JP6862842B2 - Tire mold - Google Patents

Description

The present invention relates to a tire mold. In particular, the present invention relates to the improvement of mold vent holes.

The mold has a cavity surface that forms the outer surface of the tire. In tire manufacturing, the outer surface of a low cover (uncrosslinked tire) is pressed against this cavity surface. The air existing between the low cover and the cavity surface is discharged to the outside of the mold. Bears may form on the surface of the tire if the air is not exhausted sufficiently. Bears impair the appearance and durability of the tire.

Vent holes are provided in the mold for the purpose of promoting air discharge. As described above, since the low cover is pressurized in the mold, the rubber composition of the low cover R flows into the vent hole after the air is discharged. The rubber composition in the vent hole is crosslinked to form a spew. This spew is integrated with the tire. From the viewpoint of the appearance of the tire and the like, it is preferable that the size of the spew is small.

When the tire is removed from the mold, the spew may tear off the tire. The torn spew remains in the vent hole. The vent hole with the remaining spew cannot contribute to the exhaust of air. Residual spews lead to defective tires that are subsequently vulcanized and molded in this mold.

Japanese Unexamined Patent Publication No. 2004-98815 discloses a mold having a tapered vent hole. The spew formed by this vent hole is less likely to tear off the tire as it is removed from the mold.

JP-A-2004-98815

A tapered cutting tool is used to form the vent hole described in JP-A-2004-98815. When the tip of this cutting tool comes into contact with the cavity surface and advances, the metal is scraped and the vent hole is completed. When the traveling distance of the cutting tool is a predetermined value, a vent hole having an appropriate frontage is obtained. When the traveling distance of the cutting tool is excessive, since the cutting tool has a tapered shape, a vent hole having an excessive front diameter is obtained. If the traveling distance of the cutting tool is too small, the cutting tool has a tapered shape, so that a vent hole having an too small diameter can be obtained. Controlling the distance traveled is important. Since the mold has a complicated shape, it is not easy to control the traveling distance of the cutting tool. In other words, it is not easy to form a vent hole with an appropriate diameter.

An object of the present invention is to provide a tire mold that is easy to manufacture and is less likely to cause spew tearing.

The tire mold according to the present invention includes a main body and a vent piece inserted into the main body. This vent piece has a vent hole for communicating the outside air with the cavity formed by the mold. The vent hole has a tapered portion whose inner diameter gradually decreases as the distance from the cavity increases.

According to another viewpoint, the tire manufacturing method according to the present invention is:
(1) Process of preparing low cover,
(2) A main body and a vent piece inserted into the main body are provided, and this vent piece has a vent hole for communicating the outside air and the cavity, and the inner diameter of the vent hole increases as the distance from the cavity increases. The process of inserting the low cover into a mold having a tapered portion where
And (3) includes a step of pressurizing and heating the low cover in the mold and discharging air in the cavity through the vent hole.

In the tire mold according to the present invention, the vent hole has a tapered portion. When the rubber composition advances through the vent hole while receiving heat from the mold, the leading rubber composition reaches a high temperature. The leading rubber composition is prematurely crosslinked and cured, thus preventing further progress of the rubber composition. The tires obtained with this mold have a small spew length. This spew is hard to tear.

Cutting that forms a vent hole in the vent piece is excellent in workability. Therefore, the production of this mold is easy.

FIG. 1 is a plan view showing a tire mold according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is an exploded perspective view showing a part of the mold of FIG. FIG. 4 is a cross-sectional view showing the vent piece of the mold of FIG. FIG. 5 is an enlarged cross-sectional view showing a part of the vent piece of FIG. FIG. 6 is a cross-sectional view showing the vent piece of FIG. 4 together with the rubber composition. FIG. 7 is a cross-sectional view showing the manufacturing process of the vent piece of FIG.

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

1 and 2 show a part of the tire mold 2. In FIG. 1, the direction perpendicular to the paper surface is the axial direction of the mold 2, and the direction indicated by the arrow A1 is the circumferential direction of the mold 2. In FIG. 2, the vertical direction is the axial direction of the mold 2, the left-right direction is the radial direction of the mold 2, and the direction perpendicular to the paper surface is the circumferential direction of the mold 2. The axial direction of the mold 2 corresponds to the axial direction of the tire, the circumferential direction of the mold 2 corresponds to the circumferential direction of the tire, and the radial direction of the mold 2 corresponds to the radial direction of the tire.

What is indicated by the reference numeral R in FIG. 2 is a low cover. This low cover R is in an uncrosslinked state. The tire has a plurality of rubber members such as treads, sidewalls and beads. In the manufacture of this tire, a plurality of rubber members are assembled to prepare a low cover R.

In the manufacture of this tire, the low cover R is put into the mold 2. In FIG. 2, the low cover R is located inside the mold 2. Although not shown, a bladder is located further inside the low cover R. The low cover R charged into the mold 2 is placed in a space (that is, a cavity) between the mold 2 and the bladder. Instead of the bladder, a rigid core may be used.

