VULCANIZING MOLD FOR IDENTIFYING BLOWING-LIMIT VULCANIZATION DEGREE AND TEST APPARATUS INCLUDING THE SAME

Abstract

A vulcanizing mold includes an upper mold and a lower mold. At least the lower mold is provided with a cavity in which unvulcanized sample rubber is charged, heated, and subjected to press vulcanization, so as to be formed into a rubber specimen for blowing limit observation continuously changing in vulcanization degree in a longitudinal direction. The cavity is provided with a first cavity that changes in depth in the longitudinal direction and is for producing the rubber specimen, and additionally provided with a second cavity that connectedly extends from the first cavity and is a space in which a temperature sensor is disposed to plot a temperature rise curve of the sample rubber during the vulcanization.

Claims

1. A vulcanizing mold for identifying a blowing-limit vulcanization degree comprising: an upper mold and a lower mold that pair off vertically, at least the lower mold being provided with a cavity in which unvulcanized sample rubber is charged, heated, and subjected to press vulcanization, so as to be formed into a rubber specimen for blowing limit observation changing in vulcanization degree in a longitudinal direction; a first cavity, in the cavity, for forming the rubber specimen, the first cavity changing in depth from one end side to another end side in the longitudinal direction; a second cavity that connectedly extends from the first cavity, the second cavity being a space in which a temperature sensor is disposed to plot a temperature rise curve of the sample rubber during the vulcanization; and a temperature sensor insertion opening that is provided in a predetermined wall portion of the second cavity, the temperature sensor insertion opening allowing the temperature sensor to be disposed at a predetermined temperature-sensing site in the second cavity from an outside, in an insertable and removable manner.

2. The vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 1, wherein the first cavity is set so as to gradually increase in depth from the one end side to the other end side in the longitudinal direction, and the second cavity is provided connectedly to the other end of the first cavity and is set so as to have a uniform depth shallower than a deepest portion of the first cavity and deeper than a shallowest portion of the first cavity.

3. The vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 1, wherein the predetermined temperature-sensing site in the second cavity is set at or in a vicinity of a center part in a depth direction of the second cavity, and when the temperature sensor is disposed in the second cavity via the temperature sensor insertion opening, a hot junction of the temperature sensor is positioned in the temperature-sensing site.

4. The vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 2, wherein the predetermined temperature-sensing site in the second cavity is set at or in a vicinity of a center part in a depth direction of the second cavity, and when the temperature sensor is disposed in the second cavity via the temperature sensor insertion opening, a hot junction of the temperature sensor is positioned in the temperature-sensing site.

5. A test apparatus for identifying a blowing-limit vulcanization degree comprising: the vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 1, wherein the rubber specimen for blowing limit observation is obtained from the first cavity of the vulcanizing mold, the rubber specimen continuously changing in degree of blowing, associated with a vulcanization degree, in a longitudinal direction, and temperature rise curve data on the sample rubber during vulcanization is acquired from the second cavity, the test apparatus further comprising: a pressurization mechanism that causes the upper mold to descend and tightly fit with the lower mold, and heats unvulcanized sample rubber fluidized and charged into the first cavity and the second cavity to perform press vulcanization; and a temperature sensor that is disposed at a predetermined temperature-sensing site in the second cavity via the temperature sensor insertion opening in an insertable and removable manner and configured to plot a temperature rise curve of the sample rubber during the vulcanization.

6. A test apparatus for identifying a blowing-limit vulcanization degree comprising: the vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 2, wherein the rubber specimen for blowing limit observation is obtained from the first cavity of the vulcanizing mold, the rubber specimen continuously changing in degree of blowing, associated with a vulcanization degree, in a longitudinal direction, and temperature rise curve data on the sample rubber during vulcanization is acquired from the second cavity, the test apparatus further comprising: a pressurization mechanism that causes the upper mold to descend and tightly fit with the lower mold, and heats unvulcanized sample rubber fluidized and charged into the first cavity and the second cavity to perform press vulcanization; and a temperature sensor that is disposed at a predetermined temperature-sensing site in the second cavity via the temperature sensor insertion opening in an insertable and removable manner and configured to plot a temperature rise curve of the sample rubber during the vulcanization.

7. A test apparatus for identifying a blowing-limit vulcanization degree comprising: the vulcanizing mold for identifying a blowing-limit vulcanization degree of claim 3, wherein the rubber specimen for blowing limit observation is obtained from the first cavity of the vulcanizing mold, the rubber specimen continuously changing in degree of blowing, associated with a vulcanization degree, in a longitudinal direction, and temperature rise curve data on the sample rubber during vulcanization is acquired from the second cavity, the test apparatus further comprising: a pressurization mechanism that causes the upper mold to descend and tightly fit with the lower mold, and heats unvulcanized sample rubber fluidized and charged into the first cavity and the second cavity to perform press vulcanization; and a temperature sensor that is disposed at a predetermined temperature-sensing site in the second cavity via the temperature sensor insertion opening in an insertable and removable manner and configured to plot a temperature rise curve of the sample rubber during the vulcanization.

8. The test apparatus for identifying a blowing-limit vulcanization degree of claim 5, further comprising: a decompression retention mechanism configured to, after the sample rubber is subjected to the press vulcanization for a predetermined time period, release a pressure of the pressurization mechanism to atmospheric pressure, thereby retaining a decompressed state in which the upper mold is slightly lifted up by reaction force accumulated in a spring by the pressurization, wherein the rubber specimen is taken out from the vulcanizing mold after an end of the retention of the decompressed state by the decompression retention mechanism.

9. The test apparatus for identifying a blowing-limit vulcanization degree of claim 6, further comprising: a decompression retention mechanism configured to, after the sample rubber is subjected to the press vulcanization for a predetermined time period, release a pressure of the pressurization mechanism to atmospheric pressure, thereby retaining a decompressed state in which the upper mold is slightly lifted up by reaction force accumulated in a spring by the pressurization, wherein the rubber specimen is taken out from the vulcanizing mold after an end of the retention of the decompressed state by the decompression retention mechanism.

