Coupling Safety Pin Setback for Seizing Prevention
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Solution Overview
Problem
Existing couplings with safety pins face issues with high friction and seizing after the pin breaks, leading to unreliable movement transmission, and increasing the material hardness to mitigate this is costly.
Innovation Solution
The design includes a setback in the guide surface where the safety pin breaks, containing the bead formed and preventing seizing, with the setback's depth ensuring the pin works in shear and exceeding the bead's height, allowing relative movement between the driving and driven parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the guide surface acts as a shear blade to cut the pin, then the pin breaking function is achieved, but the male portion deforms and forms a bead that causes seizing
Solution Approach 1:
The guide surface is segmented into two functional zones: an upper shear zone for cutting the pin and a lower setback zone for containing the bead. This segmentation separates the pin-cutting function from the bead-containing function, preventing the bead from causing seizing while maintaining the pin breaking capability.
Solution Approach 2:
The setback zone acts as an intermediary structure between the shear zone and the bulk material. It provides a dedicated space that mediates the interaction between the breaking pin and the guide surface, containing the bead before it can cause harmful seizing.
2Object-generated harmful factors
If the material hardness is increased to reduce seizing, then the seizing risk is reduced, but the manufacturing cost increases considerably
Solution Approach 1:
Instead of increasing the hardness of the entire male portion, the invention applies a localized solution by creating a setback zone with specific geometric properties. This local structural modification addresses the seizing problem without requiring costly material hardening treatments across the entire component.
Solution Approach 2:
The invention changes the geometric parameter of the guide surface by introducing a setback zone with a specific depth (greater than the theoretical bead height). This parameter change modifies the interaction between the pin and guide surface, containing the bead and preventing seizing without altering material properties or increasing cost.
3Object-generated harmful factors
If the setback depth is sufficient to contain the bead, then seizing is prevented, but the pin may not work essentially in shear
Solution Approach 1:
The setback depth is designed to be excessive relative to the bead height, ensuring complete bead containment. This partial excess in depth guarantees that the bead is fully contained while the upper portion of the guide surface maintains the appropriate geometry for shear action, balancing both requirements.
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 effectively reduces the risk of seizing and maintains reliable movement transmission by containing the bead within the setback, ensuring the safety pin's shear action without increasing material costs.
Implementation Method 1
The safety pin is designed to have shear strength sufficient to transmit forces that are below a threshold: above the threshold, the safety pin breaks
Implementation Method 2
a bead forms on the side where the safety pin bears against the edge of the hole before breaking
Data Source
AI summary
A coupling comprising a driven part and a driving part that is connected by a safety pin so as to drive the driven part together with the driving part in a travel direction, one of the parts having a male portion engaged in a female portion of the other part, the male and female portions respectively having a first guide surface and a second guide surface facing each other in such a manner that, in the event of the pin breaking, the driving part is capable of moving relative to the driven part in the travel direction, the pin extending perpendicularly to said direction through corresponding holes made in the male and female portions, the coupling being characterized in that the hole made in the male portion opens out in the bottom of a setback in the second guide surface.