U.S. patent application number 09/886379 was filed with the patent office on 2002-04-04 for method and device for manufacturing a metal cord for reinforcing elastomeric products, particularly tyres.
Invention is credited to Noferi, Omero.
Application Number | 20020038538 09/886379 |
Document ID | / |
Family ID | 26152198 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020038538 |
Kind Code |
A1 |
Noferi, Omero |
April 4, 2002 |
Method and device for manufacturing a metal cord for reinforcing
elastomeric products, particularly tyres
Abstract
A machine for manufacturing metal cords includes a supporting
structure, a rotor engaged with respect to the supporting
structure, a cradle fastened to the supporting structure, feeding
devices operatively fitted on the cradle to feed a plurality of
elementary wires from respective feeding spools, and at least one
preforming device operatively engaged with the cradle and operating
on at least one of the elementary wires in a section upstream with
respect to a first end section of the stranding path. The
elementary wires are driven onto the rotor according to a stranding
path. The stranding path has end sections coinciding with the
rotation axis of the rotor and a central section distanced from the
rotation axis of the rotor. The at least one preforming device
provides the at least one of the elementary wires a substantially
sinusoidal deformation lying in a plane.
Inventors: |
Noferi, Omero; (San Giovanni
Valdarno, IT) |
Correspondence
Address: |
Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
1300 I Street, N.W.
Washington
DC
20005-3315
US
|
Family ID: |
26152198 |
Appl. No.: |
09/886379 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09886379 |
Jun 22, 2001 |
|
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PCT/EP99/10055 |
Dec 14, 1999 |
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60122391 |
Mar 2, 1999 |
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Current U.S.
Class: |
57/58.49 ;
156/156; 57/311 |
Current CPC
Class: |
D07B 3/022 20210101;
D07B 2201/2008 20130101; D07B 1/0646 20130101; D07B 2501/2046
20130101; D07B 2207/202 20130101; D07B 7/025 20130101 |
Class at
Publication: |
57/58.49 ;
57/311; 156/156 |
International
Class: |
D07B 001/06; D01H
001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1998 |
EP |
98830785.6 |
Claims
1. Device for manufacturing metal cords to be used particularly for
reinforcing composite elastomeric products, comprising: a
supporting structure; a rotor engaged with respect to said
supporting structure and rotatable according to a predefined axis;
a cradle fastened to said supporting structure according to an
oscillation axis which coincides with the rotation axis of the
rotor; feeding devices operatively fitted on said cradle to feed
several elementary wires from respective feeding spools, said
elementary wires being driven onto said rotor according to a
stranding path with end sections coinciding with the rotation axis
of said rotor and with a central section distanced from said
rotation axis; at least one preforming device operatively engaged
with the cradle and operating on one of said elementary wires in a
section upstream with respect to the first end section of the
stranding path; characterized in that said at least one preforming
device is suitable for providing said elementary wire with a
deformation which is substantially sinusoidal without sharp
edges.
2. Device according to claim 1, characterized in that it comprises
a preforming device for each elementary wire of said metal
cords.
3. Device according to claim 1, characterized in that said at least
one preforming device comprises a first and a second pulley
fastened to a suitable supporting structure free to rotate about
its axis, each pulley having a plurality of opposed pins suitable
for reciprocal penetration for a predefined distance so as to
induce a sinusoidal deformation without sharp edges on a wire
passing through the space between the pins of the first pulley and
the corresponding pins of the second pulley.
4. Device according to claim 3, characterized in that said first
and second pulleys are driven in rotation by the wire.
5. Device according to claim 3, characterized in that said distance
is variable.
6. Process for manufacturing a metal cord, particularly for
reinforcing composite elastomeric products, comprising at least two
elementary wires, with a diameter preferablly between 0.10 and 0.50
mm, said procedure comprising the following phases: permanently
deforming at least one of said elementary wires by means of a
deformation which is substantially sinusoidal without sharp edges;
stranding said elementary wires together by means of helicoidal
double twisting around the longitudinal axis of said cord.
7. Metal cord, particularly for reinforcing composite elastomeric
products, comprising at least two elementary wires of which at
least one is preformed according to the process of claim 6.
8. Tire for vehicle wheels, comprising a torus-shaped carcass, a
tread located on the periphery of said carcass, a pair of axially
facing side walls ending with beads reinforced with bead wires and
respective bead filling elememnts for fixing said tire to a
corresponding mounting rim, said tire comprising rubberized fabrics
reinforced with metal reinforcing cords, comprising at least two
elementary wires helicoidally twisted together and around the axis
of longitudinal extension of the cord, characterized in that at
least one of said elementary wires is permanently deformed by a
substantially sinusoidal deformation without sharp edges.
Description
[0001] This invention relates to a device for preforming one or
more elementary wires forming a metal reinforcing cord. This cord
is especially suitable for reinforcing composite elastomeric matrix
products, such as tires.
[0002] In particular, the preforming device according to the
present invention is suitable for operating on highcradlebon
content metal wires, which are preferred for manufacturing high
elongation cords.
