JP7461828B2 - Tire building method - Google Patents

Description

The present invention relates to a tire molding method.

There is known a pneumatic tire in which a protrusion that protrudes outward in the tire width direction from the outer surface is formed on the tire side portion (e.g., buttress portion) as a traction element and/or design element. When manufacturing such a pneumatic tire, it is necessary to increase the rubber volume of the portion of the tire side portion that corresponds to the protrusion in the green tire used to manufacture the pneumatic tire.

Patent Document 1 discloses a method for manufacturing a pneumatic tire with a convex portion on the tire side, and according to this method, first, a green tire is formed by expanding the carcass band in the tire radial direction and attaching it to the inner diameter portion of the tread band. Next, an additional rubber member is wrapped around the tire side of the green tire to form an annular convex portion, thereby increasing the rubber volume of the part of the pneumatic tire that corresponds to the convex portion, and the green tire is vulcanized to produce a pneumatic tire with a convex portion on the tire side.

JP 2009-039961 A

According to Patent Document 1, it is necessary to wrap an additional rubber member around the tire side of the molded green tire, but because the tire side is curved, it is not easy to attach the additional rubber member so that it follows the curve.

The objective of the present invention is to provide a tire molding method that can easily mold green tires for molding pneumatic tires with protruding portions on the tire side portions.

The present invention relates to
A side rubber constituting a tire side portion in a vulcanized pneumatic tire is prepared by dividing it into a first rubber and a second rubber,
The first rubber is wound around a forming drum;
The second rubber is wound around the molding drum so as to overlap the ends of the first rubber wound around the molding drum in the central axial direction of the molding drum, thereby forming a cylindrical carcass band;
The carcass band is expanded in a tire radial direction and joined to an inner peripheral surface of a tread band disposed on an outer peripheral side to form a green tire.
The present invention provides a tire molding method in which, in the green tire, a laminated portion in which the first rubber and the second rubber are laminated increases the rubber volume of a portion corresponding to a convex portion protruding outward in the tire width direction from the outer surface of the tire side portion in the pneumatic tire after vulcanization molding.

According to the present invention, the thickness of the side rubber can be easily increased at the laminated portion by winding the second rubber around the molding drum while overlapping the ends of the first rubber in the central axial direction of the molding drum. Since the first rubber and the second rubber are wound around the molding drum, it is easier to wind the additional rubber member compared to winding it along the curvature of the green tire, and a green tire with increased rubber volume in the tire side portion can be easily molded.

In addition, when the side rubber is extruded as a single unit, if the rubber volume is large, the amount of rubber extruded from the nozzle tends to vary, and the widthwise dimension of the side rubber tends to vary. Variations in the widthwise dimension of the side rubber lead to increased mass imbalance in the circumferential direction of the manufactured pneumatic tire.

In contrast, in the present invention, the side rubber is divided into a first rubber and a second rubber, thereby reducing the rubber volume of each. As a result, compared to when the side rubber is extruded as a single unit, the first rubber and the second rubber can be extruded stably from the mouthpiece, and the variation in the width direction dimension can be reduced. Therefore, in a pneumatic tire manufactured using the first rubber and the second rubber, the variation in the mass of the first rubber and the second rubber in the tire circumferential direction is suppressed, and the mass imbalance in the circumferential direction can be reduced.

In addition, when forming the side rubber integrally, if an attempt is made to reduce variation in the amount of rubber extruded by reducing the extrusion speed, productivity will deteriorate. In contrast, according to the present invention, the rubber volume of the first rubber and the second rubber is smaller than that of the side rubber with which they are integrally formed, so that the first rubber and the second rubber can be easily extruded stably from the nozzle without reducing the extrusion speed. This prevents deterioration in productivity.

Furthermore, for example, by adjusting the amount of overlap between the first rubber and the second rubber in the central axial direction of the molding drum, the size of the laminated portion can be adjusted and the length of the side rubber in the tire radial direction can be adjusted.

Furthermore, by forming the first joint portion that joins the start and end ends of the first rubber when it is wound around the molding drum, and the second joint portion that joins the start and end ends of the second rubber when it is wound around the molding drum, for example, at different phases in the circumferential direction of the molding drum, it is possible to distribute the joint portions, which are prone to increasing in mass, in the circumferential direction of the tire. This makes it possible to further reduce mass imbalance in the circumferential direction.

