Cold-Expansion Compression Collar Gating to Eliminate Knitlines
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Solution Overview
Problem
Conventional injection molding of compression collars for cold-expansion tubing connections often introduces knitlines, which are weak points prone to failure, and requires additional material to reinforce these areas.
Innovation Solution
A method using a continuous gate at the axial end of the precursor form to prevent material flow into itself during injection molding, eliminating knitlines and allowing for a stronger, more robust compression collar design without thickened wall sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional injection molding is used to manufacture compression collars, then production efficiency is maintained, but knitlines are introduced creating weak regions prone to failure
Solution Approach 1:
The mold cavity is segmented into multiple sections with separate injection gates, allowing independent control of material flow into different regions of the collar. This segmentation prevents knitlines by ensuring material flows from multiple directions simultaneously rather than merging single streams
Solution Approach 2:
The injection gating system transitions from conventional planar gating to a three-dimensional radial gating arrangement where material flows from the center outward in multiple dimensions, eliminating the linear flow paths that create knitlines in traditional molding
2Strength
If wall thickness is increased at knitline regions to reinforce weakness, then structural strength is improved, but material usage and manufacturing complexity increase
Solution Approach 1:
The harmful knitline feature is completely extracted and eliminated from the design by using a gating system that prevents material flow convergence. This removes the need for compensatory design features like thickened wall sections, achieving strength without additional material
Solution Approach 2:
The collar maintains uniform wall thickness throughout by eliminating localized weaknesses (knitlines) through proper gating design, rather than adding material locally. The uniform structure provides consistent strength without regional variations in material distribution
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 solution eliminates knitlines, enhancing the structural integrity of the compression collar and reducing material usage, resulting in a more reliable and efficient cold-expansion joining system.
Implementation Method 1
imbue it with shape memory properties (e.g., through cross-linking, irradiation, steam, etc.) such that when the tubing is stretched or deformed, the tubing returns to the shape set in its memory during the manufacturing process
Implementation Method 2
The elastic forces within the cold-expansion tubing material can be applied to any object that interferes with the cold-expansion tubing as it returns to its original shape
Implementation Method 3
knitlines are lines within the injection molded part, often not visible by the naked eye, at which two fronts of material have flowed together during the injection molding process
Data Source
AI summary
A compression collar is manufactured for reinforcing an interference fit between an end of a pipe and a fitting. A precursor form is injection molded using a cold-expansion material. The precursor form has a tubular body with an initially closed axial end and a bore initially blind formed in the other axial end. Material is removed from the initially closed axial end to form an opening that connects to the bore thereby forming the compression collar. The opening has an inner periphery with a profile in axial cross section that is different than any profile in axial cross section of an inner periphery of the bore. The collar formed lacks knitlines and includes tabs which help to position the collar on a pipe.