[0003] The expression "high elongation" is used to indicate the
capacity of the reinforcing elements to be stretched under stress,
at least initially, to a considerable extent, thanks to the
employment of specific materials and/or certain specifically
selected geometrical shapes so as to fulfil particular
manufacturing phases of tires and/or conditions of use of
tires.
[0004] In particular, these cords, defined as "HE" (High
Elongation), present an ultimate elongation between 4% and 10%.
[0005] The wires led out of this preforming device according to the
invention are subsequently fed to a traditional stranding station
known from the art where the wires thus preformed are twisted
around the longitudinal axis of the cord thus obtained.
[0006] A further object of the present invention is a procedure for
manufacturing said cord, comprising the following phases:
preforming one or more elementary wires forming said cord by
subjecting them to a permanent deformation along their longitudinal
development; stranding the elementary wires by means of a
helicoidal twisting around the longitudinal axis of the cord.
[0007] Furthermore, the present invention relates to a metal cord,
preferably a reinforcing cord, obtained by means of a preforming
process and of a subsequent stranding of the aforesaid type.
[0008] The cord hereof is specifically designed to be used in
manufacturing tire components for motor vehicles but can be easily
employed to manufacture other items, such as for example pipes for
high pressure fluids, belts, belt conveyors or any other product
made of elastomer-based composite material.
[0009] As is known, the metal cords usually employed to reinforce
elastomeric products are generally made of several elementary wires
helicoidally twisted around an axis which coincides with the
longitudinal development of the cords themselves.
[0010] Preferably said cords are produced by means of stranding
machines comprising: a supporting structure; a rotor coupled to
said supporting structure which is rotatable according to a
predefined axis; a cradle fastened to the supporting structure
according to an oscillation axis which coincides with the axis of
rotation of the rotor; feeding devices operatively assembled on
said cradle and/or on its outside, suitable for feeding one or more
elementary wires coming from respective feeding spools, said one or
more elementary wires being driven along suitable stranding paths;
and preferably at least one preforming device operating on one or
more elementary wires in a section of the wires which preceeds the
subsequent stranding phase.
[0011] This preforming device imposes to said one or more
elementary wires a permanent flexure deformation suitable for
supporting and improving the subsequent arrangement of the wires
according to a helicoidal development which ensures the necessary
keeping of the structural compactness of the cord.
[0012] Furthermore, it is important to note that these cords,
especially when employed in the manufacturing of tires, are
generally required to be provided with high mechanical resistance
and to allow a good physico-chemical adhesion with the elastomeric
material in which they are embedded, as well as an efficient
penetration of said material in the space surrounding each wire of
said cord.
[0013] In fact it is known that in order to eliminate the risk of
the cords undergoing undesired corrosion phenomena once introduced
in a tire, or inside any product made of elastomeric material, it
is very important that the elementary wires forming the cords are
entirely coated, for their entire superficial extension, by the
elastomeric material in which the cord is embedded.
[0014] This result, which is more difficult to be achieved when
more complex cords are considered, is not easily achieved even when
dealing with cords formed by a low number of elementary wires.
[0015] In fact, in order to confer the required geometric and
structural stability to the cord, the elementary wires forming the
cord are compacted, i.e. positioned intimately in contact with one
another, leading to the formation of one or more closed cavities
inside said cord which extend along the longitudinal development of
the cord.
[0016] These cavities are closed and, consequently, cannot be
reached by the elastomeric material during the normal rubberizing
phases of the cord and, as a consequence, corrosion may develop
inside said closed cavities and propagate along the elementary
wires forming the cord.
[0017] As a consequence, this means, for example, that owing to
cuts or punctures in the tire structure, or to any other reason,
humidity and/or external agents can penetrate into said closed
cavities inevitably starting a rapid process of corrosion of the
elementary wires, thus severely compromising the structural
resistance of the cord and of the tire.
[0018] Furthermore, the presence of said closed cavities which
cannot be reached by the elastomeric material involves a reduced
adhesion of the wires to the elastomer, which--above all if said
cords are used for manufacturing tires--in use can cause an
undesired tendency of the wires to separate from the elastomer.
[0019] An additional disadvantage due to insufficient rubberizing
of the wires, caused by the presence of said closed cavities, is
the development of fretting of the wires in contact with one
another. This generates an inevitable degeneration of resistance to
fatigue of the wires and, consequently, of the cord.
[0020] An attempt to overcome this type of problem known in the art
consists of using so-called "open" cords, where the wires
(generally from three to five) are kept distant from one another
during the entire rubberizing phase, carried out according to known
procedures consisting of keeping a traction load not exceeding five
kilograms applied to the cord.
[0021] Said cords are, for example, described in U.S. Pat. No.
4,258,543 in the name of the Applicant. These cords allow a greater
penetration of the rubber between the wires forming the cords.
[0022] However, the cords thus obtained present several problems,
especially in use, since the wires forming the cords tend to be
distanced also when they are subjected to considerable traction
stress during tire manufacturing and in tire use. This fact causes
undesired geometric and structural instability of the cords which
damages the performance of the tire.