The first rubber has a first thickness decreasing portion at an end portion overlapping the second rubber in the axial direction of the molding drum, the thickness of which gradually decreases toward the end portion,
The second rubber may have a second tapered portion at an end portion overlapping the first rubber in the axial direction of the molding drum, the thickness of which gradually decreases toward the end portion.

According to this configuration, the first rubber and the second rubber have a first gradually tapering thickness portion and a second gradually tapering thickness portion, respectively, at the ends on the overlapping sides. This prevents a sudden increase in thickness in the laminated portion, thereby preventing air from entering due to the sudden change in thickness.

The first and second tapered portions do not have to overlap in position in the axial direction of the forming drum.

This configuration makes it possible to efficiently increase the rubber volume in the laminated section while suppressing sudden changes in thickness.

In the axial direction of the forming drum, the length of the first and second tapered portions may be 30% or more and 70% or less of the length of the laminated portion.

According to this configuration, the first thickness increasing/decreasing portion and the second thickness increasing/decreasing portion can be formed long, and the rubber volume can be increased while suppressing abrupt changes in thickness. If the length of the first thickness decreasing portion and/or the second thickness decreasing portion is shorter than 30% of the length of the laminated portion, the thickness is likely to change abruptly in the first thickness decreasing portion and/or the second thickness decreasing portion, which is likely to lead to air filling problems in a pneumatic tire formed by vulcanization molding. Furthermore, if the length of the first thickness decreasing portion and/or the second thickness decreasing portion is longer than 70% of the length of the laminated portion, the area where the first thickness decreasing portion and the second thickness decreasing portion overlap in the central axial direction of the molding drum becomes wider, making it difficult to efficiently increase the thickness in the laminated portion.

According to the present invention, it is possible to easily mold a green tire for molding a pneumatic tire with protrusions on the tire side portions.

FIG. 4 is a diagram conceptually showing one of the carcass band forming steps according to one embodiment of the present invention. FIG. 2 is a diagram conceptually showing a step of winding a first rubber band in comparison with FIG. 1 . FIG. 3 is a diagram conceptually showing a step of winding a second rubber band in addition to the step shown in FIG. 2 . A conceptual diagram showing the process of joining the carcass band to the tread band to form a green tire. FIG. 2 is a diagram showing a pneumatic tire manufactured by vulcanizing a green tire. FIG. 13 is a diagram showing a green tire according to a modified example. FIG. 11 is a diagram showing a carcass band according to a modified example. FIG. 13 is a diagram showing a carcass band according to a further modified example.

Embodiments of the present invention will now be described with reference to the accompanying drawings. Note that the following description is essentially merely illustrative and is not intended to limit the present invention, its applications, or its uses. The drawings are schematic, and the ratios of dimensions, etc., differ from the actual ones.

Figures 1 to 3 are diagrams conceptually illustrating the carcass band molding process in the tire molding direction according to one embodiment of the present invention. Referring to Figure 1, first, an inner liner 11 is cylindrically wrapped around the outer peripheral surface of a cylindrical first molding drum D1. In the following description, the central axis direction of the first molding drum D1 is referred to as the drum axis direction AD, and the radial direction is referred to as the drum radial direction RD. Also, in Figure 1 and other figures, the first molding drum D1, the second molding drum D2 (see Figure 4), the carcass band 30 (see Figures 3 and 4), the tread band 40 (see Figure 4), the green tire 50 (see Figure 4), and the pneumatic tire 60 (see Figure 5) are shown only on one radial side.

The carcass ply 12 is wrapped cylindrically around the outer circumferential surface of the inner liner 11. In this embodiment, the carcass ply 12 is a single piece, and is made up of multiple carcass cords arranged in parallel and covered with topping rubber.

A pair of annular beads 13 are attached to the outer peripheral surface of the carcass ply 12. The pair of beads 13 are located on both sides of the outer peripheral surface of the carcass ply 12, spaced apart in the drum axial direction AD. The bead 13 includes a bead core 14 made of a rubber-coated bundle of steel wires or the like, and a bead filler 15 made of hard rubber and having a roughly triangular cross section, attached to the outer peripheral surface of the bead core 14.

