JPH01120319A - Method for controlling temperature of heating body - Google Patents

Abstract

PURPOSE:To strictly and stably control the temp. of a heating body, by sealing a substance having a predetermined m.p. in the cavity provided in the heating body and controlling heating on the basis of the temp. of the heating body. CONSTITUTION:A cavity 31 is provided in a heating body 21 and sealed with a substance having a m.p. within the control objective temp. range of the heating body 21 and desirably having large heat of fusion and the temp. of the heating body is measured and the heating thereof is controlled on the basis of the measured value. The heating body 21 becomes high temp. by induction heating or infrared heating and the sealed substance is melted to emit heat of radiation. Since the substance having a definite m.p. is sealed in the heating body, when the control objective temp. is set so that the sealed substance becomes such a state that a solid and a liquid coexist, the temp. of the heating body can be stably controlled to a narrow range even when the absorption and radiation quantities of heat are largely varied.

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 an iniG material 1 is inserted into the preform and the preform is heated by the radiant heat of the high temperature material iτ (Patent Application No. 142299 filed in 1988 by the present applicant).
issue).

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 are used in a heating zone and a heat radiation zone (a zone in which solid metal is inserted into a preform, the solid metal radiates heat, and the preform is heated).
heating and heat dissipation are repeated. In order to accurately control the heating temperature of the preform, the temperatures of multiple solid metals that serve as heat sources must be kept at exactly the same temperature, but this is difficult to achieve with the methods described above. .

In other words, the temperature of a solid metal increases when it is heated, and its temperature decreases when it releases heat, but the degree of thirst in the upper stomach and the temperature drop are proportional to the 1 channel of heat release and heating, and the amount of heating and heat release is large (pre-heating). In addition, when the preform comes out, the 1'Jl heating element receives heat energy from the outside in the heat radiation zone, so the amount of heat radiation is always constant. However, it was extremely difficult to keep the temperature fluctuating within a narrow range.Furthermore, it was also extremely difficult to heat the entire heating element to a uniform temperature.

The present invention was made to solve the above-mentioned problems, and aims 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. The 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 fusion 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.

[For production]

A substance with a fixed melting point undergoes heating and heat radiation when solid and liquid coexist, and the temperature does not change, only the amount of solid or liquid changes. Therefore, if one person suspends such a substance in the cavity of the heating body, the temperature of the heating body will be similar to the temperature of the enclosed substance, and when the enclosed substance is in a solid-liquid coexistence state, it will be at a constant temperature. The greater the heat of fusion of a substance, the longer it will remain at a constant temperature. If the radiation from the heating element containing the enclosed substance exceeds a certain limit and all the enclosed substance solidifies, the temperature of the heating element will drop, and by detecting this, the heating element will be heated. Even if the applied energy 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 encapsulated material remains until the low melting point substance has completely solidified. The temperature drop in the heating element is suppressed, and even if the amount of heating is too large, 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 method of heating a preform when blow molding a plastic bottle will be described below with reference to the drawings.

As shown in FIG. 1, the mandrels 3, 3, . . . supporting the brief form 1 circulate between the rotary tables in the order indicated by the arrows. That is, from the preform delivery table 4, through the transfer table 5, the heating station table 6, the annealing station table 72.8, the transfer table 9, the blow molding station table 10, the transfer table 11, and then back to the preform delivery table 4 he mandrel 3.3. ... is circulated, but the mandrel holding mechanism and delivery mechanism at each table are carried out using conventionally known methods.
It is not shown in the figure because it is performed. On the mandrels 3, 3, . . . which are circulated in this manner, preforms 1.1, .
is installed. The brief A-arm 1 has the cross-sectional shape shown in FIG. 2, and consists of a bottomed cylindrical body 15 and a mouth 16 having a screw thread or an annular protrusion. This preform 1
is attached to the mandrel 3 and as it travels along the above-mentioned route, the body is heated at the heating station table 6 and blow molded at the blow molding station table by a conventionally known method, producing the thermoplastic plastic bottle 2 shown in FIG. be done. The manufactured thermoplastic plastic bottle 2 is extracted from a mandrel 3 held on a delivery table 4 by a conventionally known device and sent out via a delivery table 14. The mandrel 3 has a cross-sectional shape shown in FIG. 4, and is integrally provided with circumferential grooves 17, 17 for holding on each table, and sprockets 18, 18 for rotationally driving.

