Field of the invention
[0001] The present invention is directed to a method of manufacturing reinforcement steel
for reinforcement of concrete structures, said reinforcement steel having an elongated
shape of arbitrary length and cross-section, said method comprising the steps of:
providing a steel base wire; and rolling the steel base wire for modifying a cross-sectional
dimension thereof, and for creating a bonding profile on a surface of said wire.
[0002] The invention is further directed to an apparatus for use in a method as described
above, and to a manufacturing arrangement for performing the method described. Moreover,
the invention is directed at reinforcement steel manufactured using a method as described.
Background
[0003] Roughly since the second half of the twentieth century, concrete has become the preferred
choice of building material for building all kinds of structures. Its popularity is
evidently based on the fact that it is conveniently mouldable in any preferred shape
(enabling for example prefabrication) while at the same time it provides a very strong
and durable building material.
[0004] An important factor in providing the strength and robustness of concrete is the use
of embedded reinforcement steel inside the concrete. The reinforcement steel for example
determines how well a concrete structure can withstand vibrations or shocks. To this
end, the industry and governmental bodies have defined standards for the use of various
kinds of reinforcement steel for different purposes. For example, an office building
in an arbitrary environment and subject to average weather and geologic conditions
(i.e. a low risk area) may safely be build using concrete with reinforcement steel
having relatively relaxed properties with respect to its yield strength. On the other
hand, a highway bridge to be built for spanning a ravine in an area where earthquakes
are known to happen from time to time, must be designed to withstand the most extreme
conditions. Such a bridge may be built using concrete with reinforcement steel with
excellent properties with respect to tensile strength and yield strength.
[0005] Since the production method of reinforcement steel plays an important role in determining
the properties of the end product, until recently, the European standards for reinforcement
steel distinguished the reinforcement steel types based on their manner of manufacturing.
As known to the skilled person, if reinforcement steel is manufactured and rolled
at high temperatures in a blast-furnace, the properties with respect to the capacity
to withstand vibrations and tensile forces improve. Therefore, the former classification
well distinguished the high-grade reinforcement steel types from the lower-grade types.
However, this manner of standardizing also comes with disadvantages. For example,
although one would expect that the furnace based production methods usually provide
high-grade metals, the classification leaves room for errors - i.e. furnace manufactured
reinforcement steel being of accidental low-grade due to errors in the production
process. Moreover, this standardisation only enabled the definition of two classes,
being FeB500HKN (low grade) and FeB500HK/HWL (high grade) where the indications HKN,
HK and HWL indicated the production process.
[0006] Since recently, the standardization has been adapted and is now only based on the
properties of the end product. The existing European norms presently categorizes reinforcement
steel types in three different ductility classes, being B500A, B500B and B500C, where
the classes A and B more or less correspond to the earlier two classes and the additional
class B500C is a new class indicating very high grade reinforcement steel. Where the
number 500 in fact indicates the mandatory yield strength of the reinforcement steel
(which must be 500 MPa or higher), the classes further define the property ranges
in terms of two parameters: the tensile strength to yield strength ratio R
m/R
e, and the percentage uniform elongation at maximum force A
gt. These latter two parameters are different for each of the classes B500A, B500B and
B500C.
[0007] Existing methods for production of reinforcement steel are not really different from
how it has been done for years; only the standardization has changed. This comes to
no surprise, since the technical reality has not changed either. It is still furnace
based manufacturing methods that enable to provide reinforcement steel types that
satisfy the requirements of high grade steel types in classes B500B and C. The cold
methods performed at room temperatures on steel base wire give rise to micro fractures,
making the steel more prone to metal fatigue. An example of such a micro fracture
can be seen in figure 6 (inside the white circle), which provides a photo taken with
a scanning electron microscope of a micro fracture at the surface of a reinforcement
steel wire. In this respect, it is to be noticed that the cold methods differ from
the furnace based methods in that the rolling step for imprinting a profile on the
wire is performed outside a furnace. In the furnace based methods, the rolling step
is performed inside a furnace and an axial stretching step is performed after leaving
the furnace.
