U.S. patent application number 11/596226 was filed with the patent office on 2008-12-25 for wire rope for a tire.
Invention is credited to Denis Alvarez, Henri Barguet, Thibaud Pottier, Christian Signoret.
Application Number | 20080318077 11/596226 |
Document ID | / |
Family ID | 34946602 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080318077 |
Kind Code |
A1 |
Barguet; Henri ; et
al. |
December 25, 2008 |
Wire Rope for a Tire
Abstract
Metal cable having two layers of construction 4+N comprising an
inner layer C1 of four wires of diameter d.sub.1 wound together in
a helix at a pitch p.sub.1, this layer C1 itself being surrounded
by an outer layer C2 of N wires of diameter d.sub.2 wound together
in a helix at a pitch p.sub.2. The cable has the following
characteristics (d.sub.1, d.sub.2, p.sub.1 and p.sub.2 in mm):
0.25<d.sub.1<0.40, 0.25<d.sub.2<0.40,
3.5<p.sub.1<7<p.sub.2<14. Such a cable, of preferred
construction 4+9, is in particular usable for reinforcing tires, in
particular as an anchoring means for a carcass reinforcement of a
tire without a solid bead wire.
Inventors: |
Barguet; Henri; (Les Martres
D'Artiere, FR) ; Pottier; Thibaud; (Malauzat, FR)
; Alvarez; Denis; (Clermont-Ferrand, FR) ;
Signoret; Christian; (Cournon-D'Auvergne, FR) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE LLP
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Family ID: |
34946602 |
Appl. No.: |
11/596226 |
Filed: |
May 11, 2005 |
PCT Filed: |
May 11, 2005 |
PCT NO: |
PCT/EP05/05086 |
371 Date: |
February 14, 2008 |
Current U.S.
Class: |
428/592 |
Current CPC
Class: |
D07B 2205/3053 20130101;
B60C 15/0018 20130101; D07B 2201/2032 20130101; D07B 2205/3046
20130101; D07B 2801/10 20130101; Y10T 428/12333 20150115; B60C
15/04 20130101; D07B 2201/2023 20130101; D07B 2201/2006 20130101;
D07B 2201/2039 20130101; D07B 1/062 20130101; D07B 2201/2061
20130101; D07B 2205/3053 20130101; D07B 2501/2046 20130101 |
Class at
Publication: |
428/592 |
International
Class: |
D07B 1/06 20060101
D07B001/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2004 |
FR |
0405162 |
Claims
1. A metal cable having two layers of construction 4+N comprising
an inner layer C1 of 4 wires of diameter d.sub.1 wound together in
a helix at a pitch p.sub.1, this layer C1 itself being surrounded
by an outer layer C2 of N wires of diameter d.sub.2 wound together
in a helix at a pitch p.sub.2, wherein said cable has the following
characteristics (d.sub.1, d.sub.2, p.sub.1 and p.sub.2 in mm):
0.25<d.sub.1<0.40; 0.25<d.sub.2<0.40;
3.5<p.sub.1<7<p.sub.2<14.
2. The cable according to claim 1, in which the wires of the layers
C1 and C2 are of identical diameter (d.sub.1=d.sub.2).
3. The cable according to claim 1, in which the layers C1 and C2
are wound in the same direction of twist.
4. The tire according to claim 1, in which the layer C2 comprises
from 8 to 12 wires (8.ltoreq.N.ltoreq.12).
5. The cable according to claim 4, in which the layer C2 comprises
from 8 to 10 wires (8.ltoreq.N.ltoreq.10).
6. The cable according to claim 1, in which the outer layer C2 is
an unsaturated layer.
7. The cable according to claim 6, in which the cable has the
construction 4+9.
8. The cable according to claim 1, having the following
characteristics (d.sub.1, d.sub.2, p.sub.1 and p.sub.2 in mm):
0.30<d.sub.1<0.40; 0.30<d.sub.2<0.40;
4.0<p.sub.1<7 and 8<p.sub.2<14.
9. The cable according to claim 8, having the following
characteristics: 4.5.ltoreq.p.sub.1.ltoreq.6.5 and
8.5.ltoreq.p.sub.2.ltoreq.13.5.
10. The cable according to claim 1, the metal of the metal cable
being steel.
11. The cable according to claim 10, the steel being a carbon
steel.
12. The cable according to claim 11, the carbon steel having a
carbon content of between 0.1% and 1.2%.
13. The cable according to claim 12, the carbon steel having a
carbon content of between 0.5% and 1.1%.
14. The cable according to claim 13, the carbon steel having a
carbon content of between 0.6% and 1.0%.
15. The cable according to claim 1, the total elongation at break
(At) of the cable being greater than 2.5%.
16. The cable according to claim 15, wherein the total elongation
at break (At) is greater than 3.0%.
17. The cable according to claim 16, wherein the total elongation
at break (At) is greater than 3.5%.
18. The cable according to claim 1, the operational elongation
(structural and elastic) (Af) of the cable being greater than
4.0%.
19. The cable according to claim 18, wherein the operational
elongation (Af) is greater than 5.0%.
20. The cable according to claim 19, wherein the operational
elongation (Af) is greater than 6.0%.
21.-33. (canceled)
Description
[0001] The present invention relates to metal layered cables usable
for manufacturing tires, in particular for reinforcing their beads
enabling these tires to be fixed to a vehicle wheel rim.
[0002] Patent specification EP-A-582 196 was the first to describe
a tire comprising a crown surmounted by a tread, a crown
reinforcement, two sidewalls and two beads, a carcass reinforcement
passing into the two sidewalls and anchored by means for anchoring
in the beads, in which the carcass reinforcement comprises at least
one circumferential alignment of reinforcing members (referred to
as `radial`) oriented radially, arranged adjacently and practically
parallel to one another, aligned circumferentially in at least one
circumferential alignment from the beads towards the sidewalls, and
in which the anchoring means of these radial reinforcing members
comprise at least one circumferentially oriented reinforcing member
(referred to as `anchoring reinforcing member`) axially bordering
said circumferential alignments of said radial reinforcing members
and cooperating with an adjacent portion of the carcass
reinforcement by means of an appropriate rubber composition
(referred to as `anchoring rubber`), of great hardness, in contact
with the anchoring reinforcing member and the adjacent lengths of
the first radial reinforcing members, and transmitting the forces
between the radial reinforcing members and the anchoring
reinforcing members. For the detailed description of such tires,
which are referred to as "bead-wire-less" because they do not have
a conventional solid bead wire, of a relatively large diameter,
around which the carcass reinforcement usually winds, reference may
also be made, by way of examples, to patent specifications EP-A-664
231, EP-A-664 232, EP-A-664 233 (or U.S. Pat. No. 5,660,656),
WO-A-98/54006 or WO-A-2004/009380.
[0003] Although this new tire bottom-zone architecture has yielded
excellent results, in particular in terms of endurance, it has
however been noted that the great rigidity of the beads could cause
difficulties when mounting and/or demounting the tires, in
particular during manual operations, this problem being
particularly true for tires of large dimensions such as for example
heavy-vehicle tires.
