The invention relates to a method for blow molding containers, in which a preform of a thermoplastic material is, after a thermal conditioning along a transport path in the area of a heating section, deformed within a blow mold into the container by the application of blowing pressure, and in which the preform is provided, at least along a portion of its transport path in the area of the heating section, with a temperature profile which extends in a longitudinal direction of the preform. The temperature profile is provided by at least one heating device which is provided with at least one tubular heating radiator.
Moreover, the invention relates to a device for blow molding containers of a thermoplastic material, the at least one heating section arranged along a transport path of the preform, and a blow molding station provided with a blow mold and in which, along at least a portion of the transport path of the preform, a device for producing a temperature profile is arranged in the area of the preform, wherein the temperature profile extends in a longitudinal direction of the preform, and wherein, for generating a heat radiation, at least one tubular heating radiator is used in the area of the heating device.
When forming containers by the influence of blowing pressure, preforms of a thermoplastic material, for example, preforms of PET (polyethylene terephthalate) are fed within a blow molding machine to various processing stations. Typically, such a blow molding machine has a heating device as well as a blowing device in whose areas the previously thermally conditioned preform is expanded by biaxial orientation into a container. The expansion takes place by means of compressed air which is introduced into the preform to be expanded. The technical sequence in such an expansion of the preform is explained in DE-OS 43 40 291. The introduction of the pressurized gas mentioned in the beginning, also includes the introduction of pressurized gas into the developing container bubble as well as the compressed gas introduction into the preform at the beginning of the blow molding process.
The basic construction of a blow molding station for forming containers is described in DE-OS 42 12 583. Possibilities for thermally conditioning the preforms are explained in DE-OS 23 52 926.
Within the device for blow molding, the blow molded containers can be transported by means of various manipulating devices. Particularly the use of transport mandrels, onto which the preforms are placed, has been found to be advantageous. However, the preforms can also be manipulated by other support devices. The use of gripping tongs for manipulating preforms and the use of spreading mandrels, which for support can be inserted into an area of the opening of the preform, are also among the available constructions.
A manipulation of containers with the use of transfer wheels is described, for example, in DE-OS 199 06 438, in an arrangement of the transfer wheel between a blow wheel and a discharge section.
The manipulation of the preforms already explained above takes place, on the one hand, in the so-called two-stage methods, in which the preforms are initially manufactured by an injection molding process, are subsequently subjected to intermediate storage, and are only later thermally conditioned and blown up into a container. On the other hand, the manipulation takes place in the so-called single-stage methods in which the preforms are thermally conditioned directly after their manufacture by injection molding technology and, after a sufficient solidification, the preforms are thermally conditioned and blown into a container.
With respect to the blow molding stations used, different embodiments are known. In blow molding stations, which are arranged on rotating transport wheels, a book-like opening of the mold carriers can be found frequently. However, it is also possible to utilize mold carriers which are moveable relative to each other or are guided in another manner. In stationary blow molding stations, which are particularly suited for receiving several cavities for forming containers, plates extending parallel to each other are typically used as mold carriers.
Prior to carrying out heating, the preforms are typically placed on transport mandrels which either transport the preform through the entire blow molding machine, or which merely circulate in the area of the heating device. In the case of an upright heating of the preforms, such that the openings of the preforms are oriented downwardly in the vertical direction, the preforms are usually placed on a sleeve-shaped holding element of the transport mandrel. In the case of a hanging heating of the preform, in which the preforms are oriented with their openings upwardly in the vertical direction, as a rule spreading mandrels are inserted into the openings of the preforms, which tightly clamp the preforms.
A significant problem in the use of conventional infrared radiators for heating the preforms resides in that the predominant portion of the radiation is converted into heat already in the immediate vicinity of the surface of the preform, and that a thermal conditioning of the inner wall areas of the preform takes place only due to the spreading of heat within the thermoplastic material. Since the thermoplastic material has distinct thermally insulating properties, a sufficient spreading of heat requires a time for heating of the preform of about 20 seconds. For avoiding overheating of the surface areas of the preform, blowing against the preform with cooling air is carried out simultaneously with heating. This results in relatively high energy consumption for carrying out heating.
For reinforcing an active heating of the preform, which is as uniform as possible through the wall thickness of the preform, it is also known, alternatively or as a supplement to heating with infrared radiators, to carry out heating with HF-radiation or microwave radiation. However, these types of radiation make it necessary to use screens in order to prevent or reduce the escape of radiation. Moreover, a conversion of this radiation in the preform material into heat has been found to be time consuming, so that no significant reduction of the heating required heating times could be achieved.
