JP4604783B2 - Manufacturing method of rigid core for tire vulcanization and pneumatic tire - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a tire vulcanizing rigid core and a method for manufacturing a pneumatic tire, and more particularly, a tire vulcanizing rigid core that improves tire uniformity and a pneumatic using the core. The present invention relates to a tire manufacturing method.

  Conventionally, in order to improve the uniformity of the tire, instead of the bladder, the tire is vulcanized using a rigid core for vulcanizing the tire having a shape corresponding to the inner surface of the hollow portion of the unvulcanized tire as an inner mold. A tire manufacturing method has been proposed (see, for example, Patent Document 1).

  The rigid core for tire vulcanization used for such vulcanization molding is made of a metal material and has a configuration in which a plurality of segments are arranged in an annular shape. The tire components are sequentially pasted onto the core to form an unvulcanized tire, which is set on the lower mold of the vulcanizer, and then the upper mold is closed and heated using heating means such as electromagnetic induction heating. Sulfur molding. After vulcanization, the annularly arranged segments are removed one by one and the core is disassembled to obtain a vulcanized tire.

When the upper mold is gradually closed, the projections such as groove forming ridges that form grooves on the tread surface first hit the surface of the unvulcanized tire, but when the upper mold is closed, there is a gap between the mold and the core. Since the inner volume of the tire is configured to have a volume that substantially matches the volume of the unvulcanized tire, there is sufficient space for the rubber to escape when the protruding portion hits the surface of the unvulcanized tire and presses it. As a result, there is a large pressure locally, and the rubber flows in an unintended direction during vulcanization due to the pressure, and the reinforcing cords of the tire components also flow in unintended positions. It has not yet achieved high uniformity.
JP 2000-141380 A (prior art, FIG. 6)

  An object of the present invention is to provide a rigid core for tire vulcanization capable of realizing high uniformity of a tire and a method for manufacturing a pneumatic tire using the core.

The rigid core for tire vulcanization according to the present invention that achieves the above object has a shape corresponding to the inner surface of the hollow portion of the unvulcanized tire, and has a plurality of segments arranged in an annular shape. Each segment is composed of at least two segment bodies having different thermal expansion coefficients divided in the core radial direction, and the ratio (large / small) of the thermal expansion coefficients of the at least two segment bodies is set to 3 or more . In addition, the segment body having the larger coefficient of thermal expansion is configured to have a plurality of left and right segment members positioned on the left and right in the core width direction, and the plurality of segment members are locked to the segment body having the smaller coefficient of thermal expansion. Then, the locking position of each segment member is set in a range of 5 mm or more and 40 mm or less inward from the core width direction end of the segment body having the smaller coefficient of thermal expansion, and the width between the left and right segment members is 0.2 mm. Characterized in that a void above.

  The method for producing a pneumatic tire according to the present invention is a method for vulcanizing an unvulcanized tire placed on a rigid core for tire vulcanization when the unvulcanized tire is vulcanized in a mold of a tire vulcanizer. It is characterized by vulcanization in a mold of a vulcanizer.

According to the present invention described above, each segment is composed of at least two segment bodies having different thermal expansion coefficients divided in the core radial direction, and the ratio (large / small) of the thermal expansion coefficient is set to 3 or more , The segment body having a larger coefficient of thermal expansion is configured to have a plurality of left and right segment members positioned to the left and right in the core width direction, and the plurality of segment members are locked to the segment body having a smaller coefficient of thermal expansion, The engagement position of each segment member is set in the range of 5 mm to 40 mm inward from the end in the core width direction of the segment body having the smaller coefficient of thermal expansion, and the gap between the left and right segment members is 0.2 mm or more in width. Therefore, the tire vulcanization rigid core is formed with a small diameter so that the tire vulcanization rigid core expands, and the inner volume between the closed mold and the tire vulcanization rigid core is increased. Unvulcanized to vulcanize It can be divided by a large volume of inflation than the volume of the tire.

