JPH01184118A - Heating of preform - Google Patents

Abstract

PURPOSE:To shorten a required time for heating and to attempt to improve productivity, by heating a trunk part of a preform from the inside and the outside at the same time, measuring temp. of a metal rod for heating the preform from the inside and controlling the heating. CONSTITUTION:Holding apparatus 19 each holding a mandrel 3 on which a preform 1 is attached, piston rods 23 each holding a metal rod 21 heating the preform 1 from the inside by radiating radiation heat, through an insulating body 22 and driving it in the upward and downward direction and air cylinders 20 are attached on a heating station table 6 in its circumferential direction. A heating unit 26 is constituted of a plurality of infrared heaters 24, a reflective mirror 25 and a reflective mirror 25' intercepting infrared ray and heats the preform rotating on its own axis from the outside by radiating infrared ray. In a heating zone 27 heated by means of the metal rod, induction heating coils 29-31 control respectively heating the upper, middle and lower parts of the metal rod 21. Output from three infrared radiation thermometers 32... are input in electric power controlling apparatus controlling electric power given to each heating coil and the metal rods are each heated at a specified temp.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for heating a preform, and in particular to a method for heating a preform by blow molding a thermoplastic plus deck preform consisting of a right-bottom cylindrical body and a mouth. In manufacturing /υ, the body of the preform is heated uniformly in the wall thickness and circumferential direction in a short time, and the body is heated in the length direction to a temperature suitable for blow molding. Regarding the method.

[Conventional technology]

BACKGROUND OF THE INVENTION Biaxially stretched blow molded bottles such as polyester are common today and are widely used for containers for carbonated drinks such as colas and ciders, and other beverage containers such as fruit juices, coffee, and mineral drinks. When molding such plastic bottles, a preform manufactured by injection molding is heated, and the heated pref A- is stretched in the axial direction with a stretching rod in the mold, and at the same time in the circumferential direction. Blow stretching is widely used.

A non-contact heating method using an externally placed infrared heater is generally used to heat the preform, but in recent years, as containers have become more portable and manufacturing methods have become faster, preform As the wall thickness increases, it takes time to heat uniformly in the thickness direction, and there is a limit to the molding speed. Therefore, in addition to the conventional external heater,
Method of inserting a medium heater inside the preform (Japanese Patent Application Laid-open No. 6
1-261024) and a jig (Japanese Patent Publication No. 62-43852) that heats a stretching rod by high-frequency induction heating and heat-forms the preform from the inside and outside surfaces, or inserts a heat pipe into the preform. method (Japanese Unexamined Patent Publication No. 61-163828) is used.

[Problem that the invention seeks to solve]

In all of the above methods of heating the preform from the outside with an infrared heater, the southern part of the preform is heated from the outside, and the heat is transmitted from the outside to the inside through the plastic resin tube wall. In this case, the thermal conductivity of plastic resin is low, and it takes a long time to sufficiently raise the temperature inside the preform, especially in thick preforms. In addition, in order to rapidly raise the temperature of the inside to the desired temperature, the temperature of the outside surface must be raised (pull), which causes overheating of the outside and deteriorates the properties of the material. It is difficult to obtain a uniform temperature distribution.

Additionally, plastic bottles are molded to have the optimal axial wall thickness distribution to maintain the strength and shape of the bottle, but in order to do so, it is necessary to adjust the heating temperature of the preform along the axial direction. It is. For this reason, in the heating method using an infrared heater, a plurality of heaters are arranged at each position in the axial direction of the preform, and the power applied to each heater is adjusted. However, in such a method, it is difficult to bring a desired temperature to a desired temperature due to thermal interference between the heaters.

Also, the method of JP-A-61-261024 and the method of JP-A-61-261024
In the method of -163828, it was difficult to add temperature distribution in the axial direction.

In addition, in the method shown in Japanese Patent Publication No. 62-43852, the metal rod is heated by induction inside the preform, so it is not possible to measure the temperature of the metal rod during induction heating or just before induction heating.
It is not possible to control the heating of the metal rod. Therefore, it is difficult to control the humidity of each metal rod when the preform is not properly supplied and the preform is pulled out.

- Page - The present invention has been made to solve the above problems, and provides a method for heating a preform made of a thermoplastic resin uniformly in the thickness direction and circumferential direction in a short time, and The object of the present invention is to provide a method for arbitrarily controlling temperature distribution in the axial direction.

