Injection Molding Process for Laboratory Test Tubes
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Solution Overview
Problem
Current injection molding processes for plastic test tubes struggle to produce containers with perfectly vertical side walls and constant thickness, essential for accurate erythrocyte sedimentation rate measurements, due to operational difficulties in centering the male mold and expelling air, leading to irregularities and unreliable measurements.
Innovation Solution
An injection molding process and mold design featuring radially alternating wedges that move to create slits for air evacuation and side injection points for centered mold alignment, eliminating the need for traditional air expellers and ensuring consistent wall thickness and verticality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional injection molding processes are used with bottom injection, then air evacuation is facilitated, but the male mold bends under high pressure causing non-vertical side walls and non-constant thickness
Solution Approach 1:
The injection system is segmented into multiple injection points (at least two) positioned at different locations including the bottom and side walls of the male mold. This segmentation distributes the injection pressure across multiple entry points, preventing the male from bending while still facilitating air evacuation through coordinated injection sequences.
Solution Approach 2:
The injection process uses periodic action by sequentially activating different injection points in a controlled sequence. The injection unit injects melted plastic material through different points at different times, allowing air to be progressively evacuated while maintaining male stability throughout the filling process.
2Ease of operation
If injection pressure is applied at the bottom of the test tube, then air is pushed toward the mouth for easy evacuation, but the male is less rigid at the free end causing bending
Solution Approach 1:
Different injection points are positioned at locations with different rigidity characteristics of the male. Injection points are placed not only at the bottom but also at intermediate positions and side wall positions where the male has greater structural support and rigidity, allowing pressure application without causing bending.
Solution Approach 2:
The injection approach transitions from purely axial injection (bottom only) to multi-dimensional injection by adding side wall injection points. This allows pressure to be applied from multiple spatial dimensions, distributing forces to prevent male bending while maintaining effective air evacuation pathways.
3Manufacturing precision
If injection pressure is applied at the mouth or along the longitudinal axis, then male bending is reduced, but air must be expelled through complex expellers increasing device complexity
Solution Approach 1:
The complex air expeller system is extracted and replaced by a simplified approach using multiple injection points. The injection unit itself performs the air evacuation function through strategic positioning and sequencing of injection points, eliminating the need for separate mechanical expeller components.
Solution Approach 2:
The injection system is given multi-functionality by using the same injection points and injection unit for both plastic material delivery and air evacuation. The injection points serve dual purposes: filling the mold with plastic and progressively expelling air, eliminating the need for dedicated air expeller mechanisms.
4Strength
If the male is made larger to increase rigidity, then bending resistance improves, but the test tube dimensions become unacceptable
Solution Approach 1:
Support structures are pre-positioned within the male mold at strategic locations before injection begins. These support bases are integrated into the male design at positions that provide maximum rigidity without affecting the external dimensions of the final test tube, preparing the male to resist bending forces during injection.
Solution Approach 2:
Support structures act as intermediaries between the injection pressure and the male structure. These supports are positioned to intercept and distribute injection forces, preventing direct transmission of pressure that would cause bending, while remaining hidden within the male and not affecting the final test tube dimensions.
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
The process enables the production of plastic test tubes with perfectly vertical side walls and constant thickness, reducing production idle times and maintenance costs by preventing air bubble formation and ensuring accurate measurements.
Implementation Method 1
at least the second wedges are susceptible to move elastically... under pressure of the melted plastic material injected into the mold
Implementation Method 2
injecting the melted plastic material under pressure into the mold
Data Source
AI summary
A laboratory test tube is formed between male and female mold elements by injection of molten plastic material. The female element has a bottom element formed by first and second alternating complementarily shaped wedges. At least the second wedges are able to move under the pressure of the molten plastic from a rest position to an operative position in order to form slits which allow air, but not molten plastic, to exit from the mold.