  As a result, the upper mold gradually closes, and there is a space for the rubber that is pushed by the projection to escape when the projection of the mold hits the surface of the unvulcanized tire. It does not occur. Further, since the tire vulcanization rigid core expands and presses the inner surface of the unvulcanized tire, it does not act on the unvulcanized tire where a large local pressure is vulcanized during vulcanization. Therefore, it is possible to increase the uniformity of the tire by suppressing the occurrence of a large deviation in the rubber flow during vulcanization and the occurrence of a large deviation in the reinforcing cord of the tire constituent member.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an embodiment of a rigid core for tire vulcanization according to the present invention. The core X is configured by arranging a plurality of segments 1 in an annular shape, and the outer surface 2 is vulcanized. It has a shape corresponding to the hollow portion inner surface 24 of the sulfurized tire 20 (see FIG. 4).

  As shown in FIGS. 2 and 3, each segment 1 has three segment bodies 3, 4, and 5 divided in the core radial direction, and is located on the outer peripheral side with the first segment body 3 positioned on the inner peripheral side. The third segment body 5 is made of a rigid material having the same thermal expansion coefficient, for example, a metal such as iron or an aluminum alloy. The second segment body 4 disposed between the first segment body 3 and the third segment body 5 is different in thermal expansion coefficient from the segment bodies 3 and 5 and has a larger thermal expansion coefficient than the segment bodies 3 and 5. The thermal expansion material is made of.

  The first segment body 3 and the third segment body 5 having a smaller coefficient of thermal expansion are divided into two first segment members 3A and 3B and third segment members 5A and 5B that are divided into left and right in the core width direction. It is configured. The second segment body 4 having a larger coefficient of thermal expansion is configured to have a plurality of left and right second segment members 4A and 4B positioned on the left and right in the core width direction.

  The left and right second segment members 4A and 4B are arranged via the gap a. Each left second segment member 4A is locked to the left first segment member 3A and the left third segment member 5A by a pin 6, and each right second segment member 4B is a right first segment. The pin 3 is engaged with the member 3B and the right third segment member 5B.

  The ratio (large / small) of the thermal expansion coefficient between the second segment body 4 with the larger thermal expansion coefficient and the first and third segment bodies 3 and 5 with the smaller thermal expansion coefficient is 3 or more, Since the second segment body 4 expands larger than the segment bodies 3 and 5 in the core radial direction due to heat during tire vulcanization, the core X has a diameter smaller than the inner diameter of the vulcanized tire by the amount of expansion. is doing. Thereby, the inner volume between the mold 30 (see FIG. 4) and the core X of the vulcanizer is larger than the volume of the unvulcanized tire to be vulcanized and expanded. ing.

  The pneumatic tire is manufactured as follows using the core X described above.

  First, the core X is assembled by arranging the plurality of segments 1 in an annular shape by using the fastening ring member 11 (see FIG. 4) arranged on the inner peripheral side. Tire constituent members such as a carcass layer, a belt layer, and a tread rubber layer are sequentially attached onto the core X to form an unvulcanized tire 20 (see FIG. 4).

  After this is set in the lower mold 31 of the mold 30 of the tire vulcanizer, the upper mold 32 is closed. At that time, a protruding portion such as a groove forming protrusion 33 that forms a groove on the tread surface first hits the surface of the unvulcanized tire 20, but the internal volume between the closed mold 30 and the core X is increased. Since it is larger than the volume of the unvulcanized tire 20 to be vulcanized, there is a space for the rubber of the tire constituent material to escape when the protruding portion hits the surface of the unvulcanized tire 20 and presses, so a locally high pressure To avoid this.

  After closing, the mold 30 and the core X are heated using a heating means (for example, a pressure heating medium or electromagnetic induction heating), and the unvulcanized tire 20 is vulcanized. At this time, since the core X is also heated, the core X, in particular, the second segment body 4 expands greatly in the radial direction, whereby the core X becomes the inner surface 22 on the tread portion 21 side of the unvulcanized tire 20. The whole is pressed so that the internal volume between the mold 30 and the core X substantially matches the volume of the tire after vulcanization (state shown in FIG. 4). In addition to avoiding the generation of a large local pressure when the mold is closed, a large local pressure does not act even during expansion, so there is a bias in the rubber flow during vulcanization and the large reinforcement cords of the tire components. Deviation is suppressed.

  After the vulcanization is completed, the fastening ring member 11 is removed, and then each segment 1 is removed one by one to disassemble the core X to obtain a vulcanized tire.

