Rounded Thread Plug Screw for Dowel-Safe Anchor Expansion
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Solution Overview
Problem
Self-tapping screws often damage dowel anchors when screwed in, especially at angles, leading to impaired holding functions due to digging into the anchor wall and potential damage to the dowel nut.
Innovation Solution
The screw features a rounded thread flank tip with a radius of 1% to 10% of the nominal diameter, along with a thread configuration of two flank sections forming obtuse angles, and a concave screw tip with specific angle measurements, which reduces wall penetration and enhances spreading and centering effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the screw thread has a sharp flank tip for effective penetration, then the screwing speed and thread formation improve, but the anchor wall is damaged and holding function is impaired
Solution Approach 1:
The patent applies curvature by rounding the thread flank tip with a radius r between 0.1mm and 0.5mm. This rounded geometry prevents the sharp cutting edge from gouging the anchor wall while maintaining sufficient penetration capability, directly resolving the contradiction between screwing efficiency and anchor wall preservation
Solution Approach 2:
The patent changes the geometric parameter of the thread flank tip from sharp (zero radius) to rounded (radius r = 0.1-0.5mm). This parameter modification allows the thread to distribute stress more evenly during insertion, reducing localized damage to the anchor wall while maintaining effective thread engagement
2Force
If the screw tip is sharp for easy insertion, then the insertion force required is reduced, but the dowel nut is damaged when used with hollow wall anchors
Solution Approach 1:
The patent rounds the screw tip with a radius R between 0.3mm and 0.8mm, preventing the tip from acting as a piercing point that could damage the dowel nut. The rounded geometry distributes the insertion force over a larger area, reducing stress concentration on the nut while maintaining adequate penetration capability
3Ease of manufacture
If the thread flanks are designed with standard geometry for general use, then the manufacturing simplicity is maintained, but the expansion effect when screwing into anchors is insufficient
Solution Approach 1:
The patent modifies only the local geometry of the thread flank tip and screw tip, while maintaining standard thread geometry elsewhere. This localized modification achieves improved expansion effect through better stress distribution during insertion, without significantly complicating the overall manufacturing process
Data Source
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AI summary
The present invention relates to a screw, in particular a plug screw, having a screw shank (1), a screw head (2) and a tapering screw tip (4), and having a screw thread (6) that extends at least over a portion of the screw shank (1) and over the screw tip (4), the flight (6a) of said screw thread (6) having a triangular cross section as seen in longitudinal section, with two thread flanks (8, 9) that intersect at a flank tip (7). The flank tip (7) is rounded, wherein a radius of the rounding of the rounded flank tip (7) is selected to be from 1% to 10% of the nominal diameter of the screw. The thread flanks (8, 9) are each formed from two flank portions which enclose an obtuse angle with one another.