Rigid core mold and method for manufacturing pneumatic tire using the same

A technique for easily taking out a main body of a core mold is proposed. An annular core-mold main portion 11 having a molding surface 18 for shaping an inner surface of a pneumatic tire is included, and the core-mold main portion 11 is composed of a plurality of segments each of which is taken out toward the inside in a radial direction. In the molding surface 18 of the core-mold main portion 11, a ratio Bd/W of a maximum width W lying in regions for shaping sidewall portions and a width Bd in the tire axial direction measured at toe-end shaping positions 18e for shaping toe ends of bead portions is not less than 0.80. In an inside zone 30 from the toe-end shaping position 18e of the molding surface 18 to the position of the maximum width W, the angle α of a tangent T drawn to the molding surface 18 is not more than 15 degrees. The inside zone 30 includes an oblique part 32 in which the angle α of the tangent T is 30 to 45 degrees, and a ratio h/H of a length h in a radial direction of the oblique part 32 and a length H from the toe-end shaping position 18e to an intersecting point P of a line drawn in the tire radial direction from the toe-end shaping position 18e outwardly in the radial direction with the molding surface 18 is less than 0.25.

TECHNICAL FIELD

The present invention relates to a rigid core mold having an outer surface for shaping the inner surface of a pneumatic tire and a method for manufacturing of a pneumatic tire using the same.

BACKGROUND ART

In order to improve the finishing accuracy of a tire, a method for manufacturing a pneumatic tire which utilizes a rigid core mold has been proposed in patent documents 1-2 for example.

In this manufacturing method, unvulcanized rubber members which become tire constructional members are applied in series on the outer surface of the rigid core mold, and a green

The tire constructional members are an inner liner, carcass ply, belt ply, sidewall rubber, tread rubber and the like.

The green tire is put in a vulcanization mold together with the rigid core mold and vulcanization-molded.

The rigid core mold is an inner mold. The vulcanization mold is outer mold.

The rigid core mold includes an annular core-mold main portion. The core-mold main portion has an outer surface equivalent to the inner surface of the tire. The core-mold main portion is split in a plurality of core segments.

After the vulcanization-molding, each core segment is pulled out inwardly in the tire radial direction from the vulcanized tire in series. Thereby, the rigid core mold is taken out through the bead portion side of the tire (Core-mold taking-out step).

As is commonly known, the cross-sectional shape of the inner surface of a pneumatic tire protrudes outwardly in the tire axial direction mostly in the sidewall portions.

In contrast, the width of the bead portions is less than the sidewall portions.

Accordingly, in order to take out the core segment from the tire, a particularly large force is required to pass through the bead portions.

In order to increase the production efficiency of the tire, it is necessary to save the labor to take out the core-mold main portion and to reduce the cycle time of the core-mold taking-out step.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The present invention was made with the view to the above-mentioned actual circumstances, and a primary object is to provide a rigid core mold and a method for manufacturing a pneumatic tire in which, essentially by improving the shape of the molding surface of the core-mold main portion, the cycle time of a rigid core-mold taking-out step is reduced.

Means of Solving the Problems

An invention according to claim1of the present invention is a rigid core mold for manufacturing a pneumatic tire including an annular core-mold main portion having a molding surface for shaping the inner surface of a toroidal pneumatic tire having a tread portion, sidewall portions and bead portions,

the core-mold main portion composed of a plurality of core segments arranged in the tire circumferential direction and each taken out from the pneumatic tire by moving inwardly in the tire radial direction, and

the molding surface characterized in that,

in a meridian section of the core-mold main portion including a tire revolution axis,

the ratio Bd/W of a maximum width W in the tire axial direction lying in regions for shaping the sidewall portions, and a width Bd in the tire axial direction measured at toe-end shaping positions for shaping the toe ends of the bead portions is not less than 0.80,

an inside zone of the molding surface from the toe-end shaping positions to the position of the maximum width W has a width in the tire axial direction gradually decreasing toward the inside in the tire radial direction,

the angle α of the tangent to the molding surface in the inside zone is not more than 45 degrees with respect to a line in the tire radial direction,

the inside zone includes an oblique part where the angle α of the tangent is 30 to 45 degrees, and

the ratio h/H of the length h in the tire radial direction of the oblique part and the length H in the tire radial direction measured to an intersecting point at which a line in the tire radial direction drawn outwardly in the tire radial direction from the toe-end shaping position intersects with the molding surface is less than 0.25.