[0008] A disadvantage of the present manufacturing methods for making high grade reinforcement
steel of class B500B, however, is that furnace based processing steps leave a thin
oxidation layer on the surface of the reinforcement steel. By performing the rolling
process inside the furnace, causes the reinforcement steel to have an irregular cross-sectional
shape. This is known to be problematic when the reinforcement steel is later processed
after manufacturing (e.g. when being lashed or otherwise handled by a client). On
the other hand, the existing cold processes only yield low grade reinforcement steel
types, and cannot be applied for achieving the more stringent requirements in terms
of material properties required for B500B type steel.
Summary of the invention
[0009] In view of the above, it is an object of the present invention to provide a method
of manufacturing high grade reinforcement steel that may be performed at low temperatures,
preferably room temperature. It is a further object of the invention to provide such
a method enabling at least the production of reinforcement steel satisfying the standard
for B500B type steels.
[0010] The above mentioned objects of the invention are achieved in that there is provided
a method of manufacturing reinforcement steel for reinforcement of concrete structures,
said reinforcement steel having an elongated shape of arbitrary length and cross-section,
said method comprising the steps of: providing a steel base wire; and rolling the
steel base wire for modifying a cross-sectional dimension thereof, and for creating
a bonding profile on a surface of said wire, wherein said step of rolling is a cold
rolling step; characterized in that, prior to the step of rolling, the method further
comprises a step of: surface layer breaking for breaking of a surface layer, and surface
cleaning of said steel base wire for removing the surface layer from said steel base
wire; and wherein, subsequent to said step of rolling, the method further comprises
a step of applying a plurality of bending actions to the steel base wire for improving
tensile properties thereof, such as to provide said reinforcement steel having a tensile
strength to yield strength ratio R
m/R
e of at least 1,08, and having a percentage uniform elongation at maximum force A
gt of at least 5,0.
[0011] The threshold properties for providing B500B type standardized reinforcement steel
is that the parameter tensile strength to yield strength ratio R
m/R
e of the reinforcement steel is at least 1,08 as presently defined, and that the percentage
of total or uniform elongation at a maximum force A
gt is at least 5,0. For reinforcement steel on a roll the latter, the uniform elongation
at a maximum force A
gt, must even be 5,5. As will be appreciated although these thresholds are not expected
to be redefined in the future, these thresholds are merely definitions following from
agreement between industry and governmental bodies which maybe subject to change.
[0012] The inventive concept surprisingly has found a manner of fabricating high grade reinforcement
steel satisfying the requirements for at least class B500B, wherein the step of rolling
of the reinforcement steel may be performed at low temperatures (i.e. outside (or
after the steel base wire has left) the furnace). The inventive manner as described
above is based on insight in the material processes taking place in a steel wire upon
bending the wire. The inventors have recognised that after applying just a few bending
actions the properties of the metal wire in terms of the above mentioned parameters
will in fact improve. This can surprisingly be applied successfully to such an extend
that it becomes possible to create reinforcement steel falling within the class requirements
for B500B. This process enables to improve the properties of steel base wire in such
a manner that a B500B class type reinforcement steel wire may be achieved using a
cold process. Whereas existing methods for manufacturing these kinds of reinforcement
steel rely on a hot rolling step inside a furnace, as will be appreciated, the inventive
cold process provides an important technological advantage which allows the reinforcement
steel to be produced having a more accurately defined cross-sectional shape. Preferably,
the bending actions are applied to the steel base wire after the step of rolling the
steel base wire has been concluded.
[0013] By definition, whether a rolling process is either a cold rolling process or a hot
rolling process is determined by the temperature at which the rolling process takes
place in relation to the recrystallization temperature of the kind of steel to be
rolled at the given ambient pressure. A cold rolling process, such as the rolling
step used in the method of the present invention, takes place at a temperature below
the recrystallization temperature of the steel. Any temperature below the recrystallization
temperature at the given ambient pressure will be suitable, including atmospheric
pressures and temperatures (these are evidently most preferred).
