JPH02310021A - Temperature control method of preform heating body - Google Patents

Abstract

PURPOSE:To manufacture plastic bottles which are free from dispersion in qualities by fixing a temperature of an individual preform, by fixing a feeding quantity of heating while making at least a heating body's round of a rounding path. CONSTITUTION:A temperature of a heating body 21 is sampled once by an infrared thermometer 32 while making a heating body's round of a station table 6, a result of which is sent to a controlling device. An established reference value is compared with a sampled result, based on which a necessary amount of electric power is fed to the first induction heating coil 28 from a high-fre quency oscillator until the next measured value is applied to the controlling device, in the controlling device. Therefore, since the same amount of heat is given to the whole of the heating body 21 from a heating body heating zone 27, even if a temperature difference is generated on the individual heating bodies 21 in the beginning, the difference is reduced with the lapse of time. Since an amount of electric power is fed by operating a difference with a desired temperature, temperatures of the whole heating bodies 21 can be held under a uniform state at a desired established temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling the temperature of a heating element that heats a preform for molding a plastic bottle from the inside.

[Conventional technology]

The molding preform is made of thermoplastic plastic such as polyester and is cylindrical with a cavity inside.It is blow-stretched in a mold and molded into a plastic bottle, which is often used as a container for fruit juice drinks or carbonated drinks. It is something that will be done. This preform is generally heated from the outside with an infrared heater prior to blow stretching in the mold, but recently, in order to shorten the heating time, it is heated from the outside and a heating device is installed inside. [2] A method of heating from the inside is also used.

The heating bodies are metal rod-shaped bodies arranged at equal intervals in a circumferential circuit, and the heating body is placed in a preform at a point where the circuit of the heating body partially intersects with the preform conveyance path. The heated preform leaves the circuit and is sent to the mold, while
The heating element that heated the preform returns to its original position and is heated to a predetermined temperature in the heating element heating zone.

High frequency induction heating is generally used in the heater heating zone, and for this purpose induction coils for quantitative heating and induction coils for control are provided along the circuit. An induction coil for quantitative heating provides the heating element with the minimum amount of heat so that the temperature of the heating element never exceeds the set temperature.
It is a relatively thick pipe with a long overall length. On the other hand, the control coil has a short overall length because it heats each heating element individually according to the temperature of the heating element. However, since the coil is a hollow copper pipe that does not pass cooling water, it was difficult to bend it with a small curvature and shorten the overall length.

For this reason, it was made of thin hollow pipes, but due to the small diameter, blockages often occurred due to water stains in the cooling water.
Moreover, heating efficiency was poor because each heating element was heated individually using a coil with a short overall length and a small diameter. Therefore, by increasing the total length of the induction coil for control so that it can heat multiple heating elements at the same time, it is easier to manufacture coils with large curvature using thick pipes, improving heating efficiency, and preventing malfunctions such as blockages. It is originally desirable to do this because it can be formed into fewer pieces.

[Problem to be solved by the invention]

However, if an induction coil, which has a long overall length and heats multiple heating elements simultaneously, is heated by controlling the heating elements using the usual feedback control concept, fluctuations in the amount of power supplied to the induction coils and There were cases in which periodic temperature changes occurred along the circuit in the heating element, coinciding with the temperature fluctuations. In other words, the power of the induction coil may be reduced because the temperature of the heating element facing the temperature measuring device is high because the temperature of the heating element is low and it should be heated, while the temperature of all
Since the temperature of the heating element facing the meter was low, power was supplied to the induction coil to further raise the temperature of the heating element, which had a high temperature. Therefore, there is a problem in that the temperature of the heating element on the circuit is not uniform, and conversely the temperature difference increases over time, causing variations in the heating temperature of the preform and hindering the molding of plastic bottles. Ta.

[Means to solve the problem]

In order to solve the problem described in item 2, the heating device of the heating element in the preform heating device is heated while the heating element makes at least one circuit around the circuit after measuring the temperature of the heating element and determining the necessary heating amount. The decision was made not to change the heating amount of the body heater.

