MOLD FOR FORMING A TIRE AND TIRE PRODUCTION METHOD

Provided are a mold for forming a tire including an annular tread molding part a plurality of segments divided into arranged in a circumferential direction arranged in a circumferential direction, and a tire production method and using the same. The mold for forming a tire includes a rotatable shaft perpendicular to a direction of movement of the segment and also to the axis of the tread molding part; a base member supporting the segment to be rotatable around the rotatable shaft; and an external force application mechanism which, when the tread molding part is opened, applies external force to the segment to rotate the segment toward a direction in which a side of the other end of the segment in the direction of the axis is moved around the rotatable shaft toward a radially outer side.

TECHNICAL FIELD

This disclosure relates to a mold for forming a tire and a tire production method.

BACKGROUND

In a known conventional mold for forming a tire for use in vulcanization molding of an unvulcanized raw tire to produce a tire, it is known that an annular tread molding part (a tread mold) for forming a tread of a tire is divided into a plurality of segments arranged in a circumferential direction and is configured to be opened and closed by moving each of the segments in a radial direction (for example, see PTLs 1 to 3).

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

However, in the above-described conventional mold for forming a tire or the above-described conventional tire production method, when the tire is released from the tread molding part after vulcanization molding, each of the segments is moved toward a radially outer side with maintaining the orientation of each of the segments to a tread of the tire. As a result, all portions of the tread design surface for forming the tread of the segment are to peel off from the tread simultaneously. Therefore, there has been a problem in that a great driving force is required for driving the segments in the initial stage of mold releasing of the tire.

This disclosure has been accomplished in view of the above-described problem and it is an object of this disclosure to provide a mold for forming a tire and a tire production method which can reduce driving force required for driving the segments in the initial stage of mold releasing of the tire.

Solution to Problem

The mold for forming the tire of this disclosure is a mold for forming a tire for vulcanization molding of an unvulcanized raw tire into a tire, the mold including an annular tread molding part which is divided into a plurality of segments arranged in a circumferential direction, wherein a rotatable shaft which is provided on a side of one end of the segment in a direction of an axis of the tread molding part and which is perpendicular to a direction of movement of the segment and also to the axis of the tread molding part; a base member supporting the segment to be rotatable around the rotatable shaft; and an external force application mechanism which, when the tread molding part is opened, applies external force to the segment to rotate the segment toward a direction in which a side of the other end of the segment in the direction of the axis is moved around the rotatable shaft toward a radially outer side.

In an embodiment, the mold for forming the tire of this disclosure can be configured in such a way that the external force application mechanism includes a for-rotation spring member for application of spring force as external force to the segment.

In an embodiment, the mold for forming the tire of this disclosure can be configured in such a way that an outer ring which is disposed on a radially outer side of the segment and movable between a retention position at which the segment is retained at a predetermined position and a release position which allows for rotation of the segment around the rotatable shaft toward the radially outer side.

In an embodiment, the mold for forming the tire of this disclosure can be configured in such a way that the mold includes a guide rail supporting the base member to be movable in a radial direction of the tread molding part; and a for-sliding spring member biasing the base member toward a radially outer side of the tread molding part, wherein the segment is moved toward a radially outer side with the segment being rotated about the rotatable shaft.

In an embodiment, the mold for forming the tire of this disclosure can be configured in such a way that when the tread molding part is opened after vulcanization molding of the tire, the first segment is rotated around the first rotatable shaft, and subsequently, the second segment is rotated around the second rotatable shaft.

The tire production method of this disclosure is a tire production method for vulcanization molding of an unvulcanized raw tire to produce a tire by using a mold for forming a tire including an annular tread molding part which is divided into a plurality of segments arranged in a circumferential direction, wherein when the tread molding part is opened after vulcanization molding of the tire, by applying external force to the segment by an external force application mechanism, the tire is released from the tread molding part with the segment being rotated around a rotatable shaft which is provided on a side of one end of the segment in a direction of an axis of the tread molding part and which is perpendicular to a direction of movement of the segment and also to the axis of the tread molding part.

