JPS61225033A - Closed end type bladder for vulcanizing pneumatic tire - Google Patents

Abstract

PURPOSE:To uniformize pressurizing force and to shorten a pressurizing time, by providing a U-shaped bent point to the outside of a bladder main body and making the wall thickness of said bladder main body gradually thin from the part corresponding to the bead part of a green tire to the part corresponding to the tread part thereof. CONSTITUTION:A bladder 30 is formed so as to make the wall thickness thereof gradually thick from a second bent part 44 and a third bent part 46 to a ball nose receiving part 48 and received in a cylindrical member 16 by the falling of a ball nose 5 and vacuum drawing. Subsequently, a green tire 10 is fallen and a bead part is engaged with an engaging part 12a. Then, a pressurizing fluid is introduced into the bladder 30 to contact the outer wall thereof with the inner wall of the tire 10. At this time, a part of a first bent part 38 and the second and third bent parts 44, 46 are respectively expanded outwardly to be contacted with the bead part of the tire 10. Because of this, pressurizing force is applied to the entire inner wall surface of the green tire 10 and pre- shaving is performed in this state. Next, vulcanization treatment is applied to a tire 30.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a closed-end bladder for curing a pneumatic tire. The present invention relates to a bladder that is capable of uniformly inflating the green tire to apply pressing force uniformly to the entire inner wall of the green tire, thereby making it possible to hold the green tire in the correct position on the inner surface of the vulcanization mold.

Traditionally, regardless of the type of bias tire or radial tire, vulcanization is performed using high-temperature, high-pressure fluid to form tire beads, sidewalls, and treads.
A bladder is used to press the green tire into close contact with the mold. After the bladder is inserted into the green tire and before the vulcanization stage, the bladder supports the green tire from the inner wall and expands in diameter, so that the green tire is properly supported in contact with the inner surface of the vulcanization mold. In charge of pre-shaving.

The vulcanization mold is completely closed when the pre-shaving is completed. When the vulcanization mold is closed, a heating medium such as steam is fed into the vulcanization mold and the bladder.

During preshaving, an inert gas such as air, carbon dioxide gas, or nitrogen gas is supplied into the bladder as an expansion medium. On the other hand, in the vulcanization stage, a heating medium such as steam replaces the expansion medium in the bladder. The pressure of the heated fluid injected into the bladder is higher than the pressure of the expanding medium during pre-shaving, and pressurizes the green tire to every corner of the uneven portion forming the tire tread pattern molding on the inner surface of the mold. That is, during vulcanization, the bladder is expanded by a high-temperature, high-pressure medium introduced into the bladder, and has the function of pressing the green tire into tight contact with the mold. Bladders are generally classified into closed-end types in which the lower end is open, and oven-end types in which the upper and lower ends are open.

FIG. 1 shows a closed-end bladder according to this type of prior art. The bladder 2 has a slightly thicker portion 4 corresponding to the end of the tire to be vulcanized under pressure, and a concave central portion 3 into which a ball nose 5 is fitted. I'll keep it. On the other hand, the sidewalls and the trend-corresponding portions 6 are formed uniformly and relatively thinly, and the outer surface of the portions 6 is usually provided with air vent groups. In the figure, reference numeral 8 indicates an opening that opens in one axial direction of the bladder 2, and reference numeral 9 indicates a metal fastening margin that defines the opening 8.

Therefore, a case in which pre-shaving of a green tire is performed using the bladder 2 having the above-described shape will be described below using FIGS. 2a and 2b.

First, a cylindrical member 14 extending downward is disposed at the center of a lower mold 12 for vulcanizing a tire 10 to be described later, and a cylindrical member 16 is disposed inside this cylindrical member 14. A first ring body 18 that expands upward is attached to the upper end of the cylindrical member 16 . This first
The ring body 18 and the second ring body 20 are configured to sandwich the metal fitting interference 9 of the bladder 2.

Therefore, in the above-described configuration, in the closed-end type bladder, until the green tire 10 descends and approaches the lower mold 12, the bladder 2 moves inside the cylindrical member 16, as shown in FIG. 2a. It is in a state where it is stored in. That is, the inside of the cylindrical member 16 is evacuated by a vacuum device (not shown), so that the bladder
2 is positioned inside the cylindrical member 16 in a contracted state as shown.

