JP2020015239A - Method for vulcanizing pneumatic tire - Google Patents

Abstract

To provide a method for vulcanizing a pneumatic tire making it easier to control the inner temperature of a vulcanization bladder, and capable of enhancing the freedom of steam pressure setting, thus enabling tire quality to be improved.SOLUTION: A method for vulcanizing a pneumatic tire stops the injection after injecting a non-condensable gas HG into a bladder 2 inside a green tire G after shaping, the non-condensable gas HG having a higher pressure than a pressure of a shaping gas injected into the bladder 2 when shaping, and the green tire G being disposed in a vulcanization mold 9. While leaving the non-condensable gas HG in the bladder 2, it keeps injecting steam S into the bladder 2, and sets its inner pressure and inner temperature in a target range. While maintaining the bladder 2 in an inflated state, it pressurizes and heats up the green tire G from the inside by the bladder 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of vulcanizing a pneumatic tire, and more particularly, to facilitate control of the internal temperature of a vulcanizing bladder, increase the degree of freedom in setting steam pressure, and improve tire quality. And a method for vulcanizing a pneumatic tire.

  In the vulcanizing step of a pneumatic tire, a green tire placed in a vulcanizing mold is pressurized and heated from the inside by an inflated vulcanizing bladder. Generally, in a vulcanization process, after a predetermined amount of steam is poured as a heating medium into a vulcanization bladder, the injection is stopped, and then a pressurized medium (such as nitrogen gas) higher in pressure than the steam is injected. Green tires are vulcanized.

  In this method, the temperature of the mixed gas of the steam and the pressurized medium inside the vulcanizing bladder decreases due to the decrease in the partial pressure of the steam due to the heat release and condensation of the injected steam, and it is difficult to control the temperature. Also, since the temperature of the steam to be injected first follows the saturated steam curve, it is necessary to set the steam pressure lower than the pressure required in the vulcanization step in order to prevent over-vulcanization of the green tire. is there. That is, in the initial stage of vulcanization, the bladder internal pressure is lower than the target value, and vulcanization failure such as insufficient pressurization of the green tire is likely to occur.

  A method of injecting steam as a heating medium after injecting nitrogen gas as a pressurizing medium into a vulcanizing bladder has also been proposed (see Patent Document 1). In the method proposed in this document, after the injected nitrogen gas is discharged from the vulcanization bladder, steam is injected into the vulcanization bladder, and the nitrogen gas is completely replaced with steam. Therefore, when the steam pressure is increased, the temperature also increases. If the steam pressure is reduced to prevent overvulcanization, vulcanization failures such as insufficient pressurization will occur.

JP 2007-38539 A

  An object of the present invention is to provide a vulcanizing method for a pneumatic tire that facilitates controlling the internal temperature of a vulcanizing bladder, increases the degree of freedom in setting steam pressure, and improves tire quality. To provide.

  In order to achieve the above object, the method of vulcanizing a pneumatic tire of the present invention includes the steps of: expanding a vulcanization bladder inside a shaped green tire placed in a vulcanization mold; In a method of vulcanizing a pneumatic tire that vulcanizes by pressurizing and heating, a non-condensable gas having a pressure higher than the pressure of a shaping gas injected into the vulcanizing bladder is injected into the vulcanizing bladder. After the expansion, the injection is stopped, and while the non-condensable gas remains in the vulcanization bladder, steam is continuously injected into the vulcanization bladder, and the internal pressure and the internal temperature are set to the target ranges. The green tire is vulcanized while maintaining the inflated state.

  According to the present invention, after the non-condensable gas is injected into the vulcanization bladder and expanded, the injection is stopped, and the vulcanization is performed while the non-condensable gas remains in the vulcanization bladder. Since steam is continuously injected into the vulcanizing bladder, even if the injected steam condenses, the internal temperature of the vulcanizing bladder can be controlled by the heat of the sequentially injected steam. By injecting non-condensable gas before steam, the injection pressure of steam is set to the pressure required for vulcanization, and the injection pressure of non-condensable gas is set based on the partial pressure of steam injected later. Can be set to the required temperature. That is, the steam pressure can be appropriately set independently of the steam temperature. Furthermore, since the previously injected non-condensable gas remains in the vulcanization bladder, there is a problem that the internal pressure of the vulcanization bladder becomes lower as in the case of completely replacing the non-condensable gas with steam. Can be avoided. With the vulcanizing bladder expanded in this way, it is possible to appropriately pressurize and heat from the inside of the green tire, which is advantageous for improving the quality of the vulcanized tire.