Both sides of the carcass ply 12 that are located outside the pair of beads 13 in the drum axial direction AD are folded inward around the pair of beads 13 to form folded-back portions 12a.

Next, as shown in Figures 2 and 3, a pair of side rubbers 20 constituting the tire side portion 62 (see Figure 5) of the pneumatic tire 60 are further wrapped cylindrically around both sides of the outer peripheral surface of the carcass ply 12 in the drum axial direction AD to form the carcass band 30. In this embodiment, the side rubber 20 is divided into a first rubber 21 located on the inside and a second rubber 22 located on the outside in the drum axial direction AD.

As shown in FIG. 2, first, a pair of first rubbers 21 are wrapped cylindrically around the outer peripheral surface of the carcass ply 12. Next, as shown in FIG. 3, a pair of second rubbers 22 are wrapped cylindrically around the outer peripheral surface of the carcass ply 12 so that they are shifted outward in the drum axis direction AD relative to the first rubbers 21 and their positions in the drum axis direction AD partially overlap. Specifically, the inner end 28 of the second rubber 22 located on the inside in the drum axis direction AD is wrapped around the outer end 27 of the first rubber 21 located on the outside in the drum axis direction AD so as to cover it from the radial outside.

As shown in FIG. 2, the first rubber 21 is formed by integrally extruding the underbelt rubber 23 and the first sidewall rubber 24 using an extrusion molding machine (not shown) to have a generally trapezoidal cross section. In the drum axial direction AD, the underbelt rubber 23 is located on the inside and the first sidewall rubber 24 is located on the outside.

In the drum axis direction AD, the first rubber 21 has, at the end on the side overlapping with the second rubber 22, i.e., the outer end 27, a first gradually decreasing thickness portion 27a whose thickness in the drum radial direction RD gradually decreases toward the outside in the drum axis direction AD, and a first constant thickness portion 27b that is continuous with the first gradually decreasing thickness portion 27a on the inside in the drum axis direction AD and has a substantially constant thickness T1. The first gradually decreasing thickness portion 27a and the first constant thickness portion 27b are formed in the first sidewall rubber 24.

As shown in FIG. 3, the second rubber 22 is formed by integrally extruding the second sidewall rubber 25 and the rim strip rubber 26 using an extrusion molding machine (not shown) to have a generally trapezoidal cross section. In the drum axial direction AD, the second sidewall rubber 25 is located on the inside and the rim strip rubber 26 is located on the outside. The second sidewall rubber 25 is made of the same rubber material as the first sidewall rubber 24.

In the drum axis direction AD, the second rubber 22 has, at the end on the side overlapping with the first rubber 21, i.e., the inner end 28, a second gradually decreasing thickness portion 28a whose thickness in the drum radial direction RD gradually decreases toward the inside of the drum axis direction AD, and a second constant thickness portion 28b that is continuous with the second gradually decreasing thickness portion 28a on the outside of the drum axis direction AD and has a substantially constant thickness T2. The second gradually decreasing thickness portion 28a and the second constant thickness portion 28b are formed in the second sidewall rubber 25.

As shown in the enlarged view of FIG. 3, in this embodiment, the second rubber 22 is wrapped around such that the second tapered portion 28a does not overlap the first tapered portion 27a in the drum axial direction AD. In the laminated portion 20a in which the first rubber 21 and the second rubber 22 are laminated in the drum radial direction RD, the first tapered portion 27a is located on the outside and the second tapered portion 28a is located on the inside in the drum axial direction AD. In other words, the length L0 of the laminated portion 20a in the drum axial direction AD corresponds to the length from the outer end point P1 of the first tapered portion 27a to the inner end point P2 of the second tapered portion 28a in the drum axial direction AD.

The thickness T0 of the laminated portion 20a in the drum radial direction RD corresponds to the sum of the thickness T1 of the first constant thickness portion 27b and the thickness T2 of the second constant thickness portion 28b.

That is, by appropriately adjusting the positions of the first and second tapered portions 27a and 28a in the drum axial direction AD, the laminated portion 20a can be adjusted to the desired length L0, and the side rubber 20 can be adjusted to the desired length L3. In addition, by appropriately adjusting the thickness T1 of the first constant thickness portion 27b and the thickness T2 of the second constant thickness portion 28b, the thickness T0 of the laminated portion 20a can be adjusted to the desired thickness.

