JP7475136B2 - TIRE BUILDING MOLD AND METHOD FOR MANUFACTURING PNEUMATIC TIRE - Google Patents

Description

The present invention relates to a tire molding mold for vulcanizing an unvulcanized raw tire having a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and a tread portion that is connected to the radially outer ends of each of the sidewall portions to form a tread surface.

When manufacturing pneumatic tires, which are rubber products, the vulcanization process is the most time-consuming process, and efforts to shorten the vulcanization process are currently being made. On the other hand, if the rubber part is not sufficiently vulcanized during the vulcanization process, air generated by the vulcanization reaction of the rubber will remain in the vulcanized rubber, and this remaining air may cause tire failure at the product stage. Therefore, at normal tire production sites, the time required for the vulcanization process is set by adding a surplus time that takes into account all the variations in the vulcanization process, taking into account the fact that the temperature of the raw unvulcanized tires, the temperature inside the mold, and the ambient temperature, for example, vary due to seasonal factors.

However, setting a leeway time is not desirable from the perspective of improving tire productivity, and it is desirable to determine the end time of vulcanization for each tire and carry out the vulcanization process efficiently.

The following Patent Document 1 describes a real-time vulcanization control method for a vulcanized sample, in which the impedance of the vulcanized sample is measured while the vulcanization process is in progress, and the optimal vulcanization stop time is determined to be the point at which the rate of increase in the polymer resistance value Rp of the vulcanized sample suddenly slows down. However, this method requires that the impedance of the vulcanized sample be measured by sandwiching the vulcanized sample between two electrodes, and since tires are usually laminated composite materials, it is difficult to apply this method to tires during tire vulcanization.

JP 2003-211459 A

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a tire molding mold that can accurately measure the temperature of a pneumatic tire during vulcanization in order to reliably determine the end point of the vulcanization process for each tire, and that has a temperature measurement probe with excellent durability, as well as a method for manufacturing pneumatic tires using the tire molding mold.

The above objective can be achieved by the present invention as described below. That is, the present invention relates to a tire molding die for vulcanizing an unvulcanized raw tire having a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and a tread portion that is connected to the radially outer ends of each of the sidewall portions to form a tread surface, the tire molding die having at least a tread mold portion that can be pressed against the tread portion, the tread mold portion being divided in the circumferential direction and having a plurality of segments that can move in the radial direction of the raw tire, at least one of the segments having a fixing means for fixing the outer peripheral end of a temperature measurement probe, a temperature measurement probe insertion hole extending from the fixing means toward the inner peripheral side, and a temperature measurement probe whose outer peripheral end is fixed by the fixing means, which extends inside the temperature measurement probe insertion hole toward the inner peripheral side, and whose inner peripheral end exceeds the inner peripheral end of the temperature measurement probe insertion hole and is attached in a position that allows it to be embedded in the shoulder portion of the tread portion, and the inner peripheral side surface of the temperature measurement probe insertion hole and the temperature measurement probe surface are formed so that they can be screwed together.

In the tire molding mold, it is preferable that the female thread formed on the inner peripheral side of the temperature measurement probe insertion hole and the male thread formed on the surface of the temperature measurement probe are formed so as to be able to be screwed together.

In the tire molding die, the female thread portion is formed in a range of L1 in the depth direction from the inner peripheral end of the temperature measurement probe insertion hole, and it is preferable that the depth L of the temperature measurement probe insertion hole from the inner peripheral end to the outer peripheral end of the temperature measurement probe insertion hole is 0.02≦L1/L≦0.05.

In the tire molding mold, it is preferable that the inner diameter D2 at the outer peripheral end of the temperature measurement probe insertion hole is larger than the inner diameter D1 at the inner peripheral end.

In the tire molding mold, it is preferable that the temperature measurement probe has an outer diameter of 1 to 10 mm.

In the tire molding mold described above, it is preferable that the temperature measurement probe is a platinum resistance thermometer.

The present invention also relates to a method for manufacturing a pneumatic tire, which includes a vulcanization step of vulcanizing the tire in any one of the tire molds described above, characterized in that the vulcanization step includes a step of measuring the temperature of a shoulder portion included in a tread portion of an unvulcanized raw tire having a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and a tread portion that is connected to the radially outer ends of each of the sidewall portions to form a tread surface, by embedding a temperature measurement probe in the shoulder portion.

