JPH0624764B2 - Preform heating body temperature control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature control method for a heating body for internally heating a preform for molding a plastic bottle.

[Conventional technology]

The molding preform is a cylindrical one made of a thermoplastic such as polyester and having a cavity inside,
Blow stretching is performed in a mold to be molded into a plastic bottle that is often used as a container for juice drinks, carbonated drinks and the like. This preform is generally heated from the outside by an infrared heater before blow stretching in the mold, but recently, in order to shorten the heating time, it is heated from the outside and a heating element is used inside. The method of inserting and heating from the inside is also adopted.

The heating body is a metal rod-shaped body and is arranged at equal intervals in a circular circuit, and the heating body is preformed at a portion where the circuit of the heating body and the carrying path of the preform intersect. Enters the inside of and heats the preform from the inside, and the heated preform leaves the circuit and is sent to the mold,
The heating element that has 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 heating element heating zone, and for this purpose, an induction coil for quantitative heating and an induction coil for control are provided along the circuit. The induction coil for quantitative heating imparts a minimum amount of heat to the heating body so that the temperature of the heating body never exceeds the set temperature, and is formed with a relatively thick pipe and a long overall length. On the other hand, the control coil has a short overall length because it individually heats the heating elements according to the temperature of the heating elements. However, since the coil is a hollow copper pipe through which cooling water passes, it is difficult to bend the coil with a small curvature to shorten the total length. For this reason, it was made from a thin hollow pipe, but due to its small diameter, it often clogs due to water stains in the cooling water, and since the heating elements are individually heated by coils with a short overall length and a small diameter, heating efficiency is improved. It was bad. Therefore, by increasing the total length of the induction coil for control so that multiple heating elements can be heated at the same time, it is possible to make a coil with a large curvature using a thick pipe, it is easy to manufacture, and heating efficiency can be improved. This is originally desirable because it can be formed in a small number.

[Problems to be Solved by the Invention]

However, when the heating coil is heated by controlling the induction coil, which has a long overall length and is heated by a plurality of heating elements at the same time, using the general idea of feedback control, the fluctuation of the power supply amount to the induction coil and the temperature of the heating element are changed. There was a case where the temperature coincided with the fluctuation, and the temperature of the heating element was periodically changed along the circuit. That is, the temperature of the heating element facing the temperature measuring device is low because the temperature is low and the heating element facing the temperature measuring device has a high temperature. Therefore, the induction coil is supplied with electric power to raise the temperature of the heating body having 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 with the passage of time, causing variations in the heating temperature of the preform, which hinders the molding of plastic bottles. It was

[Means for Solving the Problems]

In order to solve the above problems, the heating device of the heating element in the preform heating device, after determining the required heating amount by measuring the temperature of the heating element, the heating element of the heating element during at least one round of the circuit. It was decided not to change the heating amount of the heater.

[Action]

Since at least the heating supply amount to the heating body is not changed while the heating body goes around the circuit, each heating body receives the same energy and is controlled to a constant temperature. Even if there is a temperature change in each heating element, heating elements lower than the temperature determined by the fixed heating supply amount for each rotation lower the temperature, while heating elements with lower temperature increase the temperature and overall average The temperature gradually becomes closer to the desired set value and the temperature becomes uniform.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the whole heating apparatus for carrying out the invention. The apparatus shown in the figure reaches the heating station table 6 via the transfer table 5 from the preform delivery table 4 in the lower center of the figure, and blow molding is performed from this heating station 6 through the annealing station tables 7 and 8 and the transfer table 9. It reaches the station table 10, passes through the transfer table 11 and again the preform delivery table 4
A patrol route is formed so as to return to, and the preform 1 shown in FIG. 2 is circulated on the patrol route according to the above route while being supported by the mandrel 3 (shown in FIG. 4) from below. Meanwhile, it is heated at the heating station 6 and blow-molded at the blow molding station table 10 to be molded into the plastic bottle 2 shown in FIG. More specifically, as shown in FIG. 4, the mandrel 3 has a cylindrical shape, and is provided with circumferential grooves 17, 17 for holding it on each table and sprockets 18, 18 for rotationally driving it on the outer circumference. On the other hand, on the heating station table 6 and the annealing station tables 7 and 8, a chain (not shown) is stretched around the mandrel 3 in a stepped manner, and sprockets 18 and 18 above or below the mandrel 3 are provided. When the mandrel 3 circulates while meshing with each other, the mandrel 3 is caused to perform a rotation motion accordingly. Then, the preforms 1, 1 ... Are mounted on the circulating mandrels 3, 3 ... from the conventionally known feeding device via the feeding tables 12, 13, and are heated by the heating station table 6 as described above.
Next, it is blow-molded on the blow molding station table 10 by a conventionally known method to be molded into the plastic bottle 2. After that, the plastic bottle 2 is transferred to the delivery table 4
From the mandrel 3 held by the above-mentioned device, the mandrel 3 is taken out by a conventionally known device and sent out through the sending table 14 to the next step.

