JPH0571027B2 - - Google Patents

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, and particularly to a method of controlling the temperature of a heating element that serves as a heat source for heating a plastic material for molding or the like.

[Conventional technology]

When heating a preform, etc., which is a molding material for a plastic bottle, a method of heating from the inside and outside of the preform is preferred because uniform heating can be achieved. In this case, a method has been proposed in which a high-temperature substance is inserted into the preform and the preform is heated by the radiant heat of the high-temperature substance (Patent Application No. 142299 of 1988 filed by the present applicant).

In the method described above, a solid metal is used as a high-temperature substance serving as a heating body, the temperature of the solid metal is measured, and the heating of the solid metal is controlled based on the measured value.

[Problem that the invention seeks to solve]

In the prior art, a large number of solid metals circulate between a heating zone and a heat radiation zone (a zone in which the solid metal is inserted into a preform, the solid metal radiates heat, and the preform is heated), and heating and radiation are repeated. In order to accurately control the heating temperature of the preform, it is necessary to make the temperatures of a large number of solid metals serving as heat sources exactly the same, but it has been difficult to achieve this with the above method. In other words, the temperature of a solid metal increases when it is heated, and its temperature decreases when it radiates heat, but the rising and falling temperatures are proportional to the amount of heat radiated and the amount of energy used for heating, and the wider the amount of heating and the amount of heat radiated, the wider the range of temperature fluctuations. I don't get it. In addition, if the preform comes off, the heating element receives heat energy from the outside in the heat radiation zone, so the amount of heat radiation is not always constant and it is extremely difficult to keep the temperature fluctuation range within a narrow range. It was hot. Furthermore, it is also extremely difficult to heat the entire heating element to a uniform temperature. The present invention was made to solve the above problems, and it is possible to strictly and stably control the temperature of a heating element that is inserted into a preform and serves as a heat source for heating it. An object of the present invention is to provide a method for controlling the temperature of a heating element.

[Means for solving problems]

A cavity is provided inside the heating body, a substance having a melting point within the control target temperature range of the heating body and preferably having a large heat of melting is sealed in the cavity, the temperature of the heating body is measured, and the measured value is The heating of the heating body is controlled based on the following.

[Effect]

When a substance with a fixed melting point coexists with a solid and a liquid, even if heating or heat radiation is performed, only the amount of the solid or liquid changes, but the temperature does not change. Therefore, if a sufficient amount of such a substance is sealed in the cavity of a heating body, the temperature of the heating body becomes equal to the temperature of the sealed substance, and when the sealed substance is in a solid-liquid coexistence state, the temperature remains constant, and the substance melts. The greater the heat, the longer the constant temperature is maintained. When the amount of heat dissipated from the heating element containing the enclosed substance exceeds a certain amount and all the enclosed substance solidifies, the temperature of the heating element decreases, and by detecting this, the heating element is heated. Even if the energy given is enough to liquefy all of the enclosed material, the temperature change of the heating element is slight and stable control is possible. When encapsulating two or three types of substances with slightly different melting points, the temperature at which the low melting point substance begins to solidify is detected and heating is performed, but the temperature of the heating element and the enclosed substance must be maintained until all the low melting point substances have solidified. The temperature drop is suppressed, and even if the amount of heating is too large during heating, only partial liquefaction of the substance with a slightly high melting point begins, making it easy to stably control the temperature of the heating element within a narrow range.

〔Example〕

An example in which the present invention is applied to a preform heating method for blow molding plastic bottles will be described below with reference to the drawings.

As shown in FIG. 1, the mandrels 3, 3, . . . supporting the preform 1 circulate between the rotary tables in the order indicated by the arrows. That is, the mandrels 3, 3, etc. are transferred from the preform delivery table 4 through the transfer table 5, the heating station table 6, the annealing station tables 7, 8, the transfer table 9, the blow molding station table 10, the transfer table 11, and then back to the preform delivery table 4. Although the mandrels are circulated, the mandrel holding mechanism and delivery mechanism at each table are not shown because they are carried out by conventionally known methods. Preforms 1, 1, . . . are mounted onto the mandrels 3, 3, . The preform 1 has a cross-sectional shape shown in FIG. 2, and has a bottomed cylindrical body 15.
and a mouth portion 16 having a screw thread or an annular protrusion. While this preform 1 is attached to a mandrel 3 and circulates along the above-mentioned route, the body is heated at a heating station table 6 and blow-molded at a blow-molding station table by a conventionally known method to form a thermoplastic plastic bottle as shown in FIG. 2 is produced. The produced thermoplastic bottles 2 are delivered from a mandrel 3 held on a delivery table 4 via a delivery table 14, where they are extracted by a conventionally known device. The mandrel 3 has a cross-sectional shape shown in FIG. 4, and is integrally provided with circumferential grooves 17, 17 for holding it on each table, and sprockets 18, 18 for rotationally driving it. Chains are strung around the parts of the heating station table 6 and the annealing station tables 7, 8 through which the mandrels 3, 3, . . . Driven to grant. However, the chain is not shown.