10. The test apparatus for identifying a blowing-limit vulcanization degree of claim 7, further comprising: a decompression retention mechanism configured to, after the sample rubber is subjected to the press vulcanization for a predetermined time period, release a pressure of the pressurization mechanism to atmospheric pressure, thereby retaining a decompressed state in which the upper mold is slightly lifted up by reaction force accumulated in a spring by the pressurization, wherein the rubber specimen is taken out from the vulcanizing mold after an end of the retention of the decompressed state by the decompression retention mechanism.

11. The test apparatus for identifying a blowing-limit vulcanization degree of claim 8, further comprising: the lower mold that is allowed to move in a horizontal direction relative to the temperature sensor by a predetermined drive mechanism, wherein forward movement of the lower mold toward the temperature sensor causes the temperature sensor to be disposed in the second cavity via the temperature sensor insertion opening, and backward movement of the lower mold relative to the temperature sensor causes the temperature sensor to be removed out from the second cavity.

12. The test apparatus for identifying a blowing-limit vulcanization degree of claim 9, further comprising: the lower mold that is allowed to move in a horizontal direction relative to the temperature sensor by a predetermined drive mechanism, wherein forward movement of the lower mold toward the temperature sensor causes the temperature sensor to be disposed in the second cavity via the temperature sensor insertion opening, and backward movement of the lower mold relative to the temperature sensor causes the temperature sensor to be removed out from the second cavity.

13. The test apparatus for identifying a blowing-limit vulcanization degree of claim 10, further comprising: the lower mold that is allowed to move in a horizontal direction relative to the temperature sensor by a predetermined drive mechanism, wherein forward movement of the lower mold toward the temperature sensor causes the temperature sensor to be disposed in the second cavity via the temperature sensor insertion opening, and backward movement of the lower mold relative to the temperature sensor causes the temperature sensor to be removed out from the second cavity.

14. The test apparatus for identifying a blowing-limit vulcanization degree of claim 8, further comprising: the temperature sensor that is allowed to move in the horizontal direction relative to the lower mold, wherein with forward movement of the temperature sensor toward the vulcanizing mold, the temperature sensor is disposed in the second cavity via the temperature sensor insertion opening, and with backward movement relative to the vulcanizing mold, the temperature sensor is removed out from the second cavity.

15. The test apparatus for identifying a blowing-limit vulcanization degree of claim 9, further comprising: the temperature sensor that is allowed to move in the horizontal direction relative to the lower mold, wherein with forward movement of the temperature sensor toward the vulcanizing mold, the temperature sensor is disposed in the second cavity via the temperature sensor insertion opening, and with backward movement relative to the vulcanizing mold, the temperature sensor is removed out from the second cavity.

16. The test apparatus for identifying a blowing-limit vulcanization degree of claim 10, further comprising: the temperature sensor that is allowed to move in the horizontal direction relative to the lower mold, wherein with forward movement of the temperature sensor toward the vulcanizing mold, the temperature sensor is disposed in the second cavity via the temperature sensor insertion opening, and with backward movement relative to the vulcanizing mold, the temperature sensor is removed out from the second cavity.

17. The test apparatus for identifying a blowing-limit vulcanization degree of claim 8, further comprising: a temperature sensor that includes a rod-shaped thermocouple temperature sensor including a hot junction at a tapered leading end portion of the thermocouple temperature sensor; and a cooling mechanism that cools the temperature sensor being removed out from the second cavity.

18. The test apparatus for identifying a blowing-limit vulcanization degree of claim 9, further comprising: a temperature sensor that includes a rod-shaped thermocouple temperature sensor including a hot junction at a tapered leading end portion of the thermocouple temperature sensor; and a cooling mechanism that cools the temperature sensor being removed out from the second cavity.

19. The test apparatus for identifying a blowing-limit vulcanization degree of claim 10, further comprising: a temperature sensor that includes a rod-shaped thermocouple temperature sensor including a hot junction at a tapered leading end portion of the thermocouple temperature sensor; and a cooling mechanism that cools the temperature sensor being removed out from the second cavity.

20. The test apparatus for identifying a blowing-limit vulcanization degree of claim 11, further comprising: a temperature sensor that includes a rod-shaped thermocouple temperature sensor including a hot junction at a tapered leading end portion of the thermocouple temperature sensor; and a cooling mechanism that cools the temperature sensor being removed out from the second cavity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 is a diagram of a test apparatus for identifying a blow point being an embodiment of the present invention, illustrating a schematic configuration of the test apparatus, in which a lower mold moving forward to cause a temperature sensor to be inserted into the lower mold;

[0060] FIG. 2 is a diagram of the test apparatus for identifying a blow point, illustrating a schematic configuration of the test apparatus with the lower mold moving backward to cause the temperature sensor to be removed out from the lower mold;

[0061] FIGS. 3A and 3B each are a schematic configuration of the lower mold, where FIG. 3A is a plan view, and FIG. 3B is a front view;

[0062] FIGS. 4A and 4B each are a side view illustrating the configuration of the lower mold, where FIG. 4A is a diagram of an internal configuration illustrating a state in which a temperature sensor is inserted into the lower mold, with broken lines, and FIG. 4B is a diagram of an internal configuration illustrating a state in which the temperature sensor is removed out from the lower mold, with broken lines;

[0063] FIGS. 5A to 5C each are an illustrative diagram for illustrating the operation of the embodiment;

[0064] FIG. 6 is a schematic diagram illustrating the distribution state of bubbles generated in internal sections orthogonal to the longitudinal direction of a rubber specimen;

[0065] FIG. 7 is a graph illustrating a temperature rise curve of sample rubber acquired from the temperature sensor in a second cavity (temperature-sensing-purpose space);

[0066] FIG. 8 is a graph illustrating a time dependency of a temperature rise unsaturation degree (t) in logarithm obtained by performing data processing on the temperature rise curve;

[0067] FIG. 9 is a graph obtained by normalizing the time dependency of the temperature rise unsaturation degree (t) in logarithm illustrated in FIG. 8;

[0068] FIG. 10 is an analysis diagram used for identifying a blow point based on a vulcanization degree curve obtained using an oscillation vulcanization degree testing machine;

[0069] FIG. 11 is an illustrative diagram for illustrating how to analyze the vulcanization degree curve;

[0070] FIGS. 12A to 12C each are an illustrative diagram for illustrating a conventional, relevant apparatus; and

[0071] FIG. 13 is an illustrative diagram for illustrating another conventional, relevant apparatus.

