Injection Mould Core Modification for Uniform Container Walls
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Solution Overview
Problem
Sharps containers with non-uniform side walls are prone to needle penetration when crushed, posing a risk to public health and safety, as the thinner sections of the walls can be penetrated by needle tips, leading to potential infections and injuries during disposal and handling.
Innovation Solution
A method of injection moulding that involves moulding a trial container, observing and adjusting the molten plastic flow to achieve substantially uniform side walls by redirecting the plastic material from the base to thinner areas, ensuring no single location is weaker than others, thus preventing needle penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If injection moulding is performed with a standard mould configuration, then the manufacturing process is simple and quick, but the side walls of the container become non-uniform in thickness
Solution Approach 1:
The patent applies local quality by modifying specific regions of the mould rather than the entire structure. Material is added to or removed from localized areas of the base to redirect plastic flow specifically to thinner side wall sections, achieving uniform thickness without redesigning the complete mould system.
Solution Approach 2:
The patent employs preliminary action by pre-modifying the mould geometry before injection moulding occurs. The material redistribution features are built into the mould structure in advance, so that when molten plastic is injected, it naturally flows along predetermined paths to achieve uniform side wall thickness without requiring real-time adjustments during the moulding process.
2Ease of manufacture
If the side walls are made thinner to reduce material usage, then the manufacturing cost decreases, but the containers become vulnerable to needle penetration when crushed
Solution Approach 1:
The patent applies local quality by concentrating additional material specifically at the side wall regions that require enhanced protection, rather than uniformly thickening the entire container. This localized reinforcement redirects plastic flow to strengthen vulnerable areas while maintaining overall material efficiency and cost-effectiveness.
3Object-affected harmful factors
If the side walls are made thicker to prevent needle penetration, then the safety increases, but the material usage and manufacturing cost increase
Solution Approach 1:
The patent applies local quality by providing targeted material reinforcement only where side wall thickness is insufficient, rather than uniformly increasing wall thickness throughout the container. This approach achieves the necessary safety level against needle penetration while minimizing overall material consumption and manufacturing costs.
Solution Approach 2:
The patent employs partial action by applying material redistribution only to the extent necessary to achieve uniform side wall thickness and adequate protection. Rather than over-engineering the entire container with excessive material, the solution applies just enough additional material to vulnerable regions to achieve the required safety level.
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 method results in sharps containers with uniformly thick side walls, reducing the likelihood of needle penetration and enhancing safety during disposal and handling, including resistance to crushing forces from garbage compactors and seatbelt-induced pressure.
Implementation Method 1
the flow of plastic into the mould is not exactly even in all directions and thus molten plastic flows more to one side of the core than the other
Implementation Method 2
the core deforms slightly so as to bend away from the side which has the more plastic and towards the side which has the less plastic
Data Source
AI summary
A method of injection moulding a plastics container 1 having wall(s) 2 of substantially uniform thickness using an injection mould 10 with an unsupported core 12 is disclosed. A small sliver 17 is removed from the free end of the core 12 of the mould 10 from that side of the wall which is thinnest. As a consequence on the next injection more plastic flows in that direction. Repeated optical inspection of the containers enables a balance to be achieved in which slightly asymmetric injection conditions are balanced by a slightly asymmetric container base with the result being a container with substantially uniform wall thickness.