Next, the devices attached to the heating station table 6 and the heating operation will be explained with reference to FIGS. 4 to 9. A holding device 19, a piston rod 23 for holding a heating body 21 via a heat insulating body 22 and driving it in the vertical direction, and an air cylinder 20 are attached to the heating station table 6 at equal intervals with their circumferential positions aligned. The heating body 21 has a cavity 31 as shown in FIG. 9 as an embodiment of the first heating body.
Zinc, a high-melting point metal, is sealed inside the hole, and its melting point is 420°C. Further, as an embodiment of the second heating body, as shown in FIG. 10, a first cavity 31 and a second cavity 32 are bored, and a high melting point metal and a low melting point metal are respectively sealed. There is. The above-mentioned zinc is used as the high melting point metal, and an alloy of tin and tellurium is used as the low melting point metal.The alloy has a composition in which the eutectic point occurs in the phase diagram, and when expressed in atomic percent, tin
It is 15% tellurium and 85% tellurium, and the eutectic stagnation temperature, which corresponds to the melting point, is approximately 410°C.

Next, as an example of the third heating body, as shown in FIG.
3 is bored, and tin-tellurium alloy, zinc, and tellurium are sealed in each hole. The tin-tellurium alloy has the above composition, and the melting point of tellurium is about 450°C.

The heating station table 6 receives the mandrel 3 from the holding device 19 at a fixed position while rotating in a fixed direction, and sends it out from the holding device at the fixed position. Therefore, around the heating station table 6 there are parts through which the mandrel passes and parts through which it does not pass.
A heating unit 2 is installed in the part through which the mandrel 3 passes.
6, 26..., and an induction heating zone 27 is arranged in the part through which the mandrel does not pass.

The heating unit 26 is composed of an infrared heater 24 and a reflecting mirror 25, and is a device that irradiates infrared rays toward the preform 1 rotating together with the mandrel 3 to heat it from the outside. Heating body 21
is made of a metal that is easily heated by induction heating, and is driven by the air cylinder 20 so as to assume two positions: a state where it is inserted into the preform 1 and a state where it passes through the induction heating zone 27.

On the heating station table, as shown in FIG. 1, a large number of preforms 1 are sequentially sent and heated.
A situation may occur in which the preform 1 is not fed, that is, the preform 1 is not supplied to one of the many mandrels 3. In such a case, the heating element 21 is directly exposed to the infrared heater 24, and therefore releases less thermal energy than other heating elements. In the heating zone 27, all heating elements must be heated to a constant temperature. For this purpose, the heating zone 27 consists of two induction heating coils. The induction heating coil 28 is a multi-layered hairpin shaped like an arc and elongated so as to cover the moving path of the heating element, and both ends thereof are biased upward so as not to obstruct the movement of the heating element.

The induction heating coil 29 has a multilayer hairpin shape as shown in FIG. 6, and is wound on both sides of a U-shaped ferrite core 31. A high frequency current is flowing in the direction. The length of the induction heating coil 29 is determined to be approximately equal to the spacing between the individual heating bodies 21. If the heating capacity of the induction heating coil 29 is increased, it is also possible to omit the constant heating induction heating coil.

As shown in FIGS. 7 and 8, when the heating body 21 passes through the induction heating coils 28 and 29, it is heated by induction by the high-frequency current flowing through the induction heating coils 28 and 29, and reaches a high temperature, and the enclosed metal melts and emits radiant heat. It begins to radiate. As shown in FIG. 1, the heating element 2 immediately after passing through the induction heating coil 28
1 is detected by a radiation thermometer 30. FIG. 12 shows a temperature rise curve when a constant electric power is applied to the heating element of the first embodiment. Further, FIG. 13 shows the natural cooling curve of the heating element when it is heated to point A in FIG. 12. In the figure, t is time, T is heating element 2
1 and T1 indicates the melting point of zinc. The heating element 21 normally approaches the heating coil 29 at T1, the melting point temperature of the high-melting point metal corresponding to the flat curved part in FIG. If the temperature is substantially lower than the melting point T1 of the encapsulated high-melting point metal, that is, for example, point C in FIG. The induction heating coil 29 is supplied with programmed high-frequency power determined by the temperature for a very short time (0.5 seconds), and is preferably heated to point B, where all of the encapsulated high-melting point metal is liquefied. In the second embodiment, the temperature rise curve of the heating element 21 is the first one.
Figure 4 and the natural cooling curve are as shown in Figure 15.
In the figure, T2 is the melting point of a low melting point metal, ie, a tin-tellurium alloy.

