Protective Cover Gate Mark Thickness Reduction Prevents Jetting
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Solution Overview
Problem
The existing protective covers for bearing devices with thin separation walls in injection molding are prone to jetting during the molding process, leading to reduced strength, poor appearance, and internal defects due to the formation of small-scale welds and uneven resin flow.
Innovation Solution
A protective cover design with a thickness reduction part around the gate mark, where the thickness T around the gate mark satisfies d ≤ T ≤ 3d, and a columnar part protruding toward the gate to change the flowing direction of the molten resin, preventing jetting and ensuring stable resin flow and charging into the thin separation wall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gate is set close to the thin separation wall and injection speed is increased to charge molten resin into the separation wall, then the separation wall can be properly filled, but jetting occurs causing small-scale welds and reducing the strength of the protective cover
Solution Approach 1:
A thickness reduction part is formed in advance at a specific position between the gate and the separation wall. This pre-formed feature serves to intercept and redirect the molten resin flow before it reaches the separation wall, preventing jetting and small-scale weld formation while ensuring proper charging of the thin separation wall.
Solution Approach 2:
The thickness reduction part acts as an intermediary element between the gate and the separation wall. It mediates the molten resin flow by providing a controlled path that prevents direct high-speed injection into the separation wall, thereby eliminating jetting while maintaining proper filling.
2Measurement precision
If a thin separation wall is used in the protective cover, then the magnetic sensor can be positioned closer to the magnetic encoder improving detection accuracy, but jetting occurs during injection molding reducing manufacturing quality
Solution Approach 1:
The thickness reduction part is pre-formed in the protective cover structure to control the injection flow path. This allows the thin separation wall to be maintained for improved magnetic sensor detection accuracy while preventing manufacturing defects through controlled resin flow redirection.
Solution Approach 2:
The thickness reduction part serves as an intermediary structure that enables the thin separation wall design for better detection accuracy while simultaneously preventing jetting-related manufacturing defects, thus resolving the contradiction between measurement precision and manufacturing precision.
3Productivity
If high injection speed is used to charge the thin separation wall, then the molding cycle can be reduced, but jetting occurs causing internal defects and poor appearance
Solution Approach 1:
The thickness reduction part is formed in advance to create a controlled flow path that allows high injection speeds to be used without causing jetting. The pre-formed feature redirects the molten resin flow, enabling fast cycling while maintaining appearance and internal quality.
Solution Approach 2:
The thickness reduction part acts as a mediator that allows high injection speeds for improved productivity while preventing jetting-related defects. It provides a controlled intermediate path that maintains resin flow stability even at high speeds.
Data Source
Figure 1
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AI summary
Occurrence of jetting is prevented in injection molding of a protective cover having a thin separation wall in a disc part. A protective cover 1 is molded through injection molding of a synthetic resin and includes a disc part 2, a sensor holder part 4 protruding inward from the disc part 2, and a protruding part 6 protruding inward from the disc part 2 and continuous with the sensor holder part 4. The disc part 2 includes a separation wall which is thinner than other portions of the disc part 2 and separates a magnetic encoder and a magnetic sensor from each other. The protruding part 6 has, at the inward-side face thereof, a gate mark GM caused by the injection molding. The protruding part 6 is provided with, at the outward-side face thereof, a thickness reduction part 7 extending inward so as to be close to the gate mark GM. In the injection molding, a molten synthetic resin material injected from a gate at the position of the gate mark GM collides with a columnar part for providing the thickness reduction part 7, thereby changing the flowing direction of the resin material to flow along the wall faces of the die. This prevents jetting from occurring.