MX2008003333A - Preform heating device - Google Patents

Abstract

Preform heating device able to perform a precise and strongly localised heating of the preforms before the blow moulding phase of the plastic bottle or container production process. This device has an innovative construction configuration, thus allowing high efficiency thanks to the significant reduction in the energy required to reach the project temperatures in the heating element in a very rapid way. The inductor does not heat the preform directly, but takes to the temperature set, through the concentration of the magnetic flow, generated by the passage of current, a conductor material of a particular form that, by irradiation and convection, in turn heats the PET.

Description

PREFORMA HEATING DEVICE TECHNICAL FIELD The present invention relates to a preform heating device, suitable in particular for induction heating of preforms for the production of bottles and containers by means of blow molding.

STATE OF THE ART The different devices are known by heating preforms used in the production of hollow bodies in plastic material by means of the blow molding technique. An example of such devices is described in WO92 / 15442. This device provides additional heat by irradiation and convection, by means of a dedicated heating element, to a transition region in the preform wall between parts of the wall subjected to different degrees of expansion during blowing, in particular between a subject region to little or even no expansion and another region in which the expansion is even greater. However, in the known devices, this heating element is heated in turn by direct conduction, thus causing the problems of overheating with significant temperatures reached by the components of the complete device; the presence of electrical resistances supposes the wear of the same through time and, consequently, greater maintenance. The thermal profile of the components, determined by the design of such devices also supposes a high dissipation of energy in order to allow the reach of the project temperature in the element that heats the preform. This also leads to a non-precise localization of the heat flow, also due to the structure difficult to customize, scarce rapid heating of preform due to a significant thermal inertia of the structure and the maximum temperature limit that can be achieved with traditional resistances. An innovative preform heating device is required which makes it possible to overcome the above deficiencies.

BRIEF DESCRIPTION OF THE INVENTION A primary process of the present invention is that of making a preform heating device that allows a precise and strongly localized heating of the preforms before the blow molding phase of the container or bottle production process. plastic. An additional purpose is to provide a preform heating device having an innovative construction configuration, thus allowing better performance with respect to the solution with hot air conditioning systems, thanks to the reduction in energy required to reach the temperature project in the heating element. Finally, a further purpose is to provide an infrared heating device with a simple and easily replaceable irradiation component. The present invention therefore proposes to achieve the purposes described above in preparing a preform heating device for the production of plastic hollow bodies which, according to claim 1, comprises at least one induction means (2) suitable for inducing when a current passes therein, a magnetic flux on at least one heat transfer medium (4), in order to transmit by irradiation a predefined amount of heat to at least one preform (10) suitable for being inserted in said device. Advantageously, this device is capable of guaranteeing, within the predetermined tolerances, a thermal profile assigned both along the thickness and in the direction of the length of the piece of heat, usually in PET. The inductor does not directly heat the piece, also because the preform is constituted by a non-conductive material but, by means of a magnetic flux, it takes the temperature of a ring of conductive material with a timely section that, by irradiation, to its it once heated the PET preform area. Advantageously, a flow concentrator may be provided suitable for the best concentration of the useful magnetic flux towards the heating element. This further provides the thermal profile of the inventive device components, in order to avoid the deficiencies of overheating and to considerably improve the performance and efficiency of the complete system. In certain applications it is in any case possible to avoid the use of the flow concentrator, thus simplifying the structure of the device. The dependent claims describe the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The additional features and advantages of the invention will be apparent in view of the detailed description of a preferred embodiment, although not exclusive, of an illustrated preform heating device, such as illustrated by way of example not limiting with the aid of the accompanying drawings in which: Fig. 1 shows a section of a first embodiment of the heating device according to the present invention; Fig. 2 shows a section of the heating device in Fig. 1 with a variant in relation to a component; Fig. 3 shows a section of a second embodiment of the device of the invention; Fig. 4 shows a section of the device in Fig. 3 with a variant in relation to a component; Fig. 5 shows an axonometric view of a section of the device of the invention; Fig. 6 shows an axonometric view of various devices, according to the device, placed linearly. Figures 7 and 7a show a different mode of the inductors 2 'with a different installation of the power connection to the inductors.

