U.S. patent application number 13/787308 was filed with the patent office on 2013-07-18 for method and apparatus for manufacturing 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, Fiorenzo Mariani, Pierangelo Misani.
Application Number | 20130180646 13/787308 |
Document ID | / |
Family ID | 36636880 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130180646 |
Kind Code |
A1 |
Marchini; Maurizio ; et
al. |
July 18, 2013 |
METHOD AND APPARATUS FOR MANUFACTURING TYRES
Abstract
A green tyre is built on a rigid toroidal support externally
having a forming surface of a conformation corresponding to the
inner conformation of the tyre. The built tyre is removed from the
rigid toroidal support and engaged on an expandable toroidal
support comprising a bladder. The green tyre engaged on the
expandable toroidal support is introduced into a vulcanization
mould and submitted to a vulcanization cycle.
Inventors: |
Marchini; Maurizio; (Milano,
IT) ; Mariani; Fiorenzo; (Milano, IT) ;
Misani; Pierangelo; (Milano, IT) ; Cantu'; Marco;
(Milano, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pirelli Tyre S.p.A.; |
Milano |
|
IT |
|
|
Assignee: |
Pirelli Tyre S.p.A.
Milano
IT
|
Family ID: |
36636880 |
Appl. No.: |
13/787308 |
Filed: |
March 6, 2013 |
Current U.S.
Class: |
156/123 |
Current CPC
Class: |
B29D 30/0016 20130101;
B29D 2030/0647 20130101; B29D 2030/0022 20130101; B29D 2030/0622
20130101; B29D 30/10 20130101; B29D 30/0645 20130101 |
Class at
Publication: |
156/123 |
International
Class: |
B29D 30/10 20060101
B29D030/10; B29D 30/16 20060101 B29D030/16 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2005 |
IT |
PCT/IT2005/000704 |
Claims
1-45. (canceled)
46. An apparatus for manufacturing tyres, comprising: at least one
rigid toroidal support externally having a forming surface of a
conformation corresponding to an inner conformation of a built
green tyre; devices for building a green tyre on the rigid toroidal
support; at least one expandable toroidal support comprising at
least one bladder; devices for removing a built green tyre from the
rigid toroidal support; devices for engaging the built green tyre
on the expandable toroidal support; devices for introducing the
built green tyre engaged on the expandable toroidal support into a
vulcanisation mould; and devices for curing the tyre enclosed in
the vulcanisation mould.
47. The apparatus as claimed in claim 46, wherein the rigid
toroidal support is made up of a plurality of removably-engaged
circumferential sectors disposed in mutual circumferential
alignment relationship.
48. The apparatus as claimed in claim 46, wherein said forming
surface is substantially exempt from concavities or undercuts.
49. The apparatus as claimed in claim 46, wherein the rigid
toroidal support has bead seats axially spaced apart by a distance
greater than 95% of the maximum axial distance measurable between
axially opposite portions of the forming surface in parallel with a
geometric axis of the toroidal support itself.
50. The apparatus is claimed in claim 46, wherein said bladder has
a main portion in the form of a layer made of elastomeric material
substantially devoid of reinforcing inserts.
51. The apparatus as claimed in claim 46, wherein the expandable
toroidal support comprises: a pair of flanges coaxially facing each
other and sealingly engaging opposite circumferential edges of the
bladder; and an inflow duct radially opening between said flanges
into the bladder.
52. The apparatus as claimed in claim 46, wherein the bladder is
elastically deformable from a rest condition at which it has a
substantially cylindrical conformation, to a work condition at
which it is radially expanded and acts against the tyre taking the
shape of an inner conformation of the tyre.
53. The apparatus as claimed in claim 51, wherein the expandable
toroidal support further comprises a centring member coaxially in
engagement with said flanges.
54. The apparatus as claimed in claim 53, wherein said centring
member comprises at least one shank which is insertable in a
centring seat arranged in the vulcanisation mould.
55. The apparatus as claimed in claim 51, further comprising a pair
of counter-rings in which each counter-ring is peripherally
associated with one of said flanges to compress one bead of the
tyre being processed against an inner surface of the vulcanisation
mould.
