Elliptical Preform Base for Uniform Blow Molding Thickness
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Solution Overview
Problem
Traditional preforms with hemispherically shaped closed ends in stretch blow molding processes suffer from non-uniform material thickness distribution, particularly at the bottle base, leading to unstretched amorphous material remaining around the gate nub, which affects the quality and weight of the final plastic bottle.
Innovation Solution
The preform design features an elliptical inner and outer face with flat circular bottom portions at the base, providing a continuous reduction in wall thickness and increasing the surface-to-volume ratio, allowing effective heat profiling and ensuring uniform material distribution during stretch blow molding, thus preventing unstretched material from remaining at the bottle base.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a hemispherically shaped closed end is used in traditional preform design, then the preform structure is simple and easy to manufacture, but the material thickness distribution becomes non-uniform at the bottle base with unstretched amorphous material remaining around the gate nub
Solution Approach 1:
The patent applies asymmetry by transitioning from a traditional hemispherical base to an elongated base shape with a flat circular bottom portion and an elliptical upper portion. This asymmetric geometry creates a surface-to-volume ratio greater than 2, enabling effective heat profiling. The elongated shape with reduced wall thickness in specific regions allows material to stretch more uniformly during blow molding, eliminating the accumulation of unstretched amorphous material at the gate nub while maintaining manufacturing feasibility.
Solution Approach 2:
The patent implements local quality by creating specific geometric features at the base region - particularly the flat circular bottom portion with diameter less than the preform body diameter, and the elliptical upper portion with reduced wall thickness. These localized geometric modifications create areas with different thermal and mechanical properties, enabling targeted heat profiling and controlled material flow during stretching, thereby achieving uniform material thickness distribution in the critical base region.
2Manufacturing precision
If heat profiling is applied to improve material thickness distribution in the preform body, then the sidewall uniformity improves, but the closed end region remains ineffective due to low surface to volume ratio
Solution Approach 1:
The patent applies asymmetry by transitioning from a traditional hemispherical base to an elongated base shape with a flat circular bottom portion and an elliptical upper portion. This asymmetric geometry creates a surface-to-volume ratio greater than 2, enabling effective heat profiling. The elongated shape with reduced wall thickness in specific regions allows material to stretch more uniformly during blow molding, eliminating the accumulation of unstretched amorphous material at the gate nub while maintaining manufacturing feasibility.
Solution Approach 2:
The patent changes the geometric parameters of the base region - specifically creating an elongated shape with length greater than diameter, a flat circular bottom portion with reduced diameter, and an elliptical upper portion. These parameter changes increase the surface-to-volume ratio above 2, which fundamentally alters the thermal characteristics of the base region, enabling effective heat profiling and controlled material flow during stretching.
3Volume of stationary object
If the preform base is designed with traditional hemispherical shape, then the volume is compact, but the surface to volume ratio is low preventing effective heat profiling and material distribution
Solution Approach 1:
The patent applies asymmetry by transitioning from a traditional hemispherical base to an elongated base shape with a flat circular bottom portion and an elliptical upper portion. This asymmetric geometry creates a surface-to-volume ratio greater than 2, enabling effective heat profiling. The elongated shape with reduced wall thickness in specific regions allows material to stretch more uniformly during blow molding, eliminating the accumulation of unstretched amorphous material at the gate nub while maintaining manufacturing feasibility.
Solution Approach 2:
The patent applies dimensionality change by extending the base shape from a compact hemispherical form to an elongated form with increased length dimension. This dimensional transformation increases the surface area relative to volume, creating a surface-to-volume ratio greater than 2. The elongated geometry with flat bottom and elliptical upper portion provides enhanced thermal contact area, enabling effective heat profiling while maintaining compact overall volume through optimized spatial arrangement.
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 design enhances the uniformity of material thickness across the bottle sidewall, improves bottle performance, reduces base weight, and allows for effective heat profiling of the preform base, resulting in a more consistent and lightweight final product.
Implementation Method 1
heat profiling. That is, selected regions within the preform stretch are changed by changing the material temperature in those selected regions
Data Source
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AI summary
According to the present invention there is provided a preform suitable for subsequent blow molding, and a mold stock for producing the preform. The preform comprises a base having an elliptical inner face with a fist flat circular bottom portion, and an elliptical outer face with a second flat circular bottom portion. The first and second flat circular bottom portions each have a center on a vertical center axis of the preform and a radius of equal size. The mold stack comprises a core insert comprising a first cavity defining portion with a gate defining portion, and a gate insert comprising a second cavity defining portion. The gate defining portion has a first elliptical curvature with a first flat circular bottom portion, and the second cavity defining portion has a second elliptical curvature with a second flat circular bottom portion. The first and second flat circular bottom portions each have a center on a vertical axis of the mold stack and a radius of equal size.