[Effect]

Since at least the amount of heat supplied to the heating element is not changed while the heating element goes around the circuit, each heating element receives the same energy and is controlled to a constant temperature. Furthermore, even if there is a temperature change in each individual heating element, the heating element whose temperature is higher than the temperature determined by the fixed heating supply amount for each cycle will lower the temperature, while the heating element with a lower temperature will increase in temperature and the overall temperature will increase. The temperature is averaged and gradually approaches the desired set point, resulting in a uniform temperature.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the entire heating device for carrying out the invention. The apparatus shown in the figure runs from a preform delivery table 4 at the lower center of the figure via a transfer table 5 to a heating station table 6, and from this heating station 6 passes through an annealing station table 7, 8, a transfer table 9, and performs blow molding. A circulating route is formed to reach the station table 10, pass through the transfer table 11, and return to the preform delivery table 4. The preform 1 shown in FIG. 2 is transferred to the mandrel 3 (shown in FIG. 4).

) while being supported from below by the gin table 1-0.
It is blow molded to form a plastic bottle 2 shown in FIG. More specifically, the mandrel 3 has a cylindrical shape as shown in FIG. 4, and has circumferential grooves 1, 7, and 17 for holding on each table and subrockets 1-18, 18 for rotationally driving the mandrel 3 on its outer periphery. ing.

On the other hand, chains (not shown) are strung across the heating stage table 6 and the annealing station table 7.8 in different levels in the part through which the mandrel 3 passes, and the sprocket 18 above or below the mandrel 3.
．． 18, and as the mandrel 3 rotates, it rotates. Then, on top of the circulating mandrels 3, 3..., the briefcases 1, 1... are mounted from a conventionally known supply device via the supply tables 1.2, 1.3, and as mentioned above, heating stations are installed. heated on a table 6, then blow molded on a blow molding station table 10 by a conventionally known method;
It is molded into a plastic bottle 2. Thereafter, the plastic bottle 2 is extracted from the mandrel 3 held on the delivery table 4 by a conventionally known device and placed on the delivery table 4.
4 and then sent to the next process.

Next, the heating station table 6 will be explained using FIGS. 5 to 8. The outer periphery of the heating station table 6 is a circular circuit, and as shown in FIG. Air cylinder 20
etc. are taken at equal intervals. Said holding device] 9
is for holding the circumferential groove 17 of the mandrel 3, and is designed to hold the mandrel 3 at a predetermined position and release the holding at a predetermined position. The heating body 21 is a rod-shaped body made of metal that is easily subjected to induction heating, and is connected to the piston rod 23 of the air cylinder 2o via a heat insulator 22, and when raised by the operation of the air cylinder 2o, it is attached to the holding device 19. It is set to pass through the inside of the mandrel 3 held. Further, in the outer direction of the heating station table 6, there is a heating unit 26 forming a heated object heating zone, and a heating element heating zone 27 that heats the heating element 21.
is installed. The heating unit 26 is composed of a plurality of infrared heaters 24, a reflecting mirror 25, etc., and is opposed to the part through which the mandrel 3 passes, and irradiates the preform 1 rotating with the mandrel 3 with infrared rays to heat the preform from the outside. This is a device that heats 1. On the other hand, the heating element heating zone 27 includes an infrared radiation thermometer 32 that measures the temperature of the heating element 21, a first induction heating coil 28 that controls the heating of the heating element 21 by induction heating according to the temperature, and a fixed-rate heating coil 28. The second induction heating coil 29 is provided so as to face the heating body 21 which is pulled down as shown in FIG. An example of the first induction heating coil 28 is shown in FIGS. 7 and 8. The first induction heating coil 28 is formed by stacking hollow copper pipes formed into elongated hairpin shapes and forming them into an arc shape along the moving path of the heating element 21, with both ends blocking the movement of the heating element 21. Move it upwards so that it doesn't. The second induction heating coil 29 has substantially the same configuration as the first induction heating coil 28, and constantly heats the heating element 21 with a heating amount within a range that does not exceed the set temperature.

