Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUMD OF THE INVE~TION .;,~
This invention is a continuation-in part o~ copend- ~-
ing United States application Serial No. 595,880, ~iled
July 1~, 1975.
This inventi~ relates to vulcanlzation devices
and more particularly to elastomeric vulcanization membranes.
~uring vulcanization o~ many elastomeric articles `~in a mold, a device re~erred to generally as a vulcanizing
or curing membrane is used to force the elastomeric article `~
firmly against the mold. In the manu~acture o~ pneumatic
tires, ~or example, a curing membrane seats the uncured tirè
in the vulcanization mold and retains it until properly cured.
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Hot fluid such as steam or extremely hot water is circulated
within the membrane during the curing process. Heat ls trans~
ferred from the hot fluid through the membrane to the tire~
thereby e~fectin~ a vulcanization. `~
Curing membranes~ particularly those used in the -
vulcanization of pneumatic tires, are often re~erred to as
"bladdsrs" or "water ba~s". The chief distinction between
bladders and water bags or "bags~' is that the ~ormer are
generally much thinner and are designed to be much more
expansible.
Although water bags may contain a ~luid under high ~ ;
pressure, they rarely are designed to expand beyond about 5~,
whereas a bladder can be stretched up to about 100~ circum~
~erentially and up to about 25~ laterally or radially.
To accommodate expansions, curing membranes are commonly
made of some type of elastomeric material. The elastomeric
material must be strong enough to withstand repeated~
pressurizations~ expansions and contractians ~ithout
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splitting or othèrwise deteriorating.
The cure time o~ a tire will vary with thickn:ess
o~ the membrane, among other factors. Since elastomeric
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materials are a relativel~ poor conductor of heat, a sllght
difference in the thickness o~ a membrane can mean a sub-
stantial difference in cure time of a tire. In order to
reduce the cure time, attemp-ts have been made to ~educe ;
membrane thickness. A buckling problem emerges when the
memhrane thickness is reduced below a minimum point.
; Buckling of a tire curing membrane, particularly ;~
a bladder, is primarily due to -the fric-tiorlal sliding forces
between the membrane and the uncured tire as the membrane
expands and forces the tire against the mold. Many of these
; forces are applied to the membrane at a portion associated
with the bead area of the uncured tire.
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Reducing the thickness of a membrane reduces its
strength. Below a given thickness, portions of the membrane
cannot carry the stress applied to them~ causing erratlc
expansion and possibly causing port:Lons of the membrane to
buckle or crease. This can result ln an uneven heat distri-
bution to the tire and thus in a no~uniform cure. `
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In an attempt to decrease the thickness oP a curing
membrane while still retaining suf~icient strength, specially~
designed rein~orcements can be employed. For example, U.S.
Patent 2,695,424 discloses a thin walled curing "bag" with
ribs on its inside surface. In memhranes such as disclos~d
in U.S~ Patent 2,695,42~, the curing time can allegedly be
reduced bec~use of the thinner bag~ while the ribs supply
i the strength that was lost by decrei~sing the bag thickness.
Un~ortunately~ since the ribs of a curing bag of the type
disclosed in patent 2~695,424 work essentially independent ~ -~
; of each other, a bladder with such a ribbed design can still ~ ;
buckle or kink due to the more extreme expansion of a bladder.
A bag o~ the type mentioned above expands ve~y little compared
to a bladder and therefore stress levels are much lower.
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To avoid the aforementioned bulkling problems, it is
desirable to create a membrane with stress carrying
capabilities equal in all directions. Some attempts at rein- '
forced curing membranes have employed rectangular rib patterns
such as disclosed in U.S. Patent 2,695,424 and British Patent
938,797. It can be seen that such rectangular rib patterns
have maximum stress carrying capabilities only in the two
directions parallel to the ribs. These two previous attempts
at reinforcing a curing membrane have been aimed at providing
maximum stress carrying capabilities only in the circumferential
and radial directions of the membrane. Buckling and kinking
can still occur in such membranes because stresses are often ~ ~
exerted on the membrane in directions other than the ~ -
circumferential and radial directions.
It is an object of the present invention to provide
an elastomeric curing membrane which resists buckling or
kinking.
It is a further object of the present invention to
provide an elastomeric curing me~brane that has an increased
life.
It is a further object of the present invention to
provide an elastomeric curing membrane that resists buckling
or kinking and decreases curing time.
