Stretch Blow Mold Central Well and Hemispherical Rod
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Solution Overview
Problem
The manufacturing of containers, particularly those with large cubic capacity and concave recesses for handles, faces challenges in achieving sufficient structural rigidity at the bottom and even material distribution due to uneven stresses during the blow-molding process, leading to potential sliding and instability.
Innovation Solution
A mold design for stretch blow-molding with a central bulb and slug configuration, combined with a stretching rod that grips the material between its distal end and a truncated conical side wall, ensures even material distribution and structural rigidity by minimizing sliding and offsetting under asymmetrical tensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the bottom is given a concave shape with stiffeners to provide structural rigidity, then the bottom rigidity is improved, but the material distribution becomes uneven and sliding occurs
Solution Approach 1:
The mold base is segmented into multiple functional zones: a central well for the slug, an annular groove for the base, and a peripheral face for the arch. This segmentation allows each zone to independently control material flow and distribution, preventing sliding while maintaining even thickness throughout the bottom structure.
Solution Approach 2:
Different regions of the mold base are given different geometries to achieve local optimization: the central well provides vertical support for the slug, the annular groove defines the base perimeter, and the peripheral face forms the arch. This local differentiation ensures that each area contributes appropriately to both rigidity and material distribution.
2Shape
If protuberances are used to form handle recesses, then the handle shape is achieved, but material sliding occurs due to uneven stresses
Solution Approach 1:
The mold base geometry is designed in advance to preemptively counteract the sliding forces generated by handle-forming protuberances. The central well and annular groove are positioned and dimensioned beforehand to create a material distribution pattern that compensates for the localized material removal at the handle zones, ensuring uniform thickness is maintained despite the asymmetrical stresses.
3Reliability
If the distal end of the rod is shaped to complement the mold base, then material gripping is improved, but excessive resisting forces cause machine faults
Solution Approach 1:
The stretching rod's distal end is designed with a hemispherical shape that provides sufficient gripping action through partial contact with the preform material, rather than attempting to grip the entire surface. This partial action achieves the necessary material control while significantly reducing the resisting forces transmitted to the machine, avoiding faults while maintaining adequate material securing.
Data Source
AI summary
The invention relates to a mold for a container that includes a mold base. The mold base includes a peripheral face, a central dome, and a central well formed in the dome and extending along a frustoconical sidewall from a top edge of the dome having a top diameter, to a bottom having a bottom diameter smaller than the top diameter. The mold also includes a stretching rod that ends with a hemispherical distal end having a radius, the value of which is between that of the bottom radius and that of the top radius of the central well. When the rod is in the bottom position, it is separated from the sidewall of the central well by a distance smaller than the distance that separates it from the bottom of the well.