U.S. patent application number 14/014039 was filed with the patent office on 2014-01-02 for method and apparatus for manufacturing pneumatic tyres.
This patent application is currently assigned to PIRELLI TYRE S.p.A.. The applicant listed for this patent is PIRELLI TYRE S.p.A.. Invention is credited to Marco CANTU', Maurizio MARCHINI, Pierangelo MISANI.
Application Number | 20140004216 14/014039 |
Document ID | / |
Family ID | 36764206 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140004216 |
Kind Code |
A1 |
MARCHINI; Maurizio ; et
al. |
January 2, 2014 |
METHOD AND APPARATUS FOR MANUFACTURING PNEUMATIC TYRES
Abstract
A green pneumatic tyre is built on a rigid toroidal support
externally having a forming surface of a conformation corresponding
to the inner shape of a tyre. The green tyre engaged on the
expandable toroidal support is introduced into a vulcanisation
mould and submitted to a vulcanisation cycle. During vulcanisation,
axial moving apart of side portions of the toroidal support is
caused so as to press the beads and sidewalls of the tyre against
the vulcanisation mould.
Inventors: |
MARCHINI; Maurizio; (Milano,
IT) ; CANTU'; Marco; (Milano, IT) ; MISANI;
Pierangelo; (Milano, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PIRELLI TYRE S.p.A. |
Milano |
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IT |
|
|
Assignee: |
PIRELLI TYRE S.p.A.
Milano
IT
|
Family ID: |
36764206 |
Appl. No.: |
14/014039 |
Filed: |
August 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12084298 |
Oct 16, 2009 |
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PCT/IT2005/000743 |
Dec 19, 2005 |
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14014039 |
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Current U.S.
Class: |
425/36 |
Current CPC
Class: |
B29D 30/0661 20130101;
B29D 30/08 20130101; B29D 30/12 20130101; B29D 30/0601
20130101 |
Class at
Publication: |
425/36 |
International
Class: |
B29D 30/08 20060101
B29D030/08 |
Claims
1-51. (canceled)
52. An apparatus for manufacturing pneumatic tyres, each tyre
comprising a crown region extending between side regions axially
spaced apart from each other and each carrying a respective bead at
a radially internal position, comprising: at least one toroidal
support having an outer forming surface of a conformation
corresponding to an inner shape of a built tyre and provided with
axially opposite side portions; devices for building a green
pneumatic tyre on the toroidal support; at least one vulcanisation
mould set to engage the green tyre disposed on the toroidal
support; devices for curing the tyre enclosed in the vulcanisation
mould; and devices for axially moving apart said side portions of
the toroidal support at the side regions of the tyre enclosed in
the vulcanisation mould.
53. The apparatus as claimed in claim 52, wherein the toroidal
support comprises a plurality of circumferential sectors removably
engaged in circumferential mutual alignment relationship.
54. The apparatus as claimed in claim 53, wherein said devices for
axially moving apart said side portions comprise for each
circumferential sector, at least one pair of stop struts, each
strut being divided into two portions adapted to enable an axial
movement of said side portions.
55. The apparatus as claimed in claim 52, wherein the forming
surface is obtained on a shaped wall confining at least one
circumferential cavity in the toroidal support.
56. The apparatus as claimed in claim 55, wherein said shaped wall
substantially extends along a U-shaped outline in a diametral
section plane of the toroidal support.
57. The apparatus as claimed in claim 55, wherein said axially
opposite side portions of the shaped wall are movable in an axial
direction.
58. The apparatus as claimed in claim 52, wherein said
vulcanisation mould further comprises stop seats set to act against
said side portions of the toroidal support in a maximum axial
spacing apart condition.
59. The apparatus as claimed in claim 52, wherein said devices for
axially moving apart the side portions act between a rest condition
and an axially spread apart condition, in which the side portions
are mutually spaced apart relative to the rest condition by a
stroke between about 0.1 mm and about 0.5 mm, measurable at
respective bead seats arranged in correspondence with each bead of
the tyre.
60. The apparatus as claimed in claim 54, wherein said stop struts
have abutment surfaces axially acting against respective locating
seats to stop axial approaching movements between said side
portions.
61. The apparatus as claimed in claim 60, wherein said abutment
surfaces and locating seats, in the absence of stresses on the
toroidal support, are disposed at such a distance as to stop said
axial approaching movements upon reaching of an axial contraction
stroke between about 0.01 mm and about 0.15 mm.
