U.S. patent application number 12/522332 was filed with the patent office on 2010-01-14 for cable with low structural elongation.
This patent application is currently assigned to NV BEKAERT SA. Invention is credited to Paul Bruyneel, Stijn Vancompernolle, Bert Vanderbeken.
Application Number | 20100009184 12/522332 |
Document ID | / |
Family ID | 38024110 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100009184 |
Kind Code |
A1 |
Bruyneel; Paul ; et
al. |
January 14, 2010 |
CABLE WITH LOW STRUCTURAL ELONGATION
Abstract
A cable (211) is provided comprising a steel cord (212) and a
polymer material (215). The steel filaments (213) of the steel cord
(212) are coated with an adhesive before the penetration of the
polymer material (215). The cable (211) has a structural elongation
less than 0.025% and an E module 4% greater than the E module of
the steel cord (212). These two improvements further decrease the
total elongation of the cable at certain load.
Inventors: |
Bruyneel; Paul; (Ooigem,
BE) ; Vancompernolle; Stijn; (Gent, BE) ;
Vanderbeken; Bert; (Waregem, BE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NV BEKAERT SA
|
Family ID: |
38024110 |
Appl. No.: |
12/522332 |
Filed: |
January 4, 2008 |
PCT Filed: |
January 4, 2008 |
PCT NO: |
PCT/EP08/50053 |
371 Date: |
July 7, 2009 |
Current U.S.
Class: |
428/379 |
Current CPC
Class: |
D07B 1/16 20130101; D07B
2201/2079 20130101; Y10T 428/294 20150115; D07B 2501/2084 20130101;
D07B 2401/201 20130101; D07B 1/0673 20130101 |
Class at
Publication: |
428/379 |
International
Class: |
D07B 1/16 20060101
D07B001/16; D07B 1/00 20060101 D07B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 2007 |
EP |
07000237.3 |
Claims
1. A cable comprising a steel cord and a polymer material, wherein
the structural elongation of said cable is less than 0.025%.
2. A cable as claimed in claim 1, wherein the E module of said
cable is 4% greater than the E module of said steel cord.
3. A cable as claimed in claim 1, wherein characterized in that the
polymer filling rate is more than 70%.
4. A cable as claimed in claim 3, wherein the polymer filling rate
is more than 90%.
5. A cable as claimed in claim 1, wherein the thickness of the
polymer coating is less than 100 .mu.m.
6. A cable as claimed in claim 5, wherein the thickness of polymer
coating is less than 100 .mu.m.
7. A cable as claimed in claim 1, wherein said polymer material is
a thermoplastic polymer.
8. A cable as claimed in claim 7, wherein said thermoplastic
polymer is polyurethane.
9. A rope comprising at least one cable as claimed in claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a cable. More specifically
present invention relates to a cable with limited elongation.
BACKGROUND OF THE INVENTION
[0002] Cables and more specifically control cables are widely used
to transmit movement, such as cable for window elevator system,
cables used to open and close braks of scooters, bicycles and other
vehicles. In these and many other applications, a limited
elongation of the cable is required.
[0003] Cables are also widely used as tension member to reinforce
polymer materials, such as steel cords to reinforce radial tires,
cables to reinforce transmission belts, timing belts or flat
hoisting belts. In these applications, a limited elongation of the
cable is also required.
[0004] Generally, the tensile curve of a cable of prior art takes
the form of "hockey stick" curve as illustrated by FIG. 1. At the
initial elongation period, the elongation of the cable is large
while the tension is low, and the curve is relative flat. At the
terminal elongation period, the elongation of cable is almost
linear to the tension of the cable as illustrated by line 120 in
FIG. 1. The elongation of the cable increases steadily with the
increase of the tension. At this stage, the increase of the
elongation of the cable is proportional to the increase of the
tension of the cable, i.e. .DELTA..epsilon.=.DELTA..delta./E,
wherein .DELTA..delta. is the increase of the elongation of the
cable, .DELTA..epsilon. the increase of the tension of the cable,
and E the module of the cable. This is called the elastic
elongation. If we extend line 120 to intersect with the abscissa
axis, the intersection point .epsilon.0 represents the structural
elongation at low tensile stresses of the cable. Therefore, the
elongation of a cable at certain tensile stress can be expressed by
.epsilon.=.epsilon.0+.delta./E. From this equation, we can see that
the total elongation of a cable at certain tensile stress comprises
two portions of elongations: structural elongation and the elastic
elongation.
