CA1060162A

CA1060162A - Reinforced membrane

Info

Publication number: CA1060162A
Application number: CA253,588A
Authority: CA
Inventors: William F. Mattson
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1976-04-02
Filing date: 1976-05-28
Publication date: 1979-08-14
Also published as: IT1071515B; DE2626856A1; JPS52121081A; AU1502176A

Abstract

REINFORCED MEMBRANE

ABSTRACT OF THE DISCLOSURE

A generally annular tire curing membrane has a plurality of interconnected ribs integrally molded on its inside surface. The ribs collectively define a plurality of adjacent polygons. A portion of at least one of the ribs is disposed at an oblique angle to the circumferential centerline of the membrane. The polygons may have an infinite number of sides, thereby having a curved boundary.

Description

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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 , 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. `
, ., 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 , 1060~6Z

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. ~;

~ 5 -~1~60~L62 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 , 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 ;
be considered as the angle o~ the tangent to the curved rib at that portion. In Fig. 2, curved boundary 28 ~ s a tangent . ~

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 -6~

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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 .
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 . ii .
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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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A curing membrane of an elastomeric material having a generally annular configuration and a circumferential center-line, said membrane comprising:
a) a wall having an inside surface, b) a plurality of interconnected ribs integrally molded to said inside surface; and c) a plurality of adjacent polygons defined by said interconnected ribs, the improvement wherein at least a portion of one of said interconnected ribs is disposed at an oblique angle to the plane of said circumferential centerline.

2. A curing membrane as defined in claim 1, wherein the widths of each of said ribs are essentially equal.

3. A curing membrane as defined in claim 1, wherein at least one of the ribs is curved, said curved rib defining a smoothly curved boundary of at least one of said polygons, the angle of each portion of said curved rib being the same as the angle of the tangent to the curve at that portion.

4. A curing membrane as defined in claim 3, wherein said at least one of said adjacent polygons is a circle.

5. A curing membrane as defined in claim 1, comprising a plurality of adjacent polygons extending essentially over the entire inside surface of the wall.

6. A curing membrane as defined in claim 1, wherein the height of each rib is from about 35% to 50% of the thickness of the wall.

7. A curing membrane as defined in claim 1 wherein the nonribbed area of the inside surface is about 60% of the total area of the inside surface of the membrane.

8. A curing membrane of an elastomeric material having a generally annular configuration and a circumferential centerline, said membrane having a plurality of interconnected ribs integrally molded to its inner surface, said ribs provid-ing a network of reinforcement with portions of said ribs extending obliquely relative to said circumferential center-line.

9. A curing membrane as defined in claim 8 wherein each of said plurality of interconnected ribs forms a plurality of adjacent polygons, each of said ribs being smoothly curved through its entire length.

10. A curing membrane as defined in claim 8 further comprising axially spaced margins extending parallel to said centerline wherein said plurality of ribs extend continuously from one of said margins to the other.