Advantageous Effect

This disclosure can provide a mold for forming a tire and a tire production method which can reduce driving force required for driving the segments in the initial stage of mold releasing of the tire.

DETAILED DESCRIPTION

By way of example, a mold for forming a tire and a tire production method according to an embodiment of this disclosure will now be described in detail with reference to the drawings. In this regard, common members and portions appearing in the drawings have the same reference signs.

A mold for forming a tire1illustrated inFIG.1according to an embodiment of this disclosure is for use in forming an unvulcanized (before vulcanization) raw tire based on a synthetic rubber into a predetermined shape with the raw tire being vulcanized to produce a tire2.

In this regard, the tire2is a hollow tire based on a synthetic rubber including a pair of sidewalls2a,2band a tread2c, and is shaped to provide the interior of the tire2with a space for filling of a gas such as air or nitrogen.

The mold for forming the tire1includes a sidewall molding part10and a tread molding part20.

For example, the sidewall molding part10can include an annular lower sidewall molding part11fixed to a top surface of a lower container3, and an annular upper sidewall molding part12fixed to a bottom surface of an upper container4.

The sidewall molding part10can dispose (accommodate) an annular tire2or a raw tire between the lower sidewall molding part11and the upper sidewall molding part12to be in an orientation by which the central axis of the raw tire becomes coaxial with the central axis O of the sidewall molding part10. The lower sidewall molding part11includes a lower sidewall design surface11a, which is in the form of a ring around the central axis O and is oriented toward the upward direction. The lower sidewall molding part11can form an outer surface of a sidewall2aof one of the tire2or the raw tire (any of which is oriented toward the downward direction inFIG.1) by the lower sidewall design surface11a. Similarly, the upper sidewall molding part12includes an upper sidewall design surface12a, which is in the form of a ring around the central axis O and is oriented toward the downward direction. The upper sidewall molding part12can form an outer surface of a sidewall2bof the other of the tire2or the raw tire (any of which is oriented toward the upward direction inFIG.1) by the upper sidewall design surface12a. By moving the upper container4, from a position illustrated inFIG.1, upwardly (the direction in which the upper container4and the lower container3is moved away from each other along the central axis of the tire2) and relatively to the lower container3, the sidewall molding part10is opened and the tire2is released from the sidewall molding part10. By moving the upper container4downwardly to its original position illustrated inFIG.1, the sidewall molding part10in an opened configuration is closed to allow for forming of the tire2or the raw tire.

In this regard, modifications can be made to the configuration of the sidewall molding part10as appropriate, and examples of such modifications include a configuration in which the sidewall molding part10is opened by moving the lower container3downwardly and relatively to the upper container4.

The tread molding part20is annular and coaxial with the sidewall molding part10and is disposed adjacent to a radially outer side of the lower sidewall molding part11and the upper sidewall molding part12. The inner circumferential surface oriented toward the radially inner side of the tread molding part20is a tread design surface20afor forming an outer circumferential surface of the tread2cof the tire2.

As illustrated inFIG.2, the tread molding part20is divided into a plurality of segments21arranged in a circumferential direction. Each of the segments21is in the form of arc in a planar view and the segments21are combined in a circumferentially arranged manner to constitute a tread molding part20, which is an annular mold as a whole. In this embodiment, the tread molding part20is divided into nine segments21having the same length in a circumferential direction. In this regard, the division number of the tread molding part20in a circumferential direction is preferably, but not limited to,7to13and can be changed as appropriate.

As illustrated inFIG.3, in this embodiment, each of the plurality of the segments21constituting the tread molding part20includes a holder22and a design surface dividing mold part23.

The holder22can be formed, for example, by cutting a block made of metal such as low carbon steel.

The design surface dividing mold part23is a portion which constitutes a tread design surface20afor forming the tread2cof the tire2and is in the form of arc in a planar view and, and a surface oriented toward the radially inner side constitutes a circumferential divided portion of the tread design surface20a. The design surface dividing mold part23is disposed on the radially inner side of the holder22corresponding to the design surface dividing mold part23, and is fixed to the holder22by using a fixing member such as a bolt (not illustrated).

