U.S. patent application number 10/791580 was filed with the patent office on 2004-08-26 for process and device for cross-linked/expanding a blank for a safety support for a tire and support obtained by this process.
This patent application is currently assigned to Michelin Recherche et Technique S.A.. Invention is credited to Durif, Pierre, Menard, Gilbert, Morel, Noel, Peyron, Georges.
Application Number | 20040166315 10/791580 |
Document ID | / |
Family ID | 8850457 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040166315 |
Kind Code |
A1 |
Durif, Pierre ; et
al. |
August 26, 2004 |
Process and device for cross-linked/expanding a blank for a safety
support for a tire and support obtained by this process
Abstract
A process for cross-linking/expanding at least one
cross-linkable, expandable blank, which is intended to form all or
part of an elastomeric safety support for a tire in which: the
cross-linking consists of curing the expandable or expanded blank
in a bath of fluid at excess pressure which is contained in an
enclosure, such that the blank interacts with the bath
independently of the enclosure, the temperature of the bath having
a maximum value of between 110.degree. C. and 210.degree. C. and
the absolute pressure of said bath having at least a value equal to
or greater than 14 bar, and the expansion consists of curing the
cross-linkable or cross-linked blank in the bath, the temperature
of the bath having a maximum value of between 110.degree. C. and
210.degree. C., and the absolute pressure of the bath having at
least a value equal to or greater than 5 bar and a final
pressure-relief value substantially equal to 1 bar, for expanding
the blank such that its increase in volume is unlimited with
respect to the enclosure.
Inventors: |
Durif, Pierre; (Enval,
FR) ; Morel, Noel; (Enval, FR) ; Peyron,
Georges; (Riom, FR) ; Menard, Gilbert;
(Volvic, FR) |
Correspondence
Address: |
Baker Botts L.L.P.
30 Rockefeller Plaza
New York
NY
10112
US
|
Assignee: |
Michelin Recherche et Technique
S.A.
|
Family ID: |
8850457 |
Appl. No.: |
10/791580 |
Filed: |
March 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10791580 |
Mar 2, 2004 |
|
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09860075 |
May 17, 2001 |
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6716380 |
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Current U.S.
Class: |
428/398 ; 264/51;
425/4R; 425/73 |
Current CPC
Class: |
B60C 17/0009 20130101;
B29C 44/022 20130101; B60C 2001/0033 20130101; Y10T 428/2975
20150115; B60C 17/065 20130101; B29C 44/105 20130101; B60C 17/06
20130101 |
Class at
Publication: |
428/398 ;
264/051; 425/004.00R; 425/073 |
International
Class: |
B29C 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2000 |
FR |
00/06488 |
Claims
We claim:
1. A process for expanding at least one partially cross-linked
blank which is intended to form, in the cross-linked, expanded
state, all or part of an elastomeric safety support of cellular
structure having closed cells, said support being intended to be
mounted on a wheel rim within a tire, comprising curing said or
each blank in a bath of fluid at excess pressure which is contained
in an enclosure, the temperature of said bath having a maximum
value of between 110.degree. C. and 210.degree. C., and the
absolute pressure of said bath having at least a value equal to or
greater than 5 bar and a final pressure-relief value substantially
equal to 1 bar, for expanding said or each blank such that the
increase in volume thereof is unlimited with respect to said
enclosure.
2. An expansion process according to claim 1, including varying,
discretely or continuously, said absolute pressure of said fluid
between a maximum value less than or equal to 26 bar and a value
less than said maximum value.
3. An expansion process according to claim 1, including using a
liquid fluid for curing said or each blank.
4. An expansion process according to claim 1 including using a
gaseous fluid for curing said or each blank.
5. An expansion process according to claim 1, including cooling
said bath to a temperature less than or equal to 100.degree. C. and
at an absolute pressure of between 1 and 26 bar, following the
curing of said or each blank.
6. An expansion process according to claim 1, including curing in
said bath a plurality of blanks of linear and/or curved forms.
7. A process for cross-linking and expanding at least one
cross-linkable, expandable blank which is intended to form, in the
cross-linked, expanded state, all or part of an elastomeric safety
support of cellular structure having closed cells, said support
being intended to be mounted on a wheel rim within a tire, in which
said cross-linking includes curing said or each expandable or
expanded blank in a bath of fluid at excess pressure which is
contained in an enclosure, such that said or each blank interacts
with said bath independently of said enclosure, the temperature of
said bath having a maximum value of between 110.degree. C. and
210.degree. C., and the absolute pressure of said bath having at
least a value equal to or greater than 14 bar, and said expansion
includes subjecting said or each cross-linkable or cross-linked
blank to an expansion process according to claim 1.
8. A cross-linking and expansion process according to claim 7,
characterized in that it includes: in a first step, subjecting said
or each cross-linkable, expandable blank to said cross-linking in
order to obtain a practically cross-linked, expandable blank, then
in a second step, subjecting said or each blank which is
practically cross-linked and expandable following said first stage
of said expansion, in order to obtain all or part of said
corresponding cross-linked, expanded safety support.
9. A cross-linking and expansion process according to claim 7,
characterized in that it includes: in a first step, subjecting said
or each cross-linkable, expandable blank to said expansion in order
to obtain a cross-linkable, practically expanded blank, then in a
second step, subjecting said or each blank which is cross-linkable
and practically expanded to said cross-linking, in order to obtain
all or part of said corresponding cross-linked, expanded safety
support.
10. A curing device for implementing the cross-linking and
expansion process according to claim 7, the device comprising an
enclosure which is provided with at least one opening for the
introduction and extraction of said or each blank, means for
receiving said or each blank, means for filling said enclosure with
liquid or gaseous fluid, and heating and pressurization means for
the fluid contained within said enclosure, characterized in that
said enclosure comprises: an introduction compartment provided at
its inlet with an opening for introducing into said compartment a
unit of cross-linkable, expandable blanks for the curing thereof,
said introduction opening being provided with a means for closing
it, a curing compartment provided downstream of said introduction
compartment and provided at its inlet with a first mobile partition
for allowing it to communicate with said introduction compartment,
said curing compartment being intended to contain said heated,
pressurized fluid in order to obtain a unit of cross-linked,
expandable blanks, and an extraction compartment downstream of said
curing compartment and provided at its inlet with a second mobile
partition for allowing it to communicate with said curing
compartment and at its outlet with an opening to atmospheric
pressure for extracting a unit of cross-linked, expanded blanks
from said enclosure, said extraction opening being provided with a
means for closing it, and means for alternately transferring said
fluid at excess pressure from said extraction compartment towards
said introduction compartment, and from said introduction
compartment towards said extraction compartment.
