Cladding Screw Structure for Wood Swelling and Shrinking
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Solution Overview
Problem
Existing screws used for cladding elements made of wood materials fail to accommodate relative movements due to climate-related swelling and shrinking, leading to damage and visible defects on the surface.
Innovation Solution
A self-drilling and self-tapping screw design with a broaching section followed by a smooth shank section and a countersunk screw head, featuring multiple coaxial circular cylinder sections of different diameters and lengths, allowing for relative movement without causing damage or visible defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional self-drilling and self-tapping screw is used to fasten cladding elements, then the screw provides holding function and connects the cladding to the substructure, but the screw cannot accommodate relative movements caused by wood swelling and shrinking, leading to damage and visible defects
Solution Approach 1:
The screw shaft is divided into multiple functional sections: a threaded section for fastening, a smooth section for movement accommodation, and a broaching section for hole formation. This segmentation allows each section to perform its specific function independently, resolving the contradiction between maintaining holding force and allowing relative movement.
Solution Approach 2:
The smooth section of the screw shaft is designed to allow relative movement between the cladding element and substructure while maintaining connection. This dynamic capability enables the screw to accommodate wood swelling and shrinking without causing damage, while the threaded section maintains the holding function.
2Shape
If the screw head is countersunk into the cladding element to provide a flush finish, then the visible surface appears smooth without elevations, but shavings and debris become jammed on the visible edge line of the contact surface
Solution Approach 1:
The broaching section is designed to extract and remove shavings and debris from the countersink hole during the screw driving process. By actively removing debris rather than allowing it to accumulate, the flush surface finish is achieved without shavings jammed on the visible edge line.
Solution Approach 2:
The broaching section acts as an intermediary between the threaded section and the countersunk head, performing the function of debris removal and hole smoothing. This intermediate section resolves the contradiction by handling the debris issue while allowing the countersunk head to provide the flush finish.
3Strength
If the screw creates a tight fit in the cladding element to ensure secure fastening, then the holding function is strong, but the screw cannot accommodate expansion and contraction of the wood material over time
Solution Approach 1:
The screw shaft is segmented into a threaded section for strong fastening and a smooth section for movement accommodation. This allows the screw to provide both strong holding strength and the ability to accommodate wood dimensional changes over time.
Solution Approach 2:
Different sections of the screw shaft have different local qualities: the threaded section provides high friction and strong holding, while the smooth section provides low friction and movement capability. This local differentiation resolves the contradiction between strength and adaptability.
4Manufacturing precision
If a broaching area is added to remove material and smooth the hole surface, then the hole quality improves and debris is removed, but the screw design becomes more complex and handling becomes difficult
Solution Approach 1:
The broaching function is merged with the screw threading function by forming the broaching section as an integral part of the screw shaft. This combining approach improves hole quality without requiring separate broaching operations or significantly increasing overall design complexity.
Solution Approach 2:
The screw design incorporates multiple functions in a single component: drilling (tip), threading (threaded section), broaching (broaching section), and fastening (threaded section). This multi-functionality achieves high manufacturing precision while maintaining reasonable design complexity through functional integration.
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 screw effectively forms the required through-hole during installation, ensuring secure fastening while allowing for wood expansion and contraction without damage to the cladding material or visible surface imperfections.
Implementation Method 1
From the tip of the screw, along the longitudinal direction of the screw, there follows a long area with a self-tapping thread
Implementation Method 2
The broaching area is used to move removed material, which is located in the screw through hole, away from the screw head into the hole and also to smooth the lateral surface of the hole
Implementation Method 3
the screw head fits well in it and that disruptive indentations, tears, bulges, etc. on the part to be fastened in the vicinity of the screw head are avoided
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a cladding for a building surface and a corresponding screw. The cladding comprises cladding elements (1) made of a wood material, a substructure (4), and screws (2), wherein the screws (2) are self-drilling and self-tapping and extend through screw through holes (5) in the cladding elements (1) and engage in threaded engagement with the material of the substructure (4), wherein the screw (2) has, starting from the screw tip (6), a drill point, a threaded section (7), a reaming section (8), a smooth shaft section (10) thinner than the reaming section, and a countersunk screw head (12), wherein the reaming section (8) is designed as a thread oriented in the opposite direction to the threaded section (7).The distance between the free end face of the screw head (12) and the reaming section (8) is at least equal to the thickness of the cladding element in the axial direction of the screw (2).