62. The apparatus as claimed in claim 61, wherein said axial
contraction stroke is less than about 0.1 mm.
63. The apparatus as claimed in claim 52, wherein the vulcanisation
mould is movable between an open condition and a closed condition
which defines a moulding cavity having a shape corresponding to the
outer conformation of a cured tyre,
64. The apparatus as claimed in claim 52, wherein said devices for
vulcanisation of the tyre comprise a feeding circuit opening into
the vulcanisation mould to feed a vulcanisation fluid into the
toroidal support.
65. The apparatus as claimed in claim 52, wherein control devices
operate on the feeding circuit to supply vulcanisation fluid to a
first pressure value, over a predetermined period of time, and
subsequently supply vulcanisation fluid to a second pressure value
higher than the first pressure value.
66. The apparatus as claimed in claim 65, wherein the first
pressure value is between about 7 and about 17 bars.
67. The apparatus as claimed in claim 65, wherein the second
pressure value is between about 20 bars and about 30 bars.
68. The apparatus as claimed in claim 65, wherein said feeding
circuit further comprises at least one auxiliary feeding circuit to
admit a counter-pressure fluid into the vulcanisation mould to
generate a first pressure gradient, so as to press the radially
internal surface of the tyre against a radially external surface of
the toroidal support concurrently with admission of the
vulcanisation fluid to said first pressure value, and to evacuate
said counter-pressure fluid to generate a second pressure gradient,
so as to press a radially external surface of the tyre against a
radially internal surface of a moulding cavity concurrently with
admission of the vulcanisation fluid to said second pressure
value.
69. The apparatus as claimed in claim 52, wherein said devices for
building a green tyre on the toroidal support comprise a plurality
of building stations distributed along a building line, each
building station being set to form one component of the green tyre
directly on said toroidal support.
70. The apparatus as claimed in claim 69, wherein the building
stations distributed along the building line each operate on a
respective green tyre being processed carried by a respective
toroidal support sequentially transferred from a building station
to the next one by means of robotized arms.
71. A toroidal support for building pneumatic tyres, each pneumatic
tyre comprising a crown region extending between side regions
axially spaced apart from each other and each carrying a respective
bead at a radially internal position, said toroidal support
comprising: an outer forming surface of a conformation
corresponding to the inner shape of a built tyre and having axially
opposite side portions; and devices for axially moving apart said
side portions at the side regions of said built tyre.
72. The toroidal support as claimed in claim 71, comprising a
plurality of circumferential sectors removably in engagement in
circumferential mutual alignment relationship.
73. The toroidal support as claimed in claim 72, wherein said
devices for axially moving apart said side portions comprise for
each circumferential sector, at least one pair of stop struts, each
stop strut being divided into two portions adapted to allow an
axial movement of said side portions.
74. The toroidal support as claimed in claim 71, wherein the
forming surface is obtained on a shaped wall confining at least one
circumferential cavity in the toroidal support.
75. The toroidal support as claimed in claim 74, wherein said
shaped wall substantially extends along a U-shaped outline in a
diametral section plane of the toroidal support.
76. The toroidal support as claimed in claim 74, wherein said
axially opposite side portions of the shaped wall are movable in an
axial direction.
77. The toroidal support as claimed in claim 71, wherein said
devices for axially moving apart the side portions act between a
rest condition and an axially spread apart condition, in which the
side portions are mutually spaced apart relative to the rest
condition by a stroke between about 0.1 mm and about 0.5 mm,
measurable at respective bead seats arranged in correspondence with
each bead of the tyre built on said toroidal support.
78. The toroidal support as claimed in claim 73, wherein said stop
struts have abutment surfaces axially acting against respective
locating seats to stop axial approaching movements between said
side portions.
79. The toroidal support as claimed in claim 78, wherein said
abutment surfaces and locating seats, in the absence of stresses on
the toroidal support, are disposed at such a distance as to stop
said axial approaching movements upon reaching of an axial
contraction stroke between about 0.01 mm and about 0.15 mm.
80. The toroidal support as claimed in claim 79, wherein said axial
contraction stroke is less than about 0.1 mm.
Description
[0001] The present invention relates to a method and an apparatus
for manufacturing pneumatic tyres.