[0014] The advantages of the method of the present invention are evident. This is due to
the fact that heating of the wire in a furnace leaves a thin and irregular layer of
metal oxide on the surface of the steel wire. When rolling is performed inside the
furnace, the oxidation surface layer will be present on the outer surface of the acquired
shape provided by the rolling mill. This weak brittle surface layer easily comes off
the surface of the wire in use, yielding a reinforcement steel wire with a slight
irregular shape. By performing the rolling step outside the furnace, the oxidation
layer already comes off upon cold handling of the steel base wire, and the shape is
imprinted more accurately. The subsequent bending actions allow to achieve the material
properties required for B500B type steel. A further advantage of the invention is
that the process requires less steps and is overall more easy to perform than a furnace
based process.
[0015] Conventionally, the oxidation layer is at least partly removed at some point during
the process by performing a surface layer breaking step, regardless of whether the
process is a cold or warm production process. In accordance with the invention, a
further improvement of the production process has surprisingly be found. In accordance
with a specific embodiment of the present invention, a further improvement of the
method is achieved by performing an additional step of surface cleaning prior to the
step of rolling, for removing a surface layer such as an oxidation layer from the
steel base wire. This step of surface cleaning, although the specific type of surface
cleaning may be chosen freely by the skilled person, may comprise for example a step
of brushing, polishing, spooling of the wire, a chemical treatment such as staining
or a high pressure fluid jet for cleaning the wire. The conventional surface breaking
step removes the major part of the oxidation layer, however, it will leave remnants
of the oxide layer on the surface of the steel base wire. Upon performing the cold
rolling step, the rolling process pushes these small remnant parts of the oxidation
layer into the steel underneath the surface, creating very small micro fractures,
such as depicted in figure 6 (inside the white circle). These micro fractures have
a negative effect on the strength of the reinforcement steel created.
[0016] The inventors have recognized that the properties with respect to metal fatigue of
the reinforcement steel are greatly improved by complete removing the oxidation layer
prior to rolling of the steel base wire, which may be achieved by performing an additional
cleaning step in addition to the surface breaking step.
[0017] By removing the oxidation layer using an additional step of surface cleaning, the
above mentioned effect is prevented from happening, yielding a stronger end product
which is less prone to metal fatigue. As a result, the requirements of the high grade
class B500B are more easily achieved using a cold process in accordance with the present
invention, including the additional surface cleaning step.
[0018] As described above, the properties of the reinforcement steel rods of the present
invention with respect to tensile strength to yield strength ratio and percentage
uniform elongation at maximum force, are sufficiently improved for producing reinforcement
steel rods of grade B500B and better using a cold rolling process in accordance with
the method steps of the invention. However, although the obtained performance is good
with respect to the these material properties, the cold rolling step that is applied
for imprinting the profile diminishes the performance with respect to metal fatigue
in comparison with conventional hot rolling processes. Imprinting the desired bonding
profile on the surface of the steel wire in a cold rolling mill unit introduces sharp
edges and areas of tensile stress on the surface of the wire. These sharp edges and
areas of tensile stress have a negative effect on the strength of the reinforcement
steel wire created. Cracks promulgate easily in areas of tensile stress because the
tensile stresses are already working to pull the atoms of the metal apart. The sharp
edges and corners of the imprinted profile act as potential starting points for cracks.
This problem appears to be absent or in hot rolling processes.
[0019] The requirements with respect to metal fatigue for reinforcement steel rods for building
purposes are stringent. The table below provides the requirements with respect to
metal fatigue for reinforcement steel rods having a diameter D≤28mm (table 1) and
D>28mm (table 2). The term 2*σ
a relates to the amount of stress applied during the tests.
