U.S. patent application number 09/945685 was filed with the patent office on 2002-05-30 for steel cord with waved elements.
Invention is credited to De Vos, Xavier, Lippens, Yvan, Somers, Albert R., Van Giel, Frans.
Application Number | 20020062636 09/945685 |
Document ID | / |
Family ID | 8228980 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020062636 |
Kind Code |
A1 |
De Vos, Xavier ; et
al. |
May 30, 2002 |
Steel cord with waved elements
Abstract
A steel structure adapted for the reinforcement of elastomeric
members has steel elements containing a plurality of steel
filaments at least one of which filaments is provided with first
and second crimps. The first crimp lies in a plane that is
substantially different from the plane of the second crimp.
Application of the both crimps can be carried out efficiently using
two pairs of toothed wheels which are not externally driven. This
arrangement renders it possible to obtain steel structures with an
increased penetration of rubber or with an increased elongation at
break.
Inventors: |
De Vos, Xavier; (Oudenaarde,
BE) ; Lippens, Yvan; (Anzegem, BE) ; Somers,
Albert R.; (Gentbrugge, BE) ; Van Giel, Frans;
(Kortrijk, BE) |
Correspondence
Address: |
Glenn Law
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
8228980 |
Appl. No.: |
09/945685 |
Filed: |
September 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09945685 |
Sep 5, 2001 |
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09555045 |
May 24, 2000 |
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6311466 |
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Current U.S.
Class: |
57/212 |
Current CPC
Class: |
D07B 1/0613 20130101;
D07B 7/025 20130101; D07B 2201/2022 20130101; D07B 1/0626 20130101;
D07B 2201/2023 20130101; Y10S 57/902 20130101; Y10T 428/12333
20150115; D07B 2201/2007 20130101; D07B 2501/2046 20130101; D07B
2501/2076 20130101; D07B 2201/2018 20130101; B60C 9/0064 20130101;
D07B 1/0646 20130101; D07B 1/0653 20130101; B60C 9/0057 20130101;
D07B 2401/208 20130101 |
Class at
Publication: |
57/212 |
International
Class: |
D02G 003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 1997 |
BE |
97203712.1 |
Claims
1. A steel structure adapted for the reinforcement of elastomers,
said steel reinforcement comprising one or more steel elements,
characterized in that at least one of said steel elements is
provided with a first crimp and a second crimp, the first crimp
lying in a plane that is substantially different from the plane of
the second crimp.
2. A steel structure according to claim 1 wherein said steel
element has a round transversal cross-section.
3. A steel structure according to claim 2 wherein said first crimp
has a first crimp amplitude and said second crimp has a second
crimp amplitude, said first crimp amplitude and said second crimp
amplitude varying between a minimum value of 1.05.times.d and
between a maximum value of 5.times.d, d being the diameter of the
steel element.
4. A steel structure according to any one of claims 1 to 3 wherein
said steel element is a steel filament.
5. A steel structure according to any one of claims 1 to 3 wherein
said steel element is a steel strand of twisted filaments.
6. A steel structure according to any one of claims 1 to 3 wherein
said steel element is a steel bundle of non-twisted filaments.
7. A structure according to any one of the preceding claims wherein
said first crimp has a first crimp pitch and said second crimp has
a second crimp pitch, said first crimp pitch being different from
said second crimp pitch.
8. A structure according to claim 7 wherein said structure exhibits
two substantially different moduli of elasticity during a tensile
test.
9. A structure according to any one of claims 3 to 8 said first
crimp amplitude being different from said second crimp
amplitude.
10. A structure according to any one of the preceding claims
wherein said structure comprises more than one steel element.
11. A structure according to claim 10 wherein said steel elements
are twisted with each other.
12. A structure according to claim 11 wherein said first crimp
pitch and/or said second crimp pitch is/are smaller than the twist
pitch of the element with said crimps in said structure.
13. A structure according to any one of claims 11 to 12 wherein
said structure essentially consists of two to five steel filaments,
one to four steel filaments of which are provided with said first
and second crimp in order to allow rubber penetration.
14. A steel structure according to any one of claims 11 to 12
wherein said structure essentially consists of two to five steel
filaments and wherein all these filaments are provided with said
first and second crimp in order to obtain an increased elongation
at fracture.
15. A steel structure according to any one of claims 11 to 12
wherein said structure comprises a core and a layer of steel
filaments twisted around said core, said core comprising one or
more steel core filaments, at least one of said steel core
filaments being provided with said first and second crimp in order
to obtain rubber penetration in said core.
16. A steel structure according to any one of claims 11 to 12
wherein said structure comprises between nine and twenty-seven
steel filaments which all are twisted in the same twisting sense
and with the same twisting pitch, some of said filaments being
provided with said first and second crimp in order to obtain rubber
penetration.
17. A steel structure according to claim 16, said structure
comprising central elements, said central elements being provided
with said first and second crimp in order to prevent these
filaments from migrating.
18. A steel structure according to any one of claims 16 to 17
wherein said structure comprises four strands, each of said strands
consisting of two filaments, all of said filaments being provided
with said first and second crimp in order to obtain an increased
elongation at break.
19. A method of giving to a steel filament a spatial wave form,
said method comprising the following steps: (a) applying a first
crimp to said steel filament, said first crimp lying in a first
plane; (b) applying a second crimp to said steel filament, said
second crimp lying in a second plane substantially different from
said first plane.
