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EP-3082381-B1 - DEVICE FOR HEATING PLASTIC PRE-FORMS BY MICROWAVE

EP3082381B1EP 3082381 B1EP3082381 B1EP 3082381B1EP-3082381-B1

Inventors

  • Kammerl, Martin
  • KURSAWE, ANDREAS
  • SENN, KONRAD
  • ZIMMERER, JOHANN

Dates

Publication Date
20260513
Application Date
20160418

Claims (7)

  1. Apparatus (1) for heating plastic preforms (10), having a plurality of resonator units (2a, 2b, 2c), into which in each case plastic preforms (10) can be introduced in order to heat the latter, having at least one central microwave generating unit (4) for generating microwaves, and having at least one supply device (6) for supplying to at least one resonator unit (2a, 2b, 2c) the microwaves generated by the central microwave generating unit (4), characterized in that a central rectifier unit (12) is provided for providing a rectified voltage and a central high-voltage source is provided and the central rectifier unit (12) and the central high-voltage source provide voltage for operating at least two resonator units (2a, 2b, 2c), that the resonator units (2a, 2b, 2c) itself are arranged stationary and the individual plastic preforms (10) are pushed through the stationary resonator units (2a, 2b, 2c) and are heated thereby, and that at least one bottom reflector device is provided in the resonator units (2a, 2b, 2c), which reflects microwave radiation onto bottom regions of the plastic preforms (10).
  2. Apparatus (1) according to claim 1, characterized in that the apparatus (1) has a transport device (18) for introducing the plastic preforms (10) into the resonator units (2a, 2b, 2c) and/or for taking the plastic preforms (10) out of the resonator units (2a, 2b, 2c).
  3. Apparatus (1) according to at least one of the preceding claims, characterized in that the high-voltage source (8) operates a generator of high frequency voltage.
  4. Apparatus (1) according to at least one of the preceding claims, characterized in that the apparatus (1) has at least one transport device which transports the resonator units (2a, 2b, 2c) along a predefined transport path.
  5. Apparatus (1) according to at least one of the preceding claims, characterized in that the central microwave generating unit (4) is selected from a group of microwave generating units which includes magnetrons, klystrons or solid-state sources.
  6. Method for heating plastic preforms (10), wherein the plastic preforms (10) are introduced into resonator units (2a, 2b, 2c) and are heated within these resonator units (2a, 2b, 2c) through the application of microwaves, wherein these microwaves are generated by a central microwave generating unit (4), characterized in that a central rectifier unit (12) provides a rectified voltage for operating a central microwave generating unit (4), and a central high-voltage source is provided and the central rectifier unit (12) and the central high-voltage source provide voltage for operating at least two resonator units (2a, 2b, 2c), that the resonator units (2a, 2b, 2c) itself are arranged stationary and the individual plastic preforms (10) are pushed through the stationary resonator units (2a, 2b, 2c) and are heated thereby, and that at least one bottom reflector device is provided in the resonator units (2a, 2b, 2c), which reflects microwave radiation onto bottom regions of the plastic preforms (10).
  7. Method according to claim 6, characterized in that the central rectifier unit (12) supplies the central high-voltage generating unit (8a, 8b, 8c) with voltage and the central high-voltage generating unit (8a, 8b, 8c) supplies at least two resonator units (2a, 2b, 2c).

Description

The present invention relates to a device and a method for heating plastic preforms. Such devices have been known in the art for some time. Typically, plastic preforms are moved into a resonator and heated within this resonator by exposure to microwaves. The heated plastic preforms are then transported further, for example to a stretch blow molding machine, to be expanded into plastic containers, in particular plastic bottles, by applying compressed air. More recently, microwaves have been used to heat plastic preforms, either alongside or instead of infrared radiation. Microwave heating devices known in the prior art typically feature a multitude of heating stations, each operating independently of the others. To heat the plastic preforms using microwaves, several individual process stations are generally operated in parallel. These individual process stations have the same design and can also be operated independently. Several device components are provided to generate the microwave radiation, including, in particular, a high-voltage generator, a magnetron, a waveguide for transmitting the microwaves, and an applicator or resonator within which the microwaves are applied to the plastic preforms. The microwave generator typically includes functional groups such as a rectifier and a high-voltage cascade. This high-voltage cascade converts direct current into high voltage. Typically, a mains voltage is first rectified and then high voltage is generated again using the aforementioned high-voltage cascade. This means that each individual station contains the necessary components, such as the generator, magnetron, waveguide, and applicator, each with low power output, and operates them in parallel. This approach requires a large number of functional groups, which increases costs and can sometimes lead to unsatisfactory results. Devices for heating objects using microwaves are, for example, made of DE 10 2010 055 188 A1 , DE 10 2008 039 375 A1 , US 2012/061384 A1 , EP 0 252 889 , WO 99/54033 A1 or EP 2 743 057 A1 known. The present invention is therefore based on the objective of reducing the costs of such heating devices and, if necessary, also increasing the reliability of the system. This is achieved according to the invention by the subject matter of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims. An inventive device for heating plastic preforms comprises a plurality of resonator units into which plastic preforms can be inserted for heating. Furthermore, the device comprises a central microwave generation unit for generating microwaves and a feed device for supplying the microwaves generated by the central unit. The microwaves generated by the microwave generation unit are supplied to at least one resonator unit. Furthermore, the device has at least one central rectifier unit for providing a rectified voltage. According to the invention, the central rectifier unit provides voltage for the operation of at least two resonator units. This central rectifier unit provides the entire voltage required for operation. It is therefore proposed within the scope of the invention that a specific unit of the invention, namely a central rectifier unit which rectifies the mains voltage, is provided for the operation of several resonator units. A rectified voltage is not necessarily understood to mean a completely rectified and smoothed voltage; it may also be sufficient if the rectified voltage is rectified at least in relation to an alternating voltage or the mains voltage, whereby any voltage fluctuations may also be included. The feed device described above, which supplies the microwaves to the resonator units, can in particular be a waveguide into which microwaves are fed, for example, from a microwave generating unit such as a magnetron, and which then transmits these microwaves to the resonator. Advantageously, each resonator unit is assigned at least one, and preferably exactly one, waveguide. It would be possible for at least one tuning element, such as a tuning pin that can be inserted into this waveguide to regulate the power, to be arranged on and/or in this waveguide. According to the invention, the rectifier section of a microwave generator is removed from the individual microwave generators, and the DC voltage is generated centrally. In this way, a common intermediate circuit can be provided to supply several resonator units. It is possible for the rectifier unit to be stationary, thus transferring the rectified voltage to the movable resonator unit (more precisely, to the high-voltage generation unit, and from there to the microwave generation unit, and from there again to the resonator unit), for example, by means of a slip ring. However, it is also possible that the rectifier unit is located on a moving, for example rotating, part. In this case, the mains voltage supplied to the rectifier unit is transmitted via the slip ring. If, as mentio