[0023] According to a further embodiment of the prior art,
so-called double-diameter cords are used, i.e. cords with two pairs
of wires where the diameter of the wires of the first pair is
suitably differentiated from that of the second pair.
[0024] It is also known (see EP Patent 168,857) to make a metal
cord having a first pair of elementary wires of equal diameter and
a second pair of elementary wires with a diameter smaller than that
of the first pair. Said first and second pairs are fed into a
conventional internal collection stranding machine after crossing a
circular preforming head where the wires of the first and second
pair follow paths which ensure differentiated preforming actions
with respect to each other.
[0025] The cord thus obtained, consequently, presents the pair of
wires with a larger diameter helicoidally twisted together and in
reciprocal contact, while each wire of the second pair is
interposed between the two wires of the first pair and extends in
parallel to the latter, being suitably distanced from them.
[0026] In this way, the aforesaid closed cavities are eliminated
from the cross section of the cord, ensuring total coverage of
elementary wires by the elastomeric material used during the
rubberizing phase.
[0027] However, the suggested technical solution involves that the
wires with the smallest diameter are distanced from those with the
largest diameter also when the cord is subjected to traction stress
in use. This fact, as for the aforesaid "open" cords, causes a
certain geometric and structural instability of the cord which is
not advantageous.
[0028] Furthermore, it is very difficult to confer to the cord thus
obtained an accurate and regular geometrical configuration in each
point of its longitudinal development since the constant reciprocal
position of the wires in the cord is ensured by the particular type
of used preforming device but the distance between the wires with
the smallest diameter and the wires with the largest diameter tends
to vary randomly in the various points of the longitudinal
development, both in conditions of rest and of use of the cord.
[0029] According to a further preforming method for known in the
art and described in the aforesaid U.S. Pat. No. 4,258,543 in the
name of the Applicant, a roller preforming machine can be used. The
roller is idle and presents several preforming seats, each located
so as to operatively engage a respective elementary wire of the
cord.
[0030] These preforming seats are circumferential grooves in the
surface of the roller, the width of which is substantially equal to
the diameter of the corresponding elementary wire, with a
semicircular profile end portion having an axis coplanar to that of
the end portions of the other circumferential grooves.
[0031] In this way, preforming can be varied by adjusting the
radius of curvature of said grooves or by adjusting the tension
applied to the wire. However, even this solution presents problems
since the preforming action operated on the wire is often thwarted
by the dynamic stranding pulls.
[0032] To solve the problem of poor rubberizing of the wires of a
given cord--fact which can, as mentioned, cause consequent
undesired corrosion problems--a suggested solution consists of
cords generally formed with a low number of wires, where at least
one of the elementary wires is deformed during preforming so as to
acquire a pattern which is no longer continuous but presents a
suitable broken line.
[0033] Such embodiment is described, for example, in U.S. Pat. No.
5,020,312 according to which at least one wire of a given cord is
subjected to a zigzag pattern along the longitudinal direction of
said cord.
[0034] This renders a continuous contact between at least two
adjacent wires along the longitudinal development of the cord
impossible, thus causing the formation of detachment areas between
said two wires, i.e. inlet openings allowing the introduction of
rubberizing material at each zigzag bend of the wire.
[0035] According to the matter disclosed in this document, one or
more wires suitable for forming a given cord are unwound from
respective storage spools and fed to a pair of opposed cog wheels
through which the above mentioned one or more wires are passed and
preformed according to the axial direction conferring the aforesaid
zigzag pattern.
[0036] This type of preforming is exhaustively described and
illustrated in detail also in U.S. Pat. No. 5,581,990.
[0037] However, the greatest problem presented by the cords
manufactured according to this operative method resides in a
remarkable crushing of the external fibers of the wires forming a
given cord at the bending apex. This fact involves an inevitable
and undesired decrease in the fatigue resistance values of said
cord and, consequently, a decrease in the qualitative level of the
tire in which said method is used.
[0038] Furthermore, it is known to use preforming devices provided
with preforming heads for impressing an axial deformation to one or
more of said wires. More in particular, U.S. Pat. No. 5,319,915
discloses the positioning of a flat surface, which extends in
parallel to the axis of a wire, before stranding. Said flat surface
is provided with preforming heads consisting of several pins
positioned perpendicularly with respect to this flat surface at a
regular distance from one another.
[0039] As illustrated in U.S. Pat. No. 5,722,226, said pins can be
located on a supporting structure which may also be conical or
cylindrical (i.e. not necessarily flat) and may be aligned or
suitably staggered to provide the wire to be preformed with the
desired zigzag path.
[0040] This device, consequently, is positioned so that said wire
passes alternatively over and under said sequence of heads, while
the entire device is rotated around its axis which is parallel to
the axis of the wire.
[0041] The Applicant has surprisingly found a stranding system for
manufacturing a metal cord provided with a good elastomeric
material penetration between the wires forming said metal cord, as
well as provided with a good fatigue resistance with respect to
similar cords known in the art.
[0042] In particular, the Applicant has found that by applying a
soft preforming action--substantially sinusoidal--to one or more
metal wires forming a given cord, the cord presents a better
fatigue resistance, for example, with respect to cords obtained by
means of a preforming process employing cog wheels.