Next, the green tire IO suspended by a not-illustrated roller moves downward, and its bead portion 10a fits into the bead fitting portion of the lower mold 12. At this timing, an expansion medium, for example, air, is introduced into the bladder 2, and the bladder 2 expands and comes into pressure contact with the inner wall of the green tire 10. On the other hand, the ball nose 5 descends and fits into the concave central portion 3 to restrict upward expansion of the bladder 2. As a result, green tire 10
pre-shaving is achieved.

Thereafter, the upper mold (not shown) descends and comes into close contact with the lower mold 12, and vulcanization is performed.

However, by selecting the shape of the bladder 2 as described above, when introducing the inert gas which is the expansion medium into the inside of the bladder 2, the gap between the bladder 2 and the green tire 10 is reduced. A pressure difference is generated between each part of the green tire 10 on the contact surface of the green tire 10, and each part randomly contacts the inner surface of the tire, so that the expansion distribution of the bladder 2 is not uniform, and furthermore, when shaving each part, There are also differences.

That is, as the preshave time elapses,
First, the pressure contact point of the bladder 2 with respect to the tire 10 changes from the bead portion to a portion of the tread center. Then, when pre-shaving is finally completed, pressure differences appear at each location. After all, it has been pointed out that the bladder 2 according to the prior art has the following disadvantages.

That is, according to the shape of the bladder 2 as described above, when introducing the expansion medium into the bladder 2, air is sealed between the outer surface of the bladder and the inner surface of the green tire 10 (the second (See the dashed line in the figure). As a result, a pock-like appearance of the unvulcanized tire is left in the portion where the air is sealed, resulting in a defective product, that is, a so-called bare tire. In addition, in the forming process of laminating each member of the tire 10, the air sealed between the laminated members is released to the outside of the tire as a result of the preshaving of the bladder according to the prior art sealing the bead portion. Instead, it remains inside the tire. That is, air is trapped between the rubber members, cords, etc. that make up the tire, resulting in so-called air intrusion in the vulcanized tire. This is not only a product defect, but also an inconvenience that may lead to an accident if such a pneumatic tire is overlooked. Furthermore, if such inconveniences exist, quality control will be more stringent, which will make the production process more complicated.

On the other hand, since the bladder 2 contacts various parts of the inner wall of the green tire during pre-shaving and expands in diameter under different pressures, the position of contact with the inner wall of the green tire may sometimes shift. As a result, groove-like wrinkles appear on the rubber surface inside the tire. This is the so-called Chris outbreak. Furthermore, as mentioned above, in order to compensate for the unstable pre-shaving, the center portion of the bladder 2 may be positioned slightly above the green tire 10 (see Figure 2).
. As a result, the bead portion of the tire 10 is deformed and stamped, resulting in a defective product.

The present invention has been made in order to overcome the various disadvantages mentioned above, and includes forming a pressurized extension part of the bladder corresponding to a part of the center from the bead part of the tire so as to gradually become thinner. It has at least one concave inflection point between the parts corresponding to the tire bead parts, so that when pressurized fluid is introduced, the pressurized wall surface of the bladder almost simultaneously and uniformly forms a green tire as a whole. To press the vulcanizing mold, to eliminate slippage between the green tire and the bladder when the green tire is inflated, to optimize the shaving shape, and to uniformly contact the green tire with the vulcanizing mold. An object of the present invention is to provide an open-closed-end bladder for curing pneumatic tires.

To achieve the above object, the present invention provides a closed-end bladder that introduces pressurized fluid into the green tire, pressurizes the green tire, shaves the green tire, and supports the tire during vulcanization. A first U-shaped curved inflection point whose center of curvature is located outside the bladder body is provided between the portion corresponding to one bead portion and the metal fastening portion constituting this bladder. It has a main body that is greatly curved from the bending point and extends to the ball nose accommodating part, and further, the wall thickness is gradually increased from the part corresponding to the bead part of the green tire to the part corresponding to the tread part of the green tire. It is characterized by being formed thinly.

Next, preferred embodiments of the closed-end bladder according to the present invention will be described in detail with reference to the accompanying drawings.