56. The apparatus as claimed in claim 55, wherein each of said
counter-rings comprises a plurality of counter-sectors rotatably
engaged in the vicinity of a peripheral edge of the respective
flange and movable between a work position at which they have the
respective end edges consecutively disposed along a circumferential
alignment direction radially external to the flange, and a rest
position at which they have the respective end edges in a radially
internal position relative to the circumferential alignment
direction.
57. The apparatus as claimed in claim 56, wherein each
counter-sector has an abutment tailpiece projecting from a rotation
axis of the counter-sector on the opposite side from said end edge
and set to act in abutment against the vulcanisation mould to
inhibit rotation of the counter-sectors toward the rest position
when the tyre is enclosed in the vulcanisation mould.
58. The apparatus as claimed in claim 56, wherein the
counter-sectors are movable from the work position to the maximum
opened wide position to compress beads of the tyre enclosed in the
vulcanisation mould against said vulcanisation mould.
59. The apparatus as claimed in claim 58, wherein said
vulcanisation mould further comprises stop seats set to act against
the counter-sectors in the maximum opened wide position.
60. The apparatus as claimed in claim 46, wherein said devices for
curing the tyre comprise a feeding circuit opening into the
vulcanisation mould and adapted to be operatively coupled with an
inflow duct formed in the expandable toroidal support to supply a
vulcanisation fluid into the expandable toroidal support.
61. The apparatus as claimed in claim 60, wherein control devices
operate on the feeding circuit to admit the vulcanisation fluid to
a first pressure value for a predetermined time.
62. The apparatus as claimed in claim 61, wherein the control
devices operate on the feeding circuit to subsequently admit
vulcanisation fluid to a second pressure value higher than the
first pressure value.
63. The apparatus as claimed in claim 61, wherein the first
pressure value is about 1 bar to about 2.5 bars.
64. The apparatus as claimed in claim 62, wherein the second
pressure value is about 18 bars to about 30 bars.
65. The apparatus as claimed in claim 46, further comprising
devices for carrying out a lubricating treatment on the expandable
toroidal support.
66. The apparatus as claimed in claim 65, wherein said devices for
carrying out a lubricating treatment operate on the expandable
toroidal support positioned externally of the vulcanisation
mould.
67. The apparatus as claimed in claim 46, wherein said devices for
building a green tyre on the rigid 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 rigid toroidal support.
68. The apparatus as claimed in claim 67, wherein each of the
building stations distributed along the building line operates on a
respective green tyre being processed and carried by a respective
rigid toroidal support being sequentially transferred from a
building station to the next building station through robotized
arms.
Description
[0001] The present invention relates to a method and an apparatus
for manufacturing tyres.
[0002] A 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 heat 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 rigid toroidal support, the
conformation of which is coincident with the inner conformation of
the finished tyre. For achieving 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 build.
[0008] WO 01/00395, in the name of the same Applicant, discloses
use of a toroidal support having an outer diameter slightly smaller
than the inner diameter of the finished tyre. The crown portion of
the tyre 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.
[0009] U.S. Pat. No. 5,853,526 discloses building of a tyre carried
out through formation of the different components on an expandable
toroidal support comprising a reinforced bag the inner end flaps of
which are sealingly fastened to mutually coaxial anchoring flanges
which are integral with two half-shafts telescopically in
engagement with each other. The reinforced bag, inflated to a
predetermined pressure, keeps a predetermined geometric structure
corresponding to the inner conformation of the tyre to be built, so
that it lends itself to support the components of the tyre being
processed. When building has been completed, the tyre is shut up in
the vulcanisation mould together with the expandable toroidal
support. The reinforced bag is adapted to receive steam or other
working fluid under pressure, to cause pressing of the tyre against
the inner surfaces of the moulding cavity and simultaneous heat
supply to the tyre itself to achieve vulcanisation.
[0010] In practical implementation of said processes, the Applicant
could observe some difficulties correlated with the moulding and
curing treatment of the tyre.
[0011] In a tyre vulcanisation and moulding process as the one
disclosed in WO01/00395, an "imposed-volume" moulding is required
on wide regions of the tyre, by way of indication extending from
the tyre beads along the sidewalls, until the shoulders.
[0012] The Applicant could observe that in "imposed-volume"
moulding the different tyre parts must show 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, inferring therefrom that in
such a process precise work tolerances are required in forming the
individual components during building of the tyre itself.
[0013] The Applicant could also ascertain the necessity to adopt
particular expedients to prevent steam introduced into the green
tyre from seeping into the liner structure coating the inner tyre
surfaces, thereby impairing the structural tyre integrity.