The tire molding mold according to the present invention is a so-called "segmental mold" in which at least the tread mold portion is divided in the circumferential direction, and at least one of the segments is equipped with the above-mentioned specific temperature measurement probe. This makes it possible to accurately measure the temperature of the pneumatic tire during vulcanization, particularly the temperature of the shoulder portion of the tread portion, where vulcanization of the tire is most difficult to progress.

In the tire molding die according to the present invention, a temperature measurement probe is embedded in the shoulder portion of the tread portion of a raw tire while being pushed into it. Generally, even if the rubber portion constituting the shoulder portion is in an unvulcanized state, a large load is applied to the temperature measurement probe when it is pushed into the rubber, and in some cases, the temperature measurement probe may bend. However, in the tire molding die according to the present invention, the inner peripheral side surface of the temperature measurement probe insertion hole and the surface of the temperature measurement probe are formed so that they can be screwed together. This allows the temperature measurement probe to be held more stably than a configuration in which the outer peripheral end of the temperature measurement probe is fixed only by a fixing means, preventing deformation such as bending of the temperature measurement probe and improving the durability of the temperature measurement probe.

FIG. 1 is a tire meridian cross-section showing an example of a tire that can be manufactured according to the present invention. FIG. 1 is a cross-sectional view conceptually showing a tire molding die of the present invention. FIG. 2 is a cross-sectional view conceptually showing a state in which a temperature measuring probe is embedded in a shoulder portion of a segment constituting a tread mold portion of a mold of the present invention.

The embodiment of the present invention will be described with reference to the drawings. The raw tire 9 shown in FIG. 1 is a pneumatic tire having a pair of bead portions 1, sidewall portions 2 extending radially outward from each of the bead portions 1, and a tread portion 3 that is connected to the radially outer ends of each of the sidewall portions 2 to form a tread surface. An annular bead core 1a is arranged in the bead portion 1.

The carcass layer 4 extends from the tread portion 3 through the sidewall portion 2 to the bead portion 1, and its end is folded back via the bead core 1a. The carcass layer 4 is composed of at least one carcass ply. The carcass ply is formed by covering the carcass cords, which extend at an angle of approximately 90° to the tire circumferential direction, with topping rubber.

The belt layer 5 is bonded to the outside of the carcass layer 4 in the tread portion 3 and is covered from the outside by the tread rubber 6. The belt layer 5 is composed of multiple belt plies (two in this embodiment). Each belt ply is formed by covering a belt cord that extends at an angle to the tire circumferential direction with a topping rubber, and the belt cords are layered so that they cross each other in opposite directions between the plies.

The tread rubber 6 may be constructed of only one layer, or may have a so-called cap-base structure, which has a base tread on the inside in the tire radial direction and a cap tread located on the outer periphery of the base tread.

The raw tire 9 shown in Figure 1 is an unvulcanized raw tire, which is shaped into the shape of a product tire in the vulcanization process described below (see Figure 2), and various tread patterns are formed on the tread surface.

A tire molding die (hereinafter, simply referred to as a "die") according to the present invention is used in the vulcanization molding of a raw tire 9. Figure 2 shows a cross-sectional view conceptually illustrating the tire molding die of the present invention. A raw tire 9 is set in this die 10 in an unvulcanized state, and the vulcanization process is carried out by applying heat and pressure to the raw tire 9 inside the die 10.

The mold 10 includes at least a tread mold portion 11 that can be pressed against the tread portion 3 of the raw tire 9. In this embodiment, the mold 10 includes the tread mold portion 11 that contacts the tread surface of the raw tire 9, a lower mold portion 12 that contacts the tire outer surface facing downward, and an upper mold portion 13 that contacts the tire outer surface facing upward. These are configured to be freely displaceable between a mold closed state and a mold open state by an opening/closing mechanism (not shown) installed around them, and the structure of such an opening/closing mechanism is well known. The tread mold portion 11 is further divided into a plurality of segments in the circumferential direction, and is movable in the radial direction of the raw tire 9 placed in the mold 10. In addition, the mold 10 is provided with a platen plate (not shown) having a heat source such as an electric heater or a steam jacket, which heats each mold portion.

At the center of the mold 10, a central mechanism 14 is provided coaxially with the tire, and a tread mold section 11, a lower mold section 12, and an upper mold section 13 are installed around it. The central mechanism 14 has a rubber bag-shaped bladder 15 and a center post 16 that extends in the axial direction of the tire, and the center post 16 is provided with an upper clamp 17 and a lower clamp 18 that grip the ends of the bladder 15.