DETAILED DESCRIPTION

[0072] An upper mold and a lower mold are clamped to form a first cavity to be a specimen forming space in such a manner that the first cavity gradually increases in depth from one end side to the other end side in a longitudinal direction, and similarly to form a second cavity to be a temperature-sensing-purpose space in such a manner that the second cavity is connected to the other end of the first cavity, and the second cavity is set to have a predetermined uniform depth shallower than the deepest portion of the first cavity and deeper than the shallowest portion of the first cavity, whereby the present invention is implemented.

[0073] In addition, a temperature-sensing site in the second cavity is set at or in the vicinity of the center part of the second cavity in a depth direction, and when the temperature sensor is put and disposed in the second cavity via a temperature sensor insertion opening, the leading end portion (a hot junction) of the temperature sensor is accurately positioned at the temperature-sensing site, whereby the present invention is implemented.

[0074] In addition, in order to put and dispose the temperature sensor at the temperature-sensing site in the second cavity via the temperature sensor insertion opening in an insertable and removable manner, the lower mold is configured to be movable in a horizontal direction relative to the temperature sensor by a predetermined drive mechanism, whereby the present invention is implemented.

Embodiment 1

[0075] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0076] FIG. 1 is a diagram of a test apparatus for identifying a blow point being an embodiment of the present invention, illustrating the schematic configuration of the test apparatus, in which the lower mold moving forward to cause the temperature sensor to be inserted into the lower mold, and FIG. 2 is a diagram of the test apparatus for identifying a blow point, illustrating a schematic configuration of the test apparatus with the lower mold moving backward to cause the temperature sensor to be removed out from the lower mold. FIGS. 3A and 3B each are a schematic configuration of the lower mold, where FIG. 3A is a plan view, and FIG. 3B is a front view, and FIGS. 4A and 4B each are a side view illustrating the configuration of the lower mold, where FIG. 4A is a diagram of an internal configuration illustrating a state in which the temperature sensor is inserted into the lower mold, with broken lines, and FIG. 4B is a diagram of an internal configuration illustrating a state in which the temperature sensor is removed out from the lower mold, with broken lines;

[0077] First, the general configuration of the main part of the apparatus in the present embodiment will be described.

[0078] The test apparatus in the present embodiment relates to an apparatus that is configured to obtain a vulcanized rubber specimen for blowing limit observation and to acquire temperature rise curve data on sample rubber during heating and press vulcanization. The schematic configuration of the main part of the apparatus includes a vulcanizing mold, a pressurization mechanism, a temperature sensor fixed to the apparatus in an immovable state, a decompression retention mechanism, and a frame structure supporting, fixing, and housing these components.

[0079] Next, referring to FIG. 1 to FIG. 4B, each component of the apparatus in the present embodiment will be described.

[0080] The main part of the vulcanizing mold is constituted by an upper mold 1 and a lower mold 2, which pair off vertically. The upper mold 1 includes a tightly-fit surface that faces the lower mold 2 and is formed into a planar shape. The lower mold 2 includes a first cavity 3 and a second cavity 4 on a tightly-fit surface thereof that faces the upper mold 1. The first cavity 3 has a rectangular shape in plan view and has a wedge shape that gradually increases in depth as it extends from one end side in a longitudinal direction thereof (the right of the drawings) toward the other end side (the left of the drawings). The second cavity 4 connectedly extends from the other end of the first cavity 3 with no partition wall and is uniform in depth. The upper mold 1 is configured so as to ascend and descend under the operation of the pressurization mechanism that will be described later. In addition, the lower mold 2 is configured to be driven and controlled in a horizontally movable manner in a direction toward a temperature sensor 5 or a direction away from the temperature sensor 5 by a lower mold drive mechanism (to be described later), so that the movement of the lower mold 2 causes the temperature sensor 5 to be inserted into or removed from the lower mold 2, the temperature sensor 5 being fixed to the body of the apparatus in an immovable state.

[0081] Here, when the upper mold 1 and the lower mold 2 are clamped under the operation of the pressurization mechanism, the first cavity 3 serves as a specimen forming space that forms unvulcanized sample rubber cast and charged therein into an approximate wedge shape. In the space, fluidized and charged sample rubber is heated and subjected to the press vulcanization, thereby formed into a rubber specimen for blowing limit observation, the vulcanization degree of which continuously varies in the longitudinal direction.

[0082] Next, as illustrated in detail in FIG. 4A and FIG. 4B, in spatial terms, the second cavity 4 connectedly extends from the first cavity 3 in the longitudinal direction of the first cavity 3 with a step interposed therebetween. However, after the clamping, the second cavity 4 serves as a temperature-sensing-purpose space that is separated from and independent of the first cavity 3 (specimen forming space), and sample rubber to be vulcanized in the space becomes a subject of temperature rise curve plotting using the temperature sensor 5. As illustrated in the drawings, the depth of the second cavity 4 is set to be shallower than the deepest portion and deeper than the shallowest portion, of the first cavity 3. This is because a blowing limit site lies at the midpoint between the deepest portion and the shallowest portion of the first cavity 3, and thus the second cavity 4 is preferably set to a depth equivalent to the midpoint in depth of the first cavity, in terms of increasing the reliability of test results. In the present embodiment, the shallowest portion of the first cavity 3 is set at 6 mm, the deepest portion of the first cavity 3 is set at 22 mm, the depth of the second cavity 4 is set at 14 mm, the step is set at 8 mm, and the overall length of the first cavity 3 and the second cavity 4 is set at 160 mm. These dimensions are merely an example and can be changed as appropriate in accordance with the scale of the apparatus, the scale of the measurement, and other factors.