[0014] In addition, the Applicant could find that an expandable
toroidal support of the type disclosed in U.S. Pat. No. 5,853,526
has a great manufacture complexity, and sophisticated arrangements
for control of the inflating pressure of the bag are required to
ensure the geometric and dimensional steadiness of said bag during
the whole tyre building process. In addition, manufacture of the
reinforced bag itself is very complicated and said bag is submitted
to such important thermal and mechanical stresses that replacement
of same is required after some vulcanisation cycles.
[0015] It was also ascertained by the Applicant that the high
number of expandable toroidal supports required for operation of a
building plant under normal working conditions involves heavy
investments and high management and servicing costs.
[0016] In accordance with the present invention, the Applicant has
become aware of the possibility of improving the final product
quality while at the same time achieving an important
simplification of the plants and the production processes through
building of the tyre on a rigid toroidal support to transfer then
the green tyre onto a toroidal support provided with an expandable
bladder to be introduced into the mould together with the tyre
itself to carry out the moulding and curing treatment thereon.
[0017] In more detail, in a first aspect, the present invention
relates to a method of manufacturing tyres comprising the steps of:
building a green tyre on a rigid toroidal support externally having
a forming surface of a conformation corresponding to the inner
conformation of the built green tyre; removing the built green tyre
from the rigid toroidal support; engaging the green tyre on an
expandable toroidal support comprising at least one bladder;
introducing the green tyre engaged on the expandable toroidal
support into a vulcanisation mould; curing the tyre enclosed in the
vulcanisation mould.
[0018] To enable easy removal of the rigid toroidal support from
the green tyre without impairing the geometric and structural
integrity of the tyre, the rigid toroidal support is preferably
provided to be made of a plurality of circumferential sectors in
engagement with each other in a removable manner, in a
circumferential mutual alignment relationship.
[0019] For the same reason, said forming surface is preferably
provided to be substantially exempt from concavities or
undercuts.
[0020] In more detail, to this aim the rigid toroidal support may
advantageously be adapted to engage the tyre beads at the so-called
"tyre seats" axially spaced apart by a distance higher than 95% of
the maximum axial distance measurable on the forming surface.
[0021] In fact, by carrying out tyre building on a rigid toroidal
support, a great structural and dimensional accuracy of the built
tyre is ensured without resorting to the sophisticated expedients
required for manufacturing the reinforced bags of the known art and
for controlling the geometric and dimensional features of same
through a constant management of the inflating pressure.
[0022] Carrying out the moulding and vulcanisation step through an
expandable bladder enables a high quality product to be obtained
with an important simplification of the production processes and a
reduction in the work scraps.
[0023] In addition, carrying out pressing by means of the bladder
allows less narrow tolerances to be adopted during formation of the
tyre components for building of the tyre itself. In fact the
bladder can adapt itself to the tyre conformation and compensate
for possible geometric and dimensional inaccuracies close to the
sidewalls, without encountering the problems correlated with an
"imposed-volume" moulding, arising when a rigid toroidal support is
used in the moulding and curing treatment.
[0024] Furthermore the bladder is adapted to enable a spreading
action eliminating possible surface discontinuities on the inner
tyre surfaces.
[0025] The bladder associated with the expandable toroidal support
must not bear the tyre during the building process, and therefore a
reinforced or particularly sophisticated structure is not required.
Therefore a low-cost bladder can be associated with the expandable
toroidal support so that periodical replacement of the bladder does
not involve high expenses.
[0026] In a plant made in accordance with the present invention, a
reduced number of expandable toroidal supports is required, i.e.
the number strictly necessary for bearing the tyres submitted to
the moulding and curing process, since the tyres along the building
line are supported by rigid toroidal supports.
[0027] Advantageously, the expandable toroidal support also lends
itself to be submitted to lubricating treatments aiming at
increasing surface smoothness between the bladder and the inner
surfaces of the tyre.
[0028] The possibility of carrying out the above treatments
directly on the expandable toroidal support externally of the
vulcanisation mould, instead of carrying them out on the inner
surfaces of the tyre or internally of the vulcanisation mould
greatly reduces the risks of contamination of the tyre and/or the
mould with the lubricating materials used in executing said
treatment.