11. A curing device for implementing the cross-linking and
expansion process according to claim 7, the device comprising an
enclosure which is provided with means for the introduction and
extraction of said or each blank, a means for receiving said or
each blank, means for filling said enclosure with liquid or gaseous
fluid, and heating and pressurization means for the fluid contained
within said enclosure, characterized in that said enclosure is
provided with a plurality of receiving means mounted adjacent each
other on a conduit intended for filling said enclosure with fluid
and extending into the interior thereof.
12. A curing device according to claim 11, characterized in that
said enclosure comprises an outlet conduit connected to means for
circulating said fluid to said means for filling the enclosure.
13. A curing device for implementing the cross-linking and
expansion process according to claim 7, the device comprising an
enclosure which is provided with at least one opening for the
introduction and extraction of said or each blank, means for
receiving said or each blank, means for filling said enclosure with
liquid or gaseous fluid, and heating and pressurization means for
the fluid contained within said enclosure, characterized in that
said means for filling the enclosure are formed of a conduit
opening into an opening in said enclosure, said conduit being
provided with a means which slides hermetically on an inner face of
a wall of said conduit for pressurizing the fluid contained within
said enclosure, this conduit also permitting emptying of said
enclosure, and in that said means for heating said fluid are
mounted around said enclosure and said conduit.
14. A safety support for a tire or section of said support obtained
by a process according to claim 7, said support or said section
being formed of a cross-linked, expanded rubber composition having
a cellular structure having closed cells, said support being
intended to be mounted on a wheel rim within a tire, characterized
in that it comprises, radially towards the inside of its outer
surface, an intermediate layer, the thickness of which is between
5% and 30% of the smallest dimension of a cross-section through
said section and a core and in which the density of the
intermediate layer is less than that of the core.
15. A support or section of said support according to claim 14,
characterized in that it has a maximum density in a surface layer
at the location of its outer surface, radially to the outside of
said intermediate layer.
16. A support or section of said support according to claim 14,
characterized in that it has an average density of between 0.04 and
0.4.
17. A support or section of said support according to claim 16,
characterized in that it has an average density substantially equal
to 0.13.
18. A support or section of said support according to claim 14,
characterized in that the respective diameters of said cells vary
on average from 0.1 mm to 2 mm over a cross-section of said support
or section.
19. A support or section of said support according to claim 14,
characterized in that it consists of one or more blanks each of
which are based on a copolymer of isoprene and isobutylene.
20. A support or section of said support according to claim 14,
characterized in that it comprises, as reinforcing filler, a blend
of 10 to 30 phr silica and 10 to 30 phr carbon black (phr: parts by
weight per hundred parts of elastomer(s)).
21. A support or section of said support according to claim 14,
comprising a base intended to be mounted on a wheel rim and a crown
intended to bear on the tread of said tire following a drop in
pressure within the tire, characterized in that it has at least one
longitudinal groove extending over said crown substantially level
with the latter, in the direction of the length of said support or
section of support.
22. A support or section of said support according to claim 14,
characterized in that it has at least one longitudinal cutout in
its mass, which extends in the direction of the length of said
support or section of support.
23. A support according to claim 14, characterized in that it is
substantially in the form of a torus.
24. A section of a support according to claim 14, characterized in
that it is substantially in the form of a portion of a torus.
25. A section of a support according to claim 14, characterized in
that it is substantially of linear form.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to a process for expanding at
least one cross-linkable or cross-linked blank which is intended to
constitute, in the cross-linked, expanded state, all or part of an
elastomeric safety support of cellular structure having closed
cells, said support being intended to be mounted on a wheel rim
within a tire. The invention also relates to a process for
cross-linking and expanding said or each blank, a device for
implementing said expansion or cross-linking/expansion process, and
finally a section of cross-linked, expanded support and such a
support which are obtained by this process.
[0002] The safety supports according to the invention can be used
for equipping tires, for example, of machinery or vehicles of the
two-wheeler, automobile or heavy-vehicle type.
[0003] The use of elastomeric safety supports having closed cells
is well-known for competition tires which are intended to travel on
bumpy courses of the "cross-country rally" type.
[0004] These cellular supports, which are usually of substantially
toric form, are supposed to permit travel following a significant
drop in pressure over a distance which depends in particular on the
more or less severe conditions characterizing this travel, for
example, following perforation of the tire.
[0005] Such supports are generally obtained by extruding a
cross-linkable, expandable rubber composition which has been
subjected to thermomechanical working in order to obtain a blank,
then by cross-linking and expanding the blank, the origin of the
expansion being the thermal decomposition of a blowing agent which
is initially present in the rubber composition.
[0006] More precisely, in a first step of thermomechanical working,
the rubber composition, which comprises in particular a diene
elastomer such as butyl rubber (copolymer of isoprene and
isobutylene), a reinforcing filler such as carbon black, a blowing
agent to permit later obtaining of the expanded cellular structure,
and a cross-linking system, is kneaded.
[0007] In a third step, which is carried out in an oven, the blank
thus obtained is preheated, to a temperature usually of between
70.degree. C. and 100.degree. C.
[0008] In a fourth step, performed in a mold, at least partial
cross-linking of the preheated blank is effected, at a temperature
usually of between 130.degree. and 150.degree. C.
[0009] In a fifth step, which is performed in an oven, the demolded
blank is subjected to expansion, at atmospheric pressure and at a
temperature usually of between 130.degree. C. and 150.degree.
C.
[0010] Thus a cross-linked, expanded support is obtained.
[0011] French patent specification FR-A-2 095 535 describes a
process for foaming and hardening an elastomeric filler material,
such as polyisoprene, dimethyl-methylvinyl polysiloxane or
polybutadiene, within a mounted assembly formed of a
previously-vulcanised tire which is mounted on a wheel rim. This
filler material is intended to equip tires intended for vehicles of
the heavy-vehicle type, and the main object desired is to minimize
the surface oxidation within the body of the vulcanised tire.
[0012] This object is achieved in that document by implementing a
process consisting of heating in an oven the mounted assembly by
means of saturated steam at a temperature of approximately
149.degree. C., then either removing the mounted assembly from the
oven or carrying out therein a plurality of heating cycles followed
by removal of the steam within the oven, in order to permit blowing
of the filler material.
[0013] It will be noted that this mounted assembly is intended to
form an enclosure of the mold type for the filler material which it
contains, owing to the fact that the foam being blown presses on
the wall of this mounted assembly.
[0014] It will also be noted that the foam which presses against
the wall of the mounted assembly is the seat of local chemical
reactions at the location of this wall (rim or tire), which induces
heterogeneity of structure of the foam which is finally formed.
[0015] The conventional cross-linking/expansion processes which use
a mold for cross-linking have one major drawback, which is linked
to the density characteristics of the cross-linked, expanded
supports which are obtained. In fact, the cross-linked, expanded
supports which are obtained by these processes using a mold are
generally characterized by an intermediate layer having a
significantly higher density (usually in a ratio of 1.5) than that
of the core or center of the support. There is shown
diagrammatically in FIG. 5 appended to the present description a
view in cross-section through such a support having, radially
towards the inside of its outer surface (at the location of which
there is a surface layer or skin A of the support), this
intermediate layer B and said core C.