[0020] D≤28mm:
Table 1
2*σa = 175 MPa |
2*σa = 200 MPa |
Number of samples: 10 2) |
Number of samples: 8 2) |
No. of actions *106 |
No. broken samples |
No. of actions *106 |
No. broken samples |
< 1,5 |
None allowed |
< 0,75 |
None allowed |
< 2,0 |
≤ 1 sample |
0,75 ≤ n <1,0 |
≤ 1 sample |
≥ 2,0 |
≥ 9 samples |
1,0 ≤ n < 2,0 |
≤ 2 samples 1) |
|
|
≥ 2,0 |
≥ 5 samples |
1) ≤ 3 samples in case no break occurred at up to 1,0 * 106 applied action |
2) Total number of samples: 10 + 8 = 18 |
[0021] D>28mm
Table 2
2*σa = 145 MPa |
2*σa = 170 MPa |
Number of samples: 10 2) |
Number of samples: 8 2) |
No. of actions *106 |
No. broken samples |
No. of actions *106 |
No. broken samples |
< 1,5 |
None allowed |
< 0,75 |
None allowed |
< 2,0 |
≤ 1 sample |
0,75 ≤ n <1,5 |
≤ 1 sample |
≥ 2,0 |
≥ 9 samples |
1,5 ≤ n < 2,0 |
≤ 2 samples 1) |
|
|
≥ 2,0 |
≥ 4 samples |
1) ≤ 4 samples in case no break occurred at up to 1,5 * 106 applied action |
2) Total number of samples: 10 + 8 = 18 |
[0022] The method of the present invention, in accordance with a preferred embodiment, comprises
a step of shot peening of the steel base wire subsequent to applying the bending actions.
The inventors have recognized that the material properties with respect to metal fatigue
of the cold rolled reinforcement steel rods are greatly improved by performing the
step of shot peening.
[0023] Shot peening is a cold-working process in which the rolled wire is bombarded with
small spherical media called shot. By shot peening the material a layer of compressive
stress is introduced by compacting the material. As the shot peening is performed,
the atoms on the surface of the metal become crowded, i.e. locally concentrated, and
try to restore the metal's original shape, i.e. the original lattice structure, by
pushing outward. The atoms deeper into the metal are pulled toward the surface by
their bonds with the atoms in the compressive layer. These deeper atoms resist the
outward pull creating internal tensile stress that keeps the part in equilibrium with
the compressive stress on the surface. On the other hand tensile stress near the surface
is relieved by the step of shot peening. Moreover the sharp edges and corners of the
profile are rounded. The latter reduces the number of cracks and microfractures that
may occur in these locations, while the reduced tensile stress near the surface decreases
the chance that any micro fractures may propagate. As a result, the requirements of
the high grade class B500B are more easily achieved using a cold process in accordance
with the present invention, including the additional shot peening step.
[0024] Tests were performed on two reinforcement steel samples manufactured with process
embodiments as described herein with and without a step of shot peening. Using a working
stroke ('Schwingbreite', applied stress) of 260 MPa. the sample created without a
step of shot peening was destroyed as a result of metal fatigue after approximately
600.000 stroke cycles. The sample created using the process including shot peening
was put to the same test with the same working stroke; however this latter sample
survived over 10.000.000 stroke cycles without breaking, after which the test was
stopped leaving the reinforcement steel in tact.
[0025] In the method of the present invention, a number of cold-working process steps are
combined in a specific sequence. By combining these steps in the sequence indicated,
a high-grade type reinforcement steel wire may be obtained that is conventionally
only obtainable using a hot rolling process.
[0026] In accordance with a second aspect of the present invention, there is provided an
apparatus for applying a plurality of bending actions to a steel base wire in a manufacturing
method in accordance with the first aspect, said apparatus comprising a plurality
of consecutive roller wheels arranged in a single plane of rotation, wherein each
roller wheel is rotatable by means of a shaft such as to be rotatable in the plane
of rotation of the plurality of roller wheels, said roller wheels being placed such
that in use for providing the bending action the steel base wire is moved across or
with at least a part of the circumference of each wheel.
[0027] In accordance with a third aspect of the invention there is provided a manufacturing
arrangement, for the manufacturing of reinforcement steel using a method in accordance
with the first aspect, said arrangement comprising: a lead-in unit for receiving a
steel base wire; and a rolling mill unit for a rolling the steel base wire for modifying
a cross-sectional dimension thereof, and for creating a bonding profile on a surface
of said wire; said arrangement characterized by further comprising an apparatus in
accordance with the second aspect for applying a plurality of bending actions to the
steel base wire for improving tensile properties thereof, such as to provide said
reinforcement steel having a tensile strength to yield strength ratio R
m/R
e of at least 1,08, and having a percentage uniform elongation at maximum force A
gt of at least 5,0.
