JP2020019235A - Raw tire manufacturing method - Google Patents

Abstract

To suppress an occurrence of air reservoir and suppress a winding disturbance of a rubber strip, thereby increasing an accuracy of forming a bead apex rubber, when forming the bead apex rubber composed of a first rubber part and a second rubber part by a strip wind method.SOLUTION: A step S1b of forming a bead apex rubber 8 on a cylindrical carcass ply 6A on a tire axial direction inner side from a bead core 5 includes a first step S1b1 of spirally winding a first rubber strip G1 to form a first rubber part 8B, and a second step S1b2 of forming a second rubber part 8B by spirally winding a second rubber strip G2 on the first rubber part 8B. The first and second rubber strip G1 and G2 are respectively wound from inside to outside in the tire axial direction.SELECTED DRAWING: Figure 4

Description

  TECHNICAL FIELD The present invention relates to a method for producing a green tire in which bead apex rubber is formed by winding a rubber strip.

  2. Description of the Related Art Conventionally, a technique (strip wind method) of forming a tire constituent member using a narrow band-shaped rubber strip has been known.

  FIG. 8 of Patent Document 1 shows that a rubber strip is spirally wound on the outer peripheral surface of a cylindrical carcass ply formed on a molding former, whereby the bead apex rubber is turned sideways in the tire axial direction. It has been proposed to form it in a state.

  In this case, since the bead apex rubber is formed in a horizontal state, the rubber strip can be stably wound. However, at the time of shaping, it is necessary to raise the bead apex rubber in a horizontal state to a vertical state (a state of rising in the radial direction). However, at this time, the wound portion of the rubber strip that is located radially outward is more strongly pulled radially inward. As a result, winding irregularities occur, which tends to cause deformation of the bead apex rubber, thereby lowering the forming accuracy.

  This tendency becomes more remarkable as the bead apex rubber has a larger radial height.

  In addition, the bead apex rubber having a large height in the radial direction is formed of a radially inner first rubber portion made of hard rubber and a radially outer second rubber portion made of soft rubber from the viewpoint of rigidity balance and the like. Often done. When such a bead apex rubber is formed by a strip wind method, the first rubber portion and the second rubber portion are formed by winding separate rubber strips, and at this time, the first rubber portion and the second rubber portion are formed. Air accumulation tends to occur at the boundary with the part, and the tire quality tends to be impaired.

JP 2007-168241 A

  The present invention suppresses the generation of air pockets and suppresses the turbulence of winding of a rubber strip when forming a bead apex rubber composed of a hard first rubber portion and a soft second rubber portion by a strip wind method. An object of the present invention is to provide a method for producing a raw tire that can increase the precision of forming a bead apex rubber.

The present invention provides a first step of forming a cylindrical primary molded body including a carcass ply, a bead core, and a bead apex rubber on a molding former,
And a second step of expanding and shaping the primary molded body in a toroidal shape, comprising:
The first step includes, on a cylindrical carcass ply, a core setting step of setting a bead core, and an apex forming step of forming a bead apex rubber at a position on the tire axial direction inside of the bead core,
The apex forming step,
On the cylindrical carcass ply, a first step of forming a first rubber portion by spirally winding an unvulcanized first rubber strip having a high rubber hardness after vulcanization,
A second step of spirally winding an unvulcanized second rubber strip having a reduced rubber hardness after vulcanization on the first rubber part to form a second rubber part,
Moreover, the first and second rubber strips are respectively wound from the inside in the tire axial direction to the outside.

  In the raw tire manufacturing method according to the present invention, it is preferable that in the first step, the bead apex rubber is formed at a distance inward of the bead core in the tire axial direction.

  In the raw tire manufacturing method according to the present invention, it is preferable that the bead apex rubber formed in the first step is joined to a radially outer surface of the bead core by shaping in the second step.

  As described above, in the present invention, the apex forming step includes a first step and a second step. In the first step, a first rubber strip is spirally wound on a cylindrical carcass ply to form a hard first rubber portion. In the second step, the second rubber strip is spirally wound on the first rubber portion to form the second rubber portion on the soft side.