[Means for solving problems]

In order to achieve the above object, the present invention provides a method for heating a preform by supplying heat from the outside and inside thereof.
A preform heating zone in which a preform is adhered to at least a metal rod in a circuit in which a large number of metal rods circulate at substantially equal intervals, and a metal rod heating zone in which a preform is removed. In the metal rod heating zone, the temperature of each metal rod is measured, and the metal rods are sequentially heated by high frequency induction according to the measured values, and in the preform heating zone, the temperature of the heated metal rod is heated. A rotating preform is attached to a rod, and heat is supplied from the inside of the preform as well as from the outside of the preform.

For the induction heating of the metal rod, induction heating coils are installed to heat at least the upper, middle, and lower parts of the metal rod, respectively.
The power of each heating coil is controlled according to the measured humidity of the upper, middle, and lower parts. In addition, if the winding bit of the induction heating coil that heats the metal rod by induction or the diameter of the metal rod is changed in the length direction of the metal rod to give a predetermined temperature distribution in the length direction of the metal rod, the preform The preform 11 can be heated to a temperature distribution suitable for blow molding.

Also, the metal rod is preferably heated in a range of 300 to 600'C.

[For production]

Since the thermoplastic tube wall is heated from the inner and outer surfaces, the temperature distribution in the thickness direction of the tube wall is lowest in the center and higher on both surfaces. Heat is transferred from both surfaces to the center, but since the heat transfer distance is shortened by 1/2, the time required for heat transfer is shortened. Also, since heat is transferred from both the inner and outer surfaces, twice the heat transfer area is utilized compared to when heating only from the outside.

For the above reasons, in the case of the present invention, the time required to raise the temperature of the object to be heated to a predetermined temperature is shortened to about ⅓ compared to a method of heating only from the outside.

In addition, the temperature of the metal rod that is heated from the inside is measured one by one at several positions along the length of the metal rod with a temperature sensor, and each position of the metal rod is induction heated according to the measured temperature value. A predetermined temperature distribution can be added along the axial direction. Therefore, even if the individual temperatures of the metal rods differ for some reason, the preform is heated to the desired humidity, and the quality of the molded product is improved.

(Example) Examples of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the mandrels 3, 3, . In other words, brief A-me delivery table 4
Transfer table 5, heating station table 6, annealing station table 7, 8, transfer table 9, blow molding station table 10. The preform transfer table 11 is passed through the preform transfer table 4, the mandrel 3.3... is circulated again, but the mandrel holding mechanism and transfer mechanism at each table are not shown because they are carried out by conventionally known methods. .This J: Preforms 1, 1, . . . are fed from a conventionally known feeding device onto the mandrels 3, 3, .
・is installed. The preform 1 has the cross-sectional shape shown in FIG. 2, and consists of a right bottom cylindrical body 15 and a mouth 16 having a thread or an annular protrusion. While this preform 1 is mounted on a mandrel 3 and circulates through the above-mentioned route, the body is heated on a heating station table 6 and blow molded on a blow molding station table by a conventionally known method. A plastic bottle 2 is manufactured. 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 1 to 18, 18 for rotationally driving. Chains are stretched around the parts of the heating station table 6 and the annealing station table 7.8 through which the mandrels 3°3... Driven to impart rotational motion. 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 15. The heating station table 6 has a holding device 19 and a metal rod 2.
A piston rod 23 and an air cylinder 2o, which hold the piston 1 via a heat insulator 22 and drive it in the vertical direction, and an air cylinder 2o are mounted at equal intervals with their circumferential positions coincident. The heating station table 6 rotates in a fixed direction and receives the mandrel 3 at a fixed position with a holding device 19 (picks it up, and sends it out from the holding device at a fixed position. Therefore, there is a part around the heating station table 6 where the mandrel 3 passes through and There is a part through which the mandrel 3 does not pass.Heating units 26, 26... are installed in the part through which the mandrel 3 does not pass, and a metal rod heating zone 27 which heats the metal rod by induction heating is located in the part through which the mandrel 3 does not pass.
is located. The heating unit 26 is composed of a plurality of infrared heaters 24, a reflector 25, and a reflector 25' that cuts off infrared rays so as not to heat the preform 7 ohm section 16. This is i+i, which heats it from the outside by irradiating infrared rays.