20. A method according to claim 19 wherein said first and second
crimps are applied by means of pairs of toothed wheels which are
driven by the steel filament itself.
21. A method according to claim 19 or 20 wherein an additional
third crimp is applied to said steel filament.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a steel structure adapted
for the reinforcement of elastomers such as rubber conveyor belts,
rubber tires, rubber hoses, rubber timing belts or timings in
polyurethane. The steel reinforcement comprises one or more steel
filaments.
[0002] The present invention also relates to a method of treating a
steel filament so that the steel filament receives a spatial wave
form.
BACKGROUND OF THE INVENTION
[0003] Such steel structures are widely known in the art.
[0004] Recent prior art documents have disclosed a tendency towards
steel structures where the steel filaments present one or another
type of waviness, i.e. where, in addition to the plastic
deformation as a consequence of the possible twisting of the steel
filaments, the steel filaments have another plastic deformation.
This additional and other plastic deformation is conveniently a
consequence of a preforming operation, and results in a wavy
pattern on the steel filament.
[0005] In this way U.S. Pat. No. 5,020,312 (Kokoku - priority 1989)
and U.S. Pat. No. 5,111,649 (Kokoku) disclose steel cord structures
consisting of three to five steel filaments. At least one steel
filament is provided with a so-called `crimp`: this is a zigzagged
form with relatively sharp angles, the sharpness depending upon the
formation tools. The crimp is a planar wave form and is formed by
means of two toothed wheels. The holes created at the level of the
angles promote penetration of elastomer into the steel cord
structure.
[0006] Another wave form has been disclosed in EP-A-0 462 716
(Tokusen - priority 1990). According to this document, the steel
cords have three to twenty-seven steel filaments, 25% to 67% of
which have a particular helix or helicoidal form. The plastical
helix deformation is carried out by means of rotating preforming
pins. The purpose is to promote penetration of the elastomer into
the steel cord structure without increasing the so-called part load
elongation (PLE, for definition see below). These steel cords are
marketed under the name SPACY.RTM. cord. An important drawback of
this card is that its manufacture is energy-consuming or
inefficient or both. Indeed, if the pitch of the helix is taken
smaller than the twist pitch, then the rotation speed of the
preforming pins must be more than twice as high as the rotation
speed of a down-stream double-twister.
[0007] Still another wave form has been disclosed in WO-A-95/16816
(Bekaerit - priority 1993). According to this document, the steel
structure comprises steel filaments and at least one steel filament
has been polygonally preformed. This is a spatial wave form and is
the result of a preforming device with varying radii of curvature.
The steel structures are marketed under the name BETRU.RTM..
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide still
another wave form to steel filaments of steel structures.
[0009] It is another object of the present invention to provide a
wave form to steel filaments where the wave form combines
advantages of existing wave forms.
[0010] It is still another object of the present invention to
provide a wave form which can take a lot of specific forms
depending upon the choice of the parameters of the wave form.
[0011] It is yet another object of the present invention to provide
a wave form, the manufacture of which does not necessitate
energy-consuming tools.
[0012] It is also an object of the present invention to provide a
steel structure with an oval transversal cross-section as a
consequence of the wave form of some filaments, e.g. a core
filament.
[0013] According to the invention, there is provided a steel
structure adapted for the reinforcement of elastomers. The steel
reinforcement comprises one or more steel elements. At least one of
these steel elements is provided with a first crimp and a second
crimp. The first crimp lies in a plane that is substantially
different from the plane of the second crimp.
[0014] In this way a spatial wave form is obtained without using
driven and energy-consuming preforming tools.
[0015] Another advantage of this steel structure is that a lot of
wave forms become possible. Indeed, the first crimp has a first
crimp pitch and a first crimp amplitude. The second crimp has a
second crimp pitch and a second crimp amplitude. This means already
four design parameters which each can be varied, independently of
each other over a certain range.
[0016] The first crimp pitch may be equal to or different from the
second crimp pitch. With equal crimp pitches circular or oval
spatial helixes can be obtained. Different crimp pitches, however,
lead to spatial forms different from helixes.
[0017] The first crimp amplitude may be equal to or different from
the second crimp amplitude. A different crimp amplitude enables to
obtain a spatial form with an oval transversal cross-section on
condition that the filament which is provided with the first crimp
and the second crimp is not rotated around its own axis in the
final steel structure.
[0018] Still another parameter which can be varied is the angle
between the two planes. It is preferable, however, that the planes
differ as much from each other as possible: so the best choice is a
maximum difference of about 90.degree..
[0019] The steel element of the steel structure according to the
invention can be a steel filament, a bundle of non-twisted steel
filaments or a steel strand of twisted steel filaments. The steel
structure according to the invention may also be constituted by any
combination hereof.
[0020] The steel structure may be an untwisted structure consisting
of one or more steel filaments lying parallel adjacent to each
other and bound by each other by means of another wrapping filament
or by means of an adhesive that is compatible with the elastomer to
be reinforced.
[0021] An alternative embodiment is that the steel filaments lie
nearly parallel adjacent to each other, which can be obtained by
twisting them with a very large twist pitch e.g. by passing them at
a relatively high linear speed through a twisting apparatus
rotating at a convenient or relatively low rotation speed.
[0022] The steel structure may also be a twisted structure with
some or all of the composing filaments twisted in to a coherent
structure.
[0023] At least one of the first crimp pitch and the second crimp
pitch is preferably smaller than the twist pitch of the steel
filament provided with the first and the second crimp.