[0083] Now, as illustrated in FIG. 3A to FIG. 4B, of the wall portions of the second cavity 4, a wall portion corresponding to the surface of the one end of the lower mold 2 (shown in the left of the FIG. 4A and FIG. 4B) is provided with a temperature sensor insertion opening 6 having a function with which to allow the leading end portion of the temperature sensor 5 to be disposed from the outside at a desired depth at the width center on the depth center plane of the second cavity 4 (a predetermined proper temperature-sensing site, simply stated, a proper temperature-sensing point) in an insertable and removable manner. To implement this function, the whole or part of the temperature sensor insertion opening 6 is tapered, so that the temperature sensor insertion opening 6 has a wide opening on its external side and has a narrow opening on its side close to the second cavity 4.

[0084] The pressurization mechanism includes, as illustrated in FIG. 1 and FIG. 2, a double-shaft air cylinder 7 and an ascending-descending base 8, and is configured to descend the upper mold 1 to tightly fit with the lower mold 2 and heat unvulcanized sample rubber fluidized and charged into the first cavity 3 and the second cavity 4 to perform press vulcanization. The pressurization operation of the double-shaft air cylinder 7 is controlled by a first timer (not illustrated) for setting a press vulcanization time period.

[0085] In the present embodiment, while the temperature sensor 5 is fixed to the body of the apparatus and brought into an immovable state on its temperature-sensor side, the lower mold 2 moves, as illustrated in FIG. 4A and FIG. 4B, forward and backward in the horizontal direction under drive control by the lower mold drive mechanism (not illustration), so that the temperature sensor 5 is disposed relatively to the proper temperature-sensing site in the second cavity 4 in an insertable and removable manner through the temperature sensor insertion opening 6, and plots the temperature rise curve of the sample rubber during the vulcanization. In the present embodiment, the plotting of the temperature rise curve is performed using only the single temperature sensor 5. This is because it has been confirmed that, as described above, not by simultaneous plotting using a plurality of hot junctions, plotting at only one point using a single hot junction allows for obtaining temperature rise curve data of a measurement reliability as high as in the case of simultaneous multiple-point plotting.

[0086] The temperature sensor 5 is made up of a rod-shaped thermocouple temperature sensor, and in the present embodiment, made up of a thermocouple wire housed in and protected by a metal tubule on a sensor holder (not illustrated) side, having an outer diameter of about 8 mm, and a resin tubule on a temperature sensor insertion opening 6 side, having an outer diameter of about 6 mm. The resin tubule includes a tapered leading end portion 9 that has the same cross-sectional shape and the same dimensions as those of the whole or part of the temperature sensor insertion opening 6. The tip of the leading end portion 9 is opened in the form of a small hole having a diameter of about 1 mm, and a hot junction of a thermocouple is bared from the small hole, so as to be brought into thermal contact with sample rubber.

[0087] As seen from the above, the leading end portion 9 of the temperature sensor 5 and the temperature sensor insertion opening 6 are wholly or partially formed into tapered shapes having the same cross-sectional shape and the same dimensions, whereby the leading end portion 9 of the temperature sensor 5 is closely fit with the temperature sensor insertion opening 6, so as to function as a sealing plug for preventing the sample rubber charged into the second cavity 4 from flowing to the outside (FIG. 4A). Meanwhile, the temperature sensor insertion opening 6 is configured to, at the time of the forward movement of the lower mold 2, function as a tapered positioning stopper that engages with and stops the leading end portion 9 of the temperature sensor 5 entering the second cavity 4, at the proper temperature-sensing site (FIG. 4A). In place of the tapered positioning stopper, dedicated positioning means or a dedicated stopper may be provided separately.

[0088] In the state of being removed out from the second cavity 4 (FIG. 4B), the temperature sensor 5 is quickly cooled down to, for example, room temperature by the operation of an auto cooling mechanism (not illustrated). The auto cooling mechanism is made up of a blower and the like, and provided integrally with or separately from the body of the apparatus. As necessary, a manual cooling mechanism may be used in place of the auto cooling mechanism.

[0089] The above-described decompression retention mechanism includes, as illustrated in FIG. 1 and FIG. 2, the double-shaft air cylinder 7 and the ascending-descending base 8, and a toroidal leaf spring 10, and is configured to, after the sample rubber is subjected to the press vulcanization for a predetermined time period, release the pressure of pressurization mechanism to atmospheric pressure and then retain a decompressed state in which the upper mold 1 is slightly lifted up by reaction force accumulated in the leaf spring 10 by the pressurization. The decompression retention operation of the double-shaft air cylinder 7 is controlled by a second timer for setting a decompression retention time period. The frame structure is made up of an upper base plate 11, a lower base plate 12, and poles 13, and supports, places, fixes, and houses the main part of the apparatus.

[0090] Next, referring to FIG. 1 to FIG. 4B, each component of the apparatus will be described in more detail.

[0091] An upper soaking plate 14 is configured to maintain the upper mold 1 on its lower side in a soaked state by supporting the upper mold 1 in a thermal contact state. Similarly, the lower soaking plate 15 is configured to maintain the lower mold 2 on its upper side in a soaked state by supporting the lower mold 2 in a thermal contact state.