[0002] A pneumatic tyre for vehicle wheels generally comprises a
carcass structure including at least one carcass ply having
respectively opposite end flaps in engagement with respective
annular anchoring structures, integrated into the regions usually
identified as "beads".
[0003] Associated with the carcass structure is a belt structure
comprising one or more belt layers, disposed in radial superposed
relationship with respect to each other and to the carcass ply and
having textile or metallic reinforcing cords with a crossed
orientation and/or substantially parallel to the circumferential
extension direction of the tyre. Applied to the belt structure at a
radially external position is a tread band also made of elastomeric
material like other semifinished products constituting the
tyre.
[0004] It is to be pointed out, to the aims of the present
description, that by the term "elastomeric material" it is intended
a composition comprising at least one elastomer polymer and at
least one reinforcing filler. Preferably, this composition further
comprises additives such as cross-linking agents and/or
plasticizers, for example. Due to the presence of the cross-linking
agents, this material can be cross-linked through heating so as to
form the final manufactured article.
[0005] Respective sidewalls of elastomeric material are also
applied to the side surfaces of the carcass structure, each
extending from one of the side edges of the tread band until close
to the respective annular anchoring structure to the beads. In
tyres of the tubeless type, an airtight coating layer, usually
called "liner" covers the inner surfaces of the tyre.
[0006] Generally, in the manufacture of tyres for vehicle wheels it
is provided that subsequently to building of the green tyre through
assembly of the respective components, a moulding and curing
treatment be carried out which aims at determining the structural
stabilisation of the tyre through cross-linking of the elastomeric
compositions and also at forming a desired tread pattern thereon,
as well as possible graphic distinctive marks at the tyre
sidewalls.
[0007] Manufacturing processes of recent conception are known in
which building of the green tyre is carried out by making the
different components thereof on a forming surface externally shaped
as a toroidal support, the conformation of which is coincident with
the inner conformation of the finished tyre. For carrying out the
moulding and curing treatment, the green tyre is enclosed in the
moulding cavity of a vulcanisation mould of a shape matching the
outer conformation to be given to the finished tyre, together with
the toroidal support on which the tyre itself has been built.
[0008] WO 01/00395, in the name of the same Applicant, depicts a
method of the above mentioned type involving use of a toroidal
support the forming surface of which has a substantially U-shaped
outline in a diametral section plane of the toroidal support.
[0009] During closure of the vulcanisation mould, circumferential
seats defined in the mould itself interfere against the radially
internal edges of the shaped wall causing such an elastic
deformation of the toroidal support that a high contact pressure is
ensured between the circumferential seats of the mould and the
radially internal edges of the shaped wall.
[0010] The toroidal support has an outer diameter slightly smaller
than the inner diameter of the finished tyre. The tyre crown region
is moulded against the inner surface of the moulding cavity
following a radial expansion induced by steam under pressure
introduced into a diffusion interspace defined between the toroidal
support and the inner surface of the tyre itself.
[0011] WO-2004/045837 in the name of the same Applicant as well,
proposes that preliminary heat be supplied to the tyre through
feeding of a fluid in counter-pressure into the mould externally of
the tyre, to counteract the pressure of steam or other fluid fed to
the inside of the toroidal support. Thus heat can be supplied to a
temperature high enough and for a time sufficiently long to ensure
a correct consolidation of the beads an a sufficient crosslinking
of the liner before carrying out moulding of the tyre crown portion
through feeding of high-pressure steam into the diffusion
interspace.
[0012] On practically carrying out said processes the Applicant
could note different difficulties correlated with the tyre moulding
and curing treatment.
[0013] In a moulding and vulcanisation process for tyres as the one
disclosed in WO-01/00395, and/or in WO-2004/045837 an
"imposed-volume" moulding is required on wide tyre regions
extending, by way of indication, from the beads along the sidewalls
and to the shoulders.
[0014] By observing that in the imposed-volume moulding the
different tyre parts must have a geometry substantially identical
with that of the spaces that when the mould is closed are confined
between the toroidal support and the inner surfaces of the moulding
cavity, the Applicant could deduce that in such a process precise
working tolerances are required in forming the individual
components during building of the tyre itself.
[0015] The Applicant has found the possibility of improving the
quality of the finished product while at the same time achieving an
important simplification in setting up the production processes, by
building the tyre on a substantially rigid toroidal support to be
introduced into the mould together with the tyre for carrying out
the moulding and vulcanisation process and by imposing to the
toroidal support, a movement in an axial direction of at least one
portion thereof during said moulding and vulcanisation step.