[0016] Now, experience shows that this density gradient is at the
origin of increased propagation towards the core of the support of
the deformations which are imposed on the latter when travelling at
zero pressure, which results in likewise increased internal heating
of the support, which may cause the destruction thereof within a
relatively short period of travel.
SUMMARY OF THE INVENTION
[0017] The object of the present invention is to propose a process
for expanding at least one partially cross-linked blank which is
intended to form, in the cross-linked, expanded state, all or part
of an elastomeric safety support of cellular structure having
closed cells, said or each support being intended to be mounted on
a wheel rim within a tire, which makes it possible to overcome the
aforementioned disadvantage in relation to the use of a mold for
the cross-linking.
[0018] To this end, an expansion process according to the invention
is such that it consists of curing said or each blank in a bath of
fluid at excess pressure which is contained in an enclosure, the
temperature of said bath having a maximum value of between
110.degree. C. and 210.degree. C., and the absolute pressure of
said bath having at least a value equal to or greater than 5 bar
and a final pressure-relief value substantially equal to 1 bar, for
expanding said or each blank such that the increase in volume
thereof is unlimited with respect to said enclosure.
[0019] According to one example of embodiment of the invention,
this expansion process consists in varying, discretely or
continuously, said absolute pressure of said fluid between a
maximum value less than or equal to 26 bar and a value less than
said maximum value.
[0020] According to the invention, this expansion process consists
in using a liquid fluid, such as water, or a gaseous fluid, such as
hot air, steam or nitrogen, for curing said or each blank.
[0021] According to an optional characteristic of the invention,
this expansion process consists of cooling said bath to a
temperature less than or equal to 100.degree. C. and to an absolute
pressure of between 1 and 26 bar, following the curing of said or
each blank.
[0022] According to another characteristic of the invention, this
expansion process consists of curing a plurality of blanks of
linear and/or curved forms in said bath.
[0023] It will be noted that the supports or parts of supports thus
obtained may have forms and dimensions which are variable according
to the desired applications.
[0024] The subject of the present invention is also a process for
cross-linking and expanding at least one cross-linkable, expandable
blank which is intended to form, in the cross-linked, expanded
state, all or part of an elastomeric safety support of cellular
structure having closed cells, said support being intended to be
mounted on a wheel rim within a tire.
[0025] This cross-linking and expansion process according to the
invention also makes it possible to overcome the aforementioned
drawback in relation to cross-linked, expanded supports, which
drawback results from the use of a mold for the cross-linking, and
it is such that:
[0026] said cross-linking consists of curing said or each
expandable or expanded blank in a bath of fluid at excess pressure
which is contained in an enclosure, such that said or each blank
interacts with said bath independently of said enclosure, the
temperature of said bath having a maximum value of between
110.degree. C. and 210.degree. C., and the absolute pressure of
said bath having at least a value equal to or greater than 14 bar,
and in that
[0027] said expansion consists of subjecting said or each
cross-linkable or cross-linked blank to an expansion process
according to the invention such as defined above.
[0028] It will be noted that in the present description
"cross-linkable blank" is understood to mean a blank which can
still be cross-linked, independently of prior heat treatments which
may have caused the start of cross-linking. Consequently, a blank
which has previously been subjected to heat treatment involving
surface cross-linking is for example considered as being
cross-linkable. This heat treatment may have consisted of
preheating in an oven of an extruded blank and/or in the operation
of forming a blank itself, in the event that it is injection or
transfer molding, for example, which is being effected.
[0029] It will also be noted that this cross-linking and expansion
process according to the invention makes it possible to be set free
from the toric geometry of the blank which is conventionally
imposed by using a mold, and that it also makes it possible to
obtain cross-linked, expanded supports or parts of supports having
complex geometries which would be difficult to demold under
satisfactory conditions, such as for example, grooves and/or lobes
and/or cutouts in any one of the directions of the support or the
part of the support.
[0030] It will also be noted that this mold-less
cross-linking/expansion operation for cross-linking makes it
possible to obtain supports or parts of supports which do not have
a parting line, which does not weaken the corresponding support or
part of the support.
[0031] According to one embodiment of the invention, this
cross-linking and expansion process may consist:
[0032] in a first step, of subjecting said or each cross-linkable,
expandable blank to said cross-linking in order to obtain a
practically cross-linked, expandable blank, then
[0033] in a second step, of subjecting said or each blank which is
practically cross-linked and expandable which is obtained following
said first stage to said expansion, in order to obtain all or part
of said corresponding cross-linked, expanded safety support.
[0034] According to another embodiment of the invention, this
cross-linking and expansion process may consist:
[0035] in a first step, of subjecting said or each cross-linkable,
expandable blank to said expansion in order to obtain a
cross-linkable, practically expanded blank, then
[0036] in a second step, of subjecting said or each blank which is
cross-linkable and practically expanded to said cross-linking, in
order to obtain all or part of said corresponding cross-linked,
expanded safety support.
[0037] Advantageously, the cross-linking and expansion process
according to the invention consists of using one or more blanks
each of which are based on a copolymer of isoprene and isobutylene
(butyl rubber or IIR).
[0038] This elastomer has in particular reduced air
permeability.
[0039] According to other examples of embodiment, there could also
be used for the blank(s) the halogenated, in particular chlorinated
or brominated, versions of this copolymer (BIIR or CIIR rubbers,
bromobutyl and chlorobutyl rubbers respectively), copolymers of
dienes and of alpha-olefins, for example terpolymers of ethylene,
propylene and a diene (EPDM), polychloroprene (CR), or also a blend
of natural rubber (NR) and polybutadiene (BR) in substantially
identical proportions.
[0040] According to one example of embodiment of the invention, a
curing device according to the invention for implementing said
cross-linking and expansion process of the type comprising an
enclosure which is provided with at least one opening for the
introduction and extraction of said or each blank, means for
receiving said or each blank, means for filling said enclosure with
liquid or gaseous fluid, and heating and pressurization means for
the fluid contained within said enclosure, in which said enclosure
comprises:
[0041] an introduction compartment provided at its inlet with an
opening for introducing into said compartment a unit of
cross-linkable, expandable blanks for the curing thereof, said
introduction opening being provided with a means for shutting it
off,
[0042] a curing compartment provided downstream of said
introduction compartment and provided at its inlet with a first
mobile partition for allowing it to communicate with said
introduction compartment, said curing compartment being intended to
contain said heated, pressurised fluid in order to obtain a unit of
cross-linked, expandable blanks, and
[0043] an extraction compartment provided downstream of said curing
compartment and provided at its inlet with a second mobile
partition for allowing it to communicate with said curing
compartment and at its outlet with an opening to atmospheric
pressure for obtaining a unit of cross-linked, expanded blanks and
their extraction from said enclosure, said extraction opening being
provided with a means for shutting it off,
[0044] means for alternately transferring said fluid at excess
pressure from said extraction compartment towards said introduction
compartment, and from said introduction compartment towards said
extraction compartment.