[0092] Specifically, the upper soaking plate 14 is heated uniformly by an electrical heater embedded in its inner portion and further regulated at a certain temperature by a temperature sensor and a temperature regulator, so that the upper mold 1 disposed abutting the lower surface of the upper soaking plate 14 is caused to act as a heat source in the soaked state for sample rubber during vulcanization. Similarly, the lower soaking plate 15 is also heated uniformly by an electrical heater embedded in its inner portion and further regulated at a certain temperature by a temperature sensor and a temperature regulator, so that the lower mold 2 disposed abutting the upper surface of the lower soaking plate 15 is caused to act as a heat source in the soaked state for the sample rubber during the vulcanization. Here, it is preferable, of course, that the upper soaking plate 14, the lower soaking plate 15, the upper mold 1, and the lower mold 2 are made of high-heat-conductivity materials.

[0093] The double-shaft air cylinder 7 includes shafts that penetrate vertically, and vertically ascends and descends the ascending-descending base 8 that is connected to the lower ends of the shafts, with the ascent and descent of the shafts. The ascending-descending base 8 moves the upper mold 1 vertically via the upper soaking plate 14 disposed on the lower portion thereof with the ascent and descent of the shafts of the double-shaft air cylinder 7, so as to cause the upper mold 1 and the lower mold 2 to open, close, tightly fit with each other, and detach from each other.

[0094] Next, in the above-described decompression retention mechanism, the toroidal leaf spring 10 is fit into the upper shaft of the double-shaft air cylinder 7, and during clamping, the leaf spring 10 is compressed at a tightly-fit position of the upper mold 1 and the lower mold 2 by a cover plate 16 fixed to the upper end of the shaft, whereby upward reaction forces are generated in the shafts of the double-shaft air cylinder 7. In the present embodiment, this upward reaction force is set so as to, when the internal pressure of the double-shaft air cylinder 7 is released, lift up the gross weight of an object that ascends and descends with the double-shaft air cylinder 7, and to form a gap of about several millimeters between the upper mold 1 and the lower mold 2. By this upward reaction force, the upper mold 1 is slightly lifted up, so that the decompressed state is retained.

[0095] An upper thermal insulation spacer 17 is made of a hard thermal insulator, suppressing heat leakage from the upper soaking plate 14. A lower thermal insulation spacer 18 is also made of a hard thermal insulator, suppressing heat leakage from lower soaking plate 15. An upper soaking guard 19 is made up of light-alloy-square-bar members that surround the upper mold 1 in parallel crosses, preventing heat dissipation from the side surfaces of the upper mold 1. A lower soaking guard 20 is made up of light-alloy-square-bar members that surround the lower mold 2 in parallel crosses, preventing heat dissipation from the side surfaces of the lower mold 2.

[0096] In addition, the lower mold drive mechanism includes guard rails (not illustrated) used for driving the lower mold 2 so that the lower mold 2 can travel relative to the temperature sensor 5 fixed to the body of the apparatus, and a controller (not illustrated) that controls the forward movement and backward movement of the lower mold 2.

[0097] In the present embodiment, as illustrated in FIG. 4A, when the lower mold 2 moves forward toward the temperature sensor 5 under the drive control by the lower mold drive mechanism, the temperature sensor 5 is automatically inserted into the second cavity 4 through the temperature sensor insertion opening 6. Then, when the temperature sensor 5 reaches the proper temperature-sensing site in the second cavity 4, the positioning stopper function of the temperature sensor insertion opening 6 works to disable further forward movement of the lower mold 2, and thus the lower mold 2 stops the forward movement at that time point. As a result, the temperature sensor 5 stays at the proper temperature-sensing site in the second cavity 4, that is, is automatically installed in the second cavity 4 and automatically disposed at a proper position. Meanwhile, as illustrated in FIG. 4B, when the lower mold 2 moves backward relative to the temperature sensor 5 under the control by the lower mold drive mechanism, the temperature sensor 5 is automatically removed out from the second cavity 4 via the temperature sensor insertion opening 6.

[0098] On the tightly-fit surface of the lower mold 2 (facing the upper mold 1), as illustrated in FIGS. 3A and 3B, a U-shaped flash groove 21 is provided surrounding the first and second cavities 3 and 4 on three sides (FIG. 3A) or four sides, the flash groove 21 storing a surplus of the sample rubber flowed out to the outside from the first and second cavities 3 and 4 when the press vulcanization is started. Furthermore, on the peripheral edge portion of the lower mold 2, alignment pins 22 are provided as aligning means for engaging the upper mold 1 and the lower mold 2 accurately in clamping, the alignment pins 22 being to be fitted into alignment pin holes (not illustrated) provided on the peripheral edge portion of the upper mold 1.

[0099] Next, referring to FIG. 1 to FIG. 5C, the operation of the test apparatus having the above configuration will be described.

[0100] First, the temperatures of the heat sources are set and kept at, for example, 170 C. Here, the temperatures of the heat sources refer to the temperatures of the upper mold 1 and the lower mold 2 heated by the upper soaking plate 14 and the lower soaking plate 15, respectively.

[0101] When the temperatures of the heat sources reach their stationary state, an operator puts unvulcanized sample rubber 23 made of, for example, an SBR-based compounded rubber containing carbon black 50PHR into the first cavity 3 of the lower mold 2 (FIG. 5A). The amount of putting the sample rubber is set to be slightly larger than the total sum of the volume of the first cavity 3 and the volume of the second cavity 4. However, the operator does not put the sample rubber 23 into the second cavity 4. Therefore, at this point, the second cavity 4 is a void, recessed space with no put sample rubber and with no temperature sensor inserted.

[0102] Thereafter, the lower mold 2 starts forward movement toward the apparatus-fixed temperature sensor 5 under the drive control by the lower mold drive mechanism. As the forward movement of the lower mold 2 progresses, the temperature sensor 5 is automatically inserted into the void second cavity 4 via the temperature sensor insertion opening 6. Then, when the temperature sensor 5 reaches the proper temperature-sensing site in the second cavity 4, the positioning stopper function of the temperature sensor insertion opening 6 works to disable further forward movement of the lower mold 2, and thus the lower mold 2 stops the forward moving at that time point (FIG. 1 and FIG. 4A). As a result, the hot junction at the leading end portion 9 of the temperature sensor 5 is accurately retained at the proper temperature-sensing site in the second cavity 4, that is, automatically installed in the second cavity 4, and automatically disposed at a predetermined proper position (FIG. 5A). Note that the temperature of the temperature sensor 5 is set at room temperature as an initial temperature.