Further, the power of each of the plurality of heaters can be adjusted. The metal rod 21 is made of a metal that is easily heated by induction, and is inserted into the preform 1 by the air cylinder 20 in the preform heating zone where the heated metal rod heats the preform from the inner and outer surfaces together with the heating unit 26. In the metal rod heating zone, the metal rod passes through an induction heating coil. That is, the metal rod can be driven to assume two positions.

Further, the metal rod 21 is connected to the piston rod 23 via a heat insulator 22, and as shown in FIG.
It is mounted in a position opposite to. Therefore, the heat insulator has the role of preventing heat from the metal rod from being transferred to the piston [lrad], and at the same time has the effect of suppressing heating of the mandrel core.

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 metal rod 21 is directly connected to the infrared heater 2.
11, the temperature decreases less than other types.

In the metal rod heating zone 27, all metal rods must be heated to a predetermined temperature. For this purpose, the metal rod heating zone is constructed into two sections: an induction heating coil 28 for quantitative heating and a heating coil 29.30.31 for controlling heating.

As shown in FIG. 6, the induction heating coil 28 is a multi-layered hairpin shaped like an elongated arc so as to cover the movement path of the metal rod, and both ends of the coil are arranged so as not to obstruct the movement of the metal rod. is biased upward.

The induction heating coils 29, 30, 31 are as shown in FIG.
Three infrared radiation thermometers 32, 32, etc. are arranged to control the heating of the upper, middle, and lower parts of the metal rod 21, respectively, and measure the temperature of the upper, middle, and lower parts of the metal rod.
Power control that the output from I gives to each heating coil
The I-wave device is input to heat the metal rod to a predetermined temperature.

In this case, the detected temperature of the infrared radiation thermometer 32 and the metal rod 21
The relationship between the temperature difference from the set temperature and the power needed to heat the metal rod to the set temperature is determined in advance, and the power determined from this relationship is supplied to the heating coil to heat the metal rod to the specified temperature. It is something that

The induction heating coils 29, 30, and 31 heat the upper, middle, and lower parts, respectively), so they have the shape shown in Figure 9 or Figure 11, and either can be used. , the coil shown in FIG. 11 is more desirable in terms of efficiency. The copper plate 36 in FIGS. 11 and 12 is used to prevent the metal rod facing the copper plate from being heated by the heating coil, and is necessary when limiting the heating area of the metal rod. It is. A more desirable coil shape is as shown in FIG. 13, which is composed of two spiral coils that become narrower as they move upward in the axial direction and then fold back over each other.

In the heating region, as shown in Figures 13 and 14, the coils are wound so that the distance between the coil sides is narrowed, and in the area where heating is to be suppressed, the folded vertices are shifted so that the distance between the coil sides is widened.

With such a shape, if the metal rod 21 and the coil are perfectly electromagnetically coupled, the electric power entering the portion of the metal rod corresponding to each coil side is proportional to the square of the current density, so the metal rod In the axial direction, there is a temperature distribution approximately inversely proportional to the square of the distance between the coil sides, and the heating area can be limited. What's more, weak electric power is applied to the areas where the spacing between the coil sides is widened, resulting in good heating efficiency.

-14= Also, in this coil, the two spiral coils are tightly spaced so that the metal rods do not touch each other, so the magnetic flux cancels each other outside the coil, and the metal rod is easily pulled out of the coil. When it is exposed, it hardly gets heated. Therefore, when the metal rod 21 passes through the coil, the effective length of the coil in which the metal rod is substantially heated can be defined. Also, one of the two spiral coils can be used as a heating coil, but the heating efficiency is poor and the effective length is unclear. The coil 34 shown in FIG. 9 is a multilayer hairpin-shaped coil wound around two magnetic cores 33, and the coil 35 shown in FIG. 11 is the same as that shown in FIG. The coils are similar, and each has an open structure so as not to obstruct the passage of the metal rod 21.

Also, when the metal rods 21 pass through the individual coils of the induction heating coils 29, 30, 31, the effective length of the coils over which the metal rods are substantially heated is approximately equal to the spacing between successive metal rods. The 53 heating coils are arranged at a distance approximately equal to the spacing between the metal bars. The magnetic flux generated by each heating coil does not interfere with each other.

