JP2017001372A - Vent plug for tire molding mold, tire molding mold and tire production method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely discharge air in a cavity from the cavity even when a valve shaft cannot return.SOLUTION: A vent plug comprises: a cylindrical case 6 having a discharge path 9; a valve shaft 7 inserted into the case 6; and energization means 8 for energizing the valve shaft 7 to a front side. A cone-shaped valve seat surface 10 whose diameter increases toward the front side, is provided on a front end part of the discharge path 9. The valve shaft 7 comprises a head part 13 having a cone-shaped contact surface 15 for closing the discharge path 9 by contacting the valve seat surface 10, on a front end of a base shaft part 12 extending in the discharge path 9. The contact surface 15 has at least one air discharge groove 20 for conducting a cavity 2 and the discharge path 9 in a contact state.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a vent plug for a tire molding die that exhausts air in a cavity during tire vulcanization molding, a tire molding die using the vent plug, and a tire manufacturing method.

  The tire molding die is provided with a large number of vent holes for exhausting air between the cavity surface and the green tire. However, the vent hole exhausts air, but the rubber also flows into the vent hole, so that a spear-like spew is generated on the surface of the vulcanized tire.

  Therefore, Patent Document 1 below proposes a vent plug that can prevent the inflow of rubber into the vent hole and eliminate the spew cutting work. As shown in FIG. 5A, the proposed vent plug a includes a cylindrical case c having an exhaust passage c1 and a valve shaft d inserted into the case c. A cone-shaped valve seat surface c1a having a diameter increasing toward the front side (cavity side) is provided at the front end of the exhaust passage c1. The valve shaft d includes a head portion d2 having a cone-shaped contact surface d2a whose diameter increases toward the front side at the front end of the base shaft portion d1 extending in the exhaust passage c1.

  The valve shaft d is biased forward by the spring e, and the valve seat surface c1a and the contact surface d2a are separated from each other, whereby the air in the cavity is exhausted to the exhaust path c1. Further, after exhaust, the raw tire comes into contact with the head d2, and the valve seat surface c1a is closed to prevent inflow of rubber.

  However, in the case of the vent plug having the above structure, as shown in FIG. 5B, a part of the rubber tends to flow into the valve seat before the valve seat surface c1a is closed. As a result, there is a problem that rubber adheres between the valve seat surface c1a and the contact surface d2a, and thereafter, the valve shaft d cannot be restored and air is not exhausted.

JP 09-141660 A

  Therefore, the present invention is based on the provision of an air exhaust groove on the abutting surface, and even when the valve shaft cannot be restored, the air in the cavity can be exhausted reliably, and a tire that can prevent molding defects. It is an object to provide a vent plug for a molding die, a tire molding die using the vent plug, and a tire manufacturing method.

The first invention of the present application is a vent plug attached to a vent hole of a tire molding die having a cavity for tire molding,
A cylindrical shape having an exhaust path, and a case mounted in the vent hole;
A valve shaft for opening and closing the exhaust passage inserted into the case;
Urging means for urging the valve shaft toward the front side facing the cavity and opening the exhaust passage;
In addition, the case includes a cone-shaped valve seat surface whose diameter increases toward the front side at the front end of the exhaust passage,
The valve shaft has a base shaft portion extending in the axial direction in the exhaust passage, and has a cone shape that expands at the front end of the base shaft portion and expands in diameter toward the front side, and abuts on the valve seat surface. And a head having a contact surface that closes the opening of the exhaust passage.
The head has at least one air exhaust groove on the contact surface for electrically connecting the cavity and the exhaust passage in the contact state.

  In the vent plug for a tire molding die according to the present invention, the valve shaft is inclined in a direction to reduce the diameter toward the front side at a corner portion where the front end surface of the head and the contact surface intersect. It is preferable to provide a cone-shaped chamfered surface.

  In the vent plug for a tire molding die according to the present invention, the valve shaft preferably has a front end surface of the head having a rough surface with a surface roughness (Ra) of 1.6 μm or more.

  In the vent plug for a tire molding die according to the present invention, it is preferable that a coating layer having rubber releasability is formed on the surface of the case and the valve shaft facing the exhaust passage.

  The second invention of the present application is a tire molding die, wherein the vent plug for the tire molding die is attached to a vent hole.

  The third invention of the present application is a tire manufacturing method, characterized by comprising a step of vulcanizing and molding a raw tire using the tire molding die.

  In the present invention, as described above, at least one air exhaust groove is provided on the contact surface of the valve shaft so as to connect the cavity and the exhaust passage in a contact state with the valve seat surface. Therefore, even when the valve shaft cannot be restored, the air in the cavity can be surely exhausted, and molding defects can be prevented. Moreover, since the air exhaust groove can prevent the passage of rubber by setting its cross-sectional area to be small, it is possible to suppress the occurrence of spear-like spew.