[0029] In a further aspect the invention relates to an apparatus
for manufacturing tyres, comprising: at least one rigid toroidal
support externally having a forming surface of a conformation
corresponding to the inner conformation of the built green tyre;
devices for building a green tyre on the rigid toroidal support; at
least one expandable toroidal support comprising at least one
bladder; devices for removing a built green tyre from the rigid
toroidal support; devices for engaging the built green tyre on the
expandable toroidal support; devices for introducing the built
green tyre engaged on the expandable toroidal support into a
vulcanisation mould; devices fur curing the tyre enclosed in the
vulcanisation mould.
[0030] 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:
[0031] FIG. 1 diagrammatically shows a top view of an apparatus for
manufacturing tyres in accordance with the present invention;
[0032] FIG. 2 is a diametrical section view of a tyre disposed on a
rigid toroidal support, at the end of the tyre building cycle;
[0033] FIG. 3 shows a step of introducing an expandable toroidal
support into the green tyre disengaged from the rigid toroidal
support;
[0034] FIG. 4 shows a step of expanding the expandable toroidal
support internally of the green tyre;
[0035] FIG. 5 shows the tyre enclosed in a vulcanisation mould
together with the expandable toroidal support;
[0036] FIG. 6 is a view showing a detail seen in FIG. 5 to an
enlarged scale.
[0037] With reference to the drawings, an apparatus for tyre
manufacture in accordance with the present invention has been
generally identified by reference numeral 1.
[0038] Apparatus 1 is designed to manufacture tyres 2 (FIG. 2)
essentially comprising at least one carcass ply 3 internally coated
with a layer of an airtight elastomeric material, a so-called liner
4, two annular anchoring structures 5a in engagement with the
circumferential edges of the carcass ply in the vicinity of 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, and two
sidewalls 8 applied to the carcass ply 3 at laterally opposite
positions and each extending from the corresponding bead 5 to the
corresponding side edge of the tread band 7.
[0039] Apparatus 1 essentially comprises devices for building tyres
2 operating along a building line altogether identified by 9, and
devices for curing the tyres built along the building line 9.
[0040] The building line 9 may for example comprise a plurality of
building stations 11, 12, 13, 14, 15 distributed along the building
line 9 and each set to form a component of the tyre 2 being
processed directly on a rigid toroidal support 10 having a forming
surface 10a with a conformation corresponding to the inner
conformation of the green tyre 2 when building has been completed.
In more detail, by way of example, a first 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 10. 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 cut off from a continuous strip of
elastomeric material comprising textile or metallic cords disposed
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, in 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.
[0041] 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.
[0042] When building has been completed, the tyre 2 being processed
reaches a transfer station 17 equipped with devices 22 adapted to
remove the rigid toroidal support 10 from said tyre, tyre 2 being
preferably positioned on a suitable support base 18, as shown in
FIG. 2.
[0043] To enable release from tyre 2, the rigid toroidal support 10
is preferably provided to have a dismountable structure, made up of
a plurality of circumferential sectors 19 disposed in mutual
circumferential alignment. The circumferential sectors 19 are
interconnected with each other by a removable interconnecting
flange 20 carrying at least one grip shank 21 to be utilised in
order to enable handling of the toroidal support 10 between the
different building stations 11, 12, 13, 14, 15. The removal devices
22 may for example comprise a robotized arm set to remove the
interconnecting flange 20 and then individually pick up the
circumferential sectors 19 in succession to take them away from the
inside of tyre 2 with a combined oscillation and translation
movement substantially directed radially to the geometric rotation
axis of the tyre 2 itself, as described in patent U.S. Pat. No.
6,757,955 in the name of the same Applicant, for example.
[0044] To facilitate removal of the toroidal support 10 without any
risk of impairing the geometric and structural integrity of the
green tyre 2, the forming surface 10a of the toroidal support 10
and therefore the inner surface of the built tyre 2 are preferably
provided to be substantially exempt from concavities or undercuts
that can hinder extraction of the circumferential sectors 10 from
the inside of tyre 2. In more detail, to this aim it is provided
that the bead seats 10b arranged on the toroidal support 10 be
axially spaced apart by a distance "L" preferably greater than or
equal to the value of the maximum chord "C" of the forming surface
10a, i.e. the maximum axial distance measurable between axially
opposite portions of the forming surface 10a, in parallel to the
geometric axis X-X of the toroidal support 10 itself. An axial
distance L between the bead seats 10b that is slightly smaller than
the maximum chord C, as shown in FIG. 2 for example, is also
acceptable. However, preferably, the amount of the axial distance L
between the bead seats 10b must be higher than 95% of the above
specified maximum axial distance.