Detailed Description of the Preferred Modes With reference to Figures 1 to 4, the different embodiments of a preform heating device are illustrated, comprising: an inductor 2, an optional flow concentrator of magnetic dielectric material 3, a heating ring 4 , - at least 1 support 5 of said ring. This device further comprises a support base 1, generally in steel, and at least one external centering support 6 of the device, preferably in aluminum. Said base 1 and said at least one centering support 6 are joined by means of fastening means 1 1, such as screws, bolts or other similar elements. The inductor 2, preferably in copper, crosses the external ring support 6 and presents within the device a configuration that is preferably, but not necessarily, circular. The passage of electric current in the inductor produces a magnetic field in which the flow is advantageously transported, also by means of the flow concentrator 3, on the heating ring 4, for example in mixtures of high electrical resistance which are resistant to high temperatures , such as, for example, mixtures of Ni-Cr-Fe, in such a way as to allow this ring to reach a predetermined temperature, preferably higher than 800 ° C. This temperature of the ring 4 is suitable for transmitting the heat, by irradiation, to a preform 10, for a predefined time suitable for a suitable preheating of the preforms used in the production by blowing of plastic bottles and containers. The cover of the device in fact has a hole of suitable dimensions for introducing the preform 10 inside, in the area surrounded by the heating ring 4. Advantageously, the inductor 2 can be cooled by means of the water fluid or other cooling fluid within it. In the embodiment in Fig. 1 the ring 4, with a polygonal section, is held in place by an anchoring system, simple from the constructive point of view, which firmly fixes together the flow concentrator 3 and the inductor 2 and has a ring support 5 provided with individually insulated metal tabs 7. This solution makes it possible to have good thermal insulation between the heating ring 4 and the remaining device components, especially if the phenomena of conduction and convection are considered. In Fig. 2 an even simpler mode of the anchoring system has the ends 8 of the support 5 trapped in the housings provided in the ring 4. In the devices in Figs. 1 and 2, the concentrator 3 has a shape such as to house the inductor 2 within the device. Between the inductor-concentrator block and the ring 4 there is an opening 9. An advantageous embodiment, illustrated in FIG. 3, determines a more solid configuration of the device of invention and a greater protection of the other irradiation components of the heating ring 4. The ring support 5, in this embodiment, is in fact thicker and is constituted by one or more plates 5 ', with a complementary shape, constituted by a refractory material, such as oxides, ceramic or refractory cement reinforced by fiber, capable of resisting the operating temperature of the heating ring. The temperature of the ring is strongly influenced by its thermal conductivity, which, therefore, is preferably less than 1 W / mK. In this case, the inductor-concentrator block and the ring are joined together by said refractory plates which at the same time nevertheless prevent their direct contact. An advantageous variant illustrated in FIG. 4, in the embodiment in FIG. 3, has an opening 9 'between the ring 4 and the refractory plates 5'. The presence of this opening 9 'guarantees additional protection from overheating for the components of the device and, therefore, a lower energy dissipation. In order to focus the irradiation, an adjustable screen 1 3 can be advantageously provided, placed between the body of the preform 10, inserted in the device, and the internal components of the device by itself in such a way so as to further improve the location of heating a predetermined area of the preform, for example, the neck. In order to improve the performance of the heating device of the invention, certain embodiments were subjected to tests with components made of different material in each test. As a result of these tests, a flow concentrator 3 made of magnetic dielectric material was chosen for the device of the invention. In fact, such material makes it possible to obtain the preset temperature on the ring 4 using a feeder that provides a current less than 40% of that which could be from the concentrator 3 of another material, for example, ferrite bonded by glass. Despite the fact that ferrite joined by glass is a material at low cost, the use of the same in this application could suppose the highest consumption and a higher cost of the same feeder. The tests carried out on two devices with concentrator 3 in ferrite material joined by glass and magnetic dielectric, respectively, with a frequency generator equal to 10 kHz, have made it possible to obtain the following results, which we report as an example, in relation to the total of dissipated and active power used, for efficiency and for the distributed current in order to reach a temperature of 900 ° C in a non-transitory stationary state in ring 4: It should be noted how the magnetic dielectric material flow concentrator significantly improves the efficiency of the device, allows the use of a smaller dimension feeder and a less powerful cooling system as the total dissipated power is lower. When analyzing the value of the voltage at the ends of the feeder and the phase between the voltage and the current and consequently the reactive powers in question, one observes that with the concentrator 3, or core, made of magnetic dielectric material a reactive power more low it is observed that with the ferrite joined by glass. By means of frequency analysis, it can also be observed that the concentrator 3 of magnetic dielectric material allows a higher efficiency even in varying frequency. The thermographic analysis showed how the temperatures reached during the non-transitory operation of the device of the different components are perfectly tolerable by the materials used. Advantageously for the production of bottles and containers starting from preforms in a dedicated plant, the use of a multi-cavity plate or module is contemplated upstream of the blow molding machine, capable of accommodating in a matrix configuration, or in a row, a series of heating devices according to the present invention, suitable for housing the preforms to be heated. An example of a multi-cavity module with linear adjustment of the devices according to the invention is illustrated in FIG.

