Patent Application
20110291332
This claims the benefit of German Patent Application DE 10 2010 021 446, filed May 25, 2010 and hereby incorporated by reference herein.
The present invention relates to a method for controlling the temperature of performs. The invention furthermore relates to a heating device for controlling the temperature of performs.
Beverage containers made from thermoplastic materials, especially from the most widely used PET, are commonly produced in a stretch blow molding process. In this mostly two-stage stretch blow molding process the containers are typically produced from injection-molded, rotationally symmetric preforms. Said preforms consist of an elongated, cylindrical, lateral body section with a rounded, closed bottom and a neck section with an upper opening, which can also be referred to as mouthpiece section. Positioned close to this opening there is usually a thread section, which can be delimited toward the bottom by a collar or the like. Already during the injection-molding process of the preform is the said thread section produced to the final dimensions that will be required for later use. During the stretch blow molding process it continues to keep its original shape and later forms the thread for the screw cap of the finished beverage container. The remaining sections of the preform are, in contrast, deformed and stretched. During the manufacturing process the preforms are heated to a predefined magnitude of process temperature in order to enable forming by stretch blow molding in the desired manner, with uniform wall thickness and without causing the material to tear. The heating is mostly effected by means of infrared radiation, because in this manner it is possible to ensure defined and uniform temperature control of the preforms.
The plastic material intended for further processing (in general PET) is of such a nature that it will strain harden as it is stretched. Of decisive importance in this process is the forming temperature. The strain hardening effect is normally put to use in the production of PET containers for the purpose of controlling and optimizing wall thickness distribution. Temperature profiling has proved to be an advantageous method for heating the preforms as uniformly as possible, on the one hand, thereby however avoiding, on the other hand, mechanical damage to the neck section and the container thread, which would result from too much heat prior to the stretch blow molding process.
Depending on the production process, it is possible to apply the infrared radiation in such a way that the preforms are heated according to a desired temperature profile. The aim of this is to have the warmer sections deformed with priority to the other parts as long as is required for the stretching resistance resulting from strain hardening to become greater than the resistance of the adjacent cooler sections. Commonly, the temperature profile is uniformly distributed around the circumference of the preforms and can vary process-dependently along the longitudinal axis of said preforms.
A system and a method for pretreating preforms, whereby the said preforms are heated prior to a blow molding process, is known from EP 0 736 367 B1. The preforms are thereby uniformly pretreated with regard to their temperature before they are heated again for the following blow molding. The pretreatment should be defined by the thermal energy contained in each preform, whereby the temperature differences between the preforms are supposed to be reduced or kept at a low level.
DE 25 45 134 A1 describes a method for heating preforms made from a thermoplastic material to blowing temperature by means of infrared radiation. In this method, the preforms are heated until they have uniformly reached a first temperature level that is below blowing temperature. Starting from this first temperature level, the preforms are subsequently further heated by means of infrared radiation until they have reached the required final temperature.
The invention aims primarily at providing an improved and particularly energy-efficient method for the temperature control of preforms in connection with a stretch blow molding process, whereby the said preforms are heated according to a desired temperature profile with said temperature profile being largely predefineable, in any occurring external conditions, to an exact degree. It is intended that the thermal energy required for the temperature control can be made available as efficiently and at as low a cost as possible. A further aim of the invention is to provide an improved heating device for preforms, by means of which the temperatures and temperature profiles required for the preforms can be set and predefined as exactly and with as reduced an energy input as possible.
It is an object of the present invention to provide an at least two-stage method for the temperature control of preforms made from a thermoplastic material, especially from PET, whereby the preforms are brought to a softening temperature required for blow molding or stretch blow molding the plastic material, this heating taking place either during or prior to the said process of blow molding or stretch blow molding, whereby the thermal profile can be predefined and the said softening temperature is accordingly process-specifically distributed. In the current context, “process-specifically distributed” or “process-specifically distributed temperature” is intended to mean that a temperature profile, applied longitudinally along the preform, is adjusted in such a manner as to correspond to how the material of the preform is to be distributed during the process of blow molding in the specific instance and under the specific process-technical conditions.