3 and 4, reference numeral 30 indicates a bladder according to the present invention, and since this bladder 30 is of a closed-end type, it has an opening 32 opening the lower end in the axial direction. .

Substantially, the opening 32 is defined by a ring-shaped fitting interference 34. This metal fitting interference 34 is configured to be thicker than the portion of the bladder that expands under pressure.

From the metal fitting interference 34 configured as described above, the metal fitting interference 34 is made of an expandable material, for example, butyl rubber.
A bladder body 36 in the form of a bag, which is integrally molded with the body, extends. In this case, the bladder main body 36 has a first inflection point 38 that extends vertically from the metal clamp 34 and then curves outward at an acute angle, as shown in the figure. a first curved portion 40 that curves to slightly expand from the curved point 38; a second curved portion 42 that curves inward after rising upward from the first curved portion 40; A second inflection point 44 that bends inward of the bladder main body 36 at the terminal end of the second curved portion 42, and a smooth inclined portion extending inward from the second inflection point 44. a third inflection point 46 formed in the third inflection point 46, and a thick ball nose storage portion 48 that once extends horizontally from the third inflection point 46, then bends extremely and descends in the axial direction. Basically configured. In this case, the center of curvature of the first inflection point 38 is outside the bladder body 36, while the center of curvature of the first
The centers of curvature of the curved portion 40 and the second curved portion 42 are located inside the bladder body 36. In addition, in the figure, reference numeral 50 is
The bottom part pointing from the ball nose storage part 48 toward the opening part 32 side is shown.

Therefore, each part of the bladder according to the present invention will be explained in detail below.

First, as shown in FIG. 5, it is included in the second curved part 42,
Bladder body 3 that comes into contact with the bead part of the green tire
The thickness of the portion 52 of No. 6 is selected to be Gb. This thickness Gb is selected to be larger than the thickness Gc of the center portion 54 that defines the junction between the first curved portion 40 and the second curved portion 42, that is, the outer peripheral edge of the bladder body 36. Therefore, the wall thickness gradually decreases from the portion 52 to the center portion 54. Therefore, the portion 52 corresponding to the bead portion
The thickness of the bladder body 36 is such that there is a negative linear correlation between the part farther from the part 52 corresponding to the bead part and the part closer to the part 52 corresponding to the bead part. Set. As shown in FIG. Points N, X
And, if the distance along the wall thickness center to the center portion 54 is Ln, Lx, and Lc, this means that the wall thickness of each part is selected so that the following formula holds: L, -L, Lc = L, 1 do.

According to experiments, the value of (Gb - Gc) is l
mm or more, and furthermore, when the difference (Rc-Rh) between the outer diameter Rh of the tire bead portion and the outer diameter Rc of the center portion was 100 mm or more, it was confirmed that the effects described below are brought about.

The bladder 30 according to the present invention is basically constructed as described above. Next, the process of pre-shaving a green tire using this bladder will be described with reference to FIGS. 6a to 6C. I will explain. In addition, in the figure, the second
Reference numerals that are the same as those shown in the figures indicate the same components.

Green tires can be manufactured using the bladder 30 according to the present invention.
When performing pre-shaving on O, first, the bladder 3
0 is housed inside the cylindrical member 16 by lowering the ball nose 5 and evacuating the inside of the cylindrical member 16 by a suction device (not shown). In this case, the metal fastening allowance 34
is locked to the cylindrical member 16 by said ring body 18.20. For this purpose, the bladder 30 is deflated,
In the bladder of the present invention, the wall thickness is gradually increased from the second inflection point 4 and the third inflection point 46 to the ball nose accommodating portion 48. Therefore, the head as a whole retains its original shape. This means that when the inflation medium is introduced into the inside of the bladder 30 and the bladder 30 is inflated, a pressurizing action is applied evenly, and a part of the bladder is prevented from coming into contact with the green tire and being deformed. carry out functions.

Next, the green tire 10 is lowered, and its bead portion is fitted into a fitting portion 12a defined in the lower mold 12. Then, a pressurized fluid such as an inert gas is introduced into the bladder 30 from a fluid passage (not shown) at the appropriate timing.

