Method for molding bead portion of green tire and bead portion molding device

The method for molding a bead portion for a green tire includes a bead core supporting step for supporting the bead core through a carcass ply upon expanding a diameter of a bead core supporter including a seating surface for supporting a radially inner surface of the bead core. Since the bead core supporter comprises an outer piece outside of the seating surface in a tire axial direction that rises up towards outside in the radial direction with a clearance between the same and the bead core, that is larger than the thickness of the carcass ply, it is possible to flip a carcass outer region up, that is outside in the tire axial direction than a sandwiched region of the carcass ply, sandwiched and held between the seating surface and the bead core, and to deform the carcass outer region into an outer inclined piece that is inclined and extended towards radially outside without including any partially bent portions. It further includes a curving step of pressing the outer inclined piece inward in the tire axial direction by using a ply winding ring for curving the same towards the outside surface and the radially outer surface of the bead core, and a pressing step of pressing a tip end portion of the curved outer inclined piece towards the radially outer surface of the bead core by using a pressing roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for molding a bead portion of a green tire capable of easily winding a carcass ply without the necessity of preliminarily forming a bending portion at the carcass cords when forming a green tire of so-called bead-wind structure in which both end portions of a carcass ply are wound around bead cores, and to a bead portion molding device employed for this purpose.

2. Description of the Related Art

As illustrated inFIG. 9, it is recently being suggested to employ a bead-wind structure in heavy-duty tires utilizing a carcass ply (a) of steel cords. In such a bead-wind structure, carcass wound portions (a2), in which the carcass ply is wound by substantially a whole round around the bead cores (b), are formed on both sides of a carcass main portion (a1) that bridges between bead cores (b, b) to thereby fix both end portions of the carcass ply (a).

In such a structure, tip ends (ae) of the carcass wound portions (a2) are interrupted proximate of the periphery of the bead cores (b) so that stress through deformation of the beads hardly acts onto the tip ends (ae). It is accordingly of advantage that damages such as loosening of cords originating from the tip ends (ae) can be effectively restricted. However, in this structure, the entire length of the carcass wound portions (a2) is short and a winding radius thereof small while a flexural rigidity of the carcass cords (steel cords) is large. A drawback is thus exhibited in that it is difficult to easily and accurately wind the carcass ply (a) around the bead cores (b) in the course of manufacturing a green tire.

It has thus been suggested in, for instance, Japanese Patent Application Laid-Open No. 2001-246675 or Japanese Patent Application Laid-Open No. 2001-246676 to preliminarily form a plastic-deformed bending portion in the carcass ply in which carcass cords are partially bent at respective positions that suit corner portions of the bead cores.

However, when bending is performed to the carcass cords, the rigidity and strength of the carcass cords will be degraded due to the partial bending so that there is a danger that damages originating from the bent portions of the cords are induced during running.

SUMMARY OF THE INVENTION

The present invention thus aims to provide a method for molding a bead portion of a green tire capable of easily, accurately and stably forming carcass wound portions that are wound around the bead cores without the necessity of preliminarily forming a bending portion at the carcass cords, and to provide a bead portion molding device employed for this purpose.

In one aspect of the invention, a method for molding a bead portion for a green tire includes a carcass ply of steel cords serially provided with carcass wound portions wound around bead cores on both sides of a carcass main body portion extending from a tread portion over sidewall portions up to the bead cores of bead portions, the bead cores having a polygonal sectional shape comprised of a radially inner surface opposing a seat surface of a rim, a radially outer surface parallel to the radially inner surface, a tire-axially outside surface connecting between tire-axially outer edges of the radially inner surface and the radially outer surface, and a tire-axially inside surface connecting between tire-axially inner edges of the radially inner surface and the radially outer surface, the method including:

a carcass tube forming step of forming a carcass tube by cylindrically winding the carcass ply on an outer periphery of a former,

a bead core setting step of setting the bead core radially outside of the carcass tube, and

a bead core supporting step of employing a bead core supporter expandable and shrinkable in diameter and having a seating surface for supporting the radially inner surface of the bead core while sandwiching the carcass ply between the seating surface and the bead core by expanding the diameter of the bead core supporter,