The temperature control process comprises at least two different, consecutive heating stages, each with different tasks to fulfill. The first heating stage is intended for achieving an approximately uniform base temperature of the entire preform, with said base temperature corresponding at the most to the maximum heating temperature for maintaining the dimensional stability of the thread section at the preform's open-topped neck section. The second heating stage is intended for achieving a process-specifically distributed softening temperature according to a predefineable thermal profile, with said softening temperature being the temperature required for blow molding or stretch blow molding at least the preform's body section located below the thread section and/or a collar area located therebelow. The present invention provides an improved concept for thermal layering for the preforms. The heating is achieved in two stages, on the one hand in order to optimally prepare and temperature-control the preform for the stretch blow molding process so that the containers shaped in the process will have as uniform a wall thickness as possible and so that scrap resulting from defective containers is reduced to a minimum. On the other hand, the two-stage temperature control process is intended to be achieved at a reduced energy input, which is already to be ensured by the two-stage heating with the initially uniform preheating and the subsequent specific temperature profiling.
According to the invention, the heating is achieved in at least two consecutive sections or heating stages of the heating device. The first section provides the preforms with basic heating in order to heat them to a base temperature that is as uniform as possible and that is below the softening temperature of the plastic material. This temperature limit is necessary in order to avoid, as far as possible, that the thread section is unduly heated. Thermal layering is not yet applied during this basic heating phase, as the intention is to achieve a uniform temperature distribution over the entire body of the preform. The defined base temperature should typically range between at least 50° C. and up to 90° C., thus allowing to compensate for different input and storage conditions of the preforms. As the preforms are likely to have been stored in different locations at different temperatures before being supplied to the stretch blow molding process, it is necessary to provide uniform input conditions for the preforms in order to achieve the best forming results possible. Accordingly, a basic heating phase constitutes the first temperature control stage and a subsequent temperature profiling phase constitutes the second temperature control stage.
During the temperature profiling phase that constitutes the second heating stage, the preforms are heated with the temperatures being layered in direction of the longitudinal axis of the said preforms. As the case may be, it is possible to allow for a temperature measurement prior to temperature profiling in order to record the temperature of the preforms after the basic heating and to accordingly adjust the heating stages. It is optionally possible to allow for a further temperature measurement after the second heating stage in order to record the preforms' final temperature after the second heating stage or after the temperature profiling phase and to accordingly take the recorded temperatures into account when adjusting the first heating stage.
It is advantageous for the preforms to be heated to a largely uniform base temperature ranging between approximately 50° C. and approximately 90° C. in the section of the first heating stage or the basic heating phase. This temperature depends primarily on the maximum allowable temperature for the neck section of the preforms made from PET or another suited thermoplastic material, because this section with its thread that is to be used later is not to be changed and deformed during heating and the subsequent stretch blow molding process, but rather to remain unaltered and maintain its size and shape during all processing stages. An advantageous variant of the method according to the invention allows for the preforms to be heated to the base temperature in the section of the first heating stage by inserting heating elements into the open-topped preforms. The heating elements function as so-called boosters in that they require a very short time for bringing the respective preform from storage temperature to the desired base temperature, which is brought to a yet higher temperature level in the subsequent heating stage by applying a temperature profile. This booster or heating element may be of a typical length that corresponds to an individual radiant heater, thus enabling a largely homogeneous heating of the preforms. Moreover, it is also possible for further radiators to function as components of the said booster, with said components applying heat radiation to the outside of the preforms for achieving the desired basic heating.
Furthermore, an especially advantageous embodiment variant of the method according to the invention may be performed by applying hot air to the preforms to preheat them before they are conveyed into a heating device and/or after they are taken from a storage or store room. In this way it is possible to utilize, for instance, certain proportions of an oven's exhaust heat, which would otherwise be conducted outside, for producing the energy for the basic heating. The oven's exhaust heat can be taken advantage of by, for instance, deflecting the warm exhaust air and/or conducting this exhaust air through suitable heat exchangers for cooling it, thus representing a potential for energy saving.
