Ribbed Back Wall Electrical Junction Box
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Solution Overview
Problem
Molded plastic electrical junction boxes formed from fire-resistant materials require thick walls to meet strength and fire-resistant standards, leading to increased costs and moldability issues such as knit lines due to material flow characteristics.
Innovation Solution
A rib pattern is integrally molded on the back wall of the electrical box, increasing thickness only at specific points to enhance structural integrity and moldability, allowing for the use of high-heat fiberglass reinforced thermoset polyester without increasing overall wall thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If wall thickness is increased to meet strength and fire-resistant standards, then structural integrity and fire resistance are improved, but manufacturing cost increases due to increased material usage
Solution Approach 1:
The patent applies local quality by adding ribs only to the back wall where structural support is needed, rather than uniformly thickening all walls. The ribs create localized thickness variations that provide strength where required while keeping other areas thin, thus reducing overall material usage while meeting strength standards.
Solution Approach 2:
The patent transitions from a two-dimensional wall structure to a three-dimensional ribbed structure on the back wall. By adding ribs that extend from the back wall surface, the design utilizes the third dimension to provide structural reinforcement without increasing the overall wall thickness uniformly, thereby reducing material consumption.
2Reliability
If wall thickness is increased to meet fire-resistant standards, then fire resistance is improved, but manufacturing cost increases due to increased materials and manufacturing costs
Solution Approach 1:
The ribbed structure on the back wall provides localized fire resistance enhancement where thermal exposure is most critical, without requiring uniform wall thickening throughout the entire box. This selective reinforcement reduces material costs while maintaining fire-resistant performance.
Solution Approach 2:
By adding ribs that protrude from the back wall surface, the design creates additional thermal mass and structural complexity in the critical fire-exposure zone without proportionally increasing manufacturing complexity elsewhere, thus improving fire resistance while controlling manufacturing costs.
3Ease of manufacture
If wall thickness is reduced to decrease material usage and cost, then manufacturing cost is reduced, but the box becomes brittle and fails strength standards
Solution Approach 1:
The patent maintains thin walls in most areas to reduce material usage and cost, but adds localized rib structures on the back wall where strength is critical. This selective reinforcement allows the box to meet strength standards without requiring uniformly thick walls, thus controlling manufacturing costs.
Solution Approach 2:
By adding ribs that extend from the back wall surface into the third dimension, the design provides structural reinforcement without increasing the overall wall thickness. This allows thin-walled construction with enhanced strength at critical locations, reducing material usage while meeting strength requirements.
4Reliability
If fire rated compound is used to form molded junction box, then fire resistance is improved, but knit lines are formed on side walls due to material flow characteristics
Solution Approach 1:
The patent extracts the gating system into separate ribs that are molded integrally with the back wall. By positioning the gating system in these dedicated rib structures rather than in the side walls, the harmful knit lines are isolated to the ribs where they do not affect the cosmetic surface quality of the main box walls.
Solution Approach 2:
The ribs serve as intermediary structures that channel the molten fire-rated compound from the injection points to the side walls. By using these ribs as flow pathways, the material flow is controlled and directed, preventing knit lines from forming on the side wall surfaces while still enabling complete filling of the mold cavity.
Data Source
AI summary
A molded electrical junction box may be formed from a high-heat thermoset polyester. The box includes a back wall, a parametrical side wall bounding the back wall and an open front face. The back wall includes an integrally molded rib pattern extending therefrom. The rib pattern increases the thickness of the back wall thereat. The rib pattern is formed to be in direct flow communication with a molding gate during the molding process.