus according to the invention for the production of discontinuously stretched wire. Thus, the stretched and cut-to-length wire portions are made available directly to the wire-mesh welding machine for further processing and can be taken over from a wire feed device of the wire-mesh welding machine.

In this case, for example, two apparatuses according to the invention for the production of discontinuously stretched wire may precede a plant having a wire-mesh welding machine. One of the apparatuses according to the invention produces the transverse wires and the other apparatus produces the longitudinal wires. The stretched wires required is [sic] extracted from the corresponding intermediate stores, for example by means of two feed devices of the wire-mesh welding machine, and is [sic] positioned for further processing. By means of such an arrangement, the production times and production costs are lowered decisively, since the components of the two apparatuses and the stretching length can be coordinated with the maximum dimensions of the desired transverse and longitudinal wires, while at the same time a high quality of the stretched transverse and longitudinal wires is ensured.

In the method for the industrial production of discontinuously stretched wire, a wire portion to be machined is gripped by two clamping devices and is stretched. By means of a sensor for measuring the wire stress and of a travel sensor, a stress/strain dependence is recorded. This is stored, assigned to the wire portion, for further processing. In a first step, a new wire is stretched in what may be referred to as a start/stop operating mode, and the stress/strain dependence for this specific wire portion is recorded. Subsequently, the stretching of the further wire portions commences, with the apparatus at full capacity, and only the final values of each individual wire portion are checked. If a measured final value of a stretched wire portion lies outside a predefined tolerance range, the apparatus can be adapted correspondingly or the wire portion having the values lying outside the tolerance is separated out. As a result of this online quality control, production reliability is ensured during the entire production of the wire portions and is improved, as compared with the known methods for a discontinuous stretching of wire portions, and also the quantity of rejects is reduced. There are no wire portions of lower quality welded together with wire portions conforming to the standards, to form structural-steel mats, thus preventing the situation where entire structural-steel mats have to be discarded. This leads not only to a material saving, but also to an appreciable time saving in the production of structural-steel mats.

The method has the advantage that work can be carried out with high numbers of cycles and, compared with previous methods, production reliability is improved. If stretching is regulated by the tensile force, only stretching with low numbers of cycles is possible, since the force changes discontinuously from the commencement of stretching to the desired stretching length. At the same time, the stored values can be printed out for each rolled-wire bundle and also for each wire portion. This print-out may serve as a certificate of quality for the material of structural-steel mats. If the wires are sold on as semi-finished products, the printed-out list or a copy of this may be enclosed as a quality voucher with the wire bundle. A quality control is provided, which satisfies any ISO standard and makes it possible to have reliable evidence of rod production.

In a further method for the industrial production of discontinuously stretched wire, the stretching length for a wire portion is automatically adapted continuously on the basis of statistic evaluations of the stress/strain dependence. Automatic adaptation takes place, for example, via the travel and/or the force. If the steel quality changes or a new rolled wire is introduced into the apparatus, the machine is adapted automatically. By means of this method, operational documentation can be prepared from the production of the wire portions and may be used, on the one hand, for operating-data acquisition and, on the other hand, for quality assurance.

In another method for the industrial production of discontinuously stretched wire, the stretching length for a wire portion is related to a stress threshold value which defines the conclusion of a preflattening phase. In terms of the stress/strain diagram of the rolled wire, a value is defined as a control point on the elastic straight line, the said value ensuring that the wire portion is absolutely straight. First, the wire is flattened. The end of the “gradation phase” can be determined by means of the stress threshold value. A rolled wire delivered as a bundle must first be oriented absolutely straight, so that stretching is carried out in the required size and quality. As soon as the sensor detects that the wire is absolutely straight even at a lower value, where appropriate the stress threshold value can be reduced for the subsequent wire portions.

Preferably, the stress threshold value is determined individually for each wire portion. The sensor detects when the wire is in an absolutely straight position and the applied force is used solely for stretching and no longer straightens the wire.

Typically, in all the methods, the wire is introduced automatically in the wire longitudinal direction and is cut to length automatically after stretching.