The design surface dividing mold part23can be configured in such a way that the tread design surface20ais provided with a plurality of projections24which protrude in a radial direction from the tread design surface20atoward the radially inner side. The plurality of the projections24are used to form, for example, a groove or sipe, which constitutes a tread pattern, on the tread2cof the tire2in vulcanization molding. The plurality of the projections24can be of various shapes or sizes (length) tailored to the tread pattern, such as a plurality of projections24extending in a tire width direction and a plurality of projections24extending in a tire circumferential direction. In this regard, the tread design surface20amay not be provided with projections24.

The design surface dividing mold part23is preferably formed by casting of a metal material having high thermal conductivity such as, for example, an aluminum alloy. In this case, for example, rib-shaped or blade-shaped projections24made of steel can be provided by integrating with the design surface dividing mold part23in casting of the design surface dividing mold part23.

As illustrated inFIG.3, on the side of one end (in the case illustrated inFIG.3, the upper end side) in a direction of the axis of the tread molding part20, each of the segments21includes a rotatable shaft5which is perpendicular to a direction of movement of the segment21(radial direction) and also to the axis of the tread molding part20. In this embodiment, the rotatable shaft5is disposed on the lower end portion of the holder22.

In the downward direction of each of the segments21, an individual base member6corresponding to the segment21is disposed. The rotatable shaft5is supported by the base member6, and thus, the segment21is supported by the base member6to be rotatable around the rotatable shaft5. In other words, the segment21is rotatable around the rotatable shaft5in relation to the base member6.

The tread molding part20can be opened in such a way that after vulcanization molding of the tire2in the situation where each of the segments21is at a predetermined position, each of the segments21is rotated from the predetermined position toward the radially outer side around the rotatable shaft5to release the tread2cfrom the tread design surface20a.

In this embodiment, the base member6is supported by a guide rail25extending in a radial direction of the segment21, and the guide rail25is supported by the lower container3and the lower sidewall molding part11. As a result, can be moved in a radial direction centered on the axis of the tread molding part20(central axis O). Also, a for-sliding spring member26is disposed between the base member6and the lower sidewall molding part11, and each of the segments21is biased toward the radially outer side by the for-sliding spring member26corresponding to the each of the segments21. When the base member6is moved in a radial direction moved, the segment21supported by the base member6is moved in the radial direction together with the base member6.

Between each of the segments21and the base member6corresponding to the segment21, an external force application mechanism30is disposed which, when the tread molding part20is opened after vulcanization molding of the tire2, applies external force to the segment21to rotate the segment21toward a direction in which the side of the upper end of the segment21is moved around the rotatable shaft5toward the radially outer side.

In this embodiment, the external force application mechanism30includes a for-rotation spring member31for application of spring force as external force to the segment21.

More particularly, as illustrated inFIG.4, the external force application mechanism30includes a shaft-shaped body32fixed to the top surface of the base member6in such a way that the shaft-shaped body32is perpendicular to the top surface and extends in the up-down direction. The shaft-shaped body32is inserted into a hole22aprovided in the holder22constituting the segment21and a flange portion33provided on the upper end of the shaft-shaped body32is disposed in the hole22a. The for-rotation spring member31is a helical compression spring and disposed to be compressed between the flange portion33and a bottom wall of the hole22a. As a result of this, by the external force application mechanism30, external force is applied to the segment21to rotate the segment21toward a direction in which the side of the upper end of the segment21is moved around the rotatable shaft5toward a radially outer side.

As illustrated inFIGS.1,3and4, an outer ring7is disposed on the radially outer side of each of the segments21to retain the segment21at a predetermined position against external force applied by the external force application mechanism30. The outer ring7is fixed to an upper container4by the medium of the upper sidewall molding part12and can be moved, together with the upper container4, in the up-down direction relatively to the segment21supported by the lower container3or the base member6. In this regard, the term “predetermined position” refers to a position at which the segment21is in an orientation by which a tread design surface20aprovided on a design surface dividing mold part23is continuously connected, in a circumferentially arranged manner, with a tread design surface20aprovided on a design surface dividing mold part23of another segment21.

