Mould Base Broken-Plane Surface for PET Container Stability
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Solution Overview
Problem
Thermoplastic containers, such as PET bottles, experience base sagging due to ambient conditions like temperature and humidity, leading to instability on supports and reduced production efficiency in manufacturing.
Innovation Solution
A mould base design with a broken-plane surface portion and specific slope angles (between 12° and 8°) to form a circumferential supporting ridge, ensuring stable foot contact on a plane support despite deformation or inclination, integrated into a moulding device for blow or stretch-blow moulding processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional mould base with smooth curved surface is used, then the container base can be easily moulded, but the base sags and loses stability over time in warm and humid conditions
Solution Approach 1:
The mould base surface is segmented into distinct zones: a curved surface portion and a broken-plane surface portion with specific slope ranges (12° to 8°). This segmentation allows different functional areas to serve different purposes - the curved portion facilitates easy moulding while the broken-plane portion with ridges provides structural support and stability against sagging
Solution Approach 2:
Different regions of the mould base are given different surface qualities - the curved surface portion provides smooth contact for easy moulding, while the broken-plane surface portion with specific slope angles creates rigid supporting ridges that prevent base deformation. This local differentiation of surface properties resolves the contradiction between ease of manufacture and long-term stability
2Reliability
If the container base is designed with feet having curved contour, then the aesthetic and structural form is achieved, but the resting area moves about over the surface when base sags, causing instability
Solution Approach 1:
The mould base is pre-formed with broken-plane surface portions and supporting ridges before the container is even used. This preliminary structural preparation ensures that when the container base is moulded, the feet are formed with precise orientation and the resting areas are fixed at optimal positions, preventing any movement or instability during storage
Solution Approach 2:
Instead of trying to make the curved feet adapt to a sagging base, the invention inverts the approach by making the mould base itself rigid and stable through broken-plane surfaces and ridges. This ensures the feet maintain their curved aesthetic shape while their orientation remains fixed, as the mould base structure prevents sagging from occurring in the first place
Data Source
AI summary
The invention relates to a mold base (1) for a mold that is used for the blow molding or stretch-blow molding of thermoplastic containers (2) having a petaloid-shaped base. The mold base (1) includes several cavities (11) separated by radiating ridges (13) with concave crests (14), the bases (15) of the cavities (11) being distributed along a circular contour. As seen radially on either side of the deepest point thereof, each cavity (11) is defined towards the exterior by a curved surface portion (18) having a circular arc radial cross-section and towards the interior by a broken-plane surface portion (19) with at least two slopes that intersect the curved surface portion (18) at a straight edge (20). The plane (T) which contains the aforementioned edge (2) and which is tangent to the curved surface portion (18) is perpendicular to the axis (12) of the mold base. Moreover, the portion of plane (21) adjacent to the curved surface portion (18) has a slope (a) of between 12° and 8° in relation to the tangent plane (T).