Injection Mold Ring Runner Protrusions Prevent Weld Lines
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Solution Overview
Problem
Conventional injection molds fail to effectively prevent the formation of weld lines in molded resin articles with cylindrical or deep hole portions, especially when molten resin with low fluidity is injected at high pressure, leading to uneven flow and axis displacement of the pin member within the ring runner portion.
Innovation Solution
The injection mold design includes a ring runner portion with protrusions in specific regions to prevent pin member flexural deformation and ensure even resin flow, featuring a tapered cylindrical space and strategically placed protrusions to maintain resin flow directionality and prevent weld lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the gate is formed at a circumferential position of a cylindrical space of the cavity, then the molten resin can be introduced into the cavity, but weld lines are likely to be formed in the side wall of the cylindrical portion due to flow convergence
Solution Approach 1:
The invention transitions from a conventional single-point gate to a ring-shaped gate that extends circumferentially around the cylindrical cavity. This dimensional change allows the gate to distribute molten resin across multiple entry points simultaneously, preventing flow convergence and weld line formation while maintaining ease of manufacture
Solution Approach 2:
The ring runner portion is divided into multiple circumferential segments by protrusions that create separate flow paths. Each segment independently introduces molten resin to different angular positions of the cavity, ensuring that flows do not converge and weld lines are prevented
2Productivity
If molten resin with low fluidity is injected at high pressure, then the resin can fill the cavity, but the pin member undergoes flexural deformation and axis displacement occurs
Solution Approach 1:
Protrusions are strategically placed at specific angular positions within the ring runner to create localized flow resistance. These protrusions generate counter-pressure that balances the high injection pressure, preventing pin member flexural deformation while allowing high-speed injection to proceed
Solution Approach 2:
The protrusions are positioned to create preliminary counter-pressure against the incoming high-pressure molten resin. This pre-balancing of forces prevents the pin member from experiencing net lateral forces that would cause flexural deformation and axis displacement
3Force
If the pin member is pressed away from the circumferential position by high injection pressure, then resin flow into the ring runner portion occurs, but uneven flow distribution causes weld line formation
Solution Approach 1:
The ring runner portion is designed with asymmetric protrusions at specific angular positions rather than uniform distribution. This asymmetric configuration creates deliberate variations in flow path resistance that compensate for pressure-induced pin member displacement, maintaining uniform flow distribution to the cavity
Data Source
AI summary
Providing an injection mold used for producing a molded resin article which is free of a weld line, irrespective of an injection pressure of a molten resin. At least one protrusion is provided in a first region of a ring runner portion defined by an inner circumferential surface of a first communication hole extending toward a cavity and an outer circumferential surface of a pin member disposed coaxially within the first communication hole, such that the protrusion projects from either one of these surfaces and an end face of the protrusion is held in contact with the other of these surfaces. The first region is a half of a circumference of the ring runner portion and is opposite to a circumferential position at which the first communication hole and a second communication hole extending perpendicularly to the first communication hole communicate with each other, with respect to the pin member.