Molded Enclosure Reinforcement with Machine Screws
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Solution Overview
Problem
Molded case circuit breakers are susceptible to breaking due to high pressure and stress from gas expansion during high electrical current interruptions, and conventional thread cutting screws can be pulled out, limiting the interrupting ratings and case strength.
Innovation Solution
The use of machine screws within the exterior walls of a molded enclosure to reinforce and restrict expansion, combined with thread cutting screws to securely fasten the molded portions, forming a robust structure that encloses separable contacts and an operating mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional thread cutting screws are used to fasten molded portions, then the molded case can be assembled, but the screws can be pulled out and the molded material may crack during high pressure events
Solution Approach 1:
The patent combines two different fastening methods (machine screws with nuts and thread cutting screws) to create a composite fastening system. Machine screws with nuts provide reliable anchoring in thick molded portions, while thread cutting screws provide easy assembly in thinner portions. This composite approach resolves the contradiction by ensuring both ease of manufacture and reliability under high pressure conditions.
2Volume of moving object
If the molded case walls are made thin to reduce size, then the circuit breaker is more compact, but the walls become susceptible to breaking under high gas pressure
Solution Approach 1:
The patent applies different wall thicknesses at different locations of the molded case. Thicker walls are used in areas subjected to high gas pressure during interruption, while thinner walls are used in areas experiencing lower stress. This local differentiation allows the case to maintain overall compactness while providing sufficient strength where needed.
Solution Approach 2:
The patent creates a composite structural system by combining the molded case with a framework of machine screws and nuts. The machine screws act as internal reinforcement elements that distribute and bear the high gas pressures, allowing the molded case walls to be thinner while maintaining overall structural strength. This composite approach enables compact dimensions without sacrificing case strength.
3Strength
If machine screws and hex nuts are used to hold the molded cover, then the external walls are reinforced, but the internal walls may lack sufficient reinforcement
Solution Approach 1:
The patent applies different fastening solutions to different locations: machine screws with nuts are installed in thick external walls for reinforcement, while thread cutting screws are used in thinner internal walls. This local differentiation ensures that each wall type receives appropriate reinforcement based on its specific structural requirements, maintaining both external wall strength and internal wall integrity.
Data Source
AI summary
A circuit breaker includes separable contacts, an operating mechanism structured to open and close the separable contacts, a molded enclosure comprising a first molded portion and a second molded portion, a plurality of thread cutting screws fastening the first molded portion to the second molded portion, and a plurality of machine screws. The first molded portion and the second molded portion cooperate to form a plurality of exterior walls. The exterior walls define an interior volume, which encloses the separable contacts and at least a portion of the operating mechanism. The machine screws extend within and reinforce the exterior walls and restrict expansion of the exterior walls away from the interior volume.