[0016] More particularly, in a first aspect, the present invention
relates to a method of manufacturing pneumatic tyres, each tyre
comprising a crown region extending between side regions axially
spaced apart from each other and each carrying a respective bead at
a radially internal position, said method comprising the steps of:
[0017] building a green tyre on a toroidal support with an outer
forming surface of a conformation corresponding to the inner shape
of the built tyre, and having axially opposite side portions;
[0018] curing said tyre by the steps of [0019] introducing the
green tyre disposed on said toroidal support into the vulcanisation
mould; [0020] closing the vulcanisation mould to compress the tyre
side regions between said forming surface and the vulcanisation
mould; [0021] axially moving the side portions of the toroidal
support away from each other at the tyre side regions to cause an
additional pressing of said side regions against the vulcanisation
mould; [0022] supplying heat to the tyre enclosed in the
vulcanisation mould.
[0023] Closure of the mould thus gives rise to compression of the
tyre between the toroidal support and the inner surfaces of the
moulding cavity, so that the sidewall and bead regions are shaped
according to a moulding of the imposed-volume type, while the
moving-apart movement of the side portions of the toroidal support
in an axial direction produces an additional pressing of the tyre
side regions and shaping of the same against the moulding cavity
following an imposed-pressure moulding technique so as to eliminate
possible localised faults due to lack of material for example.
[0024] In addition, carrying out pressing by axially moving the
side portions of the toroidal support away from each other enables
less narrow tolerances to be adopted in making the tyre components
during building of same. The toroidal support in fact lends itself
to conform to the tyre shape, compensating for possible geometric
and dimensional faults close to the sidewalls, without falling into
problems typically correlated with an imposed-volume moulding,
findable in the moulding and curing treatment carried out with use
of a rigid toroidal support in accordance with the known art.
[0025] The imposed pressure resulting from axial moving apart of
the side portions of the toroidal support further gives rise to an
improved anchoring action of the tyre beads, which is particularly
advantageous where a radial expansion is wished to be imposed to
the crown region of the tyre during the moulding and vulcanisation
step.
[0026] In a further aspect, the invention relates to an apparatus
for manufacturing pneumatic tyres, each tyre comprising a crown
region extending between side regions axially spaced apart from
each other and each carrying a respective bead at a radially
internal position, said apparatus comprising: [0027] at least one
toroidal support with an outer forming surface of a conformation
corresponding to the inner shape of a built tyre and having axially
opposite side portions; [0028] devices for building said green tyre
on the toroidal support; [0029] at least one vulcanisation mould
set to engage the green tyre disposed on the toroidal support;
[0030] devices for curing the tyre enclosed in the vulcanisation
mould; [0031] devices for axially moving apart said side portions
of the toroidal support at the side regions of the tyre enclosed in
the vulcanisation mould.
[0032] In a third aspect, the invention relates to a toroidal
support for building pneumatic tyres, each tyre comprising a crown
region extending between side regions axially spaced apart from
each other and each carrying a respective bead at a radially
internal position, said toroidal support comprising: [0033] an
outer forming surface of a conformation corresponding to the inner
shape of a built tyre and having axially opposite side portions;
[0034] devices for axially moving apart said side portions at the
side regions of said built tyre.
[0035] Further features and advantages will become more apparent
from the description of a preferred, but not exclusive, embodiment
of a method and an apparatus for manufacturing tyres, in accordance
with the present invention. This description will be set out
hereinafter with reference to the accompanying drawings, given by
way of non-limiting example, in which:
[0036] FIG. 1 is a diagrammatic top view of an apparatus for
manufacturing tyres in accordance with the present invention;
[0037] FIG. 2 is a diametrical section view of a tyre disposed on a
rigid toroidal support, at the end of the tyre building cycle;
[0038] FIG. 3 is a fragmentary diametrical section view of the tyre
enclosed in a vulcanisation mould together with the toroidal
support, during a first stage of the moulding and curing
treatment;
[0039] FIG. 4 shows a detail of FIG. 3 to an enlarged scale;
[0040] FIG. 5 shows the detail in FIG. 4 during a second stage of
the tyre moulding and curing treatment.