[0043] More in particular, the Applicant has surprisingly found
that a cord according to the invention presents an increased
ultimate elongation, while the penetration of the cord into the
elastomeric material is considerably increased with respect to the
abovementioned wires of the prior art.
[0044] A first aspect of the present invention relates to a device
for manufacturing metal cords, to be used particularly for
reinforcing composite elastomeric products. Said device
comprises:
[0045] a supporting structure;
[0046] a rotor engaged with respect to the supporting structure and
rotatable according to a predefined axis;
[0047] a cradle fastened to the supporting structure according to
an oscillation axis which coincides with the rotation axis of the
rotor;
[0048] feeding devices operatively fitted on said cradle to feed
several elementary wires from respective feeding spools, said
elementary wires being driven onto the rotor according to a
stranding path with end sections coinciding with the rotation axis
of said rotor and with a central section distanced from said
rotation axis;
[0049] at least one preforming device operatively engaged with the
cradle and operating on one of said elementary wires in a section
upstream with respect to the first end section of the stranding
path,
[0050] characterized in that said at least one preforming device is
suitable for providing said elementary wire with a substantially
sinusoidal deformation without sharp edges, i.e. developing
according to a continuous curved line without points of
discontinuity.
[0051] Preferably, the device according to the invention comprises
one preforming device for each elementary wire of the cord.
[0052] More in particular, said at least one performing device of
the device according to the invention comprises a first and a
second pulley fastened to a suitable supporting structure and free
to rotate about its axis, each pulley having various opposed pins
suitable for reciprocally penetrating each other for a predefined
distance so as to induce a sinusoidal deformation without sharp
edges on a wire passing through the space between the pins -of the
first pulley and the corresponding pins of the second pulley.
[0053] A further aspect of the present invention relates to a
process for manufacturing a metal cord, particularly suitable for
reinforcing composite elastomeric products, said cord comprising at
least two elementary wires, with a diameter preferably between 0.10
and 0.50 mm, said process comprising the following phases:
[0054] permanently deforming at least one of said elementary wires
by means of a deformation which is substantially sinusoidal without
sharp edges;
[0055] stranding said elementary wires together by means of
helicoidal double twisting around the longitudinal axis of said
cord.
[0056] A further aspect of the present invention relates to a metal
cord, particularly suitable for reinforcing composite elastomeric
products, comprising at least two elementary wires at least one of
which is preformed according to the process of the invention.
[0057] A further aspect of the present invention relates to a tire
for vehicle wheels comprising a torus-shaped carcass, a tread
located on the periphery of said carcass, a pair of axially facing
side walls ending with beads reinforced with bead wires and
respective bead filling elements for fixing said tire to a
corresponding mounting rim, said tire also comprising rubberized
fabrics reinforced with metal reinforcing cords, comprising at
least two elementary wires which are helicoidally twisted together
and around the axis of longitudinal extension of the cord,
characterized in that at least one of said elementary wires is
permanently deformed by means of a substantially sinusoidal
deformation without sharp edges.
[0058] Further features and advantages of the present invention
will be better explained by the following detailed description of
some preferred embodiments hereof, reproduced with reference to the
accompanying drawings, where:
[0059] FIG. 1 illustrates, in a lateral view, a known stranding
machine where the preforming device according to this invention is
used;
[0060] FIGS. 2a and 2b illustrate in detail a preforming device
according to the present invention, in a plan top view and a
partial side view, respectively;
[0061] FIG. 3 illustrates a tire, in partial straight section,
provided with constituent elements comprising reinforcing cords
according to the invention.
[0062] With reference to the aforesaid Figures, reference sign 1
generally indicates a metal reinforcing cord to be used
particularly in composite elastomeric products, specifically tires
for motor vehicles, according to the present invention.
[0063] In a manner known per se, cord 1 comprises several
elementary wires, made of steel with acradlebon content between
0.65% and 0.98% and with a diameter between 0.10 mm and 0.50 mm,
helicoidally twisted around the axis of longitudinal extension of
the cord.
[0064] However, steel, which is the preferred material thanks to
its mechanical properties, presents the disadvantage of not
sufficiently adhering to vulcanized elastomeric material.
Consequently, to attain good adhesion to the elastomeric material,
the steel is generally coated with a layer of suitable material.
This coating material is preferably brass. Other coating materials,
however, can be used, such as alloys containing Cu, Zn, Ni, Co, Mn.
In the preferred case of brass coating, adhesion is favoured by the
formation during vulcanisation of bisulphide bridges (--S--S--)
between the elastomeric matrix and the copper which--being a
component of brass--coats the metal reinforcing element.
[0065] The known procedures for coating a metal element with a
layer of brass can be divided into two families: plating and
diffusion. The first comprises electrolytic plating of copper and
zinc while the second comprises electro-plating of one or more
layers of copper on steel, followed by the electro-plating of a
layer of zinc and by a thermal treatment with the purpose of
diffusing the zinc in the copper layers, thus forming a layer of
brass.
