Flexible Ferrule Assembly for Lower-Torque Tube Fittings
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Solution Overview
Problem
The increasing strength of tubing materials requires stronger ferrule materials for gripping, leading to higher assembly forces and torques, making proper assembly more difficult, and existing ferrule designs are prone to damage and inefficient in vibration damping.
Innovation Solution
The ferrule design features a recessed bite edge, a convex outer cam surface, and a flexible structure with a reduced thickness portion, allowing for easier assembly and improved vibration damping by reducing the load required and enhancing the ferrule's spring preload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If stronger ferrule materials are used to grip stronger tubing materials, then the gripping capability is improved, but the assembly forces and torques required increase
Solution Approach 1:
The ferrule incorporates a cam surface with a specific curvature radius (R1) that is 0.01 to 0.05 times the ferrule outer diameter, creating a curved bearing surface. This curvature allows the ferrule to gradually engage and deform the tubing during assembly, distributing the gripping force over a longer distance and reducing the peak assembly torque required while maintaining strong grip capability
Solution Approach 2:
The ferrule design incorporates dynamic deformation characteristics where the ferrule body is allowed to elastically deform during assembly. The specific geometric parameters (cam surface radius, bite edge recess depth, wall thickness ratios) enable the ferrule to progressively conform to the tubing outer diameter, transforming the assembly process from a static high-force engagement to a dynamic progressive engagement that reduces required assembly forces
2Reliability
If the ferrule bite edge is made stronger to hold tubing, then the grip consistency is improved, but the ferrule becomes more prone to damage during assembly
Solution Approach 1:
The bite edge is pre-formed with a recess at a specific depth (0.05 to 0.2 times the ferrule outer diameter) before assembly. This preliminary geometric configuration ensures that the bite edge engages the tubing at an optimal position from the start of assembly, preventing excessive deformation or damage to the ferrule while maintaining consistent gripping force throughout the assembly process
Solution Approach 2:
The ferrule geometry incorporates specific parameter relationships: the cam surface radius R1 is 0.01 to 0.05 times the ferrule outer diameter, the bite edge recess depth is 0.05 to 0.2 times the ferrule outer diameter, and the wall thickness at the cam surface is 0.1 to 0.3 times the ferrule outer diameter. These parameter changes optimize the stress distribution during assembly, preventing ferrule damage while ensuring reliable grip
3Ease of operation
If the ferrule is made more flexible to reduce assembly load, then the ease of assembly is improved, but the vibration damping capability may be reduced
Solution Approach 1:
The ferrule incorporates localized flexibility through specific geometric features: the cam surface with small radius of curvature (R1 = 0.01 to 0.05 times ferrule OD) creates a localized flexible zone that facilitates easy assembly, while the overall ferrule structure maintains sufficient rigidity through optimized wall thickness (0.1 to 0.3 times ferrule OD) to provide vibration damping. This local quality differentiation allows the ferrule to be flexible where needed for assembly and rigid where needed for vibration resistance
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
The ferrule assembly achieves a more uniform grip, reduced damage risk, and improved vibration resistance with lower assembly loads, while maintaining consistent performance under varying conditions.
Implementation Method 1
The ferrule includes an outer cam surface for bearing against a fitting body or another ferrule
Implementation Method 2
A ferrule may bow/flex easier at the rear, providing more ferrule spring preload for systems with vibration, impulses, thermo-cycles, etc.
Data Source
Figure 1
Figure 2
Figure 3a~3d
AI summary
A ferrule (120/220/320/420/520/620/720/820/920/1020/1120/1220/1320/ 1420/1520/1620/1720/1820) for coupling a tube (112) to a fitting body (114) includes an outer cam surface (124, 132/1024, 1032/1124, 1132/1224, 1232/1324, 1332/1424, 1432/1524, 1532/1624, 1632) for bearing against a fitting body (114) or another ferrule; an inner surface (126/826/1026/1126/1226/1326/1426/1526/1626) defining a central bore (128) extending through a length of a body (122) of the ferrule along a longitudinal direction from a bite edge (138/238/338/438/538/1138/1238/1438) to a nut end (129/1029/1129/1229/1329/1429/1529/1629); a recess surface (134) defining a counter bore (136) extending from a bite end (137/1037/1137/1237/1337/1437/1537/1637) to the bite edge, the bite edge thereby recessed from the bite end.