It is sectional drawing which shows notionally one Example of the tire shaping die with which the vent plug of this invention was attached. It is sectional drawing which expands and shows a vent plug. It is the top view which looked at the vent plug from the cavity side. (A), (B) is sectional drawing which expands and shows the head part of a valve shaft. (A), (B) is a fragmentary sectional view which shows the conventional vent plug.

Hereinafter, embodiments of the present invention will be described in detail.
As shown in FIG. 1, the tire molding die 1 of the present embodiment may be referred to as a mold body 3 having a cavity 2 for tire molding and a surface 2S of the cavity 2 (hereinafter referred to as “cavity surface 2S”). )), A vent hole 4 having one end opened and the other end conducting to the outside of the mold, and a vent plug 5 attached to the vent hole 4 is provided.

  And a pneumatic tire is manufactured by vulcanization-molding the raw tire T thrown into the said cavity 2 using this tire shaping die 1 like the past.

  In the tire molding die 1, the die body 3 and the vent hole 4 are not particularly restricted, and those having the same structure as the conventional one can be suitably employed. Therefore, in this specification, the vent plug 5 will be mainly described.

  2 and 4A, the vent plug 5 includes a case 6 mounted in the vent hole 4, a valve shaft 7 for opening and closing an exhaust passage inserted into the case 6, and the valve. And an urging means 8 for urging the shaft 7 toward the front side facing the cavity 2 side.

  In this example, a case where the front end surface 6S of the case 6 is mounted so as to be flush with the cavity surface 2S is shown. The case 6 has a cylindrical shape, and the central hole 6A forms an exhaust path 9 for discharging air. In addition, the case 6 includes a cone-shaped valve seat surface 10 which is inclined at a front end portion of the exhaust passage 9 in a direction in which the inner peripheral surface expands toward the front side. The rear end of the exhaust passage 9 is provided with a locking portion 11 that protrudes radially inward from the inner peripheral surface.

  The valve shaft 6 includes a base shaft portion 12 extending in the axial direction in the exhaust passage 8 and a head portion 13 swelled at a front end of the base shaft portion 12 through a step 14, for example. The head 13 is provided with a cone-shaped contact surface 15 that is inclined in a direction in which the outer peripheral surface expands toward the front side. And in the contact state Y1 (not shown) in which the contact surface 15 contacts the valve seat surface 10, the exhaust passage 9 is closed. The base shaft portion 12 extends rearward through the locking portion 11, and a stopper portion 16 having a larger diameter than the locking portion 11 is bulged at the rear end portion.

  The urging means 8 urges the valve shaft 7 forward, thereby separating the valve seat surface 10 and the contact surface 15 and opening the exhaust passage 9. The valve shaft 7 of this example is configured such that the stopper portion 16 contacts the locking portion 11 and the valve seat surface 10 and the contact surface 15 are spaced apart from each other between the maximum separated state Y2 and the contact state Y1. Can move in the direction of the heart. The urging means 8 of this example is formed of a coil spring that is extrapolated to the base shaft portion 12, and its front end is locked to the step 14 and its rear end is locked to the locking portion 11.

  In the present invention, as shown in FIGS. 3 and 4A, at least one air exhaust groove 20 is formed on the contact surface 15 for electrically connecting the cavity 2 and the exhaust passage 9 in the contact state Y1. Is done. In FIG. 3, the air exhaust groove 20 is shown in gray for clarity. In this example, a case where a plurality of (for example, eight) air exhaust grooves 20 are provided in the circumferential direction is shown. The air exhaust groove 20 needs to be able to prevent air from passing while allowing air to pass therethrough. Therefore, it is preferable to set the groove width W and the groove depth D of the air exhaust groove 20 in the range of 0.01 to 0.08 mm, respectively.

  By forming such an air exhaust groove 20 on the contact surface 15, even when rubber adheres between the valve seat surface 10 and the contact surface 15 and the valve shaft 7 cannot be restored, the air exhaust groove 20 is also provided. Air can be reliably exhausted from the groove 20.

  Further, in this example, in order to suppress the adhesion of the rubber itself, a cone shape that inclines in a direction to reduce the diameter toward the front side at the corner portion P where the front end surface 13S of the head 13 and the contact surface 15 intersect. The chamfered surface 21 is formed. The front end surface 13S is formed by a plane perpendicular to the axis of the valve shaft 7 or an arc surface approximating the plane.

  Here, the following is estimated as a cause of the adhesion of rubber to the valve seat surface 10. As shown in FIG. 5B, when the raw tire T comes into contact with the head d2, a rubber flow may occur in a direction F perpendicular to the axis of the valve shaft d. At this time, when the head portion d2 has no chamfered surface as in the prior art, the rubber G that hits the contact surface d2a flows into the valve seat along the contact surface d2a, and the valve seat surface c1a and the contact surface d2a It adheres between and induces a return failure of the valve stem d.