The first and second tapered portions 27a and 28a are formed so that their lengths L1 and L2 in the drum axial direction AD are 30% to 70% of the length L0 of the laminated portion 20a.

In this embodiment, the first and second tapered portions 27a and 28a are configured to be continuous in the drum axial direction AD. That is, the thickness T0 of the laminated portion 20a is the thickest at position P3 where the first and second tapered portions 27a and 28a are continuous in the drum axial direction AD, and the thickness T0 gradually decreases as the laminated portion 20a moves away from position P3 to both sides in the drum axial direction AD. Thus, the laminated portion 20a is formed to protrude outward in a triangular shape in the drum radial direction RD.

In addition, in this embodiment, the first and second tapered portions 27a and 28a are formed so that their lengths L1 and L2 in the drum axial direction AD are approximately equal, and their thicknesses T1 and T2 in the drum radial direction RD are approximately equal. This allows the laminated portion 20a to be inclined at approximately the same angle inward in the drum radial direction RD from the center of position P3 toward both sides of the drum axial direction AD, preventing a steep angle on either side. In addition, because the thicknesses T1 and T2 are approximately equal, it is easy to prevent either the first rubber 21 or the second rubber 22 from becoming excessively thick, making it easy to extrude.

In this embodiment, the first rubber 21 and the second rubber 22 are formed so that their lengths L4 and L5 in the drum axial direction AD are approximately the same. This prevents one of the first rubber 21 and the second rubber 22 from becoming excessively large, making it easy to form both the first rubber 21 and the second rubber 22 by extrusion molding. The lengths L4 and L5 of the first rubber 21 and the second rubber 22 respectively refer to the width direction dimensions of the belt-shaped member before it is wound around the molding drum D1. It is preferable that the length L4 of the first rubber 21 and the length L5 of the second rubber 22 are each set to 30% to 70% of the total length of L4 and L5. If one of the lengths L4 and L5 is less than 30% of the total length (in this case, the other exceeds 70%), then when considering the required amount of underbelt rubber 23 or rim strip rubber 26 required in the first rubber 21 and second rubber 22, the amount of first sidewall rubber 24 in the first rubber 21 or the amount of second sidewall rubber 25 in the second rubber 22 will be insufficient.

Next, as shown in FIG. 4, the carcass band 30 is transferred to the second molding drum D2, and the tread band 40 is placed concentrically around the carcass band 30 on the outer periphery of the second molding drum D2. The tread band 40 is formed by winding a first belt 41, a second belt 42, and a tread rubber 43 in that order. On the second molding drum D2, the portion of the carcass band 30 located between a pair of beads 13 is bulged outward in the radial direction and joined to the inner periphery of the tread band 40, forming a green tire 50.

Next, the green tire 50 is vulcanized and molded in a tire vulcanization mold (not shown) to mold a pneumatic tire 60 (see FIG. 5).

As shown in FIG. 5, the pneumatic tire 60 has a tread portion 61, a tire side portion 62 extending radially inward from the outer end of the tread portion 61 in the tire width direction, and a bead portion 63 provided at the inner end of the tire side portion 62 in the tire radial direction.

The tire side portion 62 is formed by vulcanizing the side rubber 20 at the portion located on the tire width direction outer side of the carcass ply 12 and the bead 13. The tire side portion 62 has a plurality of protrusions 62b (only one is shown in the enlarged view of FIG. 5) intermittently molded in the tire circumferential direction, protruding from the outer surface 62a to the tire radial direction outer side. The protrusions 62b are formed at radial positions corresponding to the laminated portion 20a (see FIG. 4) in the green tire 50.

The tire building method according to this embodiment provides the following advantages:

(1) The thickness of the side rubber 20 can be easily increased at the laminated portion 20a by winding the second rubber 22 around the first molding drum D1 while overlapping the inner end 28 with the outer end 27 of the first rubber 21 in the drum axial direction AD. Since the first rubber 21 and the second rubber 22 are wound around the first molding drum D1, it is easier to wind the additional rubber member compared to winding it along the curvature of the green tire 50, and it is easy to mold a green tire 50 with increased rubber volume in the tire side portion 52.