[0045] It will be noted that these compartments make it possible to
cross-link and expand units of blanks continuously, by including
automated displacement of each unit within one and the same
compartment and/or from one compartment to another, owing to the
aforementioned openings and mobile partitions.
[0046] In fact, these partitions and openings, when in the closed
position, make it possible to form locks at the location of the
introduction and extraction compartments and, when said openings
are in the closed position and said partitions are in the open
position, enable one or the other of said introduction and
extraction compartments (which is then filled with fluid) to form
alternately a pressure balance with the adjoining curing
compartment which is itself continuously filled with fluid.
[0047] It will also be noted that the total volume expansion of the
blanks is obtained in said extraction compartment when the absolute
pressure in this compartment is again made equal to atmospheric
pressure (by means of said extraction opening, which is then in the
open position, thus forming a pressure balance with the ambient
air).
[0048] It will furthermore be noted that this
cross-linking/expansion device according to the invention may be
advantageously integrated in an overall process for manufacturing
supports or sections of supports which is implemented continuously,
that is to say, directly downstream of the forming stations, for
example by extrusion or by injection, and for preheating the shaped
blanks in an oven.
[0049] A curing device according to the invention may comprise any
automated means suitable for controlling and checking parameters of
the expansion/cross-linking process, such as temperature, pressure
and the flow rate of curing water.
[0050] According to another example of embodiment of the invention,
a curing device for implementing said cross-linking and expansion
process, which is of the type comprising an enclosure which is
provided with means for the introduction and extraction of said or
each blank, means for receiving said or each blank, means for
filling said enclosure with liquid or gaseous fluid, and heating
and pressurization means for the fluid contained within said
enclosure,
[0051] is such that said enclosure is provided with a plurality of
receiving means respectively provided to receive a plurality of
blanks, said receiving means being mounted adjacent to each other
on a conduit intended for filling said enclosure with fluid and
extending into the interior thereof.
[0052] According to another characteristic of this example of
embodiment, said enclosure comprises an outlet conduit connected to
means for circulating said fluid towards said means for filling the
enclosure.
[0053] According to another example of embodiment of the invention,
a curing device for implementing said cross-linking and expansion
process, of the type comprising an enclosure which is provided with
at least one opening for the introduction and extraction of said or
each blank, means for receiving said or each blank, means for
filling said enclosure with liquid or gaseous fluid, and heating
and pressurization means for the fluid contained within said
enclosure, is such that:
[0054] said means for filling the enclosure are formed of a conduit
opening into an opening in said enclosure, said enclosure being
provided with a means which slides hermetically on the inner face
of its wall for pressurising the fluid contained within said
enclosure, this enclosure also being suitable for permitting
emptying of said enclosure, and that
[0055] said means for heating said fluid are mounted around said
enclosure and said conduit.
[0056] It will be noted that, in this example of embodiment, the
sliding means for pressurising the interior of the enclosure may be
of the piston type, and that said heating means may for example
comprise a coil through which a heat-transfer fluid flows, or an
electrical resistor.
[0057] As for the fluid which can be used in this example of
embodiment, it is preferably formed of a liquid, the boiling point
of this liquid being beyond the temperature used for the curing,
which may vary from 110.degree. C. to 210.degree. C.
[0058] However, it is also possible to use a gas, provided that a
gas is used, the relative weight of which relative to the air is
suitable to permit the pressurization of said enclosure from said
filling/emptying conduit.
[0059] A section of safety support according to the invention, or
such a safety support also according to the invention, are obtained
by the cross-linking/expansion process referred to above, said
section being formed of a cross-linked, expanded rubber composition
having a cellular structure having closed cells.
[0060] Advantageously, these cross-linked, expanded sections or
supports according to the invention may each comprise, radially
towards the inside of their outer surface, an intermediate layer,
the thickness of which is between 5% and 30% of the smallest
dimension of a cross-section through said section or said support,
and the density of which is less than that of the core of said
section or said support.
[0061] It will be noted that this density gradient could not be
obtained by the aforementioned conventional processes, that is to
say with cross-linking in a mold followed by expansion to
atmospheric pressure.
[0062] This intermediate layer of low density makes it possible to
minimize the internal heating of the support when travelling at
zero pressure.
[0063] According to another characteristic of the invention, the
cross-linked, expanded sections or supports obtained each have a
maximum density in a surface layer at the location of their outer
surfaces, radially to the outside of said intermediate layer.
[0064] It will be noted that this surface layer, which has a high
density close to that of the corresponding non-expanded blank,
imparts to the support or to the section of support a surface
resistance which is suited, firstly, to direct mounting on the rim
and, secondly, to the repeated contacts with the reliefs of the
inner face of a tire.
[0065] According to another characteristic of the invention, the
cross-linked, expanded supports or sections obtained each have an
average density of between 0.04 and 0.4 and, for example,
substantially equal to 0.13.
[0066] It will be noted that an average density of close to 0.04
makes it possible to have a support characterized by satisfactory
damping of shocks and by minimized internal heating. Such a support
is particularly intended to be fitted on tires of the cross-country
rally type for temporary use.
[0067] An average density close to 0.4 makes it possible to impart
high structural rigidity to the corresponding support, which is
particularly intended to be fitted on tires bearing heavy
loads.
[0068] As for an average density close to 0.13, it makes it
possible to impart to the core of the corresponding support
sufficient rigidity, for example to minimize the deformations of
the support during travel which are imposed by centrifuigal force,
when the tire is under inflation pressure and when the base of the
support is connected to the rim, for example by means of a
reinforcement or another means of connecting to the rim. Such a
support is particularly intended to be fitted on tires of the
automobile type.
[0069] According to another characteristic of the invention, the
respective diameters of said cells vary on average from 0.1 mm to 2
mm, over a cross-section of said support or section.
[0070] Advantageously, said cross-linked, expanded section or
support are each based on a copolymer of isoprene and
isobutylene.
[0071] According to one example of embodiment of the invention,
said cross-linked, expanded section or support each comprise, as
reinforcing filler, a blend of 10 to 30 phr silica and 10 to 30 phr
carbon black (phr: parts by weight per hundred parts of
elastomer(s)).
[0072] The silica which may be used may be any reinforcing silica
known to the person skilled in the art, in particular any
precipitated or pyrogenic silica having a BET surface area and a
CTAB specific surface area both of which are less than 450
m.sup.2/g, even if the highly dispersible precipitated silicas are
preferred.