[0004] It will be recalled here that that the conventional mounting
process of a "tubeless" tire on a generally integral rim comprising
a hollow base consists of passing part of the first bead over the
rim flange and placing this part in the hollow base, then passing
the rest of the bead over the flange due to slight ovalisation of
the corresponding bead of the tire, and repeating the same
operation to pass the second bead over the flange of the rim. The
mounting is then terminated by a final stage of inflation to a
pressure such that it ensures that the beads are put in position on
the seats bearing on the rim flanges; during this last stage, the
beads may cross "humps" which form an obstacle to the passage of
said beads as far as their respective seats and then prevent the
risks of unseating.
[0005] To overcome this problem of mounting ability, it was
proposed first of all, according to what is taught by patent
specification EP-A-751 015 (or U.S. Pat. No. 5,702,548), to use
anchoring cables of high non-structural elongation, in particular
layered cables of construction (2+7) or (3+8), which have undergone
a specific heat treatment. These cables, which are said to be of
"high-elongation" type, are characterized, before and after curing
of the tire, by a particularly high operational elongation (total
of their elastic elongation Ae and of their plastic elongation Ap),
greater than 4%. However, such an elongation is obtained at the
cost of what is called a recovery annealing heat treatment, carried
out at a low temperature of between 250.degree. C. and Ac.sub.1
(temperature corresponding to a transformation of the crystalline
structure of the steel), which has the disadvantage of being
relatively complex and expensive.
[0006] Still in order to overcome this problem of mounting ability,
patent application EP-A-1 277 600 did propose another, more
economic, solution, consisting of using a rubber composition of
reduced rigidity, having an elasticity modulus of between 10 and 20
MPa at a deformation of 10%, and a high creep resistance due to a
specific formulation, as anchoring rubber. It is however noted
nowadays that a relatively low rigidity of the anchoring rubber can
adversely affect somewhat the road behaviour of vehicles fitted
with such tires, in particular under sports running conditions;
this is the case in particular for top-of-range passenger vehicles,
the user of which wishes to have a very high level of road
behaviour, in all circumstances, without compromise on safety, in
particular on the grip properties, nor on the life of the
tires.
[0007] In continuing its research, the Applicant has discovered a
novel layered cable, each layer having in particular a high twist
(or very short assembly pitches), which makes it possible to
improve the existing compromises in terms of mounting ability of
the tires and of road behaviour, without necessitating modifying
the architecture of the bottom zone of the bead-wire-less
tires.
[0008] Consequently, a first subject of the invention relates to a
metal cable having two layers of construction 4+N comprising an
inner layer C1 of 4 wires of diameter d.sub.1 wound together in a
helix at a pitch p.sub.1, this layer C1 itself being surrounded by
an outer layer C2 of N wires of diameter d.sub.2 wound together in
a helix at a pitch p.sub.2, characterized in that said cable
furthermore has the following characteristics (d.sub.1, d.sub.2,
p.sub.1 and p.sub.2 in mm): [0009] 0.25<d.sub.1<0.40; [0010]
0.25<d.sub.2<0.40; [0011]
3.5<p.sub.1<7<p.sub.2<14.
[0012] Owing to this specific cable, the beads of the
bead-wire-less tires are advantageously ovalisable, that is to say
deformable in their plane, under industrially acceptable forces;
these beads can furthermore be more easily warped, that is to say
that their perimeter is more easily deformable, in the axial
direction. These properties very substantially improve the ability
of the tire of the invention to be ovalised and therefore its
mounting ability; it is henceforth possible to use anchoring
rubbers of great hardness, which are beneficial to road behaviour,
without necessarily having to use "high-elongation" treated
cables.
[0013] The invention also relates to the use of such a cable as a
reinforcing element for articles or semi-finished products of
plastics material and/or of rubber intended in particular for any
ground contact system for automobiles, such as tires, internal
safety supports for tires, wheels, rubber springs, elastomeric
joints, and other suspension and anti-vibration elements, and also
to these articles or semi-finished products themselves.
[0014] The tires of the invention may be intended for vehicles of
passenger-vehicle type, 4.times.4s, "SUVs" (Sport Utility
Vehicles), but also for two-wheeled vehicles such as motorcycles,
or for industrial vehicles selected from among vans, "heavy
vehicles"--i.e. subway trains, buses, road transport machinery
(lorries, tractors, trailers), off-road vehicles--, agricultural
machinery or construction machinery, aircraft and other transport
or handling vehicles.
[0015] By way of example of a preferred application, the cable of
the invention may be used for reinforcing a crown reinforcement, a
carcass reinforcement or alternatively, more preferably, the bead
zone of such tires.
[0016] The invention and its advantages will be readily understood
in the light of the description and examples of embodiment which
follow, and FIGS. 1 to 4 relating to these examples, which show,
respectively: [0017] a partial cross-section depicting essentially
a bottom zone of a bead-wire-less tire, comprising in particular in
its bead 2 an anchoring zone 5 of a carcass reinforcement 4, in two
variant embodiments (FIGS. 1 and 2); [0018] a cross-section of
cables of constructions 4+9 (FIG. 3) and 2+7 (FIG. 4) usable in
said anchoring zone.
I. DEFINITIONS AND TESTS
I-1. Definitions
[0019] In the present application, the following are understood to
mean in known manner: [0020] "axial": a direction parallel to the
axis of rotation of the tire; this direction may be "axially inner"
when it is directed towards the inside of the tire and "axially
outer" when it is directed towards the outside of the tire; [0021]
"bead": the portion of the tire adjacent radially internally to the
sidewall and the base of which is intended to be mounted on a rim
seat of a vehicle wheel; [0022] "diene elastomer (or inaccurately
rubber)": an elastomer resulting at least in part (that is to say a
homopolymer or a copolymer) from diene monomer(s) (monomer(s)
bearing two double carbon-carbon bonds, whether conjugated or not);
[0023] "essentially saturated diene elastomer": a diene elastomer
resulting at least in part from conjugated diene monomers, having a
content of members or units of diene origin (conjugated dienes)
which is less than 15% (mole %); [0024] "essentially saturated
diene elastomer": a diene elastomer resulting at least in part from
conjugated diene monomers, having a content of members or units of
diene origin (conjugated dienes) which is greater than 15% (mole
%); [0025] "highly unsaturated diene elastomer": a diene elastomer
of the essentially saturated type, having a content of members or
units of diene origin (conjugated dienes) which is greater than 50%
(mole %); [0026] "isoprene elastomer": an isoprene homopolymer or
copolymer, in other words a diene elastomer selected from the group
consisting of natural rubber (NR), synthetic polyisoprenes (IR),
the various isoprene copolymers and mixtures of these elastomers;
[0027] "sidewall": the portion of the tire, most frequently of low
flexural strength, located between the crown and the bead; [0028]
"radial": a direction passing through and perpendicular to the axis
of rotation of the tire; this direction may be "radially inner" or
"radially outer" according to whether it is directed towards the
axis of rotation of the tire or towards the outside of the tire;
[0029] "reinforcement element" or "reinforcing member": equally
well monofilaments and multifilaments, or assemblies such as
cables, plied yarns or any other equivalent type of assembly,
whatever the material and the treatment of these reinforcing
members, for example surface treatment or coating such as
rubber-coating, or alternatively pre-sizing in order to promote
adhesion to the rubber; [0030] "circumferentially oriented
reinforcing member" or "circumferential reinforcing member": a
reinforcing member oriented substantially parallel to the
circumferential direction of the tire, that is to say forming with
this direction an angle which does not deviate by more than five
degrees from the circumferential direction; [0031] "radially
oriented reinforcing member" or "radial reinforcing member": a
reinforcing member contained substantially within one and the same
axial plane or within a plane forming with an axial plane an angle
less than or equal to 10 degrees.