Next, a method for controlling the temperature of the heating element 21 will be described.

The infrared radiation temperature indicator 32 samples the temperature of the heating element 21 once while the heating element 21 goes around the heating station table 6, and sends the result to the control device. In the control device,
The set reference value that is stored is compared with the zumbling result, and based on that, the necessary amount of power is supplied from the high frequency oscillator to the first induction heating coil 28 until the next measured value is input.
(Supplied. Specifically, for example, the temperature required for the heating element 21 is 450°C, and the measured temperature of the heating element 21 is 430°C.
If the temperature is 0°C, power is applied to the first induction heating coil 28 to raise the temperature of the heating element 21 by 20°C from 430°C, and the measured heating element 21 goes around the heating station table 6. supply until they return. If the next measurement shows that the temperature of the heating element 21- is 440°C, power is applied to raise the temperature of the heating element 21 by another 10°C, and the heating element 21 goes around again. is supplied to the first induction heating coil 28 until the temperature reaches 100.

Therefore, since the same amount of heat is applied to the entire heating element 2 from the heating element heating zone 27, initially each individual heating element 2
Even if there is a temperature difference between the heating elements 21 and 1, the temperature difference decreases over time, and since the amount of electricity is supplied by calculating the difference from the desired temperature, the temperature of all the heating elements 21 can be adjusted to the desired set temperature. It is possible to maintain this condition by bringing it into a uniform state.

As a result, the preform 1 set at the desired temperature can be sent to the blow molding station table 1-0.
The plastic bottle 2 can be blow molded under optimal conditions.

Next, another embodiment of the temperature control method will be described. Immediately after the operation of the molding machine is started, the heating element 21 is at room temperature, and must be brought to a predetermined set temperature in a short period of time. Furthermore, even when the machine is temporarily stopped, the temperatures of the heating elements 21 vary, so when restarting the machine, it is necessary to raise the temperature of these elements to the set temperature H' in a short time. In these cases, the temperature of each heating element 21 is first measured, and heating is performed according to the determined temperature to raise the temperature to 1+, instead of controlling the power for each round. Furthermore, in this control, the rate of temperature increase is gradually slowed down in order to prevent overshoot (a phenomenon in which the temperature rises beyond the set temperature) of the heating element 21 (11). Select control constants so that

Then, before the temperature of the heating element 2] reaches the set temperature, the power control is changed to one-round power control.

In this way, the heating element 21 can be kept at the desired set temperature and in a uniform state with no temperature difference.

Note that the second induction heating coil 29 of the heater heating zone 27 may be configured as follows. An example of two second induction heating coils is shown in FIGS. 9 and 10.

The two second induction heating coils consist of two coils, one for heating the first part that heats the -1° part of the heating element 21 and the other for heating the lower part, and the coil for heating the second part is for heating the lower part. The coils for heating the lower part are concentrated in the first section, and each coil is individually connected to an oscillator. Otherwise, the structure is similar to that of the first induction heating coil 28, and a plurality of heating elements 2 are provided.
It is large enough to heat 1. The infrared radiation thermometer 32 is composed of three 1fiA-12 units 31 for measuring the upper, middle, and lower parts of the heating body 21, and each is individually connected to a control device (not shown). In this way, the heating body 21 is
If the heating element 21 is divided into IJj directions and controlled individually, if there is a temperature difference in the axial direction of the heating element 21, this temperature difference can be eliminated and the temperature in the axial direction can be made uniform, and the temperature of the heating element 21 can be When the temperatures are different in the axial direction, different predetermined temperatures can be set in the axial direction.

