Sheet Feed Roller Mold Design Prevents Resin Bulging
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Solution Overview
Problem
Conventional sheet feed rolling elements in electrophotographic devices often form circumferential bulges during injection molding, leading to streaks on transfer sheets due to differences in resin shrinkage, which require time-consuming post-treatments like barreling or shot blasting to remove.
Innovation Solution
A sheet feed rolling element with a mold design where the gate is positioned at one end, allowing resin to flow along the outer peripheral surface and end surface, and a step on the curved chamfer to absorb differential shrinkage, preventing bulges from forming on the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection molding is used to manufacture sheet feed rolling elements, then productivity is improved and manufacturing cost is reduced, but circumferential bulges form near the parting line causing streaks on transfer sheets
Solution Approach 1:
The patent applies preliminary action by designing the mold cavity with a stepped structure at the parting line region before injection molding occurs. The smaller-diameter portion of the cavity compensates in advance for the radial expansion that will occur during resin solidification, preventing bulge formation on the final product surface without requiring post-processing
2Manufacturing precision
If post-treatment processes like barreling or shot blasting are applied to remove bulges, then surface quality is improved, but manufacturing time increases and productivity decreases
Solution Approach 1:
The patent converts the harmful effect of resin shrinkage and radial expansion into a beneficial outcome by deliberately designing the mold cavity with a non-uniform diameter. The smaller-diameter portion of the cavity at the parting line region absorbs the expansion, transforming what would be a defect into a feature that prevents surface defects without additional processing steps
3Ease of manufacture
If the parting line is positioned at the end of the roller portion to facilitate mold opening, then ease of manufacture is improved, but circumferential bulges still form on the sheet sliding contact surface
Solution Approach 1:
The patent applies local quality by creating a localized stepped structure in the mold cavity at the specific region where the parting line is located. The cavity has a smaller diameter at the parting line portion compared to other regions, providing localized compensation for radial expansion only where needed, while maintaining the overall simplicity of the mold design and parting line positioning
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 prevents the formation of circumferential bulges on the sheet sliding contact surface, eliminating the need for post-treatments and ensuring high image quality without streaks on transfer sheets.
Implementation Method 1
a difference in shrinkage between a flow direction of resin (MD direction) and a direction perpendicular to this direction (CD direction)
Data Source
AI summary
A sheet feed rolling element for an electrophotographic device includes a roller portion and shoulders on both sides formed by curved chamfers. A parting line between the fixed mold plate and the movable mold plate of an injection mold is located at the boundary between one shoulder and the roller portion outer periphery, a step is provided at the boundary due to a difference between the opening diameter of the cavity portion defined by the fixed mold plate and the opening diameter of the cavity portion defined by the movable mold plate so the one shoulder has a smaller diameter than the outer peripheral surface, and a chamfer is provided adjacent to the one shoulder to absorb any difference in molding shrinkage rate due to a difference in molecular orientation of resin at the step, thereby preventing circumferential bulging on the outer periphery of the formed roller portion.