Temperature control is as in the embodiment of the first heating element, that is, when the temperature is at point C in FIG. 15, the induction heating coil 29 is controlled so that the temperature rises to point B in FIG. 14. Power is given to. In this case, even if the temperature of the heating element 21 is detected to be high even though the temperature is low due to a detection failure of the radiation thermometer 30, the temperature will drop too much due to the solidification heat of the tin-tellurium alloy. Never.

Furthermore, if the control target temperature is selected as point C′,
The temperature is controlled so that the temperature rises to point B', but due to a defective detector, a large temperature difference is detected, and as a result, even if too much power is supplied to the heating coil 29, the temperature of the heating element remains low Because of the heat of fusion, it does not rise too much and can be well controlled. In the third embodiment, the temperature rise curve of the heating element 21 is shown in FIG.
The natural cooling curve is as shown in FIG.

In the figure, T0 indicates the melting point of tellurium. When the temperature at point C in Fig. 17 is detected, the same control as in the first and second embodiments is performed so that the temperature rises to point B in Fig. 16. Encapsulating the metal allows for better control.

In addition, the induction heating zone 2
The heating capacity and the amount of encapsulated metal of 7 are set. Therefore, while the heating element goes around the heating station, part of the encapsulated metal is always in a liquid state and another part is in a solid state, and the heating element is kept at a temperature substantially at or between the melting points of the encapsulated metal. It can be done.

In other words, the temperature of the heating element in the first embodiment is 420°C.
The temperature of the second embodiment is kept at the control point 15.
If point C shown in the figure is selected, the temperature will be maintained at 420°C, and if point C' is selected, the temperature will be maintained at 410°C. In the case of the third embodiment, the temperature is stably maintained at 420°C.

The heated heating element 21 then becomes the preform 1.
When inserted into the interior, the preform 1 is heated simultaneously from the inside and outside by the heating body 21 and heating unit 26. The preform heated in the preform heating station 6 in this manner is heat-uniformed in the annealing stations 7 and 8, and then blown into a bottle in the blow molding station.

In this embodiment, the heating body is made of metal and heated by an induction heating method, but the invention is not limited thereto, and a ceramic heating body may be heated by an infrared heater.

〔Effect of the invention〕

Since a substance with a constant melting point is enclosed in the heating element, if the control target temperature is set so that the enclosed substance is in a state where solid and liquid coexist, heating will be possible even if the amount of heat absorption and heat radiation changes relatively greatly. The body temperature can be stably controlled within a narrow range, and if this is used as a heat source for preform heating for plastic molding, the preform will always be heated to a constant temperature, improving the quality of the molded product.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an embodiment in which the present invention is applied to heating a preform, Fig. 2 is a cross-sectional view of a preform 1 heated in this embodiment, and Fig. 3 is a fabrication process from preform 1 by blow molding. FIG. 4 is a cross-sectional view of the mandrel 3 supporting the preform 1;
Figure 5 is a sectional view taken along line A-A in Figure 1;
The figure is a perspective view showing the induction heating coil 29, FIG. 7 is a sectional view along the line B-B in FIG. 1, and FIG.
9 is an enlarged sectional view of the heating body 21 of the first embodiment, and FIGS. 10 and 11 are enlarged sectional views of the heating body 21 of the second and third embodiments, respectively. It is a diagram. FIG. 12 is a temperature rise curve showing the heating control method of the heating element in the first embodiment, and FIG. 13 is a natural cooling temperature curve. FIGS. 14 and 15 show the heating and cooling curves of the heating element of the second embodiment, respectively, and FIGS. 16 and 17 show the heating and cooling curves of the third embodiment, respectively. 1... Preform, 2... Thermoplastic 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, 15... Body part, 16
... Mouth, 17 ... Circumferential groove, 18 ... Sprocket, 19 ... Holding device, 20 ... Air cylinder,
21...Heating body, 22...Insulating body, 23...Piston rod, 24...Infrared heater, 25...Reflector, 26...Heating unit, 27...Heating zone, 28, 29...Induction heating coil, 30... Radiation thermometer, 31... First cavity, 32... Second cavity, 33... Third cavity.

Claims (1)

[Scope of Claims] 1. A cavity is provided inside the heating body, a substance having a melting point within the control target temperature range of the heating body is sealed in the cavity, the temperature of the heating body is measured, and the measured value is A method for controlling the temperature of a heating element, characterized in that the temperature of the heating element is maintained at a constant temperature by controlling the heating of the heating element. 2. The temperature control method for a heating body according to claim 1, wherein at least two cavities are provided in the heating body, and each cavity is filled with a substance having a different melting point. 3. The method according to claim 1, characterized in that an amount of heat is supplied in proportion to the magnitude of the difference between the temperature of the heating body and the melting point of the substance to be sealed. 4. The method according to claim 1, wherein the heating body is heated by induction heating.