Conical Screw Coupling Surface Contact Geometry
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Solution Overview
Problem
Existing screw couplings with line contact between screw threads experience high contact pressure, leading to plastic deformation and potential leakage under pressure, especially in sealing applications.
Innovation Solution
The screw coupling design employs a Fourier series calculation, ignoring harmonics above a chosen maximum ranking number to achieve surface contact instead of line contact, with features like symmetrical functions, specific angle of rotation, and optional sealing and locking mechanisms to prevent leakage and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If screw threads are designed with traditional line contact geometry, then the coupling structure is simple, but the contact pressure becomes excessively high causing plastic deformation
Solution Approach 1:
The patent applies parameter changes by transitioning from traditional line contact geometry to a mathematically optimized surface contact geometry based on Fourier series. This changes the fundamental contact parameters from line to surface, distributing the load over a larger area and reducing contact pressure while maintaining structural simplicity
Solution Approach 2:
The invention moves from one-dimensional line contact to two-dimensional surface contact between screw threads. This dimensional transition increases the contact area from a line to a surface, effectively reducing the contact pressure by distributing forces over a larger area without complicating the overall coupling structure
2Ease of manufacture
If screw threads make line contact, then the manufacturing is easier, but leakage occurs under pressure in sealing applications
Solution Approach 1:
The patent changes the contact parameter from line to surface through Fourier series-based geometry optimization. This creates a sealing surface that maintains reliability under pressure while remaining manufacturable through standard machining processes
Solution Approach 2:
The invention uses mathematical Fourier series to define the optimal thread profile, which can be precisely replicated during manufacturing. This ensures consistent sealing performance while maintaining ease of manufacture through mathematical precision rather than complex physical tooling
3Area of stationary object
If harmonics above maximum ranking number are included in Fourier series calculation, then the thread contact surface area increases, but sharp edges and transitions cause excessive material stresses
Solution Approach 1:
The patent applies partial action by including only harmonics up to a chosen maximum ranking number (e.g., 5) in the Fourier series calculation. This provides sufficient surface contact area for reduced pressure while avoiding the excessive complexity and sharp transitions that would result from including all higher-order harmonics
Solution Approach 2:
The invention optimizes the Fourier series parameters by selecting a maximum ranking number that balances contact surface area with smooth transitions. This parameter optimization ensures adequate sealing surface area while maintaining rounded transitions that prevent excessive material stresses
Data Source
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AI summary
The invention relates to a screw coupling between two bodies, the one of which has an external screw thread and another has an internal screw thread complementary thereto, which screw threads are superimposed onto two for instance truncated conical base surfaces monotonously narrowing and widening respectively in the direction of a central axis, the longitudinal section of each of these screw threads relative to the central axis being a periodic univalent function which is continuous at least at the inflection points. It is an object of the invention to embody a screw coupling of the described type such that the contact zones do not make line contact but surface contact with each other, whereby the contact pressure is substantially reduced and plastic deformation thereof must be considered almost precluded. In this respect the screw coupling has the feature that the first derivative of the longitudinal section of each screw thread along the base surface is a continuous function; the second derivative of the longitudinal section of each screw thread along the base surface is a continuous function; the second derivative of the longitudinal section of each screw thread relative to the central axis is a continuous function at least in the region of the inflection points; and the screw threads are in mutual contact over a substantial surface area differing from line contact.