JP2007098907A - Mold for tire and method for producing tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold which can be suitably used for producing a tire having excellent quality. <P>SOLUTION: A cavity surface 16 of a segment of the mold is equipped with a lot of projection parts 16 and a lot of recessed parts. The projection parts 16 are equipped with main parts 20 and cores 22. The cores 22 are embedded in the main parts 20. The cores 22 are extended from one side recessed part 18a down to the other side recessed part 18b. The core 22 is composed of a column-shaped body 24 and a projection 26 projecting from the body 24. The projection 26 is engaged with the main part 20. The core 22 is prevented from being pulled off from the body by the engagement. There is a small clearance between the main part 20 and the core 22. Air in one recessed part 18a is moved to the other recessed part 18b through the clearance between the main part 20 and the core 22. In vulcanization process, the air is furthermore exhausted from the mold through a divided surface or a bent hole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mold used in a tire molding / vulcanizing process.

  In the tire vulcanization process, a mold is used. Molds are roughly classified into split molds and two-piece molds. In the vulcanization process, a preformed green tire is put into a mold. The green tire is heated while being pressurized in a cavity formed by a mold and a bladder. The rubber composition of the green tire flows in the cavity by pressurization and heating. The rubber causes a crosslinking reaction by heating, and a tire is obtained. If air remains between the cavity surface of the mold and the green tire during pressurization, a bear is formed on the surface of the tire. Bears reduce tire quality.

  The mold is provided with a vent hole. The vent hole communicates the cavity and the outside air. Air existing between the green tire and the cavity surface is discharged to the outside air through the vent hole. This discharge prevents bears. After the air is discharged, some rubber composition flows into the vent hole. Spew is formed by this rubber composition. The spew is trimmed. Even when trimming is not performed, the spew on the tread surface is worn out in the early stages of tire use.

  The split mold includes an arc-shaped tread segment. A ring-shaped cavity surface is formed by arranging a large number of tread segments. A boundary between a tread segment and an adjacent tread segment is referred to as a “dividing plane”. Air is discharged not only through the vent hole but also through this dividing surface. This discharge prevents bears.

The tire has a groove on its surface. This groove is formed by a convex portion on the cavity surface. The cavity surface includes a concave portion as well as the convex portion. A block is formed in the tire by the recess. In the vulcanization process, the air in the recesses needs to move to the vent hole or the dividing surface and be discharged. From the viewpoint of promoting movement, a through hole is formed in the convex portion. This through hole is referred to as a “cross vent hole”. The cross vent hole communicates one recess with another recess. The air in the recess far from the vent hole moves to the recess close to the vent hole through the cross vent hole, and further moves to the vent hole and is discharged. The air in the concave portion far from the dividing surface moves to the concave portion close to the dividing surface through the cross vent hole, and further moves to the dividing surface and is discharged. A mold having a cross vent hole is disclosed in Japanese Patent Application Laid-Open No. 2004-181664.
JP 2004-181664 A

  In the vulcanization process, the rubber composition also flows into the cross vent hole. The rubber composition is crosslinked to form a spew. The spew goes from one block to the other. Upon demolding, the spew is pulled and breaks. The spew remains in the tire together with one or both blocks. Since this spew is in the groove, it cannot be trimmed. Moreover, it does not wear out in the initial stage of use of the tire. This spew adversely affects the appearance of the tire.

  At the time of mold removal, if the spew breaks at two or more locations, the spew may remain in the cross vent hole. By remaining, the cross vent hole is closed. Air cannot move through this cross vent hole. The remaining spew causes a bear.

  At the time of demolding, if the spew breaks at two or more locations, the spew may fall off the tire and remain in the mold. When a new tire is vulcanized and molded by this mold, spew may adhere to the tire surface. This spew is a foreign object for the tire. Spew reduces tire quality.