Heating coils 28, 29° 30. of metal rod heating zone 27.
31, as shown in Figure 7.10.12.14, the direction of the high frequency current flowing through the coils facing each other with a metal rod in between is
They are set H1 so that they are in opposite directions.

As shown in FIGS. 6, 8, and 15, the metal rod 21 passes through the induction heating coils 28, 29, 30, 31 and is induced by the high frequency current flowing through the induction heating coils 28, 29, 30. It is heated to a high temperature and emits radiant heat. As shown in FIG.
The temperature of the metal rod 21 immediately after passing through the metal rod 8 is detected by three radiation thermometers 32, 32, and 32 installed in the middle and upper part of the metal rod, and is sent to the three induction heating coils 29, 30, 31. The outputs of three high-frequency oscillators (not shown) that supply high-frequency power are automatically set so that the humidity of the metal rod 21 after passing through the induction heating coils 29, 30° 31 becomes a predetermined amount. Ru.

The tip of the preform is usually a hemispherical shell where the weight of the PlusDeck resin is concentrated, so in order to heat this area sufficiently, an induction heating coil must be wound to cover the tip of the metal rod. It is effective to make the pitch denser and heat the tip of the metal rod to a high temperature, or to make the tip of the metal rod thicker to increase the heating capacity.

It is also effective to make the tip of the metal rod hemispherical to match the shape of the tip, which is a hemispherical shell, or to change the diameter of the metal rod in the axial direction so that it resembles the inner diameter of the preform. be. Furthermore, by covering a part of the metal rod with a heat insulator, radiant heat can be suppressed, and the temperature rise of the preform in that part can be suppressed.

Therefore, the metal rod 21 can be heated uniformly as a whole by using three heating coils, and the desired heat distribution can also be applied to the top, middle, and bottom of the metal rod by changing the winding pitch of the coils and the coil. This can be easily done by adjusting the applied power.

In addition, when controlling heating without using three heating coils and using a pair of heating coils and a humidity sensor, the coils are shown in Fig. 9, Fig. 11, or Fig. 13. The coil extends to the bottom of the metal rod and is wound around it, but in this case, it is extremely difficult to add the desired heat distribution to the metal rod as the winding pitch of the coil must be finely adjusted. there were.

Also, the metal rod 21 is at room temperature when the molding machine starts operating.
must be brought to the desired temperature in a short time. In this case, each part of the metal rod dissipates heat at a different degree as it goes around and returns, with the lower part being connected to the heat insulator 22 and the screws 1 to 23, so the heat dissipation is large. Therefore, during the first round, it is necessary to increase the power supplied to the coils of each part and gradually change the power according to the degree of heat dissipation, but the degree differs for each part of the metal rod. In this way, if the temperature changes over time at each part of the metal rod are different, if three heating coils are used, the metal rod can be heated to the desired 1 rl.
− Can be adjusted to temperature. For these reasons, it is desirable to use three heating coils.

The heating capacity of the induction heating coils 29, 30, 31 can be increased (if so, the induction coil 28 for constant heating can be omitted. Also, it is desirable to heat the metal rod 21 in the range of 300°C to 600°C. .

The reason for this is that below 300℃, the radiant heat emitted is too small and there is almost no effect of heating a thick preform from the inside, and above 600℃, only the inner surface becomes too hot compared to the outer surface and the center of the thickness. This is because uniform heating cannot be achieved. In addition, a metal rod with a thin outer diameter can be heated to 600°C.
In this case, oxidative deterioration was severe and it could not be put to practical use.

In this way, when the heated metal rod 21 is inserted into the preform 1, the preform 1 is simultaneously heated from the inside and outside by the heating body 21 and the heating unit 26. The preform heated in this way at the preform heating station 6 is soaked at an annealing station 7.8 and blown into bottles at a blow molding station.

As described above, the present invention is very effective in terms of high-speed heating and uniform heating. However, since the heating element 21 is inserted close to the inner surface, a part of the mandrel core 37 as shown in FIG.
If the preform 1 inserted into the preform 1 rotates on its axis while being largely eccentric, non-uniform heating will occur in the circumferential direction. Such wobbling occurs due to the relationship between the variation in the inner diameter of the preform rolling portion and the core diameter, or the method of inserting the preform, and the degree of eccentricity also differs for each mandrel. In order to compensate for this drawback, the mandrel core part 37' is made of a spring material divided into quarters with elasticity so that it opens slightly outward before the preform is inserted, as shown in Fig. 17. Furthermore, the method of inserting the preform was to forcibly insert the preform against the elastic force while maintaining the direction of the preform so as to match the axis of the mandrel. As a result, the eccentricity of the preform was almost eliminated, and the eccentric diameter e shown in FIG. 16 was made to be within the inner diameter of the preform 2, 115. In such a case, substantially uniform heating could be achieved in the circumferential direction.