[0103] Next, when the first timer for setting a press vulcanization time period starts, the pressurization mechanism (the double-shaft air cylinder 7 and the ascending-descending base 8) causes the upper mold 1 to descend, causes the alignment pins 22 and 22 to be fit into the alignment pin holes, thereby causes the lower mold 2 and the upper mold 1 to tightly fit on each other to be clamped. When the upper mold 1 and the lower mold 2 are clamped, the first cavity 3 of the lower mold 2 joins the plane of the upper mold 1 to be a specimen forming space 3 that has a rectangular shape in plan view and has a wedge shape that gradually increases in depth from one end side in the longitudinal direction (the right of the drawings) to the other end side (the left of the drawings), and the second cavity 4 of the lower mold 2 joins the plane of the upper mold 1 to be a temperature-sensing-purpose space 4 that connectedly extends from to the other end of the specimen forming space without partition wall and has a uniform depth (FIG. 5B). At this point, the specimen forming space is filled with the unvulcanized sample rubber 23 put into the first cavity 3 of the lower mold 2 as the clamping proceeds, due to the fluidity of the unvulcanized rubber, and a surplus of the sample rubber 23 flows into the temperature-sensing-purpose space in which the hot junction of the temperature sensor 5 is already disposed properly, and the temperature-sensing-purpose space is also fully charged with the surplus of the sample rubber 23, and a further surplus of the sample rubber 23 is discharged to the U-shaped flash groove 21 surrounding the outside of the first and second cavities 3 and 4 (FIGS. 3A and 3B).

[0104] By heat conduction from the inner walls of the upper mold 1 and the lower mold 2 that begins at the instant of clamping, the unvulcanized sample rubber 23 in the specimen forming space 3 and the temperature-sensing-purpose space 4 quickly rises in temperature from room temperature, in accordance with thicknesses. In the specimen forming space 3, the charged sample rubber 23 is heated and subjected to press vulcanization to be formed into a rubber specimen 24 for blowing limit observation that continuously changes in vulcanization degree in the longitudinal direction. In the temperature-sensing-purpose space 4, by the temperature sensor 5 the hot junction of which is retained at the proper temperature-sensing site, the temperature of the sample rubber 23 around the hot junction charged in the space is traced from the room temperature, and is temperature rise curve is plotted.

[0105] In the present embodiment, when a press vulcanization time period expires that is set in advance at, for example, 240 seconds, an ending signal from the first timer causes the internal pressure of the double-shaft air cylinder 7 to be released to atmospheric pressure. As a result, the reaction force of the leaf spring 10 slightly lifts up the upper mold 1, and a gap occurs in the tightly-fit interface between the upper mold 1 and the lower mold 2, when the press vulcanization ends. At the same time, the second timer for setting a decompression retention time period starts its operation.

[0106] When the gap occurs in the tightly-fit surface between the upper mold 1 and the lower mold 2 by the reaction force of the leaf spring 10, the internal pressure of the sample rubber that is retained at a high pressure thus far declines to atmospheric pressure in an instant, and various low-boiling components (e.g., moisture) enclosed in the rubber specimen 24 by a high temperature and pressure attempt to vaporize all at once. At this point, in an under-vulcanized portion where the vulcanization does not progress to an elastic modulus level that is sufficient to suppress the occurrence of bubbles, fine bubbles are generated in the continuous solid phase of the rubber in accordance with a degree of under-vulcanization state. This is the mechanism of decompressed blowing.

[0107] Bubbles generated by the decompressed blowing do not swell in an instant, and the swell of the bubbles involves a slight time delay due to a viscoelasticity unique to rubber. For this reason, a waiting-swell time is needed to some extent until bubbles enlarge to sizes recognizable in cross section observation. Here, although it is generally known, the swelling velocity in the decompressed blowing depends on the gas pressure of bubbles, and the gas pressure increases with an increase in temperature. In contrast, the breaking strength of the rubber, being resistance force against to the swell of bubbles, declines with an increase in temperature. Thus, in the present embodiment, the process of the decompressed blowing is performed in such a manner that subjects the rubber specimen 24 to non-pressure retention at the same temperature as the temperature in the press vulcanization, for a time period as short as about 30 seconds. The reason for this is that subjecting the rubber specimen 24 to the non-pressure retention with the temperature kept at that in the press vulcanization allows the bubbles to grow to recognizable sizes quickly and stably, and as a result, the cross section observation of a blowing limit at the thickness center point of the rubber specimen 24 can be performed accurately and easily.

[0108] When the decompression retention time period set in advance expires, an ending signal from the second timer switches the operation of the double-shaft air cylinder 7 and the lower mold drive mechanism, and the upper mold 1 is lifted up via the ascending-descending base 8 (FIG. 1), and the lower mold 2 moves backward relative to the temperature sensor 5 (FIG. 2 and FIG. 4B). Accordingly, the temperature sensor 5 is automatically removed out from the second cavity 4 via the temperature sensor insertion opening 6 (FIG. 2 and FIG. 4B).

[0109] Thereafter, the wedge-shaped rubber specimen 24 continuously changing in blowing state in the longitudinal direction can be taken out from the first cavity 3, and from the second cavity 4, a sample rubber piece 25 the temperature of which has been measured can be taken out. The rubber specimen 24 and the sample rubber piece 25 are taken out collectively, and thereafter cut off and separated (FIG. 5C).

[0110] The temperature sensor 5 removed out from the second cavity 4 is quickly cooled down to room temperature (the initial temperature) by the auto cooling mechanism to prepare for the next temperature rise plotting and brought into a standby state.