[0041] With reference to the drawings, an apparatus for
manufacturing tyres in accordance with the present invention has
been generally identified by reference numeral 1.
[0042] Apparatus 1 is set to manufacture tyres 2 essentially
comprising at least one carcass ply 3 preferably internally coated
with a layer of an airtight elastomeric material or a so-called
liner 4, two annular anchoring structures 5a in engagement with
circumferential edges of the carcass ply 3 close to the regions
usually identified as "beads" 5, a belt structure 6
circumferentially applied to the carcass ply 3, a tread band 7
circumferentially superposed on the belt structure 6, in a
so-called crown region "C" of tyre 2, and two sidewalls 8 applied
to the carcass ply 3 at laterally opposite positions, each at a
side region "L" of tyre 2 and extending from the corresponding bead
5 to the corresponding side edge of the tread band 7.
[0043] Apparatus 1 essentially comprises devices for building tyres
2 including a plurality of building stations 11, 12, 13, 14, 15 for
example, that are distributed along a building line 9 and are each
set to make one component of the tyre 2 being processed directly on
a toroidal support 10 having a forming surface 10a of a
conformation corresponding to the inner shape of tyre 2 when
building has been completed.
[0044] In more detail, by way of example, a first building station
11 may be provided in which liner 4 is formed through winding of a
continuous elongated element of elastomeric material into coils
disposed close to each other and distributed along the forming
surface 10a of the toroidal support 10v In at least one second
building station 12 one or more carcass plies 3 can be formed and
they are obtained through laying of strip-like elements disposed in
a circumferentially approached arrangement on the toroidal support
10, said strip-like elements being out off from a continuous strip
of elastomeric material comprising textile or metallic cords
arranged in parallel side by side relationship. A third building
station 13 can be dedicated to manufacture of the annular anchoring
structures 5a integrated into the tyre beads 5 through laying of at
least one continuous elongated element comprising at least one
rubberised metal cord, in the form of radially superposed coils. At
least one fourth building station 14 may be dedicated to
manufacture of the annular belt structure 6 obtained by laying in a
circumferentially-approached relationship, strip-like elements cut
off from a continuous strip of elastomeric material comprising
mutually parallel preferably metallic cords, and/or through winding
of at least one preferably metallic rubberised reinforcing cord
into coils disposed in axial side by side relationship, at the
crown portion of tyre 2. At least one fifth building station 15 can
be set for manufacture of the tread band 7 and the sidewalls 8.
Tread band 7 and sidewalls 8 are preferably obtained through
winding of at least one continuous elongated element of elastomeric
material into coils disposed in mutual side by side
relationship.
[0045] The building stations 11, 12, 13, 14, 15 distributed along
the building line 9 can each simultaneously operate on a respective
tyre 2 being processed, carried by a respective rigid toroidal
support 10, sequentially transferred from a building station to the
next one, through robotized arms 16 or other suitable devices.
[0046] Advantageously, the forming surface 10a of each toroidal
support 10 is obtained on a shaped wall 17 preferably made of metal
material, an aluminium alloy for example, or other material having
a modulus of elasticity high enough to bear stresses transmitted to
the toroidal support 10 during manufacture of tyre 2 without
suffering permanent sets.
[0047] The shaped wall 17 has a radially external portion 18 placed
close to the crown portion of tyre 2, and two axially opposite side
portions 19 extending from the radially external portion 18 and
defining respective radially internal circumferential edges 17a of
the shaped wall 17.
[0048] As viewed from the accompanying drawings, the radially
external portion 18 and side portions 19 give the shaped wall 17,
in a diametral section plane of the toroidal support 10, a
substantially U-shaped outline delimiting at least one
circumferential cavity 20 in the toroidal support itself.
[0049] To enable subsequent disengagement of the toroidal support
10 from tyre 2, said toroidal support has a collapsible or
dismountable structure made up of a plurality of circumferential
sectors 21 disposed in mutual circumferential alignment
relationship. The circumferential sectors 21 are mutually
interconnected by a removable interconnecting flange 22 carrying at
least one grip shank 23 to be utilised to enable handling of the
toroidal support 10 between the different building stations 11, 12,
13, 14, 15. The interconnecting flange 22 engages each
circumferential sector 21 at an attachment plate 24 extending from
the radially external portion 18 of the shaped wall 17, preferably
in a radial middle plane "m" of the toroidal support 10.