An invention as set forth in claim2is the rigid core mold as set forth in claim1wherein

the molding surface is provided in the inside zone with a maximum inclination position at which the angle α of the tangent becomes maximum, and

a region inside in the tire radial direction from the maximum inclination position includes an inverse arc part formed by an arc having its center outside the core mold.

An invention as set forth in claim3is the rigid core mold as set forth in claim2wherein

the ratio Hr/h of the length H in the tire radial direction of the inverse arc part and the length h in the tire radial direction of the oblique part is 0.50 to 0.83.

An invention as set forth in claim4is the rigid core mold as set forth in claim2or3wherein

the angle α of the tangent at the maximum inclination position is 40 to 44 degrees.

An invention as set forth in claim5is the rigid core mold as set forth in any one of claims1-4, wherein

the ratio Bd/W is 0.80 to 0.84.

An invention as set forth in claim6is the rigid core mold as set forth in any one of claims1-5, wherein

the ratio h/H is 0.15 to 0.22.

An invention as set forth in claim7is a method for manufacturing a pneumatic tire utilizing the rigid core mold as set forth in any one of claims1-6, which is characterized by including

a green tire forming step for forming a green tire by applying unvulcanized tire constructional members on an outer surface of the rigid core mold in series,

a vulcanization step for putting the green tire in a vulcanization mold together with the rigid core mold and vulcanization-molding it, and

a core-mold taking-out step for taking out each core segment from the pneumatic tire after the vulcanization-molding by moving each core segment inwardly in the tire radial direction.

Effects of the Invention

In the present invention, the molding surface of the core-mold main portion has the ratio Bd/W not less than 0.80, which ratio is of the maximum width W in the tire axial direction lying in the regions for shaping the sidewall portions and the width Bd in the tire axial direction at the toe-end shaping positions for shaping the toe ends of the bead portions. Namely, a pneumatic tire shaped by the rigid core mold of the present invention is formed such that the width between the toe ends is relatively wide.

Accordingly, when the core segment is taken out from the tire, the resistance (frictional force) of the core segment during passing through between the toe ends of the bead portions is reduced.

In the inside zone of the molding surface from the toe-end shaping position to the position of the maximum width W, the rigid core mold of the present invention is gradually decreased in the width in the tire axial direction toward the inside in the tire radial direction. In the inside zone, the angle α of the tangent drawn to the molding surface is not more than 45 degrees with respect to the line in the tire radial direction. Namely, in the core-mold main portion of the present invention, the inclination angle α of the inside zone with respect to in the tire circumferential direction is small.

Therefore, it becomes easy to take out each core segment toward the inside in the tire radial direction.

The inside zone of the rigid core mold of the present invention includes the oblique part where the angle α of the tangent becomes 30 to 45 degrees. The ratio h/H of the length h in the tire radial direction of the oblique part and the length H in the tire radial direction from the toe-end shaping position to the intersecting point is less than 0.25. The intersecting point is the point at which the line in the tire radial direction drawn outwardly in the tire radial direction from the toe-end shaping position intersects with the molding surface. By limiting the range of the oblique part as being small as explained above, it becomes more easy to take out the core segment toward the inside in the tire radial direction.

The rigid core mold of the present invention which fulfill the above-mentioned configurations reduces the labor to take out the core segments from the tire and consequently shortens the cycle time of the core-mold taking-out step.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in conjunction with the drawings.

