Rotary Injection Mold for PET Preform Productivity
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Solution Overview
Problem
One-stage injection-compression molding plants for thermoplastic preforms, such as PET, face low production rates compared to two-stage plants, with challenges in maintaining high productivity, reducing downtime for format changes and maintenance, and ensuring consistent preform quality, especially when producing food-grade containers.
Innovation Solution
A rotary injection-compression apparatus featuring a rotating carousel with multiple molding modules and an innovative resin distribution system, including a rotary joint for consistent resin flow and modular design for rapid format changes and maintenance, allowing for higher rotation speeds and improved preform concentricity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a one-stage injection-compression molding plant is used for continuous production, then energy consumption is reduced and product quality is improved, but production rate is low compared to two-stage plants
Solution Approach 1:
The injection mold is divided into multiple independent cavities arranged in a circular pattern around a central rotation axis. Each cavity can be independently filled and molded while the entire mold rotates to different positions, enabling parallel production across multiple cavities and significantly increasing the production rate while maintaining the energy efficiency of continuous one-stage processing.
Solution Approach 2:
The mold incorporates a rotation mechanism that allows the circular array of cavities to rotate about a central axis. This dynamic element enables the mold to present different cavities to the injection unit at different times, allowing continuous operation without idle waiting time and thereby increasing productivity while maintaining the energy-efficient continuous processing characteristic of one-stage plants.
2Productivity
If multiple cavities are arranged in a circular pattern for parallel production, then production rate increases, but mold complexity increases
Solution Approach 1:
The mold design uses identical cavities arranged in a circle, where each cavity serves the same function of forming preforms. The rotation mechanism allows all cavities to share the same injection and ejection systems sequentially, reducing the need for multiple independent injection units and thereby limiting the increase in device complexity despite the multi-cavity configuration.
Solution Approach 2:
The cavities are nested within a circular mold structure that rotates about a central axis. This nested arrangement allows multiple cavities to be contained within a single rotating mold body, sharing common support structures and rotation mechanisms, which helps control overall device complexity while maintaining high productivity through parallel molding.
3Productivity
If the mold rotates at higher speeds to increase production, then productivity increases, but preform concentricity and quality may be compromised
Solution Approach 1:
The mold cavities are pre-positioned in a circular arrangement with precise geometric relationships established before rotation begins. The injection of material occurs when cavities are in the optimal position, and the rotation speed is synchronized with the injection timing, ensuring that high-speed rotation does not compromise concentricity because the critical molding action occurs at controlled positions rather than during random rotation.
Solution Approach 2:
The rotation mechanism is synchronized with the injection and ejection timing through feedback control systems. The rotation speed and position are adjusted based on real-time feedback from sensors that monitor the molding process, ensuring that optimal positioning is maintained for each cavity during injection and that high-speed rotation does not compromise preform quality or concentricity.
Data Source
Figure 1
Figure 2
Figure 2a
AI summary
An injection mold (9') of a plastic preform comprising a first part (12) and a second part (13), fixed to each other, and a third part (14); wherein the third part (14) is provided with a molding cavity (41') defining an axis (Υ') and is adapted to be integrally fixed to a first surface of a supporting frame of the mold; wherein the second part (13), arranged between the third part and the first part, is adapted to slide along said axis to close or open the cavity; wherein the first part (12) comprises a longitudinal rod (55) adapted to slide along said axis (Υ') through a second surface of the supporting frame, opposite to and spaced apart from the first surface; wherein the second part (13) is provided with: - a guiding cage comprising a first plate (18), provided with a through hole through which the longitudinal rod can slide and configured to abut on said second surface; a structure (18"); parallel guiding rods (16) fixed at a first end thereof to said first plate and fixed at a second end thereof to the structure, - an assembly (19, 18', 49) sliding inside said cage, fixed at a first end thereof to the rod by means of quick-coupling means (15), and comprising at a second end thereof a punch (59) sliding inside the structure and defining a first complementary component of the cavity, wherein the structure (18") is provided with two half-collars (66', 66") and is configured so as to define, together with the punch, a cam system for opening or closing the two half-collars which define, when closed, a second complementary component of the cavity.