[0028] The invention in accordance with the fourth aspect provides reinforcement steel manufactured
using a manufacturing method as described above.
Brief description of the drawings
[0029] The invention will further be elucidated by description of some specific embodiments
thereof, making reference to the attached drawings, wherein:
Figure 1 schematically provides an overview of the method steps of the present invention;
Figure 2 schematically illustrates the steps of brushing and rolling of a steel base
wire which may be used in accordance with the method of the present invention;
Figure 3 schematically illustrates an apparatus for applying bending actions in accordance
with the present invention;
Figure 4 schematically illustrates how the rollers of the apparatus for applying and
bending actions maybe adjusted relative to each other, in accordance with the present
invention;
Figure 5 illustrates a manufacturing arrangement in accordance with the present invention;
Figure 6 provides a photo taken with an electron microscope of a micro fracture in
the surface of a steel wire.
Detailed description
[0030] Figure 1 illustrates a method in accordance with the present invention. The method
that starts in step 2 with the providing of a steel base wire e.g. to a production
line in accordance with the present invention. The steel base wire itself is usually
created using a furnace based process which leaves, as an undesired side-effect, a
thin irregular oxidation layer on the surface thereof. In step 3, the surface layer
is broken, e.g. by twisting or vibrating the wire. In step 4, a further step of surface
cleaning is performed in order to remove the oxidation layer from the surface of the
steel base wire. Although the description below implements the step of surface cleaning
by a step of brushing of the steel base wire, the skilled person will appreciate that
many alternatives exist for performing a surface cleaning step, including but not
limited to polishing, spooling, chemical cleaning e.g. by applying a stain or coating,
or blowing using a high pressure fluid (such as air of water).
[0031] In step 6, a rolling action is performed on the steel base wire from a plurality
of sides, for modifying the shape of the cross section or a dimension thereof (i.e.
decreasing its diameter), and for imprinting a bonding profile on the surface of the
wire. The bonding profile is important for providing a good bonding between the concrete
and the reinforcement steel in use.
[0032] After the step of rolling of the steel base wire, the method in accordance with the
present invention continues by a step 8 of applying a plurality of bending actions
to the steel base wire for improving the tensile properties thereof. The bending actions
are performed in the strain hardening regime of plastic deformation of the wire. As
will be appreciated, this process maybe controlled in a number of ways, e.g. by increasing
the number of bending actions while decreasing the intensity of the bending actions.
It has been found that applying a multiple of five bending actions provides good results
with the method of the present invention. However, this should not be considered as
a limitation to the invention and desired results may be achieved upon applying a
total of three, four, six, seven, eight, or any other number of bending actions.
[0033] After applying the bending actions in step 8, the method of the present invention
continues by applying a shot peening process step 9. The shot peening step 9 improves
the properties of the reinforcement steel amongst others with respect to metal fatigue,
by bombarding the surface with spherical media. This relieves tensile stress near
the surface and rounds the corners and edges of the profile, making the reinforcement
steel less prone to metal fatigue. The method then continues by winding the reinforcement
steel on a spindle in step 10, after which a manufacturing method is completed (12).
[0034] The steps 4 and 6 are schematically illustrated in figure 2. A steel base wire 15
moved in the direction of arrow 16 through a cleaning unit 17 and through a rolling
mill unit 30. The surface cleaning unit 17 exists, in the present embodiment, of three
steel brushes 18, 19 and 20. On the circumferential surfaces of the steel brushes
18, 19 and 20 a plurality of brush hairs generally indicated by reference numeral
23 on brush 18 extend radially there from. The brush hairs 23 strike upon rotation
of the brushes 18, 19 and 20 in the direction indicated for example by arrows 25 and
26 on the surface of the steel base wire 15, removing the oxidation layer. Good results
have been achieved by rotating the brushes 18, 19 and 20 in counter direction to the
direction of movement of the steel wire 15. This is indicated by the arrows 25 and
26. As will be appreciated, the brushes 18, 19, and 20 may also rotate in the other
direction, and the number of brushes may differ from what is indicated in figure 2.
Instead of or in addition to steel brushes, a plurality of polishing brushes may be
applied.