The rigid core mold in the present embodiment is utilized to manufacture a pneumatic tire1such as shown inFIG. 1.

InFIG. 1, a passenger radial tire is shown as an example of the pneumatic tire1.

The pneumatic tire1is toroidal, having a tread portion2, sidewall portions3, and bead portions4.

The pneumatic tire1includes a carcass6, a belt layer7and an inner liner9.

The carcass6extends from the tread portion2to a bead core5of the bead portion4through the sidewall portion3.

The belt layer7is disposed on the outside in the tire radial direction of the carcass6in the tread portion2.

The inner liner9is disposed inside the carcass6.

As is commonly known, the pneumatic tire1is formed so that the sidewall portion3projects outwardly in the tire axial direction than the bead portion4.

The carcass6includes a carcass ply6A.

The carcass ply6A is composed of a layer of carcass cords arranged at an angle of 75 to 90 degrees with respect to the tire equator C for example.

Organic fiber cords, for example, polyester and the like are used as the carcass cords.

The carcass ply6A extends between the bead portions4,4in a toroidal form.

The inner ends6ein the tire radial direction of the carcass ply6A terminate in the bead portions4without being turned up.

The bead core5is disposed in the bead portion4.

The bead core5includes an inside core5A and an outside core5B. The inside core5A is disposed inside the carcass ply6A in the tire axial direction. The outside core5B is disposed outside the carcass ply6A in the tire axial direction. The inside core5A and the outside core5B are ring-shaped. In the inside core5A and the outside core5B, a bead wire5cmade of steel is helically overlap-wound around the tire revolution axis.

On the inner surface in the tire axial direction of the inside core5A, an inner apex rubber8iis disposed.

On the outer surface in the tire axial direction of the outside core5B, an outer apex rubber8ois disposed.

The apex rubber8i,8ois formed from hard rubber.

The apex rubber8i,80ois formed so as to taper toward the outside in the tire radial direction.

The belt layer7is composed of two inner and outer belt plies7A,7B. The belt ply7A,7B is a layer of belt cords arranged so as to incline at an angle of 10 to 40 degrees with respect to the tire equator C for example. In the belt plies7A,7B, the belt cords are superimposed and oriented so as to cross each other. Steel cords or organic fiber cords for example aramid and the like are used as the belt cords.

The inner liner9is disposed so as to extend between the toe ends4e,4eof the bead portions4in a toroidal form. The inner liner9is disposed over the entire area of the inner surface of the tire17. The inner liner9is made of an air-nonpermeable rubber material. For example, a butyl based rubber can be suitably used as the air-impermeable rubber material. The butyl based rubber contains not less than 60 parts by mass, preferably not less than 80 parts by mass, more preferably 100 parts by mass of butyl rubber (or its derivative) with respect to 100 parts by mass of rubber component.

The thickness t of the inner liner9is for example about 0.5 to 2.0 mm.

InFIG. 2, an exploded perspective view of the rigid core mold10is shown. InFIG. 3, a cross sectional view of the rigid core mold10is shown.

As shown inFIG. 2andFIG. 3, the rigid core mold10includes an annular core-mold main portion11, a core12and a pair of side wall bodies13L,13U.

The core-mold main portion11has a bore11h.

The core12is inserted in the bore11hof the core-mold main portion11.

The side wall bodies13L,13U are disposed separately from each other in the direction of the axis of the core-mold main portion11.

The outer surface of the core-mold main portion11forms the molding surface18.

The molding surface18shapes the inner surface17of the pneumatic tire1. In other words, after the vulcanization-molding, the inner surface17of the pneumatic tire1inFIG. 1accords with the molding surface18of the core-mold main portion11.

The core-mold main portion11is composed of a plurality of core segments14split in the tire circumferential direction.

As shown inFIG. 4, the core segments14include first core segments14A and second core segments14B.