the bead core supporting step further including a flip-up step of flipping up a carcass outer region defined as a portion of the carcass ply being outside in the tire axial direction than a sandwiched region of the carcass ply sandwiched between the seating surface and the bead core so as to become an outer inclined portion that inclines and extends towards outside in the radial direction without including any partially bent portions due to the provision of a flange at the bead core supporter that rises radially outside from a tire-axially outer end of the seating surface with a clearance between the same and the bead core, that is larger than the thickness of the carcass ply,

a curving step of pressing the outer inclined piece inward in the tire axial direction by using a ply winding ring for curving the same towards the outside surface and the radially outer surface of the bead core, and

a pressing step of pressing a tip end portion of the outer inclined piece in a curved condition towards the radially outer surface of the bead core by using a pressing roller.

In another aspect of the invention, a device employed for this purpose includes a former for forming a carcass tube by winding a carcass ply cylindrically on the outer periphery thereof, and

a bead core supporting means that includes a bead core supporter including a seating surface that is set outside of the carcass tube in the radial direction for supporting the radially inner surface of the bead core and that is expandable and shrinkable in diameter for supporting the bead core while sandwiching the carcass ply between the seating surface and the bead core when expanded in diameter,

the bead core supporter further including a winding means with

an outer piece outside of the seating surface in the tire axial direction that rises up towards outside in the radial direction, and by setting a minimum value of a clearance between the outer piece and the bead core to be larger than the thickness of the carcass ply in the diametrically expanded condition of the bead core supporter, the outer piece flips a carcass outer region outside in the tire axial direction than the sandwiched region of the carcass ply sandwiched between the seating surface and the bead core up as an outer inclined piece that inclines and extends towards outside in the radial direction without including any partially bent portions, and

a ply winding ring that is relatively movable with respect to the outer inclined piece in- and outside in the tire axial direction and that presses the outer inclined piece through relative movement towards inside in the tire axial direction for curving the outer inclined piece towards the outside surface and the radially (outer) surface of the bead core; and

a shaping means including a pressing roller for pressing a tip end portion of the outer inclined piece in the curved condition towards the radially outer surface of the bead core.

Due to the above-described arrangement of the present invention, it is possible to easily, accurately and stably wind both end portions of the carcass ply around the bead cores without the necessity of preliminary forming a bending portion at the carcass cords.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention will now be explained together with an illustrated example.

FIG. 1is a sectional view illustrating one embodiment of a bead portion of a heavy-duty tire formed by using the method for molding a bead portion of a green tire according to the present invention,FIG. 2is a sectional view illustrating a bead portion molding device for executing the method for molding a bead portion, andFIG. 3is a sectional view showing its main portion in enlarged form.

As illustrated inFIG. 1, the heavy-duty tire1comprises at least a carcass6that extends from a tread portion over sidewall portions3up to bead cores5of bead portions4. A known belt layer for reinforcing the tread is disposed radially outside of the carcass6and inward of the tread portion.

The carcass6is comprised of a single carcass ply6A in which a cord aligned body with carcass cords (steel cords) being pull-aligned in parallel is coated with a topping rubber. In case of a radial tire as in the present embodiment, the carcass cords are aligned at an angle of 75 to 90° with respect to a tire circumferential direction.

The carcass ply6A assumes a bead-wind structure comprised of a toroidal carcass main body portion6abridged between the bead cores5,5and carcass wound portion6bcontinuing from both sides of the carcass main body portion6a. The carcass wound portions6bare wound around the bead cores5from inside to outside in the tire axial direction and their tip ends E terminate while approaching the carcass main body portion6a. With this arrangement, they are fixed at the bead cores5.

Here, the bead core5comprises a core main body5A obtained by, for instance, winding bead wires made of steel in a multi-staged and multi-seriate manner. In the present embodiment, it is formed of the core main body5A and a thin coating layer5B coating its periphery. The coating layer5B is comprised of a rubberized cloth or a rubber sheet for preventing parting of the bead wires. In this respect, the bead core5may be comprised of the core main body5A only.