For reducing the necessary heating time, it is also already known to use NIR-radiators in the area of the heating section whose heat radiation is emitted in a near infrared area, typically with wave lengths of between 0.4 and 1 micrometer. For optimizing the energy utilization, such heating sections are equipped with a plurality of mirror surfaces, in order to avoid as much as possible, or at least significantly reduce, absorption of the heat radiation by structural components of the heating section. However, in the operation of such heating sections, it has been found that the heat distribution within the preforms deviates from predetermined temperature profiles.
A particular problem occurs if the preforms are not to be provided, in the areas of the entire extensions, with a temperature which is as uniform as possible, but if the temperature profiles already mentioned above are to be generated. The problem in generating such temperature profiles is the fact that the radiator tubes radiate the heating radiation relatively uniformly at least in one circumferential direction of the tubes. By using reflectors, it is ensured that a heating energy which has been radiated in a direction facing away from the preforms is cast back and conducted in the direction toward the preforms.
For generating temperature profiles, it is known to use for example, shutters which shade certain areas of the preforms relative to the heat radiation. Also already known in the art are lens-like elements for focusing the radiation, or curved reflectors, which reinforce radiation directed in the direction of the preforms.
It is the object of the present invention to improve a method of the above-mentioned type in such a way that a predetermined temperature distribution is achieved within the preforms.
In accordance with the invention, this object is met in that the radiation emission of the heat radiator is radiated by the heating device positioning the heating radiator in different spatial directions with different intensities.
Another object of the present invention is to construct a device of the above-mentioned type in such a way that the preforms are provided with a predetermined temperature profile.
In accordance with the invention, this object is met in that the heating device positioning the heating radiator is constructed for radiating the radiation emission of the heating radiator with different intensities in different spatial directions.
By constructing the heating device in such a way that the radiation emission takes place in different spatial directions with different and predetermined intensities, it is especially possible to select those portions of the heating energy which impinge upon different vertical levels of the preforms, in such a way that the respectively desired temperature profile is achieved. In this connection, the areas to be heated to a higher temperature are radiated with a higher heating power, and the areas to be heated to a lower temperature are radiated with a lower heating power. In particular, it is also possible to predetermine the distribution of the radiation emission in such a way that certain areas of the preform are not at all subjected to impinging heating radiation.
A variation of the radiation alignment resides in that a focusing reflector is used for influencing the spreading of the heating radiation.
In particular, for bundling the radiation it has been found useful if the focusing reflector is at least over areas thereof with an elliptical shape.
A long usefulness of the heating device is reinforced by positioning the heating radiator in the area of the focusing reflector with end sections which are bent in the direction toward the reflector surface.
For reinforcing a low-loss heating of the preforms it is being considered to use heating radiators for generating a NIR-radiation.
An effective focusing of the radiation can be achieved if the heating radiator is positioned within a receiving space defined by the focusing reflector and at a short distance from the reflector surface.
Another alignment of the radiation is reinforced by using at least one screen for shading.
In particular, it is intended that the screening is used for shading at least one circumferential area of the radiator tube.
A compact construction can be achieved by positioning the screening as a coating on the heating radiator.
A use even at high operating temperatures of the heating radiator is reinforced by using a ceramic material as screening.
For producing blow molded containers it has been found especially useful to position the heating device at an end of a heating section.
In the drawings, embodiments of the invention are schematically illustrated. In the drawing:
The principal construction of a device for deforming preforms 1 into containers 2 is illustrated in
The device for forming the containers 2 consists essentially of a blow molding station 3 which is provided with a blow mold 4 into which a preform 1 can be placed. The preform 1 may be an injection molded part of polyethylene terephthalate. For facilitating placement of preform 1 into the blow mold 4 and for facilitating a removal of the finished container 2, the blow mold 4 consists of mold halves 5, 6 and a bottom part 7 which can be positioned by means of a lifting device 8. The preform 1 may be supported in the area of the blow molding station 3 by a transport mandrel 9 which, together with the preform 1, travels through a plurality of treatment stations within the device. However, it is also possible to place the preform 1 directly into the blow mold 4, for example, by means of tongs or other manipulating means.
For facilitating a supply of compressed air, a connecting piston 10 is arranged underneath the transport mandrel 9 which supplies compressed air to the preform 1 and simultaneously effects a sealing action relative to the transport mandrel 9. However, in a modified construction, it is also basically conceivable to use stationary compressed air supply lines.
A stretching of the preform 1 takes place in this embodiment by means of a stretching rod 11, which is positioned by a cylinder 12. In accordance with another embodiment, a mechanical positioning of the stretching rod 11 is carried out by means of curved segments which are acted upon by gripping rollers. The use of curved segments is particularly advantageous if a plurality of blow molding stations 3 are arranged on a rotating blow wheel.