In the manufacture of this tire, the low cover R is pressurized and heated in the mold 2. The rubber composition of the low cover R flows by pressurization and heating. The rubber undergoes a cross-linking reaction due to heating, and a tire is obtained. The outer surface of the low cover R comes into contact with the mold 2. This shapes the outer surface of the tire. Of the inner surface of the mold 2, the portion that comes into contact with the low cover R is the cavity surface. The cavity surface forms the outer surface of the tire. By using the mold 2 having an uneven pattern on the cavity surface, an uneven pattern is formed on the outer surface of the tire. The inner surface of the low cover R comes into contact with the bladder (or core). This shapes the inner surface of the tire.

The manufacturing method of this tire is
(1) Process of preparing low cover R,
(2) The process of charging the low cover R into the mold 2.
And (3) the steps of pressurizing and heating the low cover R in the mold 2 are included.

Hereinafter, the structure of the mold 2 will be described in detail. The mold 2 has a main body 4 and a vent piece 6 (see FIG. 2). The main body 4 includes a large number of tread segments 8, a pair of upper and lower side plates 10, and a pair of upper and lower bead rigs 12. These parts are combined to form the cavity of the mold 2. This mold 2 is a so-called "split mold". Tires may be manufactured by so-called "two-piece molds". The two-piece mold may also have the vent piece 6.

FIG. 3 is an exploded perspective view showing a part of the mold 2 of FIG. FIG. 3 shows the segment 8 and the vent piece 6. Segment 8 has holes 14. The hole 14 penetrates the segment 8. The hole 14 opens into the cavity at one end 16. The hole 14 opens at the other end 18 to the back surface 20 of the segment 8. FIG. 3 shows one hole 14. The segment 8 may have a plurality of holes 14. The holes 14 may be formed in the side plate 10 or the bead rig 12.

In this embodiment, the vent piece 6 is generally columnar. As shown by the arrow A2 in FIG. 3, the vent piece 6 is inserted into the hole 14. The vent piece 6 is press-fitted into the hole 14. A plurality of vent pieces 6 may be inserted into the segment 8. The vent piece 6 may be inserted into the side plate 10 or the bead rig 12.

FIG. 4 is a cross-sectional view showing the vent piece 6 of the mold 2 of FIG. FIG. 5 is an enlarged cross-sectional view showing a part of the vent piece 6. The vent piece 6 has a vent hole 20. The vent hole 20 penetrates the vent piece 6. Therefore, the vent piece 6 is hollow. The vent hole 20 has an inlet 22 and an outlet 24. In this embodiment, the inlet 22 is substantially flush with the cavity surface of the mold 2. The direction from the entrance to the exit is the direction away from the cavity. The vent hole 20 communicates the outside air with the cavity. The vent hole 20 has a chamfered portion 26, a tapered portion 28, and a tapered portion 30.

The chamfered portion 26 has a truncated cone shape. The entrance 22 is one end of the chamfered portion 26. The inner diameter of the chamfered portion 26 gradually decreases as the distance from the cavity increases.

The tapered portion 28 is continuous with the chamfered portion 26. The tapered portion 28 has a truncated cone shape. As shown in FIG. 5, the tapered portion 28 has an inlet side end 32, an exit side end 34 and a side surface 36. The inner diameter of the tapered portion 28 gradually decreases as the distance from the cavity increases. Therefore, the inner diameter D2 of the outlet side end 34 is smaller than the inner diameter D1 of the inlet side end 32.

In this embodiment, the side surface 36 is smooth. The inner diameter of the tapered portion 28 may change stepwise from the inlet side end 32 to the outlet side end 34. In other words, in the cross-sectional view of FIG. 4, the side surface 36 may be stepped.

The small diameter portion 30 is continuous with the outlet side end 34 of the tapered portion 28. The small diameter portion 30 extends from the outlet side end 34 to the outlet 24 (see FIG. 4). The shape of the small diameter portion 30 in the cross section perpendicular to the longitudinal direction is a circle. The inner diameter of the small diameter portion 30 is smaller than the inner diameter D2 of the outlet side end 34.

FIG. 6 is a cross-sectional view showing the vent piece 6 of FIG. 4 together with the rubber composition 38. As described above, the low cover R is pressurized and heated in the mold 2. The rubber composition 38 of the low cover R flows by pressurization and heating. Due to this flow, first, the air between the low cover R and the cavity surface is discharged through the vent hole 20. Next, the rubber composition 38 flows into the vent hole 20.

Since the vent hole 20 has the tapered portion 28, the volume of the leading portion 40 of the rubber composition 38 flowing into the tapered portion 28 is small. Therefore, the head portion 40 receives sufficient heat from the mold 2. The leading portion 40 reaches a high temperature at an early stage. At the head portion 40, a cross-linking reaction of rubber molecules occurs at an early stage. The head portion 40 is cured by the cross-linking reaction. The cured head 40 prevents further progress of the rubber composition 38 in the taper 28. In the tire obtained by this mold 2, the spew length is small. Therefore, when the tire is taken out from the mold 2, the spew is less likely to be torn. In this mold 2, clogging of the vent hole 20 due to tearing of the spew is unlikely to occur.