[0035] In rolling mill unit 30 a plurality of rollers 33, 34 and 35 circumferentially apply
a rolling action to the surface of the steel base wire 15. Each of the rollers 33,34
and 35 comprises a slightly rounded inward shape such as is indicated for roller 35
in the dashed circle 40 by reference numeral 42. In addition, the circumferential
sides of each of the rollers 33, 34 and 35 is comprised of a plurality of surface
structures 43 which create the desired bonding profile on the surface of the steel
wire 15 by imprinting the pattern on the surface thereof. Arrows 37 and 38 indicate
the direction of rotation of roller wheels 33 and 35. Roller wheel 34 rotates in a
corresponding direction as roller wheels 33 and 35.
[0036] Figure 3 schematically illustrates an apparatus for applying a plurality of bending
actions in accordance with the present invention. This apparatus maybe used for applying
step 8 in the method illustrated schematically in figure 1. The apparatus consists
of a frame 46 which is fixedly connected to the ground 48 such as to prevent moving
thereof in use. Extending from the base structure 46 an additional top structure 50
is present for supporting a second suspension unit 52 in an adjustable manner as will
be explained below.
[0037] The bending actions itself are applied by a plurality of roller wheels 57, 58, 59,
60 and 61. The roller wheels are rotatable in a single plane of rotation, and are
alternately suspending from shafts at either a first or a second height. The shafts
extend transverse to the plane of rotation from a respective first or second suspension
53, 52. The roller wheels 57, 59, 60 and 61 are suspended from shafts from a first
height. These shafts are in turn rotatably or operationally connected to a first suspension
unit 53 attached to the frame structure 46 of the apparatus 45. The roller wheels
58 and 60 are suspended from shafts that are in turn operatively connected to a second
suspension unit 52 which is adjustably suspended from the top frame structure 50 of
the apparatus 45. The adjustable suspension of the second suspension unit 52 is provided
by a hydraulic cylinder 55 which allows for adjusting the heights of roller wheels
58 and 60 above the level of roller wheels 57, 59 and 61 as will be explained below
in connection with figure 4.
[0038] In order to apply the bending action, the sum of the radiuses of each two consecutive
roller wheels 57-61 will be at least equal to or greater than the height of the shafts
of wheels 58 and 60 above the level of the shafts of wheels 57, 59 and 61. In terms
of the wording used in connection with figure 4, the sum of the radiuses of two consecutive
wheels (e.g. r
1 and r
2 in figure 4) is greater than or equal to the pitch distance d
1. In test performed by the inventors, working with five roller wheels, good results
have been achieved using wheels having a diameter of 150 mm (i.e. r=75 mm), a height
d
1 ∼ 50 mm and a pitch distance d
2 = 150 mm. In addition, good results have been achieved with r = 125 mm, d
1 ∼ 50 mm, and d
2 = 250 mm, and with r = 130 mm, d
1 = 70 mm, and d
2 = 250 mm. As will be appreciated, these are mere test results, and the invention
can be applied across a much wider range of values for r, d
1 and d
2.
[0039] In general, it is important that a number of bending actions is applied, while the
exact number of bending actions, and the intensity of each bending action (determined
by r, d
1 and d
2) will differ dependent on the type of steel and should be determined experimentally
(e.g. by trial and error). The invention is not to be interpreted as limited to a
particular choice of these parameters. To this end, it is also important to mention
that the above dimensions have been used for the embodiment as illustrated in figure
3. However, performing bending action may be performed in a different manner than
as specifically illustrated in figure 3. The skilled person will appreciate that a
wire may be moved across the outer circumferences of a number of wheels having smaller
dimensions, instead of the illustrated embodiment wherein the wire moves in between
the consecutive wheels. Moreover, the bending actions may not even be performed all
in a single plane of rotation.
[0040] In use, the steel base wire 15, after leaving the roller mill unit 30, will be guided
via pulleys 64 and 65 to the roller wheels 57, 58, 59, 60 and 61. Each roller wheel
57-61 will apply a single bending action to the steel base wire 15 as indicated in
figure 3. After applying the bending actions the steel base wire 15 is guided via
pulleys 66 and 67 to a spindle (not shown in figure 3).
