Screw Head Recesses and Thread Crests Manage Debris
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Solution Overview
Problem
Conventional screws face high drilling resistance and instability during fastening due to entanglement with wood fibers and debris accumulation, leading to increased torque, potential breakage, and poor fastening efficiency, especially in wooden and metal workpieces.
Innovation Solution
A screw design featuring a head with a conical underside and spirally disposed threads, including recesses and concave surfaces with crests that cut and remove debris efficiently, reducing fiber entanglement and accommodating debris to prevent surface damage, while fitting flush with pre-drilled holes for enhanced stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a smooth helical structure is used for the helix, then the screw can enter the workpiece by pushing and displacing fibers, but the helix and shank become entangled in fibers causing large drilling resistance
Solution Approach 1:
The helix is segmented into multiple sections with different functions: the first section has a larger pitch for initial entry and fiber displacement, while the second section has a smaller pitch for cutting and severing fibers. This segmentation allows the screw to transition from pushing/displacing mode to cutting mode, reducing entanglement and drilling resistance.
Solution Approach 2:
Different sections of the helix are given different local qualities: the first section is designed with larger pitch for gentle fiber displacement, while the second section is designed with smaller pitch and sharper edges for efficient fiber cutting. This local differentiation optimizes performance at each stage of penetration.
2Productivity
If the shank keeps moving downwards under rotating force, then drilling action is completed, but the torque increases excessively causing the screw to snap
Solution Approach 1:
The drilling process is segmented into two phases corresponding to the two helix sections: the first phase uses the larger pitch section for rapid entry with lower torque, and the second phase uses the smaller pitch section for controlled cutting with optimized torque. This segmentation prevents excessive torque buildup that would cause snapping.
Solution Approach 2:
The pitch parameter of the helix is changed between sections: the first section has a larger pitch for faster entry, while the second section has a smaller pitch for more controlled fiber cutting. This parameter change optimizes the balance between drilling speed and torque management.
3Object-generated harmful factors
If the head presses or pushes cut debris toward the workpiece, then debris is contained, but the workpiece surface is broken or cracked
Solution Approach 1:
The harmful effect of debris pressing is extracted and redirected: instead of pressing debris against the workpiece surface, the first inclined surface guides debris into the recesses where it is contained and removed. This extraction eliminates the harmful surface damage while maintaining debris containment.
Solution Approach 2:
The recesses act as an intermediary structure between the cutting action and the workpiece surface. Debris is first contained in the recesses, then gradually pushed out by the second inclined surface in a controlled manner that prevents surface damage. The recesses mediate the debris management process.
4Ease of operation
If ribs are arranged on the underside of the head to cut wood fibers, then the head can enter the workpiece, but the ribs raise the head forming interstices that prevent flush fitting
Solution Approach 1:
Instead of having protruding ribs on the head underside that raise the head, the invention uses recesses in the head that allow the head to sit lower. The cutting function is transferred to the helix sections rather than head ribs, inverting the traditional approach and enabling flush fitting while maintaining entry capability.
Data Source
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AI summary
A screw (3) includes a head (31), a shank (32) extending downwards from the head (31) and threads (33) spirally around the shank (32). The head (31) has a top face (311), a conical underside (312) formed by a first inclined surface (3121) and a second inclined surface (3122), and spaced-apart recesses (313) formed on the first inclined surface (3121). Each recess (313) has a recessed area gradually reduced downwards from a periphery of the top face (311) and defines two different widths (W1, W2). Each thread (33) has from two to six concave surfaces (331), each of which is curved inward from 60 to 120 degrees. Two adjacent concave surfaces (331) meet at a crest (332). The crests (332) and concave surfaces (331) cut fibers of a workpiece (4) into debris easily and facilitate the removal of debris. The first inclined surface (3121) and the recesses (313) further scrape debris off and provide a space to receive debris, thereby preventing the over accumulation of debris and preventing the accumulated debris from splitting the workpiece (4).