JPS5817021B2 - High frequency preheating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for the treatment of unvulcanized rubber products, particularly green tires such as pneumatic tires, tractor tires, and solid tires, by applying microwave, UHF, etc. This invention relates to an improvement in a method of preheating to a predetermined temperature using high frequency waves.

Conventionally, in the vulcanization of unvulcanized rubber products that have a thick walled part with a large heat capacity, such as a green tire, heating at a high temperature in order to achieve an optimal vulcanization state up to the central part of the thick walled part causes the central part to vulcanize. When the optimum vulcanization state is reached, the outer surface becomes over-vulcanized, causing the inconvenience and excessive waste of thermal energy. A preheating operation is generally adopted, but compared to a preheating (conduction heating) method using continuous irradiation of infrared rays, etc., a preheating method (dielectric heating) using continuous irradiation of high frequency waves such as UHF has the highest heating temperature in conduction heating. This is extremely desirable from the standpoint of proper vulcanization, since the central part, which is difficult to heat, where vulcanization takes the longest, such as the inside of the tread, is heated and preheated first.Secondly, it is possible to preheat to a specified level in a relatively short period of time. There are advantages such as being able to shorten the total vulcanization time because the temperature is reached, but continuous irradiation quickly raises the temperature to a specified level, but due to poor thermal conductivity of rubber, the amount of heat implanted is insufficient. There is no preheating effect on the apparent temperature, and even if you try not to heat up after preheating, for example, as shown by the dotted line in Figure 1, the actual internal temperature T2 of the tire at the start of vulcanization is the same as the preheating. There is a tendency for the temperature to drop considerably below the apparent temperature T1 at the time of completion (in other words, a temperature drop phenomenon in the initial stage of vulcanization), and therefore, if vulcanization is continued for the standard time, vulcanization will be insufficient and quality will be poor. If, for example, the continuous irradiation time is extended to compensate for the lack of heat input due to heat generation, the internal temperature of the tire will rise too much, resulting in a so-called overvulcanization state where the rubber will locally burn, and the tire will not form. .

The present invention eliminates the above-mentioned drawbacks of the conventional methods and provides a high-frequency preheating method that can obtain a preheating effect according to the apparent preheating temperature without the risk of over-vulcanization, and therefore can maintain proper vulcanization in subsequent steps. Its structure is such that when preheating an unvulcanized rubber product by irradiating it with high frequency waves, the rubber in any part of the irradiated area is not vulcanized during the time it takes for the unvulcanized rubber product to reach a predetermined preheating temperature. It is characterized by uniform heating intermittently within a temperature range that does not cause a sulfur reaction, that is, by alternately repeating irradiation at a constant output and interruption of irradiation for a certain period of time by operating a timer.

First, one embodiment of an apparatus for carrying out the method of the present invention will be described in detail below with reference to the drawings.

In FIG. 2, a turntable 2 that rotates during heating is installed in the heating chamber 1, and a raw tire 3 is placed on the turntable 2 with its axial direction vertical, and positions are placed on both sides of the raw tire 3. The UHF radiation horns 4, 4 are connected to a UHF generator 6 through a waveguide 5, and this generator 6 has a first timer 7, a second timer 8, and a third timer for controlling intermittent irradiation of UHF. A timer 9 is connected, and each timer is linked to each other in chronological order by a limit switch after each set time has elapsed.1 For example, when the first timer 7 is activated and irradiates UHF for a certain period of time, Next, the second timer 8 operates to interrupt the irradiation for a certain period of time, then the third timer 9 operates to irradiate for a certain period of time, and then the second timer 8 operates to interrupt the irradiation for a certain period of time. 3rd until the total preheating time has elapsed.
Only the timer 9 and the second timer 8 operate alternately to repeat irradiation and interruption.

This operation makes it possible to input a sufficient amount of heat without causing any temperature drop in the initial stage of vulcanization while maintaining the rubber in any part of the irradiated area showing the highest temperature below the temperature range that does not cause vulcanization.

Furthermore, in this application, there may be slight variations in temperature in each part of the rubber, but what is more important is to maximize the heat input within the temperature range that does not cause vulcanization. .

Next, one embodiment of the method of the present invention will be described below using a green tire as an example.

Intermittent heating means constant output UHF for raw tires.
For example, first irradiation is performed continuously for 5 minutes, then the irradiation is interrupted for 5 minutes. by raising the temperature to a critical point, at the same time inducing heat conduction at individual irradiation interruptions.

A necessary and sufficient amount of heat input can be achieved and uniform vulcanization can be achieved.

An example of time allocation for intermittent irradiation is as follows.