[0066] These wires are then, preferably, brass-coated with a metal
composition consisting of from 30% to 40% by weight in zinc and
from 70% to 60% by weight in copper, more preferably 32.5% weight
in zinc and 67.5% weight in copper, to form a layer of brass equal
to approximately 0.25 .mu.m.+-.0.05.
[0067] The specific features and constructive features of cord 1
according to the invention will be better understood by means of
the following description, both as regards the device used and the
procedure for its manufacturing.
[0068] FIG. 1 illustrates an example of stranding machine, in
particular suitable for forming a cord consisting of 5 elementary
wires.
[0069] The machine for the production of metal reinforcing cord 1
comprises, in a known configuration, a supporting structure 100 to
which a rotor 5 is rotatively engaged, the latter being rotated by
means of a motor or similar devices (not illustrated). Furthermore,
a cradle (not illustrated in the Figure) is connected to said
supporting structure and can rock about the rotation axis of rotor
5. Several feeding spools 8 are operatively engaged on the cradle.
At least one elementary wire of said cord 1 is wound on each of the
spools.
[0070] Furthermore, suitable unwinding devices (not illustrated
because known per se and conventional) are coupled to spools 8,
which are fitted on the cradle to suitably guide the elementary
wires coming from spools 8.
[0071] In a known way, the elementary wires at the outlet from the
cradle are driven onto rotor 5 according to a predefined stranding
path along which cord 1 is formed through the effect of rotation
imposed on rotor 5 by means of said motor or equivalent device, in
combination with the drive produced on the cord by means of
collection devices (not illustrated since known and not relevant to
the scope of the invention).
[0072] More in particular, the stranding path comprises a first end
section 10a essentially coinciding with the rotation axis of rotor
5 and delimited by a first rotating transmission device 12, solidly
fastened to rotor 5, and an assembly unit 11 consisting, in a known
way, of a plate with five holes, solidly fastened to the cradle
and, consequently, stationary.
[0073] Along this first end section 10a the wires are subjected to
a first helicoidal torsion around the rotation axis of rotor 5
through the effect of the rotating pull which the rotor imposes on
the first rotating transmission device 12.
[0074] Downstream of first rotating roller 12, the wires follow a
central section 10b of the stranding path which extends to rotor 5
and is radially displaced with respect to the rotation axis of the
rotor so as to skip cradle 7 and reach a second transmission device
13 solidly coupled to the rotor on the axially opposite end.
[0075] Finally, the stranding path presents a second end section
10c substantially coinciding with the rotation axis of rotor 5 and
extending beyond second rotating transmission device 13. In this
second end section, through the effect of the rotating pull imposed
by rotor 5 on second rotating transmission device 13, a second
torsion of the elementary wires is performed, thus completing the
formation of cord 1 which is progressively pulled away by the
aforesaid collection devices.
[0076] The ratio between the speed of rotation of rotor 5,
preferably between 2000 and 6000 rpm, and the pulling speed of cord
1--and, consequently, of the elementary wires which form it,
preferably between 60 and 250 m/min--defines the value of the
stranding pitch, i.e. the pitch according to which said elementary
wires are helicoidally twisted on finished cord 1.
[0077] In a preferred embodiment of the invention, said stranding
pitch is kept at a value between 3 mm and 50 mm, preferably between
6 mm and 30 mm, more preferably equal to 16 mm.
[0078] The following elements are operatively arranged in sequence
for each elementary wire along the path of the elementary wires
inside the cradle, and more precisely upstream with respect to
assembly unit 11: a rotating transmission device 14, a preforming
device 15 according to the invention (shown in detail in FIG. 2)
and a rotating transmission device 16 consisting of a pulley turned
at 90.degree. with respect to the pair of pulleys of the invention;
said turned pulley has the purpose of conveying the wire coming out
of preforming device 15, to assembly unit 11.
[0079] With reference to FIG. 2a, preforming device 15 according to
the present invention comprises a pair of pulleys 200 and 201,
preferably a pair of steel plates, fastened to a suitable
supporting structure 202 and free to rotate about their axes. Each
pulley presents various opposed pins 203 and 204 suitable for
reciprocally penetrating for a predefined extension so as to cause
an axial deformation and a flexion deformation at the same time on
a wire crossing the space between the pins of first pulley 200 and
the corresponding pins of second pulley 201, during the aforesaid
penetration obtained by the movement of the aforesaid pair of
pulleys driven and rotated by the wire.
[0080] More in particular, the longitudinal axis of the aforesaid
supporting structure is advantageously located perpendicularly to
the direction of advancement of the wire to be subjected to the
desired preforming operation.
[0081] Aforesaid pulleys 200 and 201 are fastened to said
supporting structure 202 and opposed so that first pulley 200 is
kept in a fixed position with respect to said supporting structure
202 but is free to rotate about its axis perpendicularly to
longitudinal axis L of the supporting structure.
[0082] Second pulley 201 of this pair, on the contrary, is
advantageously mobile along a straight guide 205 on the supporting
structure and located in parallel to longitudinal axis L of the
supporting structure so as to allow fine tuning of second pulley
201, by means of a suitable graduated scale 206, with respect to
the first and thus to approach or distance-the aforesaid pair.