[0005] Therefore, there are two approaches to get a cable with
limited elongation. One way is to decrease the structural
elongation of the cable, and the other way to increase the E module
of the cable, because the elongation under tensile decreases when
the E module of the cable increases.
[0006] Besides, structural elongation .epsilon.0 of a cable is
unstable and unpredictable, because there are a lot of facts, such
as the structure of the cable, the voids between the filaments of
the cable, and the pre-tension of the filaments when cabling the
cable, that determine the structural elongation of a cable.
Therefore, the unstable and unpredictable behavior of structural
elongation of a cable causes problems to predict the total
elongation of the cable under tension and more scrap during the
start-up of machine producing for instance the high-precision
timing belts. Hence, further reducing or almost eliminating the
structural elongation .epsilon.0 can improve the predictability of
the tension-elongation curve of the cable and facilitate the
manufacturing process.
[0007] WO03044267A1 disclosed a cable with limited elongation, less
than 0.05% at a permanent force of 50N, after being subjected to a
force of 450N. This improvement is achieved by a cord comprising a
steel cord and a polymer material. The low elongation is highly
related to the penetration of polymer material into the steel cord,
but there are limits on the penetration rate and the pressure for
the extrusion process.
[0008] WO2005043003A1 disclosed a fine steel cord with low
structural elongation. The low structural elongation is achieved by
using a special cabling process. This special cabling process not
only decreases the productivity of the cabling process but also ask
for a lengthy fine tune procedure to set the tension of the
filaments or strands.
SUMMARY OF THE INVENTION
[0009] It is an objective of the present invention to eliminate the
drawback of the prior art. It is also an objective of the present
invention to further limit the elongation of a cable without
complicating the manufacturing process of the cabling process.
[0010] According to the present invention, a cable is provided
comprising a steel cord and a polymer material. The steel filaments
of the steel cord are coated with an adhesive before the
penetration of the polymer material. The cable has a structural
elongation less than 0.025%. Besides, the E module of the cable
increases by more than 4% compared with the E module of the bare
steel cord. These two improvements further decrease the total
elongation of the cable at certain load.
[0011] The cable as subject of the invention comprises a steel
cord, which on its turn comprises several steel filaments.
[0012] The tensile strength of the steel filaments for the steel
cord are preferably more than 1700N/mm.sup.2, or more than
2200N/mm.sup.2 or even more than 2600N/mm.sup.2, most preferably
more than 3000N/mm.sup.2 or even more than 4000N/mm.sup.2. The
diameter of the filaments is less than 400 .mu.m, preferably less
than 210 .mu.m, most preferably less than 110 .mu.m.
[0013] All filaments may have an identical diameter. Possible the
diameter of the filaments may differ from each other. Preferably,
the diameter of the filaments providing an inner strand of the
cable is larger than the diameter of the filaments used to provide
the outer strands or layer of filaments to the cable, which
improves the penetration of the polymer material into the void
spaces of the cable.
[0014] Steel cords have an inner layer or core, which is preferably
a strand of several steel filaments. Around such core, at least one
layer of additional steel elements is provided. The steel elements
of the additional layer can either be steel filaments or steel
strands, on its turn comprising steel filaments. Various steel cord
construction may be used.
[0015] Examples here are: [0016] Multi-strand steel cord e.g. of
the m.times.n type, i.e. steel cords, comprising m strands with
each n steel filaments, such as 4.times.7.times.0.10,
7.times.7.times.0.18, 8.times.7.times.0.18 or 3.times.3.times.0.18;
the last number is the diameter of the steel filament expressed in
mm; [0017] Multi-strand steel cord, comprising a core strand of c
metal filaments, and m strands of n steel filaments, surrounding
the core strand. These steel cords are hereafter referred to as
c+m.times.n type cords, such as 19+9.times.7 or 19+8.times.7 cords;
[0018] Warrington-type steel cords; [0019] Compact cords, e.g. of
the 1.times.n type, i.e. steel cords comprising n steel filaments,
n being greater than 8, twisted in only one direction with one
single step to a compact cross-section, such as
1.times.9.times.0.18; the last number is the diameter of the
filament expressed in mm; [0020] Layered steel cord e.g. of the
c+m(+n) type, i.e. steel cord with a core of c filaments,
surrounded by a layer of m filaments, and possibly also surrounded
by another layer of n filaments, such as 2+4.times.0.18; the last
number is the diameter of the filaments expressed in mm.