[0041] Figure 4 schematically illustrates how the rollers wheels of the apparatus for applying
the bending action 45 maybe adjusted in use. As schematically illustrated in figure
4, each of the rollers 57, 59 and 61 suspends from a corresponding shaft 77, 79 and
81, and the midpoints of the shafts 77, 79 and 81 are aligned on a notional first
line 70. Roller wheels 58 and 60 are suspended from shafts 78 and 80 which are in
turn aligned on notional second line 72. The height between the first line 70 and
the second line 72, d
1, is adjustable by means of the second suspension unit 52 and the hydraulic cylinder
55. In addition, each of the shafts 77, 78, 79, 80 and 81 is respectively connected
to the first or second suspension unit 53 or 52 in such a manner that the position
of the shaft along either the first line 70 or the second line 72 may be adjusted
such as to adjust the distance d
2 between each to consecutive rollers. Moreover, the suspension of each of the roller
wheels 57-61 from the shafts 77-81 is such that the roller wheels 57-61 are connected
in a releasable manner such as to allow replacement of the roller wheels 57-61 by
different roller wheels. This may be used for adapting the diameter of the wheels.
As will be appreciated the manner in which apparatus 45 allows for adjustment of the
various dimensions of the roller wheels 57-61 and their suspension relative to each
other, allows for accurate dimensioning of the bending actions applied by the apparatus
during the manufacturing method.
[0042] Figure 5 schematically illustrates a manufacturing arrangement in accordance with
the present invention disclosing a first spindle 92 comprising a steel base wire which
is fed to the arrangement at the input thereof. Prior to the surface cleaning step,
surface layer breaking unit 93 twists or vibrates the wire such as to break and partly
remove the brittle oxidation layer on the surface. Instead of vibrating or twisting,
the steel base wire may already be moved across one or more roller wheels for breaking
the surface layer. Unit 94 provides the additional surface cleaning by means of a
step of brushing, e.g. as indicated in figure 2 schematically. The rolling of the
steel base wire is performed by a roller mill unit 96, after which the steel base
wire is provided to the apparatus for applying the bending action schematically illustrated
by 98. After leaving apparatus 98 the reinforcement steel wire is lead to the second
spindle 100 after which the manufacturing method is completed.
[0043] Figure 6 illustrates a micro fracture at the surface of a steel wire.
The micro fracture can be clearly seen inside the wide dashed circle in the picture,
and has been discussed herein above.
[0044] The present invention has been described in terms of some specific embodiments thereof.
It will be appreciated that the embodiments shown in the drawings and described here
and above are intended for illustrative purposes only, and are not by any manner or
means intended to be restrictive on the invention. The context of the invention discussed
here is merely restricted by the scope of the appended claims.
1. Method of manufacturing reinforcement steel for reinforcement of concrete structures,
said reinforcement steel having an elongated shape of arbitrary length and cross-section,
said method comprising the steps of:
providing a steel base wire; and
rolling the steel base wire for modifying a cross-sectional dimension thereof, and
for creating a bonding profile on a surface of said wire, wherein said step of rolling
is a cold rolling step;
characterized in that, prior to the step of rolling, the method further comprises a step of:
surface layer breaking for breaking of a surface layer, and
surface cleaning of said steel base wire for removing the surface layer from said
steel base wire; and
wherein, subsequent to said step of rolling, the method further comprises a step of
applying a plurality of bending actions to the steel base wire for improving tensile
properties thereof, such as to provide said reinforcement steel having a tensile strength
to yield strength ratio Rm/Re of at least 1,08, and having a percentage uniform elongation at maximum force Agt of at least 5,0.
2. Method according to claim 1, further comprising a step of shot peening subsequent
to said step of applying the bending actions.
3. Method according to claim 1 or 2, wherein said bending actions are applied by moving
the steel base wire across a plurality of consecutive roller wheels, wherein for each
roller wheel for providing the bending action the steel base wire is moved across
or with at least a part of a circumference of the wheel.
