DESC:FIELD OF THE INVENTION
The present invention relates to the field of tyre curing bladder. More particularly, it relates to the curing bladder with gauge thickness less at the centre and gradually increasing towards shoulder zone from the centre i.e., the centre of the bladder is low as compared to the shoulder zone. Advantageously, the present invention reduces the cure cycle time by having a better heat transfer and to attain tyre profile easily during shaping.

BACKGROUND OF THE INVENTION
Typical bladders have uniform thickness from centre to shoulder zone which results in insufficient and reduced heat transfer.

US Publication No. 20160311185 relates to a curing bladder comprised of materials with varying thermal conductivity. In one embodiment, first layer comprises a substantially constant thickness throughout the axial width of bladder. In another embodiment, first layer comprises a varying thickness through the axial width of bladder, such that first layer is thicker in some portions than in other portions. In one embodiment, bladder is configured for curing a tire. Bladder may comprise any of various zones, including for example a tread zone, a shoulder zone, a sidewall zone, and a bead zone. In one embodiment, the thickness of at least one of first layer, second layer and third layer may be increased or decreased in any of various zones to at least one of: (a) increase or decrease strength of bladder in the desired zone; and (b) increase or decrease the thermal conductivity/heat transfer in the desired zone.

US Publication No. 20150336342 relates to a method for forming and curing an uncured tire-curing bladder with a bladder-curing bladder includes providing an uncured tire-curing bladder having an inner and outer surface on or in a recess of an outer-surface curing mold; inflating the bladder-curing bladder into the recess and exerting pressure on the inner surface of the uncured tire-curing bladder; and curing the uncured tire-curing bladder by providing heat, pressure, or both to the inner surface and the outer surface of the tire-curing bladder to form a cured tire-curing bladder. In an embodiment, an additional layer or layers may also be applied for shaping or reinforcing the tire-curing bladder. In an embodiment, additional layer sheets, may be used to urge the tire-curing bladder into a partial toroidal shape with sides, rather than just a flattened ring. The foot area of the tire-curing bladder may be provided with additional thickness in comparison to the center portion of the tire-curing bladder. The tire-curing bladder comprises a single or double-foot shape in the foot area according to the configuration of the tire-curing mold it is designed to be used with.

US Patent No. 8,057,204 relates to an expandable bladder for shaping a pneumatic tire. The bladder in an unmounted, relaxed state has a shaped body having a pair of opposed annular beads, said body further comprising a central portion, sidewall portions, and shoulder portions interposed between the central portion and the sidewall portions, wherein the body is defined by an outer contour surface and an inner contour surface, wherein the central portion has gauge which increases to a maximum value axially inward of the shoulder portion, and wherein the bladder gauge in the shoulder is less than the maximum value, and wherein the bladder gauge increases from the shoulder to the bead. This patent talks about different gauges at different bladder portions. It describes a bladder with the highest gauge somewhere between central and shoulder portion, and the gauge increases from shoulder to the bead area. However the present invention talks about gradual increase in gauges from centre to bead area of the bladder.

US Patent No. 7,144,236 relates to an expandable bladder for shaping a pneumatic tire to be mounted inside a tire curing press has a pair of opposing annular beads and an expansion portion located between the pair of annular beads. The expansion portion of the bladder has a central portion, shoulder portions, and sidewall portions. When the bladder is in a mounted but uninflated mode, the shoulder portions have a radius of curvature less than infinity. At a distance (x) from each end of the central portion, the bladder has an increased thickness in the shoulder and upper sidewall portions.

Publication No. US2016214340(A1) relates to a tire vulcanization bladder where a thickness of a bladder main body portion is set to a constant thickness. At least one of multiple circular ribs, helical ribs in which multiple circumferential ribs are connected in a helix, multiple circular grooves, or helical grooves in which multiple circumferential grooves are connected in a helix is formed on the inner surface of the bladder at the portions corresponding to the tread portion, the shoulder portions, and the bead portions of the tire. When the bladder is inserted into a green tire that is set in the horizontal state within a mold and expanded, the expansion state of the bladder is regulated to press against the green tire in accordance with the inner surface shape of the tread portion the shoulder portions, and the bead portions.