[0073] In the present specification, the BET specific surface area
is determined in known manner, in accordance with the method of
Brunauer, Emmett and Teller described in "The Journal of the
American Chemical Society", vol. 60, page 309, February 1938, and
corresponding to Standard AFNOR-NFT-45007 (November 1987); the CTAB
specific surface area is the external surface area determined in
accordance with the same Standard AFNOR-NFT-45007 of November
1987.
[0074] "Highly dispersible silica" is understood to mean any silica
having a very substantial ability to disagglomerate and to disperse
in an elastomeric matrix, which can be observed in known manner by
electron or optical microscopy on thin sections. As non-limitative
examples of such preferred highly dispersible silicas, mention may
be made for example of the silica Ultrasil VN3 from Degussa, and
the silicas Zeosil 1165 MP and 1115 MP from Rhodia.
[0075] Of course, "silica" is also understood to mean mixtures of
different silicas, in particular of highly dispersible silicas such
as described above.
[0076] Suitable carbon blacks are any carbon blacks, in particular
the blacks of the type HAF, ISAF and SAF, which are conventionally
used in tires, and particularly in tire treads. As non-limitative
examples of such blacks, mention may be made of the blacks N115,
N134, N234, N339, N347 and N375. The mass fraction of carbon black
present in the reinforcing filler may vary within wide limits, this
quantity preferably being from 40% to 60%, for a mass fraction of
silica of from 60 to 40%.
[0077] According to one example of embodiment of the invention, the
support or section of support, which comprises a base intended to
be mounted on said wheel rim and a crown intended to bear on the
tread of said tire following a drop in pressure within the latter,
is such that it has at least one longitudinal groove extending over
said crown substantially level with the latter, in the direction of
the length of said support or section of support.
[0078] According to another example of embodiment of the invention,
the support or section of support is such that it has at least one
longitudinal cutout in its mass, which extends in the direction of
the length of said support or section of support.
[0079] It will be noted that these two examples of profiles of
supports or of sections of supports, which may be obtained using
the cross-linking/expansion process according to the invention,
cannot be obtained under satisfactory conditions by means of the
conventional processes using a mold for cross-linking. In fact,
these particular profiles make the demolding operation particularly
difficult.
DESCRIPTION OF THE DRAWINGS
[0080] The aforementioned characteristics of the present invention,
as well as others, will be better understood on reading the
following description of several examples of embodiment of the
invention, which are given by way of illustration and not of
limitation, said description being given in relation to the
appended drawing, in which:
[0081] FIG. 1 is a diagram illustrating an example of a device for
implementing the cross-linking/expansion process according to the
invention,
[0082] FIGS. 2 and 3 are diagrammatic sectional views illustrating
another embodiment of a curing device for implementing the
cross-linking/expansion process according to the invention in two
operating positions.
[0083] FIG. 4 is a diagrammatic view in partial section of another
embodiment of a curing device according to the invention for
implementing this process, and
[0084] FIG. 5 is a diagrammatic sectional view through a support
obtained by the cross-linking/expansion process according to the
invention, and
[0085] FIGS. 6 and 7 show two embodiments of profiles of supports
according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0086] A curing device in accordance with FIG. 1 comprises an
enclosure 1 which is provided with at least one gate closable
opening 2, 3 for the introduction and extraction of units 4
comprising a plurality of blanks 5a, 5b, means for receiving each
blank, means for filling said enclosure 1 with liquid or gaseous
fluid 6, and heating and pressurization means for the fluid 6
contained within said enclosure which are controlled by control
means (these receiving, filling, heating/pressurization and control
means are not shown for reasons of clarity).
[0087] The enclosure 1 of FIG. 1 comprises:
[0088] an introduction compartment 7 provided at its inlet with an
opening 2 for introducing a unit 4 of cross-linkable, expandable
blanks 5a, said introduction opening 2 being provided with a means
2a for permitting the freeing or blocking thereof (this opening 2
is shown in the blocked position in FIG. 1),
[0089] a curing compartment 8 provided downstream of the previous
one and provided at its inlet with a first mobile partition 9 for
placing it in communication with said introduction compartment 7
(this partition 9 is shown in the hermetic partitioning position in
FIG. 1). This curing compartment 8 is intended to contain said
fluid 6 which is heated and under pressure in order to obtain at
least one unit 4 of cross-linked, expandable blanks 5b (in the
simply illustrative example of FIG. 1, the compartment 8 is
intended to receive two units 4),
[0090] an extraction compartment 10 provided downstream from the
former, which is intended to receive one unit 4 of said
cross-linked, expandable blanks 5b. This compartment 10 is provided
at its inlet with a second mobile partition 11 for placing it in
communication with said curing compartment 8 (this partition 11 is
also shown in the hermetic partitioning position in FIG. 1), and at
its outlet with an opening 3 for extracting from said enclosure 1 a
unit 4 of cross-linked, expanded blanks 5c, said extraction opening
3 (shown in the open position in FIG. 1) being provided with a
means 3a for freeing or blocking it; and
[0091] means 12 for alternately transferring the fluid 6 at excess
pressure from the extraction compartment 10 towards the
introduction compartment 7, and vice versa (an element 12a for
setting the fluid 6 in motion is shown in FIG. 1, for example a
pump).
[0092] The cross-linking operation, which is carried out in the
curing compartment 8, consists of curing each unit 4 of
cross-linkable, expandable blanks 5a in a bath of fluid 6 at excess
pressure, such that each blank interacts with said bath 6
independently of the compartment 8, the temperature of said bath 6
having a maximum value of between 110.degree. C. and 210.degree.
C., and the absolute pressure of said bath 6 having at least a
value equal to or greater than 14 bar.
[0093] As for the expansion operation, it is initiated in the
curing compartment 8 during the cross-linking (the blowing agent
present in each blank 5a decomposing, which initiates the
germination of the cells), but the expansion (in the conventional
sense of increase in volume, which is attributed to this term in
the present description) effectively taking place only in the
extraction compartment 10, when the latter is devoid of the fluid 6
and is brought to atmospheric pressure.
[0094] More precisely, the temperature of said bath 6 in the curing
compartment 8 has a maximum value of between 110.degree. C. and
210.degree. C., and the absolute pressure of said bath 6 has at
least a value equal to or greater than 5 bar.
[0095] Still in accordance with the invention, the expansion of
each cross-linked blank 5b, which takes place at a final
pressure-relief value of the absolute pressure at 1 bar, is
effected such that the increase in volume of each blank 5b is
unlimited with respect to the extraction compartment 10, to produce
the corresponding cross-linked, expanded support or part of the
support 5c.
[0096] This device can operate continuously, advantageously
directly downstream from the forming stations for the blanks (for
example consisting of extruders) and the stations for preheating
the formed blanks in an oven, by reproducing over time the
following cycle of operations.