In the embodiment illustrated in
After closing the mold halves 5, 6 arranged in the area of the supports 19, 20, the supports 19, 20 are locked relative to each other by means of a locking device 20.
For the adaptation to different shapes of the sections of an opening section 21, according to
In order to be able to deform a preform 1 into a container 2, such that the container 2 has material properties which ensure a long usability of foodstuffs filled into the container 2, particularly beverages, special method steps must be adhered to when heating and orienting the preforms 1. Moreover, advantageous effects can be achieved by adhering to special dimensioning regulations.
Various synthetic materials can be used as thermoplastic materials. For example, PET, PEN or PP can be used.
The expansion of the preform 1 during the orienting process is effected by a compressed air supply. The compressed air supply is divided into a pre-blowing phase in which gas, for example compressed air with a low pressure level, is supplied and a subsequent principal blowing phase in which gas is supplied at a higher pressure level. During the pre-blowing phase, typically compressed air, having a pressure in the interval of 10 bar to 25 bar, and during the principal blowing phase compressed air in the interval of 25 bar to 40 bar, is supplied.
From
For facilitating an arrangement of the guide wheel 29 and the input wheel 35 relative to each other, the illustrated arrangement has been found to be particularly useful because three guide wheels 34, 36 are positioned in the area of the corresponding extension of the heating section 24, namely the respectively smaller guide wheels 36 in the area of the transition to the linear patterns of the heating section 24, and the larger guide wheel 34 in the immediate transfer area to the transfer wheel 29 and the input wheel 35. As an alternative to using chain-like transport elements 33, it is also possible, for example, to use a rotating heating wheel.
After blow molding of the containers 2 is finished, the containers 2 are removed by a removal wheel 37 from the area of the blow molding stations 3, and are transported to the outlet section 32 by the transfer wheel 28 and an outlet wheel 38 to the outlet section 32.
In the modified heating section illustrated in
Opposite the bottom 43, the heating duct 42 is defined by reflector 46. In the illustrated embodiment, the reflector 46 is constructed as a wall of an air conducting element 47 which wall faces the heating duct 42, wherein the air conducting element 47 defines a flow duct 48.
In the illustrated embodiment, the reflector 46 has a collar 53 arranged adjacent the opening section 21, for screening the opening section 21, and a support ring 54 of the preform 1 against an influence of heating radiation, in order to prevent or reduce heating in this area.
In
In particular, it is also being considered to position an inlet opening 59 of the air conducting element 57 opposite the outlet opening 58. The air emerging from the cooling body 55 is thus also conducted through the air conducting element 47, and causes cooling of the reflector 46.
In the area of the heating box 45, a plurality of heating radiators 30 are arranged above each other in the vertical direction. For realizing a frequency-selective heating, a filter disk 60 is arranged between the heating radiators 30 and the heating duct 42 of a filter disk 60. In accordance with an advantageous embodiment, the heating radiators 30, as well as the filter disk 60, are thermally conditioned by the cooling air.
In the area of a direction facing away from the filter disk 60, behind the heating radiators 30, a radiation reflector 61 is arranged which preferably includes a profiled reflector surface. The reflector surface is preferably structured in such a way that a return radiation into the heating radiator 30 is avoided, and the formation of a suitable heat distribution in the area of the heating duct 42 is reinforced.
In accordance with the embodiment in
The reflector 46 is preferably made of metal. In particular, the use of polished or mirrored aluminum is contemplated.
From the top view of
From the cross sectional view of
From a combined view of
In accordance with the embodiment in
In accordance with another embodiment in
An aluminum oxide can be used, for example, as the material for the screening 76. For example, Al2O3 is being considered. A typical thickness of the screening 56 is 50 micrometers, wherein a preferred thickness range is 40 micrometers to 60 micrometers. However, layer thicknesses in a range of 10 micrometers to 100 micrometers have also been found useful.
The heating device 62 according to the invention can be provided, similar to the heating module 41 in
The heating device 62 according to the invention is preferably arranged in the area of a blow molding machine behind the heating elements as seen in a transport direction of the preforms 1 for producing a basic temperature of the preforms 1. Accordingly, the present invention also relates to a blow molding machine which is constructed with the use of the appropriate basic temperature, as well as of the heating device 62 according to the invention. The measures described above for reinforcing the temperature profiling, namely, the use of the focusing reflector 63 on the one hand, and on the other hand, the use of the screening 76 can take place individually as well as in combination. In a combined use, the achievable advantages add up.
Number | Date | Country | Kind |
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10 2009 033 902.7 | Jul 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE2010/000837 | 7/14/2010 | WO | 00 | 7/3/2012 |