[0024] Within the general group of twisted structures, a first
application of the invention are n.times.1 steel cords, i.e. cords
essentially consisting of two to five steel filaments.
[0025] In a first embodiment, some but not all of these filaments
are provided with the first and the second crimp in order to allow
rubber penetration. An example is a 4.times.0.28 cord with one or
two filaments provided with the first and the second crimp. Such a
cord is used in the breaker plies of a tire.
[0026] In a second embodiment, all of the filaments are provided
with the first and this second crimp in order to increase the
elongation at break above 5% or more.
[0027] An example is a 5.times.0.38 cord with the five filaments
provided with the first and second crimp. An additional advantage
is that the cord may be twisted with a relatively large twist pitch
(14 mm to 20 mm) without decreasing substantially the elongation at
break.
[0028] Another example are 4.times.0.22 and 5.times.0.22 where all
filaments are provided with the first and the second crimp. These
high elongation cords are suitable for reinforcing tires of a motor
cycle (lying at nearly 0.degree. with respect to the equatorial
plane of a motor cycle tire).
[0029] A second application of the invention are the so-called I+m
(+n) steel cords comprising a core of I core steel filaments and a
layer of m steel filaments twisted around the core. Additionally, a
second layer of n steel filaments may be twisted around the first
layer of m filaments.
[0030] One or more core steel filaments may be provided with the
first and the second crimp in order to:
[0031] a) increase the penetration of the elastomer into the core
and/or to
[0032] b) obtain an oval transversal cross-section of the core, and
as a consequence, an oval transversal cross-section of the whole
cord; and/or to
[0033] c) prevent the core steel filaments from migrating out of
the cord.
[0034] An example is a 1+6 construction where the single core
filament is provided with a first crimp and a second crimp in order
to enable rubber penetration and in order to increase the anchorage
of the single core filament in the cord, i.e. to prevent core
migration. The first crimp amplitude may be greater than the second
crimp amplitude so that an oval transversal cross-section is
obtained.
[0035] Another example is a 3+8+13 construction, where the three
core filaments are provided with a first crimp and a second crimp
in order to allow rubber penetration to the centre between the
three core filaments.
[0036] A similar application is the replacement of the core
filaments of the strands in a 7.times.7 construction by a 2.times.1
or 3.times.1 element where the two or the three filaments are
provided with the first and the second crimp.
[0037] Still another example is replacing the well-known
construction 3.times.d+9.times.d+15.times.d by a
5.times.d.sub.1+9.times.d+15.times.d, where the filament diameter
d1 of the core filaments is smaller than the diameter d of the
other filaments. The core filaments are provided with the first and
the second crimp. Rubber penetration and elongation are increased
and the stiffness is decreased.
[0038] A third application of the invention is the so-called
n.times.1 compact cords comprising n steel filaments which have
been twisted with each other in the same twist sense and with the
same twist pitch. An example is a
3.times.0.365.vertline.9.times.0.345 CC (CC=compact cord) where all
the core filaments are provided with the first and the second crimp
in order to provide rubber penetration and in order to prevent core
migration.
[0039] Another example is a 12.times.0.38 CC where all twelve
filaments are provided with the first and the second crimp in order
to obtain a high elongation. Such a cord can be used as the weft or
warp element in a woven structure adapted to reinforce rubber
conveyor belts.
[0040] A fourth application is the multi-strand steel cord, which
is a steel cord comprising two or more strands and where each
strand consists of two or more filaments. If such strands are
twisted in the cord in the same sense as the filaments are twisted
in the strand (the so-called Lang's lay cords) a high elongation at
break can be obtained. A condition hereto is that relatively small
twist pitches are used.
[0041] According to the invention, however, if some or preferably
all filaments are provided with the first crimp and the second
crimp, then much larger twist pitches are possible without loosing
any elongation at break, and thus cords are possible which can be
manufactured in a more efficient way.
[0042] It is also possible, still according to the invention, to
combine the existing small twist pitches with a first and second
crimp applied to all steel filaments. This allows to obtain a still
higher elongation at break. The unavoidable loss in tensile
strength and breaking load can be compensated by using an addition
strand as core. The filaments of this core strand can also be
provided with the first and second crimp.
[0043] A fifth application is a multi-strand steel cord, e.g. for
use as reinforcement of conveyor belts, where the strands as a
whole are provided with a first crimp and a second crimp, e.g. in
order to obtain a rubber penetration between the strands.
[0044] According to another aspect of the invention, there is
provided a method of giving to a steel filament a spatial wave
form. The method comprises the following steps:
[0045] (a) applying a first crimp to said steel filament, said
first crimp lying in a first plane;
[0046] (b) applying a second crimp to said steel filament, said
second crimp lying in a second plane substantially different from
said first plane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] The invention will now be described into more detail with
reference to the accompanying drawings wherein
[0048] FIG. 1 schematically illustrates how a first and a second
crimp are provided to a steel filament;
[0049] FIG. 2 shows the first crimp given to a steel filament;
[0050] FIG. 3 shows the second crimp given to a steel filament;
[0051] FIG. 4 shows a transversal cross-section of a 1.times.4
steel cord with two filaments provided with the first and the
second crimp;
[0052] FIG. 5 shows a transversal cross-section of a 1.times.5
steel cord with all five filaments provided with the first and the
second crimp;
[0053] FIG. 6 shows a transversal cross-section of a 1+6 steel cord
with the core filament provided with the first and the second
crimp;
[0054] FIG. 7 shows a transversal cross-section of a 12.times.1
compact cord where the three central filaments are provided with
the first and the second crimp;
[0055] FIG. 8 shows a transversal cross-section of a 4.times.2
multi-strand cord where all filaments are provided with the first
and the second crimp;
[0056] FIG. 9 shows a load-elongation curve of an invention
5.times.0.38 cord.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0057] FIG. 1 schematically illustrates how a first crimp and a
second crimp are provided to a steel filament 10.