I-2. Tests
A) Dynamometric Measurements
[0032] As regards the wires and metal cables, the measurements of
breaking load Fm (maximum load in N), tensile strength Rm (in MPa)
and elongation at break At (total elongation in %) are carried out
under tension in accordance with Standard ISO 6892 of 1984.
[0033] As regards the rubber compositions, the modulus measurements
are carried out under tension, unless indicated otherwise in
accordance with Standard ASTM D 412 of 1998 (test piece "C"): the
true secant moduli (or Young's moduli), reduced to the real section
of the test piece at 10% elongation, referred to as E10 and
expressed in MPa, are measured in a second elongation (that is to
say after an accommodation cycle) (normal conditions of temperature
and humidity in accordance with Standard ASTM D 1349 of 1999).
B) Static Creep Test
[0034] The so-called "static creep" test is a test in which test
pieces of rubber composition the useful part of which has a length
of 70 mm, a width of 5 mm and a thickness of 2.5 mm (these test
pieces are cut from vulcanized sheets of a thickness of 2.5 mm) are
prepared; the test pieces are placed in an oven at 150.degree. C.
and a 3 kg weight is immediately hung from them; the test is thus
carried out with an initial stress of:
.sigma. 0 = Mg S 0 = 2.35 MPa ##EQU00001##
where M is: weight applied, g is: gravity acceleration and S.sub.0
is: initial section of the test piece being measured; the
elongation of the useful part of the test piece is measured as a
function of time; the "amount of static creep" corresponds to the
variation of deformation over a given time, for example between 3
and 5 hours' testing:
.tau. = .DELTA. .DELTA. t ##EQU00002##
where: .DELTA..epsilon.=.epsilon.(t.sub.2)-.epsilon.(t.sub.1):
variation in the deformation measured during
.DELTA.t=t.sub.2-t.sub.1 in minutes (min).
C) Rheometry Test
[0035] The "rheometry" test is an alternating shearing test at a
deformation of .+-.0.2 degrees, a frequency of 100 cycles/min., a
temperature of 197.degree. C. and a duration of 10 min (rheometer
from Monsanto). The test is carried out on a disc of uncured rubber
composition, the change in the torque resulting from the shearing
imposed between the two faces of the disc over the min. is recorded
and the change in the torque after the maximum measured is noted:
if the torque measured remains stable, there is no reversion, that
is to say, reduction in the stiffness of the test piece; if the
torque measured decreases, there is reversion. The phenomenon of
reversion results in a reduction in the rigidity of the test piece
under the test conditions; it is therefore a test of the thermal
stability of the mix at high temperature.
r = C max - C 10 C max .times. 100 ##EQU00003##
denotes the amount of reversion at the end of the test; C.sub.max
is the maximum torque measured and C.sub.10 is the torque measured
after 10 min.
II. DETAILED DESCRIPTION OF THE INVENTION
[0036] In the present description, unless expressly indicated
otherwise, all the percentages (%) indicated are mass %.
II-1. Layered Cable 4+N
[0037] The metal cable according to the invention is a cable having
two layers of construction 4+N comprising a core or inner layer
(C1) of 4 wires of diameter d.sub.1 wound together in a helix at a
pitch p.sub.1, this layer C1 itself being surrounded by an outer
layer (C2) of N wires of diameter d.sub.2 wound together in a helix
at a pitch p.sub.2, this cable furthermore having the following
characteristics (d.sub.1, d.sub.2, p.sub.1 and p.sub.2 in mm):
[0038] 0.25<d.sub.1<0.40; [0039] 0.25<d.sub.2<0.40;
[0040] 3.5<p.sub.1<7<p.sub.2<14.
[0041] All the above characteristics are of course measured when
the cable is at rest and its axis rectilinear.
[0042] "Metal cable" is understood here by definition to mean a
cable formed of wires made majoritarily (that is to say to more
than 50% of these wires) or fully (for 100% of the wires) of a
metallic material.
[0043] The wires of layers C1 and C2 may have a diameter which is
identical or different from one layer to the other. Preferably
wires of the same diameter from one layer to the other (i.e.
d.sub.1=d.sub.2) are used, in particular to simplify the cabling
process, as shown, for example, in the appended FIG. 3.
[0044] It will be recalled here that in known manner the pitch "p"
represents the length, measured parallel to the axis of the cable,
at the end of which a wire having this pitch makes a complete turn
around said axis of the cable.
[0045] Using different pitches p.sub.1 and p.sub.2 means that, in
known manner, the wires of the layers C1 and C2 are essentially
arranged in two cylindrical (or tubular), adjacent and concentric
layers, such that, at least in the cable at rest, the thickness of
the outer layer C2 is substantially equal to the diameter of the
wires which constitute it; as a result, the cross-sections of the
inner layer C1 and of the outer layer C2, like that of the cable,
have an outer enveloping surface or a contour (denoted for example
E1 and E2 respectively in FIGS. 3 and 4) which is substantially
circular.
[0046] The cables having cylindrical or tubular layers must in
particular not be confused with what are called "compact" layered
cables, which are assemblies of wires wound with the same pitch and
in the same direction of twist; in such cables, the compactness is
such that practically no distinct layer of wires is visible; as a
result, the cross-section of such cables has a contour which is no
longer circular, but polygonal.
[0047] Preferably, the layers C1 and C2 are wound in the same
direction of twist (either S/S or Z/Z), which has the significant
advantage of minimising the contact pressure between the wires.
[0048] Preferably, the layer C2 of the cable of the invention
comprises from 8 to 12 cords (8.ltoreq.N.ltoreq.12), more
preferably from 8 to 10 cords (8.ltoreq.N.ltoreq.10).
[0049] According to another preferred embodiment of the invention,
for better ability of the cables to be penetrated by the anchoring
rubber, the outer layer C2 is a tubular layer of N wires referred
to as "unsaturated" or "incomplete", that is to say that, by
definition, there is sufficient space in this tubular layer C2 to
add at least one (N+1)th wire of diameter d.sub.2, several of the N
wires possibly being in contact with each other, Reciprocally, this
tubular layer C2 would be referred to as "saturated" or "complete"
if there was not sufficient space in this layer to add at least one
(N+1)th wire of diameter d.sub.2.