  When the mold is used repeatedly, residue of the rubber composition gradually accumulates in the cross vent hole, and communication between the cavity and the outside air is hindered. The accumulation of residue causes the generation of bears. From the viewpoint of reducing defects, the mold is cleaned when debris is accumulated in the vent hole. Since the inner diameter of the cross vent hole is small, cleaning requires labor. When cleaning, the convex part adjacent to the convex part provided with the cross vent hole becomes an obstacle to cleaning. Cleaning adversely affects tire productivity.

  An object of the present invention is to provide a mold from which a tire having excellent quality can be obtained. Another object of the present invention is to provide a tire manufacturing method excellent in productivity.

  The tire mold according to the present invention includes a large number of convex portions and a large number of concave portions on the cavity surface. The convex portion includes a main portion and a core embedded in the main portion. The core extends from one of the concave portions located on both sides of the convex portion to the other.

  Preferably, the material of the convex portion and the material of the core are different. Preferably, the core includes two or more members stacked on each other. Preferably, the core includes an engaging portion. When the engaging portion engages with the main portion, the core is prevented from being detached from the main portion.

The tire manufacturing method according to the present invention includes:
The cavity surface has a large number of convex portions and a large number of concave portions. The convex portion includes a main portion and a core embedded in the main portion, and both sides of the core are located with the convex portion interposed therebetween. The step of putting the green tire into the mold that extends from one of the recesses to the other and the rubber composition of the green tire flows by pressurization and heating in the mold, and between the green tire and the cavity surface A step of moving air through a gap between the main portion and the core.

  In this mold, air moves through a minute gap between the main part and the core. In this mold, air hardly remains. In this mold, there is no spew due to the cross vent hole. Therefore, the tire obtained with this mold is excellent in appearance. Moreover, the spew does not adhere to the tire as a foreign object. Furthermore, the cleaning operation is easy with this mold.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a plan view showing a part of a tire mold 2 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view taken along the line II-II in FIG. The mold 2 includes a large number of tread segments 4, a pair of upper and lower side plates 6, and a pair of upper and lower bead rings 8. The planar shape of the segment 4 is substantially arcuate. A large number of segments 4 are connected in a ring shape. The number of segments 4 is usually 3 or more and 20 or less. The side plate 6 and the bead ring 8 are substantially ring-shaped. This mold 2 is a so-called “split mold”.

  FIG. 3 is a perspective view showing the segment 4 of the mold 2 of FIG. The segment 4 includes a cavity surface 10, a back surface 12, and a pair of split surfaces 14.

  FIG. 4 is an enlarged view showing a part of the cavity surface 10 of the segment 4 of FIG. The cavity surface 10 includes a large number of convex portions 16 and a large number of concave portions 18. The convex portion 16 has a streak shape. The convex portion 16 corresponds to a tread groove of the tire. By this convex portion 16, a tread pattern is formed on the tire.

  FIG. 5 is a cross-sectional view taken along line VV in FIG. As shown in FIG. 5, the convex portion 16 includes a main portion 20 and a core 22. The core 22 is embedded in the main part 20. The core 22 penetrates the main part 20. Both ends of the core 22 are exposed on the surface of the main portion 20. The core 22 extends from one recess 18a to the other recess 18b. The core 22 is solid. The core 22 exists only in the convex part 16 and does not reach any part other than the convex part 16.

  FIG. 6 is a perspective view showing the core 22 of FIG. The core 22 includes a cylindrical main body 24 and a protrusion 26 protruding from the main body 24. The protrusion 26 is engaged with the main portion 20. This engagement prevents the core 22 from being detached from the main portion 20. The protrusion 26 is an engaging portion referred to in the present invention. The shape of the core 22 may be a truncated cone, a prism, a truncated pyramid, or the like.

  In the production of this segment 4, the core 22 is inserted into the mold. The core 22 is fitted into the groove of the mold. This groove corresponds to the convex portion 16 of the segment 4. Next, molten metal (typically an aluminum alloy) is poured into the mold. This molten metal is solidified to obtain a segment 4. In this segment 4, the core 22 is embedded in the convex portion 16 by casting. In FIG. 5, what is indicated by a two-dot chain line is the core 22 immediately after casting. A portion of the core 22 that protrudes from the main portion 20 is removed by grinding. Due to the shrinkage of the main portion 20 and the core 22 during solidification and cooling, a minute gap is generated between the main portion 20 and the core 22.