[0058] The steel filament 10 is moved downstream towards a first
pair of toothed wheels 12. The axes of rotation of toothed wheels
12 lie parallel to the y-axis, and the first crimp given is a
planar crimp lying in plane xz.
[0059] The thus crimped filament 10 is further moved to a second
pair of toothed wheels 14. The axes of rotation of toothed wheels
14 lie parallel with the x-axis. The second crimp given by toothed
wheels 14 is also a planar crimp and lies in plane yz.
[0060] Obviously the resulting wave given to the steel filament 10
is no longer planar but spatial.
[0061] Neither the first pair of toothed wheels 12 nor the second
pair of toothed wheels 14 need to be driven by external means. They
are both driven and rotated by the passing steel filament 10.
[0062] It is important that the second pair of toothed wheels 14 is
a positioned as close as possible to the first pair of toothed
wheels 12 in order to prevent the first crimp from tilting or
rotating from plane xz to plane yz under influence of the second
crimp.
[0063] From a more general point of view and in order to control
the two crimps given to the filaments, the bending moment, i.e. the
moment necessary to give the two crimps, must be kept as small as
possible. This can be done, e.g. by applying first the crimp with
the smaller amplitude and only thereafter the crimp with the
greater amplitude.
[0064] Still from a more general point of view, the torsion moment,
i.e. the moment necessary to rotate the filament, should be kept as
high as possible, since the rotating of the filament must be
prevented during or between the two crimping operations. One way to
keep the torsion moment as high as possible is the above-mentioned
minimum distance between the two pairs of crimping wheels.
[0065] A third and following pairs of toothed wheels may be
provided in other planes or in the same planes. In this way the
spatial structure obtained by the subsequent crimping operations
may be optimised or varied to a further degree.
[0066] FIG. 2 shows the first crimp lying in plane xz and FIG. 3
shows the second crimp lying in plane yz.
[0067] The first crimp has a first crimp amplitude A.sub.1, which
is measured from top to top, with inclusion of filament diameter d.
The first crimp has a first crimp pitch P.sub.c1, which is equal to
the distance between two minima of the first crimp.
[0068] The second crimp has a second crimp amplitude A.sub.2, which
is measured from top to top, with inclusion of filament diameter
d.
[0069] The second crimp has a second crimp pitch P.sub.c2, which is
equal to the distance between two minima of the second crimp.
[0070] The spots 16 where the second crimp reaches its maxima are
hatched in parallel with the axis of the steel filament 10, and the
spots 18 where the second crimp reaches its minima are hatched
vertically in FIG. 2.
[0071] The spots 20 where the first crimp reaches its maxima are
hatched in parallel with the axis of the steel filament 10, and the
spots 22 where the first crimp reaches its minima are hatched
vertically in FIG. 3. Both the first crimp amplitude A.sub.1 and
the second crimp amplitude A.sub.2 may be varied independently of
each other. So A.sub.1 may be equal to A.sub.2 or may be different
from A.sub.2. Both amplitudes may vary between a minimum value
which is slightly above value of the filament diameter (e.g.
1.05.times.d, which means almost no crimp), and a maximum value of
about four to five times the filament diameter (4-5.times.d). This
maximum value is dictated for reason of constructional
stability.
[0072] Both the first crimp pitch P.sub.c1 and the second crimp
pitch P.sub.c2 may be varied independently of each other. So
P.sub.c1 may be equal to P.sub.c2 or may be different from
P.sub.c2. The more P.sub.c1 differs from P.sub.c2, the more easy it
is to prevent the first crimp from tilting. Both pitches may vary
between a minimum value which is about five times the filament
diameter d (5.times.d), and a maximum value of about fifty times
the filament diameter d (50.times.d). It is, however, to be
preferred, that in twisted structures at least one, and most
preferably both, of the crimp pitches is smaller than the twist
pitch of the steel filament in the twisted structure.
[0073] Having regard to the above parameters which may be chosen
quite freely, i.e. independent of each other, a large variety of
wave forms can be obtained.
[0074] A first example is that by choosing A.sub.1 equal to A.sub.2
and P.sub.c1 equal to P.sub.c2 and by shifting the second crimp
with a quarter of a pitch in respect of the first crimp, a spatial
helix form can be obtained or at least be approximated without the
need for driven rotatory preforming pins.
[0075] A second example is that by choosing A.sub.1 substantially
greater than A.sub.2 an oval or elliptical transversal
cross-section is obtained.
[0076] The steel filament 10 provided with the first and second
crimp can be used as single steel filament, e.g. to reinforce the
breaker ply of a rubber tire.
[0077] The steel filament 10 provided with the first and second
crimp can also be used in a more complex steel structure, next to
other reinforcing elements. This more complex structure can be an
untwisted structure or a twisted structure where two or more steel
filaments are twisted with each other.
[0078] Conveniently, a twisted structure can be made in two ways
which differ basically from each other.