The length L1in the circumferential direction, of the first core segment14A gradually decreases toward the inside in the tire radial direction.

The length L2in the circumferential direction, of the second core segment14B gradually increases toward the inside in the tire radial direction.

The first core segments14A and the second core segments14B are alternately arranged in the tire circumferential direction. Thereby, the core-mold main portion11becomes an annular body continuous in the tire circumferential direction.

As shown inFIG. 5, the molding surface18of the core-mold main portion11includes a tread molding surface18a, sidewall molding surfaces18b, and bead molding surfaces18c. The tread molding surface18ashapes the inner surface17of the tread portion2of the pneumatic tire1(green tire1L).

The sidewall molding surfaces18bshape the inner surfaces17of the sidewall portions3. The bead molding surfaces18cshape the inner surfaces17of the bead portions4.

The sidewall molding surfaces18bare formed so as to project outwardly in the tire axial direction than the bead molding surfaces18c. The sidewall molding surfaces18binclude a maximum width position20having a maximum width W in the tire axial direction.

As shown inFIG. 2andFIG. 3, the core12is cylindrical. As shown inFIG. 3, the core12is inserted in the bore11hof the core-mold main portion11.

In the outer circumferential surface of the core12, there are formed dovetail grooves19aextending in the direction of the axis of the rigid core mold10. In the inner circumferential surface of the core segment14A,14B, there is formed a dovetail tenon19bextending in the direction of the axis of the rigid core mold10. The dovetail grooves19aand the dovetail tenons19bare engaged with each other.
If the core12is inserted in the bore11h, the first core segments14A and the second core segment14B are prevented from moving in the tire radial direction and in the tire circumferential direction.

As shown inFIG. 3, one of the side wall bodies13L is fixed to one side of the core12in the direction of the axis with bolts.

The other side wall body13uis fixed to the other side in the direction of the axis, of the core12. The other side wall body13uis fixed to an internal thread portion15detachably by being screwed therein. The internal thread portion15is formed in the bore11hof the core12.
As shown inFIG. 3, a pair of side wall bodies13L,13U prevent the core-mold main portion11from moving in the direction of the axis of the core12.

The outer surface of each side wall body13L,13U is provided with a support shaft part16protruding outwardly in the direction of the axis. A chuck part23is detachably coupled with the support shaft part16. The chuck part23is for example, a conveyer (not shown) or the like for conveying the rigid core mold10to the vulcanization mold or the like.

As shown inFIG. 5, unvulcanized tire members and the like are applied onto the outside of the molding surface18of the rigid core mold10. Thereby, the green tire1L is formed.

As shown inFIG. 6, the green tire1L is put in the vulcanization mold22together with the rigid core mold10.

The vulcanization mold22has a cavity22sfor forming the outer surface of the green tire1L.

The green tire1L is vulcanization-molded so that the outer surface coincides with the cavity22s, and the inner surface17coincides with the molding surface18of the core-mold main portion11.

After the vulcanization, the vulcanized tire1is taken out from the vulcanization mold22together with the rigid core mold10. As shown inFIG. 7, the side wall bodies13L,13U and the core12are removed from the rigid core mold10.

Thereby, on the inside of the pneumatic tire1, only the core-mold main portion11is remained.

Next, the first core segments14A and the second core segments14B of the core-mold main portion11are pulled out inwardly in the tire radial direction in order. Namely, the core-mold main portion11is taken out from the inside of the pneumatic tire1, while being disassembled.

As shown inFIG. 8, in the meridian section of the core-mold main portion11including the tire revolution axis, the molding surface18is such that the ratio Bd/w of a maximum width W and a width Bd between the toe ends4eis not less than 0.80.

The maximum width W is a maximum width in the tire axial direction which lies in the sidewall molding surfaces18b.

The width Bd between the toe ends4eis the width in the tire axial direction at the toe-end shaping positions18efor shaping the toe ends4eof the bead portions.