  The melting point of the metal material of the core 22 is preferably higher than the melting point of the metal material of the segment 4 from the viewpoint that the molten metal does not melt even if it is poured. Preferably, the difference between the melting points of the two is 100 ° C. or higher. When the segment 4 is made of an aluminum alloy, a suitable material for the core 22 is steel. Specifically, the core 22 is preferably made of carbon steel or alloy steel. From the viewpoint of corrosion resistance, the core 22 is particularly preferably made of stainless steel.

  In the tire manufacturing method using the mold 2, first, a green tire is obtained by a preforming process. Next, the green tire is put into the mold 2 in a state where the mold 2 is open and the bladder is contracted. At this stage, the rubber composition of the green tire is in an uncrosslinked state. Next, the mold 2 is tightened and the bladder expands. The green tire is pressed against the cavity surface 10 of the mold 2 by a bladder and pressurized. The green tire G in this state is shown in FIG. At the same time, the green tire G is heated. The rubber composition flows by pressurization and heating. The rubber causes a crosslinking reaction by heating, and a tire is obtained. The process in which the green tire G is pressurized and heated is referred to as a vulcanization process.

  As is apparent from FIG. 4, the one recess 18 a is surrounded by the protrusion 16. The other recess 18 b reaches the dividing surface 14. In the vulcanization process, the air in one recess 18 a moves to the other recess 18 b through the gap between the main portion 20 and the core 22. The air is further discharged from the mold 2 along the dividing surface 14. This discharge prevents bears. Air may be exhausted through the vent hole.

  Since the gap between the main portion 20 and the core 22 is very small, the rubber composition does not flow into this gap. In this mold 2, spew due to this gap hardly occurs. The tire obtained with this mold 2 is excellent in appearance. Since no spew occurs, the gap is not blocked. Furthermore, there is no harmful effect caused by the remaining spewed spew. This mold 2 is easier to clean than a conventional mold having a cross vent hole.

  From the viewpoint of air discharge, the width of the gap is preferably 0.001 mm or more, and more preferably 0.002 mm or more. From the viewpoint of the appearance of the tire, the width of the gap is preferably 0.10 mm or less, and more preferably 0.08 mm or less.

  The surface of the core 22 is preferably subjected to uneven processing. In the core 22 subjected to the uneven processing, a gap with the main portion 20 is easily secured. A typical uneven process is knurling. In the concavo-convex processing, the height difference between the concave portion and the convex portion is preferably 0.001 mm or more, and more preferably 0.003 mm or more from the viewpoint of bear suppression. From the viewpoint of the appearance of the tire, the height difference is preferably 0.10 mm or less, and more preferably 0.08 mm or less.

  The surface of the core 22 may be roughened. Roughening helps to expel air. Roughening is performed prior to casting. Specific examples of the rough surface processing include blasting and polishing.

  When the mold 2 is used repeatedly, deposits adhere to the cavity surface 10. This deposit impairs the tire quality. The deposit needs to be removed. Usually, shot blasting is employed for the removal. Due to the shot blasting process, the main portion 20 undergoes minute plastic deformation. Due to this plastic deformation, the gap between the main portion 20 and the core 22 may disappear. If the mold 2 is heated to a high temperature, the main part 20 and the core 22 expand. By this expansion, the main portion 20 is compressed and the gap is regenerated. In this mold 2, recovery of the vent effect is easy. From the viewpoint of ensuring the reproduction, it is preferable that the main portion 20 and the core 22 are made of different metal materials. Preferably, the core 22 whose thermal expansion coefficient is smaller than the thermal expansion coefficient of the main part 20 is preferable.

  FIG. 7A is a perspective view showing a core 28 of a mold according to another embodiment of the present invention, and FIG. 7B is a sectional view thereof. The structure of the mold other than the core 28 is the same as that of the mold 2 shown in FIGS. The core 28 is embedded in a main part (not shown). The core 28 extends from one recess 18a (see FIG. 4) to the other recess 18b. This core 28 is generally solid. The core 28 has a hole 30. Molten metal flows into this hole 30 during casting. The main part after solidification includes an anchor that has entered the hole 30. By engaging the hole 30 with this anchor, the core 28 is prevented from being detached from the main part. The hole 30 is an engaging portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 28.