[0079] A first way, sometimes referred to as "cabling", is carried
out by means of a rotary tubular strander. According to this
technique, the individual steel filaments are not rotated around
their own axis. This be derived, e.g. by means of a microscope,
from non-rotating drawing lines (drawing lines are unavoidable
imperfections caused by the final cold drawing steps in the
relatively soft brass layer; these drawing steps conveniently
immediately precede the twisting step).
[0080] A second way, sometimes referred to as "bunching", is
carried out by means of a double-twister. According to this
technique, the individual steel filaments are rotated around their
own axes. This can be derived from rotating drawing lines.
[0081] Both ways are known as such in the art.
[0082] The inventors have developed following procedure to detect
whether or not a steel filament has been provided with a first
crimp and a second crimp according to the invention.
[0083] If the structure has been "cabled", then the filaments are
simply disentangled from the steel structure. If it is possible,
e.g. by means of a microscope to discover on a disentangled
filament
[0084] a) two crimps lying in different planes, e.g. by rotating
the steel filament; or
[0085] b) two different crimp pitches; or
[0086] c) two different crimp amplitudes; or
[0087] d) any combination of a), b) or c),
[0088] then this filament has been provided with a first crimp and
a second crimp according to the invention.
[0089] If the structure has been "bunched", then the structure must
be untwisted to such a degree that no applied torsions and no
residual torsions are present any more. After this untwisting, one
can proceed as for the "cabled" structures.
[0090] Of course other detection techniques can be developed.
[0091] For example, a KEYENCE LS laser scan, such as disclosed in
WO-A-95/16816, can be made of steel filaments and a Fourrier
analysis can be applied. In case of "bunching" the bunching
frequency can be filtered out and two crimp frequencies and their
higher harmonics will remain.
[0092] FIGS. 4 to 8 all show transversal cross-sections of twisted
steel structures which comprise one or more steel filament provided
with a first crimp and a second crimp. The steel filaments provided
with a first crimp and a second crimp are all referred to by
reference number 10 and their cross-section is cross-hatched,
whereas the cross-section of other steel filaments, if any, is only
hatched obliquely in one direction.
[0093] FIG. 4 shows the cross-section of a 4.times.0.28 steel cord
24. Two filaments 10 are provided with a first and a second crimp
in order to allow rubber penetration into the steel cord 24 even if
the steel cord 24 is put under a certain tensile load. Two
filaments 26 are not provided with these crimps.
[0094] The number of filaments which should be provided with the
crimps in order to promote rubber penetration depends upon the
total number of filaments in the steel cord. The higher total
number of filaments, the higher the number of filaments to be
provided with the crimps.
[0095] The number of filaments which should be provided with the
crimps in order to promote rubber penetration also depends upon the
amplitude and the pitch of the crimps. Generally, the higher the
amplitudes and the smaller the pitches, the more rubber is able to
penetrate and the smaller the number of filaments provided with the
crimps.
[0096] FIG. 5 shows a cross-section of a 5.times.0.38 steel cord 28
where all the five steel filaments 10 are provided with the two
crimps in order to obtain a high elongation at break (see results
in table 5 hereafter).
[0097] FIG. 6 shows a cross-section of a 1+6 steel cord 30 where
the single core filament 10 is provided with the first and the
second crimp. All filaments 26 of the layer surrounding the core
filament 10 are not provided with those crimps. The first crimp
amplitude is much greater than the second crimp amplitude of the
core filament so that an oval cross-section of the steel cord can
be obtained. In case it is desired that this oval shape does not
rotate along the length of the steel cord, the core filament must
not rotate in the final twisted steel cord. This is no problem if
the cabling technique is applied. If the bunching technique is
applied, use can be made of the teaching of EP-A1-0 676 500 to
compensate for the rotating of the core filament around its own
axis.
[0098] As an alternative of this embodiment, the core filament is
provided with the first and the second crimp and the six filaments
of the layer are provided with a polygonal form as has been
disclosed in WO-A-95/116816.
[0099] As another alternative of this embodiment, both the core
filament and the six outer filaments are provided with the first
and the second crimp.
[0100] FIG. 7 shows a cross-section of a 12.times.0.20 compact cord
where the three central filaments 10 are provided with a first and
a second crimp. The nine outer filaments 26 are not provided with
these crimps. Dependent upon the crimp amplitudes and crimp pitches
applied, the wavy form of the central filaments 10 can give the
necessary rubber penetration to the compact steel cord without
necessitating the use of central filaments which are thicker than
the outer filaments. In case the rubber penetration is still not
satisfactory, or in case a satisfactory rubber penetration requires
too high a crimp amplitude, the nine outer filaments 26 may also be
provided with a first and a second crimp.
[0101] FIG. 8 shows a cross-section of a 4.times.2.times.0.35
elongation cord 34 where all composing filaments 10 are provided
with a first and second crimp according to the invention. The twist
pitch of the 0.35 filaments in the 2.times.0.35 strand can be
increased from 3.5 mm to 6.0 mm and the twist pitch of the four
2.times.0.35 strands in the 4.times.2.times.0.35 cord can be
increased from 9 mm to 16 mm without decreasing the elongation at
fracture.
EXAMPLE 1
[0102] A first steel filament with a diameter of 0.28 mm has been
provided with a first crimp with first crimp amplitude A.sub.1=0.50
mm and first crimp pitch P.sub.c1=5.0 mm, and with a second crimp
with second crimp amplitude A.sub.2=0.50 mm and with a second crimp
pitch P.sub.c2=3.0 mm.