[0083] Furthermore, as mentioned above, each pulley 200 and 201 of
the preforming device according to the present invention is
provided with a plurality of pins 203 and 204 of suitable length,
located perpendicularly to the plate surface of the pulley and
positioned consecutively one from the other so as to follow the
peripheral profile of the pulley according to a predetermined pitch
defined by the distance between the axes of two consecutive
pins.
[0084] With reference to FIG. 2b, which illustrates a partial side
view of preforming device 15 according to the invention, in order
to allow reciprocal penetration of the pins possessed by said pair
of pulleys, it is necessary that they are differently distanced
from longitudinal axis L of the supporting structure, i.e. the
plate surfaces of said pulleys belong to two different planes P1
and P2 parallel to one another and parallel to the plane containing
longitudinal axis L of supporting structure 202.
[0085] Furthermore, to ensure the aforesaid penetration, pins 203
and 204 provided on first pulley 200 and second pulley 201 have to
be located on opposed plate surfaces so that, during the rotation
of said pulleys, the respective pins are in reciprocally opposite
positions.
[0086] More in particular, the penetration of the pins of the pair
of pulleys is variable and adjusted by moving second mobile pulley
201 closer or farther by means of aforesaid straight guide 205.
This adjustment is performed by means of a graduated scale 206
which is calibrated so as to define the level of penetration of the
pins and consequently the degree of preforming resulting on the
wire downstream with respect to the preforming device according to
the present invention.
[0087] The level of penetration of the pins represents,
consequently, the shift--longitudinal with respect to supporting
structure 202--made by second mobile pulley 201 in the direction of
first pulley 200, which is fixed.
[0088] In particular, said level of penetration represents the
distance D between the axis of a first pin 203 possessed by fixed
pulley 200 and the axis of a second pin 204 on mobile pulley 201.
Said second pin 204 is in consecutive position with respect to the
first so that aforesaid distance D is measured in the penetration
area of said first and second pin. Said area defines the preforming
path of said wire.
[0089] Finally, the stranding machine comprises a stretching device
(capstan), a device for collecting the produced cord and the usual
wire straightening devices, such as the false twister, to eliminate
residual tension in the finished cord. These devices are not
illustrated since known, conventional and not particularly relevant
for the purposes of the invention.
[0090] According to a further embodiment of the invention, the
stranding operation is such as to ensure that at least one wire of
a given cord is subjected to preforming according to the present
invention while the remaining wires of said cord are treated as
described in the prior art. For example, said remaining wires can
be subjected to preforming using a roller preforming machine, such
as that described in aforesaid U.S. Pat. No. 4,258,543 in the name
of the Applicant.
[0091] Preforming devices 15 according to the present invention are
applicable to all types of known stranding systems, for example a
double twist system or an arrangement system. More in particular, a
double twist system can present internal collection (if the
collection spool of the finished product is inside of the cradle,
between the rotors) or external collection (if the feeding spools
are inside of the cradle while the collection spool of the finished
product is outside the cradle). The arrangement system, finally,
differentiates from the double twist system as in arrangement
machines each rotor turn corresponds to a single stranding pitch
while in double twist machines each turn of the rotors corresponds
to an advancement equal to two stranding pitches. Consequently, the
difference between these two systems lies in their
productivity.
[0092] According to a preferred embodiment of the invention, the
pulleys used in the preforming device are overall identical, i.e.
they have equal diameter, an equal number of pins and the pins used
on both pulleys have the same diameter.
[0093] With preforming machine 15--thanks to its structure--it is
possible to obtain a wire with a substantially sinusoidal wavy
deformation on a plane that is parallel and intermediate to planes
P1 and P2 containing the plate surfaces of the pulleys. Said wire
does not present sharp edges, spikes or cuts on its surface. The
elementary wire passing through the pins of the two pulleys is
subjected to an alternating deformation defined by the circular
shape of the pins, and does not present, as a consequence, sections
with the aforesaid edges, spikes or cuts which are found, for
example, on the external surface of the wires which pass through a
pair of cog wheels according to the prior art. In fact, said cog
wheels, due to the their geometric conformation, inevitably cut the
surface of the wire during the take-up action which occurs during
the preforming advancement of the wire. As mentioned above, this
take-up action causes stresses of the wire.
[0094] Table I illustrates the main technical-constructive
parameters of one embodiment of preforming device 15 according to
the present invention. According to this embodimentn, the pulleys
of the device according to the invention present equal diameter, an
equal number of pins and pins of equal diameter. However, other
embodiments are possible, e.g. pulleys presenting pins with
different diameters.