A medium supply passage 21 for supplying the heating medium into the bladder 15 extends vertically in the central mechanism 14, and an outlet 22 is formed at the upper end of the medium supply passage 21. A supply pipe 24 is connected to the medium supply passage 21, through which the heating medium supplied from the heating medium supply source 23 and the pressurized medium supplied from the pressurized medium supply source 26 flow. The heating medium is supplied in response to the opening and closing operation of the valve 25, and the pressurized medium is supplied in response to the opening and closing operation of the valve 28.

The central mechanism 14 also has a medium discharge passage 31 extending vertically for discharging the high-temperature, high-pressure fluid that is a mixture of the heating medium and the pressurized medium in the bladder 15, and a recovery port 32 is formed at the upper end of the medium discharge passage 31. A discharge pipe 34 through which the high-temperature, high-pressure fluid flows is connected to the medium discharge passage 31, and a blow valve 33 for opening and closing the discharge pipe 34 is provided on the discharge pipe 34. The pump 35 may use a method of forced circulation of the high-temperature, high-pressure fluid so that the high-temperature, high-pressure fluid passing through the medium discharge passage 31 is resupplied to the inside of the bladder 15 via the medium supply passage 21.

The segment 41 constituting the tread mold portion 11 of the mold 10 of the present invention will be described below. FIG. 3 is a cross-sectional view conceptually showing a state in which a temperature measurement probe 44 is embedded in a shoulder portion 3S of a segment constituting the tread mold portion of the mold of the present invention. In FIG. 3, the "inner peripheral surface side" means the side closer to the raw tire 9 when the raw tire 9 is set in the mold 10. The segment 41 is one of the tread mold portion 11 divided into, for example, 6 to 12 in the circumferential direction, and each of the segments can be pressed against the tread portion 3 of the raw tire 9 by moving in the radial direction of the raw tire 9. It is more preferable that the number of divisions of the segment 41 is an odd number within the range of 6 to 12.

At least one of the segments 41 includes a fixing means 42 for fixing a temperature measurement probe 44, a temperature measurement probe insertion hole 43 extending from the fixing means 42 toward the inner circumferential surface side, and a temperature measurement probe 44 fixed by the fixing means 42, extending through the temperature measurement probe insertion hole 43 toward the inner circumferential surface side, and attached in a position such that the inner circumferential surface side end exceeds the inner circumferential surface side end I of the temperature measurement probe insertion hole 43 and can be embedded in the shoulder portion 3S of the tread portion 3. Such a temperature measurement probe 44 may be attached to one of the multiple segments 41, may be attached to multiple segments 41, or may be attached to all of the segments 41.

The fixing means 42 for fixing the temperature measurement probe 44 can be designed so that the protruding height of the temperature measurement probe 44 from the temperature measurement probe hole 43 can be adjusted, for example, by configuring the outer peripheral surface side with a double nut or the like and the inner peripheral surface side with a screw structure.

A temperature measurement probe insertion hole 43 is formed on the inner peripheral surface side of the fixing means 42. As described later, the temperature measurement probe insertion hole 43 is preferably arranged in the radial direction of the raw tire 9. The inner peripheral surface side of the temperature measurement probe insertion hole 43 is open, and the temperature measurement probe 44 is designed to protrude into the cavity of the mold 10 and be embedded in the shoulder portion 3S of the tread portion 3.

The temperature measurement probe 44 is attached in a position in which its outer peripheral end is fixed by a fixing means 42, extends through the temperature measurement probe insertion hole 43 toward the inner peripheral end, and its inner peripheral end passes beyond the inner peripheral end I of the temperature measurement probe insertion hole 43 so that it can be embedded in the shoulder portion 3S of the tread portion 3. As described below, the temperature measurement probe 44 is preferably disposed in the radial direction of the raw tire 9. The cross-sectional shape of the temperature measurement probe 44 is not particularly limited, but is preferably circular.

As described above, since the segment 41 moves in the radial direction of the raw tire 9, it is preferable to set the temperature measurement probe 44 in the radial direction of the raw tire 9, since this minimizes the load when the temperature measurement probe 44 is embedded in the shoulder portion 3S. When considering the reduction of the load on the temperature measurement probe 44, it is preferable that the deviation between the traveling direction of the segment 41 when moving in the radial direction and the radial installation direction of the temperature measurement probe 44 be 3° or less, and more preferably 1° or less.