[0050] Axially extending between the side portions 19 of the shaped
wall 17, preferably in the vicinity of the radially internal
circumferential edges 17a of said wall are stop struts 25 each
carrying an abutment surface 26 axially opposite to a respective
locating seat 27. The abutment surfaces 26 and locating seats 27
are adapted to act against each other to stop axial approaching
movements between the side portions 19, in order to efficiently
hinder undesirable axial contractions of the to support 10 so as to
maintain the structural integrity of the shaped wall 17 even under
the effect of important axial thrusts transmitted to said side
portions 19.
[0051] In more detail, in the embodiment shown, at least one pair
of stop struts 25 is provided for each circumferential sector 21 of
the toroidal support 10; they are axially in alignment with each
other and each extend from the corresponding side portion 19 of the
shaped wall 17 until the attachment plate 24. In addition, each
stop strut 25 is divided into an axially internal portion 25a
integral with the attachment plate 24 and carrying the locating
seat 27, and an axially external portion 25b integral with the side
portion 19 of the shaped wall 17 and carrying the abutment surface
26.
[0052] In the absence of stresses on the toroidal support 10, the
abutment surfaces 26 and locating seats 27 can already be in
mutual-contact relationship or at all events disposed to such a
distance that axial approaching of the side portions 19 is stopped
upon reaching of a maximum axial contraction stroke included, by
way of indication, between about 0.01 mm and about 0.15 mm,
preferably shorter than about 0.1 mm.
[0053] To this aim, in the embodiment shown, the distance "n"
between each abutment surface 26 and the respective locating seat
27 in a rest condition to which corresponds the absence of stresses
on the toroidal support 10, must be included between about 0.01 mm
and about 0.15 mm, preferably shorter than 0.1 mm.
[0054] When building has been completed, the tyre 2 and toroidal
support 10 reach a transfer station 28 for introduction into a
vulcanisation mould 29. In the example shown in FIG. 1 a plurality
of vulcanisation moulds 29 is provided which are disposed in a
rotatable structure 30 so as to be sequentially brought to a
loading unloading position 31 where removal of the cured tyre 2 is
carried out, followed by introduction of a green tyre 2 coming from
the building line 9.
[0055] Each vulcanisation mould 29 essentially has a pair of
axially opposite plates 32 mutually movable in an axial direction
to abut against the side regions of tyre 2, and a plurality of
moulding sectors 33 circumferentially distributed between the
plates 32 and mutually movable in an axial direction to act on the
crown region C of tyre 2.
[0056] In more detail, the vulcanisation mould 29 can be changed
over between an open condition at which the plates 32 and moulding
sectors 33 are mutually spaced apart to enable introduction and
removal of tyre 2 together with the toroidal support 10, and a
closed condition at which, as shown in FIGS. 3 to 5, the plates and
moulding sectors are disposed close to each other to define a
moulding cavity 34 having a conformation corresponding to the outer
shape to be given to the cured tyre 2.
[0057] Preferably, the moulding cavity 34 has diametrical sizes
slightly larger than the diametrical sizes of the green tyre 2, so
that the inner surface in the moulding cavity 34 is suitably spaced
apart from the tread band of the green tyre 2 enclosed in the
vulcanisation mould 29.
[0058] During introduction of tyre 2 into the vulcanisation mould
29, the grip shank 23 carried by the toroidal support 10 is adapted
to be inserted in at least one centring seat 23a formed in the
vulcanisation mould 29, to ensure a centred positioning of tyre
2.
[0059] Then a vulcanisation cycle of tyre 2 is initiated. To this
aim, the vulcanisation mould 29 is closed through axial approaching
of the axially opposite plates 32 and simultaneous radial
approaching of the moulding sectors 33.
[0060] Under this circumstance, the side portions 19 of the shaped
wall 17 lend themselves to efficiently act against the side regions
of tyre 2, to counteract the axial thrust exerted by plates 32
during the end step for closure of the vulcanisation mould 29. The
side regions of tyre 2, and in particular the beads 5 and the
radially inner part of the sidewalls 8 are therefore compressed
between the plates 32 of the vulcanisation mould 29 and the side
portions 19 of the shaped wall 17 and consequently submitted to an
efficient moulding action substantially of the imposed-volume
type.
