Fiber Cement Plank Mounting Screw with Segmented Threads
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Solution Overview
Problem
Existing screws, such as nails and traditional countersunk screws, cause breakage and cracking in fiber cement planks due to internal tensile stress during imbricated mounting, and are not suitable for quick and secure mounting of fiber cement planks without risking damage or improper installation.
Innovation Solution
A screw with a first thread near the tip, a second, larger thread near the head, and a milling section between the threads to minimize tensile stress, featuring a flat head with milling fins for countersinking, which reduces radial pressure and tangential stress, allowing for secure and quick mounting of fiber cement planks without causing breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional countersunk screws or nails are used to mount fiber cement planks, then the planks can be secured to the underlying surface, but internal tensile stress causes breakage and cracking of the planks
Solution Approach 1:
The screw thread is divided into two distinct segments: a first thread with smaller diameter for initial engagement and a second thread with larger diameter for final securing. This segmentation allows the mounting process to occur in two stages, first creating a pilot hole path and then expanding to secure the plank without excessive radial pressure that would cause tensile stress and cracking.
Solution Approach 2:
The first thread performs a preliminary action by cutting a pilot hole path through the fiber cement plank before the second thread engages. This preliminary hole creation reduces the radial expansion force needed during final securing, thereby minimizing tangential tensile stress that would otherwise cause plank breakage or cracking.
2Reliability
If high mounting force is applied to secure the planks, then the mounting becomes secure, but the risk of breakage and cracking increases
Solution Approach 1:
The mounting force is segmented into two phases: the first thread engages with lower force to create a pilot hole, and the second thread engages with higher force to secure the plank. This force segmentation ensures that high mounting force is only applied after the plank has already been partially secured by the first thread, distributing the stress and reducing breakage risk.
Solution Approach 2:
The first thread performs a preliminary engagement that secures the plank at a preliminary position before the second thread applies the full mounting force. This preliminary securing action prevents sudden high-force impacts that would cause breakage, allowing the mounting force to be applied gradually and safely.
3Device complexity
If a single-thread screw is used, then the screw design is simple, but it cannot effectively minimize tensile stress during mounting
Solution Approach 1:
The screw thread is segmented into two distinct threads with different diameters and functions. The first thread (smaller diameter) cuts the pilot hole with minimal radial pressure, while the second thread (larger diameter) provides the final securing engagement. This segmentation directly addresses the stress minimization requirement while maintaining relatively simple screw geometry.
Solution Approach 2:
Different portions of the screw thread have different local qualities: the first thread has smaller diameter suited for pilot hole creation, while the second thread has larger diameter suited for final securing. This local differentiation optimizes each thread's function to minimize tensile stress during the mounting process.
Data Source
AI summary
A screw and method for the mounting of boards/planks, in particular fiber cement planks, on a support of wood. The screw comprises milling wings and a first thread between the milling wings and the tip, and a second, larger thread with smaller pitch between the milling wings and the screw head.