[0021] The steel composition of the steel cord is preferably a
plain carbon steel composition, i.e. it generally comprises a
minimum carbon content of 0.40% (e.g. at least 0.60% or at least
0.80%, with a maximum of 1.1%), a manganese content ranging from
0.10 to 0.90% and a silicon content ranging from 0.10 to 0.90%; the
sulfur and phosphorous contents are each preferably kept below
0.03%; additional micro-alloying elements such as chromium (up to
0.2 to 0.4%), boron, cobalt, nickel, vanadium . . . may be added to
the composition; stainless steel compositions are, however, not
excluded. The production of the steel filaments and the steel cords
is performed according to known prior art techniques of wet drawing
followed by cabling or bunching.
[0022] After an optional cleaning operation, the steel cord is then
coated with an adhesive selected from organo functional silanes,
organo functional titanates and organo functional zirconates which
are known in the art for the improvement of adhesion between the
steel cord and polymer material. Preferably, but not exclusively,
the organo functional silanes are selected from the compounds of
the following formula:
Y--(CH.sub.2).sub.N--SiX.sub.3
[0023] Wherein:
[0024] Y represents an organo functional group selected from
--NH.sub.2, CH.sub.2.dbd.CH--, CH.sub.2.dbd.C(CH.sub.3)COO--,
2,3-epoxypropoxy, HS-- and, Cl--
[0025] X represents a silicon functional group selected from --OR,
--OC(.dbd.O)R', --Cl wherein R and R' are independently selected
from C1 to C4 alkyl, preferably --CH3, and --C2H5; and
[0026] n is an integer between 0 and 10, preferably from 0 to
3.
[0027] Besides the organo functional silanes mentioned above, there
are other steel PU adhesives commercially available on the market.
They are sold under the name Chemosil (made by the German company
Henkel) and Chemlock (made by Lord Corporation).
[0028] The polymer material used for the present invention can be
any elastomeric material that can conveniently be applied to the
steel cord with sufficient adhesion. More preferably a
thermoplastic elastomer (TPE) can be used. Non-delimiting examples
are polystyrene/elastomer block copolymers, polyurethane (PU) or
polyurethane copolymers, polyamide/elastomer block copolymers,
thermoplastic vulcanizates. Preferably thermoplastic polyurethane
is used. Homopolymers of ester, ether or carbonate polyurethane may
be used, as well as copolymers or polymer blends. Preferably, the
polymer material has a shore hardness varying between 30 A and 90
D.
[0029] The polymer penetration rate of a cable as subject matter of
the present invention is more than 70%, and preferably more than
90%. The steel cord used to provide a cable as subject matter of
the present invention comprises several steel filaments being
transformed into a steel cord, using a steel cord construction. Due
to the steel cord construction, void spaces are provided between
the steel filaments of the steel elements of the cord. Also void
spaces are provided between the steel elements. "Void space" as
used hereafter is to be understood as all area of a radial
cross-section of the cord, located inwards of the imaginary circle
which encircles a radial cross section of the steel cord which area
is not occupied by steel. Therefore, the polymer penetration rate
of a cable of present invention is defined as the ratio in
percentage of the void space filled by polymer to the void space
which is not occupied by steel.
[0030] The thickness of the polymer coating of the present
invention is less than 100 .mu.m, and preferably less than 10
.mu.m. The optical diameter of the steel cord used to provide a
cable as subject matter of the present invention is the diameter of
the smallest imaginary circle, which encircles a radial cross
section of the steel cord. The optical diameter of the cable of the
present invention is the diameter of the smallest imaginary circle,
which encircles a radial cross section of the cable. Therefore, the
thickness of the polymer is defined as the half of the difference
of the optical diameter between the cable and the steel cord.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The invention will now be described into more detail with
reference to the accompanying drawings wherein [0032] FIG. 1 is a
tensile curve of a cable of prior arts; [0033] FIG. 2 is a
cross-sectional view of a cable incorporating the present
invention; [0034] FIG. 3 is a tensile curve of a cable
incorporating the present invention.