The inner circumferential surface of the outer ring7oriented toward the radially inner side is provided with a tapered surface7ainclined in such a way that the outer diameter of the tapered surface7agradually becomes smaller toward the upward direction. The outer circumferential surface of each of the segments21oriented toward the radially outer side is provided with a tapered surface21ainclined in such a way that the outer diameter of the tapered surface21agradually becomes smaller toward the upward direction. In this embodiment, the tapered surface21ais provided on the outer circumferential surface of the holder22. When the outer ring7is at a retention position illustrated inFIGS.1and3, the tapered surface7aabuts the tapered surface21aof the segment21to retain the segment21at a predetermined position. Also, when the tread molding part20is opened by moving the upper container4in the upward direction, the outer ring7can be moved to a release position located on the side of the upper direction in relation to the retention position together with the upper container4.

The mold for forming the tire1includes a bladder8which is disposed in the interior of the raw tire and expanded by supplying of pressurized steam. Also, the mold for forming the tire1includes a heater (not illustrated) for heating the sidewall molding part10and the tread molding part20. The location of the heater can be determined as appropriate.

Next, a method for vulcanization molding of a raw tire to produce a tire2having a predetermined shape by using a mold for forming a tire1having the above-described configuration, that is, a tire production method as an embodiment of this disclosure will be described.

First of all, a sidewall molding part10and a tread molding part20are opened to dispose a raw tire in the interior of a mold for forming a tire1, and subsequently, the sidewall molding part10and the tread molding part20are closed.

Next, a bladder8is expanded by supplying pressurized steam to the bladder8disposed in the interior of the raw tire. As a result, sidewalls of the raw tire are pressed against a lower sidewall design surface11aand an upper sidewall design surface12aof the sidewall molding part10, respectively, and a tread is pressed against a tread design surface20aof the tread molding part20. In this situation, a heater is used to heat the sidewall molding part10and the tread molding part20, and such heat causes vulcanization of the synthetic rubber constituting the raw tire to form a tire2having a predetermined shape.

After forming of the tire2is completed, the sidewall molding part10and the tread molding part20are opened to remove a formed tire2.

When the outer ring7is moved in the upward direction from the retention position toward the release position in relation to each of the segments21to open the tread molding part20after vulcanization molding of the tire2, as illustrated inFIG.5, for rotation of the segment21around the rotatable shaft5toward the radially outer side is allowed and the segment21is driven by the external force application mechanism30to spontaneously rotate (panning action) around the rotatable shaft5from a predetermined position toward the radially outer side.

As described above, in the tire production method by using the mold for forming the tire1of this embodiment, when the tread molding part20is opened after vulcanization molding of the tire2, by applying external force to the segment21by the external force application mechanism30, the tire2can be released from the tread molding part20with the segment21being rotated around the rotatable shaft5provided on the side of one end (the side of lower end) of the segment21. As a result of this, the tread2cof the tire2is gradually released from the side of one end (inFIG.5, the upper end side) of the design surface dividing mold part23in a width direction of the tire2, followed by releasing from the side of the other end (inFIG.8, the lower end side). Thus, outside air is gradually introduced between the tread2cand the tread design surface20afrom the side of one end to allow for reducing mold releasing resistance of the tread2cof the tire2from the tread design surface20ain the initial stage of mold releasing of the tire2. Therefore, force required for mold releasing of the tread2cof the tire2from the tread design surface20ain the initial stage of mold releasing of the tire2is reduced, and thus, the tire2can be reliably released from the tread molding part20by external force applied by the external force application mechanism30. Also, driving force applied to the segment21in mold releasing of the tire2can be reduced, and as a result, the external force application mechanism30can be downsized to reduce the production costs. In addition, mold releasing resistance of the tread2cof the tire2from the tread design surface20acan be reduced, and as a result, the generation of residual strain (permanent deformation) in the tire2after mold releasing can be suppressed to improve the initial performance of the tire2.