4. Method according to claim 3, wherein each roller wheel is rotatable in a plane of
rotation of the plurality of roller wheels, each roller wheel being rotatable by means
of a shaft, and wherein from the plane of rotation of the roller wheels the shafts
alternately extend transverse to the plane of rotation from positions along a first
and a second line respectively, the first and the second line being parallel to each
other and to the plane of rotation, wherein for each two consecutive roller wheels
the sum of radiuses of the roller wheels is larger than or equal to a distance between
the first and second line for forcing said bending action upon the steel base wire
upon moving the wire across or with the circumference of the roller wheels.
5. Method according to any of the previous claims, wherein the step of applying a plurality
of bending actions comprises applying at least three bending actions.
6. Method according to any of the previous claims, wherein said additional step of surface
cleaning comprises at least one step selected from a group comprising brushing, polishing,
spooling of the steel base wire, a chemical treatment such as staining, or a high
pressure fluid jet for cleaning the steel base wire.
7. Manufacturing arrangement for the manufacturing of reinforcement steel using a method
in accordance with at least one of the claims 1-6, said arrangement comprising:
a lead-in unit for receiving a steel base wire; and
a rolling mill unit for applying a cold rolling step for rolling the steel base wire
for modifying a cross-sectional dimension thereof, and for creating a bonding profile
on a surface of said wire;
said arrangement characterized by further comprising, in use upstream of said rolling mill, a surface cleaning unit
for applying surface cleaning of said steel base wire prior to said step of rolling
for removing a surface layer such as an oxidation layer from said steel base wire;
and, in use downstream of said rolling mill, a bending unit for applying a plurality
of bending actions to the steel base wire for improving tensile properties thereof,
such as to provide said reinforcement steel having a tensile strength to yield strength
ratio Rm/Re of at least 1,08, and having a percentage uniform elongation at maximum force Agt of at least 5,0.
8. Manufacturing arrangement in accordance with claim 7, further comprising a shot peening
unit downstream of said bending unit for applying a step of shot peening subsequent
to said step of applying the bending actions.
9. Manufacturing arrangement in accordance with claim 7 or 8, further comprising a shot
peening unit downstream of said bending unit for applying a step of shot peening subsequent
to said step of applying the bending actions.
10. Manufacturing arrangement in accordance with any of the claims 7-9, the bending unit
comprising a plurality of consecutive roller wheels arranged in a single plane of
rotation, wherein each roller wheel is rotatable by means of a shaft such as to be
rotatable in the plane of rotation of the plurality of roller wheels, said roller
wheels being placed such that in use for providing the bending action the steel base
wire is moved across or with at least a part of the circumference of each wheel.
11. Manufacturing arrangement in accordance with claim 10, wherein from the plane of rotation
the shafts of the roller wheels alternately extend transverse to the plane of rotation
from positions along a first and a second line respectively, the first and the second
line being parallel to each other and to the plane of rotation, wherein for each two
consecutive roller wheels the sum of radiuses of the roller wheels is larger than
or equal to a distance between the first and second line for forcing said bending
action upon the steel base wire upon moving the across or with the circumference of
the roller wheels.
12. Apparatus in accordance with claim 11, wherein the shafts extending from the first
line are structurally connected by a first suspension unit, and wherein the shafts
extending from the second line are structurally connected by a second suspension unit,
wherein at least one of the first and second suspension units is adjustably connected
to a structure of the apparatus such as to enable adjustment of the distance between
the first and second line in use.
13. Apparatus in accordance claim12, wherein one or more of the shafts is adjustably connected
to the first or second suspension unit, for enabling adjustment of the position of
the one or more shafts along the first or second line respectively.
14. Apparatus in accordance with any of the claims 10-13, wherein the roller wheels are
suspended to the shafts in a releasable manner such as to enable replacement thereof,
for adapting a diameter of one or more rollers wheels in use.
15. Reinforcement steel manufactured using a manufacturing method in accordance with any
of the claims 1-6, or manufactured using a manufacturing arrangement in accordance
with any of the claims 7-14, said reinforcement steel having a tensile strength to
yield strength ratio Rm/Re of at least 1,08, and having a percentage uniform elongation at maximum force Agt of at least 5,0.