It is explanatory drawing which illustrates the vulcanizing apparatus used for this invention by longitudinal cross section. It is explanatory drawing which simplifies and illustrates the vulcanizing apparatus of FIG. It is a graph which illustrates change with time of the internal pressure and internal temperature of the bladder for vulcanization in embodiment of this invention. FIG. 4 is a graph illustrating the change over time in the internal pressure and internal temperature of a vulcanizing bladder in a conventional vulcanizing step.

  Hereinafter, a method for vulcanizing a pneumatic tire according to the present invention will be described based on an embodiment shown in the drawings.

  The pneumatic tire vulcanizing apparatus 1 (hereinafter, referred to as vulcanizing apparatus 1) illustrated in FIGS. 1 and 2 has a rubber-made cylindrical vulcanizing bladder 2 (hereinafter, referred to as bladder 2). . The upper clamp portion 3a and the lower clamp portion 3b of the bladder 2 are held by a disk-shaped upper clamp holding portion 5a and a lower clamp holding portion 5b attached to a center post 4a constituting the center mechanism 4, respectively.

  The center post 4a has an injection port 6 for injecting steam S as a heating medium and a non-condensable gas HG as a pressurized medium into the bladder 2, and steam S and a non-condensable gas HG inside the bladder 2. A discharge port 7 for discharging to the outside is formed. As the non-condensable gas HG, an inert gas is mainly used, and specific examples thereof include a nitrogen gas and a helium gas.

  The inlet 6 and the outlet 7 are respectively connected to a supply line 6L and a discharge line 7L extending downward from the vulcanizing apparatus 1. The inlet 6 is disposed above the outlet 7.

  The supply line 6L includes a gas supply line 6L1 connected to the gas supply source P1, and a steam supply line 6L2 connected to the steam supply source P2. The gas supply line 6L1 supplies the non-condensable gas HG sent from the gas supply source P1 to the inside of the bladder 2. The steam supply line 6L2 supplies the steam S sent from the steam supply source P2 to the inside of the bladder 2.

  The gas supply line 6L1, the steam supply line 6L2, and the discharge line 7L are provided with on-off valves 8a, 8b, 8c for opening and closing the respective lines. The operation of opening and closing each of the on-off valves 8a, 8b, 8c is controlled by the control unit 8d.

  In order to vulcanize the green tire G using the vulcanizing apparatus 1, the green tire G is placed in a vulcanizing mold 9 which is open in a horizontal state. In this embodiment, the vulcanizing mold 9 is composed of an annular sector 9a divided into a plurality in the circumferential direction, an annular side plate 9b arranged on the upper side, and an annular side plate 9c arranged on the lower side. ing. The vulcanizing mold 9 is not limited to the sectional type as in this embodiment, and a so-called upper and lower split mold can also be used.

  The green tire G is shaped before vulcanization by injecting and inflating a shaping gas into the bladder 2 inserted and arranged inside the green tire G. As the shaping gas, a non-condensable gas HG such as a nitrogen gas is used. The pressure of the shaping gas injected into the bladder 2 is much smaller than the pressure of the non-condensable gas HG or steam S injected at the time of vulcanization, for example, about 0.05 MPa. The vulcanization mold 9 is closed with the bladder 2 disposed inside the green tire G.

  Next, the non-condensable gas HG and the steam S are supplied to the bladder 2 as illustrated in FIG. The solid thick line Sp in the drawing indicates the injection pressure of the steam S supplied to the bladder 2, and the solid thin line Hp indicates the injection pressure of the non-condensable gas HG supplied to the bladder 2. The broken line T indicates the internal temperature of the bladder 2, that is, the temperature of the gas existing in the bladder 2. The vertical length of Spv in the figure indicates the magnitude of the partial pressure of the steam S in the bladder 2.

  The procedure for supplying the non-condensable gas HG and the steam S will be described in detail. The on-off valves 8b and 8c are closed, and only the on-off valve 8a is opened, and the normal-temperature non-condensable gas sent from the gas supply source P1. HG is supplied into the bladder 2 through the gas supply line 6L1. The injection pressure Hp of the non-condensable gas HG is set to a pressure higher than the pressure of the shaping gas. The injection pressure Hp is set so that the temperature in the bladder 2 of the steam S calculated based on the partial pressure Svp in the bladder 2 of the steam S to be injected later is within a preset target temperature range. Is set.