As shown in FIG. 3, in this embodiment, a female thread is formed on the inner peripheral side of the temperature measurement probe insertion hole 43, and a male thread is formed on the surface of the temperature measurement probe 44, so that the inner peripheral side of the temperature measurement probe insertion hole 43 and the surface of the temperature measurement probe 44 can be screwed together. With this configuration, the temperature measurement probe 44 is stably held within the temperature measurement probe insertion hole 43, preventing deformation such as bending of the temperature measurement probe 44 and improving the durability of the temperature measurement probe 44.

The female screw portion formed on the inner peripheral surface side of the temperature measurement probe insertion hole 43 may be formed anywhere on the inner peripheral surface side of the temperature measurement probe insertion hole 43, but is preferably formed from the inner peripheral surface end I of the temperature measurement probe insertion hole 43 toward the outer peripheral surface side. In addition, the female screw portion is formed in a range of L1 in the depth direction from the inner peripheral surface end I of the temperature measurement probe insertion hole 43, and it is preferable that the depth L of the temperature measurement probe insertion hole 43 from the inner peripheral surface end I to the outer peripheral surface end O of the temperature measurement probe insertion hole 43 is 0.02≦L1/L≦0.05. With this configuration, the temperature measurement probe 44 is more stably held in the temperature measurement probe insertion hole 43, so that deformation such as bending of the temperature measurement probe 44 can be more reliably prevented, and the durability of the temperature measurement probe 44 can be further improved. The length of L1 can be designed arbitrarily according to the length of the temperature measurement probe 44, but it is preferable that it is 5 mm or more, for example.

In this embodiment, the temperature measurement probe insertion hole 43 is designed to have an inner diameter D2 at the outer peripheral end O larger than the inner diameter D1 at the inner peripheral end I. With this configuration, a larger gap can be secured between the temperature measurement probe 44 and the temperature measurement probe hole 43 on the outer peripheral side. This makes it possible to reduce the radiant heat conduction from the mold 10 to the temperature measurement probe 44 when measuring the temperature in the shoulder portion 3S of the tread portion 3 with the temperature measurement probe 44, and thus makes it possible to more accurately measure the temperature in the shoulder portion 3S of the tread portion 3. When the depth direction length of the portion of the temperature measurement probe insertion hole 43 where the inner diameter is larger than D1 is L2, it is preferable that L2/L≦0.9.

The outer diameter of the temperature measurement probe 44 may be designed to be equal to the inner diameter D1 at the inner circumferential end of the temperature measurement probe insertion hole 43, or may be designed to be smaller within a range in which the inner circumferential side surface of the temperature measurement probe insertion hole 43 and the surface of the temperature measurement probe 44 can be screwed together. The outer diameter of the temperature measurement probe 44 is preferably, for example, about 1 to 10 mm.

In the present invention, a resistance thermometer that utilizes the property that the electrical resistance of a metal changes with temperature can be used as the temperature measurement probe used when measuring the vulcanization temperature. Examples of such metals include platinum, nickel, and copper, but in the present invention, a platinum resistance thermometer, which has a large change in resistance value (sensitivity) with respect to temperature changes and is therefore very sensitive to temperature changes, is particularly suitable for use.

Next, we will explain in detail the vulcanization process in the manufacturing method of the pneumatic tire of the present invention.

First, as shown in FIG. 2, a raw tire 9 is set in a mold 10, and the raw tire 9 is shaped to the inner shape of the mold 10 by an inflated bladder 15. As a result, the raw tire 9 is held by the bladder 15 and assigned to each of the tread mold portion 11, the lower mold portion 12, and the upper mold portion 13. At this point, a temperature measurement probe is embedded in the slowest vulcanization part of the raw tire 9. The slowest vulcanization part means the part where the vulcanization of the tire is most difficult to progress, and usually means the shoulder part of the tread portion 3. In particular, among the shoulder parts, it is preferable to set the position where the thickness of the tread portion 3 is maximum, measured along the normal line of the inner surface of the tread portion 3 after vulcanization, as the slowest vulcanization part. In any case, in the present invention, a temperature measurement probe is embedded in the slowest vulcanization part of the raw tire 9 in order to measure the vulcanization temperature in the slowest vulcanization part. As a method of embedding, for example, the temperature measurement probe 44 may be arranged at a position corresponding to the shoulder portion of the tread mold portion 11, and when the tread mold portion 11 moves in the radial direction of the raw tire 9 to assign the raw tire 9, the temperature measurement probe 44 may be designed to be embedded while being pressed into the raw tire 9. The temperature measurement probe 44 embedded in the raw tire 9 in this way measures the temperature of the raw tire 9 during the vulcanization process, and when the tire is removed from the mold 10 including the tread mold portion 11 at the end of the vulcanization process, the temperature measurement probe may be simultaneously removed from the slowest vulcanization portion.