Also, in mold releasing of the tire2from the tread molding part20, each of the design surface dividing mold parts23rotates around the rotatable shaft5to reduce undercut resistance of the tread2cof the tire2caused by the projections24. As a result, driving force required for driving the segments21in the initial stage of mold releasing of the tire2can be further reduced. In addition, in mold releasing of the tire2from the tread molding part20, defects such as permanent deformation in the formed tread2cof the tire2and the failure of the projections24can be suppressed by preventing excessively high undercut resistance.

Also, the mold for forming the tire1of this embodiment is configured to include a guide rail25supporting the base member6to be movable in a radial direction of the tread molding part20; and a for-sliding spring member26biasing the base member6toward the radially outer side of the tread molding part20. In the mold for forming the tire1of this embodiment, when the outer ring7is moved to the release position, as illustrated inFIG.6, the segment21is biased by the for-sliding spring member26to be moved together with the base member6along the guide rail25toward the radially outer side with the segment21being spontaneously rotated around the rotatable shaft5from a predetermined position toward the radially outer side external force applied by the external force application mechanism30. As a result of this, in the case where the protruding height of the projections24provided on the tread design surface20ais high, for example, in the case of forming a large tire for use in construction vehicles and the like, undercut resistance of the tread2cof the tire2caused by the projections24in rotation of segment21around the rotatable shaft5can be reduced can be reduced. In addition, in mold releasing of the tire2, it is possible to move the segment21to a position at which obstruction by the projections24does not occur, and as a result, mold releasing of the tire2can be performed more easily.

In addition, the mold for forming the tire1of this embodiment is configured in such a way that the external force application mechanism30includes the for-rotation spring member31for application of spring force as external force to the segment21. Therefore, the configuration of the external force application mechanism30is simplified, and thus, the production costs of the tire2can be further reduced.

In this regard, the external force application mechanism30may not be configured to include a for-rotation spring member31for application of spring force as external force to the segment21and can be configured in such a way that external force is applied to the segment21by a driving force source such as an air cylinder.

In addition, the mold for forming the tire1of this embodiment is configured to include an outer ring7which is disposed on the radially outer side of the segment21and movable between a retention position at which the segment21is retained at a predetermined position and a release position which allows for rotation of the segment21around the rotatable shaft5toward the radially outer side. As a result, the mechanism of opening and closing the segment21can be simplified to reduce the production costs of the tire2further.

The mold for forming the tire1of this embodiment can be configured in such a way that when the tread molding part20is opened after vulcanization molding of the tire2, one segment (first segment)21of a plurality of segments21is rotated around the rotatable shaft5(first rotatable shaft) toward a radially outer side, and subsequently, another segment (second segment)21of the plurality of the segments21is rotated around the rotatable shaft (second rotatable shaft)5toward the radially outer side. In other words, the plurality of the segments21can be rotated sequentially with time differences between rotation of the segments21. In this case, the segments21can be rotated, in a circumferentially sequential manner, around the rotatable shaft5toward the radially outer side in such a way that one segment21is rotated around the rotatable shaft5toward the radially outer side, and subsequently, a segment21adjacent to the segment21is rotated around the rotatable shaft5toward the radially outer side, and then, a segment21adjacent to the segment21is rotated around the rotatable shaft5toward the radially outer side. As a result of the above-described configuration, in the initial stage of mold releasing of the tire2, the tread2cis released from the tread design surface20cin such a way that portions of the tread2cis released sequentially in a circumferential direction. In consequence, the tread2cof the tire2can be released from the tread design surface20aby more small driving force.

As a matter of course, this disclosure is not limited to the above-described embodiment and a variety of modifications are possible without departing from the scope of this disclosure.

For example, in the above-described embodiment, each of the segments21is provided with the holder22, the design surface dividing mold part23is fixed to the holder22, and the holder22is supported by the rotatable shaft5to be rotatable in relation to the base member6. However, it is also possible that the holder22is not provided, and the design surface dividing mold part23is supported on the base member6by the rotatable shaft5.

Also, the tread molding part20can be configured in such a way that the base member6cannot be moved in a radial direction and the tread molding part20is opened purely by rotation of the segment21around the rotatable shaft5.

REFERENCE SIGNS LIST