Chains are strung around the parts of the heating station table 6 and annealing station table 7.8 where the mandrels 3.3... pass through, so that they are sequentially arranged at different stages, and engage with the upper or lower sprockets 18, 18 to cause the mandrels to rotate. Driven to impart motion.

However, the chain shown in the diagram is 4 pieces long.

Next, the equipment δ attached to the heating station table 6 and the heating operation will be explained with reference to FIGS. 4 to 9. The heating station table 6 includes a holding device 19 and a heating body 21.
A piston rod 23 and an air cylinder 20, which are held via a heat insulator 22 and driven vertically, and an air cylinder 20 are mounted 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 is sealed therein as a high melting point metal, and its melting point is 420°C.

Further, as an example of the second heating body, as shown in FIG. 10, a first cavity 31 and a second cavity 32 are bored,
Each contains a high melting point metal and a low melting point metal. 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, The composition is 15% tin and 85% tellurium, and the stagnation humidity corresponding to the melting point is about 410°C.

Next, as an example of the third heating body, as shown in FIG.
First, second, and third cavities 31, 32, and 33 are drilled into which are filled tin-tellurium alloy, zinc, and tellurium, respectively. The tin-tellurium alloy has the above-mentioned composition, and the melting point of tellurium is about 450°C.

While rotating in a fixed direction, the heating station table 6 picks up the mandrel 3 at a fixed position by a holding device 19 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 26.2 is installed in the part through which the mandrel 3 passes.
6..., 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 that rotates together with the mandrel 3 to heat it from the outside. The heating element 21 is made of a metal that is easily heated by X''J heating, and can be placed in two positions using the air cylinder 20: inserted into the preform 1 and passed through the induction heating zone 27. It is driven as follows.

On the heating station table, as shown in FIG. 1, a large number of preforms 1 are sequentially fed and heated. There may be a case where the preform 1 is not supplied to one of them. In such a case, the heating element 21 is directly connected to the infrared heater 2.
4, so less heat energy is released compared to other types. 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 prevent the heating element from moving fJj.

The induction heating coil 29 has a multilayer hairpin shape as shown in FIG. 6, and is wound on both sides of the U-shaped ferrite core 31. A high frequency current is flowing in the direction. The quality 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.

When the heating body 21 passes through the induction heating coils 28 and 29 as shown in FIGS.
．． The high frequency current flowing through the tube 29 causes induction heating to reach a high temperature, and the sealed metal melts and emits radiant heat.

As shown in FIG. 1, the temperature of the heating body 21 immediately after passing through the 2.1 heating coil 28 is detected by the radiation temperature a130.

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 heated to point A in FIG. 12. In the figure, t (work time), ■ indicates the temperature of the heating element 21, and T1
indicates the melting point of zinc. The heating element 21 is normally heated at the melting point humidity of the high melting point metal, T, which corresponds to the flat curved portion in FIG.
1 approaches the heating coil 29, but the temperature detected just before the heating coil 29 by the radiation thermometer 30 is substantially lower than the melting point T1 of the encapsulated refractory metal, that is, the first
In Figure 3, for example, if the temperature is at point 0,
As shown in FIG. 12, programmed high-frequency power determined by the temperature difference between the melting point and the melting point is supplied to the induction heating coil 29 for a short period of time (0.5 seconds), preferably to It is heated to point B, where everything liquefies.

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. T in the diagram
2 is the low melting point, that is, the melting point of the fried tellurium alloy.