  FIG. 8 is a perspective view illustrating a core 32 of a mold according to still another embodiment of the present invention. The structure of the mold other than the core 32 is the same as that of the mold 2 shown in FIGS. The core 32 is embedded in a main part (not shown). The core 32 extends from one recess 18a to the other recess 18b. The core 32 is solid. The core 32 includes a main body 34 and an enlarged diameter portion 36. The enlarged diameter portion 36 is located at the center of the main body 34. The main body 34 and the enlarged diameter portion 36 are integrally formed. The main body 34 has a cylindrical shape, and the enlarged diameter portion 36 has a ring shape. The main body 34 and the enlarged diameter part 36 are located concentrically. The diameter of the enlarged diameter portion 36 is larger than the diameter of the main body 34. When the core 32 is embedded in the main part, the enlarged diameter part 36 engages with the main part. This engagement prevents the core 32 from being removed from the main part. The enlarged diameter portion 36 is an engagement portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 32.

  FIG. 9 is a perspective view illustrating a core 38 of a mold according to still another embodiment of the present invention. The structure of the mold other than the core 38 is the same as that of the mold 2 shown in FIGS. The core 38 is embedded in a main part (not shown). The core 38 extends from one recess 18a to the other recess 18b. The core 38 is solid. The core 38 includes a small diameter portion 40. The small diameter portion 40 is located at the center of the core 38. At the time of casting, the molten metal flows into the small diameter portion 40. The main part after solidification is provided with an anchor that has entered the small-diameter part 40. By engaging the narrow diameter portion 40 with this anchor, the core 38 is prevented from being detached from the main portion. The small diameter portion 40 is an engagement portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 38.

  FIG. 10A is a front view showing a core 42 of a mold according to still another embodiment of the present invention, and FIG. 10B is a cross-sectional view taken along line BB in FIG. 10A. FIG. 10C is a cross-sectional view taken along the line CC of FIG. 10B. The structure of the mold other than the core 42 is the same as that of the mold 2 shown in FIGS. The core 42 is embedded in a main part (not shown). The core 42 extends from one recess 18a to the other recess 18b. The core 42 includes a pair of main bodies 44 and a wire 46. The main body 44 is solid. As is clear from FIG. 10B, the cross-sectional shape of the main body 44 is semicircular. One main body 44 is overlaid on the other main body 44. There is a minute gap between the main bodies 44. The wire 46 is wound around the main body 44. A pair of main bodies 44 are bundled by the wire 46. The wire 46 protrudes from the main body 44. When the core 42 is embedded in the main part, the wire 46 is engaged with the main part. This engagement prevents the core 42 from being removed from the main portion. The wire 46 is an engaging portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 42. In this mold, air can also move through the gap between the main body 44 and the main body 44.

  FIG. 11A is a front view showing a mold core 48 according to still another embodiment of the present invention, and FIG. 11B is a cross-sectional view taken along the line BB in FIG. 11A. FIG. 11C is a cross-sectional view taken along the line CC in FIG. The structure of the mold other than the core 48 is the same as that of the mold 2 shown in FIGS. The core 48 is embedded in a main part (not shown). The core 48 extends from one recess 18a to the other recess 18b. The core 48 includes four main bodies 50 and wires 52. The main body 50 is solid. As is clear from FIG. 11B, the cross-sectional shape of the main body 50 is a rectangle. The main bodies 50 are overlapped. There is a minute gap between the main bodies 50. The wire 52 is wound around the main body 50. Four main bodies 50 are bundled by wires. The wire 52 protrudes from the main body 50. When the core 48 is embedded in the main part, the wire 52 engages with the main part. This engagement prevents the core 48 from being detached from the main part. The wire 52 is an engaging portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 48. In this mold, air can also move through the gap between the main body 50 and the main body 50.

