Three-Injector PET Injection for Stable Bottle Preform Flow
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Solution Overview
Problem
The use of PET flakes in plasticization processes requires a continuous flow of molten plastic, which leads to hydraulic shocks and degradation issues when using traditional injection apparatuses with two injectors, potentially damaging components and producing undesired compounds like acetaldehyde and benzene.
Innovation Solution
An injection apparatus with three injectors, including a third auxiliary injector, is designed to receive molten plastic during valve switching, minimizing residence time and controlling piston movement to maintain constant pressure, thereby avoiding hydraulic shocks and degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two injectors are used to receive continuous molten plastic flow from the extruder, then productivity is improved, but hydraulic shocks occur during valve switching that can damage components
Solution Approach 1:
The system divides the injection function into three separate injectors (first injector, second injector, and third auxiliary injector) instead of using two. This segmentation allows the third injector to act as a buffer during valve switching transitions, absorbing hydraulic shocks that would otherwise damage components while maintaining continuous productivity.
Solution Approach 2:
The third auxiliary injector is positioned and configured to receive molten plastic before the main injectors are fully switched between operation. This beforehand cushioning captures the flow during valve transition periods, preventing hydraulic shocks from propagating back to the extruder and damaging components like the molten plastic pump.
2Manufacturing precision
If valves are switched to alternate between two injectors, then manufacturing precision is improved, but molten plastic degradation occurs during switching transitions
Solution Approach 1:
The third auxiliary injector serves as an intermediary receiver during valve switching transitions. Instead of directly switching between two main injectors which causes flow interruption and degradation, the third injector mediates the transition by temporarily receiving the flow, maintaining continuous processing and preventing the formation of harmful degradation products like acetaldehyde and benzene.
3Manufacturing precision
If the screw moves forward and backward during plasticization, then manufacturing precision is improved, but the flow becomes discontinuous requiring complex valve control
Solution Approach 1:
The injection system is segmented into three independent injectors with individual valve control. This segmentation allows each injector to be controlled independently, simplifying the overall valve control system compared to a two-injector system where precise synchronization and switching are required to maintain continuous flow.
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
The apparatus effectively prevents hydraulic shocks and minimizes plastic degradation, ensuring a stable continuous flow for producing high-quality bottle preforms.
Implementation Method 1
there can be conditions such that both valves simultaneously prevent the molten plastic from entering into the respective injector, e.g., during the switching of the valve position. It is possible that, when both valves prevent the molten plastic from entering into the respective injector, a hydraulic shock or fluid hammer occurs in the conduit
Implementation Method 2
controlling piston movement to maintain constant pressure
Implementation Method 3
the screw rotates and moves backward along the longitudinal axis thereof while melting the granules
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An injection apparatus (100) for injecting molten plastic, in particular PET, into a mold for molding bottle preforms; the injection apparatus (100) comprising - a first injector (1) and a second injector (2) adapted to receive molten plastic and inject it into the mold alternately to each other; - a conduit (8) adapted to carry molten plastic from a plasticization apparatus (102) towards the first injector (1) and towards the second injector (2); - a third injector (3) provided with a piston (32), the third injector (3) being connected to the conduit (8) so as to receive molten plastic from the conduit (8) and then inject it into the conduit (8); - actuation means (34) adapted to cause the piston (32) of the third injector (3) to move forward to inject the molten plastic into the conduit (8); wherein said actuation means (34) are adapted to control the backward movement of the piston (32) of the third injector (3) while it receives the molten plastic from the conduit (8).