1TABLE I Maximum Maximum Maximum Maximum pin pin pin pin Pin
penetra- penetra- penetra- penetra- dia- Number Pin tion tion tion
tion meter of pitch level level level level (mm) pins (mm) (mm)
(mm) (mm) (mm) wire .O slashed. wire .O slashed. wire .O slashed.
wire .O slashed. 0.12 0.25 0.35 0.38 1 48 2 0.480 0.430 0.357 0.325
1.5 32 3 0.740 0.710 0.663 0.640 2 24 5 0.990 0.968 0.936 0.925 3
16 7.6 1.495 1.479 1.458 1.450 4 12 9.8 1.996 1.984 1.969 1.963 5
12 11.13 2.497 2.487 2.475 2.470
[0095] The most suitable selection of values to be attributed to
the machine parameters is to be defined specifically according to,
for example, the desired degree of preforming of the wire, the
diameter of the wire (between 0.10 and 0.50 mm) and the desired
value of the final features of the cord. Furthermore, it is
important to underline that the pull exerted on the cord also
depends on precise process parameter choices according to the
features of the machines used, e.g. torsion angles, speed of
rotors, stranding pitch.
[0096] It is also important to note that, to produce a cord, and
consequently a rubberized fabric containing said cord, having high
elasticity features, it is preferable to subject all the wires
forming said cord to the preforming process according to the
invention.
[0097] However, if the main requirement resides in the rubber
penetration inside the cord, it may suffice to preform a limited
number of the wires forming the cord. This number can be defined on
the basis of the total number of wires forming the cord and the
desired penetration degree.
[0098] FIG. 3 illustrates a generic tire comprising rubberized
fabrics provided with reinforcing cords according to the invention.
With reference to this Figure, the tire to which the invention
refers comprises a carcass 100, preferably internally covered with
an air-tight sheet of rubber 110, a tread 120 located on the
periphery of this carcass, a pair of axially facing side walls 130
ending with beads 140 reinforced with bead wires 150 and respective
bead filling elements 160 in order to fix said tire to a
corresponding mounting rim 170. The tire can additionally include
reinforcing edges 190 and, in the case of radial carcass tires,
also a belt structure 210 interposed between carcass and tread.
[0099] Carcass 100 comprises one or morecarcass plies fixed to said
bead wires 150, for example, folded around said bead wires from the
inside towards the outside. The carcass ply or plies can be formed
by sections of rubberized fabric reinforced with textile or metal
cords embedded in the fabric rubber.
[0100] Belt structure 210 comprises two belt strips 230 and 240,
radially overlapping, and a third belt strip 250 in a radially
outermost position.
[0101] Belt strips 230 and 240 are formed by sections of rubberized
fabric incorporating metal cords, parallel with respect to each
other in each strip and crossed with those of the adjacent strips,
inclined preferably in a symmetrical manner with respect to the
equaterial plane of the tire at an angle of between 10.degree. and
30.degree., while belt strip 250 is provided with cords which are
circumeferentially oriented, i.e. at 0.degree. with respect to said
equaterial plane. This strip 250 can be made, in particular for
truck tires and the like, by a pair of bands symmetrically located
with respect to the equaterial plane of the tire. For truck tires,
an auxiliary strip (not shown in the figure) may be used in
external radial position with respect to belt structure 210,
provided with reinforcing cords inclined with respect to the
equaterial plane by an angle of between 10.degree. and 70.degree.,
usually called "breaker layer".
[0102] Similarly, other constructive elements of the tire can be
formed by sections of rubberized fabric with suitably reinforcing
cords inclined with respect to the axial, radial and/or
circumferencial directions of the tire, as required. For example,
aforesaid reinforcing edge 190 employs inclined cords according to
an angle included between 30.degree. and 60.degree. with respect to
the axial direction.
[0103] A sample of cord (5.times.0.35, pitch 16 mm, i.e. a cord
formed by the concatenation of five wires with a diameter equal to
0.35 mm) was made according to the procedure of the invention. The
wires forming said cord were made of steel with a carbon content
equal to 0.7%. Furthermore, said wires were advantageously
brass-coated, with a deposit coating equal to 3.74 g of brass in
relation to 1 kg of steel; the percentage of copper in the brass is
preferably equal to 64.4%. Preforming device 15 according to the
invention used to obtain said cord sample presented pins with a
diameter of 1.5 mm to attain a wire with a wavy (sinusoidal) shape
of width equal to 0.75 mm and pitch equal to 3.25 mm.
[0104] Table II hereinbelow illustrates the results achieved by the
Applicant in comparative tests between a 5.times.0.35 cord
subjected to preforming according to the known method of the cog
wheels and the same cord preformed according to the method of the
invention as described above in detail. The values shown in Table
II are the average values obtained by performing an arithmetical
average among a plurality of values resulting from the tests
performed by the Applicant.
2TABLE II Cord according to the cog Cord according to Main
parameters wheels method the invention Cord diameter 1.22 1.11 (mm)
Cord weight 3.93 3.88 (KTex) Ultimate tensile strenght 1070 1089
(bare cord) (N) Ultimate elongation 4.77 5.92 (bare cord) (%)
Ultimate tensile strength 1060 1125 (rubberized/vulcanised cord)
(N) Ultimate elongation 4.36 6.30 (rubberized/vulcanised cord) (%)
Flexion fatigue 5405 7970 (Kcycles) Fabric penetration 0.56 1.07
(crude) (mm.sup.3/cm of cord) Fabric penetration 0.03 0.05
(vulcanised) (mm.sup.3/cm of cord)
[0105] The ultimate tensile strenght and ultimate elongation tests
were carried out both on bare cord and on cord embedded in the
elastomer matrix and subjected to vulcanisation according to
methods not described herein since typically known in the prior
art.