[0097] There is extracted from the extraction compartment 10 a unit
of cross-linked, expanded supports or parts of supports 5c of rank
n, then the partition 11 is moved into the de-partitioning position
in order to fill this compartment 10, the opening 3 of which has
been blocked, with fluid 6, so as to be able to displace each unit
4 contained in the enclosure 1 by one rank. The unit of rank n+1 of
cross-linked, expandable blanks 5b is thus in said compartment 10,
for the expansion thereof.
[0098] There is introduced in parallel a unit 4 of higher rank (n+3
in the example of FIG. 1) into the introduction compartment 7,
which has previously been open to atmospheric pressure, then the
opening 3 of the compartment 10 is blocked in order to transfer the
fluid 6 contained in the extraction compartment 10 to the
compartment 7, as is indicated by the arrow A of FIG. 1 (the
partition 11 of the compartment 10 having first been moved into the
closed position).
[0099] Then the opening 3 of the compartment 10 is opened to permit
expansion of the blanks 5b of the unit 4 of rank n+1, owing to the
equilibrium at atmospheric pressure, then the cross-linked,
expanded blanks 5c of this unit are extracted.
[0100] In parallel, the units 4 are displaced within the enclosure
1 by one rank, as indicated previously, the pressure equalization
between the compartments 7 and 8, on one hand, and 8 and 10, on the
other hand, making this displacement possible (the arrow B in FIG.
1 illustrates the transfer of the fluid 6 from the compartment 7 to
the compartment 10), and so on.
[0101] There is shown in FIGS. 2 and 3 another example of
embodiment of a curing device according to the invention for the
cross-linking/expansion of a unit 4 of blanks 5a.
[0102] This curing device comprises an opening 2 for the
introduction of a unit 4 of cross-linkable, expandable blanks 5a
(see FIG. 2) and for the extraction of the corresponding unit 4 of
the cross-linked, expanded supports or parts of supports 5c, which
are shown in broken lines in FIG. 3 (at the end of the expansion
operation). This device also comprises means for filling the
enclosure 1 which are provided by a conduit 13 which communicates
through an opening 14 with said enclosure 1.
[0103] The conduit 13 is provided with a means 15 which slides
hermetically on the inner face of its wall to pressurise the fluid
6 contained within said enclosure 1 (see arrow C in FIG. 3, in
which the opening 2 has been closed in order to fill the enclosure
1 with the fluid 6). This means 15 is for example of the piston
type.
[0104] The fluid 6 which can be used in this embodiment is
preferably formed of a liquid, the boiling point of this liquid
being above the temperature used for the cross-linking/expansion,
which may vary from 110.degree. to 210.degree. C.
[0105] Furthermore, the conduit 13 is also suitable to permit
emptying of said enclosure 1.
[0106] This curing device also comprises means 16 for heating the
fluid 6 which are mounted around said enclosure 1 and said conduit
13. These heating means 16 may be formed of a coil through which a
heat-transfer fluid flows, or an electrical resistor.
[0107] Of course, the curing device of FIGS. 2 and 3 comprises
means for receiving the blanks 5a in the enclosure 1, and also
means for controlling the pressure and temperature parameters.
[0108] Another example of a curing device according to the
invention is shown in FIG. 4.
[0109] This device is essentially formed of an enclosure 21 which
is provided with a fluid inlet conduit 23 (see arrow D) which opens
onto the inside of the enclosure 21 via its end 23a, said conduit
23 being connected to a heating and pressurization circuit for the
bath 6 of fluid contained in the enclosure 21, and of a fluid
outlet conduit separate from said inlet conduit 23 (this
heating/pressurization circuit and said outlet conduit are not
shown).
[0110] Of course, this device also comprises means for introducing
cross-linkable, expandable blanks 5a into the enclosure 21, and for
extracting the corresponding cross-linked, expanded supports or
parts of supports 5c.
[0111] In the example of embodiment of FIG. 4, the inlet conduit 23
is suitable for supporting, at regular height intervals, plates 25
which are each intended to receive a blank 5a, for the
cross-linking/expansion thereof.
[0112] There are shown in FIG. 4 blanks 5a of overall toric form,
but it will be noted that each plate 25 could receive blanks 5a of
any shape, for example linear, in order to obtain linear sections
of supports instead of toric supports.
[0113] Each plate 25 is provided with means 26 for centering the
corresponding blank 5a when it is put in position. In the example
of FIG. 4, these means 26 are formed of a positioning block around
which the blank 5a is intended to be positioned.
[0114] Each of the two examples of a device according to the
invention which have been described above, on one hand, in relation
to FIGS. 2 and 3 and, on the other hand, in relation to FIG. 4,
operate as follows.
[0115] In the manner of what has been described in relation to FIG.
1, the cross-linking operation consists of curing the
cross-linkable, expandable blanks 5a in the bath 6 of fluid at
excess pressure, such that each blank interacts with said bath 6
independently of the walls of the enclosure 1, 21. More precisely,
the temperature of the bath 6 has a maximum value of between
110.degree. C. and 210.degree. C., and its absolute pressure
comprises at least a value equal to or greater than 14 bar.
[0116] As for the expansion operation, it is initiated in said bath
6 provided that the temperature thereof comprises a maximum value
of between 110.degree. C. and 210.degree. C., and that its absolute
pressure has at least a value equal to or greater than 5 bar, and
the increase in volume of the blank 5a, which is a result of the
expansion, takes place actually once the latter is at atmospheric
pressure by opening the enclosure 1, 21 (see the supports 5c in
broken lines in FIGS. 3 and 4).
[0117] As has been indicated in relation to FIG. 1, it will be
noted that this expansion is unlimited with respect to the walls of
the enclosure 1, 21.
[0118] As far as the curing device of FIG. 4 is concerned, it will
be noted that curing in the bath 6 may be advantageously effected
with a continuous flow of fluid, owing to the permanent circulation
of the fluid from said outlet conduit to said inlet conduit 23.
First Series of Tests for Cross-Linking/Expansion
[0119] A plurality of tests were carried out, using for the blanks
two cross-linkable, expandable rubber compositions which are both
based on butyl rubber but which differ essentially from one another
in that a first composition A comprises a reinforcing filler formed
of carbon black, whereas a second composition B comprises a
reinforcing filler made of a blend of carbon black and silica.
[0120] Table I hereafter sets forth these essential
differences.
1TABLE I (phr: parts by weight per hundred parts of elastomer).
Constituents Composition A Composition B introduced into the mixer
(amount in phr) (amount in phr) Carbon black N683 40 20 Silica
"Zeosil 1165 MP" -- 20 Blowing agent: 13 13 (azobisformamide)
[0121] Each blank was prior to this preheated by means of hot air
in an electric oven without pressure, for a period of 70 minutes
and at a temperature of 90.degree. C.
[0122] The cross-linking/expansion operation was carried out using
water as curing fluid.
[0123] A device was used such as that described in relation to FIG.
4, such that the water circulation rate from said outlet conduit to
said inlet conduit 23 was maintained at 15 liters of water per
minute.