[0050] FIG. 3 shows, in a section perpendicular to the axis of the
cable (assumed to be rectilinear and at rest), an example of a
preferred cable of construction 4+9 (cable denoted C-II in the
following examples). The inner layer C1, which is formed of four
wires 20 wound together in a helix at a pitch p.sub.1, is itself
surrounded by and in contact with an outer layer C2 of nine wires
20 wound together in a helix at a pitch P.sub.2, and therefore of a
thickness substantially equal to the diameter d.sub.2 of said
wires. It can clearly be seen that the wires 20 are thus arranged
in two adjacent, concentric, tubular layers (layer C1 of contour
E1, and layer C2 of contour E2).
[0051] According to a preferred embodiment of the invention, the
following characteristics are satisfied (d.sub.1, d.sub.2, p.sub.1
and p.sub.2 in mm): [0052] 0.30<d.sub.1<0.40; [0053]
0.30<d.sub.2<0.40; [0054] 4.0<p.sub.1<7 and
8<p.sub.2<14.
[0055] It is within these narrow ranges of diameters d.sub.1 and
d.sub.2 on one hand, and of short pitches p.sub.1 and p.sub.2 on
the other hand, that the best compromise of performances has been
obtained. More preferably still, for these same reasons, the
following relationships are satisfied (p.sub.1 and p.sub.2 in mm):
[0056] 4.5.ltoreq.p.sub.1.ltoreq.6.5 and
8.5.ltoreq.p.sub.2.ltoreq.13.5.
[0057] The total elongation at break (At) of the cable, the total
of its structural, elastic and plastic elongations (At=As+Ae+Ap),
is preferably greater than 2.5%, more preferably greater than 3.0%,
even more preferably greater than 3.5%.
[0058] The present cable could also be high-elongation treated, to
impart thereto an operational elongation Af (Af=Ae+Ap) of greater
than 4%, preferably greater than 5%, more preferably still greater
than 6%. It will be recalled that such a treatment may consist of a
heat treatment by Joule effect, by static convection or
alternatively by induction, performed directly on the cable, as
described in the aforementioned application EP-A-751 015.
[0059] The invention is preferably carried out with a steel cable,
more preferably one made of perlitic (or ferrito-perlitic) carbon
steel hereinafter referred to as "carbon steel", or alternatively
of stainless steel (by definition, steel comprising at least 11%
chromium and at least 50% iron) such as are described for example
in applications EP-A-648 891 or WO-A-98/41682. However, it is of
course possible to use other steels or other alloys.
[0060] The metal or steel used, be it in particular a carbon steel
or a stainless steel, may itself be coated with a metallic layer
which improves for example the processing properties of the metal
cable and/or its constituent elements, or the use properties of the
cable and/or of the tire themselves, such as the properties of
adhesion, corrosion resistance or alternatively ageing
resistance.
[0061] According to a preferred embodiment, the steel used is
covered with a layer of brass (Zn--Cu alloy) or of zinc; it will be
recalled that during the process of manufacturing the wires, the
brass or zinc coating facilitates the drawing of the wire, as well
as the sticking of the wire to the rubber. However, the wires could
be covered with a fine metal layer other than brass or zinc, having
for example the function of improving the corrosion resistance of
these wires and/or the adhesion thereof to the rubber, for example
a fine layer of Co, Ni, Al, or of an alloy of two or more of the
compounds Cu, Zn, Al, Ni, Co, Sn.
[0062] When the cables of the composites of the invention are used
for reinforcing beads of bead-wire-less tires, they are preferably
made of carbon steel and have a tensile strength (Rm) greater than
2000 MPa.
[0063] The person skilled in the art will know how to manufacture
carbon steel wires having such strength, by adjusting in particular
the composition of the steel and the final work-hardening ratios of
these wires, according to his own particular needs, using for
example micro-alloyed carbon steels containing specific alloying
elements such as Cr, Ni, Co, V, or various other known elements
(see for example Research Disclosure 34984--"Micro-alloyed steel
cord constructions for tires"--May 1993; Research Disclosure
34054--"High tensile strength steel cord constructions for
tires"--August 1992).
[0064] When a carbon steel is used, its carbon content is
preferably of between 0.1% and 1.2%, in particular between 0.5% and
1.1%. It is more preferably of between 0.6% and 1.0% (% by weight
of steel), such a content representing a good compromise between
the mechanical properties required for the composite and the
feasibility of the wires.
[0065] The cable presently described might be provided with an
external wrap, formed for example of a single wire, whether or not
of metal, wound in a helix about the cable at a pitch shorter than
that of the outer layer, and in a direction of winding opposite or
identical to that of this outer layer. However, owing to its
specific structure, the cable of the invention, which is already
self-wrapped, does not generally require the use of an external
wrapping wire, which advantageously solves the problems of wear
between the wrap and the wires of the outermost layer of the
cable.
[0066] The layered cable previously described is manufactured using
cabling devices and using processes well-known to the person
skilled in the art which are not described here in order to
simplify the description. Owing to the different pitches p.sub.1
and p.sub.2, it requires two successive operations (manufacture of
the first, inner, layer C1 then cabling of the second, outer, layer
C2 around this layer C1), these two operations possibly
advantageously being effected in-line using two cablers (for
example Barmag cablers) arranged in series.
II-2. Use in a Rubber Matrix
[0067] The cables according to the invention are particularly
intended for reinforcing the bead zones of tires, in particular
tires without a solid bead wire such as described in the
aforementioned patent specifications, as anchoring cables for the
carcass reinforcements of such tires.
[0068] Advantageously, such a cable, oriented circumferentially,
cooperates with an adjacent portion of the carcass reinforcement by
means of a rubber composition or diene elastomer (as "anchoring
rubber") in contact with said cable and said carcass
reinforcement.
[0069] The diene elastomers, in known manner, may be classed in two
categories, those referred to as essentially unsaturated and those
referred to as essentially saturated. Thus, for example, butyl
rubbers or copolymers of dienes and of alpha-olefins of the EPDM
type fall within the definition of essentially saturated diene
elastomers (low or very low content of units of diene origin which
is always distinctly less than 15%).
[0070] Although it is applicable to any type of diene elastomer,
the person skilled in the art of tires will readily understand that
the present invention is preferably used with diene elastomers of
the highly unsaturated type.
[0071] The diene elastomer is in particular selected from among the
group consisting of polybutadienes (BR), natural rubber (NR),
synthetic polyisoprenes (IR), the various butadiene copolymers, the
various isoprene copolymers and mixtures of these elastomers. Such
copolymers are more preferably selected from the group consisting
of butadiene/styrene copolymers (SBR), whether the latter be
prepared by emulsion polymerisation (ESBR) or by solution
polymerisation (SSBR), isoprene/butadiene copolymers (BIR),
isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene
copolymers (SBIR).
[0072] More preferably at least one isoprene elastomer is used,
even more preferably natural rubber or a synthetic polyisoprene of
the cis-1,4 type; of these synthetic polyisoprenes, preferably
polyisoprenes having a content (mole %) of cis-1,4 bonds greater
than 90%, more preferably still greater than 98%, are used.
[0073] The isoprene elastomer may be used on its own or in a blend
with other diene elastomers, in particular SBR and/or BR elastomers
such as those mentioned above, whether or not the isoprene
elastomer be present in a majority proportion among all the diene
elastomers used.