  Therefore, the bead apex rubber having a large height in the radial direction can be formed by the strip wind method while securing the rigidity balance.

  Here, when the bead apex rubber formed in the horizontal state is raised in the vertical state, the winding portion on the outer side in the radial direction is strongly pulled inward in the radial direction under strong tension. As a result, conventionally, the winding is disturbed, and the bead apex rubber is deformed.

  However, in the present invention, the first and second rubber strips are respectively wound from the inside in the tire axial direction to the outside.

  In this case, when rising in the vertical state, the winding start end (the inner end in the tire axial direction) which is most strongly pulled inward in the radial direction is sequentially superimposed on the winding portions of the second, third,. , Pressed against the carcass ply. As a result, the movement of the winding start end portion is restricted, and the winding disturbance of the rubber strip at the time of rising can be suppressed. In addition, from the viewpoint of adhesiveness, the first rubber strip on the hard side is inferior in adhesiveness to the second rubber strip on the soft side, so that winding disorder generally tends to occur. However, since the second rubber portion presses the first rubber portion against the carcass ply, the winding disturbance can be further suppressed from this point.

  In addition, since the winding directions of the first and second rubber strips are the same, it is possible to suppress the occurrence of air accumulation at the boundary between the first rubber portion and the second rubber portion.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the pneumatic tire formed using the raw tire manufacturing method of this invention. It is sectional drawing which shows a 1st process notionally. It is sectional drawing which shows a 2nd process notionally. (A) is a partial cross-sectional view conceptually showing a first step in an apex forming stage, and (B) is a partial cross-sectional view conceptually showing a second step.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a sectional view of a pneumatic tire 1 formed by using the raw tire manufacturing method of the present invention. As shown in FIG. 1, the pneumatic tire 1 includes a carcass 6 extending from the tread portion 2 to the bead core 5 of the bead portion 4 through the sidewall portion 3 and a bead apex rubber 8 extending radially outward from the bead core 5. Equipped.

  The carcass 6 is formed of one or more carcass plies 6A in which carcass cords are arranged at an angle of, for example, 75 to 90 ° with respect to the tire circumferential direction, in this example, one carcass ply 6A. The carcass ply 6A includes a toroidal ply body 6a extending between the bead cores 5, 5, and a ply turnover 6b connected to both ends thereof and turned around the bead core 5 from the inside in the tire axial direction to the outside.

  A belt layer 7 is disposed radially outside the carcass 6 and inside the tread portion 2. The belt layer 7 is formed of two or more belt plies 7A and 7B in this example, in which belt cords are arranged at an angle of, for example, 10 to 45 ° with respect to the tire circumferential direction. In the belt layer 7, the belt cords cross each other between the plies, thereby increasing the belt rigidity.

  The bead apex rubber 8 has a triangular cross section, and extends radially outward from the bead core 5 through between the ply body 6a and the ply turnup 6b.

  The bead apex rubber 8 includes a first rubber portion 8A and a second rubber portion 8B separated by a boundary line X. The boundary line X is inclined radially outward toward the inside in the tire axial direction. Further, the first rubber portion 8A is disposed radially inward of the boundary line X, and the second rubber portion 8B is disposed radially outward of the boundary line X.

  The first rubber portion 8A is formed of rubber having a higher rubber hardness than the second rubber portion 8B, and the second rubber portion 8B is formed of rubber having a lower rubber hardness than the first rubber portion 8A. In this manner, by forming the bead apex rubber 8 by the first rubber portion 8A and the second rubber portion 8B having different rubber hardness, the radial height of the bead apex rubber 8 can be increased while maintaining excellent rigidity balance. It is possible to improve the steering stability, durability and the like.

Next, a method of manufacturing a raw tire for the pneumatic tire 1 will be described.
The method for producing a green tire includes a first step S1 (shown in FIG. 2) and a second step S2 (shown in FIG. 3).