  According to the present invention described above, each segment 1 constituting the core X is composed of the segment bodies 3, 4, 5 having different thermal expansion coefficients divided in the core radial direction, and the ratio of the thermal expansion coefficients (large / (Small) is set to 3 or more, the core X is formed to have a small diameter corresponding to the expansion, and the inner volume between the closed mold 30 and the core X is expanded from the volume of the unvulcanized tire 20. The volume can be increased as much as possible.

  Therefore, when the protruding portion of the mold 30 to be closed hits against the surface of the unvulcanized tire 20, there is a space for the rubber of the tire constituent member to escape, so that it is possible to avoid the generation of a large pressure locally. On the other hand, since the core X expands and presses the entire inner surface of the unvulcanized tire, a large pressure is not locally applied to the unvulcanized tire 20 during vulcanization. Accordingly, it is possible to suppress the occurrence of a large deviation in the rubber flow during vulcanization and the occurrence of a large deviation in the reinforcing cords of the tire constituent members, thereby achieving higher uniformity than before.

  If the ratio (large / small) of the thermal expansion coefficient is smaller than 3, the expansion amount of the second segment body 4 is reduced, and as a result, the diameter of the core X needs to be made close to the tire inner diameter after vulcanization. Therefore, it is difficult to secure a sufficient space for the rubber to escape when the mold is closed. The upper limit of the ratio (large / small) of the thermal expansion coefficient is preferably 20 or less from the viewpoint of suppressing the step on the tire inner surface and maintaining the accuracy, which will be described later. The ratio of thermal expansion (large / small) is preferably 5 or more.

In the present invention, as the thermal expansion material used for the second segment body 4, a material having a thermal expansion coefficient of 5 × 10 ⁻⁴ cm / ° C. or more can be preferably used. For example, PTFE (polytetrafluoroethylene), Examples thereof include PCTFE (polychlorotrifluoroethylene), vulcanized rubber, and the like. Preferably, PTFE is preferable in terms of expansion rate and mechanical strength.

If the coefficient of thermal expansion of the second segment body 4 is lower than 5 × 10 ⁻⁴ cm / ° C., the amount of expansion of the second segment body 4 decreases, making it difficult to secure a sufficient space for the rubber to escape when the mold is closed. Become. The upper limit value is preferably 2 × 10 ⁻³ cm / ° C. or less from the viewpoint of suppressing the step on the inner surface of the tire and maintaining accuracy.

  The thickness t in the core radial direction of the second segment body 4 is preferably set to 30% or less of the sectional height SH of the tire in the mold 30 after vulcanization of 10 mm or more. When the thickness t is less than 10 mm, the amount of expansion in the tire radial direction is small, and it is difficult to secure a sufficient space for the rubber to escape when the mold is closed. When the thickness t exceeds 30% of the cross-sectional height SH, the mechanical strength of the core X itself is insufficient.

As the locking positions of the second segment members 4A and 4B by the pins 6 and 7, the core width direction end 3x of the first segment body 3 (the core width in the core width direction end of the segment bodies 3 and 5) you from the core width direction end) towards located inward in the range of M 5 mm above 40mm in the core width direction inside. When the locking position is positioned outside the range M in the core width direction, the second segment members 4A and 4B are securely locked to the first and third segment bodies 3 and 5 by the locking members such as the pins 6 and 7. It becomes difficult. When located on the inner side in the core width direction from the range M, the second segment members 4A and 4B are likely to expand greatly outside the inner side in the core width direction, whereby the second segment members 4A and 4B become the first and third segments. It expands to the outside of the bodies 3 and 5 and becomes a factor that forms a significant step on the inner surface of the vulcanized tire.

Left and right second segment member 4A, the width b of the gap a between 4B, by more than 0.2 mm, avoid both be interfere when inflated. The upper limit of the gap a width b is not particularly limited as long as the second segment members 4A and 4B can withstand the clamping force for closing the mold 30, and the size of the second segment members 4A and 4B. It can be set appropriately depending on the material used.

  In the above embodiment, each segment 1 is composed of segment bodies 3, 4, and 5 that are divided into three in the core radial direction. However, the segment 1 is composed of at least two segment bodies 3, 4 that have different coefficients of thermal expansion, such as two or four. The thermal expansion coefficient ratio (large / small) of the at least two segment bodies 3 and 4 may be 3 or more.