Furthermore, in the "-kiden", the heating state is not changed while the heating body 21 goes around the heating station table 6 once, but the heating state is not limited to the "-time" and may be changed as long as it goes around the heating station table 6 once or more. Furthermore, if the heating capacity of the first induction heating coil 28 is greatly varied, the second induction heating coil 29 is not necessarily required; By setting the winding pitch of the first induction heating coil 28, different temperatures (Ii) can be applied to the heating body 21 in the axial direction without the need for the second induction heating coil 29. Now, since the amount of two-eyed back is constant while the heating element 21 goes around the circuit, if the heating element 21 is not inserted into the brif l, ],
The thermometer can be installed anywhere on the circuit. Also heating body 2
Although the heating element 1 is made of metal and heated by induction heating, the present invention is not limited thereto, and the heating element 2] may be made of ceramic 1-2 and heated with an infrared heater.

〔Effect of the invention〕

According to the temperature control method of the present invention, in a preform heating method in which the heating bodies are arranged at equal intervals on a circuit, and the heating bodies are inserted into the preform to heat the preform from the inside, the heating body When heating the heating element to the set temperature based on the measured temperature, the heating element is heated to the set temperature while the heating element goes around the circuit at least once (since the supply amount is constant, all the heating elements are heated to the set temperature Can you warm up?
1 (This state can be maintained. Therefore, the temperature of each preform is always constant, and it is possible to manufacture plastic bottles with no variation in quality. When the temperature rises at the start of work, the temperature of each heating element is initially controlled by 1.IJ to raise the temperature to 1.IJ, and then, before reaching the set temperature, the heating supply amount is increased until the heating element goes around the circuit at least once. is constant, so
All heating elements can be heated to the set temperature quickly and uniformly.

[Brief explanation of drawings]

Fig. 1 is an f-plane view schematically showing an embodiment of the present invention, Fig. 2 is a cross-sectional view of a preform heated in this embodiment, and Fig. 3 is a heated i Figure 4 is a cross-sectional view of the mandrel that supports the preform, Figure 5 is a cross-sectional view of the v-■ direction in Figure 1, and Figure 6 is a cross-sectional view of the VI-Vl node in Figure 1. 7 is a perspective view showing the first induction heating coil, FIG. 8 is a sectional view in the ■-■ direction of FIG. 7, FIG. 9 is a front view of the second induction heating coil, and FIG. 10 is the 0th
FIG. In the drawings] Preform, 2 Plastic bottle, 3 Mandrel, 4 Delivery table, 5.9.11 Transfer table, 6 Heating stain table, 7.8 Annealing station table, ]0・
・Blow molding station table, 1.2.1.3・
- Supply table, 14... Delivery table, 17... Circumferential groove, 18... Sprocket, 1... Holding device, 20
...Air cylinder, 21.. Heating body, 22.. Heat insulator, 25.. Reflector, 26.. Heating unit, 27..
Heating element heating zone, 28... first induction heating coil. Two second induction heating coils, '32 Infrared radiation temperature 51° Applicant's agent Fujimoto 1117 Hikari-16
= Figure 3 Figure 5: 19:37 Figure 4 Figure 6 27
Vinyl r-1 □□□- r□□-- 28te" 1 022go1 [2〇Figure 7■] Figure 8

Claims (1)

[Scope of Claims] 1) A plurality of heating elements disposed on a circuit are sequentially heated in a heating element heating zone provided along the circuit, and the heated heating elements are inserted into a preform to heat at least the inside of the preform. In a molding method in which a preform is heated and molded into a plastic bottle in a mold, the amount of feedback from a temperature measuring device of the heating element to the heating element heating zone is constant while the heating element makes at least one circuit around the circuit. A method for controlling the temperature of a heating element. 2) When the temperature of the heating element increases at the start of molding work, the temperature of each heating element is measured and feedback control is performed to heat each heating element, and then the heating is performed before the heating element reaches the working temperature. 2. A temperature control method for a heating body according to claim 1, wherein the heating method is switched to a heating method in which the amount of feedback to the body heating zone is kept constant while the heating body goes around at least one circuit.