[0074] Thus, according to a specific embodiment of the invention,
it is possible to use for example, in a blend with the isoprene
elastomer (in particular natural rubber), an SBR copolymer having a
Tg (glass transition temperature, measured in accordance with ASTM
D3418) of preferably between -70.degree. C. and -10.degree. C.,
whether it be prepared in emulsion (E-SBR) or in solution (S-SBR),
in a proportion of 0 to 70 phr (parts by weight per hundred parts
of elastomer), the remainder (namely 30 to 100 phr) being
constituted by the isoprene elastomer. In that case, more
particularly an SSBR is used. There may also be associated with
said SBRs a BR having preferably more than 90% (mole %) of cis-1,4
bonds, said BR having a Tg preferably between -110.degree. C. and
-50.degree. C.
[0075] Finally, the diene elastomer(s) may be used in association
with any type of synthetic elastomer other than a diene elastomer,
or even with polymers other than elastomers, for example
thermoplastic polymers.
[0076] Such a composition furthermore comprises all the
conventional constituents usually used in rubber matrices intended
in particular for the manufacture of bottom zones of tires, such as
for example reinforcing fillers such as carbon black or inorganic
fillers such as silica, inorganic-filler coupling agents,
anti-ageing agents, antioxidants, plasticising agents or extender
oils, whether the latter be aromatic or non-aromatic in nature (in
particular oils which are only very slightly or not aromatic, for
example of naphthenic or paraffinic type, of high or preferably low
viscosity, MES or TDAE oils), agents which facilitate processing
(processability) of the compositions in the uncured state,
stearamides, tackifying resins, a cross-linking system based on
either on sulfur, or on sulfur and/or peroxide donors,
vulcanization accelerators, activators or retarders, anti-reversion
agents such as for example sodium hexathiosulfonate or
N,N'-m-phenylene-biscitraconimide, methylene acceptors and donors,
reinforcing resins, bismaleimides, known adhesion-promoting systems
of the type "RFS" (resorcinol/formaldehyde/silica) or metal salts,
in particular cobalt or nickel salts.
[0077] The person skilled in the art will be able, in the light of
the present description, to adjust the formulation of the rubber
composition in order to achieve the desired levels of rigidity
(elasticity modulus), and to give excellent high-temperature creep
resistance and very good high-temperature stability.
[0078] The creep resistance is essential in obtaining solid and
durable anchoring of the carcass reinforcements in the beads and
the high-temperature thermal stability is also important owing to
the very harsh thermal conditions to which some tire beads may be
subjected during operation, in particular those for heavy-vehicle
tires, whether road tires or not.
[0079] Thus, preferably, the anchoring rubber withstands without
breaking a static creep stress at 150.degree. C. under an initial
stress of 2.35 MPa for at least 5 hours; more preferably, its
amount of static creep at 150.degree. C. under an initial stress of
2.35 MPa remains less than 2.times.10.sup.-3/min for between 3 and
5 hours' applied stress. On the other hand and preferably, said
rubber has an amount of reversion, after 10 min at 197.degree. C.,
which is less than 10% and more preferably less than 5%.
[0080] The cross-linking system is preferably a vulcanization
system based on sulfur and a vulcanization accelerator. Any
compound capable of acting as a vulcanization accelerator for the
diene elastomers in the presence of sulfur may be used, in
particular those selected from among the group consisting of
2-mercaptobenzothiazyl disulfide (abbreviated to "MBTS"),
N-cyclohexyl-2-benzothiazyl sulfenamide (abbreviated to "CBS"),
N,N-dicyclohexyl-2-benzothiazyl sulfenamide (abbreviated to
"DCBS"), N-tert butyl-2-benzothiazyl sulfenamide (abbreviated to
"TBBS"), N-tert butyl-2-benzothiazyl sulfenimide (abbreviated to
"TBSI") and mixtures of these compounds. Preferably a primary
accelerator of sulfenamide type is used.
[0081] To this vulcanization system there are added, incorporated
during the first, non-productive, phase and/or during the
productive phase, various known secondary accelerators or
vulcanization activators such as zinc oxide, stearic acid,
guanidine derivatives (for example diphenylguanidine), etc.
[0082] The sulfur is used in a preferred amount of between 3 and 15
phr (parts by weight per hundred parts of elastomer), more
preferably of between 5 and 12 phr. The primary vulcanization
accelerator, for example a sulfenamide, is used in a preferred
amount of between 0.5 and 7 phr, more preferably of between 1 and 5
phr.
[0083] The amount of reinforcing filler, for example carbon black
or reinforcing inorganic filler such as silica, is preferably
greater than 50 phr, for example of between 60 and 140 phr. It is
more preferably greater than 70 phr, for example between 70 and 120
phr.
[0084] Suitable carbon blacks are all the carbon blacks,
particularly blacks of the type HAF, ISAF and SAF conventionally
used in tires (what are called tire-grade blacks). Of the latter,
reference will more particularly be made to the reinforcing carbon
blacks of series 100, 200 or 300 (ASTM grades), such as, for
example, the blacks N115, N134, N234, N326, N330, N339, N347, N375,
or alternatively, depending on the intended applications, the
blacks of higher series (for example N660, N683, N772).
[0085] Suitable reinforcing inorganic fillers are in particular
mineral fillers of siliceous type, in particular silica
(SiO.sub.2), or of aluminous type, in particular alumina
(Al.sub.2O.sub.3). The silica used may be any reinforcing silica
known to the person skilled in the art, in particular any
precipitated or fumed silica having a BET surface area and a CTAB
specific surface area both of which are less than 450 m.sup.2/g,
preferably from 30 to 400 m.sup.2/g. As highly dispersible
precipitated silicas (referred to as "HD"), mention will be made of
for example the silicas Ultrasil 7000 and Ultrasil 7005 from
Degussa, the silicas Zeosil 1165MP, 1135MP and 1115MP from Rhodia,
the silica Hi-Sil EZ150G from PPG, and the silicas Zeopol 8715,
8745 and 8755 from Huber. Examples of reinforcing aluminas are the
aluminas "Baikalox" "A125" or "CR125" from Baikowski, "APA-100RDX"
from Condea, "Aluminoxid C" from Degussa or "AKP-G015" from
Sumitomo Chemicals.
[0086] For coupling the diene elastomer to the reinforcing
inorganic filler, if applicable, a coupling agent (or bonding
agent) which is at least bifunctional which is intended in known
manner to provide a sufficient chemical and/or physical connection
between the inorganic filler (surface of its particles) and the
diene elastomer, in particular bifunctional organosilanes or
polyorganosiloxanes, is used.
[0087] The rubber composition or matrix has the preferred
characteristic of having, in the vulcanized state, a secant tensile
modulus, at 10% elongation (E10), which is greater than 20 MPa,
more preferably greater than 30 MPa. It is within these ranges of
rigidity, in particular between 40 and 70 MPa, that the best
compromise of performances has been observed.