Next, the heating station table 6 will be described with reference to FIGS. The outer circumference of the heating station table 6 is a circular circuit, and as shown in FIG. 5, a holding device 19 for holding the mandrel 3, a heating body 21, and an air cylinder 20 for operating the heating body 21.
Etc. are attached at equal intervals. The holding device 19 holds the circumferential groove 17 of the mandrel 3, and holds the mandrel 3 at a predetermined position and releases the holding at the predetermined position. The heating body 21 is a rod-shaped body made of a metal that is easily subjected to induction heating, and is connected to the piston rod 23 of the air cylinder 20 via a heat insulating body 22,
It is set so as to pass through the inside of the mandrel 3 held by the holding device 19 when the air cylinder 20 is raised by the operation. A heating unit 2 that forms a heating zone for the object to be heated is provided outside the heating station table 6.
6 and a heating body heating zone 27 for heating the heating body 21 are provided. The heating unit 26 includes a plurality of infrared heaters 24, a reflecting mirror 25, and the like, and the mandrel 3
Is a device that heats the preform 1 from the outside by irradiating the preform 1 that rotates with the mandrel 3 with infrared rays. On the other hand, the heating body heating zone 27 includes an infrared radiation thermometer 32 that measures the temperature of the heating body 21, a first induction heating coil 28 that controls heating of the heating body 21 by induction heating according to the temperature, and a fixed amount heating. The second induction heating coil 29 is provided so as to face the heating body 21 pulled downward as shown in FIG. 7 and 8 show an example of the first induction heating coil 28.
Shown in the figure. The first induction heating coil 28 is formed by stacking hollow copper pipes elongated in a hairpin shape and stacking them on the heating element 2.
It is formed in an arc shape along the movement path of No. 1, and both side ends are moved upward so as not to hinder the movement of the heating body 21. The second induction heating coil 29 is the first induction heating coil 2
The configuration is substantially the same as that of 8, and the heating body 21 is constantly heated with a heating amount within a range that does not exceed the set temperature.

Next, a method for controlling the temperature of the heating body 21 will be described. The infrared radiation thermometer 32 samples the temperature of the heating body 21 once while the heating body 21 goes around the heating station table 6, and sends the result to the control device. The control device compares the stored set reference value with the sampling result, and supplies the required amount of power from the high frequency oscillator to the first induction heating coil 28 until the next measured value is input based on the comparison.
Specifically, for example, the temperature required for the heating body 21 is 450 ° C.
When the measured temperature of the heating element 21 is 430 ° C., the temperature of the heating element 21 is further increased from 430 ° C. to 20 ° C.
Electric power that raises the temperature is applied to the first induction heating coil 28, and is supplied until the measured heating body 21 makes one circuit around the heating station table 6 and returns. Then, when the temperature of the heating body 21 is 440 ° C., which is measured next time, the heating body 21 makes one round and returns again by applying electric power to further raise the temperature of the heating body 21 by 10 ° C. Up to first
Supply to the induction heating coil 28.

Therefore, since the entire heating body 21 is given the same amount of heat from the heating body heating zone 27, the individual heating bodies 2 are initially heated.
Even if there is a temperature difference in 1, the temperature difference decreases with the passage of time, and the amount of electric power is supplied by calculating the difference from the desired temperature. Can be kept in a uniform state.
As a result, the preform 1 set to a desired temperature can be sent to the blow molding station table 10, and the blow molding of the plastic bottle 2 can be performed in an optimum state.

Next, another embodiment of the temperature control method will be described. Immediately after the operation of the molding machine is started, the heating body 21 is in a room temperature state, and this must be brought to a predetermined set temperature in a short time. Further, even when the machine is temporarily stopped, the temperatures of the heating elements 21 are different from each other, and therefore, when restarting, it is necessary to raise these to the set temperature in a short time. In these cases, the temperature of each heating element 21 is first measured, and heating is performed according to the measured temperature to raise the temperature, instead of controlling the electric power for each cycle. Further, in this control, a control constant is selected so that the rate of temperature increase gradually becomes gentle in order to prevent an overshoot (a phenomenon in which the temperature rises above a set temperature) when the temperature of the heating element 21 rises. And the heating element 2
Before the temperature of No. 1 reaches the set temperature, the power control is changed to every one cycle. By doing so, the heating element 21 can be quickly raised to a desired set temperature and to a uniform state with no temperature difference.

