Roller Shaft Flanges Prevent Resin Leakage in Injection Molding
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Solution Overview
Problem
Existing methods for producing roller members, such as press-fitting a rubber roller portion onto a shaft, result in inaccuracies, resin leakage, and increased costs due to clearance issues and insufficient bonding, leading to defective products and the need for secondary processing like deburring.
Innovation Solution
A method involving a mold with specific flat portions that allow for the injection of molding material around a roller shaft, ensuring close contact and preventing resin leakage, with flange portions on the shaft to secure the material and enhance bonding, thereby improving shape and positional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If two-color molding is used to integrally mold the roller portion to the roller shaft, then the need for downstream assembly processes is eliminated, but resin leakage occurs due to clearance between the roller shaft and friction material
Solution Approach 1:
The invention applies preliminary action by forming protrusions on the roller shaft surface before the injection molding process. These protrusions pre-establish the necessary mechanical interlocking features that prevent resin leakage during two-color molding, eliminating the need for downstream assembly while maintaining manufacturing precision.
Solution Approach 2:
The invention applies local quality by creating localized protrusions at specific positions on the roller shaft surface where resin leakage is most likely to occur. This targeted approach provides precise control over resin flow and bonding at critical locations without affecting the overall design of the roller shaft or friction material.
2Manufacturing precision
If the roller shaft and friction material are molded without clearance, then shape accuracy is improved, but the resin leaks into the clearance causing sink marks and burrs
Solution Approach 1:
The protrusions are formed on the roller shaft before injection molding to pre-prevent resin leakage. This preliminary structural feature ensures that when resin is injected, it cannot leak into clearances and cause sink marks or burrs, while still allowing the friction material to be molded with high shape accuracy.
Solution Approach 2:
The invention converts the potential harm of resin leakage into a benefit by using the protrusions to control resin flow. The protrusions guide the resin into desired areas while preventing it from leaking into clearances, transforming what would be a harmful leakage issue into a controlled bonding process that enhances the integral molding quality.
3Ease of operation
If press-fitting is used to assemble the roller portion onto the roller shaft, then the roller portion can be positioned, but the bonding strength is insufficient causing displacement
Solution Approach 1:
The invention merges the positioning function and bonding function into a single integral molding process. The protrusions on the roller shaft work together with the friction material during injection molding to achieve both precise positioning and strong bonding simultaneously, eliminating the need for separate press-fitting operations and preventing displacement.
Solution Approach 2:
The invention creates a composite structure where the roller shaft (with protrusions) and friction material are integrally bonded through injection molding. This composite construction provides both the positioning capability of mechanical features and the bonding strength of molded joints, preventing displacement while maintaining ease of positioning.
4Ease of operation
If flange portions are used for positioning the roller portion, then axial positioning is achieved, but clearance causes decreased positioning accuracy and requires additional grinding processes
Solution Approach 1:
The protrusions are formed on the roller shaft before molding to pre-establish accurate positioning features. This preliminary structural feature ensures that when the friction material is molded, it achieves high axial positioning accuracy without clearance issues, eliminating the need for subsequent grinding processes to correct positioning errors.
Solution Approach 2:
The invention uses partial action by implementing positioning features (protrusions) only at the necessary locations where axial positioning is required, rather than using full flange portions. This provides sufficient positioning accuracy while avoiding the clearance and deformation issues associated with traditional flange-based positioning methods.
Data Source
AI summary
A roller shaft is inserted into a mold including molding members respectively having a first mold surface that defines an outer circumference of a roller portion and second and third mold surfaces that respectively define first and second flat portions of the roller portion, and the mold is then closed. A molding material is injected around the roller shaft to integrally mold the roller portion. The roller portion includes the outer circumference and the first and second flat portions rising from the roller shaft to the outer circumference. The roller shaft includes flange portions at portions corresponding to the first and second flat portions. The flange portions prevent the molding material from leaking outside the first and second flat portions when the roller portion is integrally molded around the roller shaft by injection molding.