Note: Descriptions are shown in the official language in which they were submitted.
CA 02411623 2002-11-13
Apparatus for the production of stretched wire
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 15o 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 1000 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 (Re) and the tensile
strength (Rm) are achieved without any particular
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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
s point ratio (Rm/RP) 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 (Re) 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
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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 t.o what may be referred
to as the start/stop mode c>f operation, this method is
appreciably slower than continuous methods.
Presentation of the invention
The obj ect 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
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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
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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.
Tn 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
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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.
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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
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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 5o 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 50 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
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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
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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, i.n
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
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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
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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 cyc7_es 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 ware portions and may be used, on the
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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.
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Brief description of the draraings
In the drawings used for explaining the exemplary
embodiment:
Fig. 1 shows a stress/strain diagram for a hot-
rolled and ribbed wire (WR) in the rolled and
stretched state; and
Fig. 2 shows an exemplary arrangement of a
stretching machine according to the
invention.
Identical parts are basically given the same reference
symbols in the figures.
Ways of implementing the invention
Figure 1 illustrates a stress/strain diagram for a hot-
rolled and ribbed wire (WR) in the rolled and stretched
state. The strain s is plotted on the abcissa axis 2 of
the diagram 1 and the stress a 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 Re. 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 Re, 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 Rm (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
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the tensile strength Rm (point 6) is designated as the
plastic strain. If, after the tensile strength Rm is
reached, further tensile force is exerted on the steel,
the stress 6 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 s of the wire is in this case normally in the
range from 3o to 50. 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 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 Rer which, i.n terms of the value
of the stress a, is nearer (by the difference between
the yield point Re and the yield point Rer) to the
tensile strength Rm than 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 4,
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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/mm'~, 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/mm') .
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 4.
An exemplary arrangement of a stretching machine
according to the invention is shown in Figure 2. The
stretching machine 21 comprises on the entry side (on
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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 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 2.7 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
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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 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
4 000 mm and the usual degree of stretching of 3o 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 8 000 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 5 000 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 6 000 mm is to be produced on a stretching
machine 21 with a maximum straightening section 32 of
4 000 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 stretr_hing of 50, is stretched by the
amount of 200 mm. Subsequently, the wire is advanced
once again by the amount of 2 000 mm and is stretched
once more by the amount of 100 mm. A wire portion with
a length of 6 000 mm, which has been stretched by the
amount of 50, has thus been produced.
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The method for producing a discontinuously stretched
wire is described below with reference to the
stretching 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 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 2.3 are mounted displaceably in
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6 December 2001 Patentanwalte AG
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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 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 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. Subse~~uently, the first clamping
device is moved, in the clamping state, opposite to the
push-in direction by the amount of the desired degree
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6 December 2001 Patentanwalte AG
CA 02411623 2002-11-13
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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-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 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
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6 December 2001 Patentanwalte AG
CA 02411623 2002-11-13
- 22 -
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.
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 st:ress/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/mm2 and 500 N/mm2 in
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.
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6 December 2001 Patentanwalte AG
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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 2 000 mm, allow a number of
cycles of 110 off/min (= 3.66 m/s).
For a change of diameter, the 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.
The stretching 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
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6 December 2001 Patentanwalte AG
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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.
WR/JK/pe-25114 Keller & Partner
6 December 2001 Patentanwalte AG