  As shown in FIG. 2, in the first step S <b> 1, a cylindrical primary molded body 10 including the carcass ply 6 </ b> A, the bead core 5, and the bead apex rubber 8 is formed on the molding former F.

  More specifically, in the first step S1, a core setting step S1a for setting the bead core 5 on the cylindrical carcass ply 6A, and the bead apex rubber 8 in a lateral direction Ka at a position inside the bead core 5 in the tire axial direction. Apex forming step S1b.

  The cylindrical carcass ply 6A is formed by winding the sheet-like carcass ply 6A on the forming former F (for example, by winding around one round). As the sheet-like carcass ply 6A, a composite sheet in which an inner liner rubber (not shown) is laminated on the inner surface thereof can be used. However, prior to winding the carcass ply 6A, a sheet-like inner liner rubber may be wound on the forming former F.

  As the forming former F, a former used in a so-called single-stage forming method is suitably adopted. The forming former F has a well-known structure including bead lock means (not shown) for supporting the bead core 5 and winding means (not shown) for winding the ply turn-up portion 6b outward in the radial direction.

  In the core setting step S1a, a pair of bead cores 5 inserted from both outer sides in the tire axial direction of the molding former F are moved to a predetermined set position P, and the bead cores 5 are set by operating a bead lock unit. This core setting step S1a can be performed prior to the apex forming step S1b, but is preferably performed after the apex forming step S1b.

Apex forming step S1b includes a first step S1b ₁ to form a first rubber portion 8A (shown in FIG. 4 (A)), the second step S1b ₂ to form a second rubber portion 8B (FIG. 4 (B) Shown).

As shown in FIG. 4 (A), the first step S 1 b _1, on the cylindrical carcass ply 6A, overlap winding a first rubber strip G1 unvulcanized first rubber portion 8A formed in a spiral shape . Thereby, the unvulcanized first rubber portion 8A is formed as a strip wound body 21 at a position on the inner side in the tire axial direction from the set position P.

  The first rubber strip G1 is spirally wound outward in the tire axial direction from the inner winding start end E1a in the tire axial direction to the outer winding end E1b in the tire axial direction.

  As shown in FIG. 4B, in the second step S1b2, the unvulcanized second rubber strip G2 for forming the second rubber portion 8B is formed on the first rubber portion 8A (strip wound body 21). Wrap spirally. Thus, the unvulcanized second rubber portion 8B is formed as the strip wound body 22.

  The second rubber strip G2 is spirally wound outward in the tire axial direction from the inner winding start end E2a in the tire axial direction to the outer winding end end E2b in the tire axial direction.

  The winding start end E2a is arranged on the inner side in the tire axial direction than the winding start end E1a. Therefore, the second rubber portion 8B (strip wound body 22) overlaps the carcass ply 6A in the area Yi inside the winding start end E1a in the tire axial direction, and is closer to the tire shaft than the winding start end E1a. In the region Yo on the outer side in the direction, it is superposed on the first rubber portion 8A (strip wound body 21).

  The cross-sectional shape and size of the strip wound bodies 21 and 22 are appropriately set according to the cross-sectional shape and size of the first rubber portion 8A and the second rubber portion 8B after vulcanization molding.

  The cross-sectional shape and size of the first and second rubber strips G1 and G2 are not particularly limited, and the cross-sectional shape and size of a conventional rubber strip used in a strip wind method can be suitably used.

  As shown in FIG. 4B, in the first step S1, the bead apex rubber 8 is formed at a distance L inward in the tire axial direction from the bead core 5 at the set position P. This distance L is preferably equal to or less than the radial height H of the bead core 5, and particularly preferably equal to or more than 0.6 times the height H. The side surface fo of the bead apex rubber 8 on the outer side in the tire axial direction is joined to the outer surface 5s of the bead core 5 in the radial direction. In this example, a case where the bead core 5 has a substantially rectangular cross section is shown. However, a hexagonal cross section may be used.

  As shown in FIG. 3, in the second step S2, shaping is performed by expanding the cylindrical primary molded body 10 into a toroidal shape. In the shaping, the inflated portion of the inflated primary molded body 10 and the tread ring 11 are integrally connected to form a green tire.