These and other objects of the present invention
which will become evident by the following detailed description
are achieved by a generally annular curing mem~rane comprising
a membrane wall and a plurality of interconnected ribs
integrally molded on the inslde surface of the wall. Suit-
ably the ribs collectively form a plurality of adjacent
30 polygons, with each rib being a common side of at least two
adjacent polygons. A portion of at least one of the ribs is
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disposed at an oblique angle to the circumferential centerline
of the membrane. ;~
Thus the invention provides a curing membrane of an ;
elastomeric material having a generally annular configuration `~
and a circumferential center~ine, the membrane has a plurality
of interconnected ribs integrally molded to its inner surface
at least a portion of one of the ribs extends obliquely relative
to the circumferential centerline. The ribs provide a network ~-
of reinforcements and preferably form a plurality of adjacent ~ ~
polygons. , -
In a particular embodiment there is provided, in
accordance with the invention a curing membrane of an elasto~
meric material having a generally annular configuration and a
circumferential centerline, the membrane comprising:
a) a wall having an inside surface;
b) a plurality of interconnected ribs integrally
molded to the inside surface; and
c) a plurality of adjacent polygons defined by J' ;~
the interconnected ribs,
the improvement wherein at least a portion of one of the inter-
connected ribs is disposed at an oblique angle to the plane of ;
the circumferential centerline.
Fig. 1 is a fragmented side elevation of a tire ~ '
. ~ :curing membrane of the present invention;
Fig. 2 is an enlarged view of a portion of the inside
surface of the membrane of Fig. l; and
Fig~ 3 is a cross-section o the membrane taken along
line 303 of Fig. 2. ,~
Figs. 4, 5 and 6 are enlarged views of portions of
inside suraces of alternative embodim0nts ofa membrane of
the present invention. ~;
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Referring to Fig, 1, a tire curing membrane of the
present invention is shown as a bladder 10. The bladder 10 is
hollow and has a generally annular or barrel shape, It is `~
formed of a typical high strength elastomeric material such
as butyl compound or other similar substance, The bladder
10 is basically comprised of a bladder wall 15 having two end i" ~ :
or "bead" portions 12, a middle or "crown" portion 13, and two
intermediate or "sidewall" portions 14, The bladder 10 is ~ ~:
sym~etrically formed about an axis V, The bladder has two
10 parallel and axially spaced margins 16 which define the end
portions of the bladder, The plane in which each margin 16
lies is perpendicular to the axis V. The bladder has its ~;
largest diameter around the circumferential centerline 17, -.
When an uncured tire tnot shown) is fitted over the outside
- surface 9 of the bladder 10 and the bladder is subsequently
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expanded, portions of the outside ~urface 9 expand into direct
contact with portions of the uncured tire thereby forcing it
against the inner surface of a tire mold (not shown)
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As is more readily seen in Figs. 2 and 3, a plural-
ity of interconnected ribs 20 providing a network of reinforce~
ment are integrally molded on the inside surface ll of the
bladder lO. Se~eral of the ribs 20 extend from one margin 16
to the other. Collectlvely, the interconnected ribs 20 de~ine
a plurality of adaacent polygons 25. To create desirable
stress carrying and heat transfer capabilities, the rib
widths W are about equal, f`orming a tightly f`itted patte m
of polygons 25, with each rib 20 ~orming a common bo~mdary
o~ two adàacent polygons 25.
It can be seen in Figs. l and 2 that the ribs 20
extend between each margin 16 in a random f`ashion. Several o~
the ribs 20 are curved ribs, thereby giving several polygons 25 ~
smoothly curved boundaries, such as 28. The curved boundaries ?
15 are comprised of an in~inite number of sides. It should be
; noted that when the word "polygon" is used in this specif`ica-
tion and in the appended claims, a polygon havlng an infinite
number of sides is included.
Each rib 20 partially defines at least two adjacent
20 polygons 25. A portion of each polygon is de~lned by a por~
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tion of a rib which is disposed at an oblique angle "a" to
the plane of the axially spaced margins 16 and to the plane o~
the circumferential centerline 17.
For curved ribs, the angle to the margin or to the
25 circum~erential centerline at each portion of the rib can
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be considered as the angle o~ the tangent to the curved rib
at that portion. In Fig. 2, curved boundary 28 ~ s a tangent
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2~ ~orming the oblique angle "a" with the circum~erential
centerline 17. It should be noted that "oblique", when
30 referred to in this specification or in the amended claims,
re~ers to directions substantially nonradial and noncircum-
; ~erential, notwithstanding that a radially extending rib may
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be oblique to the plane of a margin or circumferential centerline
merely because of the "barxel" shape of the bladder.
