Preform Bottom Parting Lines for Uniform Thickness
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Solution Overview
Problem
The existing extrusion blow molding process results in a preform with a single straight parting line, causing uneven thickness in the bottom, which can lead to rupture during biaxial stretch blow molding.
Innovation Solution
The preform is designed with four bottom parting lines arranged in a cross shape, dividing the bottom into equal parts, and the mold structure is adapted to have a four-part splittable section to ensure uniform thickness and stability during biaxial stretch blow molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a two-part mold is used for extrusion blow molding, then the mold structure is simple and easy to manufacture, but a single straight parting line is formed causing uneven thickness distribution in the preform bottom
Solution Approach 1:
The mold structure is divided into multiple parts (at least three parts) instead of using a simple two-part mold. This segmentation allows the formation of multiple parting lines that radiate from the bottom center, distributing the material flow more evenly and preventing the formation of a single thick ridge that causes uneven thickness distribution in the preform bottom.
2Device complexity
If a single straight parting line is formed in the preform bottom, then the molding process is simple, but the preform may rupture during biaxial stretch blow molding due to thickness variation
Solution Approach 1:
The single straight parting line is segmented into multiple parting lines that radiate from the bottom center in different directions. This segmentation distributes the stress during biaxial stretch blow molding across multiple lines rather than concentrating it along a single line, preventing preform rupture and improving reliability during the molding process.
3Manufacturing precision
If the mold portion corresponding to the bottom is splittable into at least three parts, then uniform thickness distribution is achieved, but the mold structure and manufacturing process become more complex
Solution Approach 1:
The mold parts are designed with asymmetric splitting patterns where the parting lines radiate from the bottom center at specific angles (e.g., 120 degrees apart for three parts). This asymmetric segmentation achieves uniform thickness distribution by distributing material flow evenly from the center outward, while the modular design keeps the manufacturing complexity manageable through standardized part interfaces.
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 configuration ensures uniform thickness distribution in the preform and container bottom, preventing rupture and enabling stable molding without thickness variations, even with liquid blow molding.
Implementation Method 1
pressurized gas is blown into the parison to mold the parison into a shape conforming to an inner surface of the mold
Implementation Method 2
stretching the preform in the longitudinal direction by using a stretching rod and stretching the preform in the lateral direction by using a pressurizing medium supplied into the preform
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
Provided is a preform (1) to be biaxially stretch blow molded into a container (11) by using a liquid as a pressurizing medium. The preform (1) is formed in a bottomed tubular shape including a mouth (4), a trunk (3), and a bottom (2) by extrusion blow molding. The preform (1) includes bottom parting lines (2a∼2d), which are formed in the bottom (2) due to the extrusion blow molding, and the bottom parting lines (2a∼2d) are configured to extend to the outer side from the axis of the bottom (2) to divide the bottom (2) into at least three parts in the circumferential direction. Also provided is a container (11) that is formed by biaxially stretch blow molding the preform (1) by using the liquid as the pressurizing medium.