Further advantageous embodiments and feature combinations of the invention may be gathered from the following detailed description and from the whole of the patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings used for explaining the exemplary embodiment: [0038]
FIG. 1 shows a stress/strain diagram for a hot-rolled and ribbed wire (WR) in the rolled and stretched state; and [0039]
FIG. 2 shows an exemplary arrangement of a stretching machine according to the invention. [0040]
Identical parts are basically given the same reference symbols in the figures.[0041]

WAYS OF IMPLEMENTING THE INVENTION

FIG. 1 illustrates a stress/strain diagram for a hot-rolled and ribbed wire (WR) in the rolled and stretched state. The strain ε is plotted on the abcissa axis [0042] 2 of the diagram 1 and the stress C is plotted on the ordinate axis 3. The curve 4 illustrates the characteristic curve of a naturally hard steel—here a rolled wire—In the stress/strain diagram. The wire is drawn and reaches its yield point R_e. Up to this point, the steel is in its elastic range and would resume its original length if the tensile force were removed. Beyond the yield point R_e, under a further action of force, the steel begins to flow (what is known as the flow plateau) . At the end of the flow plateau 5, the stress in the steel rises further from the end of the flow plateau 5 to the maximum tensile strength R_m(here also designated as the point 6). The region 7 from the zero point to the yield point Re is designated as elastic strain. The region 8 from the yield point Re to the tensile strength R_m(point 6) is designated as the plastic strain. If, after the tensile strength R_mis reached, further tensile force is exerted on the steel, the stress σ falls and the steel begins to contract at its weakest point until it breaks. As a result of the stretching, the wire is extended into the range of plastic strain (for example up to the point 9). The strain ε of the wire is in this case normally in the range from 3% to 5%. The wire was cold-formed by stretching.
As soon as the stretched wire portion is relieved of stress, the wire portion is minimally shortened, as illustrated by the point [0043] 10. If the stretched wire is loaded once again, the steel behaves essentially the same way as a cold-formed wire on which the ribs and also the reduction in diameter due to elongation have been produced by cold-forming. In contrast to this, however, the stretched WR has better strain properties than a ribbed KR. As a result of the stretching, the WR has a new yield point R_erwhich, in terms of the value of the stress σ, is nearer (by the difference between the yield point R_eand the yield point R_er) to the tensile strength R_mthan in the case of a non-stretched wire. The wire behaves elastically again in the region 11 and plastically in the region 12. A preferred yield-point ratio is achieved by means of the stretching, the better strain properties of the rolled wire being essentially maintained.
On the apparatus according to the invention, mainly wire from rolled-wire bundles in the form of coils is used. The wire introduced into the apparatus is not oriented absolutely straight. Consequently, at the commencement of the application of stress, the characteristic diagram, as illustrated by the curve [0044] 4, is not obtained. Until the wire is oriented absolutely straight, a discontinuous curve 13 is obtained. The actual stretching of the wire commences from the intersection point 14 of the curve 13 with the elastic straight line 15 of the curve 4. A stress threshold value 16 can therefore be defined, which either is determined individually for each wire portion to be stretched or is determined as a fixed value. As soon as, for example, a pressure cell measures the stress threshold value, there is the certainty that the preflattening phase is concluded and actual stretching commences. The stress threshold value 16 amounts, for example, to 200 N/mm², which corresponds approximately to one third of the yield point Re of the wire material. This stress threshold value 16 may be set even higher in the case of sharply bent wire material, in which case the value of the stress threshold value 16 should lie preferably clearly below the value of the yield point Re (<500 N/mm²)
By means of the sensors, all the values can be recorded and are available to the control, on the one hand, for preparing a stress/strain dependence which is stored, assigned to the wire portion, for further processing. On the other hand, the measured values may be used for continuously automatic adaptation of the stretching length on the basis of the statistic evaluation of the stress/strain dependence. Further, the stored values may be printed out and used for operational and/or quality documentation. Further, by means of the stored values, the various phases can be determined computationally from the characteristic curve [0045] 4.
An exemplary arrangement of a stretching machine according to the invention is shown in FIG. 2. The stretching [0046] machine 21 comprises on the entry side (on the left in relation to the drawing) a roll-type straightening mill 22 which is followed by a first roll-type advancing unit 23. There then follows a first clamping device 24 arranged on a hydraulic linear booster 25, on which the first clamping device 24 is capable of being moved horizontally in a controlled manner. These components form a first part 26 of the stretching machine 21. A second part 27 is formed by a second clamping device 28 which comprises a cutting device 29. The second part 27 may comprise, further, a second roll-type advancing unit. By means of the second roll-type advancing unit, for example, the wire 31 can be maintained under prestress, or the said unit serves for assisting the first roll-type advancing unit 23 during the advance of the wire 31.