  For example, when the internal pressure of the bladder 2 required in the vulcanization step is 2 MPa and the internal temperature is 200 ° C., when the non-condensable gas HG and the steam S are injected into the bladder 2, the internal pressure and the internal temperature are set to the target values (actual values). It is necessary to set the target value to the target range including the allowable range). Therefore, the partial pressure Spv at which the temperature of the steam S reaches the target value (200 ° C.) is calculated using the saturated steam pressure curve. Next, the injection pressure Hp of the non-condensable gas HG is calculated by subtracting the calculated partial pressure Spv from the target value of the internal pressure (2 MPa). The specific injection pressure Hp is 0.55 MPa.

  After the bladder 2 is expanded by injecting the non-condensable gas HG, the supply of the non-condensable gas HG is stopped by closing the on-off valve 8a. The inner peripheral surface of the green tire G is pressed by the inflated bladder 2, and the green tire G is pressed by the mold 9. The time during which the on-off valve 8a is opened (the time during which the non-condensable gas HG is supplied to the bladder 2) is extremely shorter than the vulcanization time. The specific time during which the on-off valve 8a is open varies depending on the tire size (the internal space volume of the bladder 2) and the supply flow rate of the non-condensable gas HG. For example, in the case of vulcanizing a general passenger car tire, it takes about 10 to 20 seconds, and in the case of a truck / bus tire, it takes about 30 to 50 seconds.

  The steam S, which is saturated steam sent from the steam supply source P2, is supplied to the inside of the bladder 2 through the steam supply line 6L2 together with the closing of the opening / closing valve 8a or immediately after the valve closing, by opening only the opening / closing valve 8b. I do. At this time, while the non-condensable gas HG injected into the bladder 2 is left in the bladder 2, steam S is continuously injected into the bladder 2 so that the internal pressure and the internal temperature T of the bladder 2 are set to target ranges, respectively. This state is maintained for a predetermined time.

  The injection pressure Sp of the steam S is set to a pressure required for vulcanization. The temperature of the steam S injected into the bladder 2 is set to be within the target temperature range by adjusting the injection pressure Hp of the non-condensable gas HG as described above. Therefore, the internal temperature T of the bladder 2 after injecting the steam S becomes a target value (actually, a target range including an allowable range in the target value). The green tire G is pressurized and heated from the inside by the inflated bladder 2 and vulcanized.

  The bladder 2 is sufficiently heated by the supplied steam S, and the unvulcanized rubber of the green tire G starts to flow in earnest. When the steam S is supplied to the bladder 2, the bladder 2 has already been given a certain internal pressure by the non-condensable gas HG. In the present invention, since the non-condensable gas HG previously injected into the bladder 2 is not completely replaced by the steam S which is injected later, the problem that the internal pressure of the bladder 2 decreases can be avoided.

  After maintaining the internal pressure of the bladder 2 within the preset target range for a predetermined time, the on-off valve 8b is closed to stop the supply of the steam S. Accordingly, the internal temperature of the bladder 2 is also maintained in the target range for a predetermined time. Next, by opening the on-off valve 8c, the steam S and the non-condensable gas HG inside the bladder 2 are discharged to the outside of the bladder 2 through the discharge line 7L. Then, the mold 9 is opened by moving the upper side plate 9b upward and moving each sector 9a in the radially expanding direction. Next, the vulcanized tire is moved upward, extracted from the contracted bladder 2, and taken out of the vulcanizing apparatus 1.

  FIG. 4 shows a conventional vulcanization process in which steam S is first supplied to the bladder 2 at an injection pressure Sp, the supply is stopped, and then a non-condensable gas (nitrogen gas) HG is supplied to the bladder 2 at an injection pressure Hp. Of the internal pressure and the internal temperature of the bladder 2 with time. Comparing this conventional vulcanization step (FIG. 4) with the vulcanization step of the embodiment (FIG. 3), in the conventional vulcanization step, the previously supplied steam S is radiated and condensed in the bladder 2. , The partial pressure Spv decreases. As a result, the internal temperature T of the bladder 2 gradually decreases, so that it is difficult to control the temperature. The degree of decrease in the internal temperature T differs depending on the size and temperature of the green tire G, the external environmental temperature, and the like. Therefore, the degree of vulcanization of the green tire G varies, which is disadvantageous for securing stable tire quality. Become. On the other hand, in the embodiment, even if the injected steam S is condensed, control can be performed so that the internal temperature T of the bladder 2 is maintained in the target range by the heat of the sequentially injected steam S.

