Segmented Cardboard Tray Walls for Uniform Plastic Foil Stretching
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Solution Overview
Problem
Existing cardboard trays with a single upstanding wall design require thicker plastic foils at edges and corners to prevent rupture, which violates weight and cost regulations by exceeding the 5% plastic content limit, leading to increased material and manufacturing costs.
Innovation Solution
The upstanding wall is composed of first and second wall part sections with angles between 15°-60° to the bottom, approximating a curved shape, reducing plastic foil thickness and stretch variation, and using a horizontal flange with complementary shapes for enhanced sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single upstanding wall design with 90° angle is used, then the tray structure is simple, but the plastic foil stretches unevenly and requires thicker foil to prevent rupture
Solution Approach 1:
The single upstanding wall is divided into multiple wall part sections (first and second wall part sections) with different angles. The first wall part sections have angles between 15°-60° relative to the bottom, while the second wall part sections have angles closer to 90°. This segmentation allows different regions of the tray to have optimized angles for their specific functions, reducing uneven stretching of the plastic foil.
Solution Approach 2:
The tray design approximates a curved or spherical shape by using multiple wall part sections with varying angles rather than a single flat wall. This curvature distributes the stress more evenly across the plastic foil, preventing concentrated stretching at sharp corners and edges.
2Reliability
If thicker plastic foil is used to prevent rupture at edges and corners, then the reliability of the tray is improved, but the plastic content exceeds 5% weight limit
Solution Approach 1:
The angle parameter of the wall sections is changed from a uniform 90° to varied angles (15°-60° for first wall part sections). This parameter change fundamentally alters the stress distribution pattern, allowing thinner plastic foil to be used while maintaining rupture resistance at edges and corners.
3Strength
If thicker plastic foil is used to ensure edges and corners do not rupture, then the strength of the tray is improved, but the weight of the cardboard tray increases
Solution Approach 1:
The wall structure is segmented into multiple sections with optimized angles, concentrating structural strength at specific locations rather than uniformly throughout. This allows the tray to maintain high strength at critical edges and corners while using less overall material.
4Manufacturing precision
If the angle between wall and bottom is increased to approximate curved shape, then the plastic foil stretching is more even, but the tray structure becomes more complex
Solution Approach 1:
The complex curved wall shape is achieved through segmentation into discrete wall part sections that can be folded from a single sheet. This maintains manufacturing simplicity while achieving the beneficial curved geometry for even plastic foil stretching.
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
AI summary
The invention relates to a cardboard tray folded out of a single sheet, which tray comprises: - a bottom; - an upstanding wall arranged along the periphery of the bottom, the upstanding wall having an upper edge defining the access opening of the cardboard tray; - plastic foil lined against the inside of the cardboard tray and extending at least on the bottom and the upstanding wall; wherein the upstanding wall is composed out of at least first upstanding wall part sections bordering the bottom and a second upstanding wall part sections bordering the upper edge, wherein the angle between the normal vector of each first upstanding wall part section with the normal vector of the bottom is larger than the angle of the cord extending between the peripheral edge bordering the respective first upstanding wall part section and the upper edge with the normal vector of the bottom.