The second induction heating coil 29 of the heating element heating zone 27 may be configured as follows. An example of the second induction heating coil 29 is shown in FIGS. 9 and 10. The second induction heating coil 29 is composed of two coils for heating the upper part of the heating body 21 for heating the upper part and for heating the lower part for heating the lower part. The coil for the upper heating is the coil for the upper part and the coil for the lower part is the lower part. The coils are concentrated in each, and each is individually connected to the oscillator. Others have the same structure as the first induction heating coil 28 and are of a size capable of heating a plurality of heating bodies 21. The infrared radiation thermometer 32 is located above the heating body 21,
It is composed of three thermometers for measuring the middle part and the lower part, each of which is individually connected to a control device (not shown). By thus dividing the heating element 21 in the axial direction and controlling each of them, when there is a temperature difference in the heating element 21 in the axial direction, this temperature difference is eliminated and the temperature in the axial direction is made uniform. In addition, when the temperature of the heating element 21 is made different in the axial direction, it can be set to a predetermined temperature which is different in the axial direction.

Further, in the above example, the heating state is not changed while the heating element 21 makes one round of the heating station table 6, but the heating state is not limited to one round and may be one round or more. Further, if the heating capacity of the first induction heating coil 28 is increased, the second induction heating coil 29 is not necessarily required, and the first induction heating coil is provided so as to give an optimum temperature distribution in the axial direction of the heating body 21. By setting the winding pitch of the coil 28, different temperature distributions can be given to the heating body 21 in the axial direction without the need for the second induction heating coil 29. Further, in the present embodiment, the feedback amount is constant while the heating element 21 makes one round of the circuit, so that if the heating element 21 is not inserted in the preform 1, the thermometer can be set to any position of the circuit. Can be installed in place. Although the heating element 21 is made of metal and heated by induction heating, the present invention is not limited to this. The heating element 21 may be made of ceramic and heated by an infrared heater.

[Effect of the Invention] According to the temperature control method of the present invention, the heating elements are arranged at equal intervals on the circuit, and the heating elements are inserted into the preform to heat the preform from the inside. In the method, when measuring the temperature of the heating element and heating the heating element to the set temperature based on this, the heating supply amount was kept constant while the heating element made at least one round of the circuit, so all heating elements were set. The temperature can be raised to a uniform temperature and this state can be maintained. Therefore, the temperature of the individual preforms that flow continuously is always constant, and it is possible to manufacture plastic bottles with consistent quality.
When the temperature rises at the start of work, the temperature of each individual heating element is initially controlled to increase the temperature, and then the heating supply amount is kept constant at least while the heating element goes around the circuit before reaching the set temperature. Therefore, it is possible to quickly and uniformly raise all the heating elements to the set temperature.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing an embodiment of the present invention, FIG. 2 is a sectional view of a preform heated in this embodiment, and FIG. 3 is a thermoplastic bottle produced from the preform by blow molding. 4 is a sectional view of a mandrel supporting a preform, FIG. 5 is a sectional view taken along line VV in FIG. 1, and FIG. 6 is a sectional view taken along line VI-VI in FIG. FIG. 8 is a perspective view showing the first induction heating coil, FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7, FIG. 9 is a front view of the second induction heating coil, and FIG. 10 is X- of FIG. Sectional view in the X direction. In the drawings 1 ... Preform, 2 ... Plastic bottle, 3 ... Mandrel, 4 ... Delivery table, 5, 9, 11 ... Transfer table, 6 ... Heating station table, 7, 8 ... Annealing station table, 10 ... Blow molding station table , 12, 13 ... Supply table, 14 ... Delivery table, 17 ... Circumferential groove, 18 ... Sprocket, 19 ... Holding device, 20 ... Air cylinder, 21 ... Heating body, 22 ... Insulator, 25 ... Reflecting mirror, 26 ... Heating Unit, 27 ... Heating body heating zone, 28 ... 1st induction heating coil, 29 ... 2nd induction heating coil, 32 ... Infrared radiation thermometer.

Claims (2)

[Claims] 1. A plurality of heating bodies arranged on a circuit are sequentially heated in a heating body heating zone provided along the circuit, the heated heating bodies are inserted into a preform, and at least the inside of the preform is preformed. In a molding method in which the heating element is heated and molded into a plastic bottle in a mold, heating is performed with a constant feedback amount from the temperature measuring device of the heating element to the heating zone of the heating element while the heating element makes at least one round of the circuit. Body temperature control method. 2. When the temperature of the heating element is raised at the start of the molding operation, feedback control for measuring the temperature of each heating element and heating each heating element is performed, and then before the heating element reaches the working temperature. The method for controlling the temperature of a heating element according to claim 1, further comprising switching to a heating method in which the amount of feedback to the heating element heating zone is made constant while the heating element makes at least one round of the circuit.