[0061] In this way all or most of the surface unevennesses given to
the beads 5 and sidewalls 8 during building, for example due to the
above described laying of continuous elongated elements of
elastomer material in the form of coils disposed close to each
other, are eliminated.
[0062] The presence of the stop struts 25 between the side portions
19 of the shaped wall 17 eliminates or in any case stops axial
approaching of the side portions 19 to a predetermined extent, by
effect of the imposed axial thrusts upon closure of the
vulcanisation mould 29. It is therefore possible to move the plates
32 quickly close to each other thereby achieving an important
reduction in the time that would be required for closing the
vulcanisation mould 29 if, due to the absence of the stop struts
25, particular care should be taken not to overstress the toroidal
support 10.
[0063] When closure of the vulcanisation mould 29 has been
completed, heat supply to tyre 2 is carried out by vulcanisation
devices, with the aid of at least one vulcanisation fluid fed to
the inside of the circumferential cavity 20 of the toroidal support
10, through at least one feeding circuit 35 opening into the
vulcanisation mould 29.
[0064] Preferably, control devices not described or shown because
they can be made in any convenient manner, operate on the feeding
circuit 35 to govern feeding of the vulcanisation fluid and
consequently heat supply during two stages in succession.
[0065] A first heat-supply stage aims at obtaining a localised
cross-linking at the inner surface of the tyre 2, to enable liner 4
to acquire sufficient imperviousness for execution of a subsequent
second heat-supply stage aiming at causing full vulcanisation of
tyre 2.
[0066] In addition to the localised cross-linking of liner 4 or as
an alternative thereto, the first heat-supply stage also causes a
localised cross-linking aiming at achieving a structural
consolidation of the side regions of tyre 2, particularly at the
beads and the radially internal portions of the sidewalls 8.
[0067] In more detail, the first heat-supply stage, of a duration
included by way of indication between about 2 and about 6 minutes,
preferably equal to about 3 minutes, preferably involves supply of
vulcanisation fluid, steam and/or nitrogen for example, under such
temperature and pressure conditions that a suitable heat
transmission to liner 4 and/or the side regions of tyre 2 is
allowed, without causing the side portions 19 of the shaped wall 17
to open wide to an important degree.
[0068] To this aim, the vulcanisation devices can further comprise
an auxiliary feeding circuit 35a that, concurrently with feeding of
the vulcanisation fluid to the inside of the circumferential cavity
20 of the toroidal support 10, introduces an auxiliary
counter-pressure fluid, nitrogen for example, into the moulding
cavity 34, externally of tyre 2, said fluid preferably being to a
temperature lower than 50.degree. C. and preferably a pressure at
least as high as the feeding pressure of the vulcanisation
fluid.
[0069] In more detail, the feeding pressure of the counter-pressure
fluid is preferably adapted to generate a first pressure gradient
included by way of indication between about 1 bar and about 3 bars,
between the exterior of tyre 2 and the circumferential cavity 20
defined within the toroidal support 10.
[0070] Just as an indication, the feeding pressure of the
vulcanisation fluid during the first stage can be less than 16
bars, equal to about 14 bars for example, while the
counter-pressure fluid is admitted to a pressure included between
about 7 bars and about 17 bars, equal to about 16 bars for
example.
[0071] Thus a "negative" pressure gradient is generated, i.e. a
pressure in the circumferential cavity 20 that is lower than the
pressure present in the moulding cavity 34, externally of tyre 2,
by about 2 bars and is capable of advantageously causing pressing
of the inner surface of tyre 2 against the forming surface 10a of
the toroidal support 10, in the same manner as described in
document WO-2004/045837, in the name of the same Applicant.
[0072] At the same time, due to heat transmitted through the side
portions 10 of the shaped wall 17 by effect of the vulcanisation
fluid admitted to the toroidal support 10, and through the mould
plates 32 upon effect of further heating devices associated with
said plates 32, a localised cross-linking of the liner and/or the
side regions of tyre 2 is produced, particularly at the beads 5 and
the radially internal parts of the sidewalls 8, without giving rise
to an important cross-linking of the radially external parts of
tyre 2 extending, just as an indication, on the tread band 7 and
the radially external portions 18 of the sidewalls 8.
[0073] Then the second heat-supply stage is initiated during which
tyre 2 receives the required heat for full cross-linking, i.e. a
cross-linking sufficient to ensure the geometric and structural
stability of the tyre itself in accordance with the design
specifications.
