Pipe Fastening Structure with Spherical End Member
Solution Overview
Problem
The omission of a sleeve in pipe fastening structures for high-pressure fuel lines leads to direct torque application on metal pipes, causing them to turn with the nut, resulting in sealing surface damage and potential fuel leakage, especially with stainless steel components which are prone to frictional seizure and thermal expansion issues.
Innovation Solution
A pipe fastening structure featuring an end member with integrated spherical parts and a neck, where the ratio of contact diameters between the spherical parts and the nut's sliding surface is optimized to prevent the metal pipe from turning with the nut, using a design that includes a reduced nut diameter and specific shoulder configurations to distribute forces effectively, ensuring the metal pipe remains stationary under axial force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the sleeve is omitted and the spherical end is fastened directly to the counterpart with the nut, then the device complexity and weight are reduced, but the metal pipe turns together with the nut causing sealing surface damage and fuel leakage
Solution Approach 1:
The invention uses a spherical end member with a specific spherical geometry (radius R1) that contacts the sealing surface. The spherical shape distributes the fastening load over a curved contact area rather than a point contact, preventing localized stress concentration and pipe rotation. The sphere radius is specifically designed to be R1 ≥ 0.5D (where D is the pipe outer diameter) to ensure adequate contact area and prevent turning.
Solution Approach 2:
The invention changes the geometric parameters of the spherical end, specifically the radius R1, to optimize the contact area with the sealing surface. By setting R1 ≥ 0.5D, the contact area increases sufficiently to prevent pipe rotation during tightening while maintaining the simplified structure without a sleeve. This parameter optimization resolves the contradiction between simplicity and reliability.
2Object-affected harmful factors
If stainless steel fastening parts are used to resist corrosion, then the resistance to corrosive action is improved, but the friction increases causing the parts to turn together and seizure
Solution Approach 1:
The spherical geometry of the end member creates a distributed contact area with the sealing surface. This curved contact interface reduces the friction force concentration compared to flat surfaces, making it easier to overcome static friction during tightening without causing pipe rotation. The spherical shape allows smoother engagement and reduces the tendency for stainless steel parts to seize.
Solution Approach 2:
The spherical contact interface enables a more dynamic tightening process where the contact area adjusts during assembly. The sphere can rotate slightly during tightening, distributing the frictional heating and preventing seizure. This dynamic characteristic helps manage the high friction inherent in stainless steel connections.
3Force
If a higher torque is applied to fasten stainless steel parts with predetermined axial force, then the axial force is sufficient to withstand high injection pressure, but the metal pipe turns with the nut causing sealing surface galling
Solution Approach 1:
The spherical end member with radius R1 ≥ 0.5D creates a large contact area with the sealing surface. This distributed contact area increases the friction torque resistance, allowing the application of high fastening torque to achieve the required axial force for withstanding injection pressure without causing pipe rotation or sealing surface galling.
Solution Approach 2:
The spherical geometry is designed in advance with specific radius requirements (R1 ≥ 0.5D) to pre-establish the necessary contact area and friction characteristics. This preliminary design ensures that when high torque is applied during assembly, the pipe will not turn and the sealing surface will not be damaged, while still achieving the required axial clamping force.
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
This design effectively prevents the metal pipe from turning with the nut, thereby avoiding sealing and sliding surface damage, maintaining a secure connection under high pressure and allowing for repeated connection/disconnection without leakage, even with stainless steel components.
Implementation Method 1
the ratio of a diameter D2 of a contact circle on the first spherical part in contact with the sealing surface to a diameter D3 of a contact circle on the second spherical part in contact with a sliding surface of the nut meets an expression: 1.0≧α/β≧0.80, where α=D2/D, β=D3/D
Implementation Method 2
If the metal pipe turns together with the nut, the sealing surface is galled and damaged due to intense friction between the spherical end and the sealing surface
Implementation Method 3
Since stainless steel parts are coated with a chromium oxide film, stainless steel parts are more frictional than steel parts
Implementation Method 4
The coefficient of thermal expansion of stainless steels is high as compared with that of steels, the thermal expansion of stainless steel parts caused by frictional heat increases pressure acting on contact surfaces
Implementation Method 5
the thermal expansion of stainless steel parts caused by frictional heat increases pressure acting on contact surfaces
Implementation Method 6
the ratio of a diameter D2 of a contact circle on the first spherical part in contact with the sealing surface to a diameter D3 of a contact circle on the second spherical part in contact with the sliding surface of the nut meets an expression: 1.0≧α/β≧0.80
Data Source
AI summary
A pipe fastening structure includes an end member attached to an end part of a metal pipe, and a nut for fastening the end member attached to the metal pipe to a counterpart. In the pipe fastening structure, the end member has a first spherical part to be brought into contact with a sealing surface of the counterpart, a second spherical part formed integrally with the first spherical part so as to be in contact with a sliding surface formed in the nut, and a neck continuous with the second spherical part and having the shape of a straight pipe.