The bead core5has a polygonal sectional shape comprised of a radially inner surface SL opposing a seat surface Js of a rim J, a radially outer surface SU parallel to the radially inner surface SL, a tire axially outside surface SO connecting between tire-axially outer edges P2, P4of the radially inner surface SL and the radially outer surface SU, and a tire-axially inside surface SI connecting between tire-axially inner edges P1, P5of the radially inner surface SL and the radially outer surface SU. The present embodiment particularly illustrates a bead core5having a hexagonal sectional shape with the outside surface SO being comprised of a flexed surface including an upper inclined surface SOa and a lower inclined surface Sob while the inside surface SI is comprised of a flexed surface including an upper inclined surface SIa and a lower inclined surface SIb. In this respect, reference numerals P3, P6illustrate peak portions of the flexed surfaces. The engaging force of the bead core5with the rim is improved over a wide range since the radially inner surface SL becomes substantially parallel to the rim seat Js. In the present embodiment, the rim J is a 15° tapered rim for tubeless use, and the radially inner surface SL is thus inclined with respect to a tire axial line at an angle of substantially 15°.

The carcass wound portion6bis formed of a main portion8opposing the inside surface SI, the radially inner surface SL, and the outside surface SO, and a sub-portion9continuing into the main portion8and opposing the radially outer surface SU. In the present embodiment, a band in which a wrapping wire10is spirally wound is disposed on the sub-portion9. This band presses and restricts the sub-portion9towards the radially outer surface SU of the bead core5to reliably prevent spring-back of the carcass cords and the following problems originating therefrom. In this respect, such problems include occurrence of air-accumulation between the sub-portion9and the bead core5when performing vulcanization molding to thus harm the durability or tendency of occurrence of blow-by phenomena or cord loosening through degraded engaging force with respect to the carcass6.

Next, when forming a green tire for such a heavy-duty tire1, a bead portion molding device11(hereinafter referred to as “molding device11”) as illustrated inFIG. 2is used. With this arrangement, it will be possible to simply, accurately and stably form the carcass wound portions6bwithout the necessity of preliminary forming a bending portion at the carcass cords.

The molding device11is arranged to include

(I) a former13for forming a carcass tube12in which the carcass ply6A is wound in a cylindrical manner,

(II) a bead core supporting means15that supports the bead core5, which is set radially outside of the carcass tube12, upon expanding in diameter,

(III) a winding means16that curves and winds cylindrical sub-portions12b, which comprise both end portions of the carcass tube12, around the bead cores5, and

(IV) a shaping means17that presses tip end portions27eof the cylindrical sub-portions12btowards the radially outer surface SU of the bead core5by using a pressing roller32. In this respect, the tip end portions27ecorrespond to the sub-portions9of the carcass wound portions6b.

More particularly, the former13of the present embodiment is a first-stage former that is employed in a green tire molding step of two-staged style. The former13includes a cylindrical drum18that is driven to rotate through a driving device (not shown) such as motor. By winding a sheet-like carcass ply6A around a former outer periphery, which is the outer periphery of the drum18, by a single round, the cylindrical carcass tube12is formed. The carcass tube12is comprised of a cylindrical main portion12ahaving a length capable of forming the carcass main body portion6a, and cylindrical sub-portions12b,12bhaving a length capable of forming the carcass wound portions6b. In the present embodiment, the axial-directional length of the former13is not more than the length of the cylindrical main body12aso that the cylindrical sub-portions12bare accordingly formed to project outside in the axial direction from both ends of the former13.

As illustrated inFIG. 3in enlarged form, the bead core supporting means15comprises a bead core supporter14that is expandable and shrinkable in diameter and that is comprised of a plurality of segments19partitioned in the circumferential direction. The bead core supporter14is disposed on both outer sides of the former13and at the position of the cylindrical sub-portion12b. The segments19are guided between guide plates21,22in- and outside in the tire axial direction that rise up in the radial direction from a sleeve20that uniformly rotates with the former13. Through lateral movement in the tire axial direction of a sliding ring23that is outwardly fitted onto the sleeve20, it is possible to move in- and outside in the radial direction from a shrunk diameter condition Y1(FIGS. 3,4) to the expanded diameter condition YS (FIG. 5). In the present embodiment, cone-like engaging surfaces t of identical inclination are formed on the radially inner periphery of the segments19and the radially outer periphery of the sliding ring23. While lateral movements in the tire axial direction are converted into movements in radial directions through these engaging surfaces t, it is possible to employ a known mechanism such as a link mechanism.