Publication No. US4293293(A) relates to a tire retreading bladder which includes a generally angular member of a U-shaped cross-sectional configuration defined by a bight portion and a pair of legs with the annular member defining an interior volume, each leg terminating in a terminal edge of a generally circular configuration, each leg having interior and exterior surfaces, a plurality of pairs of closely adjacent ribs along the exterior surfaces for venting air from between such exterior surfaces and an interior surface of an associated tire adapted to receive there within the bladder, each pair of ribs setting off a venting groove there between, and venting means further including transverse venting slots disposed lengthwise along the ribs. The tire retreading bladder has a cross-sectional thickness greatest at the beads and the thickness of the legs diminish in a direction toward the bight portion, and the venting means include ribs projecting above the exterior surfaces and being disposed generally radially.

Publication No. CN109049783(A) relates to a giant tire curing bladder. The curing bladder comprises a circular-ring-shaped bladder body, the two ends of the bladder body are provided with bladder shoulder portions, bladder side portions and bladder neck portions which are bent towards the center of the bladder body, and the thickness of the bladder neck portions is gradually decreased towards the middle of the bladder.

Publication No. CN202293132(U) relates to an injection type wide-cross-section curing bladder, which is applied to the field of the curing manufacture of tires. Through adopting an injection process manner, the height of the curing bladder is appropriately increased, and the external diameter of the curing bladder is appropriately reduced, so that the injection type wide-cross-section curing bladder can be applicable to the curing and the shaping of low-cross-section wide-base tires; meanwhile, the thickness of shoulders of the curing bladder is increased to strengthen the strength of the shoulders of the curing bladder when the curing and the shaping are carried out, and exhaust ribs which are regularly arranged are arranged on the external surface of the curing bladder, so that the exhaust performance of the curing bladder is improved, and the quality and the effect in the shaping and the curing of the low-cross-section wide-base tires are effectively improved.
Publication No. KR20040036836(A) relates to a thin bladder for vulcanizing a tire is provided to shorten vulcanizing time and to improve vulcanizing efficiency by inserting a support bar into the bladder and preventing the thin bladder from sagging.

Publication No. KR20040017149(A) relates to a method for curing a tire is provided to improve productivity by reducing the thickness of a bladder and shortening curing time. A method for curing a tire comprises the steps of: supplying steam having a pressure of 12 - 16 kilograms to the square centimeter for 4 - 7 minutes to the inside of a bladder; and supplying nitrogen gas having a pressure of 20 - 30 kilograms to the square centimeter for 2 - 11 minutes to the inside of the bladder. A bead part and a shoulder part are 4 - 8mm, and a side part and a center part in the bladder are 3 - 7mm in thickness.

The even gauged bladder results in reduced heat transfer which causes inner defects in tyre and reduces the quality of appearance. It also increases the cure cycle time.

Hence, the present invention aims to provide bladder thickness i.e., the gauge increases gradually from centre to shoulder zone on either sides thereby increasing the rate of heat transfer and helping to attain tyre inner profile quickly.

OBJECTS OF INVENTION
Principal object of the present invention is to provide a curing bladder having increasing thickness from centre to shoulder zone i.e., the centre gauge of bladder is low as compared to shoulder zone to reduce cure cycle time by having a better heat transfer and to attain tyre inner profile easily during shaping.

Another object of the present invention is to improve tyre inner appearance and reduce tyre inner defects.

Yet another object of the present invention is to vary bladder thickness by use of uniform bladder material.

SUMMARY OF THE INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary aspect of the present invention to provide a curing bladder for curing tyres, comprising a shoulder zone and a bead zone,
wherein the thickness of the curing bladder is gradually increased from the centre of the curing bladder to the shoulder zone of the curing bladder.

It is another aspect of the present invention to provide a curing bladder for curing tyres, wherein the rate of increase from the centre of the curing bladder to the shoulder zone of the curing bladder is 4% to 6% at predetermined distance intervals.

It is another aspect of the present invention to provide a curing bladder for curing tyres, wherein the thickness at the centre of the curing bladder is less than the thickness at the shoulder zone.

It is another aspect of the present invention to provide a curing bladder for curing tyres, wherein the thickness increasing is performed for either 60% of the periphery of the curing bladder distributed equally on either side of the centre of the curing bladder or till the thickness/gauge reaches maximum of 8.0 mm on either side of the centre based on the rate of increase, whichever is earlier.

