Microwave Resonator Heating for Plastic Preforms
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Solution Overview
Problem
Infrared heating devices used in the production of plastic hollow bodies, such as food containers, have low efficiency at around 20%, necessitating a more energy-efficient method for heating plastic preforms.
Innovation Solution
A microwave-based heating method that utilizes a resonator to generate a suitable electromagnetic field for isotropic or anisotropic heating of plastic preforms, allowing for precise temperature control and energy-saving heating by dividing the preform into sections and adjusting the microwave power and field strength distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If infrared radiation is used for heating preforms, then the heating process is simple, but the heating efficiency is very low at around 20%
Solution Approach 1:
The patent replaces the infrared heating system with a microwave heating system. Microwaves directly excite the plastic material molecules, generating heat internally within the preform rather than heating from the outside surface. This substitution increases heating efficiency dramatically while maintaining process simplicity through automated control systems.
Solution Approach 2:
The patent changes the heating parameter from infrared radiation (electromagnetic wave at infrared frequency) to microwave radiation (electromagnetic wave at microwave frequency). This parameter change allows direct interaction with the plastic material's molecular structure, particularly the dipoles in PET and other polymers, enabling efficient internal heat generation and solving the low efficiency problem of infrared heating.
2Productivity
If the entire preform is heated simultaneously, then the heating process is fast, but energy is wasted heating areas that do not need to be deformed
Solution Approach 1:
The patent applies local quality by creating different field strength distributions within the microwave resonator. Specific regions of the preform receive different microwave power levels according to their heating requirements. The resonator geometry and positioning allow concentrated heating in deformation zones while minimizing or eliminating heating in non-deformation areas such as the mouth region, thus reducing energy waste while maintaining fast heating speed.
Solution Approach 2:
The patent segments the heating process by dividing the preform into different heating zones corresponding to different deformation requirements. The microwave field is distributed non-uniformly to match these zones, with higher power in areas requiring deformation and lower or zero power in areas that do not. This segmentation enables selective heating of only the necessary areas.
3Productivity
If microwave power is increased to heat preforms faster, then heating efficiency improves, but temperature control precision decreases
Solution Approach 1:
The patent employs periodic action by using pulsed microwave heating instead of continuous high-power heating. The microwave generator operates in cycles, delivering power in controlled pulses with specific duty cycles. This allows the material to heat during pulse periods and distribute heat during off periods, preventing thermal runaway and enabling precise temperature control even at high average power levels, thus maintaining both heating speed and temperature precision.
Solution Approach 2:
The patent implements feedback control by monitoring the preform's temperature or dielectric properties during microwave heating and adjusting the microwave power accordingly. Sensors detect the heating state in real-time, and the control system modifies the microwave generator output to maintain the desired temperature profile. This feedback mechanism ensures precise temperature control while optimizing heating speed through dynamic power adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly improves the heating efficiency, allowing for precise temperature profiling and reduced energy consumption by heating only the necessary areas of the preform, enabling the production of containers with complex shapes and optimizing the heating process.
Implementation Method 1
A microwave generator (21) generates the electromagnetic radiation
Implementation Method 2
The preform (1) is heated in a resonator (11)
Implementation Method 3
into which this radiation is kept for a specific period of time by constant reflection
Implementation Method 4
The preform (1) is heated in a resonator (11)
Data Source
Figure 1
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Figure 3
AI summary
The invention relates to a method and a device for heating preforms made of a thermoplastic material, wherein the preforms are subjected to a forming process after their heating and wherein the preforms are exposed to microwaves in a resonator at least during part of the heating time.