[0106] The flexion fatigue test, known as FFF (Firestone Flexion
Fatigue) test or Wallace test, was carried out on a strip of
rubberized fabric. Said strip underwent a series of flexion cycles
made by alternatively moving the strip of fabric around a suitably
dimensioned roller with an adequately selected pre-load related to
the dimensions of the reinforcing cords in the fabric sample.
[0107] The aforesaid test was conducted on a strip of rubberized
fabric reinforced with metal cords arranged having a thickness
equal to 100 cords/decimeter by applying to the roller a pre-load
of 150 pounds (68 kg) by means of a lever mechanism and by using a
roller with a diameter equal to 50 mm. This lever mechanism caused
on the roller, and consequently on the sample, a force opposite and
equal to said weight. The sample was positioned and the test
consisted in counting the traction cycles made by the aforesaid
alternating movement. The test ended when the sample broke.
[0108] The test related to the penetration in the fabric consisted
in measuring the penetration degree of the rubber between the wires
forming said cord and in identifying, as a consequence, the quality
of the elastomer coating around each of said wires. A suitable
funnel advantageously made of glass was reversed on the bottom of a
bowl containing ethyl alcohol. This funnel presented a scale along
the cylindrical stem and ended, on the free end of this stem, with
a suction device generally worked by the operator. The operation of
the suction device caused the ethyl alcohol to rise in the
cylindrical stem to reach a predefined level, called zero level. In
this phase, the sample to be examined, consisting of a strip of the
type described above with dimensions equal to 5 cm.times.5 cm, was
submerged in the bowl and positioned at the inlet of the funnel.
Ethyl alcohol has the property of expelling the air which may be
contained in the elastomer matrix and to take its place. This fact
caused a decrease with respect to the aforesaid zero level of the
level of ethyl alcohol in the scaled stem. This measurement allowed
to define the volume of air possessed by the elastomeric material
in which the wires are embedded and, consequently, the penetration
degree of the rubber between the wires forming the cord. This test
was carried out both on the crude sample and on the vulcanised
sample.
[0109] By analysing the figures reported in Table II, it appears
evident that a given cord obtained according to the procedure of
the invention presents physico-chemical features remarkably better
with respect to an equal cord obtained according to a stranding
process comprising a preforming device with cog wheels.
[0110] In the case of the invention, the ultimate elongation of the
cord is considerably higher, as well as the flexion fatigue, which
is considerably increased. This results in a cord with improved
mechanical features with respect to the prior art.
[0111] Furthermore, te achieved results confirm the obtainement of
a greater rubber penetration and a considerably higher ultimate
elongation which results in a greater elasticity of the cord. This
aspect is particularly desired when these cords are used as
reinforcing cords for elastomers used to manufacture tires.
[0112] From the results achieved by the Applicant it arises that: a
greater pin penetration degree, and consequently a greater
preforming degree of the wires forming a cord, corresponds to a
greater elongation reached by the cord.
[0113] The Applicant carried out the texts especially on a
1.times.5.times.0.35 cord obtained by a stranding process according
to the invention. Said cord appeared particularly suitable for
being used to form, for example, the so called breaker layer in the
belts for heavy-load tires and the like, advantageously used on
"off-road" paths.
[0114] It is important to note that the cords obtained according to
the invention can be used as reinforcing cords for any type of
elastomeric structure to be used for manufacturing tires, with
particular preference for the elastomers requiring a high
elongation cord, for example in reinforcing edges 190 shown in FIG.
3.
[0115] The Applicant has, in fact, observed that the ultimate
elongation of a 1.times.5.times.0.35 cord is clearly better with
respect to the ultimate elongation of a 3.times.4.times.0.22 cord,
widely used in practice. Said cord consists of three strands, each
of which formed by four 0.22 diameter wires.
[0116] More in particular, the ultimate elongation of a
3.times.4.times.0.22 bare cord is equal to 5.5% and this value
drops to approximately 3% after vulcanisation. In the case of the
invention, on the other hand, the 5.times.0.35 cord presents an
ultimate elongation of approximately 6% also after vulcanisation.
This fact, as mentioned above, allows an advantageous use in
breaker layers for heavy-load tires which must absorb accidental
knocks which can occur on "OFF" type roads.
[0117] Furthermore, this aspect appears particularly advantageous
also in terms of costs, production time and process productivity
according to the invention, since necessarily two working cycles
with very limited stranding pitches (in particular equal to 3.15 mm
for each strand and equal to 6.3 for the final cord) are required
for making a 3.times.4.times.0.22 cord, while the cord according to
the invention is obtained in a single working cycle and presents a
higher stranding pitch (in particular equal to 16 mm).
[0118] Furthermore, making a 5.times.0.35 cord instead of a
3.times.4.times.0.22 cord allows to perform a milder drawing
process with consequent savings in terms of working times and wear
of the machines used.
* * * * *