Boss Structure for CNG Tank Axial Strength and Torque Resistance
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Solution Overview
Problem
Composite Type-4 CNG Tanks face challenges in integrating a metal boss section with a plastic internal liner to withstand high-pressure axial forces and rotational torque without compromising the integrity of the sealing connection.
Innovation Solution
A boss structure featuring a composite outer shell, a plastic internal liner, and a metal boss part with strategically designed recesses and surfaces for enhanced integration, including first, second, and third recesses, and a threaded inner wall, which are filled with plastic material for axial strength and flat surfaces for torque resistance, preventing torque transmission to the internal liner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the metal boss section part is rigidly fixed into the plastic internal liner to withstand high-pressure axial forces, then the axial strength is improved, but the rotational torque from valve tightening may compromise the integrity of the sealing connection
Solution Approach 1:
The metal boss section part is segmented into distinct functional zones: an upper portion with axial reinforcement features (first recess, second recess, third recess) for withstanding axial forces, and a lower portion with torque resistance features (flat surfaces, fourth recess) for preventing rotational torque transmission. This segmentation allows each zone to specialize in resisting specific force directions without compromising the other.
Solution Approach 2:
Different regions of the metal boss section part are given different geometric qualities to address local requirements: the upper region has recesses filled with plastic material for axial strength, while the lower region has flat surfaces and torque-resistant geometry to prevent rotation. This local differentiation resolves the contradiction by providing appropriate mechanical properties in each critical zone.
2Reliability
If the metal boss section part is designed with features to resist rotational torque, then the sealing connection integrity is improved, but the axial strength may be compromised
Solution Approach 1:
The boss section is divided into axial load-bearing zones (upper portion with recesses) and torque resistance zones (lower portion with flat surfaces), allowing each to optimize its geometry for its specific function without interfering with the other's performance.
Solution Approach 2:
The metal boss section part combines metallic material with plastic material fills in specific recesses, creating a composite structure that leverages the high strength of metal for axial loads while using the plastic material to enhance torque resistance and distribute stresses.
3Ease of manufacture
If different production methods are used for metal boss section part and plastic internal liner, then manufacturing flexibility is improved, but the integration complexity increases
Solution Approach 1:
The design merges the metal boss section part and plastic internal liner into a single integrated assembly where the plastic material fills recesses in the metal part, creating a unified structure that functions as one component while allowing each material to be produced by its optimal manufacturing process.
Solution Approach 2:
The metal boss section part is pre-formed with specific recesses and geometric features during its manufacturing process, preparing it in advance to receive and integrate with the plastic material, thereby simplifying the subsequent integration step.
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to the boss structure (1) of the CNG (compressed natural gas) tanks. The boss structure (1), which is manufactures in a single stage, can resist the forces created by the pressure of compressed natural gas in the axial direction of the tank. The boss structure (1) of the present invention has a boss part (4) which can be fixed on an outer apparatus during torquing and tightening of the valve and which thus enables to prevent transmission of the resulting torque to the internal liner which has a weak strength.