The bead core supporter14comprises, on its radially outer periphery, a seating surface24for supporting at least the radially inner surface SL of the bead core5for supporting the bead core5and an outer piece25that rises up outside of the seating surface24in the tire axial direction towards outside in the radial direction. In this respect, while the present embodiment illustrates an example in which there is provided an inner piece26also inside of the seating surface24in the tire axial direction, it is possible to omit this inner piece26.

In the present embodiment, the seating surface24is formed to have a V-shaped form comprised of a first seating surface24A that has the same inclination as the radially inner surface SL of the bead core5for supporting the radially inner surface SL and a second seating surface24B that has the same inclination as the lower inclined surface SIb of the bead core5for supporting the lower inclined surface SIb. In the expanded diameter condition Y2(FIG. 5), the beat core5may seat at the seating surface24to be supported thereby through the carcass ply6A. Simultaneously therewith, the carcass ply6A is sandwiched between the seating surface24and the bead core5for preventing positional shifts of the carcass ply6A. For purpose of convenience, the region of the carcass ply6A that is sandwiched between the seating surface24and the bead core5is referred to as a sandwiched region Ka while a region further outside than this sandwiched region Ka in the tire axial direction is referred to a carcass outer region Ko and a region further inside thereof as carcass inner region Ki.

The outer piece25is arranged in that the carcass outer region Ko may be flipped up to radially outward accompanying the expansion in diameter. In the expanded diameter condition Y2(FIG. 5), a large clearance d that is larger than the thickness of the carcass ply6A is formed between the outer piece25and the bead core5. Accordingly, the outer piece25is capable of deforming the carcass outer region Ko into an outer inclined piece27that is inclined and extended towards radially outside without including any partially bent portions. In this respect, a similar clearance is formed between the inner piece26and the bead core5such that the carcass inner region Ki is deformed into an inner inclined piece28that is inclined and extended towards radially outside without including any partially bent portions.

Where the clearance d is too small or a distance h in the radial direction from a tire axial outer edge of the radially inner surface SL of the bead core5to an upper end of the outer piece25is too large, partial bent portions are apt to be generated in the carcass ply6A. On the other hand, where the clearance d is too large or the distance h is too small, the flip-up to the carcass outer region Ko tends to be insufficient. Accordingly, the clearance d is preferably in the range of 1.0 to 4.0 times the thickness of the carcass cords (steel cords). The distance h is preferably in the range of 0.2 to 0.7 times the thickness H (FIG. 4) between the radially inner surface SL and the radially outer surface SU of the bead core5. In this respect, setting the clearance d and the distance h such that an inclination angle α of the outer inclined piece27from the tire axial line to not less than 45°, and further to not less than 60° is desirable in view of winding processes that are to follow.

Next, the winding means16comprises a lateral moving body29that may rotate uniformly with the former13and that is capable of performing relative lateral movements with respect to the former13in- and outside in the tire axial direction, and an annular ply winding ring30that is supported by the lateral moving body29. In the present embodiment, the ply winding ring30includes a first winding surface31A that inclines along the upper inclined surface SOa of the bead core5and a second winding surface31B that continues into an radially outer edge of the first winding surface31A and that projects inwardly in the tire axial direction by a short length. As illustrated inFIG. 6, through the lateral movement of the lateral moving body29, the ply winding ring30presses the outer inclined piece27inward in the tire axial direction and curves the outer inclined piece27towards the outside surface SO and the radially outer surface SU of the bead core5.

At this time, while the outer inclined piece27is compressed between the first winding surface31A and the upper inclined surface SOa, a radially inner edge of the first winding surface31A is located radially outward than the peak portion P3of the bead core5by distance h1. With this arrangement, the outer inclined piece27is allowed to smoothly curve between a compressed region La and the sandwiched region Ka so that occurrence of partially bent portions at the peak portions P2, P3are prevented. The distance h1is preferably 2.0 to 4.0 times the thickness of the carcass cords.

The second winding surface31B comprises a clearance g between the same and the bead core5, that is larger than the thickness of the carcass ply6A. Accordingly, the tip end portion27efurther on the tip end side than the compressed region La can be curved towards the radially outer surface SU of the bead core5without causing occurrence of partially bent portions at the peak portion P4. At this time, and angle β between the tip end portion27eand the radially outer surface SU of the bead core5is preferably reduced to be not more than 45°, and further to not more than 30° in view of shaping processes that are to follow. In this respect, the first and second winding surfaces31A,31B can also be formed as convex arc-like shapes or concave arc-like shapes, and the first and second winding surfaces31A,31B may alternatively be formed of a single curved surface.

