Polyethylene Preform Cooling for Injection Stretch Blow Molding
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Solution Overview
Problem
Conventional injection stretch blow molding methods for polyethylene containers face challenges in reducing molding cycle times due to the formation of uneven thickness and rupture during blowing, as the preform is released from the injection mold before achieving the desired skin layer thickness and temperature.
Innovation Solution
The method involves cooling the injection mold to a temperature range of 5°C to 25°C to quickly form crystalline skin layers on the preform, allowing for early release and subsequent blowing within a ±2-second time frame, utilizing infrared detection for temperature measurement, and setting a stretch ratio of 1.5 to 2.5 for efficient molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the injection mold temperature is set to around 100°C to form skin layers, then the preform can be released without deformation, but the molding cycle time becomes long
Solution Approach 1:
The injection mold temperature is changed from the conventional 100°C to a lower range of 5°C to 25°C. This parameter change enables rapid formation of thin skin layers on the preform surface, allowing early release from the mold while maintaining preform quality, thus resolving the contradiction between reliability and time loss
Solution Approach 2:
The injection mold is pre-cooled to 5°C to 25°C before injection. This preliminary action ensures that when molten resin is injected, skin layers form immediately on the contact surfaces, enabling early mold release without waiting for prolonged cooling, thereby reducing molding cycle time while ensuring preform quality
2Productivity
If the preform is released early to reduce cycle time, then productivity improves, but defects such as uneven thickness and rupture occur
Solution Approach 1:
By changing the mold temperature parameter to 5°C to 25°C, thin skin layers form rapidly on the preform surface even with early release. This ensures the preform has sufficient structural integrity and uniform thickness distribution, preventing defects while enabling short cycle times for high productivity
Solution Approach 2:
The cooling effect is concentrated at the mold-contact surfaces where skin layers form. This local quality change creates a thin hard skin layer on the preform surface while the interior remains appropriately temperatured, allowing early release without compromising overall preform quality or causing thickness uniformity issues
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 approach enables the production of favorable polyethylene containers with reduced molding cycle times by forming thin, hard skin layers and maintaining the preform's heat for increased stretchability, thus preventing deformation and achieving uniform thickness.
Implementation Method 1
the temperature of the preform reaches a first minimum point after a point in time when the injection mold completes being opened
Data Source
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AI summary
An object is to provide an injection stretch blow molding machine and a method for molding a polyethylene container capable of molding a favorable hollow container even if its preform is released from an injection mold (10M) early. The injection stretch blow molding machine and the method for molding a polyethylene container molds a preform by injecting and filling a molten polyethylene resin into an injection mold (10M) , which includes a cavity mold (12) and a core mold (13) both cooled to a temperature range of 5°C to 25°C, transfers the molded preform to a blow molding mold (20M) , and molds a hollow container by blowing the preform within a time range of ±2 sec from a point (B1, B3, B4) in time when a temperature of the preform reaches a first minimum point (B1, B3, B4) after a point (B1, B3, B4) in time when the injection mold (10M) completes being opened.