The diameter D1 of the inlet side end 32 (see FIG. 5) is preferably 1.0 mm or more and 2.0 mm or less, and the diameter D2 of the outlet side end 34 from the viewpoint that a spew of an appropriate size is formed and therefore tears are unlikely to occur. Is preferably 0.8 mm or more and 1.8 mm or less. The ratio D2 / D1 is preferably 0.6 or more and 0.9 or less. The length L of the tapered portion 28 is preferably 3 mm or more and 15 mm or less. The inclination angle θ (degree) of the side surface 36 with respect to the length direction of the vent hole 20 is preferably 0.5 ° or more and 30 ° or less.

The vent piece 6 is particularly suitable for manufacturing a tire having a low vulcanization temperature. The reason is that even if the vulcanization temperature is low, the progress of the rubber composition 38 in the vent hole 20 can be prevented. The vent piece 6 is particularly suitable for tires formed from a rubber composition 38 having a low high temperature breaking strength. The reason is that even with this rubber composition 38, the tearing of the spew can be suppressed.

FIG. 7 is a cross-sectional view showing the manufacturing process of the vent piece 6 of FIG. In the production of the vent piece 6, the block 42, the fixture 44, and the cutting tool 46 are prepared. A typical material for block 42 is metal. The block 42 is chucked by the fixture 44. The cutting tool 46 has a tapered shape. The cutting tool 46 travels in the direction indicated by the arrow A4 while rotating as indicated by the arrow A3. The block 42 is cut by this rotation and progress. When the progress of the cutting tool 46 reaches a predetermined distance, this progress is stopped, and the tapered portion 28 is completed.

In this manufacturing method, the block 42, which is a member different from the main body 4 of the mold 2, is cut. The block 42 can be chucked at a position where cutting is easy and in a posture where cutting is easy. Therefore, cutting can be performed without imposing an excessive burden on the operator. Moreover, the traveling distance of the cutting tool 46 can be controlled accurately. Therefore, even though the cutting tool 46 has a tapered shape, a tapered portion 28 having an accurate diameter D1 can be formed. The vent piece 6 is easy to manufacture.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example 1]
The mold shown in FIG. 1-6 was prepared. This mold has a large number of vent pieces. Each vent piece has a vent hole. This vent hole is formed by cutting the block. This vent hole has a tapered portion. In this tapered portion, the diameter D1 of the inlet side end is 1.5 mm, and the diameter D2 of the outlet side end is 1.2 mm. The distance L of this tapered portion is 8.0 mm.

[Example 2-6]
Molds of Example 2-6 were obtained in the same manner as in Example 1 except that the diameters D1 and D2 were as shown in Table 1 below.

[Comparative Examples 1 and 2]
Molds of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1 except that the diameters D1 and D2 were set as shown in Table 2 below. In these molds, the diameter D2 is equal to the diameter D1. In other words, these molds do not have a taper.

[Comparative Example 3]
A mold of Comparative Example 3 was obtained in the same manner as in Example 1 except that the segment was directly cut to form a vent hole. This mold does not have a vent piece.

[Workability]
In each mold, the workability when forming a vent hole by cutting was evaluated. The results are shown in Tables 1 and 2 below.

[Manufacturing of tires]
Tires were vulcanized and molded in each mold. A large number of spews were formed on this tire due to the vent holes. We evaluated the difficulty of tearing the spew when removing the tire from this mold. In addition, the tire was trimmed to remove the spew. The appearance of the tire after removal was evaluated. These results are shown in Tables 1 and 2 below.

As shown in Tables 1 and 2, the molds of the examples are excellent in various performances. From this evaluation result, the superiority of the present invention is clear.

The techniques relating to vent pieces described above can be applied to molds for various tires.

2 ... Mold 4 ... Main body 6 ... Vent piece 8 ... Segment 10 ... Side plate 12 ... Bead ring 14 ... Hole 26 ... Chamfered part 28 ... Tapered part 30 ... Small diameter part 32 ... Entrance side end 34 ... Exit side end 36 ... Side surface 38 ... Rubber composition 40 ... Head part 42 ... Block 44 ... Fixture 46 ・ ・ ・ Cutting tool R ・ ・ ・ Low cover

Claims (3)

A tire mold with a main body and a vent piece inserted into this main body.
The vent piece has a vent hole for communicating the outside air with the cavity formed by the mold.
The vent hole has a tapered portion whose inner diameter gradually decreases as the distance from the cavity increases .
The main body has a hole into which the vent piece is inserted, and this hole penetrates the main body.
A tire mold in which the length of the vent piece is the same as the length of the hole. The tire mold according to claim 1, wherein the vent piece is inserted into the hole from the outside air side toward the cavity side. (1) Process of preparing low cover,
(2) A main body and a vent piece inserted into the main body are provided, and this vent piece has a vent hole for communicating the outside air and the cavity, and the inner diameter of the vent hole increases as the distance from the cavity increases. The process of inserting the low cover into a mold having a tapered portion where
And (3) the raw cover in the mold under pressure and heat, and viewed including the step of discharging the air in the cavity through the vent hole,
A tire manufacturing method, wherein the main body has a hole into which the vent piece is inserted, the hole penetrates the main body, and the length of the vent piece is the same as the length of the hole.

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