[0124] In Table II below there are shown the specific operating
conditions which are relative to each test performed, before the
final pressure-relief of the inner space of the enclosure 21 to
atmospheric pressure to effect the expansion of the cross-linked
blanks.
[0125] With reference to an operating stage of predetermined
duration (in minutes), there are indicated the corresponding values
of relative pressure in the enclosure 21 (in bar) and of
temperature (in .degree. C.). The same applies to the final cooling
step.
[0126] As far as the emptying of the enclosure 21 is concerned,
which makes it possible to make the pressure within the latter pass
from an excess pressure value to the final pressure-relief value in
order to effect the expansion of the cross-linked blanks
(atmospheric pressure), the rate of emptying is controlled such
that the change from said ultimate excess pressure value to
atmospheric pressure is effected in a sufficiently long time, which
in the tests performed is at least 30 seconds.
2TABLE II Cross- linkable, blank first stage second stage cooling
expandable length (bar, min., (bar, min., (bar, min., Test
composition (mm) .degree. C.) .degree. C.) .degree. C.) No. 1 A 412
12 - 90 - 142 -- 12 - 20 - 20 No. 2 A 355 23 - 90 - 142 -- 23 - 20
- 20 No. 3 A 275 23 - 50 - 142 -- 23 - 10 - 20 No. 4 A 275 16 - 90
- 142 -- 16 - 20 - 20 No. 5 A 275 23 - 60 - 142 9 - 40 - 142 9 - 20
- 20 No. 6 A 275 16 - 90 - 142 9 - 40 - 142 9 - 20 - 20 No. 7 A 275
23 - 60 - 142 12 - 40 - 142 9 - 20 - 20 No. 8 B 275 23 - 60 - 142 9
- 40 - 142 9 - 20 - 20
[0127] The supports obtained by means of these tests were analysed.
Table III hereafter summarises the dimensional and cellular
characteristics of the supports obtained.
[0128] Each of these cross-linked, expanded supports is
characterized, on one hand, by an intermediate layer B of a
thickness of several mm radially towards the inside of its outer
surface and, on the other hand, by a surface layer A at the
location of said external surface (see FIG. 5).
[0129] As far as the measurement of the size of cells in the
central layer C of each support is concerned, the sizes at the core
and at mid-thickness were distinguished.
[0130] As far as the measurement of the size of cells in the
intermediate layer B is concerned (last column of Table III), these
are measurements of maximum sizes at 5 mm from the outer surface
(surface layer A) of each support.
3TABLE III maximum maximum maximum Cross- diameters diameters of
diameters linked, of the the cells at of the cells expanded width
height cells at the mid-thickness in the layer supports (mm) (mm)
core (mm) (mm) B (mm) No. 1 115 63 not measured not measured not
measured (2 165 110 supports produced) No. 2 182 123.5 0.2 0.2
0.3-0.5 No. 3 105 50 not measured not measured not measured No. 4
190 130 0.3 0.3 0.5 No. 5 193 106 0.5 0.5 0.5 No. 6 197 111 1 1 0.7
No. 7 192 121 0.3 0.3 0.4 No. 8 208 118 1.8 1.3 0.7
[0131] The support obtained by test No. 1 has insufficient
cross-linking, owing to the insufficient value of the pressure
which is used, which value is not in accordance with the invention
(12 bars relative pressure).
[0132] The support obtained by test No. 2, which corresponds to the
use of a relative pressure of 23 bar in the enclosure (maximum
value used for all the tests), has a cell size in accordance with
the invention (since it is between 0.1 and 2 mm).
[0133] The support obtained by test No. 3 has insufficient
cross-linking and expansion, owing to too short a dwell time in the
curing bath, this insufficient expansion resulting from the
premature stopping of the decomposition reaction of the blowing
agent.
[0134] It will be understood that an increase in the dwell time of
the blank in the curing bath would have made it possible, in
particular, to impart increased expansion to a support, such as the
one obtained in test No. 3, for example.
[0135] The support obtained by test No. 4 (using a single stage at
the relative pressure of 16 bar) has satisfactory cross-linking and
expansion, and also a cell size in accordance with the
invention.
[0136] The support obtained by test No. 5 (using two stages, the
relative pressure values of which are 23 bar and 9 bar
respectively) also has satisfactory cross-linking and
expansion.
[0137] The support obtained by test No. 6 (using two stages, the
relative pressure values of which are 16 bar and 9 bar
respectively) has increased expansion compared with that of the
preceding support (test No. 5), as shown by the cell size, which
has substantially doubled.
[0138] The support obtained by test No. 7 (using two stages, the
relative pressure values of which are 23 bar and 12 bar
respectively) also has satisfactory cross-linking and expansion
characteristics.
[0139] As for the support obtained by test No. 8, which support
comprises a blend of carbon black and silica as reinforcing filler,
it also has satisfactory cross-linking and expansion. Furthermore,
this expansion is very high in the core of the support.
[0140] It will be noted that each of the supports obtained by the
process according to the invention is characterized by cell
diameters which are relatively close to each other, from the core
to the surface of the supports. Furthermore, it was confirmed that
the intermediate layer B of each support according to the invention
was of a thickness less than that of the known supports obtained by
conventional processes, and that this layer B had an overall lower
density than that of the corresponding layer B of such a known
support.
[0141] It will also be noted that the average cell size over a
cross-section of the support is highest when the relative pressures
of the first and second stages are respectively 16 bar and 9 bar
(test No. 6), whereas on the other hand it is lowest when a single
stage of relative pressure of 23 bar is used (test No. 2).
Second Series of Tests for Cross-Linking/Expansion
[0142] A plurality of tests according to the invention were carried
out, using for the blanks 4 rubber compositions comprising said
compositions A and B and two other cross-linkable, expandable
compositions C and D, which are all based on butyl rubber.
[0143] Table IV hereafter gives the respective formulations of
these compositions C and D.
4TABLE IV (phr: parts by weight per hundred parts of elastomer).
Constituents Composition C Composition D introduced into the mixer
(amount in phr) (amount in phr) Carbon black N683 40 40 Silica
"Zeosil 1165 MP" -- -- Blowing 12 11 agent(azobisformamide)
[0144] Each blank was prior to this preheated by means of hot air
in a ventilated oven, for a period of 70 minutes and at a
temperature of about 100.degree. C.
[0145] The cross-linking/expansion operation, as previously, is
effected by means of a continuous flow of water, by means of a
device such as that of FIG. 4, such that the circulation and
emptying rates (for the cross-linking and the expansion,
respectively) are maintained at 15 liters of water per minute.
[0146] In Table V below there are shown the specific operating
conditions which relate to each test performed, before effecting
the final pressure-relief of the inner space of the enclosure 21 to
atmospheric pressure to effect the expansion of the cross-linked
blanks.