A decrease in polygon size from the crown portion 13
to the bead portions 12 may be desired because buckling or kink-
ing the bladder 10 has most frequently occurred in the bead
portions 12. If the rib width W is kept constant as the size
of the polygons 25 decreases, more of a ribbed area will exist
at the bead portions 12, thereby permitting the bead regions to ~
withstand the higher buckling stresses existent there. Further- ~;
more, agreater nonribbed area in the crown portion 13 permits
maximum expansion of the bladder 10 in the crown region where
it is required. This maximum expansion will cause the wall 15
to be thinnest in the crown portion 13, permitting a more rapid
heat transfer. Because the crown or tread portion of the tire
is one of its thickest regions, more heat is desirable there to -
effect a uniform cure of the tire.
Most of the heat that effects a cure of the tire from
the inside passes through the bladder 10 via the non-ribbed area.
Using narrow ribs 20, heat is more readily passed to areas of
the associated tire directly beneath the ribbed areas thereby
effecting a more rapid and uniform cure. It is therefore prefer-
red that the bladder 10 comprises a relatively large number of
narrow ribs 20 rather than a lesser number of wider ribs giving
equivalent strength. Although the percentage of nonribbed area
' is different at each portion of the bladder 10, overall about `
60% of the total area of the inside surface 11 of the bladder
is nonribbed. Preferably, the height H of each rib 20 is from
about 35% to 40% of the thickness M of the wall 15.
Fig. 4 shows a portion of the inside surface of
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an alternate embodiment of the present in~ention. The inter~
connected ribs 40 de~ine a plurality o~ ad~acent curved poly~
gons 41. Each o~ the polygons has an infinite number of sides `
forming a continuously and smoothly cur~ed boundary. A por-
tion o~ each polygon 41 is de~ined by a rib 40 which is dis~
posed at an oblique angle "b" to axially spaced margins such
as 16 and to the circum~erential centerline 47.
Uni~orm stress carrying characteristics can best be
achieved by a ribbed pattern with ribs oriented in as many
directions as practical. It may there~ore be believed that
a pattern of tightly packed circular ribs would be one;
o~ the more uni~orm in stress carrying capability.
Fig. 5 shows a portion o~ the inside sur-~ace of ~
; another embodiment of the present invention having a plurality ~ ~;
, 15 o~ interconnected ribs 50. The ribs 50 de~ine a plurality
; o~ ad~acent circular polygons 51. A portion of each circular
¦ polygon 51 is de~ined by a rib 50 which is disposed at an
oblique angle "c" to axially spaced margins such as 16 and `~
to the circum~erential centerline 57.
For facilitating the manufacture and design of ~-
bladders, and in some instances for the improvement of heat ;
trans~er through a bladder, it may be desired to have straight
ribs. Fig. 6 shows a portion of the i~side surface o~ an
alternative embodlment o~ the present invention having a ;`-
~` 25 plurality of straight interconnected ribs 60. Th~ ribs 60 ;
3 de~ine a plurality of adjacent f~ur-sided, diamond shaped
polygons 61. A portion of each polygon 61 îs defined by a
3 rib 60 which is disposed at an oblique angle "d" to axially
3~ spaced margins such as 16 and to the circumferential center- ;~ 3
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30 line 67. Although the ribs 60 extend in only two general
directions, they are oriented such that the bladder has high
strength characteristics in the nonradial and noncirc~er
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ential directions. These diamond shaped ribs 61 are also
desirable because they can be tightly packed together ln a
uniform pattern. Triangles and hexagons are also very
desirable for this reason.
Structural reinforcement on the inside surface 11
o~ the bladder 10 leaves the outside surface 9 essenti.ally
smooth, thereby leavlng no undesired marks or patterns on
the inside of the tire. Nevertheless, additio~al patterns
or structure may be molded to the outside surface 9 without
affecting the usefulness o~ the inside structure o~ this
invention. For example, air venting or bleeding channels
as disclosed in U.S. Patent 3,143,155 may be used.
Another feature of a pattern of close ribs on the
; inside surface of the bladder 10 is increased heat transfer
through the bladder. It is believe~ that the ribs cause
sufficient turbulence of the heating medium, for example,
~ flowing water, to break up a portion of the thermal boundary
sl layer between the inside sur~ace 11 of the bladder and the
heating mèdium, thus more readily permitting heat to pass
20 through the bladder 10.
Although the foregoing structure was described for
the purpose of illustrating a presently preferred embodlment
of the invention, it should be understood that many modifica-
ticns or alterations ma~ be made without departing from the
j 25 spirit and the scope of the invention as set forth in the ~ ~
appended claims. ~ -
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