In addition, when the side rubber 20 is extruded as a single unit, if the rubber volume is large, the amount of rubber extruded from the nozzle is likely to vary, and the widthwise dimension of the side rubber 20 is likely to vary. Variations in the widthwise dimension of the side rubber 20 lead to an increase in the mass imbalance in the circumferential direction of the manufactured pneumatic tire 60.

In contrast, in the above embodiment, the side rubber 20 is divided into the first rubber 21 and the second rubber 22, so that the rubber volume of each is reduced. As a result, compared to the case where the side rubber 20 is extruded as a single unit, the first rubber 21 and the second rubber 22 can be extruded stably from the nozzle more easily, and the variation in the width direction dimension can be reduced. Therefore, in the pneumatic tire 60 manufactured using the first rubber 21 and the second rubber 22, the variation in the mass of the first rubber 21 and the second rubber 22 in the tire circumferential direction is suppressed, so that the mass imbalance in the circumferential direction can be reduced.

In addition, when the side rubber 20 is formed integrally, if an attempt is made to reduce variation in the amount of rubber extruded by reducing the extrusion speed, productivity will deteriorate. In contrast, in the above embodiment, the rubber volume of the first rubber 21 and the second rubber 22 is smaller than that of the side rubber with which they are formed integrally, so that the first rubber 21 and the second rubber 22 can be easily extruded stably from the nozzle without reducing the extrusion speed. This prevents deterioration in productivity.

Furthermore, for example, by adjusting the amount of overlap between the first rubber 21 and the second rubber 22 in the drum axial direction AD, the size of the laminated portion 20a can be adjusted and the length of the side rubber 20 in the tire radial direction can be adjusted.

Furthermore, by forming the first joint portion that joins the start and end of the application of the first rubber 21 when it is wound around the first molding drum D1, and the second joint portion that joins the start and end of the application of the second rubber 22 when it is wound around the first molding drum D1, for example, at different phases in the circumferential direction of the first molding drum D1, it is possible to disperse the joint portions, which are prone to increasing in mass, in the circumferential direction of the tire. This makes it possible to further reduce the mass imbalance in the circumferential direction.

(2) The first rubber 21 and the second rubber 22 have a first gradually tapering thickness portion 27a and a second gradually tapering thickness portion 28a, respectively, at the ends on the overlapping sides. This prevents a sudden increase in thickness in the laminated portion 20a, thereby preventing air from entering due to the sudden change in thickness.

(3) The first thickness tapering portion 27a and the second thickness tapering portion 28a do not overlap in position in the drum axial direction AD, so that the rubber volume can be efficiently increased while suppressing abrupt changes in thickness in the laminated portion 20a.

(4) In the drum axial direction AD, the lengths L1, L2 of the first and second tapered portions 27a, 28a are 30% to 70% of the length L0 of the laminated portion 20a, so that the first and second tapered portions 27a, 28a can be formed long, thereby further increasing the rubber volume while suppressing sudden changes in thickness.

If the length L1, L2 of the first and/or second tapered portions 27a, 28a is shorter than 30% of the length L0 of the laminated portion 20a, the thickness of the first and/or second tapered portions 27a, 28a is likely to change abruptly, leading to air-filling problems in a vulcanized pneumatic tire. If the length of the first and/or second tapered portions 27a, 28a is longer than 70% of the length L0 of the laminated portion 20a, the area where the first and second tapered portions 27a, 28a overlap in the drum axial direction AD becomes wider, making it difficult to efficiently increase the thickness of the laminated portion 20a.

In the above embodiment, the inner end 28 of the second rubber 22 is laminated on the outer end 27 of the first rubber 21 from the outside in the drum radial direction RD, but this is not limited to the above. As shown in FIG. 6, the first rubber 21 and the second rubber 22 may be wound around the first molding drum D1 so that the outer end 27 of the first rubber 21 is laminated on the inner end 28 of the second rubber 22 from the outside in the drum radial direction RD. When a stitcher (not shown) is applied to the carcass band 30 from the inside to the outside in the drum axial direction AD, it is easier to discharge the air between the first rubber 21 and the second rubber 22 by winding the first rubber 21 around the first molding drum D1 and then winding the second rubber 22. On the other hand, if the first rubber 21 is wound around the first molding drum D1 after the second rubber 22 is wound around it, the inner end 28 of the second rubber 22 is covered by the first rubber 21 from the inside in the drum axial direction AD and the outside in the drum radial direction RD, so air present around the inner end 28 is less likely to be discharged. Therefore, when stitching the carcass band 30, it is preferable to wind the second rubber 22 around the first molding drum D1 after winding the first rubber 21 around it, as shown in FIG. 3.

