Poly-V Belt Pulley Venting via Rib Segmentation
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Solution Overview
Problem
The existing plastic injection-molding methods for producing poly-V belt pulleys face challenges in cavity ventilation, leading to air inclusions and tool wear due to conflicting requirements of gap dimensioning, which affects the roundness and burr formation of the pulley, especially for wider rib profiles.
Innovation Solution
The method involves constructing the injection-molding cavity with a ribbed contour comprising thin and thick ribs, where gaps are radially aligned with thin ribs to prevent air inclusions and position injection points between thick ribs for improved filling behavior, using an odd number of ribs and matching injection points and slides for end-side injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gap between slides is increased to improve ventilation, then air inclusions are reduced, but burr formation and impermissible roundness errors increase
Solution Approach 1:
The patent applies local quality by differentiating rib widths: thin ribs (w1 ≤ 80% of w2) are positioned at gap locations to enable ventilation, while thick ribs are positioned between gaps to maintain structural integrity and prevent burr formation. This localized variation in rib geometry allows each region to serve its specific function optimally.
Solution Approach 2:
The rib structure is segmented into two distinct groups: thin ribs and thick ribs. This segmentation allows the cavity to have different characteristics at different locations - thin ribs provide ventilation pathways while thick ribs provide structural support and prevent material accumulation issues.
2Manufacturing precision
If the gap between slides is decreased to improve roundness, then burr formation is reduced, but air inclusions and burn marks increase
Solution Approach 1:
The patent applies local quality by differentiating rib widths: thin ribs (w1 ≤ 80% of w2) are positioned at gap locations to enable ventilation, while thick ribs are positioned between gaps to maintain structural integrity and prevent burr formation. This localized variation in rib geometry allows each region to serve its specific function optimally.
Solution Approach 2:
The rib structure is segmented into two distinct groups: thin ribs and thick ribs. This segmentation allows the cavity to have different characteristics at different locations - thin ribs provide ventilation pathways while thick ribs provide structural support and prevent material accumulation issues.
3Manufacturing precision
If the number of slides is increased to improve cavity coverage, then filling behavior improves, but tool complexity and manufacturing cost increase
Solution Approach 1:
The patent applies parameter changes by optimizing the number of injection points and slides to specific odd values (9 or 11), and setting the rib count to three times the slide count (27 or 33). These specific parameter values optimize the distribution of material flow and air evacuation, achieving good filling behavior with a manageable number of slides.
Solution Approach 2:
The patent uses an odd number of slides and injection points, creating an asymmetric distribution pattern that prevents direct alignment of injection points with gaps. This asymmetric arrangement promotes more uniform material flow and air evacuation throughout the cavity.
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
This approach enhances cavity filling and reduces burr formation, mitigating tool wear and air inclusions, as confirmed by mold-flow analysis, resulting in a more reliable and precise poly-V belt pulley production.
Implementation Method 1
these areas are filled up primarily with the plastic melt that forces the air located there in the direction of the gaps
Data Source
AI summary
Provided is a plastic injection-molding method for producing a poly-V belt pulley, which has an outer ring, an inner ring, and a ring web, which connects the outer ring to the inner ring and has a plurality of radially oriented ribs. The injection molding occurs in a circular-ring-shaped injection-molding cavity, a poly-V-ribbed inner shell of which is formed by a plurality of radially movable slides and which is vented during the injection molding by the gaps between the slides adjacent to each other. The rib contour in the injection-molding cavity are designed in such a way that the plurality of ribs is formed of a first group of thin ribs and a second group of thick ribs and that the gaps extend in radial extension of the thin ribs, the width of which is significantly less than the width of the thick ribs, which extend circumferentially between the gaps.