Fig. 6. For the serial enhancement of the same devices of the same type, for example, it is possible to use a generator with a power of only 20 kW, therefore 1 kW of power input per cavity. The device of the present invention, for heating the preforms used in the production of standard beverage bottles, has a consumption of approximately 0.8 kW / cavity with a saving of approximately 20% with respect to the consumption of jet heating devices. of known hot air. The specific heating power is even higher than that obtained with the known devices and reaches at least 15 W / cm2. The additional advantages of the device of invention with respect to the hot air jet devices are represented by: - a greater precision of heating in an area of the preform that depends only on the geometry of the device and not on the hot air flows, and therefore a greater stability of the heating process; - a control of the process carried out considering the temperature parameter alone; the presence of a perimeter heating source that makes partial rotation of the preform unnecessary. From a mechanical point of view, the device of invention has high reliability due to the presence of few mechanical components and also of high stability in which, with the configurations described in the various variants, no thermal expansion of the components is observed. The device is also less complex than for the correct heating in an absolute manner that no preform rotation is required. In addition, the absence of any electrical resistance significantly reduces the maintenance required for proper operation of the device. Finally, with such a device, it is possible to heat the preforms in various ways, such as ovals, with different thickness distributions and even at low axial stress ratios, such as in the case of containers with long collars. The particular embodiments described herein do not restrict the scope of this application, which covers all variants of the invention defined in the claims.

Claims (10)

1. REVIVAL DICTION IS 1. Heating device for heating preforms for the production of plastic objects comprising at least one induction means (2) suitable to induce, when the current passes therein, a magnetic flux on at least one thermal transmission means (4) ), in order to transmit by irradiation a predefined amount of heat to at least one preform (10) suitable to be inserted in said device. Device according to claim 1, wherein the concentration means (3) of said magnetic flux are provided on said at least one heat transfer medium (4). Device according to claim 2, wherein said concentration means (3) have a shape such as to receive said at least one induction means (2). 4. Device according to claim 3, wherein said at least one transmission means is constituted by a ring (4) with a polygonal section. Device according to claim 4, wherein said support means (5) are provided for said ring (4). 6. Device according to claim 5, wherein said support means (5) comprise metal tongues (7). 7. Device according to claim 5, wherein said support means (5) comprise ends (8) placed in corresponding housings provided on the ring (4). Device according to claim 5, wherein said support means (5) comprise at least one plate (5") in refractory material of low thermal conductivity 9. Device according to claim 8, wherein two or more plates (5 ') are provided with a complementary shape therebetween 10. Device according to claim 5, wherein an opening (9) is provided between said at least one transmission means (4) and said means of concentration (3) .1 Device according to claim 8, wherein an opening (9) is provided between said at least one transmission means (4) and said at least one plate (5 '). according to any of the previous claims, comprising a base (1) and centering supports of the device (6), reciprocally joined by means of clamping (11) 13. Device according to any of the previous claims, comprising a screen (13)