  Moreover, in the said embodiment, although the width direction outer side surface of 1st, 2nd, 3rd segment member 3A, 3B, 4A, 4B, 5A, 5B was located on the same curved surface, it is 2nd segment 4A previously. 4B, the width direction outer side surfaces of the second segment members 4A, 4B are configured to be recessed from the width direction outer side surfaces of the first and third segment members 3A, 3B, 5A, 5B. May be.

  The rigid core 1 for tire vulcanization of the present invention having the configuration shown in FIGS. 1 to 3 in which the ratio (large / small) of the thermal expansion coefficient between the second segment body and the first and third segment bodies is as shown in Table 1. 4 (Examples 1 to 4) and a conventional rigid core for tire vulcanization (conventional example) in which the segment is not divided.

  An aluminum alloy was used for the first and third segment bodies of the rigid core for tire vulcanization of the present invention, and PTFE was used for the second segment body. The thickness t of the second segment body in the core radial direction, the locking position of each second segment member (distance from the end in the core width direction of the first segment body), and the width b of the gap between the left and right second segment members Is as shown in Table 1. Aluminum alloy was used for the segment of the conventional rigid core for tire vulcanization.

Each of these test cores was used to manufacture tires of size 175 / 65R14, and the uniformity evaluation test was performed by the test method shown below. The results shown in Table 1 were obtained.
Uniformity Using a tire uniformity measurement tester, the RFV (radial force variation) of each test tire is measured, and the measurement result is defined as 100 for the tire manufactured with a conventional rigid core for tire vulcanization. Expressed as an exponent value. The greater this value, the better the uniformity.

表１から、本発明のタイヤ加硫用剛性中子は、タイヤの均一性を改善できることがわかる。

From Table 1, it can be seen that the rigid core for tire vulcanization of the present invention can improve the uniformity of the tire.

It is a front view showing one embodiment of a rigid core for tire vulcanization of the present invention. It is an expansion perspective view which shows one of the segments of FIG. FIG. 3 is an enlarged cross-sectional view of the segment of FIG. 2. It is a section explanatory view showing one process in a manufacturing method of a pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Segment 3 1st segment body 3A, 3B 1st segment member 4 2nd segment body 4A, 4B 2nd segment member 5 3rd segment body 5A, 5B 3rd segment member 6,7 Pin 20 Unvulcanized tire 24 Hollow part Inner surface 30 Mold SH Cross-sectional height M range X Rigid core for tire vulcanization a Gaps b Width t Core radial thickness

Claims (5)

A rigid core for tire vulcanization having a shape corresponding to the inner surface of a hollow portion of an unvulcanized tire and a plurality of segments arranged in an annular shape, each coefficient being divided in the core radial direction And the ratio (large / small) of the coefficient of thermal expansion of the at least two segment bodies is set to 3 or more, and the segment body having the larger coefficient of thermal expansion is arranged in the core width direction. And having a plurality of left and right segment members positioned on the left and right sides, locking the plurality of segment members to a segment body having a smaller coefficient of thermal expansion, and locking each segment member at a position having the smaller coefficient of thermal expansion. A rigid core for tire vulcanization in which a gap having a width of 0.2 mm or more is provided between the left and right segment members in the range from 5 mm to 40 mm inward from the end of the segment body in the core width direction .   2. The rigid core for tire vulcanization according to claim 1, wherein a thickness t in a core radial direction of a segment body having a larger coefficient of thermal expansion is 30% or less of a sectional height of the tire after vulcanization of 10 mm or more. 3. The rigid core for tire vulcanization according to claim 1, wherein the segment body having a larger coefficient of thermal expansion is made of a material having a coefficient of thermal expansion of 5 × 10 ⁻⁴ cm / ° C. or more. The rigid core for tire vulcanization according to any one of claims 1 to 3 , wherein the segment body having a smaller coefficient of thermal expansion is made of metal. The unvulcanized tire disposed on the rigid core for tire vulcanization according to any one of claims 1 to 4 when the unvulcanized tire is vulcanized in a mold of a tire vulcanizer. A method for producing a pneumatic tire for vulcanization in a mold of a vulcanizer.

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