[0088] In the case of the greater rigidities, the rubber
composition may advantageously comprise an additional reinforcing
resin consisting for example of a methylene acceptor such as a
phenol-formaldehyde resin, in a preferred amount of between 3 and
15 phr, more preferably of between 5 and 12 phr, and a methylene
donor such as hexamethylenetetramine ("HMT") or alternatively
hexamethoxymethylmelamine ("H3M"), in a preferred amount of between
1 and 10 phr, more preferably of between 3 and 7 phr.
[0089] But the cable of the invention is also usable with an
anchoring rubber of reduced rigidity, having in particular an
elasticity modulus of between 10 and 20 MPa, as described for
example in the aforementioned patent application EP-A-1 277
600.
II-3. Use in a Tire
[0090] The cable of the invention is advantageously usable for
reinforcing a tire, in the form of a metal/rubber composite. Such a
composite may be of varied forms, for example in the form of a ply,
band, strip or series of strips, other blocks of rubber of varied
forms and dimensions according to the intended applications, in
which are incorporated or with which cooperate the 4+N cables
previously described.
[0091] In this composite, the definitive adhesion between the metal
and the rubber composition is obtained in known manner on emerging
from the curing of the finished article, for example the tire,
comprising the composite. Preferably this curing is effected under
pressure.
[0092] Such a composite preferably constitutes part of a bead zone
of a tire devoid of a conventional solid bead wire, said part of
the bead zone being intended to anchor the carcass reinforcement of
said tire.
[0093] Such a bead-wire-less tire, such as that described for
example in terms of its general construction in the aforementioned
documents EP-A-582 196, EP-A-664 231, EP-A-664 232, EP-A-664 233,
WO-A-98/54006 or WO-A-2004/009380, generally comprises a crown
surmounted by a tread, a crown reinforcement, a carcass
reinforcement passing into the sidewalls and rejoining two beads
designed to be mounted on the wheel rim of a vehicle. Said carcass
reinforcement comprises first reinforcing members (or "radial
reinforcing members") arranged adjacent and practically parallel to
one another, aligned circumferentially in at least one
circumferential alignment from at least one of said beads towards
one of said sidewalls and anchored in said bead, the latter
comprising an anchoring zone for holding the carcass reinforcement
and comprising at least one second reinforcing member ("anchoring
reinforcing member" or "anchoring cable") oriented
circumferentially and cooperating with an adjacent portion of the
carcass reinforcement by means of a rubber composition (or
"anchoring rubber") in contact with the anchoring reinforcing
member and the adjacent lengths of the first radial reinforcing
members. In this tire, the cable and the anchoring rubber are as
defined in sections II-1 and II-2 above.
[0094] The radial reinforcing members above are for example textile
cabled yarns made of polyester (for example PET HMLS), PEN, rayon
or other cellulose, nylon, aramid or alternatively of hybrid
material (for example aramid/nylon).
[0095] By way of non-limitative example, there are depicted in FIG.
1, in partial cross-section, a bead and a sidewall of such a tire,
in which the conventional anchoring, by turning up the carcass
reinforcement about a solid bead wire, is replaced, it may be
recalled, by an arrangement in which circumferential anchoring
cables are arranged adjacent to the structure of radial reinforcing
members, the whole being embedded in a rubber mix or anchoring
rubber.
[0096] This tire comprises a sidewall 1 adjacent to a bead 2. A
carcass reinforcement 3 extends circumferentially from the bead 2
towards the sidewall 1 and comprises in the example illustrated a
circumferential alignment of first radial reinforcing members 4.
This carcass reinforcement 3 may be arranged continuously from one
bead to the other, passing through the sidewalls and the crown of
the tire, or alternatively it may comprise two or more parts,
arranged for example along the sidewalls, in particular without
covering all of the crown. The radial reinforcing members 4, for
example in this case textile cabled yarns of PET HMLS, are oriented
radially in the beads and the sidewalls and are anchored in an
anchoring zone 5 of the bead 2.
[0097] The anchoring zone 5 preferably comprises two
circumferential windings or "stacks" 6a and 6b of second
reinforcing members or anchoring cables 7 arranged on either side
of the section 4a of the adjacent first radial reinforcing members
4, said stacks 6a and 6b cooperating with an anchoring rubber 8 in
which they are incorporated.
[0098] This anchoring rubber 8 completely covers the length 4a of
the radial reinforcing members 4, and the circumferential windings
or stacks 6a and 6b of anchoring cable 7, so as to anchor the
length 4a of the radial reinforcing members 4 securely in the
anchoring zone 5 of the bead 2 and to take up the forces to which
the first reinforcing members 4 are subjected due in particular to
the inflation pressure of the tire. The stacks 6 may be produced
for example by juxtaposition of a plurality of different
circumferential cable elements 7, or by winding (substantially at
zero degrees) one and the same cable 7 in a spiral, the turns of
course being non-contiguous in any case. The anchoring cable 7 is a
cable having two layers of construction 4+9 as illustrated in FIG.
3, according to the invention. The total number of these cables or
windings of the same cable lies for example within a range from 10
to 25 approximately, for the two stacks 6a and 6b together.
[0099] By way of example, the average inter-cable (or
inter-winding) distance is of the order of 0.3 mm; the minimum
distance (to avoid any direct contact between the textile and
metal) between the length 4a and each of the two stacks 6a and 6b
is of between 0.5 and 0.8 mm.
[0100] Axially internally relative to the circumferential winding
of anchoring cables 6a, there is a conventional rubber mix 9 as
"internal rubber", the function of which is to provide tightness of
the inside of the tire casing. Axially externally relative to the
circumferential winding 6b of the anchoring cables, there is a
protective mix 10, then, radially externally, a sidewall mix 11
which gradually replaces it. Radially externally to the anchoring
zone 5, the radial reinforcing members 4 of the carcass
reinforcement 3 are in direct contact with a mix 12.
[0101] The first reinforcing members 4 of this tire bead are
therefore in contact with two different rubber mixes, the anchoring
rubber 8 in the anchoring zone 5 and the mix 12 radially to the
outside. The preferred mechanical characteristic of the anchoring
rubber is an elasticity modulus (E10) greater than 20 MPa, whereas
the mix 12 has a lesser rigidity, with a modulus of between 3 and
10 MPa.
[0102] In the anchoring zone 5 of the bead 2, the anchoring rubber
8 is the sole rubber mix in contact with the first 4 and second 7
reinforcing members. This anchoring rubber imparts to this
structure excellent mechanical resistance to the forces to which it
is subjected upon inflation of the tire and during travel.
[0103] FIG. 1, which has been commented on above, shows only a
single preferred example of an anchoring structure of the bottom
zone of a tire using the cable according to the invention.
[0104] The person skilled in the art will readily understand that a
large number of other variants are possible, for example with
anchoring zones 5 comprising three anchoring stacks 6a, 6b and 6c,
one on either side of the length 4a of the radial reinforcing
members 4, or more than three stacks.
[0105] FIG. 2 depicts a partial cross-section through another
possible example of a tire, the anchoring zone 5 of which comprises
the same anchoring rubber 8 but three circumferential stacks 6a, 6b
and 6c of anchoring cable 7 of construction 4+9, according to the
invention. The total number of these cables lies for example within
a range from 15 to 30 approximately, for the three stacks 6a, 6b
and 6c together.