  The expansion of the primary molded body 10 is performed by expanding the carcass ply 6A between the bead cores 5 and 5 in a toroidal shape while bringing the bead cores 5 and 5 closer to each other. At this time, the bead apex rubber 8 in the horizontal state Ka rises to the vertical state Kb together with the carcass ply 6A, and the side surface fo of the bead apex rubber 8 is pressed against and joined to the radial outer surface 5s of the bead core 5.

  As shown in FIG. 4 (B), if the distance L is greater than the height H, a gap is formed between the bead apex rubber 8 and the bead core 5 at the time of joining, which causes air to accumulate. When the distance L is smaller than 0.6 times the height H, the bead apex rubber 8 is strongly rubbed against the bead core 5 at the time of rising, causing deformation of the bead apex rubber 8. From such a viewpoint, the upper limit of the distance L is more preferably not more than 0.8 times the height H, and the lower limit is more preferably not less than 0.6 times the height H.

In the green tire manufacturing method, apex formation step, to include a first step S 1 b ₁ and a second step S 1 b _2, radial height a large bead apex rubber 8, a strip wind method while maintaining the rigidity balance Can be formed.

  Further, the first and second rubber strips G1 and G2 are respectively wound from the inner side to the outer side in the tire axial direction. Therefore, in the first rubber portion 8A, the winding start end E1a is sequentially pressed against the winding portions of the second rubber strip G1, the second round, the third round,.... As a result, the movement on the winding start end E1a side is restrained, and the winding disturbance of the rubber strip G1 at the time of rising is suppressed.

  Similarly, in the second rubber portion 8B, the winding start end E2a is sequentially pressed against the winding portions of the second rubber strip G2 in the second, third,... As a result, the movement of the winding start end portion E2a side is restricted, and the winding disturbance of the rubber strip G2 at the time of rising is suppressed. In addition, from the viewpoint of adhesiveness, the first rubber strip G1 is inferior in adhesiveness to the second rubber strip G2, so that winding disorder tends to occur. However, since the winding start end E1a is located outside the winding start end E2a in the tire axial direction, and the second rubber portion 8B presses the first rubber portion 8A, the winding of the bead apex rubber 8 as a whole is disturbed. Can be further suppressed.

  In addition, since the winding directions of the first and second rubber strips G1 and G2 are the same, the occurrence of air pockets at the boundary between the first rubber portion 8A and the second rubber portion 8B can be suppressed low.

  As described above, particularly preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to the illustrated embodiments, and can be implemented in various forms.

5 Bead core 5s Outer surface 6A Carcass ply 8 Bead apex rubber 8A First rubber portion 8B Second rubber portion 10 Primary molded body F Molding former G1 First rubber strip G2 Second rubber strip L Distance S1 First step S1a Core set Step S1b Apex forming step S1b ₁ First step S1b ₂ Second step S2 Second step

Claims (3)

A first step of forming a cylindrical primary molded body including a carcass ply, a bead core, and a bead apex rubber on a molding former;
And a second step of expanding and shaping the primary molded body in a toroidal shape, comprising:
The first step includes, on a cylindrical carcass ply, a core setting step of setting a bead core, and an apex forming step of forming a bead apex rubber at a position on the tire axial direction inside of the bead core,
The apex forming step,
On the cylindrical carcass ply, a first step of forming a first rubber portion by spirally winding an unvulcanized first rubber strip having a high rubber hardness after vulcanization,
A second step of spirally winding an unvulcanized second rubber strip having a reduced rubber hardness after vulcanization on the first rubber part to form a second rubber part,
Moreover, the first and second rubber strips are each wound from the inner side to the outer side in the tire axial direction.   The raw tire manufacturing method according to claim 1, wherein in the first step, the bead apex rubber is formed at a distance inward of the bead core in the tire axial direction.   The raw tire manufacturing method according to claim 2, wherein the bead apex rubber formed in the first step is joined to a radially outer surface of the bead core by shaping in the second step.

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