[0111] FIG. 6 is a schematic diagram illustrating the distribution state of bubbles generated in internal sections A, B, and C each orthogonal to the longitudinal direction of the vulcanized rubber specimen 24 taken out from the cavity of the vulcanizing mold.

[0112] As illustrated in FIG. 6, the rubber specimen 24 is formed into a wedge shape that has a rectangular shape in plan view and gradually decreases in wall thickness from one end side (the left of the drawing) to the other end side (the right of the drawing) in a longitudinal direction, an internal section closer to the left of the drawing shows a section of a site having a larger wall thickness, and an internal section closer to the right of the drawing shows a section of a site having smaller wall thickness. In FIG. 6, the internal section A shows a distribution state of bubbles that appear in, of the wedge-shaped rubber specimen 24, a section of a site having a larger wall thickness, and the internal section B shows a distribution state of bubbles that appear in a section of a site having an intermediate wall thickness, and the internal section C shows a distribution state of bubbles that appear in a section of a site having a small wall thickness.

[0113] According to the mechanism of the decompressed blowing, bubbles are generated in a site that delays in temperature rise in the rubber specimen 24, that is, under-vulcanized portion, and thus prone to be generated in sites far from the inner walls of the upper mold 1 and the lower mold 2, and hard to be generated in sites close to the inner walls. Here, the inner walls include the tightly-fit surface of the upper mold 1 that defines the specimen forming space 3 and the bottom surface of the first cavity 3, as well as side wall surfaces (i.e., side wall surfaces of the first cavity 3).

[0114] As a result, bubbles appearing in the internal sections orthogonal to the longitudinal direction of the rubber specimen 24 tends to distribute, as illustrated in FIG. 6, in an elliptical shape centering on a zone excluding both ends of the thickness center line of the rubber specimen 24. The vertical width of the ellipse narrows as a site close to the blowing limit site, as illustrated in the internal section C, and in the blowing limit site, bubbles are concentrated on the thickness center line of the rubber specimen 24. Therefore, to evaluate generated bubbles on a single cross section with efficiency, it is most preferable to select the thickness center plane of the rubber specimen 24 as a cutting plane.

[0115] Identifying Blowing Limit Site and Calculating Thickness

[0116] Thus, in the present embodiment, using a cutting machine, the vulcanized rubber specimen 24 is divided in the thickness direction into two pieces, the thickness center plane of the vulcanized rubber specimen 24 is exposed, and the exposed thickness center plane is captured by a camera. Then, the breaking point of the occurrence of confirmable fine bubbles, that is, a blowing limit site is identified from the cross section observation performed on a captured image of the thickness center plane, and a length from the reference position to the blowing limit site is measured.

[0117] Thereafter, based on the measured length from the reference position to the blowing limit site, and the thickness at the reference position, and the gradient of the rubber specimen, the thickness of the rubber specimen at the blowing limit site is calculated. As necessary, in place of the cross sectional image, an optical-automatic blowing recognition device may be used, or the cross section observation may be directly performed in a visual manner.

[0118] Calculation of Thermal Diffusion Constant

[0119] FIG. 7 is a graph illustrating a temperature rise curve of the sample rubber 23 plotted in the second cavity (the temperature-sensing-purpose space having the known thickness) 4 using the temperature sensor 5. By applying, to Expression (1), data on chronological temperature changes obtained from the plotted temperature rise curve of FIG. 7 to convert the temperature axis into a temperature rise unsaturation degree (t) of the sample rubber 23 at a thickness center point in the second cavity (temperature-sensing-purpose space) 4, and the illustration of the time dependency of the natural logarithm ln (t) yields a substantially linear graph corresponding to Expression (2) that is derived from theory of heat conduction, as illustrated in FIG. 8.

[0120] Thus, data on FIG. 8 is subjected to straight-line approximation by the method of least squares to calculate a gradient coefficient, and a heat transfer distance (h) from the heat sources to the hot junction and the gradient coefficient are substituted into Expression (3), which gives a calculation of 0.132 mm.sup.2/sec as the value of the thermal diffusion constant of the sample rubber 23 made of the SBR-based compounded rubber containing carbon black 50PHR, the current test object. In the present embodiment, since the hot junction of the temperature sensor 5 is disposed up to the thickness center point of the sample rubber charged into the second cavity (temperature-sensing-purpose space) 4, the heat transfer distance h from the heat sources to the hot junction is half the depth of the second cavity 4 (14 mm), that is, 7 mm.

[0121] In the present embodiment, 0.132 mm.sup.2/sec, the value of the thermal diffusion constant of the sample rubber 23 is calculated based on the temperature rise curve plotted at the single hot junction, as described above, and the calculation value falls within a range of the coefficient of variation 2.3% indicating the degree of variations in the thermal diffusion constants calculated based on the temperature rise curves plotted at the hot junctions in the case of applying the conventional simultaneous multiple-point plotting method. Therefore, this can be considered to show good reproducibility as a measured value of such a kind.

[0122] In FIG. 8, since the horizontal axis of the time dependency represents time t, the gradient coefficient differs according to the thickness h, but when the horizontal axis represents t/h.sup.2, as illustrated in FIG. 9, the time dependency and the gradient coefficient of the logarithm of the temperature rise unsaturation degree (t) can be generalized regardless of the thickness h. Therefore, organizing the data using FIG. 9 in which the horizontal axis is the t/h.sup.2 axis is useful in measurement using a small piece sample, in the simulation of a normal tire, as well as in the study of vulcanization conditions in a producing step of a large tire including an aircraft tire.

[0123] Calculating Equivalent Vulcanization Time Period

[0124] The thermal diffusion constant of the sample rubber 23 and the thickness 2h at the blowing limit site of the rubber specimen 24 (the breaking point of the occurrence of fine bubbles) calculated in such a manner are substituted into Expression (2) to calculate the logarithm ln (t) of the temperature rise unsaturation degree (t) of the sample rubber 23, the calculated ln (t) is converted into (t), and then based on Expression (1) that gives (t), the temperature rise curve (calculated temperature rise curve) of the sample rubber 23 at the blowing limit site is calculated.