[0103] A second steel filament with a diameter of 0.28 mm has been
provided with a first crimp with first crimp amplitude A.sub.1=0.75
mm and first crimp pitch P.sub.c1=5.0 mm, and with a second crimp
with second crimp amplitude A.sub.2=0.50 mm and with a second crimp
pitch P.sub.c2=3.0 mm.
[0104] The above parameters A.sub.1, A.sub.2, P.sub.c1 and P.sub.c2
are all parameters as tuned on the crimp wheels. As may be derived
hereinafter, the effective parameters as measured on the filaments
may deviate from the parameters as tuned, e.g. because the second
crimp influences the first crimp parameters. A possible downstream
twisting of the filaments into a steel cord may also influence both
the crimp amplitudes and the crimp pitches. Downstream operations
usually decrease the crimp amplitudes and increase the crimp
pitches.
[0105] Both filaments have been compared with a non-crimped steel
filament of 0.28 mm diameter as reference.
1TABLE 1 0.28 filament Ref. 1st 2nd filament filament filament
Breaking load F.sub.m, (N) 157 145 145 Elongation at break (%) 1.5
4.1 6.0 A.sub.1 measured on filament (mm) 0.280 0.455 0.796
P.sub.c1 measured on filament (mm) 0.000 5.319 5.265 A.sub.2
measured on filament (mm) 0.280 0.420 0.467 P.sub.c2 measured on
filament (mm) 0.000 3.126 3.119
[0106] Both the first filament and the second filament have been
used to make four invention embodiments of a 4.times.0.28 steel
cord with twisting pitch P=16.0 mm.
[0107] Embodiment no. 1 comprises one filament crimped as the first
filament hereabove and three non-crimped filaments.
[0108] Embodiment no. 2 comprises two filaments crimped as the
first filament hereabove and two non-crimped filaments.
[0109] Embodiment no. 3 comprises one filament crimped as the
second filament hereabove and three non-crimped filaments.
[0110] Embodiment no. 4 comprises two filaments crimped as the
second filament hereabove and two non-crimped filaments.
[0111] The four embodiments are compared with a reference
4.times.0.28 open cord with a twisting pitch of 16.0 mm.
2TABLE 2 4 .times. 0.28 cord Embodiment no. 1 2 3 4 Ref. breaking
load F.sub.m (N) 616 585 597 548 660 tensile strength R.sub.m 2526
2397 2444 2239 2657 (MPa) E-modulus (MPa) 178586 162527 167564
144043 permanent elongation at 1.12 0.88 0.93 0.72 max. load (%)
total elongation at break 2.5 2.4 2.4 2.3 (%) yield strength at
0.2% 2074 1976 2074 1902 permanent elongation (MPa) PLE cord at 50
N (%) 0.133 0.174 0.177 0.223 0.400 PLE of crimped filament 0.840
0.874 1.179 1.210 at 50 N (%) PLE of non-crimped 0.590 0.584 0.602
0.548 filament at 50 N (%) Rubber penetration % pressure drop 0 0 0
0 0-20 appearance rating 55 56 50 58 inside cord (%)
[0112] The "part load elongation or PLE of a steel element (whether
steel cord or steel filament) at 50 Newton" is defined as the
increase in length of the steel element, which results from
subjecting the steel element to a defined force of 50 Newton--and
is expressed as a percentage of the initial length of the steel
element measured under a defined pretension (of e.g. 2.5
Newton).
[0113] The rubber penetration has been measured in two ways.
[0114] A first way is the convenient and well-known pressure drop
test.
[0115] A second way determines the so-called appearance rating and
is measured here on the core filament in the following way. The
twisted cord is embedded in rubber under conditions comparable to
manufacturing conditions. Thereafter the individual steel filaments
are unraveled and the appearance rating is the surface area of a
particular steel filament covered with rubber compared with the
total surface area of that particular steel filament. In this
measurement of the appearance rating, the numerical results are
very dependent upon the type of rubber used.
EXAMPLE 2
[0116] A first high-tensile steel filament with a diameter of 0.38
mm has been provided with a first crimp with first crimp amplitude
A.sub.1=1.0 mm and first crimp pitch P.sub.c1=5.2 mm, and with a
second crimp with second crimp amplitude A.sub.2=0.75 mm and with a
second crimp pitch P.sub.c2=3.2 mm.
[0117] A second high-tensile steel filament with a diameter of 0.38
mm has been provided with a first crimp with first crimp amplitude
A.sub.1=1.0 mm and first crimp pitch P.sub.c1=5.2 mm, and with a
second crimp with second crimp amplitude A.sub.2=0.50 mm and with a
second crimp pitch P.sub.c2=3.2 mm.
[0118] A third high-tensile steel filament with a diameter of 0.38
mm has been provided with a first crimp with first crimp amplitude
A.sub.1=0.75 mm and first crimp pitch P.sub.c1=5.2 mm, and with a
second crimp with second crimp amplitude A.sub.2=0.75 mm and with a
second crimp pitch P.sub.c2=3.2 mm.
