Back box with mounting posts projecting from recessed portions in sidewalls
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Solution Overview
Problem
Conventional back boxes manufactured via injection molding face issues with fragile core pins, longer cooling times, and potential warping due to long mounting posts, which can lead to mold breakage and irregular surface conditions.
Innovation Solution
The design incorporates recessed portions on the sidewalls with shorter mounting posts, each less than 50% of the back box depth, reducing the need for long core pins and allowing for quicker cooling, thus enhancing mold robustness and cycle times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If long mounting posts are used to extend from the back wall to the mouth of the back box, then the mounting posts can securely hold the fire alarm device, but the core pins become fragile and may break during injection molding
Solution Approach 1:
The mounting post structure is segmented by introducing recessed portions in the sidewalls, which divides the previously continuous long mounting post into shorter segments. This segmentation reduces the length of core pins needed in the injection mold while maintaining the functional mounting capability through the distributed recessed structures.
2Length of stationary object
If long mounting posts are used, then the mounting posts can reach the mouth of the back box, but the cooling time increases due to associated plastic wall thicknesses
Solution Approach 1:
The recessed portions create segmented mounting post structures that reduce the continuous plastic wall thickness. This segmentation allows heat to dissipate more efficiently during cooling, reducing the overall cooling time required in the injection molding process.
Solution Approach 2:
By introducing recessed portions that extend from the back wall toward the mouth, the design adds a dimensional feature that reduces material volume in critical cooling paths while maintaining the functional length of mounting posts for device attachment.
3Strength
If long mounting posts are used, then the mounting posts can provide sufficient mounting surface, but the posts may warp or develop irregular surface conditions which can impair ejection
Solution Approach 1:
The recessed portions segment the mounting post structure, reducing the length of continuous plastic material that is prone to warping. This segmentation maintains structural stability for mounting while improving surface uniformity and reducing ejection problems.
4Reliability
If shorter mounting posts are used, then the mold is more robust and less susceptible to breakage, but the mounting posts must be positioned within recessed portions
Solution Approach 1:
The recessed portions are integrated into the back box structure as built-in features rather than separate components. This segmentation approach adds structural complexity only where needed while keeping the overall design simple and the mold robust.
Data Source
AI summary
A weatherproof back box for receiving a fire alarm notification or other fire alarm device includes a back wall and sidewalls that project from the back wall and define a mouth. The sidewalls further include recessed portions that extend from the back wall toward the mouth, and end prior to the mouth. The back box further includes mounting posts, which are preferably less than 50% of the depth of the back box, that project from the recessed portions into the mouth. Additionally, these mounting posts receive fasteners for securing the fire alarm notification device in the mouth of the back box.