  On the other hand, in this example, a chamfered surface 21 is formed on the head 13 as shown in FIG. Accordingly, even when a rubber flow occurs in the F direction, the rubber G can be smoothly guided along the chamfered surface 21 and the front end surface 13S, and the rubber G can be prevented from flowing into the valve seat. . The height H in the axial direction of the chamfered surface 21 is preferably 0.05 mm or more. If the height H is less than this, the above effect cannot be sufficiently exhibited. Further, the upper limit of the height H is preferably 0.5 mm or less, more preferably 0.1 mm or less. If the height H is exceeded, ring-shaped marks remain on the surface of the product tire and the appearance quality tends to deteriorate. The inclination angle θ of the chamfered surface 21 with respect to the axial direction is preferably 30 degrees or more, and more preferably 45 degrees or more.

  In this example, in order to further enhance the above effect, the front end surface 13S of the head 13 is formed of a rough surface 24 having a surface roughness (arithmetic average roughness Ra) of 1.6 μm or more. When the front end surface 13S is not the rough surface 24, the frictional resistance between the front end surface 13S and the rubber increases with respect to the rubber flow in the F direction. As a result, the head 13 is urged toward the F direction, and the gap K (shown in FIG. 4B) between the valve seat surface 10 and the contact surface 15 is large on the side opposite to the F direction (right side in the figure). At the same time, the valve shaft 7 is inclined in such a direction that the rear end edge 21e of the chamfered surface 21 rises forward. Therefore, the rubber easily flows into the gap K. On the other hand, by using the rough surface 24, the frictional resistance becomes small, and the inclination of the gap K and the valve shaft 7 can be suppressed. Therefore, the combined use with the chamfered surface 21 can more effectively suppress the inflow of rubber into the valve. The upper limit of the surface roughness (Ra) is preferably 50 μm or less from the viewpoint of frictional resistance and appearance. The chamfered surface 21 is preferably a rough surface 24. As the surface roughening, for example, a known surface treatment such as blast treatment or etching treatment can be appropriately employed.

  Further, it is more preferable to form a coating layer having rubber releasability on the surface of the rough surface 24, whereby the frictional resistance can be further reduced.

  As the coating layer, an organic material having excellent releasability such as a fluorine resin or a siloxane resin can be employed. However, from the viewpoint of wear resistance, hardness, and releasability, a composite film combining the organic material and an inorganic material such as metal, ceramics, and chemical film, specifically, a nickel metal film and a chromium metal film A composite film in which an organic material such as a fluorine-based resin or a siloxane-based resin is dispersed and mixed in an alumina film, a chemical conversion film, and a metal or ceramic sprayed film can be suitably used. In addition, 2-50 micrometers is suitable as thickness of a coating layer.

  It is also preferable to form the coating layer on the surface of the case 6 and the valve shaft 7 facing the exhaust passage 9. As a result, even when rubber enters the case 6, the rubber can be discharged from the rear end of the exhaust passage 9 without accumulating in the case 6.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

DESCRIPTION OF SYMBOLS 1 Tire molding die 2 Cavity 4 Vent hole 5 Vent plug 6 Case 7 Valve shaft 8 Energizing means 9 Exhaust path 10 Valve seat surface 12 Base shaft part 13 Head 15 Contact surface 20 Air exhaust groove 21 Chamfered surface 24 Rough surface P Corner section

Claims (6)

A vent plug attached to a vent hole of a tire molding die having a cavity for tire molding,
A cylindrical shape having an exhaust path, and a case mounted in the vent hole;
A valve shaft for opening and closing the exhaust passage inserted into the case;
Urging means for urging the valve shaft toward the front side facing the cavity and opening the exhaust passage;
In addition, the case includes a cone-shaped valve seat surface whose diameter increases toward the front side at the front end of the exhaust passage,
The valve shaft has a base shaft portion extending in the axial direction in the exhaust passage, and has a cone shape that expands at the front end of the base shaft portion and expands in diameter toward the front side, and abuts on the valve seat surface. And a head having a contact surface that closes the opening of the exhaust passage.
A vent plug for a tire molding die, wherein the head has at least one air exhaust groove on the contact surface for electrically connecting the cavity and the exhaust passage in the contact state.   The valve shaft includes a cone-shaped chamfered surface that is inclined in a direction of decreasing in diameter toward the front side at a corner portion where the front end surface of the head and the contact surface intersect. A vent plug for a tire molding die according to 1.   The vent plug for a tire molding die according to claim 1 or 2, wherein the valve shaft has a front end surface of the head having a rough surface with a surface roughness (Ra) of 1.6 µm or more.   The tire case mold according to any one of claims 1 to 3, wherein the case and the valve shaft are formed with a coating layer having rubber releasability on a surface facing the exhaust passage. Vent plug.   A tire molding die, wherein the vent plug for a tire molding die according to any one of claims 1 to 4 is attached to a vent hole. A tire manufacturing method comprising a step of vulcanizing and molding a green tire using the tire molding die according to claim 5.

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