[0045] In this way it is advantageously possible to remove the
rigid toroidal support 10 from the built tyre 2 without any risk of
impairing the geometric and structural integrity of the tyre 2 in
spite of the fact that the latter, being still in a green state,
has a very delicate and easily deformable structure when submitted
to stresses even of small amount.
[0046] The same robotized arm 22 as used for removal of the rigid
toroidal support 10, or other suitable device operating in the
transfer station 17 or other adjacent work station carries out
engagement of the built green tyre 2 previously removed from the
rigid toroidal support 10, on an expandable toroidal support
23.
[0047] The expandable toroidal support 23 essentially comprises an
elastically deformable bladder 24 having a main portion 24a in the
form of a layer, made of elastomeric material substantially devoid
of textile or metallic reinforcing inserts and carrying opposite
circumferential edges 24b integrating possible circumferential
anchoring inserts sealingly engaged with respective flanges 25
facing each other in coaxial relationship.
[0048] The flanges 25 are mutually interconnected by a centring
member preferably comprising at least one shank 26 projecting in
axially opposite directions from said flanges 25. Longitudinally
formed in the centring shank 26, preferably starting from an end of
the latter, is an inflow duct 27 radially opening between the
flanges 25, into the bladder 24.
[0049] By introduction of a fluid under pressure through the inflow
duct 27, the bladder 24 lends itself to be deformed from a rest
condition, at which it has a substantially cylindrical conformation
as shown in FIG. 3, to a work condition at which it is elastically
expanded until it acts against the inner surface of the tyre 2
being processed, as viewed from FIGS. 4 and 5.
[0050] Also peripherally associated with each of flanges 25 is a
counter-ring 28 comprising a plurality of counter-sectors 29
rotatably hinged in the vicinity of the circumferential edge of the
flange 25 itself, each according to a rotation axis Y substantially
tangent to a circumferential line concentric with the geometric
axis X-X of the expandable toroidal support 23 and passing through
the hinge point. The counter-sectors 29 are simultaneously movable
between a rest position and an operating position, in accordance
with deformation of bladder 24 from the rest condition to the work
condition. In the work condition, the counter-sectors 29 are
oriented substantially at right angles to the axis X-X of the
expandable toroidal support 23, as shown in FIG. 4, and have
respective end edges 29a consecutively disposed along a
circumferential alignment direction radially external to the
respective flange 25. In the rest position, the counter-sectors 29
are oriented substantially parallel to the axis X-X of the
expandable toroidal support 23, as shown in FIG. 3, with the
respective end edges 29a positioned at a radially inner location
with respect to said circumferential alignment direction, to enable
the bladder 24 to take a substantially cylindrical conformation in
a rest condition.
[0051] For purposes that will become more apparent in the
following, each counter-sector 29 has an abutment tailpiece 29b
projecting from the rotation axis Y of the counter-sector 29
itself, on the opposite side from the end edge 29a.
[0052] In the embodiment shown, the counter-rings 28 are positioned
externally of bladder 24 and the respective counter-sectors 29 are
pushed from the rest position to the operating position following
expansion of the bladder 24. When the bladder 24 is brought back
from the work condition to the rest condition, each counter-sector
29 is free to rotate to the respective rest position, possibly
pushed by torsion springs or other spring means associated with the
counter-rings 28.