[0106] By way of example, the average inter-cable (or
inter-winding) distance is of the order of 0.3 mm, the average
inter-stack distance (between stacks 6b and 6c in this FIG. 2) is
of the order of 0.5 mm and the minimum distance (to avoid any
direct contact between the textile and metal) between the length 4a
and each of the two stacks 6a and 6b is of between 0.5 and 0.8
mm.
[0107] Other possible variant embodiments of the tire of the
invention will consist for example of using a plurality of lengths
4a of radial reinforcing members 4 in the anchoring zone 5 of the
bead 2, or a plurality of alignments 4 of radial reinforcing
members in the same carcass reinforcement 3, including in the
sidewall 1, or even alternatively a plurality of carcass
reinforcements 3 in this sidewall 1.
[0108] Another possible variant embodiment will consist of
non-linear anchoring such as described in the aforementioned
application WO-A-2004/009380.
[0109] In another possible variant embodiment of the invention,
taken alone or in combination with at least one of the variants
previously described, the individual radial reinforcing members 4
could of course be replaced by groupings of several parallel radial
reinforcing members, grouped together for example in the form of
rubberised strips reinforced by said radial reinforcing members, as
described for example in application EP-A-919 406.
[0110] In non-limitative manner, it should be noted that the tires
according to the invention may advantageously be manufactured using
a process which does not involve any, or only a few,
transformations of forms in the uncured state. For example, the
blank of the future tire can be assembled on a rigid core which
imposes the form of its inner cavity. There are applied to this
core, in the order required by the final architecture, all the
individual constituents of the tire, which are arranged directly in
their final position, no portion of the tire later being displaced
or folded over against another, as is generally the case in
conventional assembly methods. This manufacture may in particular
use the devices described in patent specifications EP-A-243 851 (or
U.S. Pat. No. 4,795,523) for laying the radial reinforcing members
of the carcass reinforcement and EP-A-264 600 (or U.S. Pat. No.
4,963,207) for laying the rubbers or rubber compositions. The tire
can then be moulded and vulcanized as set forth for example in
patent specification EP-A-242 840 (or U.S. Pat. No. 4,895,692).
III. EXAMPLES OF EMBODIMENT OF THE INVENTION
III-1. Anchoring Cables
[0111] To produce the following examples of embodiment, cylindrical
layered cables of different constructions, 4+9 and 2+7, in
accordance with or not in accordance with the invention depending
on the case, formed of fine carbon steel wires coated with brass
are used.
[0112] The carbon steel wires are prepared in known manner,
starting, for example, from machine wires (diameter 5 to 6 mm)
which are first of all work-hardened, by rolling and/or drawing, to
an intermediate diameter close to 1 mm, or alternatively starting
directly from commercial intermediate wires, the diameter of which
is close to 1 mm. The steel used is a carbon steel of the
high-strength type (referred to as HT for "High Tensile"), the
carbon content of which is approximately 0.82%, comprising
approximately 0.5% manganese, the remainder consisting of iron and
the usual inevitable impurities linked to the manufacturing process
for the steel (for example, contents of silicon: 0.25%; phosphorus:
0.01%; sulfur: 0.01%; chromium: 0.11%; nickel: 0.03%; copper:
0.01%; aluminium: 0.005%; nitrogen: 0.003%).
[0113] The wires of intermediate diameter undergo a degreasing
and/or pickling treatment before their subsequent transformation.
After depositing a brass coating on these intermediate wires, what
is called "final" work-hardening is effected on each wire (i.e.
after the final heat treatment of patenting), by cold-drawing in a
wet medium with a drawing lubricant which is for example in the
form of an aqueous emulsion or dispersion.
[0114] The cords thus prepared (referenced 20 in FIGS. 3 and 4),
all of a diameter of approximately 0.35 mm, have the following
mechanical properties:
TABLE-US-00001 Breaking load: 265 N; Young's modulus: 210 GPa;
Tensile strength: 2790 MPa; Elongation at break: 2.2% (Ae = 1.4% +
Ap = 0.8%).
[0115] These wires are then assembled in the form of different
cylindrical layered cables, referenced C-I to C-V, the construction
and the mechanical properties of which are given in Table 1.
TABLE-US-00002 TABLE 1 p.sub.1 p.sub.2 Fm Rm At Af Cable
Construction (mm) (mm) (daN) (MPa) (%) (%) C-I 4 + 9 7.5 15.0 280
2210 5.9 5.7 C-II 4 + 9 5.0 10.0 305 2275 3.8 3.5 C-III 4 + 9 5.0
10.0 275 2105 6.5 6.2 C-IV 2 + 7 7.5 15.0 196 2275 5.3 5.2 C-V 2 +
7 5.0 10.0 215 2425 3.4 3.2
[0116] The cables of construction [4+9], denoted C-I to C-III, are
non-wrapped cables (without an external wrapping wire), and are
formed of a total of thirteen wires 20, as illustrated in FIG. 3.
They comprise an inner layer C1 of four wires 20 wound together in
a helix (S direction) at the pitch p.sub.1, this layer C1 being in
contact with a cylindrical outer layer of nine wires 20 which
themselves are wound together in a helix (S direction) around the
core, at the pitch p.sub.2.
[0117] The cable C-I (not in accordance with the invention) has
conventional long pitches p.sub.1 and p.sub.2 (p.sub.1=7.5 mm;
p.sub.2=15 mm); as the aforementioned application EP-A-751 015
teaches, it underwent a "high-elongation" treatment in order to
impart thereto an operational elongation Af of greater than
4.0%.
[0118] Only cables C-II and C-III are in accordance with the
invention, with short pitches p.sub.1 and p.sub.2 which satisfy the
aforementioned relationships 4.0<p.sub.1<7 and
8<p.sub.2<14. The total elongation At of the cable C-II,
which unlike the control cable C-I is not "high-elongation"
treated, is advantageously greater than 3.0%. For comparison, the
cable C-III, which is of the same construction as the cable C-II,
furthermore underwent a high-elongation treatment, which imparts
thereto an operational elongation Af and a total elongation At
which are very high, since both are greater than 6.0%. This
treatment consisted of heating the cable continuously during its
travel, by induction under a protective atmosphere (for example
hydrogen); the heating time was approximately 0.1 second, and the
treatment temperature was 450.degree. C. After the heating, the
cable was cooled in a protective atmosphere (H.sub.2) and then
wound on a spool.
[0119] It is furthermore noted that these cables C-II and C-III
according to the invention advantageously satisfy the following
preferred relationships (d.sub.1, d.sub.2, p.sub.1 and p.sub.2 in
mm): [0120] 0.30<d.sub.1=d.sub.2<0.40; [0121]
4.5.ltoreq.p.sub.1.ltoreq.6.5; [0122]
8.5.ltoreq.p.sub.2.ltoreq.13.5.