The hot air utilized in the first temperature control stage for preheating the preforms may however also, at least partly, be generated from the waste process heat of other components of a container production, container handling, and/or container filling machine or facility. In particular, the hot air utilized in the first temperature control stage for preheating the preforms may be generated from the waste process heat of the heating line for the heating process of the preforms prior to blow molding or stretch blow molding. Alternatively or in combination with this procedure, it is possible to generate the hot air utilized in the first temperature control stage for preheating the preforms from the waste process heat of other facilities within the container handling and/or filling line, such as the facilities for pasteurizing, sterilizing, hot filling, or the like.
In particular, exhaust air should be used from machines that are located close to the so-called preform infeed, i.e. the system for feeding in the preforms. In the simplest case the heat is transferred via a simple pipe to the preform infeed located above, and then transferred by convection. Ventilators may also be employed for conducting the hot air. Preferably, the pipes are insulated. The preforms are preferably preheated after being sorted, so that it is possible to adjust the settings for the heating process more uniformly. An advantageous embodiment can provide a small tunnel from the feeding track to the blow molding machine.
A further advantageous variant of the method according to the invention can provide temperature regulation subsequent to the preheating process or temperature detection after the preheating process and a subsequent adjustment of the heating parameters, in particular individually for each preform. The temperature range intended for preheating is between approximately 30°-90° C., preferably between 40°-70° C., and with special preference between 40°-60° C. It is preferable that only the bodies of the preforms are heated in the process, however not the support ring and the thread.
As already mentioned, the second heating stage essentially serves to apply a temperature profile to the preforms in this temperature profiling phase, with said temperature profile being adjusted and/or varying along the length of said preforms. In order for the preform's thread section to maintain dimensional stability during the subsequent process steps, special attention should be paid not to apply too much heat to the thread section when heating the neck section and the remaining preform. As the thread section and the so-called neck ring (support ring) are required for handling and transport purposes, it is important not to modify and deform these sections of the preform. In the section of the second heating stage, the preforms can be heated in particular by radiant heating devices. In order to avoid overheating, said radiant heating devices may be provided with a regulated surface cooling system.
It is alternatively possible for the temperature profiling phase to be carried out not prior to, but rather immediately together with the blow molding process. This is for instance possible when employing microwave or laser heating for profiling the temperature distribution.
In order to achieve the above mentioned object of the invention, a heating device is additionally provided for controlling the temperature of preforms made from a thermoplastic material for a subsequent blow molding or stretch blow molding process. This heating device according to the invention is provided with at least two stages and comprises a preheating stage for applying hot air to the preforms in order to achieve a largely homogeneous base temperature. The system for applying hot air is coupled to further components of a container producing, container handling, and/or container filling machine in order to utilize the exhaust heat supplied by these machine parts. In addition, it is optionally possible to provide a heating element that is inserted into the preforms in the first heating stage, so that the preforms are heated and brought to the base temperature from inside. Furthermore, it is possible to provide a temperature sensor, which is disposed downstream of the first and upstream of the second heating stage and which is coupled via signal transmission to a control unit for regulating the heat output of the first heating stage and/or the temperature profiling stage.
An especially advantageous variant of the heating device provides for the preheating stage to be coupled to a heating line, which is disposed upstream of a facility for blow molding or stretch blow molding the preforms, so that the waste process heat of said heating line can be utilized. This allows to save energy by utilizing the waste process heat that would otherwise not be used. By accordingly regulating the utilization and supplying of exhaust heat, it is in addition possible to define and maintain the conditions and parameters of the preheating process very precisely.
It is optionally possible to couple the preheating stage with at least one facility within the container handling and/or filling line for pasteurizing, sterilizing, and/or hot filling in order to utilize the waste process heat of the said facility. It is furthermore possible to use the exhaust heat of electrical machines, for instance of electrical drive motors required for driving various components in complex machines.
Other aspects, embodiment variants, and advantages in the configuration and operation of the heating device according to the invention are to be seen in the context of the method variants already mentioned above, as all the method variants are to be regarded as options for operating the heating device.