In other words, the pneumatic tire1vulcanization-molded with the core-mold main portion11of the present invention, is formed such that the width Bd between the toe ends4ebecomes relatively larger.

When the core segment14is taken out through the bead portion side of the pneumatic tire1, the maximum width position20of the core segment14passes, while increasing the width Bd between the toe ends4e,4e.

Namely, the resistance (frictional force) during the maximum width position20of the core segment14passes through between the toe ends4e,4eof the bead portions, becomes small by making the vulcanization-molding so that the width Bd between the toe ends4eis large.
Accordingly, it becomes easy to take out the core segments14through the bead portion side of the pneumatic tire1.

From results of various tests conducted by the inventor and others, it was discovered that if the ratio Bd/W is not less than 0.80, the foregoing effect can be exerted remarkably. According to the increase in the ratio Bd/W, it becomes easier to take out the core segment14from the tire1.

However, if the width Bd between the toe ends4e,4eis very large, the bead portions need to be largely deformed in order to mount the pneumatic tire1on a rim. Therefore, the tire mounting performance deteriorates.

Further, there is a possibility that the profile of the carcass is deformed and the rolling resistance and the tire weight are increased.

Therefore, the ratio Bd/W is preferably not more than 0.84, more preferably not more than 0.83.

The inside zone30is the zone from the toe-end shaping position18eto the maximum width position20.

In the inside zone30, the width in the tire axial direction of the molding surface18of the core-mold main portion11is gradually decreased toward the inside in the tire radial direction.

Further, in the inside zone30, the angle α of the tangent T drawn to the molding surface18is not more than 45 degrees with respect to a line in the tire radial direction.

When the core segment14is taken out through the bead portion side of the pneumatic tire1, the maximum width position20of the core segment14moves toward the toe end4e, while contacting with the inner surface17of the inside zone30of the pneumatic tire1.

At this time, if the angle α of the tangent drawn to the molding surface18in the inside zone30is large, the frictional force of the core segment14with the inner surface17during being taken out becomes large.

Therefore, the taking out of the core segment14from the pneumatic tire1is deteriorated.

Therefore, the present invention is intended to reduce the frictional force between the inner surface17of the inside zone30and the core segment14by setting the angle α as being not more than 45 degrees.

Thereby, the taking out of the core segment14from the pneumatic tire1becomes more easy.

The inside zone30includes an oblique part32in which the angle α of the tangent T is 30 to 45 degrees.

The oblique part32gives a large frictional force to the core segment when taking out the core segment14.

Therefore, it is preferable that the length h in the tire radial direction of the oblique part32is limited in a certain range. In the present invention, the ratio h/H of the length h in the tire radial direction of the oblique part32and the length H in the tire radial direction from the toe-end shaping position18eto the intersecting point P is less than 0.25.
Thereby, the frictional force between the inner surface17of the inside zone30and the core segment14is reduced.
From the results of the various tests, it is especially preferable that the ratio h/H is 0.15 to 0.22.
The intersecting point P is the point at which the line in the tire radial direction drawn outwardly in the tire radial direction from the toe-end shaping position18eintersects with the molding surface18.

The inside zone30of the molding surface18includes a maximum inclination position34at which the angle α of the tangent T becomes maximum.

In this example, the angle α of the tangent T is gradually increased from the toe-end shaping position18eto the maximum inclination position34and then gradually decreased from the maximum inclination position34to the maximum width position20. At the maximum inclination position34, the angle α of the tangent T is not more than 45 degrees. At the maximum inclination position34, the angle α of the tangent T is preferably 40 to 44 degrees.

A region36inside in the tire radial direction from the maximum inclination position34of the molding surface18includes an inverse arc part38formed by an arc having its center outside the core mold.

As shown inFIG. 1, such inverse arc part38forms an inverse arc part40, which is formed by an arc having its center outside the tire, on the carcass ply6A of the pneumatic tire1.