[0125] Next, based on the calculated temperature rise curve of the sample rubber 23 obtained from Expression (1) and the activation energy of the sample rubber, the definite integral of Expression (5) is performed to calculate the equivalent vulcanization time period (the reference temperature retention time period equivalent to the thermal history at the blowing limit site). In the present embodiment, as described above, since the vulcanization conditions of the sample rubber 23 is set at the reference temperature (the temperature of the heat sources) of 170 C. and the vulcanization time period of 240 seconds, the calculated temperature rise curve at the blowing limit site of the sample rubber 23, the definite integral of Expression (5) is performed in the range of [t.sub.1=0, t.sub.2=240 sec] to calculate the equivalent vulcanization time period at 170 C. The equivalent vulcanization time period calculated in such a manner is, for example, 144 seconds.

[0126] An actual value of the temperature rise curve T(t) is stored in a computer in the form of an isochronous digital sequence, and thus the definite integral of Expression (5) can be easily performed by an automatic computing process of the computer.

[0127] Identifying Blow Point (Blowing-Limit Vulcanization Degree)

[0128] In the present embodiment, the blow point is identified by applying the calculated equivalent vulcanization time period to a vulcanization degree curve that is plotted for the same sample rubber and at the same reference temperature.

[0129] FIG. 10 is an analysis diagram illustrating the vulcanization degree curve of the sample rubber 23 at a reference temperature of 170 C. that is plotted separately using an oscillation vulcanization degree testing machine (Machine name: FDR).

[0130] In the drawing, the mark on the vulcanization degree curve indicates a point corresponding to an equivalent vulcanization time period of 144 seconds, and by substituting a vertical axis value at this corresponding point, and values M.sub.L, M.sub.H, and M.sub.E shown in FIG. 11 calculated by the method of JIS K 6300-2 are into Expression (6), a blow point (BP) is identified. In such a manner, in the present embodiment, a value of 22% is obtained as the blow point (BP) of the sample rubber 23.

[0131] As seen from the above, according to the configuration of the present embodiment, the second cavity (temperature-sensing-purpose space) is provided in the lower mold independently of the first cavity (specimen forming space), it is possible to protect the temperature sensor from deformation and damage. The reason for this is that, when the sample rubber is put, the sample rubber, including sample rubber to be charged into the second cavity, may be put into the first cavity, and in clamping, the sample rubber to be charged into the second cavity flows into the second cavity, when a strong viscoelasticity hydrodynamic force of the sample rubber acts only in the shaft direction of the temperature sensor (coincident with of the flowing direction of the sample rubber), and as a result, the temperature sensor does not undergo the action of the viscoelasticity hydrodynamic force not very strongly as a whole. In addition, automatizing the insertion and removal of the temperature sensor to the second cavity prevents human-caused damage to the temperature sensor due to carelessness or unskillfulness of an operator.

[0132] In addition, as described above, since the temperature-sensing-purpose space is provided independently of the specimen forming space as described above, it is possible to avoid an overlap between the blowing limit observation region of sample rubber (a rubber specimen) and the putting disposition region of a temperature sensor, reliably. Therefore, a clear cutting plane can be obtained from the vulcanized rubber specimen along a thickness center plane with no trace of the temperature sensor, and thus it is possible to perform the blowing limit observation accurately. Furthermore, the setting of the proper temperature-sensing site in the temperature-sensing-purpose space can be determined in a temperature-sensor-based manner, without the influence of the blowing limit observation region, and thus it is possible to obtain a more accurate temperature rise rate/temperature rise curve.

[0133] Therefore, it is possible to increase reliability and the reproducibility of the test results of this kind, which in turn allows accuracy in identifying the blow point of the sample rubber.

[0134] As described above, an embodiment of the present invention is described in detail with reference to the drawings, but the specific configuration is not limited to the present embodiment, and changes in design within a range not departing the gist of the present invention are included in the present invention. For example, in the previously described embodiment, the whole of the first cavity and the whole of the second cavity are provided on the lower mold side, but configurations are not limited to this, and an upper side portion of the first cavity and an upper side portion of the second cavity may be provided in the upper mold side. In addition, in the previously described embodiment, the lower mold itself is configured to be able to move forward and backward relative to a fixed-type temperature sensor, which allows the temperature sensor to be inserted into and removed from the second cavity, but configurations are not limited to this, and the temperature sensor may be configured to be able to move forward and backward relative to a fixed lower mold, which allows the temperature sensor to be automatically inserted into and removed from the second cavity. As necessary, manual insertion and removal may be adopted in place of the automatic insertion and removal.

[0135] The test apparatus for identifying a blowing-limit vulcanization degree according to the present invention and the test method using the test apparatus are applicable not only to simulations of normal tires, but also to the study of vulcanization conditions in producing and development phase of large tires including aircraft tires, belts, rubber vibration isolators, and the like.

REFERENCE SIGNS LIST

[0136] 1 upper mold (vulcanizing mold) [0137] 2 lower mold (vulcanizing mold) [0138] 3 first cavity (cavity, specimen forming space) [0139] 4 second cavity (cavity, temperature-sensing-purpose space) [0140] 5 temperature sensor [0141] 6 temperature sensor insertion opening [0142] 7 double-shaft air cylinder (pressurization mechanism, decompression retention mechanism) [0143] 8 ascending-descending base (pressurization mechanism, decompression retention mechanism) [0144] 9 leading end portion of temperature sensor 5 [0145] 10 leaf spring (spring, decompression retention mechanism) [0146] 14 upper soaking plate (part of vulcanizing mold) [0147] 15 lower soaking plate (part of vulcanizing mold) [0148] 23 unvulcanized sample rubber [0149] 24 rubber specimen