Asymmetrical Thread Fastener for Compressible Coating Locking
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Solution Overview
Problem
Existing solutions for fixing compressible waterproofing membranes on rigid supports, such as steel decks, fail to securely lock the membrane in place under axial forces, leading to potential detachment or perforation of the sealing gasket due to deformation of the screw and plate components.
Innovation Solution
A fixing device featuring a plate with a domed bottom and a screw with an asymmetrical thread under the head, where the thread is inscribed in a cylindrical form with an inclined face, providing axial locking and resistance to deformation, allowing the insert to swivel without compromising the lock, even under off-center forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thread under the head of the screw is provided to engage with the orifice, then axial locking of the insert is achieved, but the metal of the screw and/or plate is deformed under axial forces
Solution Approach 1:
The thread under the head is designed with an asymmetrical profile where the inclination angle on the head side is at most 15°, creating a mechanically advantageous configuration that resists deformation while maintaining locking capability
Solution Approach 2:
The inclination angle of the thread face is precisely controlled to be at most 15°, optimizing the balance between locking effectiveness and resistance to deformation under axial loads
2Reliability
If a self-tapping thread with evolving shape is provided, then bearing surfaces are increased, but the bottom of the cup folds inwards under axial force, releasing the insert
Solution Approach 1:
The asymmetrical thread profile creates a mechanically advantageous configuration where the inclined face on the head side prevents the cup bottom from folding inwards under axial loads
Solution Approach 2:
The inclination angle parameter of the thread face is optimized to be at most 15°, which prevents the folding of the cup bottom while maintaining effective axial locking
3Adaptability or versatility
If the insert is allowed to swivel on the screw, then adaptability to off-center forces is improved, but axial locking may be compromised
Solution Approach 1:
The asymmetrical thread design allows the insert to swivel adaptively while the inclined face maintains axial locking by bearing against the hole edge at an optimal angle
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 solution effectively secures the membrane by reducing the diameter of the hole under axial forces, enhancing resistance to compression and torque, preventing gasket detachment or perforation, and allowing the plate to swivel without reducing driving resistance.
Implementation Method 1
when the thread under the head is screwed into the hole in the cup of the insert, the edge of the hole bears against the face located on the head side of the thread according to an angle of attack such as an axial force exerted on the insert in the direction of the tip of the screw tends to deform the cup in the direction of a narrowing of the diameter of the hole, thus confirming the axial locking of the insert on the screw
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
The device of the invention is used for securing with screws a compressible coating on a carrier structure. It comprises a plate (8) with a cup (9), the bottom of which includes a coaxial bore (O) and a screw (1) with an under-head threading (4) having a diameter larger than that of said bore (O), wherein the thread of the under-head threading (4) has a dissymmetric shape that comprises, on the head side, a face inclined at an angle not exceeding 15° relative to the radial plane of the cup, while the cup (9) has a curved bottom having a tangent, in an axial plane, that defines an angle of between 5° and 75° relative to the axis of the cup (9), preferably between 30° and 60°.