Such inverse arc part40of the pneumatic tire1forms a large space in the tire cavity as the direction of curvature of the carcass cords is reversed (namely, the inverse arc part40changes to the arc having its center within the tire).

Thereby, the taking out of each of the core segments of the core-mold main portion11becomes easy.

It is preferable that the ratio Hr/h of the length H in the tire radial direction of the inverse arc part38and the length h in the tire radial direction of the oblique part32is 0.50 to 0.83.

While description has been made of particularly preferable embodiments of the present invention, the present invention can be carried out by modifying into various embodiments without being limited to the illustrated embodiments.

Embodiments

Rigid core molds for manufacturing a passenger pneumatic tire of size 235/40R18 having the basic structure ofFIG. 1were experimentally manufactured according to the specifications shown in Table 1. The rigid core molds were tested for the performance. Test methods are as follows

Utilizing each rigid core mold, pneumatic tires were manufactured, and the cycle time of the step for taking out the core mold therefrom was measured. The results are indicated by the cycle time (second). The smaller the number, the easier the taking out of the core mold, namely, it is better.

<State of Inner Surface of Tire after Taking Out Core Mold>

The inner surface of the pneumatic tire manufactured by using each rigid core mold was visually inspected to confirm the presence or absence of damage. The results of the test are shown in Table 1.

TABLE 1comparativeembodi-embodi-embodi-comparativeembodi-embodi-example1ment 1ment 2ment 3example2ment 4ment 5number of core segments8888888maximum width W of core-mold main portion (mm)242234226242238238238width Bd between toe-end shaping positions (mm)191191191201201201201ratio Bd/W0.790.820.850.830.840.840.84maximum angle (alpha) in inside zone (deg.)44444444474543length h of oblique part (mm)17171717171717length H (mm)79797979797979ratio h/H0.220.220.220.220.220.220.22length Hr of inverse arc part (mm)10.010.010.010.010.010.010.0ratio Hr/h0.590.590.590.590.590.590.59cycle time of core-mold taking-out step (sec.)273221209212284210200damage of tire inner surface after taking out core moldnonononopresentnonoembodi-embodi-comparativeembodi-embodi-embodi-embodi-ment 6ment 7example3ment 8ment 9ment 10ment 11number of core segments8888888maximum width W of core-mold main portion (mm)238238238238238238238width Bd between toe-end shaping positions (mm)201201201201201201201ratio Bd/W0.840.840.840.840.840.840.84maximum angle (alpha) in inside zone (deg.)40384444444444length h of oblique part (mm)17172017141210length H (mm)79797979797979ratio h/H0.220.220.250.220.180.150.13length Hr of inverse arc part (mm)10.010.010.08.57.06.05.0ratio Hr/h0.590.590.500.500.500.500.50cycle time of core-mold taking-out step (sec.)197189262201195190187damage of tire inner surface after taking out core moldnononononononoembodi-embodi-embodi-embodi-embodi-embodi-embodi-ment 12ment 13ment 14ment 15ment 16ment 17ment 18number of core segments88888810maximum width W of core-mold main portion (mm)238238238238238238238width Bd between toe-end shaping positions (mm)201201201201201201201ratio Bd/W0.840.840.840.840.840.840.84maximum angle (alpha) in inside zone (deg.)44444444404444length h of oblique part (mm)17171717121217length H (mm)79797979797979ratio h/H0.220.220.220.220.150.150.22length Hr of inverse arc part (mm)8.08.514.016.08.010.010.0ratio Hr/h0.470.500.820.940.670.830.59cycle time of core-mold taking-out step (sec.)258230199195197189210damage of tire inner surface after taking out core moldnononopresentnonono

From the test results, it was confirmed that the rigid core molds as the Embodiments shorten the cycle time of the core-mold taking-out step, while preventing damage to the inner surface of the pneumatic tire.

DESCRIPTION OF REFERENCE SIGNS