Temperature control is as in the embodiment of the first heating element, that is, when the temperature is at point 0 in FIG. 15, B in FIG.
Power is applied to the induction heating coil 29 so that the temperature rises to a point. In this case, even if the temperature of the heating element 21 is low due to a detection failure of the radiation thermometer 30 and is detected to be high, the temperature will drop too much due to the solidification heat of the tin-tellurium alloy. Never.

1.182 when the control target temperature is roughly selected as point C'.
However, due to a defect in the 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 will not reach the melting point of the zinc. Due to the heat, it does not rise too much and has good control. In the third actual fk example, the temperature rise curve of the heating element 21 is as shown in FIG. 16, and the natural cooling curve is as shown in FIG. 17.

In the figure, To indicates the melting point of tellurium. When the temperature at point 0 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.
Better control can be achieved by encapsulating three metals with different melting points.

Further, the heating capacity of the induction heating zone 27 and the size of the enclosed metal are set so that the entire enclosed metal does not solidify during one round of the heating element.

Therefore, during the heating eight rounds 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 encapsulated metal is kept at substantially the melting point of each melting point of the encapsulated metal or a temperature in between. It will be done.

That is, the temperature of the heating element in the first embodiment is maintained at 420°C, and the temperature in the second embodiment is 420°C when the control point is selected as the 0 point shown in FIG. 15. 41 if you choose 2
It is kept at 0℃. In the case of the third embodiment, the temperature is stably maintained at 420°C.

Then, when the heated heating element 21 is inserted into the preform 1, the preform 1 is heated by the heating element 21 and the heating unit 2.
6, it is heated from inside and outside at the same time. The preform thus heated in the brief heating stage 6 is soaked in annealing stations 7 and 8, and then blown into bottles in a 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 heat absorption and heat radiation rates vary relatively greatly. The body temperature can be stably controlled within a narrow range, and if this is used as a heat source for heating preforms for plastic molding, the preforms will always be heated to a constant temperature, improving the quality of molded products. .

[Brief Description of the Drawings] Fig. 1 is a plan view showing an embodiment in which the present invention is applied to heating a preform, Fig. 2 is a sectional view of the preform 1 heated in this embodiment, and Fig. 3 is a plan view showing an embodiment in which the present invention is applied to heating a preform. 4 is a cross-sectional view of the mandrel 3 that supports the preform 1, FIG. 5 is a cross-sectional view along the line A-A in FIG. 1, and FIG. 6 is a perspective view showing the induction heating coil 29;
The figure is a sectional view taken along B-8 in FIG. 1, FIG. 8 is a sectional view taken along C-C in FIG. 6, and FIG.
1, FIG. 10, and FIG. 11 are the enlarged cross-sectional views of No. 2, and FIG.
FIG. 7 is an enlarged cross-sectional view of a heating element according to a third embodiment. FIG. 12 is a back temperature curve showing the ai control method for heating the heating element in the first embodiment, and FIG. 13 is a natural cooling temperature curve. 1st
4 and 15 show the heating and cooling curves, respectively, of the heating element of the second embodiment, and FIGS. 16 and 17 show the heating and cooling curves, respectively, of the third embodiment. 1... Brifohm, 2... Thermoplastic plus deck 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, 16...mouth, 17...
harmonious, 18... sprocket, 19... holding device,
20... Air cylinder, 21... Heating body, 22...
- Heating 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. Applicant's agent Hiroshi Fujiki Mitsumei Figure 4 $ Ko G Figure 6 Imo 9 Figure Sheep lOrocha ff Eye

Claims (1)

[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, and the temperature of the heating body is measured. A method for controlling the temperature of a heating element, characterized in that the heating element is maintained at a constant temperature by controlling the heating of the heating element based on the value. 2. The temperature control method of a heating body according to claim 1, wherein at least two cavities are provided in the heating body, and substances having different melting points are sealed in each cavity. 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.