It is another aspect of the present invention to provide a curing bladder for curing tyres, wherein the centre of the curing bladder is configured to merge in a gradual way with the shoulder zone.

It is another aspect of the present invention to provide a curing bladder for curing tyres, wherein the bladder thickness either remains uniform from the shoulder zone to the bead zone or comprises of a slight increase from the shoulder zone to the bead zone.
BRIEF DESCRIPTION OF THE DRAWINGS:
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawing, which form a part of this specification. It is to be noted, however, that the drawing illustrates only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.
Figure 1 illustrates the schematic view of the bladder for curing tyres according to the present invention.
Figure 2 illustrates the schematic view of the comparison between the typical and novel bladder according to the present invention.

DESCRIPTION FOR DRAWINGS WITH REFERENCE NUMERALS:
[10] Curing bladder
[11a, 11b] Shoulder zones
[12] Centre of the curing bladder
[13a, 13b] Bead zones
[20] Typical bladder
[A] Periphery of the bladder
[B, B’] Gauge at the centre, and gauge away from centre
[C] Gauge at the bead zone
[D] Gauge at the shoulder zone

DETAILED DESCRIPTION OF THE INVENTION
It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The present invention relates to the field of tyre curing bladder. More particularly, it relates to the curing bladder with gauge thickness less at the centre and gradually increases towards shoulder zone from the centre i.e., the centre of the bladder is low as compared to the shoulder zone. Advantageously, the present invention reduces the cure cycle time by having a better heat transfer and to attain tyre profile easily during shaping.

A bladder (10) for curing tyres is provided according to one embodiment of the present invention. The bladder (10) comprises of at least two opposing ends with bead zone (13) and shoulder zone (11) and a centre (12) of the gauge. The centre (12) comprises of thickness which gradually increases from the centre portion towards the shoulder zone (11). This arrangement of bladder improves tyre inner appearance, reduces tyre inner defects and reduces cure cycle time. The centre (12) merges in a gradual way with the shoulder zone. The thickness of the bladder central gauge is low as compared to the shoulder zone (11). The curing has increasing thickness from centre towards the shoulder zone(11). The bladder material preferably has a tensile strength in the range of 8-16 MPa, a percent elongation at break in the range of 400-1500, and a 300% modulus in the range of 2-8 MPa. The bladder is formed of uniform material based on thermally stable Butyl rubber compound. The features of a curing bladder are well known and conventional in the art of bladder forming. The bladder gauge either remains uniform from the shoulder zone (11) to the bead zone (13) or has slight increase from the shoulder zone (11) to the bead zone (13).

Referring to Figure 1, the schematic view of the bladder for curing tyres according to the present invention is illustrated. A curing bladder (10) for curing tyres is provided according to another embodiment of the present invention. The curing bladder (10) for curing tyres comprises shoulder zones (11a, 11b) and bead zones (13a, 13b) on opposing sides of a gauge with a centre (12). The thickness of the curing bladder (10) is gradually increased towards the shoulder zones (11a, 11b) of the curing bladder (10) on both sides from the centre (12) of the curing bladder (10). The rate of increase from the centre to the shoulder zones (11a, 11b) on both sides of the centre (12) of the curing bladder (10) is 4% to 6% at predetermined distance intervals preferably every 10 mm. The thickness at the centre (12) of the curing bladder (10) is less than the thickness at the shoulder zones (11a, 11b). The thickness increase is performed for either 60% of the periphery (A) distributed equally on either side of the centre (12) of the curing bladder (10) or till the thickness or gauge reaches a maximum of 8.0 mm on either side of the centre (12) based on the rate of increase, whichever is earlier.

Referring to Figure 2, the schematic view of the comparison between the typical bladder (20) and novel bladder (10) according to the present invention is illustrated. The curing bladder (10) has uniform stretch since centre gauges (12) are less and helps Green Tyre to attain proper shaping in curing press. Since, bladder (10) is mechanically stretched and shaped at higher temp, the lesser gauge at centre allows for quicker shaping. The thickness increase from centre concept is applicable for 60% of bladder periphery (A) or till it reaches maximum gauge of 8.0 mm, whichever is earlier. Gauge after 60% bladder periphery (A) continues till / periphery of the shoulder zone (D) location. Minimum centre gauge (B) mm and maximum shoulder gauges at zone (D) mm are as per design which varies for different bladder sizes. The increasing thickness rate is 6% increase in gauge from centre (12) for every predetermined distance preferably 10 mm increase in bladder periphery (A) for small bladders and 4% increase in gauge from centre (12) for every predetermined distance preferably 10 mm increase in bladder periphery (A) for large bladders.