[0119] The above parameters A.sub.1, A.sub.2, P.sub.c1 and P.sub.c2
are all parameters as tuned on the crimp wheels. As may be derived
hereinafter from Table 3, the effective parameters as measured on
the filaments may deviate from the parameters as tuned, e.g.
because the second crimp influences the first crimp parameters. A
possible downstream twisting of the filaments into a steel cord may
also influence both the crimp amplitudes and the crimp
3TABLE 3 0.38 mm filament Ref. 1st 2nd 3rd filament filament
filament filament Breaking load F.sub.m (N) 312 267 279 271
Elongation at break (%) 1.5 10.11 6.54 7.10 E-modulus (MPa) 200000
44830 54777 80028 A.sub.1 measured on filament 0.38 0.846 0.918
0.634 (mm) P.sub.c1 measured on 0 5.143 5.170 5.198 filament (mm)
A.sub.2 measured on filament 0.38 0.684 0.497 0.621 (mm) P.sub.c2
measured on 0 3.150 3.141 3.047 filament (mm)
[0120] With the above-mentioned three types of high-tensile
filaments nine 5.times.0.38 invention cords with twisting pitch
14.0 mm have been made according to table 4 hereunder where all of
the steel filaments have been provided with both the first and the
second crimp.
4TABLE 4 filament composition of cords Invention cord no. Filament
no. no additional much additional some additional preforming
preforming preforming 1 1 4 7 2 2 5 8 3 3 6 9
[0121] Table 5 hereunder compares the results of these nine
invention cords with a reference 5.times.0.38 high-tensile open
steel cord with twisting pitch 12.0 mm.
5TABLE 5 5 .times. 0.38 cord Ref. Invention cord no. cord 1 2 3 4 5
6 7 8 9 linear density 4.543 4.498 4.493 4.484 4.471 4.467 4.495
4.462 4.482 (g/m) max. diameter (mm) 1.495 1.239 1.236 1.412 1.402
1.296 1.334 1.277 1.310 PLE cord at 50 N 0.261 0.204 0.153 0.378
0.341 0.337 0.260 0.228 0.269 (%) PLE filament at 50 N 1.568 1.289
1.194 1.484 1.363 1.327 1.418 1.186 1.331 (%) breaking load F.sub.m
1540 1308 1373 1331 1309 1408 1316 1305 1396 1347 (N) tensile
strength R.sub.m 2686 2262 2400 2329 2295 2475 2316 2281 2459 2362
(MPa) E-modulus (MPa) 193000 70773 98615 107267 105908 135309
138711 99710 155702 122695 permanent elongation 1.7 3.95 1.83 2.89
2.52 1.58 1.78 2.74 1.29 2.32 at max. load (%) elongation at break
3.8 7.38 4.43 5.15 5.11 3.70 3.73 5.45 3.04 4.95 (%) yield strength
at 0.2% 93 48 66 59 60 73 69 56 78 62 permanent elongation (MPa)
rubber penetration 0 0 0 0 0 0 0 0 0 0 (pressure drop - %) Breaking
load F.sub.m 1667 1399 1508 1461 1376 1467 1356 1381 1506 1446
embedded in rubber (N) Total elongation at 2.09 6.39 3.33 4.3 3.21
1.93 1.98 3.8 1.95 3.59 break embedded in rubber (%) compression
modulus 19000 26326 35590 65471 54423 65707 71853 54389 75526 64140
(MPa) deformation at 4.23 1.60 1.45 0.79 1.21 1.01 0.87 1.11 0.72
0.94 instability w.sub.k (%)
[0122] Following explanation can be given with respect to the
values derived from a compression test. Due to their high
length-to-diameter ratio steel cords as such have no resistance to
compression. Once embedded in rubber, however, a steel cord can
build up a considerable compression resistance. A cylinder test has
been developed, which provides information on the compression
properties of rubber-embedded steel cords. A rubber cylinder with a
diameter of 30 mm and a height of 48.25 mm is reinforced exactly in
the center with a test steel cord. By means of a precision mold and
by tensioning the steel cord during curing, the cord is kept
straight and exactly in the axis of the cylinder. The compression
test records a force versus deformation diagram. w.sub.k is the
deformation at instability or at the buckling point. Further
details about the compression test may be read from L. BOURGOIS,
Survey of Mechanical Properties of Steel Cord and Related Test
Methods, Special Technical Publication 694, ASTM, 1980. A steel
cord for protection plies is said to have a good compression
behavior if w.sub.k exceeds 3%.
[0123] The values of the E-modulus or modulus of elasticity
mentioned in Table 5 are average values. When performing a tensile
test and recording a load-elongation curve, however, two different
E-moduli can be observed. The two different E-moduli are a
consequence of two crimps with different crimp pitches. In a
tensile test, the crimp with the smaller crimp pitch leads to the
elongation at the smaller loads, while the crimp with the greater
crimp pitch only gives effective elongation at higher loads. This
is shown in FIG. 9, which gives the load-elongation curve of
invention cord no. 1 of Table 5 hereabove. Two clearly distinct
E-moduli are shown by means of point-dash lines.
EXAMPLE 3
[0124] A number of 0.22 mm filaments have been provided with the
first and second crimp. Table 6 hereunder compares a number of
their properties each time with a straight 0.22 mm filament as
reference.