5 minutes irradiation (preheating start) - 5 minutes interrupted - 3 minutes irradiated - 5 minutes interrupted - 3 minutes irradiated - 5 minutes interrupted - 3 minutes irradiated - 5 minutes interrupted - 3 minutes irradiated - 5 minutes interrupted - 3 minutes irradiated - 5 minutes Interruption (preheating completed: specified preheating temperature reached).

The time required for each intermittent irradiation is determined by the critical temperature at which the rubber in any part of the irradiated area begins to undergo a vulcanization reaction, e.g. approximately 100°C.
The irradiation time can be set arbitrarily as long as the internal temperature of the tire stays within a range that does not exceed the limit. However, if this irradiation time is too long, the internal temperature of the tire will be preheated beyond the above limit point, which will prevent subsequent vulcanization. On the other hand, if the irradiation time is too short, the total time required for preheating becomes longer and the economical effect of preheating is diluted, so desirably, for example, 1001
Set the time required to raise the temperature to a point slightly below °C.

As intermittent irradiation progresses, heat conduction inside the tire decreases and heat accumulation progresses, so theoretically the individual intermittent irradiation time gradually decreases as the preheating process approaches the end.・Can be distributed between

The individual irradiation interruption time is the time required for the heat transfer to be completed for the amount of heat input inside the tire under conditions where heat radiation is prevented, and empirically, for example, about 5 minutes is sufficient.

ν The predetermined preheating temperature T1 is determined by the type and size of the green tire, and the time required for green tires of different sizes to reach the predetermined preheating temperature T can be determined as follows.

For example, if it takes T1 minutes to reach a predetermined preheating temperature T1 in the conventional method of preheating by continuously irradiating UHF, the time distribution for intermittent irradiation is as in the previous example, and the time for each irradiation and interruption is A plurality of intermittent irradiation patterns are prepared, each of which has a total preheating time of t2 + t3 + t4 + t5, etc.

; If this is carried out sequentially and a pattern is found in which the actual internal temperature T2 of the tire at the start of vulcanization matches the predetermined preheating temperature T1 and no temperature drop phenomenon appears, then the pattern preheating time can be determined as the predetermined preheating time for this specific tire. This is the time required to reach the preheating temperature of .

- For tires of the same type as this specific tire, the same intermittent irradiation pattern as this specific pattern may be set in the timer of the preheating device.

In addition, after completing preheating by the method of the present invention, the timing for the next vulcanization process does not match and the vulcanization process begins immediately; if the process cannot proceed, it is necessary to keep the preheated tire in the heating chamber to prevent heat radiation. Needless to say.

Furthermore, the irradiation in the method of the present invention is not limited to irradiating a specific part of an unvulcanized article (for example, the tread of a green tire shown in the figure) as shown in FIG. 2, but also irradiating the entire unvulcanized article. Of course, it is also possible.

As described above, the method of the present invention desirably maintains a temperature within a temperature range in which no vulcanization reaction occurs in the rubber in any part of the irradiation area during the time it takes for an unvulcanized rubber product such as a green tire to reach a predetermined preheating temperature. By repeatedly irradiating and interrupting irradiation with high-frequency waves at a constant output until the temperature is slightly lower than the critical temperature at which the vulcanization reaction occurs, the unvulcanized rubber article is heated uniformly, allowing the necessary and A sufficient amount of heat is input into the green tire, and there is no inconvenience that the internal temperature of the tire at the start of vulcanization is lower than the apparent preheating temperature at the end of preheating, and proper vulcanization is achieved.

Furthermore, the method of the present invention does not include any thermometer, and therefore does not monitor the temperature, but only repeats irradiation and interruption of irradiation by adjusting the constant output high frequency with simple operation of ON and OFF by operating a timer. Since only a few steps are required, the device and operation are simple in terms of effectiveness, and there are great advantages in terms of economy and operation.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a preheating device necessary to carry out the method of the present invention, and Fig. 2 shows the state of the internal temperature of green tires preheated by the conventional method and the method of the present invention from the start to the completion of vulcanization. Diagram (the solid line is the case according to the method of the present invention, the dotted line is the case according to the conventional method). ; 1... Heater, 2... Turntable, 3... Green tire, 4... Radiation horn, 5... Wave guide tube, 6... UHF generator, 7... first timer, 8...
2nd timer, 9...3rd timer k T1
・・・・・・Appearance preheating temperature when preheating is completed, T2・
...The internal temperature of the tire during and at the beginning of vulcanization.

Claims (1)

[Claims] 1. When preheating an unvulcanized rubber product by irradiating it with high frequency waves, the temperature at which no vulcanization reaction occurs in any part of the rubber in the irradiated area during the time it takes for the unvulcanized rubber product to reach the predetermined preheating temperature. A high-frequency preheating method characterized by uniformly heating an unvulcanized rubber product by alternately repeating irradiation at a constant output and interruption of irradiation within a certain range for a fixed period of time by operating a timer.