  In the conventional vulcanization process, if the internal pressure required for vulcanization is applied to the bladder 2 by the steam S to be supplied first, the bladder 2 will not be supplied when the non-condensable gas HG is supplied later. Internal temperature T becomes excessively high. Therefore, the green tire G cannot be sufficiently pressurized from the beginning of the vulcanization step, and vulcanization failure due to insufficient pressurization in the early stage of vulcanization is likely to occur. On the other hand, in the embodiment, since the steam pressure Sp can be set independently of the steam temperature by injecting the non-condensable gas HG before the steam S, the degree of freedom in setting the pressure of the steam S is increased. . Along with this, the internal pressure and the internal temperature T of the bladder 2 can be appropriately set independently from the initial stage of vulcanization. The green tire G can be appropriately pressurized and heated from the inside by the bladder 2 expanded in this way from the beginning of vulcanization, which is advantageous for improving the quality of the vulcanized tire.

  In the conventional vulcanization process, if there is a pinhole or the like in the bladder 2 and the steam S flows out of the bladder 2, the internal pressure of the bladder 2 decreases. Along with this, the partial pressure Spv of the steam S decreases, and the internal temperature T decreases, so that there is a problem that a vulcanization failure occurs. On the other hand, in the embodiment, even if the steam S flows out of the bladder 2, the steam S that flows out is supplied to the bladder 2, so that the internal temperature T does not decrease. Therefore, it is advantageous to avoid vulcanization failure.

  Furthermore, since the supply of steam S to the bladder 2 is stopped in the latter half of the conventional vulcanization process, the steam S is radiated and condensed in the steam supply line 6L2, so that drain water is accumulated. Then, at the time of the next vulcanizing step of the green tire G, the drain water flows into the bladder 2 through the supply line 6L2. Along with this, there is also a problem that the vertical temperature difference of the bladder 2 increases and the degree of vulcanization of the green tire G varies. On the other hand, in the embodiment, the time during which the on-off valve 8b is closed is short, and the steam S flows frequently, so that the possibility of condensation in the steam supply line 6L2 to generate drain water is extremely low. Therefore, it is advantageous to suppress the variation in the degree of vulcanization of the green tire G vulcanized in the horizontal state in the vertical direction.

  The present invention can be applied to the existing vulcanizing apparatus even if the supply timing of the non-condensable gas HG and the steam S to the bladder 2 is adjusted without any major modification of the equipment. There are also benefits.

DESCRIPTION OF SYMBOLS 1 Vulcanizing apparatus 2 Vulcanizing bladder 3a Upper clamp part 3b Lower clamp part 4 Central mechanism 4a Center post 5a Upper clamp holding part 5b Lower clamp holding part 6 Inlet 6L, 6L1, 6L2 Supply line 7 Outlet 7L Discharge Lines 8a, 8b, 8c On-off valve 8d Control unit 9 (9a, 9b, 9c) Mold G for vulcanization Green tire P1 Gas supply P2 Steam supply HG Non-condensable gas (pressurized medium)
S steam (heating medium)

Claims (3)

By inflating a vulcanizing bladder inside the green tire after shaping arranged in a vulcanizing mold, a method of vulcanizing a pneumatic tire for vulcanizing by pressurizing and heating the green tire,
After injecting and expanding a non-condensable gas having a pressure higher than the pressure of the shaping gas injected into the vulcanization bladder into the vulcanization bladder, the injection is stopped, and the non-condensable gas is introduced into the vulcanization bladder. With the condensable gas remaining, steam is continuously injected into the vulcanizing bladder, and the green tire is vulcanized while maintaining an expanded state with the internal pressure and the internal temperature in target ranges. Vulcanizing method for pneumatic tires.   The injection pressure of the non-condensable gas is calculated based on the partial pressure of the steam in the vulcanization bladder.The temperature of the steam in the vulcanization bladder is within a preset target temperature range. The method for vulcanizing a pneumatic tire according to claim 1, wherein the setting is made to be as follows.   The method for vulcanizing a pneumatic tire according to claim 1 or 2, wherein a nitrogen gas is used as the non-condensable gas.

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