6TABLE 6 0.22 mm filament 1.sup.st filament 2.sup.nd filament
3.sup.rd filament 2x 2x 2x Ref crimp Ref crimp Ref crimp Breaking
load 117 103 118 103 117 101 (N) tensile strength 3080 2711 3115
2705 3067 2669 (MPa) yield strength R.sub.p at 2617 2053 2525 2022
2539 1985 0.05% elongat. (MPa) R.sub.p at 0.1% 2839 2202 2851 2133
2798 2109 elongation (MPa) R.sub.p at 0.2% 3005 2350 3029 2275 2975
2259 elongation (MPa) elongation at max. 0.38 0.95 0.45 0.96 0.45
0.94 load (%) tot. elongation at 1.88 3.48 1.9 4.3 1.91 3.84
fracture (%) A.sub.1 (mm) 0 0.47 0 0.49 0 0.47 P.sub.c1 (mm) 5.20
5.16 5.31 A.sub.2 (mm) 0 0.34 0 0.40 0 0.39 P.sub.c2 (mm) 3.04 3.04
3.12
EXAMPLE 4
[0125] A 12.times.0.38 compact cord has been manufactured with all
twelve filaments provided with the double crimp. The cord can be
used as weft element in a woven structure adapted to reinforce
conveyor belts. Four embodiments of the 12.times.0.38 compact cord
(CC) are compared with a conventional 4.times.7.times.0.25
high-elongation (HE) cord. The differences between the four
embodiments of the 12.times.0.38 compact cord are as follows:
[0126] Number 1: low winding tension, low rotation speed of
buncher;
[0127] Number 2: high winding tension, low rotation speed of
buncher;
[0128] Number 3: low winding tension, high rotation speed of
buncher;
[0129] Number 4: high winding tension, high rotation speed of
buncher.
7TABLE 7 12 .times. 0.38 compact cord 12 .times. 0.38 - invention 1
2 3 4 4 .times. 7 .times. 0.25 Lay length (mm) 18 S 18 S 18 S 18 S
5/10 SS Rubber penetration 0 0 0 0 100 Pressure drop (%) Optical
diameter D.sub.min 2105 1.940 1.888 1.910 1.879 D.sub.max 2.439
2.285 2.334 2.399 2.131 Linear density 11.184 11.154 11.14 11.181
11.77 (g/m) Cross-sectional 1.42 1.42 1.42 1.41 1.50 surface
(mm.sup.2) Tensile test on not embedded cord Breaking load (N)
2856.7 2787.7 2840.7 2727.3 3149.7 Tensile strength 2008 1965 2004
1928 2103 (MPa) E-modulus (MPa) 44371 46998 49113 48907 101858
yield strength at 630 708 661 688 1156 0.01% elongation (MPa) Yield
strength at 47 52 50 54 78 0.2% elongation (%) Elongation at 3.35
2.94 3.29 2.79 2.45 maximum load (%) Total elongation at 7.88 7.12
7.38 6.73 4.66 fracture (%) Tensile test on cord embedded in rubber
Breaking load (N) 3023.47 2750.4 2905.07 2747.73 3345.07 Tensile
strength 2122 1936 2047 1940 2231 (MPa) E-modulus (MPa) 65373 70380
71446 71508 117420 yield strength at 1153 1183 1200 1219 2044 0.2%
elongation (MPa) yield strength at 54 61 59 63 92 0.2% elongation
(%) Elongation at 3.46 2.49 2.93 2.32 0.94 maximum load (%) Total
elongation at 6.71 5.24 5.8 5.05 2.91 fracture (%)
EXAMPLE 5
[0130] A 4.times.0.30 cord and a 5.times.0.30 cord have been
manufactured starting from 0.30 mm filaments which have all been
provided with the double crimp. The amplitude of the first crimp as
tuned on the toothed wheel was 0.70 mm and the pitch of the first
crimp as tuned on the toothed wheel was 5.2 mm. The amplitude of
the second crimp as tuned on the toothed wheel was 0.55 mm and the
pitch of the second crimp as tuned on the toothed wheel was 3.2 mm.
Table 8 hereunder summarizes the measured properties.
8TABLE 8 4 .times. 0.30 and 5 .times. 0.30 4 .times. 0.30 5 .times.
0.30 invention invention lay length cord (mm) 12.5 12.5 linear
density (g/m) 2.255 2.824 Surface of transversal cross- 0.29 0.36
section (mm.sup.2) Breaking load (N) 787 972.3 Tensile strength
(MPa) 2743 2706 E-modulus 115013 113222 Yield strength at 0.01%
1099 1091 elongation (MPa) Yield strength at 0.2% 1683 1707
elongation (MPa) Yield strength at 0.2% 61 63 elongation (%)
Elongation at maximum load 2.07 1.98 (%) Total elongation at
fracture 4.46 4.37 (%)
[0131] In addition to the above-mentioned characteristics and
properties, a steel cord according to the present invention has
following features which make it able for the reinforcement of
elastomers such as rubber:
[0132] the filament diameters range from 0.04 mm to 1.1 mm, more
specifically from 0.15 mm to 0.60 mm, e.g. from 0.20 mm to 0.45
mm;
[0133] the steel composition generally comprises a minimum carbon
content of 0.60% (e.g. at least 0.80%, with a maximum of 1.1%), a
manganese content ranging from 0.20 to 0.90% and a silicon content
ranging from 0.10 to 0.90%; the sulphur and phosphorous contents
are each preferably kept below 0.03% ; additional elements such as
chromium (up to 0.2 0.4%), boron, cobalt, nickel, vanadium . . .
may be added to the composition;
[0134] the filaments are conveniently covered with a corrosion
resistant coating such as zinc or with a coating that promotes the
adhesion to the rubber such as brass, or a so-called ternary brass
such as copper-zinc-nickel (e.g. 64%/35.5%/0.5%0 and
copper-zinc-cobalt (e.g. 64%/35.7%/0.3%), or a copper-free adhesion
layer such as zinc-cobalt or zinc-nickel.
[0135] The invention is suitable for all common and available final
tensile strengths from 2150 MPa to about 3000 MPa and more.
* * * * *