Furthermore, it must be pointed out here that the present invention is generally suited for use in microwave ovens, rotary ovens, linear ovens, stationary ovens, etc. It is furthermore possible to use individual heating jackets, whereby each preform is selectively temperature-controlled in a separate heating jacket. For purposes of completeness, it should be noted that in addition to the two mentioned, separate heating stages, it is possible to provide further heating stages, as the case may be, without requiring a detailed explanation here.
A further appropriate option of the heating device according to the invention or of the temperature control method according to the invention may consist in spacing the preforms at distinctly smaller intervals during preheating than during the later blow molding process in order to improve energy input and achieve a more effective utilization of the input heating energy. The spacing during heating can thus, for instance, be only about half or even less of the spacing during the blow molding process, in order to heat the preforms especially effectively when they are much closer together. Spacing during the blow molding process, on the other hand, is determined by the machine's technical parameters and usually cannot be further reduced. The spacing selected for preheating can, in particular, be smaller than approximately 80 mm, preferably even smaller than approximately 40 mm.
In the following passages, the attached figures further illustrate exemplary embodiments of the invention and their advantages. The size ratios of the individual elements in the figures do not necessarily reflect the real size ratios. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
The same or equivalent elements of the invention are designated by identical reference characters. Furthermore and for the sake of clarity, only the reference characters relevant for describing the respective figure are provided. It should be understood that the detailed description and specific examples of the device and method according to the invention, while indicating preferred embodiments, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The schematic illustration of
The schematic illustration of
The subsequent adjacent second heating stage 38 also comprises a radiator section 40 with infrared radiators, which are, however, variably regulated in order to create the desired temperature profiling, with the result that, on the one hand, the necessary forming temperature T3 of approximately 100° C. is achieved, but, on the other hand, the thread section of the preforms 28 is kept at the temperature level of T2.
The illustration in
Just behind the entry area 12 the heating line 14 comprises the booster 36 or the first heating stage 30 for the basic heating of the preforms 28. Downstream of the booster 36 are the radiator areas 40 of the second heating stage 38, which is indicated in the presented exemplary embodiment by altogether six consecutively arranged heating boxes. Upstream of the rotating entry area 12 with the entry star wheel is a linear feed path 44 for feeding the preforms 28 to the container forming device 10.
According to
It is alternatively possible for the preheating device 46, which is supplied with the exhaust heat from the heating device or the like, to function as the first heating stage 30 and thus to guarantee that the preforms 28 are uniformly preheated, before they enter the second heating stage 38 for temperature profiling. This arrangement will at any rate contribute to increasing the efficiency of the temperature control process.
Both variants according to
The detailed view in
The schematic illustration of
In particular, the exhaust air is transported without using additional ventilators, only through the heat rising to the preforms located higher above in the feeding area. It is also possible, however, to use ventilators or the recycled air from the stretch blow molding process for this purpose.
The conducts are specially insulated.
By rendering the various components of a stretch blow molding device 20 for producing containers for liquids from preforms, the schematic illustration of
As illustrated by
Via the first transfer star 18, the preforms that have been heated in preparation for the stretch blow molding process are conveyed to the so-called blowing wheel of the stretch blow molding device 20, where they are shaped to containers for liquids, and subsequently they are conveyed into an integrated container forming and filling machine and there consecutively to a rinser 70, a filling device 72, a labeling device 74, a pasteurizing device 76 as well as a subsequent adjacent packaging module 78, where they can be assembled to form packages and/or palettes or other packaging units and made ready for dispatch as required. As indicated in
The processing stations of the integrated machine illustrated in
In particular for the purpose of the uniformity of the preheating applied to the preforms, it is also possible to include a control system for regulating the preheating temperature by means of temperature sensors. According to the number of infrared radiators turned on in the oven, the exhaust air is either warmer or cooler; therefore an additional air heater can be included upstream of the preheating unit in order to ensure a constant air temperature. A sensor for recording the preforms' temperature at the end of the preheating unit can be included as well as another one upstream of the additional air heater for measuring the temperature of the oven exhaust in the exhaust air ducts.
The invention has been described with reference to preferred embodiments or embodiments that are to be regarded as optional, as illustrated in the
List of Reference Characters:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 021 446.9 | May 2010 | DE | national |
