Screw With Asymmetric Thread Flanks For Expansion Anchors
Solution Overview
Problem
The high cost of producing sawtooth-like threads for expansion screws, especially when dealing with sections of different core diameters, limits the economic viability of plastic expansion anchors that require post-expansion behavior in cracked substrates.
Innovation Solution
A screw design with a flank angle greater than 90°, featuring symmetrical threads and an unthreaded shank section, along with a reverse rotation lock and over-tightening safety device, such as an elastomer washer, to facilitate low-cost production and prevent damage during screwing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sawtooth-like thread is used for the expansion screw, then post-expansion behavior is achieved, but production cost increases significantly
Solution Approach 1:
The patent applies asymmetry by using a sawtooth-like thread profile where one flank is steep (providing expansion force) and the other is shallow (reducing cutting resistance). This asymmetric geometry enables the screw to expand the dowel sleeve radially while minimizing the effort required during screwing, thus achieving reliable post-expansion behavior without prohibitively high production costs
Solution Approach 2:
The patent changes the thread flank angle parameter to create the sawtooth profile. By specifying that one flank has a steep angle and the other has a shallow angle, the design optimizes the balance between expansion capability and manufacturing cost, resolving the contradiction between reliability and ease of manufacture
2Adaptability or versatility
If sections with different core diameters are provided in the screw, then adaptability to different substrates is improved, but production complexity and cost increase
Solution Approach 1:
The screw shank is segmented into multiple sections with different core diameters. This segmentation allows the screw to adapt to different substrate conditions and anchor requirements while maintaining a relatively simple overall structure. The segmented design enables versatility without requiring completely different screw designs for each application
3Ease of manufacture
If the thread flank angle is increased to greater than 90°, then production effort is reduced, but thread strength may be compromised
Solution Approach 1:
The patent changes the thread flank angle parameter to greater than 90°, which simplifies the manufacturing process and reduces production effort. This parameter change is combined with the asymmetric sawtooth profile to maintain adequate thread strength while achieving easier manufacture
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 proposed screw design reduces production costs and ensures reliable post-expansion behavior without axial shifting, preventing damage and ensuring secure fastening even in less experienced hands.
Implementation Method 1
the screw is also pulled outwards by a small amount, with this axial movement being converted into a radial outward force by the flat thread flanks
Implementation Method 2
an elastically or plastically deformable element, which means that shortly before the final attachment state, slower deceleration of the rotational movement occurs due to a gradually increasing resistance
Data Source
Figure 1~3
Figure 4~6
AI summary
The screw has a screw head with a rotary drive design, and a symmetrical thread (3) extending over a portion of a screw shank (2). The screw shank includes three threaded sections (2a-2c). The screw thread forms a thread edge, which extends along a helical line over the length of the threaded sections. The thread edge is formed by two thread flanks. The thread flanks include an obtuse angle with one another. An external diameter of the screw thread is constant in two threaded sections. The thread flanks run below an angle of 25 degree opposite to a longitudinal axis of the screw.