A desirable value for the eccentric diameter e is 1/ of the inner diameter of the preform 2.
10 or less, and if this condition is satisfied, uneven heating due to eccentricity between the preform and the metal rod can be substantially eliminated.

The above-mentioned wobbling can be reduced by other methods, for example, by regulating the movement of the head of the preform using a guide.

In this embodiment, the heating device that heats the preform from the outside is placed on the outer periphery of the mandrel passage, but the invention is not limited to this, and the heating device can be placed on the outer periphery and the inner periphery of the mandrel passage. . In this case, the metal rod that is not covered with the preform may be heated by a heating device, but in such a case, it may be cooled by air blowing or the like.

〔Effect of the invention〕

As explained above, the inside and outside of the body of the preform for molding thermoplastic bottles are heated at the same time, and the temperature of the metal rod that heats the preform from the inside is measured.
Since the heating is controlled, the time required for heating is shortened and productivity is improved, and each part of the preform can be heated to a predetermined temperature suitable for blow molding plastic bottles.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an outline of an embodiment of the present invention, FIG. 2 is a sectional view of a preform 1 heated in this embodiment,
FIG. 3 is a cross-sectional view of a thermoplastic bottle manufactured from the preform 1 by blow molding, FIG. 4 is a cross-sectional view of the mandrel 3 that supports the preform 1, and FIG. 5 is a direction A-Ah in FIG. 1. 6 is a perspective view showing the induction heating coil 28, FIG. 7 is a sectional view taken along the line C-C in FIG. FIG. 10 is a perspective view showing an example of the heating coils 29, 30, 31, and FIG.
The figure is a sectional view taken along the line C-C of FIG. 11, FIG. 13 is a perspective view showing an induction heating coil according to an embodiment of the present invention, and FIG.
Figure 15 is a sectional view taken along B-B in the 1st section, Figure 16 is a diagram showing the whirling state of brif A-m 1, and Figure 17 is an improved It is a sectional view showing a part of the mandrel core. 1... Preform, 2... Thermoplastic Plus Deck bottle, 3... Mandrel, 1... 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... ['' section, 17...
・Peripheral groove, 18... Sprocket, 1... Holding device, 20... Air cylinder, 21... Metal rod, 22...
...Insulator, 25.25'...Reflector, 26...Heating] Leek 1~. 27... Metal rod heating zone, 28.2
9,30.31...Induction heating"il, 32...Infrared radiation side [1,33...Magnetic side]7-134.35...
・Induction heating coil, 37.37'... Part of the mandrel core. 24? l 6 1q Z6:37 IO Z /q 〜base11 C=]Goko≧Sa

Claims (1)

[Claims] 1. Prior to blow molding of thermoplastic bottles,
In a method of heating a preform by supplying heat from the outside and inside thereof, a state in which the preform is attached to at least a metal rod in a circuit in which a large number of metal rods circulate at substantially equal intervals. A preform heating zone and a metal rod heating zone from which the preform is extracted are provided. high-frequency induction heating is applied to the preform, a rotating preform is attached to the heated metal rod in the preform heating zone, and heat is supplied from the inside of the preform as well as from the outside of the preform. Characteristic preform heating method. 2. When inductively heating a metal bar, induction heating coils are provided to heat at least the upper, middle, and lower parts of the metal bar, respectively, and the electric power of each heating coil is controlled. Heating method of preform described in section. 3. By changing the outer diameter of the metal rod to which the preform is attached in the length direction, or by changing the winding pitch of the high-frequency heating coil along the length of the metal rod, the temperature can be applied to the metal rod. 3. The method of claim 1 or 2, wherein heat distribution is imparted to the preform by adding a distribution. 4. The method for heating a preform according to claim 1, wherein the temperature of the metal rod in the heating zone of the preform is 300 to 600°C.