  12A is a front view showing a core 54 of a mold according to still another embodiment of the present invention, and FIG. 12B is a cross-sectional view taken along the line BB in FIG. 12A. FIG. 12C is a cross-sectional view taken along the line CC in FIG. The structure of the mold other than the core 54 is the same as that of the mold 2 shown in FIGS. The core 54 is embedded in the main part (not shown). The core 54 extends from one recess 18a to the other recess 18b. The core 54 includes a pair of main bodies 56 and a wire 58. As is clear from FIG. 12B, the main body 56 has a plate shape. The main bodies 56 are overlapped. There is a minute gap between the main bodies 56. The wire 58 is wound around the main body 56. A pair of main bodies 56 are bundled by the wire 58. The wire 58 protrudes from the main body 56. When the core 54 is embedded in the main part, the wire 58 engages with the main part. This engagement prevents the core 54 from being detached from the main portion. The wire 58 is an engaging portion referred to in the present invention. Even in this mold, air can move through the gap between the main portion and the core 54. In this mold, air can also move through the gap between the main body 56 and the main body 56. The main body 56 may be a waveform.

  As described above, the present invention has been described by taking the split mold as an example. However, the convex part in which the core is embedded may be provided in the two-piece mold.

  The mold according to the present invention is suitable for manufacturing various tires.

FIG. 1 is a plan view illustrating a part of a tire mold according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view taken along the line II-II in FIG. FIG. 3 is a perspective view showing a segment of the mold of FIG. FIG. 4 is an enlarged view showing a part of the cavity surface of the segment of FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a perspective view showing the core of FIG. FIG. 7A is a perspective view showing a core of a mold according to another embodiment of the present invention, and FIG. 7B is a cross-sectional view thereof. FIG. 8 is a perspective view showing a core of a mold according to still another embodiment of the present invention. FIG. 9 is a perspective view illustrating a core of a mold according to still another embodiment of the present invention. FIG. 10A is a front view showing a core of a mold according to still another embodiment of the present invention, and FIG. 10B is a cross-sectional view taken along line BB in FIG. 10A. FIG. 10C is a cross-sectional view taken along the line CC in FIG. FIG. 11A is a front view showing a core of a mold according to still another embodiment of the present invention, and FIG. 11B is a cross-sectional view taken along line BB in FIG. 11A. FIG. 11C is a cross-sectional view taken along the line CC of FIG. 11B. FIG. 12A is a front view showing a core of a mold according to still another embodiment of the present invention, and FIG. 12B is a cross-sectional view taken along the line BB in FIG. FIG. 12C is a cross-sectional view taken along the line CC in FIG.

Explanation of symbols

2 ... Mold 4 ... Segment 10 ... Cavity surface 14 ... Dividing surface 16 ... Convex part 18, 18a, 18b ... Concave part 20 ... Main part 22, 28, 32, 38 , 42, 48, 54... Core 24, 34, 44, 50, 56... Body 26 .. projection 30 .. hole 36 .. enlarged diameter part 40. 58 ... Wire

Claims (5)

The cavity surface has a large number of convex portions and a large number of concave portions,
The convex portion includes a main portion and a core embedded in the main portion,
A tire mold in which the core extends from one of the concave portions on both sides of the convex portion to the other.   The mold according to claim 1, wherein a material of the convex portion and a material of the core are different.   The mold according to claim 1, wherein the core is composed of two or more members stacked on each other.   The mold according to any one of claims 1 to 3, wherein the core includes an engaging portion, and the engaging portion is engaged with the main portion, thereby preventing the core from being detached from the main portion. The cavity surface has a large number of convex portions and a large number of concave portions. The convex portion includes a main portion and a core embedded in the main portion, and both sides of the core are located with the convex portion interposed therebetween. A step of putting a green tire into a mold that extends from one of the recesses to the other;
The tire manufacturing method including the step of flowing the rubber composition of the green tire by pressurization and heating in the mold, and moving the air between the green tire and the cavity surface through the gap between the main portion and the core.

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