The length of the straightening [0047] section 32 may be varied, as required, by the stretching machine 21 being divided into a first part 26 and a second part 27 which are capable of being moved relative to one another by means of a separate device (not illustrated here) . In order to move the two parts relative to one another, for example, the first part 26 may be mounted fixedly on a stand and the second part 27 may be fixed, for example, on a worm gear which is operated by means of a motor. The length of the straightening section 32 can consequently be adapted to the production requirements. The straightening section 32 is formed, for example, by a stable steel girder (for example, a U-profile, such as a UNP or UAP) . So that the straightening section 32 can be adapted in its length, for example, two U-profiles are arranged, which are capable of being pushed one into the other and which overlap one another according to the set length. In a variant, the second part 27 may be provided with a recess or be designed in such a way that the steel girder of the straightening section 32 passes through the said second part when the length of the straightening section 32 is shortened by the second part 27 being moved.
The [0048] straightening section 32 begins at the first clamping device 24 and ends at the second clamping device 28. The maximum straightening section 32 may be designed according to the user's wishes or requirements, the maximum stroke of the hydraulic linear booster 25 having to be taken into account. If, for example, the length of the straightening section is 4000 mm and the usual degree of stretching of 3% to 5% is to be carried out, the stroke of the moveable first clamping device 24 must amount to at least 200 mm. If the straightening section 32 is increased, for example, to 8000 mm, the stroke of the moveable first clamping device 24 would therefore have to amount to at least 400 mm according to the length of the straightening section 32. With the means available at the present time, the length of the straightening section 32 is expediently to be limited to below 5000 mm for structural reasons and with a view to the production costs and also on grounds of the serviceability of the stretching machine 21.
If, for example, a wire portion having, for example, a length of 6000 mm is to be produced on a stretching [0049] machine 21 with a maximum straightening section 32 of 4000 mm, the following procedure is adopted: the wire is advanced to the length of 4 000 mm and, in the case of a degree of stretching of 5%, is stretched by the amount of 200 mm. Subsequently, the wire is advanced once again by the amount of 2000 mm and is stretched once more by the amount of 100 mm. A wire portion with a length of 6000 mm, which has been stretched by the amount of 5%, has thus been produced.
The method for producing a discontinuously stretched wire is described below with reference to the stretching [0050] machine 21. The rolled-wire bundles 33.1 and 33.2 are provided on a double horizontal run-off 34 for machining in the stretching machine 21. By the use of a double horizontal run-off 34, for example, the end of the rolled-wire bundle 33.1 can be welded to the start of the rolled-wire bundle 33.2, so that work can be carried out without interruption. After the entire rolled-wire bundle 33.1 has been processed, a new rolled-wire bundle is positioned on the run-off, and, if appropriate, its start is welded to the end of the rolled-wire bundle 33.2. Wire portions can thus be produced in large quantities continuously and without interruption.
The start of, for example, the rolled-wire bundle [0051] 33.1 is introduced or shot into the stretching machine 21 and is prestraightened in the roll-type straightening mill 22 in such a way that it becomes easier for the wire 31 to be pushed through. The wire 31 is thereafter gripped by the first roll-type advancing unit 23 which follows the roll-type straightening mill 22. The first roll-type advancing unit 23 consists of two oppositely directed rolls 35.1 and 35.2, between which the wire 31 is advanced, and of two drives 36.1 and 36.2 which drive the rolls 35.1 and 35.2 in a controlled manner and are preferably coordinated with one another. Instead of two separate drives 36.1 and 36.2, only one drive may also drive both rolls 35.1 and 35.2, for example via a gear. So that different wire diameters can be processed in a stretching machine 21 without any particular outlay, at least the lower or upper rolls of the roll-type straightening mill 22 and of the first roll-type advancing unit 23 are mounted displaceably in one direction, for example in a vertical direction. The neutral position of the rolls corresponds to the smallest wire diameter to be processed (for example, 4 mm), and the minimum latitude of movement of the displaceable rolls must correspond to the largest wire diameter to be processed (for example, 12 mm). The setting of the interspace between the rolls may be carried out passively on the basis of the diameter of the pushed-in wire 31 or actively by mechanical control. In a variant of this, the rolling surfaces of the rolls may be coated with a deformable material which allows the machining of the entire diameter range (for example, 4 mm to 12 mm), without the rolls having to be displaced in one direction.
The [0052] wire 31 is advanced to the second clamping device 28 by means of the roll-type advancing unit 23. The first clamping device 24 and the second clamping device 28 are constructed in essentially the same way. They have at least two clamping jaws 37.1, 37.2 and 38.1, 38.2 which are moveable relative to one another and which clamp the wire 31 located between them. The clamping jaws 37.1, 37.2 and 38.1, 38.2 are moved mechanically or hydraulically in a controlled manner.