As illustrated inFIGS. 6 and 7, the shaping means17comprise a pressing roller32that presses the tip end portion27etowards the radially outer surface SU of the bead core5in a curved condition of the outer inclined piece27. The pressing roller32is supported in a freely rotating (auto-rotating) manner around a roller center and in a revolving manner around a tire axial center.

In the present embodiment, the pressing roller32is pivotally supported at a rod end of a reciprocating means33such as a cylinder including the rod reciprocating in the radial direction in a freely rotating (auto-rotating) manner though a roller holder34. The reciprocating means33is supported to be relatively rotatable with respect to the lateral moving body29around the tire axial center through a bearing35or the like.

Here, the carcass ply6A on the former13, the bead core5, and the ply winding ring30can be rotated uniformly with the former13. These and the pressing roller32may relatively rotate around the tire axial center. Accordingly, by rotating and driving the former13, the pressing roller32can go around while pressing the tip end portion27etowards the radially outer surface SU of the bead core5. In other words, the tip end portion27ecan be deformed into a direction as to face along the radially outer surface SU over the entire periphery.

In this respect, as illustrated inFIG. 8(A), the shaping means17is preferably arranged in that a plurality of pressing rollers32is disposed at intervals in the circumferential direction. At this time, as conceptually shown inFIG. 8(B), the tip end portion27ecan be more effectively deformed by disposing the plurality of pressing rollers32in a positionally shifted manner in the tire axial direction.

In the present embodiment, for pressing and restricting the deformed tip end portion27etowards the radially outer surface SU of the bead core5, a band comprised by spirally winding the wrapping wire10(FIG. 8(B)) radially outside of the tip end portion27e. Winding of the wrapping wire10is performed together with the pressing of the tip end portion27etowards the bead core5through the pressing rollers32. It is accordingly possible to effectively and highly accurately wind the wrapping wire10without causing any slacking or irregularities in the wrapping wire10. In this respect, the pressing rollers32sequentially run on the wound wrapping wire10. Besides spirally winding the wrapping wire10, the band may alternatively be comprised by a winding tape of small width in which a plurality of wrapping wires10is coated with rubber by a single round in the circumferential direction.

By employing the molding device11, it is possible to wind both ends of the carcass ply6aaround the bead cores without forming a plastic-deformed bending poriton in which carcass cords are partially bent, and the carcass wound portion6bcan be easily, accurately and stably formed. It is accordingly possible to improve the productivity of tires of bead-wind structure and to restrict degradations in cord rigidity and cord strength accompanying the bending of the carcass cords.

Next, the method for molding a bead portion employing the molding device11includes

(1) a carcass tube forming step in which a carcass tube12is formed by cylindrically winding the carcass ply6A on an outer periphery of the former13,

(2) a setting step for the bead core5in which the bead core5is set radially outside of the carcass tube12, and

(3) a bead core supporting step for supporting the bead core5while sandwiching the carcass ply6A between the seating surface24and the bead core5through the expansion in diameter of the bead core supporter14. In this respect, the bead core supporting step includes a flip-up step of flipping the carcass outer region Ko up through the outer piece25of the bead core supporter14for deforming the carcass outer region Ko into an outer inclined piece27that is inclined and extended towards radially outside without including any partially bent portions.

The method for molding a bead portion further includes

(4) a curving step of pressing the outer inclined piece27inside in the tire axial direction by using a ply winding ring30for curving the same towards the outside surface SO and the radially outer surface SU of the bead core5, and

(5) a pressing step of pressing a tip end portion27eof the outer inclined piece27in the curved condition towards the radially outer surface SU of the bead core5by using the pressing roller32.

Through these steps, it is possible to wind both end portions of the carcass ply6A, that is, the cylindrical sub-portions12b, around the bead cores5in an easily, accurately and stably without the necessity of preliminarily bending the carcass cords.

While a particularly preferred embodiment of the present invention has been explained so far, the present invention is not limited to the illustrated embodiment alone but may be executed upon modifying the same into various forms, for instance, in which the former13is arranged as a former that is used in a green tire molding step of single-staged method.