[0053] Alternatively, the counter-rings 28 can operate within the
bladder 24. In this case, shrinkage of the bladder 24 to the rest
condition causes orientation of the counter-sectors 29 to the rest
position. Following deformation of bladder 24 to the work
condition, the counter-sectors 29 are free to rotate to the
operating position, possibly urged by torsion springs or other
spring means associated with the counter-rings 28. To achieve
engagement of the built green tyre 2, the expandable toroidal
support 23 with the bladder 24 in the rest condition is coaxially
introduced into the tyre 2 preferably positioned on the same
support base 18 as used during the step of removing the rigid
toroidal support 10 therefrom, as shown in FIG. 3. More
particularly, the expandable toroidal support 23 is axially
positioned in such a manner that bladder 24 is substantially
centred in an axial direction relative to the rotation axis of tyre
2. Subsequently, introduction of nitrogen or other working fluid
into the bladder 24 is enabled, to cause elastic expansion of
bladder 24 from the rest condition to the work condition,
concurrently with a possible mutual approaching of flanges 25,
slidable along the centring shank 26. When bladder 24 comes into
contact with the inner surface of tyre 2, admission of the working
fluid is stopped. The material forming bladder 24 and the thickness
of same are such selected as to obtain a sufficiently steady
engagement between tyre 2 and bladder 24 on reaching of an inner
pressure that, just as an indication, does not exceed about 1 bar,
and is preferably in the order of about 0.5 bar (the pressure
values stated in the present description are to be intended as
values of gauge pressure with respect to the atmospheric pressure),
so as to avoid stresses capable of causing undesirable deformations
to the green tyre 2. It is to be noted that once engagement has
occurred the sidewalls 8 and beads 5 of tyre 2, due to the
conformation they are given during building, can keep an opened
wide orientation relative to the expandable toroidal support 23,
the shape of which in an operating condition is substantially
conformable to the inner configuration of the finished tyre 2, at
least close to the beads.
[0054] Through the same transfer device 22 as used for engagement
between the expandable toroidal support 23 and tyre 2, or other
suitable equipment, the expandable toroidal support 23 and the
green tyre 2 engaged thereon are introduced into a vulcanisation
mould 30 being part of the above mentioned vulcanisation
devices.
[0055] In the embodiment shown in FIG. 1 a plurality of
vulcanisation moulds 30 is provided, which moulds are disposed in a
rotatable structure 31 in such a manner as to be sequentially
brought to a loading/unloading position 32 where removal of the
cured tyre 2 is carried out, followed by introduction of a new
green tyre 2 coming from the building line 9.
[0056] Each vulcanisation mould 30 essentially has a pair of
axially opposite plates 33 set to operate on the beads 5 and
sidewalls 8 of tyre 2, and a plurality of moulding sectors 34 set
to operate against the tread band and defining, together with
plates 33, a moulding cavity 30a of a conformation corresponding to
the outer conformation to be given to the cured tyre 2. Preferably,
the moulding cavity 30a has slightly bigger diametrical sizes than
the diametrical sizes of the green tyre 2.
[0057] During introduction of tyre 2 into the mould 30, the
centring shank 26 carried by the expandable toroidal support 23 is
inserted in at least one centring seat 26a arranged in the
vulcanisation mould 30, to ensure a centred positioning of tyre 2
within the mould 30 itself.
[0058] Then starting of a vulcanisation cycle on tyre 2 takes
place. To this aim, the vulcanisation mould 30 is closed through
axial approaching of the axially opposite plates 33 and
simultaneous radial approaching of the moulding sectors 34.
Following closure of mould 30, the sidewalls 8 and beads 5 of tyre
2, previously disposed in an opened wide orientation, are moved
axially close to each other relative to the rigid toroidal support
10.
[0059] On closure of the mould 30, abutment seats 36
circumferentially distributed on the plates 33 act against the
abutment tailpieces 29b of the counter-sectors 29 belonging to the
counter-rings 28. Consequently, movement of the counter-sectors 29
to the rest position is inhibited. Under this circumstance, the
counter-rings 28 lend themselves to efficiently act against the
inner surfaces of tyre 2, particularly at the beads 5 and the
radially internal part of the sidewalls 8, to counteract the axial
thrust exerted by the plates 33 during the final step of closing
mould 30. The tyre beads and the radially internal part of the
sidewalls are therefore compressed between the plates 33 of mould
30 and the counter-rings 28, and consequently submitted to an
efficient "imposed-volume" moulding action according to a well
defined geometric configuration capable of eliminating possible
surface unevennesses given to the beads 5 and sidewalls 8 during
the building step, due for example to the above described laying of
elongated elements of elastomeric material in the form of coils
disposed close to each other.
[0060] When closure of the mould 30 has been completed, a
vulcanisation fluid is fed to the inside of bladder 24 through a
feeding circuit 37 opening into the vulcanisation mould 30 and
adapted to be operatively coupled with the inflow duct 27 formed in
the expandable toroidal support 23.