The [0053] first clamping device 24 is arranged on a hydraulic linear booster 25 which can execute freely programmable travels. In this exemplary embodiment, the stretching force generated by the linear booster 25 amounts to about 70 kN and makes it possible to stretch a wire having a diameter of 12 mm up to its maximum yield point of about 630 N/mm². The wire 31 to be stretched is held by the first clamping device 24 and the second clamping device 28. Subsequently, the first clamping device is moved, in the clamping state, opposite to the push-in direction by the amount of the desired degree of stretching. The front pair of rolls 35.1 and 35.2 has to rotate opposite to the push-in direction of the wire 31 so that the stretching travel is compensated. The first stretched wire portion is produced in a start/stop operating mode (stop-and-go). As soon as the values for this roll-wire bundle have been detected and stored, the production of the stretched wires takes place. If differences in the measured final values are detected during production, the said differences lying outside the defined tolerance range, the force or the degree of stretching is adapted. At the same time, stretched wires which do not conform to the desired requirements or have material faults can be sorted out and removed from the further production process, for example in the production of structural-steel mats.
In the next work step, the stretched wire is transported further on by means of the first roll-[0054] type advancing unit 23. If two roll-type advancing units are arranged in a stretching machine, these are preferably coordinated with one another (that is to say, synchronously) or operate actively or passively, depending on the position of the wire 31.
Arranged at the [0055] second clamping device 28 is a cutting device 29 which cuts the stretched wire 31 to the desired length, for example by means of a shear device.
In a further method for the industrial production of discontinuously stretched wire, the stretching length for a wire portion is automatically adapted continuously on the basis of statistic evaluations of the stress/strain dependence. The statistic evaluation is based on an average value which is prepared on the basis of a predefined number of, for example, fifty wire portions having measured and stored values. The automatic adaptation of the stretching length may in this case take place, for example, via the travel and/or the force. If the steel quality changes or a new rolled wire is introduced into the apparatus, the machine is adapted automatically. By means of this method, operational documentation can be prepared from the production of the wire portions and may be used, for example, for operating-data acquisition or for quality assurance. [0056]
In another method for the industrial production of discontinuously stretched wire, the stretching length for a wire portion is related to a stress threshold value which defines the conclusion of a preflattening phase. In terms of the stress/strain diagram of the rolled wire, a value is defined as a control point on the elastic straight line and ensures that the wire portion is absolutely straight. Such a stress threshold value lies in the range of 200 N/mm[0057] ²and 500 N/mm²in the case of wire material which is used for the production of structural-steel mats and which conforms to the critical standards. First the wire is stretched. When the stress threshold value is reached, the end of the “gradation phase” is determined. A rolled wire delivered as a bundle must first be oriented absolutely straight, so that stretching is carried out in the required size and quality. As soon as the sensor detects that the wire is absolutely straight even at a lower value, if appropriate the stress threshold value can be reduced for the subsequent wire portions. The advantage of this is that the number of cycles of the apparatus and therefore the quantity of stretched wire produced are increased. When the stress threshold value is reached, the stretching of the wire portion, until the desired final value is reached, can commence. The number of cycles of the apparatus according to the invention is based on the cycle time for the production of a wire portion, which is composed of the advance of the wire portion, the clamping of the two clamping devices, the stretching stroke and the opening of the clamps and also the sum of the intermediate times. The method according to the invention makes it possible to have discontinuous stretchings which, for example for a wire-portion length of 2000 mm, allow a number of cycles of 110 off/min (=3.66 m/s).
For a change of diameter, the [0058] wire 31 is drawn back completely and the new wire is pushed or shot into the stretching machine 21. Owing to the described adaptable components of the individual devices, manual adaptations of the individual devices of the stretching machine can be dispensed with, thus appreciably increasing the productivity of the stretching machine, as compared with the prior art. The change of diameter can be automated by simple means.
A further possibility for increasing productivity is the arrangement of two units which are connected in parallel. The two units can be operated by means of only one hydraulic assembly. [0059]
The stretching [0060] machine 21 may be used both as a stand-alone solution and as an integration in a plant for the production of structural-steel mats, the stretching machine preferably preceding the actual plant. That is to say, the wires stretched in the stretching machine are made available directly to the plant for the production of structural-steel mats and are taken over by the latter for further processing.
In conclusion, it must be stated that an apparatus and associated methods have been provided, which combine the stretching and straightening operations and allow discontinuous stretching with an industrially acceptable number of cycles, at the same time with quality control. [0061]