That is, an expanded medium made of air, carbon dioxide, nitrogen gas, or other inert gas is introduced into the bladder 30. In this case, the expansion medium introduced into the bladder 30 causes the bladder body 36 to expand toward the green tire, and the center portion 54 is formed to become gradually thinner from the first inflection point 38 as described above. Therefore, the bladder main body 36 is easily stretched so as to stretch the first curved portion 40, the second curved portion 42, and the center portion 54.
It expands toward each part of the inner wall of O. At that time, as shown in FIG.
Under the action of the inflection point 44 and the third inflection point 46, it takes on a bulging shape that is substantially parallel to the inner wall of the green tire 10 without coming into contact with any part of the green tire 10, in particular. That is, the center of curvature of the first inflection point 38 is at the bladder 30
, the first inflection point 38 does not come into contact with the bead part of the green tire 10, and the second inflection point 44 and third inflection point 46 are located outside the body of the bladder 30. Because it is bent inward, the green tire 1
It never comes into contact with the upper bead part of 0.

After this state, pressurizing fluid is further introduced into the bladder 30, and the outer wall of the bladder 30 comes into pressure contact with the inner wall of the green tire 10 (see FIG. 6C). At this time, since a considerably high pressure is applied to the bladder 30, a portion of the first inflection point 38, the second inflection point 44, the third inflection point 46
bulge outward and come into contact with the bead portion of the green tire 10. Therefore, the bladder 30 applies pressurizing force to the entire inner wall of the green tire 10 at approximately the same time, and pre-shaving is performed in this state. Next, the upper mold (not shown) is lowered, and the green tire 30 is subjected to a vulcanization process.

Next, an example of actually preshaving a green tire 10 using a bladder having such a shape is shown in FIG. 7 and subsequent figures in comparison with a bladder according to the prior art. In this case, green tires for passenger car radial tires, size PSR-175-5R-13, were used.

First, as shown by the solid line A in FIG. 7, the bladder 3 of the present invention
The pressure applied to 0 is approximately 0.1 to 0.2 kg/c
The time of contact with each part of the green tire 10 is equal, and the bladder 30 is in contact with each part of the inner surface of the tire substantially simultaneously. On the other hand, when using the bladder according to the prior art, as shown by the broken line B, the time required for the bladder to come into contact with the vicinity of the bead of the upper mold of the green tire is extremely short.

Therefore, when the bladder preshaves the green tire 10, distortion occurs.

Next, FIG. 8 shows a stretched state of the bladder 30.

Here, the term "stretch" refers to the degree of expansion of the bladder 30 when the green tire 10 is pressed against the mold body after the bladder 30 has completed its expansion.

According to this, as shown by the solid line C, the degree of elongation of the bladder main body 36 as a whole is approximately 155%, and this is uniform. Therefore, the bladder body 36
It is confirmed that the degree of elongation is also approximately uniform.

On the other hand, in the bladder according to the prior art, the destruction vAD
As shown in the figure, the center part is elongated by approximately 170%, while the distance between the lower part, the dot part and the center part is elongated by 180%, and the distance between the center part and the upper mold bead part is elongated by approximately 140%.
%, and no uniformity was observed at all. Therefore, according to the prior art, since the degree of expansion of the bladder is uneven, the bladder is vulnerable to repeated fatigue.

Furthermore, FIG. 9 shows a stretch gauge when the bladder body 36 is expanded, that is, a change in the wall thickness of the bladder when the green tire 10 whose diameter has been expanded is pressed against the mold body. As shown by the solid line E, in the bladder 30 according to the present invention, the stretch gauge between the center portion and the bead portion is within the range of approximately 3 to 4 degrees. On the other hand, when using the bladder according to the prior art, the thickness of the lower bead portion is approximately 5.5 m, and the thickness of the upper bead portion is approximately 6 m, as shown by the broken line F in Fig. 9.
．． 5. On the other hand, the center part is about 4R.Therefore, during pre-shaving, there is already an extremely large difference in the thickness of the conventional bladder. In the bladder according to the above, since the bladder in the bead portion is thick, vulcanization is delayed accordingly.In other words, the time required for the tire bead portion to be vulcanized is extremely long.

According to the present invention, as described above, during pre-sieving, the expansion portion of the bladder into which pressure fluid is introduced becomes uniform, and therefore, there is no difference in the degree of expansion of the bladder as a whole, so that the pressurizing force is also uniform. At the same time, the pressurization time can also be extremely shortened.