[0061] Control devices not described or shown as they can be made
in any convenient manner, operate on the feeding circuit 37 to
manage supply of the vulcanisation fluid according to two
vulcanisation stages in succession. A first vulcanisation stage
aims at obtaining consolidation of the beads of tyre 2, while a
second stage aims at determining full vulcanisation of tyre 2.
[0062] To this aim, in the first vulcanisation stage the
vulcanisation fluid, such as steam, nitrogen, a mixture thereof or
any other suitable fluid, preferably steam, is preferably provided
to be fed to a pressure included, by way of indication, between
about 1 bar and about 2.5 bars, equal to about 2 bars, for a period
of time included, just as an indication, between about 2 and about
6 minutes, equal to about 3 minutes for example. The supply
pressure of the vulcanisation fluid during the first vulcanisation
stage is adapted to enable a suitable heat transmission to the tyre
beads through the counter-rings 28, which pressure however is not
high enough to cause pressing of tyre 2 against, the inner walls of
mould 30, particularly at the radially external regions of the
same. Due to the amount of heat transmitted through the plates 33
of mould 30 and the counter-rings 28, by effect of the
vulcanisation fluid admitted into the expandable bladder, a
cross-linking localised at the beads 5 is thus obtained and
possibly in the radially internal portions of the sidewalls 8, of
such a nature as to cause a sufficient consolidation of the beads
without giving rise to an important cross-linking of the radially
external parts of tyre 2 extending, just as an indication, from the
tread band 7 and on the radially external portion of the sidewalls
8.
[0063] Subsequently, starting of the second vulcanisation stage is
caused by admitting vulcanisation fluid to the bladder 24, such as
steam, nitrogen, a mixture thereof or any other suitable fluid,
preferably steam and nitrogen, to a second pressure value included,
just as an indication, between about 18 bars and about 30 bars,
equal to about 27 bars for example, which is considerably higher
than the first pressure value used during carrying out of the first
vulcanisation stage. The high pressure created within the bladder
24 causes pressing of tyre 2 against the inner surface of mould 30,
transmitting to the whole tyre the required heat for full
cross-linking of same, i.e. a cross-linking sufficient to ensure
the geometric and structural stability of tyre 2 in accordance with
the design specifications.
[0064] The high pressure within the expandable bladder 24 during
the second vulcanisation stage also gives rise to an additional
pressing of the beads against the mould plates 33, by effect of the
axial thrust transmitted by the bladder 24 to the counter-rings 28.
It is to be pointed out in this connection that even after closure
of mould 30, the counter-sectors 29 are preferably movable from the
work position (in chain line in FIG. 6) to a maximum opened wide
position, along a stroke included by way of indication between
about 0.2 mm and about 1 mm, measured at the end edges 29a.
Mobility of the counter-sectors 29 to the maximum opened wide
position (in solid line in FIG. 6) enables an additional pressing
of the beads 5 and the radially internal portions of the sidewalls
8 to be carried out to such an extend as to eliminate possible
residual surface unevennesses. The additional pressing further
enables the components of tyre 2 to be retained in a more efficient
manner at the beads 5, counteracting the stresses induced by the
radial expansion imposed to said tyre 2. Suitable stop seats 38
(FIG. 6) associated with the plates 33 of the vulcanisation mould
30 lend themselves to act against the counter-sectors 29 so as to
stop opening wide of the same at the maximum opened wide position.
Thus an excessive compression and deformation of the beads 5 and
the radially internal portions of the sidewalls 8 is avoided.
[0065] In addition, the high pressure created in the bladder 24
during the pressing step, concurrently with the spring
deformability of the bladder itself, ensures an efficient spreading
of the elastomeric material constituting the inner surfaces of tyre
2, thus eliminating possible faults caused by laying of said
material in the form of coils disposed close to each other, also in
the radially external regions of tyre 2.
[0066] Adjustment of bladder 24 to the inner conformation of tyre 2
and subsequent separation at the end of vulcanisation can be
advantageously assisted by a possible lubricating treatment to be
carried out on the expandable toroidal support 23 before engagement
of the latter at the inside of the built tyre 2. This lubricating
treatment can be advantageously obtained by suitable devices
operating on the expandable toroidal support 23 positioned
externally of the vulcanisation mould 30, in order not to coat the
surfaces of the mould 30 itself with the lubricating material in an
undesirable manner.
* * * * *