Stretch-blow moulded container handle forming process
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Solution Overview
Problem
Existing methods for forming integral handles on stretch-blow moulded containers via the stretch-blow moulding process result in uneven material distribution, leading to irregular wall thicknesses and adverse mechanical and aesthetic properties, with previous solutions either requiring complex and expensive moulds or resulting in aesthetic defects and poor ergonomics.
Innovation Solution
A process involving stretch-blow moulding a preform to form an intermediate container with convex bubbles, which are then deformed into concave gripping regions using an inwardly moving plug while maintaining pressure above 1 bar and temperature between the glass transition temperature and melt temperature, followed by releasing pressure and ejecting the container.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If moving sections of the mould are used to compress the expanding preform and form deep wells during the blowing process, then an integral handle can be formed, but this results in highly irregular wall thickness and regular failure of the material under stress
Solution Approach 1:
The preform is pre-stretched in the blow moulding process to create a pre-stretched bubble with controlled geometry before the deep grip forming step. This preliminary stretching establishes a base structure that can be subsequently deformed into the final handle shape without causing material failure or extreme wall thickness variations
Solution Approach 2:
The process controls temperature and pressure parameters during the deep grip forming step. The preform is heated to a specific temperature range to achieve optimal material ductility, and pressure is maintained above 1 bar during plug insertion to ensure uniform deformation and wall thickness distribution in the handle area
2Ease of manufacture
If moving sections of the mould are used to form deep wells during the blowing process, then an integral handle can be formed, but this requires significant stretching of the material after contact with the mould which results in highly irregular wall thickness
Solution Approach 1:
The mould is divided into separate functional sections: a blow mould for forming the preform and a separate deep grip forming cavity. This segmentation allows each section to perform its specific function optimally without requiring complex moving mechanisms, simplifying the overall mould design while still enabling integral handle formation
Solution Approach 2:
A plug is used as an intermediary tool to form the deep grip in the pre-stretched bubble. Instead of using complex moving mould sections, the plug is inserted into the bubble and deforms the material into the desired handle shape, significantly simplifying the mould mechanism while achieving the same result
3Manufacturing precision
If an intermediate container with a convex section is mechanically deformed inwardly to form the concave grip section, then more even stretch ratios can be achieved, but this results in significant deformation of the area around the handle creating aesthetic defects
Solution Approach 1:
Temperature is controlled during the deep grip forming step to optimize material behavior. The preform is heated to a temperature that provides sufficient ductility for deformation while minimizing unwanted flow and aesthetic defects in surrounding areas. Pressure is also controlled to ensure uniform deformation without excessive material displacement
Solution Approach 2:
The deep grip forming process is localized to specific regions of the pre-stretched bubble. The plug is designed to deform only the necessary areas to create the handle, while maintaining the integrity and appearance of surrounding container surfaces. This localized deformation approach preserves aesthetic quality while achieving even stretch ratios
4Ease of operation
If the convex section is inverted to form the concave grip section, then an ergonomic handle can be created, but this results in residual stresses in the plastic sheets forming the grip resulting in undesirable wrinkles and poor ergonomics
Solution Approach 1:
The temperature of the preform is carefully controlled during deep grip forming to achieve optimal material ductility. By maintaining the temperature between the glass transition temperature and melt temperature, the material can be deformed into the ergonomic handle shape without creating excessive residual stresses that would cause wrinkles or compromise ergonomics
Solution Approach 2:
The preform is pre-stretched and heated before the deep grip forming step, preparing the material in advance to receive the plug deformation. This preliminary preparation ensures the material is in the optimal state for forming, reducing residual stresses and preventing wrinkle formation while maintaining ergonomic quality
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 process achieves a deep, concave grip with even wall thickness and improved ergonomics, reducing material stress and mould complexity, and eliminating wrinkles and deformation issues, resulting in a cost-effective and aesthetically superior handle.
Implementation Method 1
deforming the or each convex bubble (9) by means of an inwardly moving plug (5) to form one or more concave gripping region(s)
Implementation Method 2
whilst the temperature of the material in the gripping region of the intermediate container is maintained at a temperature between the glass transition temperature, Tg, and the melt temperature, Tm
Implementation Method 3
whilst maintaining the pressure within the intermediate container (8) above 1 bar
Data Source
Figure 1~2
Figure 3(i)~3(iv)
Figure 4
AI summary
The present invention relates to a process for making a container having an integral handle, comprising the steps of: a) providing a preform (6) in a mould cavity (1); b) stretch-blow moulding the preform (6) to form an intermediate container (8) which comprises at least one, preferably two, convex bubble(s) (9); c) deforming the or each convex bubble (9) by means of an inwardly moving plug (5) to form one or more concave gripping region(s), whilst maintaining the pressure within the intermediate container (8) above 1 bar and whilst the temperature of the material in the gripping region of the intermediate container is maintained at a temperature between the glass transition temperature, Tg, and the melt temperature, Tm; d) releasing excess pressure within the container, preferably prior to withdrawing the plug (5) from within the container; and c) ejecting the finished container from the mould cavity (1, 3).