[0034] [0035] Item 110 is the tensile curve of a cable of prior
arts; [0036] Item 120 is a line representing the E module of a
cable of prior arts; [0037] Item 211 is a cable incorporating the
present invention; [0038] Item 212 is a steel cord for the cable
incorporating the present invention; [0039] Item 213 is a steel
filament for the cable incorporating the present invention; [0040]
Item 214 is the optical diameter of the steel cord for the cable
incorporating the present invention; [0041] Item 215 is a polymer
material used for the cable incorporating the present invention;
[0042] Item 216 is the optical diameter of the cable incorporating
the present invention; [0043] Item 217 is the thickness of the
polymer coating of the cable incorporating the present invention;
[0044] Item 218 is the void space in the cable incorporating the
present invention; [0045] Item 219 is the steel strand for the
cable incorporating the present invention; [0046] Item 310 is the
tensile curve of a cable incorporating the present invention;
[0047] Item 320 is a line representing the E module of a cable
incorporating the present invention; [0048] .epsilon.0 is the
structural elongation of a cable; [0049] F(N) is the force in
Newton on the test specimen; [0050] E(%) is the elongation in
percentage of the test specimen.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0051] In FIG. 1, there is shown a tensile curve 110 of a cable of
prior art, and line 120 represents the E module of the cable. Line
120 extends and intersects with the abscissa axis at the
intersection point .epsilon.0, representing the structural
elongation at low tensile stresses of the cable.
[0052] As shown in FIG. 2, there is a cross section view of a cable
incorporating the present invention. The cable 211 comprises a
steel cord 212, which on its turn comprises several steel filaments
213. The present embodiment shows a steel cord with
"7.times.7.times.d" structure having seven strands 219, each strand
having seven steel filaments 213 of diameter of d mm. The steel
cord has an optical cord diameter 214. The steel cord is coated
with a polymer material 215, so providing a cable 211 as subject
matter of the present invention with an optical cable diameter 216.
The thickness 217 of the polymer coating is half of the difference
between optical cord diameter and optical cable diameter. As shown
in FIG. 2, preferably the void space 218 between the different
steel filaments 213 is substantially filled with polymer material
215.
[0053] In FIG. 3, there is shown a tensile curve 310 of a cable
incorporating the present invention, and line 320 represents the E
module of the cable. Line 320 extends and intersects with the
abscissa axis at the intersection point .epsilon.0, representing
the structural elongation at low tensile stresses of the cable.
[0054] In the following tables, there are shown comparison tests
between the cable with prior art and the cable incorporating the
present invention. The test is conducted according to ISO test
method ISO RA-30-203 on Zwick-Z020 test machine. When one test is
finished, the test machine can automatically provide the following
test results and the tensile curve of the test specimen.
[0055] Comparison Test 1:
[0056] Prior art: 1.times.3+5.times.7.times.0.15 steel cord;
[0057] Present invention: 1.times.3+5.times.7.times.0.15 steel cord
with adhesive treatment and PU coating.
TABLE-US-00001 Structural E module Elongation at elongation
.epsilon.0 N/mm.sup.2 50N Prior art 0.082% 168072 0.125% Present
invention 0.021% 184293 0.060% Improvements -74% +9.6% -52% against
prior art
[0058] The test results show that the present invention not only
substantially decreases the structural elongation of the cable by
74%, but also further improves the E module of the cable by 9.6%.
These two improvements make a substantial progress on the
elongation at certain load, the total elongation at 50N decreased
by 52%. Besides, the tensile curves in FIGS. 1 and 3 also
illustrate this improvement.
[0059] Comparison Test 2:
[0060] Prior art 1: 7.times.3.times.0.15 steel cord;
[0061] Prior art 2: 7.times.3.times.0.15 steel cord with PU
coating;
[0062] Present invention: 7.times.3.times.0.15 steel cord with
adhesive treatment and PU coating.