[0123] As for the other two control cables, of construction 2+7,
C-IV and C-V, which are also non-wrapped, they are formed of a
total of nine cords 20, as illustrated in FIG. 4. They comprise an
inner layer C1 of two wires 20 wound together in a helix (S
direction) at the pitch p.sub.1, this core being in contact with a
cylindrical outer layer of seven wires 20 which themselves are
wound together in a helix (S direction) around the core, at the
pitch p.sub.2. The cable C-IV has conventional long pitches p.sub.1
and p.sub.2 (p.sub.1=7.5 mm; p.sub.2=15 mm), and underwent a
"high-elongation" treatment in order to impart thereto an
elongation Af of greater than 4.0%. The cable C-V has short pitches
p.sub.1 and p.sub.2 (p.sub.1=5 mm; p.sub.2=10 mm), it did not
undergo a "high-elongation treatment".
III-2. Anchoring Rubber
[0124] For the following tests, the anchoring cables C-I and C-II
on one hand, and C-IV and C-V on the other hand are associated with
one and the same anchoring rubber of high rigidity in the cured
stated (modulus E10 equal to approximately 55 MPa).
[0125] This anchoring rubber is a known composition based on diene
elastomer (50/50 blend of NR and of SSBR having a Tg of
approximately -50.degree. C.), and of carbon black (approximately
75 phr) as reinforcing filler. Furthermore, it essentially
comprises an antioxidant (approximately 2 phr), a reinforcing resin
(approximately 10 phr of phenol-formaldehyde resin and 5 phr of
methylene donor H3M), a metal salt (approximately 4 phr of cobalt
naphthenate) as promoter of adhesion with respect to the metal, and
finally a vulcanization system (approximately 9 phr of sulfur, 1.5
phr of accelerator, 9 phr of ZnO and 1.5 phr of stearic acid).
III-3. Comparative Tests on Tires
[0126] The cables and anchoring rubbers above are used as anchoring
structures for a carcass reinforcement of bead-wire-less tires
having a radial carcass, of dimension 225/45 R17 (speed index Y),
which are conventionally manufactured and identical in all points
except for the construction of their anchoring zones 5.
[0127] These tires comprise in known manner a crown surmounted by a
tread, a crown reinforcement and, referring now for example to the
numbering of FIG. 1 or 2, two sidewalls 1 and two beads 2, a
carcass reinforcement 3 which passes into the two sidewalls 2 and
is anchored by means of anchoring means 5 (6a, 6b, 8) in the two
beads 2. The carcass reinforcement 3 comprises at least one
circumferential alignment of radial reinforcing members 4, which
are arranged adjacent and practically parallel to one another,
aligned circumferentially in at least one circumferential alignment
from at least one of said beads 2 towards one of said sidewalls 1.
The means 5 (6a, 6b, 8) for anchoring said radial reinforcing
members 4 in at least one bead 2 comprise at least one
circumferentially oriented anchoring cable 7, axially bordering
said circumferential alignments of the radial reinforcing members 4
and cooperating with an adjacent portion of the carcass
reinforcement 3 by means of an anchoring rubber 8 in contact with
the anchoring cable 7 and the adjacent lengths 4a of the first
radial reinforcing members 4. The anchoring cables 7 used in these
tires are the cables C-I and C-II on one hand, and C-IV and C-V on
the other hand, of Table 1.
[0128] The tires P-I, P-II, P-IV and P-V correspond to cables C-I,
C-II, C-IV and C-V respectively. They comprise more precisely a
bottom zone such as depicted in FIG. 1 with regard to tires P-I and
P-II, with only 2 anchoring stacks 6a and 6b comprising in total 15
windings of cable 7, or in FIG. 2 with regard to the tires P-IV and
P-V with in this case 3 anchoring stacks 6a, 6b and 6c comprising
in total 21 windings of cable 7. In each of the anchoring stacks,
the anchoring cables are arranged in a circumferential direction,
parallel to one another, distant from one other by approximately
0.3 mm.
[0129] These tires, whether mounted or not on a rim of appropriate
dimension according to the type of analysis carried out, were
tested under static and dynamic conditions, on different rolling
machines or other tests, in order to compare their performance in
terms of the criteria defined below.
A) Endurance During Travel of Long Duration:
[0130] The endurance during travel is assessed by a running test of
very long duration (40,000 km) on an automatic rolling machine,
under a very heavy load (overload compared with the rated load) and
at the same speed, for a predefined number of kilometres. If the
tire reaches the end of the test without being destroyed, a maximum
mark of 100 is assigned thereto; if not, its mark is reduced in
proportion to the mileage traveled before destruction.
B) Endurance During High-Speed Travel:
[0131] The endurance during high-speed travel is assessed by
subjecting each tire to a gradual increase in speed, in given
stages, up to a limit speed set beforehand (greater than 300 km/h).
If the tire reaches the end of the test without being destroyed, a
maximum mark of 100 is assigned thereto; if not, its mark is
reduced in proportion to the mileage traveled before
destruction.
C) Mounting Ability (Ability to be Ovalised):
[0132] A mounting ability test is carried out in which the tire
(not mounted on its rim) is gradually radially loaded to assess its
ability to be ovalised, that is to say its deformability in its own
plane.
[0133] The test is deliberately carried out under very harsh
deformation conditions, until the structure of the bead buckles and
at least one permanent deformation (bump visible to the naked eye)
appears on the outside of the bottom zone of the tire. The higher
the critical loading threshold, in other words the deflection
withstood, the better is the deformability and the flexural
strength of the bottom zone of the tire. A relative value of 100 is
used for the control tire acting as a reference for the test (here,
tire P-I), a higher value indicating an improved performance.
[0134] All the results obtained in these different tests have been
summarised in Table 2 below.
TABLE-US-00003 TABLE 2 Tire: P-I P-II P-IV P-V Anchoring Cable: C-I
C-II C-IV C-V Endurance during travel 100 100 100 100 of long
duration: Endurance during high-speed 100 100 100 100 travel:
Mounting ability: 100 >200 104 150
[0135] It will be noted first of all that the tire P-II according
to the invention exhibits an endurance during travel which is at
least equal to that of the control tires (P-I, P-IV and P-V).
[0136] However, above all, unexpectedly, a result which is very
substantially improved with regard to the mounting ability of the
tire P-II reinforced with the cable according to the invention is
observed compared: [0137] not only with the control tires P-I and
P-IV, the anchoring structure of which however uses cables of high
elongation, which are high-elongation treated and therefore
distinctly more expensive; [0138] but also with the tire P-V using
anchoring cables with short pitches but of a different construction
which is not in accordance with the invention.
[0139] Only the tire P-II using the cable according to the
invention exhibited excellent deformability, no permanent
deformation having been observed, even under maximum loading of the
tire. Furthermore, this tire P-II can be more easily warped
(perimeter is more easily deformable) in the axial direction.
[0140] In summary, owing to the specific cable of the invention,
the operations of mounting and demounting tires reinforced with the
cable according to the invention, in particular on/from a monobloc
wheel, can thus be carried out more simply and more quickly.
[0141] It is henceforth possible to use anchoring rubbers of great
hardness, which are moreover beneficial to the road behaviour of
the vehicles, without necessarily having to use high-elongation
treated cables.
* * * * *