[0074] Upon command of said control devices, the second heat-supply
stage is carried out by evacuating the counter-pressure fluid, if
any, previously introduced into the vulcanisation mould 29 and
admitting vulcanisation fluid, steam and/or nitrogen for example,
into the circumferential cavity 20 of the toroidal support 10 to a
second pressure value included, by way of indication, between 20
bars and 30 bars, equal to about 27 bars for example, so as to
generate a second "positive" pressure gradient between the
circumferential cavity 20 and the moulding cavity 34, i.e. a
pressure in the circumferential cavity 20 that is about 27 bars
higher than the pressure present in the moulding cavity 34,
externally of tyre 2 and is capable of advantageously determining
pressing of the outer surface of tyre 2 against the inner surface
of the moulding cavity 34.
[0075] The high pressure created inside the toroidal support 10
causes inflow of the vulcanisation fluid between the forming
surface 10a and the inner surface of tyre 2 in the crown region C,
through radial apertures (not shown) defined between the opposite
edges of circumferentially adjoining sectors 21 of the toroidal
support itself, for example. The crown region C of tyre 2 is thus
pressed against the inner surface of the moulding cavity 34 and
submitted to moulding of the "imposed-pressure" type.
[0076] In accordance with the present invention, also provided are
devices that, after tyre 2 has been shut in the vulcanisation mould
29 and preferably concurrently with execution of the second
heat-supply stage, cause axial moving apart of the side portions 19
of the shaped wall 17 of the toroidal support 10. i.e. at the side
regions L of tyre 2.
[0077] To this aim it is advantageously provided that closure of
the vulcanisation mould 29 be completed in the absence of direct
contact between the plates 32 of the vulcanisation mould 29 and the
shaped wall 17 of the toroidal support 10, to give the side
portions 19 of the shaped wall 17 the possibility of slightly
opening wide, starting from a rest condition corresponding to the
absence of stresses on the toroidal support.
[0078] Preferably, said devices for axially moving apart said side
portions 19 can be partly represented by interruptions determined
by the presence of said abutment surfaces 26 and locating seats 27
along the stop struts 25. In fact, these interruptions give the
side portions 19 of the shaped wall 17 freedom of axially moving
mutually apart.
[0079] Due to mobility of the side portions 19 of the shaped wall
17, an additional pressing of the beads 5 and the radially internal
parts of the sidewalls 8 can be carried out, which is capable of
eliminating any possibly residual surface unevenness therefrom.
[0080] Said additional pressing further allows the components of
tyre 2 at the beads 5 to be retained more efficiently, by
counteracting stresses induced by the radial expansion imposed to
tyre 2.
[0081] Axial moving apart of the side portions 19 of the toroidal
support 10 is stopped, in case of need, on achievement of a
position of maximum spreading apart of the side portions 19. Thus
too many stresses on the toroidal support 10 are avoided which
could cause permanent sets of the shaped wall 17 and/or an
excessive compression and deformation of the beads 5 and the
radially internal parts of the sidewalls 8.
[0082] To this aim, circumferentially formed on each of the plates
32 is at least one stop seat 36 arranged to act in contact with the
corresponding side portion 19 of the toroidal support 10, in the
vicinity of the radially internal circumferential edge 17a of the
shaped wall 17, internally projecting with respect to the tyre
bead.
[0083] At the end of the step of closing the vulcanisation mould
29, the circumferential stop seats 36 reach a position to a
predetermined distance "d", included by way of indication between
about 0.1 and about 0.5 mm, from the side portions 19 of the shaped
wall 17.
[0084] Consequently, each of the side portions 19, when closure is
over, is movable upon elastic deformation of the shaped wall 17 to
the position of maximum spreading apart, according to a stroke
substantially equal to the distance "d" measurable at the tyre
bead.
[0085] At the end of vulcanisation, the vulcanisation mould 29 is
brought back to the open condition to enable extraction of the
cured tyre 2 together with the toroidal support 10.
[0086] Subsequently, in a disassembling station 37 removal of the
toroidal support 10 from tyre 2 is carried out by means of an
auxiliary robotized arm 38 for example, preferably by centripetal
extraction of the individual circumferential sectors 21 after
dismantling the interconnecting flange 22, as described in patent
U.S. Pat. No. 6,757,955 in the name of the same Applicant, for
example.
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