Then, the raw tire 9 is vulcanized by heating the mold 10 to heat the tire 9 from the tire outer surface side, and by heating the tire 9 from the tire inner surface side by supplying a high-temperature heating medium to the bladder 15 in the mold 10. The mold 10 is preheated by the steam jacket or the like, and the external heating is performed by this. The internal heating is performed by supplying a heating medium into the bladder 15 through the medium supply path 21 after shaping the tire 9. After supplying the heating medium for a predetermined time, a pressurizing medium is subsequently supplied into the bladder 15 to pressurize the tire 9 at high pressure. For example, steam or high-temperature water is used as the heating medium, and for example, an inert gas such as nitrogen gas or steam is used as the pressurizing medium.

The temperature measurement probe 44 can be used to obtain time series data on the temperature of the raw tire during vulcanization. To obtain such time series data, a high-precision digital data logger (temperature resolution of approximately 0.001°C, accuracy of approximately ±0.005°C, minimum acquisition interval of temperature value of 1 second) that is commonly available on the market can be used. By analyzing the obtained time series data, the end point of the vulcanization process can be reliably determined for each tire.

After the vulcanization process is completed, the mold 10 is opened and the temperature measuring probe disposed in the mold 10 is removed from the vulcanized tire. As a result, the vulcanization end point can be determined for each tire, and pneumatic tires can be manufactured while shortening the vulcanization time.

The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the spirit of the present invention.

Claims (5)

A tire molding mold for vulcanizing an unvulcanized raw tire including a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and a tread portion continuing to radially outer ends of each of the sidewall portions to form a tread surface,
The tire includes at least a tread mold portion that can be pressed against the tread portion,
the tread mold portion is divided in a circumferential direction and has a plurality of segments movable in a radial direction of the raw tire,
At least one of the segments includes a fixing means for fixing an outer peripheral surface side end of a temperature measurement probe, a temperature measurement probe insertion hole extending from the fixing means toward the inner peripheral surface side, and a temperature measurement probe whose outer peripheral surface side end is fixed by the fixing means, which extends through the temperature measurement probe insertion hole toward the inner peripheral surface side, and whose inner peripheral surface side end exceeds the inner peripheral surface side end of the temperature measurement probe insertion hole and is attached in a position such that it can be embedded in a shoulder portion of the tread portion,
a female screw portion formed on an inner peripheral surface side of the temperature measuring probe insertion hole and a male screw portion formed on a surface of the temperature measuring probe are formed so as to be able to be screwed together;
a tire molding mold characterized in that the female thread portion is formed within a range of L1 in the depth direction from the inner circumferential surface end of the temperature measurement probe insertion hole, and a depth L of the temperature measurement probe insertion hole from the inner circumferential surface end to the outer circumferential surface end of the temperature measurement probe insertion hole satisfies 0.02≦L1/L≦0.05. 2. The tire molding mold according to claim 1 , wherein an inner diameter D2 of the temperature measuring probe insertion hole at an outer circumferential surface end is larger than an inner diameter D1 of the temperature measuring probe insertion hole at an inner circumferential surface end. 3. The tire molding mold according to claim 1, wherein the temperature measuring probe has an outer diameter of 1 to 10 mm. 4. The tire molding mold according to claim 1 , wherein the temperature measuring probe is a platinum resistance temperature detector. A method for producing a pneumatic tire, comprising a vulcanization step of vulcanizing in a tire mold according to any one of claims 1 to 4 ,
a shoulder portion of a tread portion of an unvulcanized raw tire having a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and a tread portion connected to radially outer ends of each of the sidewall portions to form a tread surface, by embedding a temperature measuring probe in the shoulder portion.

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