Two-Stage Injection Screw Minimizing Friction and Scuffing
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Solution Overview
Problem
Existing injection molding machines with multi-start screws face issues of scuffing and increased friction resistance, leading to fiber breakage and reduced molding quality due to core run-out and excessive contact with the inner wall, which results in clogging and decreased plasticizing ability.
Innovation Solution
A two-stage screw design is implemented, where the first stage includes a compression zone with a main and auxiliary flight, and the second stage features a multi-start screw portion with a fin kneading portion, optimizing the length and number of flights to minimize friction and scuffing while maintaining kneading effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a multi-start screw portion is provided across the overall length of the second stage, then the kneading effect is high, but scuffing occurs due to increased contact frequency between apex portions and inner wall surface
Solution Approach 1:
The screw is divided into three distinct stages: a first stage with a single-start screw portion, a second stage with a multi-start screw portion, and a third stage with a single-start screw portion. This segmentation allows the multi-start portion to provide intensive kneading only where needed, while the single-start portions reduce contact frequency and prevent scuffing at the entry and exit zones.
Solution Approach 2:
Different screw configurations are applied to different zones along the screw length. The multi-start screw portion with higher flight count is localized to the second stage where maximum kneading is required, while the first and third stages use single-start configurations with lower contact frequency to prevent scuffing at locations where run-out effects are more problematic.
2Strength
If the length of the multi-start screw portion reaches the overall length of the second stage, then the kneading effect is high, but clogging of molten resin and reinforcing fiber occurs inside the multi-start screw
Solution Approach 1:
The multi-start screw portion is segmented to occupy only the second stage rather than the entire screw length. This creates distinct zones with different flow characteristics, allowing the multi-start portion to intensively knead material while the single-start portions at the ends provide smoother transitions that prevent clogging.
Solution Approach 2:
The multi-start screw portion is applied partially rather than excessively across the entire screw length. By limiting the multi-start configuration to only the second stage, the patent achieves sufficient kneading effect without the excessive contact and friction that would cause clogging if the multi-start portion extended throughout the entire screw.
3Strength
If the contact frequency of apex portions and inner wall surface increases, then the kneading effect is high, but friction resistance increases and fiber breakage occurs
Solution Approach 1:
The screw is segmented into zones with different flight configurations. The single-start portions in the first and third stages reduce apex contact frequency and friction, while the multi-start portion in the second stage provides intensive kneading with higher contact frequency only where the material has already been softened and is less susceptible to fiber breakage.
Solution Approach 2:
Different screw geometries are applied locally to different stages. The single-start configuration with lower contact frequency is used where friction would cause fiber breakage, while the multi-start configuration with higher contact frequency is used locally in the second stage where the resin is more plasticized and can withstand higher shear stresses without breaking fibers.
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 design prevents scuffing and minimizes friction resistance, enhancing the dispersion of reinforcing fibers and reducing fiber breakage, thereby improving the quality of the molded products by maintaining the kneading effect while reducing the risk of clogging and temperature-related issues.
Implementation Method 1
a shearing force applied to the reinforcing fibers may be strengthened under strict conditions of mixing
Implementation Method 2
core run-out, that is, run-out whirling of a rotating axis unavoidably occurs in response to rotations of the screw
Data Source
AI summary
Provided is a screw that is for use in an injection molding machine and that makes it possible to benefit from the kneading effect of a multi-start screw while minimizing the received friction resistance. The screw for an injection molding machine is provided with a first stage 20 on the upstream side and a second stage 30 on the downstream side. The screw for an injection molding machine is characterized in that: the first stage 20 is provided with a compression section 22 comprising a main scraper 25 and an auxiliary scraper 26 having a smaller outer diameter than the main scraper 25; and the second stage 30 is provided with a multi-start screw section 31, said multi-start screw section being provided on the upstream side and comprising a plurality of scrapers, and a fin kneading section 32 provided downstream from the multi-start screw section.