Claims

1. Apparatus for the industrial production of discontinuously stretched wire (31), with two spaced-apart clamping devices (24 and 28), at least one (24) of which is capable of being moved by the amount of a stretching length, characterized in that at least one of the said clamping devices (24 or 28) is equipped with a sensor for determining the wire stress.

2. Apparatus according to claim 1, characterized in that means for introducing or advancing the wire in the wire longitudinal direction are provided.

3. Apparatus according to claim 1, characterized in that it is provided on the entry side with a roll-type straightening mill (22).

4. Apparatus according to claim 3, characterized in that a first roll-type advancing unit (23), a first clamping device (24), a straightening section (32) and a second clamping device (28) are arranged downstream of the roll-type straightening mill (22) in the direction of advance of the wire.

5. Apparatus according to claim 4, characterized in that a second roll-type advancing unit is arranged between the straightening section (32) and the second clamping device (28).

6. Apparatus according to claim 4, characterized in that the first clamping device (24) is arranged on a linear hydraulic power booster (25).

7. Apparatus according to claim 5, characterized in that the first clamping device (24) is arranged on a linear hydraulic power booster (25).

8. Apparatus according to claim 1, characterized in that a pressure cell is arranged as a sensor on the fixed clamping device (28).

9. Apparatus according to claim 1, characterized in that it has on the exit side a cutting unit (29) for cutting the stretched wire (31) to length.

10. Apparatus according to claim 8, characterized in that it has on the exit side a receptacle for the intermediate storage of the cut-to-length stretched wire (31).

11. Apparatus according to claim 1, characterized in that it comprises a control device which sets the stretching length on the basis of a measured wire stress.

12. Plant with a wire-mesh welding machine and with a preceding apparatus (21) for the production of discontinuously stretched wire (31), with two spaced-apart clamping devices (24 and 28), at least one (24) of which is capable of being moved by the amount of a stretching length, characterized in that at least one of these is equipped with a sensor for determining the wire stress.

13. Method for the industrial production of discontinuously stretched wire, a wire portion (31) to be machined being gripped by two clamping devices (24 and 28) and being stretched, characterized in that, by means of a sensor for measuring the wire stress and of a travel sensor, a stress/strain dependence is recorded, and in that the latter is stored, assigned to the wire portion, for further processing.

14. Method for the industrial production of discontinuously stretched wire, a wire portion (31) to be machined being gripped by two clamping devices (24 and 28) and being stretched, characterized in that, by means of a sensor for measuring the wire stress and of a travel sensor, a stress/strain dependence is recorded, and in that the stretching length is automatically adapted continuously on the basis of statistic evaluations of the stress/strain dependence.

15. Method for the industrial production of discontinuously stretched wire, a wire portion (31) to be machined being gripped by two clamping devices (24 and 28) and being stretched, characterized in that, by means of a sensor for measuring the wire stress and of a travel sensor, a stress/strain dependence is recorded, and in that the stretching length is related to a stress threshold value which defines the conclusion of a preflattening phase.

16. Method according to claim 15, characterized in that the stress threshold value is determined individually for each wire portion (31).

17. Method according to one of claims 13 to 16, characterized in that the wire (31) is introduced automatically in the wire longitudinal direction and is cut to length automatically after stretching.