TABLE-US-00002 Structural E module Elongation at elongation
.epsilon.0 N/mm.sup.2 50N Prior art 1 0.044% 176357 0.119% Prior
art 2 0.031% 180437 0.105% Present invention 0.004% 182778 0.077%
Improvements -91% +4% -35% against prior art 1
[0063] The test results show that the present invention not only
substantially decreases the structural elongation of the cable by
91%, but also further improves the E module of the cable by 4%.
These two improvements make a substantial progress on the
elongation at certain load, the total elongation at 50N decreased
by 35%. Besides, the tensile curves in FIGS. 1 and 3 also
illustrate this improvement.
[0064] Compared with prior art, the use of an adhesive on the
surface of steel filaments before the application of polymer
material further improves the anchorage of steel filaments inside
polymer material. The steel filaments of the steel cord are
constrained from slipping and turning even there are some void
spaces unfilled by polymer material, which further limits the
structural elongation of the cable. Besides, the improved anchorage
of steel filaments inside polymer material also improves the E
module of the cable because there is no slippage or peeling between
steel filaments and polymer material.
[0065] A further improvement to the present invention is
characterized by the thickness of the polymer coating of the cable.
A cable with polymer coating of 10 .mu.m only marginally increases
the diameter of the cable, which is especially valuable for the
cable used as tension member to reinforce synchronous belt. Because
the synchronous belt is molded in a semi-open mold where the
polymer material is poured into the mold or extruded with a low
pressure, the polymer material inside the mold has limited ability
to flow between the tension members and to form the final requested
shape (toothed, flat, even, . . . ). Therefore, a fine cable with
less than 10 .mu.m polymer coating will leave more space for the
polymer material to flow inside the mold and to form a flat and
even belt.
[0066] Another application with this fine cable with less than 10
.mu.m polymer coating is for window elevator system. Because the
cable used for window elevator system needs to be clamped by metal
nipples at the end of the cable to connect other parts, cables with
thick polymer coating can not guarantee a secured connection
between the end of the cable and the nipple. The nipple clamps on
the polymer coating and the polymer coating transfers the tension
to the steel cord inside. Since the tensile strength of the polymer
material is quite low compared with that of the steel cord, the
connection between cable and nipple breaks at low load, and the
load transmission ability of the cable is undermined due to this
weak point. When a cable with less than 10 .mu.m polymer coating is
used in a window elevator system, the metal nipple clamps directly
to the steel cord because of the deformation of thin coating of
polymer material. This application secures the connection between
cable and nipple and eliminates the weak point for the system.
Besides, when the coating thickness is less than 10 .mu.m or even 0
.mu.m, from the outside the cable is virtually the same as a bare
cable with the same friction and wear properties. This might be of
a big advantage when one would like to substitute a bare cable by
such a products in a cable system since there is no need to change
the guiding part, cable tubes, etc.
[0067] Another improvement with present invention is to use the
cable as the subject matter of present invention to build a
multi-strand rope for hoisting applications such as elevator ropes.
Firstly, the elevator industry is looking for ropes with limited
elongation. Since the strands have limited elongation, the rope
will have a limited elongation either. Hence, elevator ropes using
present invention meet this requirement. Secondly, the elevator
industry is looking for ropes that are capable of running on small
sheave diameters. The standard elevator uses ropes that respect the
generally accepted sheave diameter "d" over rope diameter "D" ratio
of 40. When traditional all steel ropes are used in conditions
where the d/D ratio is lower than 40, the fatigue life of ropes
drops significantly. One of the failure causes of the ropes under
these conditions is excessive inter-strand and inter-wire fretting.
Although a polymer coating on the rope can reduce the fretting and
improve the fatigue life of the rope, a thick polymer coating is
needed to secure an endurable polymer sheath and the thick coating
increase the diameter of the rope. Present invention solves this
dilemma. On one hand, steel strands are coated with polymer to
reduce the fretting. On the other hand, adhesive treatment improves
the connection between steel and polymer and makes a thin coating
possible. Therefore, ropes made of cables of present invention are
suitable for hoisting applications.
* * * * *