Latch Assembly Swaged Joint for Circuit Breaker Heat Treatment
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Solution Overview
Problem
Current latch assemblies in electrical switching apparatus, such as circuit breakers, face challenges with material limitations and heat treatment issues due to brazing or welding, leading to potential deformation and unreliability.
Innovation Solution
A latch assembly where the latch plate and shaft are swaged together using a positioning shoulder and seating surface, allowing for mechanical retention and subsequent heat treatment to achieve optimal hardness and toughness without compromising the joining process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If brazing or welding is used to join the latch plate to the latch shaft, then the components can be rigidly connected, but the heat treatment process is compromised and material selection is limited
Solution Approach 1:
The joining process is separated into two distinct stages: first mechanical retention through the positioning shoulder and slot engagement, then thermal bonding through brazing. This segmentation allows each process to be optimized independently - the mechanical retention provides initial strength while the brazing process creates the final reliable joint without compromising heat treatment.
Solution Approach 2:
The positioning shoulder and slot provide preliminary mechanical retention of the latch plate to the latch shaft before the brazing process occurs. This preliminary action holds the components in proper alignment and provides initial structural integrity, allowing the subsequent brazing and heat treatment to proceed without compromising the joint.
2Ease of manufacture
If copper brazing is used to join stainless steel components, then the components can be connected, but the braze material melts during heat treatment
Solution Approach 1:
The brazing alloy composition is changed to a nickel-based material with a melting point significantly higher than the heat treatment temperature. This parameter change in material composition allows the joint to withstand the heat treatment process without melting, while still providing ease of manufacture through the brazing process.
3Strength
If stainless steel components are heat treated to increase hardness, then the strength is improved, but the tip of the latch plate deforms
Solution Approach 1:
The nickel-based braze material acts as a cushioning layer that protects the latch plate tip during heat treatment. This braze layer absorbs thermal stress and prevents direct thermal damage to the hardened steel tip, maintaining dimensional stability while allowing the bulk material to achieve the required hardness through heat treatment.
4Strength
If welded joints are used to connect the latch components, then rigid connection is achieved, but cracks develop after heat treatment
Solution Approach 1:
The joining method is changed from welding to brazing with a nickel-based alloy that has superior thermal stability. This parameter change in the joining process and material composition prevents crack formation during heat treatment while maintaining the required joint rigidity, as the brazed joint distributes thermal stress more uniformly than welded joints.
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 solution enables the use of a wide range of materials and heat treatments, resulting in a more reliable and cost-effective latch assembly with improved strength and hardness, preventing deformation under stress while maintaining durability.
Implementation Method 1
the seating surface of the shaft member is swaged to retain the latch plate to the shaft member
Implementation Method 2
the latch plate 6 rotates about the longitudinal axis 9 of the latch shaft 8
Data Source
AI summary
A latch assembly includes a latch plate having an opening therethrough; and a latch shaft having a shaft member and a positioning shoulder disposed on the shaft member. The positioning shoulder has a seating surface thereon. The shaft member passes through the opening of the latch plate. The latch plate engages the positioning shoulder of the shaft member. The seating surface of the shaft member is swaged to retain the latch plate to the shaft member.