Apparatus and method for heating plastic preforms by means of microwaves using an adaptable base reflector

Abstract

Apparatus for heating plastic preforms, having a microwave generating device which generates microwaves, and having a resonator device which forms a receiving space into which the plastic preforms can be introduced so as to be acted upon by the microwaves in the resonator device in order to be heated, wherein the apparatus has a reflector element which is arranged at least partially in the receiving space and which is suitable and intended for conducting microwaves in the direction of a base region of the plastic preforms. According to the invention, the reflector element is movable relative to the receiving space and the apparatus has a drive device for moving the reflector element relative to the receiving space.

Claims

1. Apparatus for heating plastic preforms, having a microwave generating device which generates microwaves, and having a resonator device which forms a receiving space into which the plastic preforms can be introduced so as to be acted upon by the microwaves in the resonator device in order to be heated, wherein the apparatus has a reflector element which is arranged at least partially in the receiving space and which is suitable and intended for conducting microwaves in the direction of a base region of the plastic preforms, characterized in that the reflector element is movable relative to the receiving space and the apparatus has a drive device for moving the reflector element relative to the receiving space, wherein the reflector element has a ring-shaped cross-section, and wherein the apparatus preferably has a control device for controlling the drive device and this control device is suitable and intended for controlling the movement of the reflector element as a function of at least one value that is characteristic of a heating of the plastic preforms.

2. Apparatus according to claim 1, wherein a distance between the plastic preform and the reflector element in a longitudinal direction of the plastic preform is variable.

3. Apparatus according to claim 1, wherein the apparatus has a sensor device for detecting at least one parameter that is characteristic of a heating of the plastic preform.

4. Apparatus according to claim 3, wherein the sensor device is a temperature measuring device which detects, preferably in a contactless manner, a temperature of the plastic preforms.

5. Apparatus according to claim 1, wherein the apparatus has a transport device which transports the resonator device along a predefined transport path.

6. Apparatus according to claim 1, wherein the reflector is at least one of circular or ring-shaped.

7. Apparatus according to claim 6, wherein a plane of the ring-shaped reflector element is perpendicular to the longitudinal direction of the plastic preforms.

Description

(1) In the drawings:

(2) FIG. 1 shows a schematic diagram of an apparatus according to the prior art;

(3) FIG. 2 shows a diagram of an apparatus according to the invention;

(4) FIG. 3 shows a diagram of a relationship between a temperature and a distance of the reflector element from the plastic preform;

(5) FIG. 4a shows a first diagram to illustrate a heating of a plastic preform;

(6) FIG. 4b shows a second diagram to illustrate the heating of a plastic preform.

(7) FIG. 1 shows a schematic diagram of a heating process for a plastic preform 10. This plastic preform 10 has a carrying ring 10b and a dome region 10a. Reference 6 denotes in its entirety a resonator device into which the plastic preform 10 is pushed along its longitudinal direction L. Reference 62 accordingly denotes a receiving space which serves to receive the plastic preform 10. Arranged within this receiving space is a reflector element 8, for example the abovementioned metal ring.

(8) A microwave generating device 2, such as for example a magnetron, generates microwaves which pass via a feed device 4, such as a waveguide, to the resonator device 6. A movement of the reflector element 8 relative to the plastic preform or relative to the receiving space 62 is not provided in the prior art shown in FIG. 1. The arrows F indicate in a highly schematic manner the microwave field which serves to heat the plastic preforms 10.

(9) FIG. 2 shows a schematic diagram of an apparatus 1 according to the invention. In this apparatus 1, now a drive device 64 is provided, by means of which the reflector element 8 can in this case be moved likewise in the longitudinal direction L and thus can be moved closer to the plastic preform or moved further away from the plastic preform 10. This drive device 64 may be for example a linear motor.

(10) Reference 12 denotes a first sensor device which measures a parameter that is characteristic of the plastic preform, in particular a temperature. This sensor device may be for example a pyrometer. A control device 14 controls the drive device 64 and thus also the movement of the reflector element 8 along the double-headed arrow P.

(11) In addition, a power measuring device 16 may also be provided, which measures a microwave power in the interior of the resonator device 6 or in the receiving space 62.

(12) Reference 18 denotes a circumferential wall of the resonator device 6. This runs in particular around the longitudinal axis L of the plastic preform 10. The arrows F coming from this wall and directed towards the reflector element again illustrate the microwaves which are reflected by the reflector element in the direction of the plastic preform 10, more specifically towards the dome region 10a thereof.

(13) FIG. 3 shows a relationship (curve K) between a temperature of the plastic preform 10 and a distance between the plastic preform 10 and the reflector element 8. Also on the basis of such measurement results, it is possible that the stability of the entire heating process is improved, in that the field strength in the resonator device 6 is kept constant by adjusting the distance in order, as mentioned above, to prevent field strengths capable of forming a plasma.

(14) FIGS. 4a and 4b once again illustrate the adjustment of the position of the reflector element 8 (relative to the receiving space and/or the plastic preform), but here the drive device is not shown. As mentioned, one concept of the invention lies in the fact that also the distance of the reflector element 8 from the plastic preform is included in the adjustment. In this embodiment, firstly the heating of the plastic preform 10 is measured in a given position of the reflector element 8 shown in FIG. 4B. In particular, therefore, a temperature profile TP based on the longitudinal direction L of the plastic preform 10 is recorded.

(15) If it is then found that the temperature distribution is to be adapted, then, as in the upper sub-image (FIG. 4a), the reflector element is raised upwards and thus the distance from the plastic preform 10 or the dome 10a thereof is reduced. The temperature is then measured again after the heating process. It can be seen that, in the diagram shown in FIG. 4b, less microwave power reaches the dome region and therefore the dome region is only lightly heated. In the first diagram shown in FIG. 4a, in which the reflector element 8 is arranged closer to the plastic preform 10, a more favourable temperature distribution is thus obtained (see the right-hand sub-image in each case). The energy input into the preform can therefore be influenced by the variable movement of the reflector element. In particular, a temperature profile can be applied to the preform by the variable movement of the reflector element.

(16) The applicant reserves the right to claim as essential to the invention all the features disclosed in the application documents in so far as these are novel individually or in combination with respect to the prior art. It is also pointed out that also features which may be advantageous individually have been described in the individual figures. A person skilled in the art is immediately aware that a particular feature described in one figure can also be advantageous even without taking further features from this figure. A person skilled in the art is also aware that advantages may also arise through a combination of multiple features shown in individual figures or in different figures.

LIST OF REFERENCES

(17) 1 apparatus 2 microwave generating device 4 feed device, waveguide 6 resonator device 8 reflector element 10 plastic preform 10a dome region 10b carrying ring 12 sensor device 14 control device 16 power measuring device 18 circumferential wall of the resonator device 62 receiving space of the resonator device 64 drive device L longitudinal direction K curve P double-headed arrow (movement of the reflector element) TP temperature profile F microwave field