In the above embodiment, the first and second tapered portions 27a and 28a are positioned consecutively in the drum axial direction AD, but this is not limiting. As shown in FIG. 7, the first and second rubbers 21 and 22 may be wound around the first molding drum D1 so that the first and second tapered portions 27a and 28a are spaced apart in the drum axial direction AD. In this case, the length L11 of the laminated portion 20a and the length L31 of the side rubber 20 are longer than the length L0 of the laminated portion 20a and the length L3 of the side rubber 20 in the above embodiment.

In the above embodiment, the first and second tapered portions 27a and 28a are wound around the first molding drum D1 so that their positions in the drum axial direction AD do not overlap, but this is not limiting. As shown in FIG. 8, the first rubber 21 and the second rubber 22 may be wound around the first molding drum D1 so that the first and second tapered portions 27a and 28a overlap in their positions in the drum axial direction AD. In this case, the length L12 of the laminated portion 20a and the length L32 of the side rubber 20 are shorter than the length L0 of the laminated portion 20a and the length L3 of the side rubber 20 in the above embodiment.

In the above embodiment, the side rubber 20 is formed using the first rubber 21 and the second rubber 22, but the side rubber may be formed by selecting and combining multiple rubber members from three or more types. By combining the lengths of the selected rubber members in the drum axis direction AD and the thicknesses of the tapered portions in various combinations, side rubbers of various shapes can be formed. This makes it unnecessary to provide dedicated nozzles for extrusion molding each side rubber.

In the above embodiment, the first rubber 21 and the second rubber 22 are wound around the folded portion 12a of the carcass ply 12 from the outside in the drum radial direction RD, but this is not limited to the above. The present invention may also be applied to a case where the first rubber 21 and the second rubber 22 are wound directly around the outer circumferential surface of the first molding drum D1 to form the side rubber 20, and the carcass ply is wound around the outer circumferential surface of the side rubber 20.

REFERENCE SIGNS LIST 11 Inner liner 12 Carcass ply 13 Bead 20 Side rubber 20a Laminated portion 21 First rubber 22 Second rubber 27 Outer end portion 27a First tapered portion 27b First constant thickness portion 28 Inner end portion 28a Second tapered portion 28b Second constant thickness portion 30 Carcass band 40 Tread band 50 Green tire 60 Pneumatic tire 62 Tire side portion 62b Convex portion D1 First molding drum D2 Second molding drum

Claims (4)

A side rubber constituting a tire side portion in a vulcanized pneumatic tire is prepared by dividing it into a first rubber and a second rubber,
The first rubber is wound around a forming drum;
The second rubber is wound around the molding drum so as to overlap the ends of the first rubber wound around the molding drum in the central axial direction of the molding drum, thereby forming a cylindrical carcass band;
The carcass band is expanded in a tire radial direction and joined to an inner peripheral surface of a tread band disposed on an outer peripheral side to form a green tire.
a laminated portion in which the first rubber and the second rubber are laminated in the green tire, thereby increasing a rubber volume of a portion corresponding to a convex portion protruding outward in the tire width direction from an outer surface of the tire side portion in the pneumatic tire after vulcanization molding. The first rubber has a first thickness decreasing portion at an end portion overlapping the second rubber in the axial direction of the molding drum, the thickness of which gradually decreases toward the end portion,
The second rubber has a second thickness decreasing portion at an end portion overlapping the first rubber in the axial direction of the molding drum, the thickness of which gradually decreases toward the end portion.
2. The tire building method of claim 1. The first thickness decreasing portion and the second thickness decreasing portion do not overlap in position in the axial direction of the forming drum.
3. A tire building method according to claim 2. In the axial direction of the forming drum, the length of the first thickness tapering portion and the second thickness tapering portion is 30% or more and 70% or less of the length of the laminated portion.
3. A tire building method according to claim 2.

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