Moreover, as a result of this uniform elongation distribution, the force that presses the green tire through the bladder becomes even across all parts, which prevents air from stagnation between the green tire and the bladder. is prevented. That is, it becomes unnecessary to provide a group for removing air from the bladder itself, and as a result, the structure of the bladder itself can be simplified. Furthermore, since there are no groups of bladders, a synergistic effect is obtained in that the expansion distribution is made more uniform. Furthermore, when the bladder expands,
Since it is possible to form a thin film with a uniform thickness, the vulcanization time can be shortened, and the incidence of product defects can also be reduced. Furthermore, since the bladder according to the present invention does not require an air bleed group, when the tire is mounted on a vehicle, a close contact state is obtained between the tire and the tube, and as a result,
This helps avoid accidents such as punctures, and because the weight is reduced by the thickness of the concave and convex portions that make up the inner liner, it contributes to further cost reductions and improved quality of the tire itself. You can get the desired effect. Moreover, since excessive inflation pressure is not applied locally, the bladder is resistant to repeated fatigue, and therefore the durability of the bladder as a whole is significantly improved.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design are possible without departing from the gist of the present invention. Number one, of course.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a closed-end plug according to the prior art, FIG. 2 is an explanatory diagram showing the process of pre-shaving using a bladder according to the prior art, and FIG. 3 is a diagram according to the present invention. Vertical sectional view of the closed-end plug, No. 4
The figure is a partially cutaway perspective view of a closed-end plug according to the present invention, and FIG. 5 is a diagram illustrating in detail the length and thickness from the end of the bladder to a portion of the center shown in FIG.
Fig. 6 is an explanatory diagram of the process when performing pre-shaving using the bladder according to the present invention, Fig. 7 is an explanatory diagram showing the fit pattern between the bladder and the green tire, and Fig. 8 is an explanatory diagram when the bladder is extended. FIG. 9 is an explanatory diagram showing the stretched state of each part of the bladder in FIG. 8, and FIG. 9 is an explanatory diagram showing the bladder thickness of each part of the bladder in FIG. 30... Bladder 32... Opening 34... Metal fitting tightening allowance 36... Bladder body 38
・・Inflection point 40.42 ・・Curved part 44.4
6. Point of inflection 48. Pole nose storage section 50. Bottom 52. Part 54. Center partial patent applicant Bridgestone Co., Ltd. Procedural amendment stamp button April 27, 1985 1, Display of case Showa 1960 Patent Application No. 067
No. 087 2. Name of the invention: Closed-end bladder for curing pneumatic tires 3. Relationship with the case of the person making the amendment Patent applicant address: 10-1 Kyobashi-chome, Chuo-ku, Tokyo Name: Brideston Co., Ltd. 4 , agent

Claims (4)

[Claims] (1) In a closed-end bladder that introduces pressurized fluid into the interior and pressurizes the green tire, shaves it, and supports the tire internally during vulcanization, the part corresponding to one bead part of the green tire and the A first U-shaped curved inflection point with the center of curvature located outside the bladder body is provided between the metal fastening portion that constitutes the bladder, and the ball nose storage portion is greatly curved from this inflection point. The pneumatic tire has a main body extending to the tread portion of the green tire, and further has a wall thickness gradually decreasing from a portion corresponding to the bead portion of the green tire to a portion corresponding to the tread portion of the green tire. Closed-end bladder for sulfur. (2) A closed-end type for curing a pneumatic tire according to claim 1, which has a second inflection point bent inward of the bladder at a portion corresponding to the other bead portion of the green tire. Bladder. (3) A third inflection point that bends inward of the bladder is formed between the second inflection point and the ball nose storage part constituting the bladder, and when introducing pressure fluid into the bladder, the second
3. The closed-end bladder for curing a pneumatic tire according to claim 2, wherein the inflection point and the third inflection point delay the pressurizing action on the bead portion of the green tire. (4) The center of curvature forms a curved part that exists inside the bladder when the bladder expands from the first inflection point and the second inflection point to the part corresponding to the tread part of the green tire, and each curved part A closed-end bladder for curing a pneumatic tire according to claim 2 or 3, which extends to a portion of the bladder corresponding to a tread portion of a green tire.