Example 1: Small Bladder (Bladder periphery: Less than 200 mm)
Table 1: Typical bladder profile
Typical Effective Periphery (A) Centre Distance from Centre (mm)
0 10 20 30 40 50 60 70 80 90 100
80 mm 6 6 6 6 D=6.5
198 mm 6 6 6 6 6 6 6 6 6 6 D=6.5

Table 2: 60% of bladder periphery (A) (Increasing thickness concept on designed bladder as per invention)
Effective Periphery(A) Centre Distance from Centre (mm)
0 10 20 30 40 50 60 70 80 90 100
80 mm 4 4.2 4.5 4.5 D=5.5
80 mm 4 4.2 4.5 4.8 5.0 5.4 5.7 5.7 5.7 5.7 D=6.5

Example 2: Big Bladder (Bladder periphery 201 to 400 mm)
Table 3: Typical bladder profile
Typical Effective Periphery(A) Centre Distance from Centre
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
202 mm 6 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 D=6.5
326 mm 6 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 D=6.5

Table 4: 60% of bladder periphery (A) (Increasing thickness concept on designed bladder as per invention)
Effective Periphery(A) Centre Distance from Centre
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
202 mm 4 4.2 4.3 4.5 4.7 4.9 5.1 5.1 5.1 5.1 D=6.5
326 mm 4 4.2 4.3 4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9 5.9 5.9 5.9 5.9 5.9 D=6.5

The curing bladder has better heat transfer rate which helps in reducing cure cycle time. Lesser gauge in centre gives more flexibility and allows rapid, uniform heat transfer which helps in curing tread region faster and there by reduces cure cycle. The air bleeding is faster between Green tyre and bladder since gauges are less at centre and touches the inside of green tyre faster, higher gauges at bladder shoulder helps to form a shoulder profile and thereby improves tyre inner appearance and reduces inner defects. Bladder formation will be faster at centre when compared to sidewall due to less thickness.

Advantages:
• In an advantageous embodiment the bladder has uniform stretch since dimension of centre gauges are less and helps Green Tyre to attain proper shaping in curing press.
• The bladder has better heat transfer rate which helps in reducing cure cycle time.
• Faster air bleeding between Green tyre and bladder since dimension of gauges are less at centre and touches the tyre faster, higher gauges at bladder shoulder zone helps to form shoulder zone profile and thereby improves tyre inner appearance and reduces inner defects.

Although, the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention. ,CLAIMS:WE CLAIM:
1. A curing bladder (10) for curing tyres, comprising a shoulder zone (11) and a bead zone (13),
characterized in that, the thickness of the curing bladder (10) is gradually increased from the centre (12) of the curing bladder (10) to the shoulder zone (11) of the curing bladder (10).

2. The curing bladder (10) for curing tyres as claimed in claim 1, wherein the rate of increase from the centre (12) of the curing bladder (10) to the shoulder zone (11) of the curing bladder (10) is 4% to 6% at predetermined distance intervals.

3. The curing bladder (10) for curing tyres as claimed in claim 1, wherein the thickness at the centre (12) of the curing bladder (10) is less than the thickness at the shoulder zone (11).

4. The curing bladder (10) for curing tyres as claimed in claim 1, wherein the thickness increasing is performed for either 60% of the periphery (A) of the curing bladder distributed equally on either side of the centre (12) of the curing bladder (10) or till the thickness/gauge reaches maximum of 8.0 mm on either side of the centre based on the rate of increase, whichever is earlier.
5. The curing bladder (10) for curing tyres as claimed in claim 1, wherein the centre (12) of the curing bladder (10) is configured to merge in a gradual way with the shoulder zone (11).

6. The curing bladder (10) for curing tyres as claimed in claim 1, wherein the bladder thickness either remains uniform from the shoulder zone (11) to the bead zone (13) or comprises of a slight increase from the shoulder zone (11) to the bead zone (13).