[0147] With reference to an operating stage of predetermined
duration (in minutes), there are indicated the corresponding values
of pressure (in bar) and of temperature (in .degree. C.). The same
applies to the final cooling step.
5TABLE V Cross- linkable, blank blank first stage second stage
cooling expandable perimeter weight (bar, min., (bar, min., (bar,
min., Test comp. (mm) (g) .degree. C.) .degree. C.) .degree. C.)
No. 9 A 871 2785 23 - 95 - 142 23 - 15 - 20 No. 10 A 868 2738 23 -
55 - 146 No. 11 A 859 2755 23 - 60 - 142 12 - 50 - 142 12 - 20 - 20
No. 12 A 870 2782 23 - 60 - 142 9 - 40 - 142 9 - 20 - 20 No. 13 A
856 2748 16 - 60 - 142 9 - 50 - 142 9 - 20 - 20 No. 14 A 872 2778
16 - 60 - 142 12 - 40 - 142 12 - 20 - 20 No. 15 A 867 2768 23 - 60
- 142 9 - 40 - 142 9 - 20 - 20 No. 16 A 873 2768 23 - 60 - 142 9 -
40 - 142 9 - 20 - 20 No. 17 A 869 2728 16 - 60 - 142 12 - 50 - 142
No. 18 A 856 2754 23 - 30 - 142 12 - 40 - 142 12 - 20 - 20 No. 19 A
866 2763 23 - 60 - 142 9 - 40 - 142 9 - 20 - 20 No. 20 A 868 2768
23 - 60 - 142 9 - 40 - 142 9 - 20 - 20 No. 21 A 869 2772 23 - 60 -
142 9 - 40 - 142 9 - 20 - 20 No. 22 A 867 2784 23 - 30 - 142 12 -
80 - 142 12 - 20 - 20 No. 23 D 876 2765 23 - 60 - 142 9 - 40 - 142
9 - 20 - 20 No. 24 C 976 1140 23 - 30 - 146 9 - 30 - 146 9 - 10 -
20 No. 25 C 982 1144 23 - 30 - 146 9 - 40 - 146 9 - 20 - 20 No. 26
B 814 2726 23 - 60 - 142 9 - 60 - 142 9 - 20 - 20 No. 27 B 848 2746
23 - 60 - 142 9 - 50 - 142 9 - 20 - 20 No. 28 B 865 2738 23 - 60 -
142 9 - 60 - 142 9 - 20 - 20
[0148] The supports obtained by means of these tests were analyzed.
Table VI hereafter summarises the dimensional and cellular
characteristics of these supports.
[0149] The volumes of the cross-linked, expanded supports obtained
were determined using a form factor of 0.8 (actual cross-section of
the support/rectangular section in which this actual cross-section
is circumscribed).
6TABLE VI Cross- weight linked, of outer inner expanded support
perimeter perimeter width Volume Average supports (g) (mm) (mm)
(mm) (liters) density No. 9 2755 1907 1110 170 26.489 0.104 No. 10
2708 -- -- -- -- -- No. 11 2725 2007 1275 178 28.362 0.096 No. 12
2752 2018 1300 178 28.212 0.098 No. 13 2718 1987 1230 175 28.024
0.097 No. 14 2748 1978 1190 163 26.211 0.105 No. 15 2738 2002 1295
181 28.212 0.097 No. 16 2738 2028 1320 185 29.414 0.093 No. 17 2698
2050 1225 177 31.024 0.087 No. 18 2724 1975 1236 183 28.885 0.094
No. 19 2733 2022 1300 180 28.749 0.095 No. 20 2738 2060 1345 182
29.602 0.092 No. 21 2742 2048 1330 184 28.846 0.092 No. 22 2754
1975 1203 173 27.757 0.099 No. 23 2735 1800 1200 171 20.905 0.131
No. 24 1110 2005 1455 87.5 10.085 0.110 No. 25 1114 2033 1474 89
10.574 0.105 No. 26 2696 1850 1020 170 26.034 0.104 No. 27 2716
1900 1200 173 24.964 0.109 No. 28 2708 1942 1185 160 24.500
0.111
[0150] It will be noted that the average density of a cross-linked,
expanded support according to the invention may vary to a great
extent between 0.04 and 0.4, average densities close to 0.04 or 0.4
possibly being obtained respectively in a manner known to the
person skilled in the art by increasing or reducing the amount of
blowing agent in the corresponding rubber composition.
[0151] It will also be noted that the average density close to 0.13
which was obtained, for example, by test No. 23 makes it possible
to impart to the core of the corresponding support a rigidity which
is suitable for minimizing its deformation during travel owing to
centrifugal force.
[0152] The results of volume of the support which are mentioned in
this Table VI show that supports Nos. 11 to 28 have satisfactory
cross-linking and expansion, this expansion being promoted by the
second stage of pressure at 9 or 12 bar (following a first stage at
23 or 16 bar which permits cross-linking).
[0153] It was also possible to confirm that each support according
to the invention is characterized by cell diameters which are very
close to each other, from the core to the surface of the
supports.
[0154] Furthermore, it was confirmed that the intermediate layer B
of each support according to the invention has a thickness of less
than 5 mm, contrary to those of conventional supports, which are
generally between 8 and 25 mm (for supports of width and height
close to 200 mm and 120 mm, respectively), which makes it possible
to minimize the propagation in the core of the support of the
deformations due to the shearing stresses and, consequently, the
internal heating of the latter when travelling at zero
pressure.
[0155] There are shown in FIGS. 6 and 7 two examples of embodiment
of profiles of cross-linked, expanded supports which can be
obtained by the cross-linking/expansion process according to the
invention, that is to say, by a process making it possible to
dispense with a mold for the cross-linking.
[0156] According to the embodiment of FIG. 6, the support 5c
obtained comprises a base 30 which is intended to be mounted on a
wheel rim either directly, or by means of a reinforcement or
another connecting agent, and a crown 31 which is intended to bear
on a tread of a tire, following a drop in pressure within the
latter.
[0157] This support 5c has in this example a plurality of
longitudinal grooves 32 extending over the crown 31, substantially
level with the latter and in the direction of the length of the
support 5c.
[0158] It will be noted that the process according to the invention
also makes it possible to obtain profiles of supports 5c which
have, in addition to said single grooves 32, other longitudinal
grooves (not shown) in at least one of the other two directions of
the support 5c (for example grooves on the face 33 of the support
connecting the base 30 and the crown 31 together).
[0159] According to the embodiment of FIG. 7, the support 5c
obtained has between its base 40 and its crown 41 a longitudinal
cutout 42 in its mass, which extends in the direction of its
length.
[0160] It will be noted that these two examples of profiles of
supports could not be obtained under satisfactory conditions by
means of the conventional processes using a mold for cross-linking,
because their respective geometries do not permit demolding under
satisfactory conditions, that is to say, without weakening the
demolded support.
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